Rotator phases in alkane systems: In bulk, surface layers and micro/nano-confinements

Thermodynamic Analysis of n-Nonadecane (C19H40)/1-Octadecanol (C18H37OH) Blends

The article delves into the intricate phase transitions of 1-Octadecanol and n-Nonadecane within a binary system, unveiling dynamic structural changes under varying conditions. Through Fourier transform infrared (FTIR) analysis, specific molecular vibrations were identified, shedding light on the molecular composition and interactions. The study highlights the challenges in detecting subtle phase transitions and emphasises the individuality of molecular behaviours in closely related compounds. The findings underscore the complexity of phase transitions in binary systems and advocate for a nuanced approach to studying molecular structures and behaviours.

Polymorphic phase transitions in triglycerides and their mixtures studied by SAXS/WAXS techniques: In bulk and in emulsions

Triacylglycerols (TAGs) exhibit a monotropic polymorphism, forming three main polymorphic forms upon crystallization: α, β' and β. The distinct physicochemical properties of these polymorphs, such as melting temperature, subcell lattice structure, mass density, etc., significantly impact the appearance, texture, and long-term stability of a wide range products in the food and cosmetics industries. Additionally, TAGs are also of special interest in the field of controlled drug delivery and sustained release in pharmaceuticals, being a key material in the preparation of solid lipid nanoparticles. The present article outlines our current understanding of TAG phase behavior in both bulk and emulsified systems. While our primary focus are investigations involving monoacid TAGs and their mixtures, we also include illustrative examples with natural TAG oils, highlighting the knowledge transfer from simple to intricate systems. Special attention is given to recent discoveries via X-ray scattering techniques. The main factors influencing TAG polymorphism are discussed, revealing that a higher occurrence of structural defects in the TAG structure always accelerates the rate of the α → β polymorphic transformation. Diverse approaches can be employed based on the specific system: incorporating foreign molecules or solid particles into bulk TAGs, reducing drop size in dispersed systems, or using surfactants that remain fluid during TAG particle crystallization, ensuring the necessary molecular mobility for the polymorphic transformation. Furthermore, we showcase the role of TAG polymorphism on a recently discovered phenomenon: the creation of nanoparticles as small as 20 nm from initial coarse emulsions without any mechanical energy input. This analysis underscores how the broader understanding of the TAG polymorphism can be effectively applied to comprehend and control previously unexplored processes of notable practical importance.

Morphologies of Comb-like Polyacrylic Acid/Polyacrylate Copolymers as Functions of the Degree of Derivatization with n-C22H45 Side Chains

Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction.

Computational assessment of hexadecane freezing by equilibrium atomistic molecular dynamics simulations

HYPOTHESIS

Upon cooling, alkanes can form intermediate phases between liquid and crystal. They are called "rotator" or "plastic" phases and have long-range positional order with rotational freedom around the long molecular axis which gives them non-trivial and useful visco-plastic properties. We expect that the formation and structure of rotator phases formed in freezing alkanes can be understood much deeper by tracking the process at molecular level with atomistic molecular dynamics.

SIMULATIONS

We defined an appropriate CHARMM36-based computational protocol for simulating the freezing of hexadecane, which contained a sufficiently long (500 ns) equilibrium sampling of the frozen states. We employed it to simulate successfully the freezing of bulk and interface-contacting hexadecane and to provide a pioneering clarification of the effect of surfactant on the crystallization mechanism and on the type of intermolecular ordering in the crystallites.

FINDINGS

The devised computational protocol was able to reproduce the experimentally observed polycrystalline structure formed upon cooling. However, different crystallization mechanisms were established for the two types of models. Crystallites nucleate at random locations in the bulk and start growing rapidly within tens of nanoseconds. In contrast, the surfactants freeze first during the fast cooling (<1 ns), followed by rapid hexadecane freezing, with nucleation starting along the entire surfactant adsorption layer. Thereby, the hexadecane molecules form rotator phases which transition into a more stable ordered phase. This collective transition is first-time visualized directly. The developed robust computational protocol creates a foundation for future in-depth modelling and analysis of solid-state alkane-containing, incl. lipid, structures.

Computational Procedure for Analysis of Crystallites in Polycrystalline Solids of Quasilinear Molecules

In the current work, a comprehensive procedure for structural analysis of quasilinear organic molecules arranged in a polycrystalline sample generated by molecular dynamics is developed. A linear alkane, hexadecane, is used as a test case because of its interesting behavior upon cooling. Instead of a direct transition from isotropic liquid to the solid crystalline phase, this compound forms first a short-lived intermediate state known as a "rotator phase". The rotator phase and the crystalline one are distinguished by a set of structural parameters. We propose a robust methodology to evaluate the type of ordered phase obtained after a liquid-to-solid phase transition in a polycrystalline assembly. The analysis starts with the identification and separation of the individual crystallites. Then, the eigenplane of each of them is fit and the tilt angle of the molecules relative to it is computed. The average area per molecule and the distance to the nearest neighbors are estimated by a 2D Voronoi tessellation. The orientation of the molecules with respect to each other is quantified by visualization of the second molecular principal axis. The suggested procedure may be applied to different quasilinear organic compounds in the solid state and to various data compiled in a trajectory.

The composition and structure of the ubiquitous hydrocarbon contamination on van der Waals materials

The behavior of single layer van der Waals (vdW) materials is profoundly influenced by the immediate atomic environment at their surface, a prime example being the myriad of emergent properties in artificial heterostructures. Equally significant are adsorbates deposited onto their surface from ambient. While vdW interfaces are well understood, our knowledge regarding atmospheric contamination is severely limited. Here we show that the common ambient contamination on the surface of: graphene, graphite, hBN and MoS₂ is composed of a self-organized molecular layer, which forms during a few days of ambient exposure. Using low-temperature STM measurements we image the atomic structure of this adlayer and in combination with infrared spectroscopy identify the contaminant molecules as normal alkanes with lengths of 20-26 carbon atoms. Through its ability to self-organize, the alkane layer displaces the manifold other airborne contaminant species, capping the surface of vdW materials and possibly dominating their interaction with the environment.

Here, the authors attribute the ambient surface contamination of van der Waals materials to a self-organized molecular layer of normal alkanes with lengths of 20-26 carbon atoms. The alkane adlayer displaces the manifold other airborne contaminant species, capping the surface of graphene, graphite, hBN and MoS₂.

Minimum surfactant concentration required for inducing self-shaping of oil droplets and competitive adsorption effects

Surfactant choice is key in starting the phenomena of artificial morphogenesis, the bottom-up growth of geometric particles from cooled emulsion droplets, as well as the bottom-up self-assembly of rechargeable microswimmer robots from similar droplets. The choice of surfactant is crucial for the formation of a plastic phase at the oil-water interface, for the kinetics, and for the onset temperature of these processes. But further details are needed to control these processes for bottom-up manufacturing and understand their molecular mechanisms. Still unknown are the minimum concentration of the surfactant necessary to induce the processes, or competing effects in a mixture of surfactants when only one is capable of inducing shapes. Here we systematically study the effect of surfactant nature and concentration on the shape-inducing behaviour of hexadecane-in-water emulsions with both cationic (CTAB) and non-ionic (Tween, Brij) surfactants over up to five orders of magnitude of concentration. The minimum effective concentration is found approximately equal to the critical micelle concentration (CMC), or the solubility limit below the Krafft point of the surfactant. However, the emulsions show low stability at the vicinity of CMC. In a mixed surfactant experiment (Tween 60 and Tween 20), where only one (Tween 60) can induce shapes we elucidate the role of competition at the interface during mixed surfactant adsorption by varying the composition. We find that a lower bound of ∼75% surface coverage of the shape-inducing surfactant with C14 or longer chain length is necessary for self-shaping to occur. The resulting technique produces a clear visual readout of otherwise difficult to investigate molecular events. These basic requirements (minimum concentration and % surface coverage to induce oil self-shaping) and the related experimental techniques are expected to guide academic and industrial scientists to formulations with complex surfactant mixtures and behaviour.

Effect of Thermal History and Hydrocarbon Core Size on Perfluorocarbon Endoskeletal Droplet Vaporization

Vaporizable hydrocarbon-in-fluorocarbon endoskeletal droplets are a unique category of phase-change emulsions with interesting physical and thermodynamic features. Here, we show microfluidic fabrication of various morphologies, such as solid-in-liquid, liquid-in-solid, and Janus-type, of complex solid n-C₂₀H₄₂ or n-C₂₁H₄₄ and liquid n-C₅F₁₂ droplets. Furthermore, we investigated the vaporization behavior of these endoskeletal droplets, focusing on the effects of heat treatment and core size. Comparison of vaporization and differential scanning calorimetry results indicated that vaporization occurs prior to melting of the bulk hydrocarbon phase for C₂₀H₄₂/C₅F₁₀ droplets and near the rotator phase for C₂₁H₄₄/C₅F₁₀ droplets. We found that heat treatment of the droplets increased the fraction of droplets that vaporized and also increased the vaporization temperature of the droplets, although the effect was temporary. Furthermore, we found that changing the relative size of the solid hydrocarbon core compared to the surrounding liquid shell increased the vaporization temperature and the vaporizing fraction. Taken together, these data support the hypothesis that surface melting behavior exhibited by the linear alkane may trigger the fluorocarbon vaporization event. These results may aid in the understanding of the interfacial thermodynamics and transport and the engineering of novel vaporizable endoskeletal droplets for biomedical imaging and other applications.

Microencapsulated phase change material via Pickering emulsion stabilized by cellulose nanofibrils for thermal energy storage

A phase change material (PCM) has an ability to store and release a large amount of energy in a wide range of temperature by the latent heat of fusion upon melting and crystallization. Microencapsulation may protect PCM from undesirable reaction and leaching. Herein, we report the microencapsulation of n-hexadecane via oil-in-water Pickering emulsions stabilized by non-chemically modified cellulose nanofibrils (CNF). The maximum size of PCM-CNF microcapsules was 12 ± 3.4 μm in diameter. The surface coverage of the microcapsule by CNF was as high as 67%, consistent with porous morphology of the freeze-dried microcapsules. With 59% PCM loading, the PCM-CNF microcapsule exhibited 132.5 and 141.1 J/g as stored and released thermal energy, respectively. The microcapsule slurry showed a reversible change in storage modulus by one order of magnitude across the transition temperature of n-hexadecane. Combined results demonstrate the successful microencapsulation of PCM via CNF-based Pickering emulsions for a sustainable thermal energy storage material.

Preparation of Stable Phase Change Material Emulsions for Thermal Energy Storage and Thermal Management Applications: A Review

Thermal energy storage (TES) is an important means for the conservation and efficient utilization of excessive and renewable energy. With a much higher thermal storage capacity, latent heat storage (LHS) may be more efficient than sensible heat storage. Phase change materials (PCMs) are the essential storage media for LHS. PCM emulsions have been developed for LHS in flow systems, which act as both heat transfer and thermal storage media with enhanced heat transfer, low pumping power, and high thermal storage capacity. However, two major barriers to the application of PCM emulsions are their instability and high degree of supercooling. To overcome these, various strategies have been attempted, such as the reduction of emulsion droplet size, addition of nucleating agents, and optimization of the formulation. To the best of our knowledge, however, there is still a lack of review articles on fabrication methods for PCM emulsions or their latest applications. This review was to provide an up-to-date and comprehensive summary on the effective strategies and the underlying mechanisms for the preparation of stable PCM emulsions and reduction of supercooling, especially with the organic PCMs of paraffin. It was also to share our insightful perspectives on further development and potential applications of PCM emulsions for efficient energy storage.

Structure and Undulations of Escin Adsorption Layer at Water Surface Studied by Molecular Dynamics

The saponin escin, extracted from horse chestnut seeds, forms adsorption layers with high viscoelasticity and low gas permeability. Upon deformation, escin adsorption layers often feature surface wrinkles with characteristic wavelength. In previous studies, we investigated the origin of this behavior and found that the substantial surface elasticity of escin layers may be related to a specific combination of short-, medium-, and long-range attractive forces, leading to tight molecular packing in the layers. In the current study, we performed atomistic molecular dynamics simulations of 441 escin molecules in a dense adsorption layer with an area per molecule of 0.49 nm2. We found that the surfactant molecules are less submerged in water and adopt a more upright position when compared to the characteristics determined in our previous simulations with much smaller molecular models. The number of neighbouring molecules and their local orientation, however, remain similar in the different-size models. To maintain their preferred mutual orientation, the escin molecules segregate into well-ordered domains and spontaneously form wrinkled layers. The same specific interactions (H-bonds, dipole-dipole attraction, and intermediate strong attraction) define the complex internal structure and the undulations of the layers. The analysis of the layer properties reveals a characteristic wrinkle wavelength related to the surface lateral dimensions, in qualitative agreement with the phenomenological description of thin elastic sheets.

Co-assembly and Structure of Sodium Dodecylsulfate and other n-Alkyl Sulfates in Glycerol: n-Alkyl Sulfate-Glycerol Crystal Phase

HYPOTHESIS

Following the observation of a microfibrillar phase in sodium dodecylsulfate (SDS)-glycerol mixtures, it is hypothesized that this phase is a crystalline structure containing SDS and glycerol, where the interaction between sulfate and glycerol layers mediates the co-assembly, which also could be universal for similar systems formed by n-alkyl sulfate homologues. Experiment. n-alkyl sulfate glycerol solutions were studied using a combination of optical microscopy, small- and wide-angle X-ray scattering (SAXS/WAXS). Time-resolved SAXS was employed to determine the phase formation in SDS-glycerol-water mixtures.

FINDINGS

The microfibrillar crystalline phase was reproduced in even-chained n-alkyl sulfates with a chain length between 12 and 18 carbon atoms, where the phase lamellar period increased uniformly with the alkyl chain length. Reconstruction of electron density profiles from the diffraction patterns allowed the lamellar structural motif of the phase, the glycerol location and stoichiometry to be determined. When SDS-glycerol-water mixtures with water concentration below 6 wt% are isothermally solidified at 20 °C, SDS-glycerol crystals and/or anhydrous SDS form, where the former is inhibited by the latter at higher water concentrations. The learnings from the SDS-glycerol phase formation allows new gels to be created, utilising the glycerol-sulfate motif generating microfibrils. This expands the knowledge of the applicable formulation space for SDS-water containing mixtures.

Dynamics of proton, ion, molecule, and crystal lattice in functional molecular assemblies

Dynamic molecular processes, such as short- or long-range proton (H⁺) and ion (M⁺) motions, and molecular rotations in electrical conducting and magnetic molecular assemblies enable the fabrication of electron-H⁺ (or M⁺) coupling systems, while crystal lattice dynamics and molecular conformation changes in hydrogen-bonded molecular crystals have been utilised in external stimuli responsive reversible gas-induced gate opening and molecular adsorption/desorption behavior. These dynamics of the polar structural units are responsible for the dielectric measurements. The H⁺ dynamics are formed from ferroelectrics and H⁺ conductors, while the dynamic M⁺ motions of Li⁺ and Na⁺ involve ionic conductors and coupling to the conduction electrons. In n-type organic semiconductors, the crystal lattices are modulated by replacing M⁺ cations, with cations such as Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The use of polar rotator or inversion structures such as alkyl amides, m-fluoroanilinium cations, and bowl-shaped trithiasumanene π-cores enables the formation of ferroelectric molecular assemblies. The host-guest molecular systems of ESIPT fluorescent chromic molecules showed interesting molecular sensing properties using various bases, where the dynamic transformation of the crystal lattice and the molecular conformational change were coupled to each other.

Rotator phases in hexadecane emulsion drops revealed by X-ray synchrotron techniques

HYPOTHESIS

Micrometer sized alkane-in-water emulsion drops, stabilized by appropriate long-chain surfactants, spontaneously break symmetry upon cooling and transform consecutively into series of regular shapes (Denkov et al., Nature 2015, 528, 392). Two mechanisms were proposed to explain this phenomenon of drop "self-shaping". One of these mechanisms assumes that thin layers of plastic rotator phase form at the drop surface around the freezing temperature of the oil. This mechanism has been supported by several indirect experimental findings but direct structural characterization has not been reported so far.

EXPERIMENTS

We combine small- and wide-angle X-ray scattering (SAXS/WAXS) with optical microscopy and DSC measurements of self-shaping drops in emulsions.

FINDINGS

In the emulsions exhibiting drop self-shaping, the scattering spectra reveal the formation of intermediate, metastable rotator phases in the alkane drops before their crystallization. In addition, shells of rotator phase were observed to form in hexadecane drops, stabilized by C₁₆EO₁₀ surfactant. This rotator phase melts at ca. 16.6 °C which is significantly lower than the melting temperature of crystalline hexadecane, 18 °C. The scattering results are in a very good agreement with the complementary optical observations and DSC measurements.

Effective Na+-Binding Ability and Molecular Assembly of an Alkylamide-Substituted Penta(ethylene)glycol Derivative

A new amphiphilic penta(ethylene glycol) derivative (1) bearing two hydrogen-bonding -CONHC₁₄H₂₉ chains was prepared. Compound 1 exhibited ion-recognition abilities for Na⁺ and K⁺, and its properties were compared with those of the macrocyclic [18]crown-6. Although both compound 1 and [18]crown-6 have six ether oxygen atoms (-OC₂H₂-), the Na⁺-binding ability of the former was much higher than that of the latter. K⁺-binding ability of cyclic [18]crown-6 was much higher than its Na⁺-binding ability, while the reverse was true for acyclic compound 1. Single-crystal X-ray structural analysis of Na⁺·1·B(Ph)₄^-·(hexane)₂ at 100 K revealed the existence of a wrapped Na⁺-coordination by six ether and one carbonyl oxygen atoms of 1, which was further stabilized by intramolecular N-H···O═ hydrogen-bonding interactions. The complex phase transition during glass (G) formation and recrystallization was confirmed in the thermal cycle of Na⁺·1·B(Ph)₄^-, whose molten state showed two kinds of liquid phases, Na⁺-complexed (Na⁺·1) + B(Ph)₄^- and completely dissociated Na⁺ + 1 + B(Ph)₄^-. The Na⁺ conductivity of the molten state was 2 orders of magnitude higher than that of the G phase.

Benchmarking of Molecular Dynamics Force Fields for Solid-Liquid and Solid-Solid Phase Transitions in Alkanes

Accurate prediction of alkane phase transitions involving solids is needed to prevent catastrophic pipeline blockages, improve lubrication formulations, smart insulation, and energy storage, as well as bring fundamental understanding to processes such as artificial morphogenesis. However, simulation of these transitions is challenging and therefore often omitted in force field development. Here, we perform a series of benchmarks on seven representative molecular dynamics models (TraPPE, PYS, CHARMM36, L-OPLS, COMPASS, Williams, and the newly optimized Williams 7B), comparing with experimental data for liquid properties, liquid-solid, and solid-solid phase transitions of two prototypical alkanes, n-pentadecane (C₁₅) and n-hexadecane (C₁₆). We find that existing models overestimate the melting points by up to 34 K, with PYS and Williams 7B yielding the most accurate results deviating only 2 and 3 K from the experiment. We specially design order parameters to identify crystal-rotator phase transitions in alkanes. United-atom models could only produce a rotator phase with complete rotational disorder, whereas all-atom models using a 12-6 Lennard-Jones potential show no rotator phase even when superheated above the melting point. In contrast, Williams (Buckingham potential) and COMPASS (9-6 Lennard-Jones) reproduce the crystal-to-rotator phase transition, with the optimized Williams 7B model having the most accurate crystal-rotator transition temperature of C₁₅.

Fluorescent sensing system based on molecularly imprinted phase-change microcapsules and carbon quantum dots for high-efficient detection of tetracycline

Aiming at enhancing the detection efficiency and identification accuracy of tetracycline under a high-temperature condition, this study focuses on an innovative fluorescent sensing system (MIP@CQD-PCM) based on molecularly imprinted phase-change microcapsules along with the carbon quantum dots (CQDs) embedded in their shell. This system was fabricated by microencapsulating n-eicosane as a phase change material (PCM) core within a CQDs-embedded SiO₂ shell, followed by coating a tetracycline-templated molecularly imprinted polymer (MIP) layer onto the surface of the SiO₂ shell. The specific recognition sites to tetracycline molecules were finally achieved by removal of tetracycline template from the MIP layer. Comprehensive characterizations and investigations on the structure and performance of the fluorescent sensing system were given to confirm its successful fabrication in accordance to our design strategy. The resultant MIP@CQD-PCM exhibits a satisfactory thermal storage capacity and phase-change cycle stability for temperature regulation and thermal management applications under a phase-change enthalpy of over 162 J/g. Most of all, a typical fluorescence-quenching effect was obtained from the combination of the CQDs embedded in the SiO₂ shell and the tetracycline molecules adsorbed in the MIP layer. This makes the MIP@CQD-PCM achieve an enhanced capability for the fluorescence identification of tetracycline in a high-temperature environment through the in situ thermal management of its PCM core. The MIP@CQD-PCM also displays high selectivity and good reusability for tetracycline detection in industrial applications. This work provides a promising strategy for the design and development of fluorescent sensing systems with high recognition efficiency and identification accuracy in the detection of hazardous substances.

Nucleation of melt: From fundamentals to dispersed systems

The most evident aspects of a first order transition of a system from an old to a new phase, are the presence of a discontinuity at the interface between both phases and the thermal effects related to the latent heat exchanged with the surrounding environment. These effects are the result of a sequence of events promoted by thermodynamic conditions persisting over the equilibrium in a metastable state. The breakdown of metastability is promoted by infinitesimal energy fluctuations resulting in the germination of clusters of the new phase that can grow to a critical size (nucleus) and then develop or vanish. Examples of these sequences are common in various technological fields such as combustion, food processing, pharmaceutical manufacturing, condensation, and phase change heat transfer, etc. This work aims to highlight a logical path that leads the readers from the fundamental phenomenology to the most intricated aspects of the nucleation within dispersed systems such as oil-in-water emulsions. Differences between the homogeneous and heterogeneous mechanisms are, under the light of the Classical Nucleation Theory (CNT), presented in bulk and confined systems until defining a minimum confinement size. By collecting insights coming from a rich scientific literature mostly focused on the stability of emulsified systems, the discussion is then on the aspects related to the surface related mechanisms. Two main aspects are then considered: a) the wettability of the nucleating cluster by the surrounding melt; b) the affinity between the adsorbed layer, where a surfactant is located, and the oil melt phase (mainly n-alkanes and triacylglycerols with different moieties). In cases where nucleation is dominating over the dewetting of the nucleus, the contact angle can be considered as a constant value. The affinity in terms of molecular features between the surfactant and the oil phase can promote the template effect. Several factors seem to play a role in this interaction such as the thermal characteristics of the surfactant and comparable dimensions between the molecule (or fractions) of the dispersed compound and the tail of the surfactant.

Exploration of the natural waxes-tuned crystallization behavior, droplet shape and rheology properties of O/W emulsions

Lipid crystallization in O/W emulsions is essential to control the release of nutrients and to food structuring. While few information is involved in adjusting and controlling the performance of emulsions by adjusting oil phase crystallization behavior. We herein developed a novel strategy for designing lipid crystallization inside oil droplets by natural waxes to modify the O/W emulsion properties. Natural waxes, the bio-based and sustainable materials, displayed a high efficiency in modifying the crystallization behavior, droplet surface and shape, as well as the overall performance of emulsions. Specifically, waxes induced the formation of a new hydrocarbon chain distances of 3.70 and 4.15 Å and slightly decreased the lamellar distance (d₀₀₁) of the single crystallites, thus forming the large and rigid crystals in droplets. Interestingly, these large and rigid crystals in droplets tended to penetrate the interface film, forming the crystal bumps on the droplet surface and facilitating non-spherical shape transformation. The presence of rice bran wax (RW) and carnauba wax (CW) induced the droplet shape into ellipsoid and polyhedron shape, respectively. Furthermore, the uneven interface and non-spherical shape transformation promoted the crystalline droplet-droplet interaction, fabricating a three-dimensional network structure in O/W emulsions. Finally, both linear and nonlinear rheology strongly supported that waxes enhanced the crystalline droplet-droplet interaction and strengthened the network in O/W emulsions. Our findings give a clear insight into the effects of adding natural waxes into oil phase on the crystalline and physical behavior of emulsions, which provides a direction for the design and control of emulsion performance.

Bulk Nanoencapsulation of Phase Change Materials (PCMs) via Spontaneous Spreading of a UV-Curable Prepolymer

Phase change materials (PCMs) have received considerable attention for various latent heat storage systems for efficient thermal energy utilization. Herein, a facile and fast method for the bulk nanoencapsulation of organic PCMs is proposed, based on the thermodynamically spontaneous spreading phenomenon of three immiscible liquid phases. In this approach, a complete engulfing of PCM nanodroplets (core phase) by immiscible prepolymer droplets (coating phase), both of which are bulk-dispersed in another immiscible medium (continuous phase), is thermodynamically driven by the relation between the surface energies of the core, coating, and continuous phases. To demonstrate the proposed method, melted n-docosane (PCM, core phase) nanodroplets are completely engulfed within a couple of minutes by immiscible polyethylene glycol diacrylate (PEGDA, coating phase) in an aqueous poly(vinyl alcohol) solution (continuous phase), and the PEGDA layer quickly cross-linked upon UV irradiation to form a rigid shell protecting the PCM core. As-produced PCM nanocapsules display promising heat storage and release performances as well as high durability in repeated heating-cooling cycles in both dry and wet states. The proposed process may serve as a useful platform for bulk production of PCM nanocapsules with various core and shell compositions in a facile, fast, and scalable way.

Crystallization and melting of highly monodisperse poly(ethylene-oxide)

We present a quantitative study of the crystallization and melting behaviours of highly monodisperse PEO oligomers, and compare to previous studies. Through evaporative purification, we were able to isolate low molecular weight PEO oligomers that are much more monodisperse than the as-purchased material (as measured by mass spectrometry). Crystal structure, crystal growth rate and melting temperatures were characterized. Melting temperatures of isolated fractions were described by the Gibbs-Thomson relation. We show that during crystallization the isolated fractions are able to form crystal lamellae not only with extended chains, but also with once-folded chains. This chain folding is unexpected for polymers with such short chain lengths. We use these samples to investigate the effects of polydispersity on crystal formation and chain folding, and discuss both qualitative and quantitative differences from previous studies on similar but more polydisperse small chains.

Crystallization-Induced Network Formation of Tri- and Monopalmitin at the Middle-Chain Triglyceride Oil/Air Interface

Crystalline glycerides play an important role in the formation of multiphase systems such as emulsions and foams. The stabilization of oil/water interfaces by glyceride crystals has been extensively studied compared to only few studies which have been dedicated to oil/air interfaces. This study investigates the crystallization and network formation of tripalmitin (TP) and monopalmitin (MP) at the middle-chain triglyceride (MCT) oil/air interface. TP crystals were found to crystallize in the bulk before aggregating as large rectangular crystal conglomerates at the MCT oil/air interface. This leads to the slow formation of a plastic deformable, macroscopic crystal layer with high interfacial rheological moduli. MP crystals form directly at the MCT oil/air interface resulting in a comparatively fast formation of an elastic deformable network. Crystals with tentacle-like morphology were found to be responsible for the network elasticity. In this work, we show how interfacial crystallization dynamics and mechanical strength can be linked to the molecular structure and crystallization behavior of glyceride crystals.

Spontaneous particle desorption and "Gorgon" drop formation from particle-armored oil drops upon cooling

We study how the phenomenon of drop "self-shaping" (Denkov et al., Nature, 528, 2015, 392), in which oily emulsion drops undergo a spontaneous series of shape transformations upon emulsion cooling, is affected by the presence of adsorbed solid particles, like those used in Pickering emulsion stabilization. Experiments with several types of latex particles, and with added surfactant of low concentration to enable drop self-shaping, revealed several new unexpected phenomena: (1) adsorbed latex particles rearranged into regular hexagonal lattices upon freezing of the surfactant adsorption layer. (2) Spontaneous particle desorption from the drop surface was observed at a certain temperature - a remarkable phenomenon, as the solid particles are known to irreversibly adsorb on fluid interfaces. (3) Very strongly adhered particles to drop surfaces acted as a template to enable the formation of tens to hundreds of semi-liquid fibres, growing outwards from the drop surface, thus creating a shape resembling the Gorgon head from Greek mythology. Mechanistic explanations of all observed phenomena are provided using our understanding of the rotator phase formation on the surface of the cooled drops. The surface rotator phase creates positive line tension at the contact line formed between the particle surface and the fluid interface, which causes the particle ejection from the drop surface.

Methylene volumes in monoglyceride bilayers are larger than in liquid alkanes

The densities as a function of temperature of four fully hydrated saturated monoglycerides with even chain lengths ranging from eight to fourteen were determined by vibrating tube densitometry and their phase transition temperatures were determined by differential scanning calorimetry (DSC). We find the volume of a methylene group in a monoglyceride bilayer is 2% larger than in liquid alkanes at physiological temperatures, similar to the methylene group volumes found in phosphatidylcholine (PC) bilayers. Additionally, we carefully consider the traditional method of calculating component volumes from experimental data and note potential difficulties in this approach. In the literature, the ratio of terminal methyl volume (CH₃) to methylene (CH₂) volumes is typically assumed to be 2. By analysis of literature alkane data, we find this ratio actually ranges from 1.9 to 2.3 for temperatures ranging from 0 °C to 100 °C. For a rough sense of scale, we note that to effect a 2% reduction in volume requires of order 200 atmospheres of pressure, and pressures of this magnitude are biologically relevant. For instance, this amount of pressure is sufficient to reverse the effect of anesthesia. The component volumes obtained are an important parameter used for determining the structure of lipid bilayers and for molecular dynamics simulations.

Pre-Registration Assessment of Bone-Filling Products

The use of bone‐filling material to repair bone defects and fix implanted bone grafts is a developing area in medicine. Investigators can evaluate bone‐filling materials through use of several indices to make comparisons and to determine suitability for application in humans¹. However, it is quite difficult to transform their discovery into practical use, because the viability of the studied material might require examination of all aspects of properties. In addition, for a material to become a product, a complete procedure involving a declaration, registration, and approval is necessary. This article introduces the technical indices that the investigators and reporters should provide in their declaration and registration data to meet the relevant standards in China. The indices include physical and chemical properties, biocompatibility, biosecurity, pre‐clinical animal model tests, sterilization and disinfection, product duration, and packaging. Full consideration of all possible indices is crucial to realize the transformation from a designed product to a commercial medical device, which requires effective interaction between clinicians and engineers.