Towards a neutron and X-ray reflectometry environment for the study of solid-liquid interfaces under shear

A novel neutron and X-ray reflectometry sample environment is presented for the study of surface-active molecules at solid–liquid interfaces under shear. Neutron reflectometry was successfully used to characterise the iron oxide–dodecane interface at a shear rate of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$7.0\times {}10^{2}$$\end{document}7.0×102\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 using a combination of conventional reflectometry theory coupled with the summation of reflected intensities to describe reflectivity from thicker films. Additionally, the structure adopted by glycerol monooleate (GMO), an Organic Friction Modifier, when adsorbed at the iron oxide–dodecane interface at a shear rate of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$7.0\times {}10^{2}$$\end{document}7.0×102\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 was studied. It was found that GMO forms a surface layer that appears unaltered by the effect of shear, where the thickness of the GMO layer was found to be \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$24.3^{+9.9}_{-10.2}$$\end{document}24.3-10.2+9.9 Å under direct shear at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$7.0\times {}10^{2}$$\end{document}7.0×102\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {s}^{-1}$$\end{document}s-1 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$25.8^{+4.4}_{-5.2}$$\end{document}25.8-5.2+4.4 Å when not directly under shear. Finally, a model to analyse X-ray reflectometry data collected with the sample environment is also described and applied to data collected at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$3.0\times {}10^{3}$$\end{document}3.0×103\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {s}^{-1}$$\end{document}s-1.

Thiol-Bromo Click Reaction for One-Pot Synthesis of Star-Shaped Polymers

Star-shaped polymers have unique physical properties and they are sought after materials in industry. However, the ease of synthesis is essential for translation of these materials into large-scale applications. Herein, a highly efficient synthetic method to prepare star-shaped polymers by combination of Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) and thiol-bromo click reaction is described. Well-defined linear and block polymers with a very high bromine chain end fidelity are obtained via Cu-RDRP and subsequently react with multi-functional thiol compounds. High coupling efficiencies of larger than 90% are obtained owing to the quick and efficient reaction between thiols and alkyl bromides. Moreover, the arms of the obtained star-shaped polymers are linked via thioether bonds to the core, making them susceptible for oxidative degradation.

An ε-caprolactone-derived 2-oxazoline inimer for the synthesis of graft copolymers

An inimer-like structure that consists of a 2-oxazoline ring for cationic ring opening polymerisation and a typical alpha-bromo ester initiator for Cu-RDRP has been synthesised using ε-Caprolactone as the starting material.

Segregation versus Interdigitation in Highly Dynamic Polymer/Surfactant Layers

Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic^®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C₁₂TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface.

Fast track access to multi-block copolymers via thiol-bromo click reaction of telechelic dibromo polymers

Multi-block copolymers offer a plethora of exciting properties, easily tuned by modulating parameters such as monomer composition, block length, block number and dispersity.

The effect of thiamine-coating nanoparticles on their biodistribution and fate following oral administration

Thiamine-coated nanoparticles were prepared by two different preparative methods and evaluated to compare their mucus-penetrating properties and fate in vivo. The first method of preparation consisted of surface modification of freshly poly(anhydride) nanoparticles (NP) by simple incubation with thiamine (T-NPA). The second procedure focused on the preparation and characterization of a new polymeric conjugate between the poly(anhydride) backbone and thiamine prior the nanoparticle formation (T-NPB). The resulting nanoparticles displayed comparable sizes (about 200 nm) and slightly negative surface charges. For T-NPA, the amount of thiamine associated to the surface of the nanoparticles was 15 μg/mg. For in vivo studies, nanoparticles were labelled with either ^99mTc or Lumogen® Red. T-NPA and T-NPB moved faster from the stomach to the small intestine than naked nanoparticles. Two hours post-administration, for T-NPA and T-NPB, >30% of the given dose was found in close contact with the intestinal mucosa, compared with a 13.5% for NP. Interestingly, both types of thiamine-coated nanoparticles showed a greater ability to cross the mucus layer and interact with the surface of the intestinal epithelium than NP, which remained adhered in the mucus layer. Four hours post-administration, around 35% of T-NPA and T-NPB were localized in the ileum of animals. Overall, both preparative processes yielded thiamine decorated carriers with similar physico-chemical and biodistribution properties, increasing the versatility of these nanocarriers as oral delivery systems for a number of biologically active compounds.

Assembly of small molecule surfactants at highly dynamic air-water interfaces

Small-angle neutron scattering has been used to probe the interfacial structure of foams stabilised by small molecule surfactants at concentrations well below their critical micelle concentration. The data for wet foams showed a pronounced Q^-4 dependence at low Q and noticeable inflexions over the mid Q range. These features were found to be dependent on the surfactant structure (mainly the alkyl chain length) with various inflexions across the measured Q range as a function of the chain length but independent of factors such as concentration and foam age/height. By contrast, foam stability (for C < CMC) was significantly different at this experimental range. Drained foams showed different yet equally characteristic features, including additional peaks attributed to the formation of classical micellar structures. Together, these features suggest the dynamic air-water interface is not as simple as often depicted, indeed the data have been successfully described by a model consisting paracrystalline stacks (multilayer) of adsorbed surfactant layers; a structure that we believe is induced by the dynamic nature of the air-water interface in a foam.

Probing the interaction of nanoparticles with mucin for drug delivery applications using dynamic light scattering

Drug delivery via the eye, nose, gastrointestinal tract and lung is of great interest as they represent patient-compliant and facile methods to administer drugs. However, for a drug to reach the systemic circulation it must penetrate the "mucus barrier". An understanding of the characteristics of the mucus barrier is therefore important in the design of mucus penetrating drug delivery vehicles e.g. nanoparticles. Here, a range of nanoparticles - silica, aluminium coated silica, poly (lactic-co-glycolic acid) (PLGA) and PEGylated PLGA - each with known but different physicochemical characteristics were examined in the presence of mucin to identify those characteristics that engender nanoparticle/mucin interactions and thus, to define "design rules" for mucus penetrating (nano)particles (MPP), at least in terms of the surface characteristics of charge and hydrophilicity. Dynamic light scattering (DLS) and rheology have been used to assess the interaction between such nanoparticles and mucin. It was found that negatively charged and hydrophilic nanoparticles do not exhibit an interaction with mucin whereas positively charged and hydrophobic nanoparticles show a strong interaction. Surface grafted poly (ethylene glycol) (PEG) chains significantly reduced this interaction. This study clearly demonstrates that the established colloid science techniques of DLS and rheology are very powerful screening tools to probe nanoparticle/mucin interactions.

Interpolymer complexation: comparisons of bulk and interfacial structures

The interactions between the strong polyelectrolyte sodium poly(styrenesulfonate), NaPSS, and the neutral polymer poly(vinylpyrrolidone), PVP, were investigated in bulk and at the silica/solution interface using a combination of diffusion nuclear magnetic resonance spectroscopy (NMR), small-angle neutron scattering (SANS), solvent relaxation NMR, and ellipsometry. We show for the first time that complex formation occurs between NaPSS and PVP in solution; the complexes formed were shown not to be influenced by pH variation, whereas increasing the ionic strength increases the complexation of NaPSS but does not influence the PVP directly. The complexes formed contained a large proportion of NaPSS. Study of these interactions at the silica interface demonstrated that complexes also form at the nanoparticle interface where PVP is added in the system prior to NaPSS. For a constant PVP concentration and varying NaPSS concentration, the system remains stable until NaPSS is added in excess, which leads to depletion flocculation. Surface complex formation using the layer-by-layer technique was also reported at a planar silica interface.

Nanoparticles decorated with proteolytic enzymes, a promising strategy to overcome the mucus barrier

The intestinal mucus gel layer represents a stumbling block for drug adsorption. This study is aimed to formulate a nanoparticulate system able to overcome this barrier by cleaving locally the glycoprotein substructures of the mucus. Mucolytic enzymes such as papain (PAP) and bromelain (BRO) were covalently conjugated to poly(acrylic acid) (PAA). Nanoparticles (NPs) were then formulated via ionic gelation method and characterized by particle size, zeta potential, enzyme content and enzymatic activity. The NPs permeation quantified by rotating tube studies was correlated with changes in the mucus gel layer structure determined by pulsed-gradient-spin-echo NMR (PGSE-NMR), small-angle neutron scattering (SANS) and spin-echo SANS (SESANS). PAP and BRO functionalized NPs had an average size in the range of 250 and 285 nm and a zeta potential that ranged between -6 and -5 mV. The enzyme content was 242 μg enzyme/mg for PAP modified NPs and 253 μg enzyme/mg for BRO modified NPs. The maintained enzymatic activity was 43% for PAP decorated NPs and 76% for BRO decorated NPs. The rotating tube technique revealed a better performance of BRO decorated NPs compared to PAA decorated NPs, with a 4.8-fold higher concentration of NPs in the inner slice of mucus. Addition of 0.5 wt% of enzyme functionalized NPs to 5 wt% intestinal mucin led to c.a. 2-fold increase in the mobility of the mucin as measured by PGSE-NMR indicative of a significant break-up of the structure of the mucin. SANS and SESANS measurements further revealed a change in structure of the intestinal mucus induced by the incorporation of the functionalized NPs mostly occurring at a length scale longer than 0.5 μm. Accordingly, BRO decorated NPs show higher potential than PAP functionalized NPs as mucus permeating drug delivery systems.

Enzyme-Functionalized PLGA Nanoparticles with Enhanced Mucus Permeation Rate

The surface functionalization of poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) with various proteolytic enzymes (i.e., trypsin, papain, bromelain) via a two-step carbodiimide coupling method is presented. Depending on the initial Enzyme:NPs ratio, enzyme loadings up to 4.0 wt.%, 4.4 wt.% and 5.34 wt.% were achieved for trypsin, papain and bromelain, respectively. All three conjugated enzymes partially maintained their enzymatic activity after their coupling reaction with the NPs. NPs functionalized with papain and bromelain exhibited a three-fold higher permeability in porcine intestinal mucus compared to nonfunctionalized NPs whereas those conjugated with trypsin showed an almost two-fold higher permeability value. Measurements of the diffusion rates of intestinal mucin, using a nuclear magnetic resonance (NMR) technique, further confirmed these observations, as the enzyme-functionalized NPs were proven to be capable of disrupting the mucin gel structure. According to the reported results, the coupling of proteolytic enzymes to the PLGA NPs' surface largely increases the NPs mucus permeability, thus making it a potentially important mucus permeation strategy.

Adsorption and surfactant-mediated desorption of poly(vinylpyrrolidone) on plasma- and piranha-cleaned silica surfaces

Optical flow cell reflectometry was used to study the adsorption of poly(vinylpyrrolidone) (PVP) to a silica surface and the subsequent surfactant adsorption and polymer desorption upon exposure to the anionic surfactant sodium dodecyl sulfate (SDS). We have studied these effects as a function of pH and surfactant concentration, but also for two different methods of silica preparation, O2 plasma and piranha cleaning. As a function of pH, a plateau in the amount adsorbed of ∼0.6 mg/m(2) is observed below a critical pH, above which the adsorption decreases to zero within 2-3 pH units. An increase in pH leads to dissociation of surface OH groups and a decreased potential for hydrogen bonding between the polymer and surface. For the plasma- and piranha-cleaned silica, the critical pH differs by 1-2 pH units, a reflection of the much larger amount of surface OH groups on piranha-cleaned silica (for a given pH). Subsequent rinsing of the adsorbed layer of PVP with an SDS solution leads to total or partial desorption of the PVP layer. Any remaining adsorbed PVP then acts as an adsorption site for SDS. A large difference between plasma- and piranha-cleaned silica is observed, with the PVP layer adsorbed to plasma-cleaned silica being much more susceptible to desorption by SDS. For a plasma-cleaned surface at pH 5.5, only 30% of the originally adsorbed PVP is remaining, while for piranha-cleaned silica, the pH can be increased to 10 before a similar reduction in the amount of adsorbed PVP is seen. For a given pH, piranha-cleaned silica has a higher surface charge, leading to a smaller amount of adsorbed SDS per PVP chain on a piranha-cleaned surface compared to a plasma-cleaned surface under identical conditions. In that way, the high negative surface charge makes desorption by negatively charged SDS more difficult. The high surface charge thus protects the neutral polymer from surfactant-mediated desorption.

Manipulating interfacial polymer structures through mixed surfactant adsorption and complexation

The effects of a nonionic alcohol ethoxylate surfactant, C(13)E(7), on the interactions between PVP and SDS both in the bulk and at the silica nanoparticle interface are studied by photon correlation spectroscopy, solvent relaxation NMR, SANS, and optical reflectometry. Our results confirmed that, in the absence of SDS, C(13)E(7) and PVP are noninteracting, while SDS interacts strongly both with PVP and C(13)E(7) . Studying interfacial interactions showed that the interfacial interactions of PVP with silica can be manipulated by varying the amounts of SDS and C(13)E(7) present. Upon SDS addition, the adsorbed layer thickness of PVP on silica increases due to Coulombic repulsion between micelles in the polymer layer. When C(13)E(7) is progressively added to the system, it forms mixed micelles with the complexed SDS, reducing the total charge per micelle and thus reducing the repulsion between micelle and the silica surface that would otherwise cause the PVP to desorb. This causes the amount of adsorbed polymer to increase with C(13)E(7) addition for the systems containing SDS, demonstrating that addition of C(13)E(7) hinders the SDS-mediated desorption of an adsorbed PVP layer.

Surfactant-mediated desorption of polymer from the nanoparticle interface

The surfactant-mediated desorption of adsorbed poly(vinylpyrrolidone), PVP, from anionic silica surfaces by sodium dodecyl sulfate, SDS, was observed. While photon correlation spectroscopy shows that the size of the polymer-surfactant-particle ensemble grows with added SDS, a reduction in the near-surface polymer concentration is measured by solvent relaxation NMR. Volume fraction profiles of the polymer layer extracted from small-angle neutron scattering experiments illustrate that the adsorbed polymer layer has become more diffuse and the polymer chains more elongated as a result of the addition of SDS. The total adsorbed amount is shown to decrease due to Coulombic repulsion between the surfactant-polymer complexes and between the complexes and the anionic silica surface.