Recent applications of synchrotron radiation and neutrons in the study of soft matter

Colloidal phase behavior of high aspect ratio clay nanotubes in symmetric and asymmetric electrolytes

HYPOTHESIS

Imogolite nanotubes (INTs) are unique anisometric particles with monodisperse nanometric diameters. Aluminogermanate double-walled INTs (Ge-DWINTs) are obtained with variable aspect ratios by controlling the synthesis conditions. It thus appears as an interesting model system to investigate how aspect ratio and ionic valence influence the colloidal behavior of highly anisometric rods.

EXPERIMENTS

The nanotubes were synthesized by hydrothermal treatment for 5 or 20 days to modify the aspect ratio while the electrostatic interactions were investigated by comparing the colloidal stability in symmetric and asymmetric electrolytes. The phase behavior and their related microstructure were determined by optical observations and small-angle X-ray scattering measurements, coupled with interparticle distance modelling.

FINDINGS

We revealed that colloidal suspensions of Ge-DWINTs prepared in NaCl are guided by repulsive double layer forces, undergoing different liquid crystal phase transitions before stiffen into a glass-like state. We found that the microstructure can be rationalized by taking into account the anisometric nature of the particles. By contrast, dispersions prepared with asymmetric electrolytes are governed by strong attractive forces and thus form space-filling gels containing large nanotubes aggregates.

Photoresponsive arylazopyrazole surfactant/PDADMAC mixtures: reversible control of bulk and interfacial properties

In many applications of polyelectrolyte/surfactant (P/S) mixtures, it is difficult to fine-tune them after mixing the components without changing the sample composition, e.g. pH or the ionic strength. Here we report on a new approach where we use photoswitchable surfactants to enable drastic changes in both the bulk and interfacial properties. Poly(diallyldimethylammonium chloride) (PDADMAC) mixtures with three alkyl-arylazopyrazole butyl sulfonates (CnAAP) with -H, -butyl and -octyl tails are applied and E/Z photoisomerization of the surfactants is used to cause substantially different hydrophobic interactions between the surfactants and PDADMAC. These remotely controlled changes affect significantly the P/S binding and allows for tuning both the bulk and interfacial properties of PDADMAC/CnAAP mixtures through light irradiation. For that, we have fixed the surfactant concentrations at values where they exhibit pronounced surface tension changes upon E/Z photoisomerization with 365 nm UV light (Z) and 520 nm green (E) light and have varied the PDADMAC concentration. The electrophoretic mobility can be largely tuned by photoisomerisation of CnAAP surfactants and P/S aggregates, which can even exhibit a charge reversal from negative to positive values or vice versa. In addition, low colloidal stability at equimolar concentrations of PDADMAC with CnAAP surfactants in the E configuration lead to the formation of large aggregates in the bulk which can be broken up by irradiation with UV light when the surfactant's alkyl chain is short enough (C0AAP). Vibrational sum-frequency generation (SFG) spectroscopy reveals changes at the interface similar to the bulk, where the charging state at air-water interfaces can be modified with light irradiation. Using SFG spectroscopy, we interrogated the O-H stretching modes of interfacial H2O and provide qualitative information on surface charging that is complemented by neutron reflectometry, from which we resolved the surface excesses of PDADMAC and CnAAP at the air-water interface, independently.

Small-angle X-ray and neutron scattering applied to lipid-based nanoparticles: Recent advancements across different length scales

Lipid-based nanoparticles (LNPs), ranging from nanovesicles to non-lamellar assemblies, have gained significant attention in recent years, as versatile carriers for delivering drugs, vaccines, and nutrients. Small-angle scattering methods, employing X-rays (SAXS) or neutrons (SANS), represent unique tools to unveil structure, dynamics, and interactions of such particles on different length scales, spanning from the nano to the molecular scale. This review explores the state-of-the-art on scattering methods applied to unveil the structure of lipid-based nanoparticles and their interactions with drugs and bioactive molecules, to inform their rational design and formulation for medical applications. We will focus on complementary information accessible with X-rays or neutrons, ranging from insights on the structure and colloidal processes at a nanoscale level (SAXS) to details on the lipid organization and molecular interactions of LNPs (SANS). In addition, we will review new opportunities offered by Time-resolved (TR)-SAXS and -SANS for the investigation of dynamic processes involving LNPs. These span from real-time monitoring of LNPs structural evolution in response to endogenous or external stimuli (TR-SANS), to the investigation of the kinetics of lipid diffusion and exchange upon interaction with biomolecules (TR-SANS). Finally, we will spotlight novel combinations of SAXS and SANS with complementary on-line techniques, recently enabled at Large Scale Facilities for X-rays and neutrons. This emerging technology enables synchronized multi-method investigation, offering exciting opportunities for the simultaneous characterization of the structure and chemical or mechanical properties of LNPs.

Recent advances in synchrotron scattering methods for probing the structure and dynamics of colloids

Recent progress in synchrotron based X-ray scattering methods applied to colloid science is reviewed. An important figure of merit of these techniques is that they enable in situ investigations of colloidal systems under the desired thermophysical and rheological conditions. An ensemble averaged simultaneous structural and dynamical information can be derived albeit in reciprocal space. Significant improvements in X-ray source brilliance and advances in detector technology have overcome some of the limitations in the past. Notably coherent X-ray scattering techniques have become more competitive and they provide complementary information to laboratory based real space methods. For a system with sufficient scattering contrast, size ranges from nm to several μm and time scales down to μs are now amenable to X-ray scattering investigations. A wide variety of sample environments can be combined with scattering experiments further enriching the science that could be pursued by means of advanced X-ray scattering instruments. Some of these recent progresses are illustrated via representative examples. To derive quantitative information from the scattering data, rigorous data analysis or modeling is required. Development of powerful computational tools including the use of artificial intelligence have become the emerging trend.

Mesoscale self-organization of polydisperse magnetic nanoparticles at the water surface

In this study, we investigated the self-ordering process in Langmuir films of polydisperse iron oxide nanoparticles on a water surface, employing in situ x-ray scattering, surface pressure-area isotherm analysis, and Brewster angle microscopy. X-ray reflectometry confirmed the formation of a monolayer, while grazing incidence small-angle x-ray scattering revealed short-range lateral correlations with a characteristic length equal to the mean particle size. Remarkably, our findings indicated that at zero surface pressure, the particles organized into submicrometer clusters, merging upon compression to form a homogeneous layer. These layers were subsequently transferred to a solid substrate using the Langmuir-Schaefer technique and further characterized via scanning electron microscopy and polarized neutron reflectometry. Notably, our measurements revealed a second characteristic length in the lateral correlations, orders of magnitude longer than the mean particle diameter, with polydisperse particles forming circular clusters densely packed in a hexagonal lattice. Furthermore, our evidence suggests that the lattice constant of this mesocrystal depends on the characteristics of the particle size distribution, specifically the mean particle size and the width of the size distribution. In addition, we observed internal size separation within these clusters, where larger particles were positioned closer to the center of the cluster. Finally, polarized neutron reflectometry measurements provided valuable insights into the magnetization profile across the layer.

Effects of Charge Density on Spread Hyperbranched Polyelectrolyte/Surfactant Films at the Air/Water Interface

The interfacial structure and morphology of films spread from hyperbranched polyethylene imine/sodium dodecyl sulfate (PEI/SDS) aggregates at the air/water interface have been resolved for the first time with respect to polyelectrolyte charged density. A recently developed method to form efficient films from the dissociation of aggregates using a minimal quantity of materials is exploited as a step forward in enhancing understanding of the film properties with a view to their future use in technological applications. Interfacial techniques that resolve different time and length scales, namely, ellipsometry, Brewster angle microscopy, and neutron reflectometry, are used. Extended structures of both components are formed under a monolayer of the surfactant with bound polyelectrolytes upon film compression on subphases adjusted to pH 4 or 10, corresponding to high and low charge density of the polyelectrolyte, respectively. A rigid film is related to compact conformation of the PEI in the interfacial structure at pH 4, while it is observed that aggregates remain embedded in mobile films at pH 10. The ability to compact surfactants in the monolayer to the same extent as its maximum coverage in the absence of polyelectrolyte is distinct from the behavior observed for spread films involving linear polyelectrolytes, and intriguingly evidence points to the formation of extended structures over the full range of surface pressures. We conclude that the molecular architecture and charge density can be important parameters in controlling the structures and properties of spread polyelectrolyte/surfactant films, which holds relevance to a range of applications, such as those where PEI is used, including CO2 capture, electronic devices, and gene transfection.

Small-angle scattering techniques for peptide and peptide hybrid nanostructures and peptide-based biomaterials

The use of small-angle scattering (SAS) in the study of the self-assembly of peptides and peptide conjugates (lipopeptides, polymer-peptide conjugates and others) is reviewed, highlighting selected research that illustrates different methods and analysis techniques. Both small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) are considered along with examples that exploit their unique capabilities. For SAXS, this includes the ability to perform rapid measurements enabling high throughput or fast kinetic studies and measurements under dilute conditions. For SANS, contrast variation using H2O/D2O mixtures enables the study of peptides interacting with lipids and TR-SANS (time-resolved SANS) studies of exchange kinetics and/or peptide-induced structural changes. Examples are provided of studies measuring form factors of different self-assembled structures (micelles, fibrils, nanotapes, nanotubes etc) as well as structure factors from ordered phases (lyotropic mesophases), peptide gels and hybrid materials such as membranes formed by mixing peptides with polysaccharides or peptide/liposome mixtures. SAXS/WAXS (WAXS: wide-angle x-ray scattering) on peptides and peptide hybrids is also discussed, and the review concludes with a perspective on potential future directions for research in the field.

New approach for SANS measurement of micelle chain mixing during size and morphology transitions

Chain exchange in amphiphilic block polymer micelles is measurable with time-resolved small-angle neutron scattering (TR-SANS) where contrast-matched conditions reveal chain mixing as reduced intensity. However, analyzing chain mixing on short time scales e.g. during micelle transformations remains challenging. SANS model fitting can quantify chain mixing during size and morphology changes, however short acquisition times lead to lower data statistics (higher error). Such data are unsuitable for form factor fitting, especially with polydisperse and/or multimodal scenarios. An integrated-reference approach, R(t), is compatible with such data by using fixed reference patterns for the unmixed and fully mixed states that are each integrated to improve data statistics (lower error). Although the R(t) approach is tolerant of low data statistics, it remains incompatible with size and morphology changes. A new shifting references relaxation approach, SRR(t), is proposed where reference patterns are acquired at each time point to enable mixed state calculations regardless of short acquisition times. The additional experimental measurements needed are described which provide these time-varying reference patterns. The use of reference patterns makes the SRR(t) approach size/morphology-agnostic, allowing for the extent of micelle mixing to be directly calculated without this knowledge. SRR(t) is thus compatible with arbitrary levels of complexity and can provide accurate assessment of the mixed state which could support future model analysis. Calculated scattering datasets were used to demonstrate the SRR(t) approach during multiple size, morphology, and solvent conditions (scenarios 1-3). The mixed state calculated from the SRR(t) approach is shown to be accurate for all three scenarios.

Computational Reverse-Engineering Analysis for Scattering Experiments for Form Factor and Structure Factor Determination ("P(q) and S(q) CREASE")

In this paper, we present an open-source machine learning (ML)-accelerated computational method to analyze small-angle scattering profiles [I(q) vs q] from concentrated macromolecular solutions to simultaneously obtain the form factor P(q) (e.g., dimensions of a micelle) and the structure factor S(q) (e.g., spatial arrangement of the micelles) without relying on analytical models. This method builds on our recent work on Computational Reverse-Engineering Analysis for Scattering Experiments (CREASE) that has either been applied to obtain P(q) from dilute macromolecular solutions (where S(q) ∼1) or to obtain S(q) from concentrated particle solutions when P(q) is known (e.g., sphere form factor). This paper's newly developed CREASE that calculates P(q) and S(q), termed as "P(q) and S(q) CREASE", is validated by taking as input I(q) vs q from in silico structures of known polydisperse core(A)-shell(B) micelles in solutions at varying concentrations and micelle-micelle aggregation. We demonstrate how "P(q) and S(q) CREASE" performs if given two or three of the relevant scattering profiles-I _total(q), I _A(q), and I _B(q)-as inputs; this demonstration is meant to guide experimentalists who may choose to do small-angle X-ray scattering (for total scattering from the micelles) and/or small-angle neutron scattering with appropriate contrast matching to get scattering solely from one or the other component (A or B). After validation of "P(q) and S(q) CREASE" on in silico structures, we present our results analyzing small-angle neutron scattering profiles from a solution of core-shell type surfactant-coated nanoparticles with varying extents of aggregation.

Time-Resolved Small-Angle X-ray Scattering Studies during the Aqueous Emulsion Polymerization of Methyl Methacrylate

Recently, we reported time-resolved synchrotron small-angle X-ray scattering (TR-SAXS) studies during aqueous emulsion polymerization using a bespoke stirrable reaction cell (J. Am. Chem. Soc.2021, 143, 1474–1484). This proof-of-concept study utilized a semifluorinated specialty monomer (2,2,2-trifluoroethyl methacrylate) to ensure high X-ray contrast relative to water. Herein, we extend this approach to emulsion polymerization of methyl methacrylate (MMA) in the presence or absence of sodium dodecyl sulfate (SDS) at 70 °C. Solution conductivity measurements for this anionic surfactant indicated a critical micelle concentration (CMC) of 10.9 mM at this temperature. Thus, SDS was employed at either 1.0 or 20.0 mM, which corresponds to well below or well above its CMC. Postmortem analysis by ¹H NMR spectroscopy indicated MMA conversions of 93–95% for these three formulations. We demonstrate that the X-ray contrast between water and PMMA is sufficiently large to produce high-quality scattering patterns during TR-SAXS experiments. Such patterns were fitted using a hard-sphere scattering model to monitor the evolution in particle diameter. This enabled (i) determination of the time point for the onset of nucleation and (ii) the evolution in particle size to be monitored during the MMA polymerization. The final particle diameters obtained from such TR-SAXS studies were consistent with postmortem DLS analyses, while TEM studies confirmed that near-monodisperse latex particles were formed. Micellar nucleation occurs within just 2 min when the SDS concentration is well above its CMC, resulting in a high particle number concentration and relatively small latex particles. In contrast, when SDS is either absent or present below its CMC, particle nuclei are formed by homogeneous nucleation over significantly longer time scales (14–15 min). In the latter case, adsorption of SDS onto nascent particles reduces their coagulation, giving rise to a larger number of smaller particles compared to the surfactant-free polymerization. However, the characteristic time required for the onset of nucleation is barely affected because this is mainly controlled by the kinetics of homogeneous polymerization of the relatively water-soluble MMA monomer within the aqueous phase. These results suggest that the aqueous emulsion polymerization of several other (meth)acrylic monomers, and perhaps also vinyl acetate, may be amenable to TR-SAXS studies.

Anti-persister and Anti-biofilm Activity of Self-Assembled Antimicrobial Peptoid Ellipsoidal Micelles

Although persister cells are the root cause of resistance development and relapse of chronic infections, more attention has been focused on developing antimicrobial agents against resistant bacterial strains than on developing anti-persister agents. Frustratingly, the global preclinical antibacterial pipeline does not include any anti-persister drug. Therefore, the central point of this work is to explore antimicrobial peptidomimetics called peptoids (sequence-specific oligo-N-substituted glycines) as a new class of anti-persister drugs. In this study, we demonstrate that one particular antimicrobial peptoid, the sequence-specific pentamer TM5, is active against planktonic persister cells and sterilizes biofilms formed by both Gram-negative and Gram-positive bacteria. Moreover, we demonstrate the potential of TM5 to inhibit cytokine production induced by lipopolysaccharides from Gram-negative bacteria. We anticipate that this work can pave the way to the development of new anti-persister agents based on antimicrobial peptoids of this class to simultaneously help address the crisis of bacterial resistance and reduce the occurrence of the relapse of chronic infections.

X-Ray Photon Correlation Spectroscopy Towards Measuring Nanoparticle Diameters in Biological Environments Allowing for the In Situ Analysis of their Bio-Nano Interface

X-ray photon correlation spectroscopy (XPCS), a synchrotron source-based technique to measure sample dynamics, is used to determine hydrodynamic diameters of gold nanoparticles (Au NPs) of different sizes in biological environments. In situ determined hydrodynamic diameters are benchmarked with values obtained by dynamic light scattering. The technique is then applied to analyze the behavior of the Au NPs in a biological environment. First, a concentration-dependent agglomeration in the presence of NaCl is determined. Second, concentration-dependent increase in hydrodynamic diameter of the Au NPs upon the presence of proteins is determined. As X-rays in the used energy range are barely scattered by biological matter, dynamics of the Au NPs can be also detected in situ in complex biological environments, such as blood. These measurements demonstrate the possibility of XPCS for in situ analytics of nanoparticles (NPs) in biological environments where similar detection techniques based on visible light would severely suffer from scattering, absorption, and reflection effects.

A Time-Dependent Hierarchical Model for Elastic and Inelastic Scattering Data Analysis of Aerogels and Similar Soft Materials

Soft nanomaterials like aerogels are subject to thermal fluctuations, so that their structure randomly fluctuates with time. Neutron elastic and inelastic scattering experiments provide unique structural and dynamic information on such systems with nanometer and nanosecond resolution. The data, however, come in the form of space- and time-correlation functions, and models are required to convert them into time-dependent structures. We present here a general time-dependent stochastic model of hierarchical structures, with scale-invariant fractals as a particular case, which enables one to jointly analyze elastic and inelastic scattering data. In order to describe thermal fluctuations, the model builds on time-dependent generalisations of the Boolean model of penetrable spheres, whereby each sphere is allowed to move either ballistically or diffusively. Analytical expressions are obtained for the correlation functions, which can be used for data fitting. The model is then used to jointly analyze previously published small-angle neutron scattering (SANS) and neutron spin-echo (NSE) data measured on silica aerogels. In addition to structural differences, the approach provides insight into the different scale-dependent mobility of the aggregates that make up the aerogels, in relation with their different connectivities.

The interaction of styrene maleic acid copolymers with phospholipids in Langmuir monolayers, vesicles and nanodiscs; a structural study

HYPOTHESIS

Self-assembly of amphipathic styrene maleic acid copolymers with phospholipids in aqueous solution results in the formation of 'nanodiscs' containing a planar segment of phospholipid bilayer encapsulated by a polymer belt. Recently, studies have reported that lipids rapidly exchange between both nanodiscs in solution and external sources of lipids. Outstanding questions remain regarding details of polymer-lipid interactions, factors influencing lipid exchange and structural effects of such exchange processes. Here, the dynamic behaviour of nanodiscs is investigated, specifically the role of membrane charge and polymer chemistry.

EXPERIMENTS

Two model systems are investigated: fluorescently labelled phospholipid vesicles, and Langmuir monolayers of phospholipids. Using fluorescence spectroscopy and time-resolved neutron reflectometry, the membrane potential, monolayer structure and composition are monitored with respect to time upon polymer and nanodisc interactions.

FINDINGS

In the presence of external lipids, polymer chains embed throughout lipid membranes, the extent of which is governed by the net membrane charge. Nanodiscs stabilised by three different polymers will all exchange lipids and polymer with monolayers to differing extents, related to the properties of the stabilising polymer belt. These results demonstrate the dynamic nature of nanodiscs which interact with the local environment and are likely to deposit both lipids and polymer at all stages of use.

Responsive Material and Interfacial Properties through Remote Control of Polyelectrolyte-Surfactant Mixtures

Polyelectrolyte/surfactant (P/S) mixtures find many applications but are static in nature and cannot be reversibly reconfigured through the application of external stimuli. Using a new type of photoswitchable surfactants, we use light to trigger property changes in mixtures of an anionic polyelectrolyte with a cationic photoswitch such as electrophoretic mobilities, particle size, as well as their interfacial structure and their ability to stabilize aqueous foam. For that, we show that prevailing hydrophobic intermolecular interactions can be remotely controlled between poly(sodium styrene sulfonate) (PSS) and arylazopyrazole tetraethylammonium bromide (AAP-TB). Shifting the chemical potential for P/S binding with E/Z photoisomerization of the surfactants can reversibly disintegrate even large aggregates (>4 μm) and is accompanied by a substantial change in the net charging state of PSS/AAP-TB complexes, e.g., from negative to positive excess charges upon light irradiation. In addition to the drastic changes in the bulk solution, also at air-water interfaces, the interfacial stoichiometry and structure change drastically on the molecular level with E/Z photoisomerization, which can also drive the stability of aqueous foam on a macroscopic level.

Molecular Transport and Growth of Lipid Vesicles Exposed to Antimicrobial Peptides

It is well-known that lipids constituting the cytoplasmic membrane undergo continuous reorganization to maintain the appropriate composition important for the integrity of the cell. The transport of lipids is controlled by mainly membrane proteins, but also spontaneous lipid transport between leaflets, lipid "flip-flop", occurs. These processes do not only occur spontaneously under equilibrium, but also promote structural rearrangements, morphological transitions, and growth processes. It has previously been shown that intravesicular lipid "flip-flop" and intervesicular lipid exchange under equilibrium can be deduced indirectly from contrast variation time-resolved small-angle neutron scattering (TR-SANS) where the molecules are "tagged" using hydrogen/deuterium (H/D) substitution. In this work, we show that this technique can be extended to simultaneously detect changes in the growth and the lipid "flip-flop" and exchange rates induced by a peptide additive on lipid vesicles consisting of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), d-DMPC (1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine), DMPG (1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol)), and small amounts of DMPE-PEG (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000]). Changes in the overall size were independently monitored using dynamic light scattering (DLS). We find that the antimicrobial peptide, indolicidin, accelerates lipid transport and additionally induces limited vesicular growth. Moreover, in TR-SANS experiments using partially labeled lipid mixtures to separately study the kinetics of the lipid components, we show that, whereas peptide addition affects both lipids similarly, DMPG exhibits faster kinetics. We find that vesicular growth is mainly associated with peptide-mediated lipid reorganization that only slightly affects the overall exchange kinetics. This is confirmed by a TR-SANS experiment of vesicles preincubated with peptide showing that after pre-equilibration the kinetics are only slightly slower.

Data Mining of Polymer Phase Transitions upon Temperature Changes by Small and Wide-Angle X-ray Scattering Combined with Raman Spectroscopy

The complex physical transformations of polymers upon external thermodynamic changes are related to the molecular length of the polymer and its associated multifaceted energetic balance. The understanding of subtle transitions or multistep phase transformation requires real-time phenomenological studies using a multi-technique approach that covers several length-scales and chemical states. A combination of X-ray scattering techniques with Raman spectroscopy and Differential Scanning Calorimetry was conducted to correlate the structural changes from the conformational chain to the polymer crystal and mesoscale organization. Current research applications and the experimental combination of Raman spectroscopy with simultaneous SAXS/WAXS measurements coupled to a DSC is discussed. In particular, we show that in order to obtain the maximum benefit from simultaneously obtained high-quality data sets from different techniques, one should look beyond traditional analysis techniques and instead apply multivariate analysis. Data mining strategies can be applied to develop methods to control polymer processing in an industrial context. Crystallization studies of a PVDF blend with a fluoroelastomer, known to feature complex phase transitions, were used to validate the combined approach and further analyzed by MVA.

Transition kinetics of mixed lipid:photosurfactant assemblies studied by time-resolved small angle X-ray scattering

HYPOTHESIS

Photoswitchable surfactants are used in the design of many light-responsive colloids and/or self-assemblies. Photo-isomerization enables to control molecular equilibrium, and triggers transient reorganizations with possibly out-of-equilibrium intermediate states that have been overlooked. Here, we address this question by an in depth structural investigation of intermediate lipid-surfactant assemblies that occur during fast isothermal photo-triggered transition in lipid:surfactant mixtures.

EXPERIMENTS

The structural parameters of mixed assemblies of azobenzene-containing cationic surfactant (AzoTMA) and dioleoylphosphatidylcholine (DOPC) lipids were studied by light scattering and time-resolved small angle X-ray scattering. Structural and compositional information about the assemblies and unimers in bulk were determined at the photostationary states, as well as at intermediate kinetic states formed during UV or blue light illumination.

FINDINGS

DOPC:AzoTMA systems form mixed assemblies representative of phospholipid:cationic surfactant mixtures, that evolve from spheroid, to rod-like micelles, and vesicles with increasing DOPC fraction. Transient assemblies detected during the photo-triggered kinetics are similar to the ones found in stationary states. But changes of AzoTMA unimers in bulk can be considerably faster than mass reorganizations of the mixed assemblies, suggesting that out-of-equilibrium conditions are transiently reached. Mass reorganization of the surfactant-enriched assemblies is much faster than in the lipid enriched ones, providing insight into the role of lipids in a slow reorganization of the assemblies.

Machine Learning Enhanced Computational Reverse Engineering Analysis for Scattering Experiments (CREASE) to Determine Structures in Amphiphilic Polymer Solutions

In this article, we present a machine learning enhancement for our recently developed "Computational Reverse Engineering Analysis for Scattering Experiments" (CREASE) method to accelerate analysis of results from small angle scattering (SAS) experiments on polymer materials. We demonstrate this novel artificial neural network (NN) enhanced CREASE approach for analyzing scattering results from amphiphilic polymer solutions that can be easily extended and applied for scattering experiments on other polymer and soft matter systems. We had originally developed CREASE to analyze SAS results [i.e., intensity profiles, I(q) vs q] of amphiphilic polymer solutions exhibiting unconventional assembled structures and/or novel polymer chemistries for which traditional fits using off-the-shelf analytical models would be too approximate/inapplicable. In this paper, we demonstrate that the NN-enhancement to the genetic algorithm (GA) step in the CREASE approach improves the speed and, in some cases, the accuracy of the GA step in determining the dimensions of the complex assembled structures for a given experimental scattering profile.

X-ray studies bridge the molecular and macro length scales during the emergence of CoO assemblies

The key to fabricating complex, hierarchical materials is the control of chemical reactions at various length scales. To this end, the classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for assemblies of polyhedrally shaped CoO nanocrystals. Utilizing high energy-resolution fluorescence-detected X-ray absorption spectroscopy, we directly access the molecular level of the nanomaterial synthesis. We reveal that initially Co(acac)3 rapidly reduces to square-planar Co(acac)2 and coordinates to two solvent molecules. Combining atomic pair distribution functions and small-angle X-ray scattering we observe that, unlike a classical nucleation and growth mechanism, nuclei as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final spherical assemblies are smaller than 100 nm, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution.

Magnetic measurement methods to probe nanoparticle–matrix interactions

Magnetic nanoparticles (MNPs) are key elements in several biomedical applications, e.g., in cancer therapy. Here, the MNPs are remotely manipulated by magnetic fields from outside the body to deliver drugs or generate heat in tumor tissue. The efficiency and success of these approaches strongly depend on the spatial distribution and quantity of MNPs inside a body and interactions of the particles with the biological matrix. These include dynamic processes of the MNPs in the organism such as binding kinetics, cellular uptake, passage through cell barriers, heat induction and flow. While magnetic measurement methods have been applied so far to resolve the location and quantity of MNPs for therapy monitoring, these methods can be advanced to additionally access these particle–matrix interactions. By this, the MNPs can further be utilized as probes for the physical properties of their molecular environment. In this review, we first investigate the impact of nanoparticle–matrix interactions on magnetic measurements in selected experiments. With these results, we then advanced the imaging modalities magnetorelaxometry imaging and magnetic microsphere tracking to spatially resolve particle–matrix interactions.

Multiscale Structural Elucidation of Peptide Nanotubes by X-Ray Scattering Methods

This mini-review presents the structural investigations of the self-assembled peptide nanotubes using X-ray scattering techniques. As compared to electron microscopy, scattering methods enable studies of nanotubes in solution under the appropriate physicochemical conditions and probe their formation mechanism. In addition, a combination of X-ray scattering methods allow the elucidation of structural organization from the molecular scale to the dimension of nanotubes.

An alternative analysis of contrast-variation neutron scattering data of casein micelles in semi-deuterated milk

Contrast-variation small-angle neutron scattering (CV-SANS) is an excellent way to determine the structure of complex, hierarchical colloids, including self-assembled biological systems. In these experiments, the scattering length density of solvents is changed (by varying the ratio of water or [Formula: see text] and heavy water or [Formula: see text]) to highlight or mask scattering from different components in the system. This approach has been used with synthetic colloids, but it is also increasingly being used in the biological and food sciences. Perhaps the most studied food colloid is the "casein micelle," a self-assembled nanometer-scale colloid of the structure-forming casein protein in milk. CV-SANS data available in the literature are typically analyzed using approximations, which may be invalid for casein micelles, as they have been shown to be sticky spheres. To assess the applicability of this approximate approach, a comprehensive set of CV-SANS data from casein micelles in diluted milk was reanalyzed using a model-based approach, where the casein micelles were formally treated as interacting spheres. In general, the conclusions of the previous study are reproduced, but this new approach makes it more straightforward to distinguish the different components in milk and can be applied to any dairy sample with known form of interparticle interactions, which offers the possibility of studying semi-deuterated milk at its native concentration.

Time-Resolved Small-Angle X-ray Scattering Studies during Aqueous Emulsion Polymerization

The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Post-mortem SAXS studies confirmed the formation of well-defined spherical latexes, with volume-average diameters of 353 ± 9 nm and 68 ± 4 nm being obtained for the surfactant-free and SDS formulations, respectively. 1H NMR spectroscopy studies of the equivalent laboratory-scale formulations indicated TFEMA conversions of 99% within 80 min and 93% within 60 min for the surfactant-free and SDS formulations, respectively. Comparable polymerization kinetics are observed for the in situ SAXS experiments and the laboratory-scale syntheses, with nucleation occurring after approximately 6 min in each case. After nucleation, scattering patterns are fitted using a hard sphere scattering model to determine the evolution in particle growth for both formulations. Moreover, in situ SAXS enables identification of the three main intervals (I, II, and III) that are observed during aqueous emulsion polymerization in the presence of surfactant. These intervals are consistent with those indicated by solution conductivity and optical microscopy studies. Significant differences between the surfactant-free and SDS formulations are observed, providing useful insights into the mechanism of emulsion polymerization.

Increasing complexity in small-angle X-ray and neutron scattering experiments: from biological membrane mimics to live cells

Small-angle X-ray and neutron scattering are well-established, non-invasive experimental techniques to interrogate global structural properties of biological membrane mimicking systems under physiologically relevant conditions. Recent developments, both in bottom-up sample preparation techniques for increasingly complex model systems, and in data analysis techniques have opened the path toward addressing long standing issues of biological membrane remodelling processes. These efforts also include emerging quantitative scattering studies on live cells, thus enabling a bridging of molecular to cellular length scales. Here, we review recent progress in devising compositional models for joint small-angle X-ray and neutron scattering studies on diverse membrane mimics - with a specific focus on membrane structural coupling to amphiphatic peptides and integral proteins - and live Escherichia coli. In particular, we outline the present state-of-the-art in small-angle scattering methods applied to complex membrane systems, highlighting how increasing system complexity must be followed by an advance in compositional modelling and data-analysis tools.

Structure and Hydration of Asymmetric Polyelectrolyte Multilayers as Studied by Neutron Reflectometry: Connecting Multilayer Structure to Superior Membrane Performance

Porous membranes coated with so-called asymmetric polyelectrolyte multilayers (PEMs) have recently been shown to outperform commercial membranes for micropollutant removal. They consist of open support layers of poly(styrene sulfonate) (PSS)/poly(allylamine) (PAH) capped by denser and more selective layers of either PAH/poly(acrylic acid) (PAA) or PAH/Nafion. Unfortunately, the structure of these asymmetric PEMs, and thus their superior membrane performance, is poorly understood. In this work, neutron reflectometry (NR) is employed to elucidate the multilayered structure and hydration of these asymmetric PEMs. NR reveals that the multilayers are indeed asymmetric in structure, with distinct bottom and top multilayers when air-dried and when solvated. The low hydration of the top [PAH/Nafion] multilayer, together with the low water permeance of comparable [PAH/Nafion]-capped PEM membranes, demonstrate that it is a reduction in hydration that makes these separation layers denser and more selective. In contrast, the [PAH/PAA] capping multilayers are more hydrated than the support [PSS/PAH] layers, signifying that, here, densification of the separation layer occurs through a decrease in the mesh size (or effective pore size) of the top layer due to the higher charge density of the PAH/PAA couple compared to the PSS/PAH couple. The [PAH/PAA] and [PAH/Nafion] separation layers are extremely thin (∼4.5 and ∼7 nm, respectively), confirming that these asymmetric PEM membranes have some of the thinnest separation layers ever achieved.

Structural Characterization of Biomaterials by Means of Small Angle X-rays and Neutron Scattering (SAXS and SANS), and Light Scattering Experiments

Scattering techniques represent non-invasive experimental approaches and powerful tools for the investigation of structure and conformation of biomaterial systems in a wide range of distances, ranging from the nanometric to micrometric scale. More specifically, small-angle X-rays and neutron scattering and light scattering techniques represent well-established experimental techniques for the investigation of the structural properties of biomaterials and, through the use of suitable models, they allow to study and mimic various biological systems under physiologically relevant conditions. They provide the ensemble averaged (and then statistically relevant) information under in situ and operando conditions, and represent useful tools complementary to the various traditional imaging techniques that, on the contrary, reveal more local structural information. Together with the classical structure characterization approaches, we introduce the basic concepts that make it possible to examine inter-particles interactions, and to study the growth processes and conformational changes in nanostructures, which have become increasingly relevant for an accurate understanding and prediction of various mechanisms in the fields of biotechnology and nanotechnology. The upgrade of the various scattering techniques, such as the contrast variation or time resolved experiments, offers unique opportunities to study the nano- and mesoscopic structure and their evolution with time in a way not accessible by other techniques. For this reason, highly performant instruments are installed at most of the facility research centers worldwide. These new insights allow to largely ameliorate the control of (chemico-physical and biologic) processes of complex (bio-)materials at the molecular length scales, and open a full potential for the development and engineering of a variety of nano-scale biomaterials for advanced applications.

Nonsymmetrical Dynamics of the HBV Capsid Assembly and Disassembly Evidenced by Their Transient Species

As with many protein multimers studied in biophysics, the assembly and disassembly dynamical pathways of hepatitis B virus (HBV) capsid proteins are not symmetrical. Using time-resolved small-angle X-ray scattering and singular value decomposition analysis, we have investigated these processes in vitro by a rapid change of salinity or chaotropicity. Along the assembly pathway, the classical nucleation-growth mechanism is followed by a slow relaxation phase during which capsid-like transient species self-organize in accordance with the theoretical prediction that the capture of the few last subunits is slow. By contrast, the disassembly proceeds through unexpected, fractal-branched clusters of subunits that eventually vanish over a much longer time scale. On the one hand, our findings confirm and extend previous views as to the hysteresis phenomena observed and theorized in capsid formation and dissociation. On the other hand, they uncover specifics that may directly relate to the functions of HBV subunits in the viral cycle.

How Detergents Dissolve Polymeric Micelles: Kinetic Pathways of Hybrid Micelle Formation in SDS and Block Copolymer Mixtures

Mixtures of amphiphilic polymers and surfactants are used in a wide range of applications, e.g., pharmaceuticals, detergents, cosmetics, and drug delivery systems. Still, many questions remain on how the structure and, in particular, the kinetics of block copolymer micelles are affected in the presence of surfactants and what controls the solubilization kinetics. In this work, we have studied the stability and solubilization kinetics of block copolymer micelles upon the addition of the surfactant sodium dodecyl sulfate (SDS) using small-angle X-ray/neutron scattering. The ability of the surfactant to dissolve polymer micelles or form mixed micelles has been investigated using two types of amphiphilic polymers, poly(ethylene-alt-propylene)-poly(ethylene oxide) (PEP1-PEO20) and n-alkyl-functionalized PEO (C28-PEO5). The exchange kinetics of C28-PEO5 micelles are in the order of hours, while PEP1-PEO20 micelles are known to be frozen on a practical timescale. In this work, we show that the addition of SDS to PEP1-PEO20 provides virtually no solubilization, even after an extended period of time. However, upon adding SDS to C28-PEO5 micelles, we observe micellar dissolution and formation of mixed micelles occurring on the timescale of hours. Using a coexistence model of mixed and neat micelles, the SAXS data were analyzed to provide detailed structural parameters over time. First, we observe a fast fragmentation/fission step followed by a slow reorganization process. The latter process is essentially independent of concentration at low volume fraction but is greatly accelerated at larger concentrations. This might indicate a crossover from a predominance of molecular exchange to fusion/fission processes.

Molecular exchange in spherical diblock copolymer colloids synthesised by polymerisation-induced self-assembly

HYPOTHESIS

To study molecular exchange between colloids requires the preparation of suitably labelled species. Deuterium isotopic labelling has been used to prepare two chemically identical yet isotopically distinguishable poly(lauryl methacrylate)-poly(methyl methacrylate) (PLMA-PMMA) diblock copolymer colloids by polymerisation-induced self-assembly (PISA) directly in an alkane solvent. Molecular exchange should be detectable by performing small-angle neutron scattering (SANS) measurements on the dispersions.

EXPERIMENTS

SANS measurements were performed on fully hydrogenous PLMA₃₉-PMMA₅₇ and deuterated core PLMA₃₉-P(MMA-d₈)₅₇ colloids. They were mixed in equal amounts and heated to determine if molecular exchange occurred. PISA syntheses are often thermally initiated, and diblock copolymers self-assemble at elevated temperature, making this an important parameter to study. Experimental data for the mixture were compared to predicted curves for exchanged and non-exchanged colloids.

FINDINGS

The scattering of a mixture of fully hydrogenous and deuterated core copolymers does not disappear upon molecular exchange, due to the remaining contrast between the stabiliser and the core and solvent even after the cores fully exchange. By simultaneously fitting the SANS data from dispersions before mixing and using these parameters to constrain fitting the SANS data of mixtures, the molecular exchange between diblock copolymer micelles upon heating is clearly observed.

In situ SAXS studies of a prototypical RAFT aqueous dispersion polymerization formulation: monitoring the evolution in copolymer morphology during polymerization-induced self-assembly

Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate at 70 °C using a poly(glycerol monomethacrylate) steric stabilizer. 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphology being pure vesicles. Analysis of time-resolved SAXS patterns for this prototypical polymerization-induced self-assembly (PISA) formulation enables the evolution in copolymer morphology, particle diameter, mean aggregation number, solvent volume fraction, surface density of copolymer chains and their mean inter-chain separation distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diameter and membrane thickness during the final stages of polymerization supports an 'inward growth' mechanism.

Halogenation as a tool to tune antimicrobial activity of peptoids

Antimicrobial peptides have attracted considerable interest as potential new class of antibiotics against multi-drug resistant bacteria. However, their therapeutic potential is limited, in part due to susceptibility towards enzymatic degradation and low bioavailability. Peptoids (oligomers of N-substituted glycines) demonstrate proteolytic stability and better bioavailability than corresponding peptides while in many cases retaining antibacterial activity. In this study, we synthesized a library of 36 peptoids containing fluorine, chlorine, bromine and iodine atoms, which vary by length and level of halogen substitution in position 4 of the phenyl rings. As we observed a clear correlation between halogenation of an inactive model peptoid and its increased antimicrobial activity, we designed chlorinated and brominated analogues of a known peptoid and its shorter counterpart. Short brominated analogues displayed up to 32-fold increase of the activity against S. aureus and 16- to 64-fold against E. coli and P. aeruginosa alongside reduced cytotoxicity. The biological effect of halogens seems to be linked to the relative hydrophobicity and self-assembly properties of the compounds. By small angle X-ray scattering (SAXS) we have demontrated how the self-assembled structures are dependent on the size of the halogen, degree of substitution and length of the peptoid, and correlated these features to their activity.

A microvolume shear cell for combined rheology and x-ray scattering experiments

An experimental setup is presented for x-ray scattering studies of soft matter under shear flow that employs a low-background coaxial capillary cell coupled to a high-resolution commercial rheometer. The rotor of the Searle type cell is attached to the rheometer shaft, which allows the application of either steady or oscillatory shear of controlled stress or rate on the sample confined in the annular space between the stator and the rotor. The shearing device facilitates ultrasmall-angle x-ray scattering and ultrasmall-angle x-ray photon correlation spectroscopy measurements with relatively low scattering backgrounds. This enables the elucidation of weak structural features otherwise submerged in the background and probes the underlying dynamics. The performance of the setup is demonstrated by means of a variety of colloidal systems subjected to different rheological protocols. Examples include shear deformation of a short-range attractive colloidal gel, dynamics of dilute colloids in shear flow, distortion of the structure factor of a dense repulsive colloidal suspension, shear induced ordering of colloidal crystals, and alignment of multilamellar microtubes formed by a surfactant-polysaccharide mixture. Finally, the new possibilities offered by this setup for investigating soft matter subjected to shear flow by x-ray scattering are discussed.

Interactions of anticancer drugs doxorubicin and idarubicin with lipid monolayers: New insight into the composition, structure and morphology

We quantify directly here for the first time the extents of interactions of two different anthracycline drugs with pure and mixed lipid monolayers with respect to the surface pressure and elucidate differences in the resulting interaction mechanisms. The work concerns interactions of doxorubicin (DOx) and idarubicin (IDA) with monolayers of the zwitterionic DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) and negatively charged DMPS (1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (sodium salt)) as well as a 7:3 mixture of the two lipids. These drugs are used in current cancer treatments, while the lipid systems were chosen as phosphocholines are the major lipid component of healthy cell membranes, and phosphoserines are the major lipid component that is externalized into the outer leaflet of cancerous cell membranes. It is shown that DOx interacts with DMPS monolayers to a greater extent than with DMPC monolayers by lower limits of a factor of 5 at a surface pressure of 10 mN/m and a factor of 12 at 30 mN/m. With increasing surface pressure, the small amount of drug (~0.3 µmol/m²) bound to DMPC monolayers is excluded from the interface, yet its interaction with DMPS monolayers is enhanced until there is even more drug (~3.2 µmol/m²) than lipid (~2.6 µmol/m²) at the interface. Direct evidence is presented for all systems studied that upon surface area compression lipid is reproducibly expelled from the monolayer, which we infer to be in the form of drug-lipid aggregates, yet the nature of adsorption of material back to the monolayer upon expansion is system-dependent. At 30 mN/m, most relevant to human physiology, the interactions of DOx and IDA are starkly different. For DOx, there is a conformational change in the interfacial layer driven by aggregation, resulting in the formation of lateral domains that have extended layers of drug. For the more lipophilic IDA, there is penetration of the drug into the hydrophobic acyl chain region of the monolayer and no indication of lateral segregation. In addition to the Langmuir technique, these advances were made as a result of direct measurements of the interfacial composition, structure and morphology using two different implementations of neutron reflectometry and Brewster angle microscopy. The results provide new insight into key processes that determine the uptake of drugs such as limited drug penetration through cell membranes by passive diffusion as well as activation of drug removal mechanisms related to multidrug resistance.

Scattering Form Factor of Block Copolymer Micelles with Corona Chains Discretely Distributed on the Core Surface

Small-angle scattering is a powerful tool to investigate micellar structure, and a model form factor proposed by Pedersen and Gerstenberg [Pedersen, J. S.; Gerstenberg, M. Macromolecules 1996, 29, 1363-1365] has been used quite frequently to analyze experimentally obtained scattering data of block copolymer micelles. Their model consists of a spherical core and the Gaussian corona chains attached to the core surface; the corona chains are considered to be approximately continuously (evenly) distributed on the core surface. In this paper, we present a micellar form factor model in which the corona chains are discretely distributed on the core surface. Our proposed discrete model was found to deviate from the Pedersen-Gerstenberg model as well as another model [Svaneborg, C.; Pedersen, J. S. Phys. Rev. E 2001, 64, R01802.], which incorporates the approximate interference effect between the corona chains, in conditions in which the scattering from the corona chains is stronger than that from a core with lower number density of the corona chains.

Enhanced protein adsorption upon bulk phase separation

In all areas related to protein adsorption, from medicine to biotechnology to heterogeneous nucleation, the question about its dominant forces and control arises. In this study, we used ellipsometry and quartz-crystal microbalance with dissipation (QCM-D), as well as density-functional theory (DFT) to obtain insight into the mechanism behind a wetting transition of a protein solution. We established that using multivalent ions in a net negatively charged globular protein solution (BSA) can either cause simple adsorption on a negatively charged interface, or a (diverging) wetting layer when approaching liquid-liquid phase separation (LLPS) by changing protein concentration (cp) or temperature (T). We observed that the water to protein ratio in the wetting layer is substantially larger compared to simple adsorption. In the corresponding theoretical model, we treated the proteins as limited-valence (patchy) particles and identified a wetting transition for this complex system. This wetting is driven by a bulk instability introduced by metastable LLPS exposed to an ion-activated attractive substrate.

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

Synergy, competition, and the "hanging" polymer layer: Interactions between a neutral amphiphilic 'tardigrade' comb co-polymer with an anionic surfactant at the air-water interface

Understanding the structure of polymer/surfactant mixtures at the air-water interface is of fundamental importance and also of relevance to a variety of practical applications. Here, the complexation between a neutral 'tardigrade' comb co-polymer (consisting of a hydrophilic polyethylene glycol backbone with hydrophobic polyvinyl acetate grafts, PEG-g-PVAc) with an anionic surfactant (sodium dodecyl sulfate, SDS) at the air-water interface has been studied. Contrast-matched neutron reflectivity (NR) complemented by surface tension measurements allowed elucidation of the interfacial composition and structure of these mixed systems, as well as providing physical insights into the polymer/surfactant interactions at the air-water interface. For both polymer concentrations studied, below and above its critical aggregation concentration, cac, (0.2 cac and 2 cac, corresponding to 0.0002 wt% or 0.013 mM and 0.002 wt% or 0.13 mM respectively), we observed a synergistic cooperative behaviour at low surfactant concentrations with a 1-2 nm mixed interfacial layer; a competitive adsorption behaviour at higher surfactant concentrations was observed where the polymer was depleted from the air-water interface, with an overall interfacial layer thickness ~1.6 nm independent of the polymer concentration. The weakly associated polymer layer "hanging" proximally to the interface, however, played a role in enhancing foam stability, thus was relevant to the detergency efficacy in such polymer/surfactant mixtures in industrial formulations.

Block Copolymer Nanoparticles Prepared via Polymerization-Induced Self-Assembly Provide Excellent Boundary Lubrication Performance for Next-Generation Ultralow-Viscosity Automotive Engine Oils

Core cross-linked poly(stearyl methacrylate)-poly(benzyl methacrylate)-poly(ethylene glycol dimethacrylate) [S₃₁-B₂₀₀-E₂₀] triblock copolymer nanoparticles were synthesized directly in an industrial mineral oil via polymerization-induced self-assembly (PISA). Gel permeation chromatography analysis of the S₃₁-B₂₀₀ diblock copolymer precursor chains indicated a well-controlled reversible addition-fragmentation chain transfer dispersion polymerization, while transmission electron microscopy, dynamic light-scattering (DLS), and small-angle X-ray scattering studies indicated the formation of well-defined spheres. Moreover, DLS studies performed in THF, which is a common solvent for the S and B blocks, confirmed successful covalent stabilization because well-defined solvent-swollen spheres were obtained under such conditions. Tribology experiments using a mini-traction machine (MTM) indicated that 0.50% w/w dispersions of S₃₁-B₂₀₀-E₂₀ spheres dramatically reduce the friction coefficient of base oil within the boundary lubrication regime. Given their efficient and straightforward PISA synthesis at high solids, such nanoparticles offer new opportunities for the formulation of next-generation ultralow-viscosity automotive engine oils.

In Situ Small-Angle X-ray Scattering Studies During Reversible Addition-Fragmentation Chain Transfer Aqueous Emulsion Polymerization

Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g., spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci. 2016 , 7 , 5078 - 5090 ). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellization and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aqueous emulsion polymerization.

Novel O/W nanoemulsions for nasal administration: Structural hints in the selection of performing vehicles with enhanced mucopenetration

We propose novel oil-in-water nanoemulsions (O/W NEs) including PEGylated surfactants and chitosan, showing good biocompatibility and optimization for nasal administration of drugs or vaccines. The transmucosal route has been shown to be ideal for a fast and efficient absorption and represents a viable alternative when the oral administration is problematic. The critical structural features in view of optimal encapsulation and transmucosal delivery were assessed by characterizing the NEs with complementary scattering techniques, i.e. dynamic light scattering (DLS), small angle X-ray (SAXS) and neutron scattering (SANS). Combined results allowed for selecting the formulations with the best suited structural properties and in addition establishing their propensity to enter the mucus barrier. To this scope, mucin was used as a model system and the effect of adding chitosan to the NEs, as adjuvant, was investigated. Remarkably, the presence of chitosan had a positive impact on the diffusion of the NE particles through the mucin matrix. We can infer that chitosan-mucin interaction induces density inhomogeneity and an increase in the pore size within the gel matrix that enhances the PEGylated NEs mobility. The coupling of mucoadhesive and mucopenetrating agents is shown to be a promising strategy for innovative transmucosal delivery systems.

3D Micromachined Polyimide Mixing Devices for in Situ X-ray Imaging of Solution-Based Block Copolymer Phase Transitions

Advances in modern interface- and material sciences often rely on the understanding of a system's structure-function relationship. Designing reproducible experiments that yield in situ time-resolved structural information at fast time scales is therefore of great interest, e.g., for better understanding the early stages of self-assembly or other phase transitions. However, it can be challenging to accurately control experimental conditions, especially when samples are only available in small amounts, prone to agglomeration, or if X-ray compatibility is required. We address these challenges by presenting a microfluidic chip for triggering dynamics via rapid diffusive mixing for in situ time-resolved X-ray investigations. This polyimide/Kapton-only-based device can be used to study the structural dynamics and phase transitions of a wide range of colloidal and soft matter samples down to millisecond time scales. The novel multiangle laser ablation three-dimensional (3D) microstructuring approach combines, for the first time, the highly desirable characteristics of Kapton (high X-ray stability with low background, organic solvent compatibility) with a 3D flow-focusing geometry that minimizes mixing dispersion and wall agglomeration. As a model system, to demonstrate the performance of these 3D Kapton microfluidic devices, we selected the non-solvent-induced self-assembly of biocompatible and amphiphilic diblock copolymers. We then followed their structural evolution in situ at millisecond time scales using on-the-chip time-resolved small-angle X-ray scattering under continuous-flow conditions. Combined with complementary results from 3D finite-element method computational fluid dynamics simulations, we find that the nonsolvent mixing is mostly complete within a few tens of milliseconds, which triggers initial spherical micelle formation, while structural transitions into micelle lattices and their deswelling only occur on the hundreds of milliseconds to second time scale. These results could have an important implication for the design and formulation of amphiphilic polymer nanoparticles for industrial applications and their use as drug-delivery systems in medicine.