Small-angle Neutron Scattering Research Articles

A time-resolved investigation at multiple-length scales of the structure of liquid foam stabilized by albumins from pea

HypothesisThe structural details of foams made with pea albumins are affected by the pH of the initial solution and followed heat treatment. ExperimentsAn in situ, time-resolved investigation of foams prepared with pea albumins was conducted using small-angle neutron scattering (SANS) in combination with imaging and conductance measurements. Solutions were tested at pH three pH values (3, 4.5, and 8) before and after heating (90 °C for 1 and 5 min). FindingsThe characteristic structures present in the foam from the nano to the meso-scale differed during drainage depending on solution pH. Foams obtained at pH 3, had the largest bubble radius and thinnest plateau border, as well as the highest extent of liquid drainage. At pH 4.5, close to the isoelectric point of the proteins, foams displayed similar bubbles’ behavior to those at pH 8, but with the largest film thickness. In this case, the proteins were extensively aggregated. Heating of the solutions prior to foaming did not significantly affect the foam aging regardless of pH. The quantification of specific surface areas and film thickness over time without sample disruption shows to be a powerful approach to designing foam structures.

Wetting mechanism and alteration of nano-sized shale pores: Insights from contrast variation small angle neutron scattering

Wettability of tight shale is crucial for fluid flow and mass transport process in energy geosciences. However, understanding the interfacial chemistry and wetting mechanisms at sub-nano-pore scales remains a formidable challenge. In this study, the Contrast Variation technique of Small Angle Neutron Scattering (CV-SANS) is employed to investigate shale’s interfacial chemistry using reagents that possess a range of different polarities, including water, n-decane, toluene, and dimethyl methanamide. Through five different experimental strategies, we have demonstrated a successful modification of shale wettability, ranging from enhancement, weakening, to reversal. Delving into the mechanisms, we illustrated the crucial role of pre-existing liquid films in these changes, where the uniquely co-existing polar and non-polar functional groups in dimethyl methanamide acted as a conduit for interfacial chemistry adjustments. Furthermore, a solvent immersion led to matrix dilation as well as liberation of residual oil-occupied pores, resulting in altered pore size distributions, with hydrogen bonding playing a significant role in the polar groups. Interestingly, despite shale exhibiting a stronger affinity for oil over water, hydrophilic solvents induced more substantial dilation than lipophilic ones. Collectively, this work elucidates the dynamic change of interfacial chemistry via the configuration of polarity using chemical reagents, and the CV-SANS technique underscores its invaluable utilities in decoding the interfacial wettability traits in nanopore space of shale.

Legume Protein Gelation: the mechanism behind the formation of homogeneous and fractal gels

Protein gelation can provide texture in plant-based foods and can be influenced by many factors, including protein extraction method and salt addition. However, the protein gelation mechanism is still not well understood for plant proteins, especially for isolates obtained using commercial protein extraction processes. Therefore, the structural changes that legume sources such as yellow pea, faba bean, and soybeans undergo during the gelation process to understand the differences in their gelation mechanisms was investigated herein by using Small-Angle Neutron Scattering. Among these protein sources, the commercial extraction method was found to play a major part in the gelation pathway. Intensive protein extraction methods involving isoelectric precipitation led to lower protein solubility (∼ 1 – 38% w/w), larger insoluble protein particle sizes (60 – 100 μm), and a gelation pathway that is dependent on the changes of the insoluble protein particles. In contrast, extraction using ultrafiltration instead of precipitation resulted in higher protein solubility (∼18 – 88% w/w) and smaller insoluble protein particle sizes (40 – 70 μm), and the structural changes observed during gelation involved the structural changes of both soluble proteins and insoluble proteins. SEM imaging also showed different gel networks, with fractal networks formed by insoluble proteins (for sources with low solubility) or more homogenous networks formed by the interactions between the soluble proteins (for sources with high solubility). Despite the differences observed in the gelation network and the protein solubility, the gelation strength exhibited by protein sources at low protein solubility were similar to the ones by protein sources at high protein solubility, demonstrating the potential of fractal gel networks in providing texture.

SANS investigation of fungal loosenins reveal substrate dependent impacts of protein 1 action on inter-fibril distance and packing order of cellulosic substrates.

Microbial expansin-related proteins include fungal loosenins, which have been previously shown to disrupt cellulose networks and enhance the enzymatic conversion of cellulosic substrates. Despite showing beneficial impacts to cellulose processing, detailed characterization of cellulosic materials after loosenin treatment is lacking. In this study, small-angle neutron scattering (SANS) was used to investigate the effects of three recombinantly produced loosenins that originate from Phanerochaete carnosa, PcaLOOL7, PcaLOOL9, and PcaLOOL12, on the organization of holocellulose preparations from Eucalyptus and Spruce wood samples. Whereas the SANS analysis of Spruce holocellulose revealed an increase in interfibril spacing of neighboring cellulose microfibrils following treatment with PcaLOOL12 and to a lesser extent PcaLOOL7, the analysis of Eucalyptus holocellulose revealed a reduction in packing number following treatment with PcaLOOL12 and to a lesser extent PcaLOOL9. Parallel SEC-SAXS characterization of PcaLOOL7, PcaLOOL9, and PcaLOOL12 indicated the proteins likely function as monomers; moreover, all appear to retain a flexible disordered N-terminus and folded C-terminal region. The comparatively high impact of PcaLOOL12 motivated its NMR structural characterization, revealing a double-psi b-barrel (DPBB) domain surrounded by three alpha-helices - the largest nestled against the DPBB core and the other two part of loops extending from the core. The SANS analysis of PcaLOOL action on holocellulose samples confirms their ability to disrupt cellulose fiber networks and suggests a progression from reducing microfibril packing to increasing interfibril distance. The most impactful PcaLOOL, PcaLOOL12, was previously observed to be the most highly expressed loosenin in P. carnosa. Its structural characterization herein reveals its stabilization through two disulfide linkages, and an extended N-terminal region distal to a negatively charged and surface accessible polysaccharide binding groove.

Probing the Distribution and Mobility of Aminopolymers after Multiple Sorption-Regeneration Cycles: Neutron Scattering Studies.

Solid-supported amines are effective CO2 adsorbents capable of capturing CO2 from flue gas streams (10-15 vol % CO2) and from ultradilute streams, such as ambient air (∼400 ppm CO2). Amine sorbents have demonstrated promising performance (e.g., high CO2 uptake and uptake rates) with stable characteristics under repeated, idealized thermal swing conditions, enabling multicycle application. Literature studies suggest that solid-supported amines such as PEI/SBA-15 generally exhibit slowly reducing CO2 uptake rates or capacities over repeated thermal swing capture-regeneration cycles under simulated DAC conditions. While there are experimental reports describing changes in supported amine mass, degradation of amine sites, and changes in support structures over cycling, there is limited knowledge about the structure and mobility of the amine domains in the support pores over extended use. Furthermore, little is known about the effects of H2O on cyclic applications of PEI/SBA-15 despite the inevitable presence of H2O in ambient air. Here, we present a series of neutron scattering studies exploring the distribution and mobility of PEI in mesoporous silica SBA-15 as a function of thermal cycling and cyclic conditions. Small-angle neutron scattering (SANS) and quasielastic neutron scattering (QENS) are used to study the amine and H2O distributions and amine mobility, respectively. Applying repeated thermal swings under dry conditions leads to the thorough removal of water from the sorbent, causing thinner and more rigid wall-coating PEI layers that eventually lead to slower CO2 uptake rates. On the other hand, wet cyclic conditions led to the sorption of atmospheric water at the wall-PEI interfaces. When PEI remains hydrated, the amine distribution (i.e., wall-coating PEI layer thickness) is retained over cycling, while lubrication effects of water yield improved PEI mobility, in turn leading to faster CO2 uptake rates.

Incorporation of short-chain alcohols into fluid bilayers and its effect on membrane dynamic properties as seen by neutron scattering

In this work, we investigate the effect of concentrated alcoholic solutions (up to 40%w) on extruded 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes using scattering techniques. Extrusion in alcoholic aqueous solutions (methanol, ethanol, or butanol) reduces liposome size, evidenced from the decrease in hydrodynamic radius (RH) obtained from dynamic light scattering. Short-chain alcohols such as ethanol and butanol soften the lipid membranes, as observed by the decrease of the unrelaxed bending modulus (κ̃ ) obtained by neutron spin-echo spectroscopy. Thus, softer membranes are easily ruptured during extrusion, leading to a reduction in vesicle radius corroborated by a reduction in both RH and radius of gyration as seen by dynamic and static light scattering. Moreover, model-free analysis of small-angle neutron scattering (SANS) curves suggests that solvent molecules become incorporated into the lipid membrane. Analysing deviations in the scattering invariant from values predicted by mass balance, we find that the volume fraction of liposomes increases, modifying the scattering length density of the assemblies. By quantifying these changes, we estimate that 12% to 18% of the liposome membrane is composed of solvent molecules (alcohol + water), depending on the type of alcohol and its concentration present in solution, with the exception of glycerol where next to no incorporation was observed. Finally, structural parameters obtained through light scattering and changes in contrast profiles calculated from analysis of the invariant were corroborated through modelling of the SANS curves. Modelling suggests that a reduction of bilayer thickness takes place for liposomes dispersed in ethanolic and butanolic solutions, but not in the presence of methanol or glycerol.

Colloidal Nafion in Liquid Media: Insight from SANS Analysis and Molecular Dynamics Simulations

Colloidal Nafion™ morphology in liquid media plays a critical role in determining the electrode performance of fuel cells and electrolyzers. In this presentation, we demonstrate that commonly reported, cylindrical morphologies of Nafion in liquid media are not ubiquitous among Nafion dispersions and assuming such may provide inaccurate information.1 Here we compare colloidal Nafion™ morphology in N-methyl-pyrrolidone (NMP) and water using small angle neutron scattering (SANS) and all atomistic molecular dynamics simulations (MD).2 Our SANS analyses using model-dependent and model-independent techniques combined with MD simulations demonstrated highly gel-like particles best describe Nafion particles in NMP, which is in stark contrast to the commonly assumed cylindrical morphology. In high dielectric constant dispersants such as water, the cylindrical morphology is a feasible choice to describe the scattering data, however, the particle radius is much lower than previous report (R = 10 Å). MD simulations support the SANS analysis and show that the sulfonic acid groups are fully dissociated and strongly solvated on the outer wall of the particle suggesting that the structure is driven by hydrophobic interactions.References Aldebert, B. Dreyfus, G. Gebel, N. Nakamura, M. Pineri, F. Volino, Macromolecules, 19, 2651-2653 (1986). Jeffrey M. Klein, Cynthia Welch, Sathish Ponnurangam, Atefeh Tarokh, Kunal Karan, Marilyn E. Hawley, Anna Sokolova, Sung-Dae Yim, Rex P. Hjelm, Yu Seung Kim, ACS Macro Letters, 12, 1648-1653 (2023).

Microstructural Analysis of Lithium-Ion Battery Cathode Carbon-Binder Domain across Processing Conditions

Improvement of lithium-ion battery (LIB) energy density and rate capability is necessary to increase adoption of electric vehicles (EVs) and curb transportation emissions. The cathode structure must support facile ion and electron transport, enabling rapid charging while maintaining near-theoretical capacity. Much investigation focuses on active material design for fast-charging cathodes, [1] but less is understood about the effect of electrode processing on carbon-binder domain (CBD) structure and its impact on rate capability. As conductive carbon facilitates electron transfer, slow Li+ diffusion through cathode micropores is rate-limiting and prevents full active material utilization at high charge rates. [2,3] However, efforts to improve Li+ diffusion, such as increasing porosity, introduce charge-transfer limitations. [4] Thus, cathode processing conditions and resulting microstructure must be carefully designed to optimize for both electronic and ionic conductivity. For example, an increase in coating shear rate and decrease in slurry solid content improves long-range electronic pathways [5,6] and calendaring strengthens active material-carbon contacts to reduce charge-transfer resistance. [2] However, the impact of processing variations on ionic transport pathways, which can be described by CBD porosity and tortuosity, is not well understood. Further, because the CBD is traditionally characterized as a single phase, the distinct influences of insulating binder and conductive carbon distributions on structure and performance are poorly defined.In this talk, I will discuss how electrode coating conditions impact pathways available to Li+ and electrons within the CBD with the goal of identifying optimal microstructures for efficient transport. We fabricate cathodes with varying solid content, coating shear rate, and degree of calendaring to explore disparate CBD microstructures. We use electrochemical impedance spectroscopy (EIS) with a symmetric cell & blocking electrolyte to determine cathode resistivity and tortuosity and plasma focused ion beam scanning electron microscopy (PFIB-SEM) to examine CBD morphology over a representative cathode volume (~80 x 80 x 50 µm3). We then use small-angle neutron scattering (SANS) with solvent contrast variation to distinguish between binder and carbon distributions and determine the surface area of each component within the CBD. Relationships between processing conditions, structural variations, and rate capability will be discussed, informing the design of the CBD for facile transport and improved fast charging performance. Further, reducing ionic transport limitations through intentional design of LIB cathodes will enable thicker electrodes to increase cell energy density.

Pegylated surfactants based on fatty acids: 12-hydroxystearic acid versus stearic acid

We describe the aqueous behavior of short Polyethylene glycol (PEG) chains of Mw 4 kDa that are either mono-functionalized or di-functionalized by 12-hydroxy stearic acid (HSA), and stearic acid (SA), respectively. The end capping of the chains by the fatty acids is achieved by Steglich esterification, after a step of protection of the 12-OH functional group in the case of HSA. Small Angle Neutron Scattering (SANS) shows that mono-functionalized chains with both SA or HSA sticky ends self-assemble in star micelles in aqueous solution, and interact through repulsive steric interactions. The di-functionalized telechelic chains self-assemble in flower micelles that interact through interactions that are attractive on average due to the formation of bridges by chains that share their both ends in two different micelles. Solutions of telechelic chains undergo a phase separation between a dilute solution of micelles and a dense hexagonal crystalline network of flower micelles above a given polymer concentration threshold. This threshold is lower for SA-PEG-SA than for HSA-PEG-HSA. We postulate that this difference of behavior arises from the formation of hydrogen bonds between the OH groups at the C12 of the alkyl chain in case of HSA that increase the stability of the hydrophobic core of the micelles.

Study of readout system for 3He linear position sensitive detectors

This study introduces a readout system for 3He linear position-sensitive detectors (LPSDs), tailored for the Small Angle Neutron Scattering (SANS) spectrometer of the Compact Pulsed Hadron Source (CPHS) at Tsinghua University. Central to this system is the employment of a trapezoidal filter as the primary signal shaper, selected for its enhanced noise filtering capabilities and efficacy in mitigating ballistic deficit. Additionally, the integration of a digital CR filter aims to counteract baseline drift within trigger signals. This innovative architecture underwent validation via computer programs using experimental data, demonstrating superior performance in spatial resolution compared to conventional Gaussian filter-based approaches. Meanwhile, the improvement in spatial resolution comes with a narrower pulse width, promising a higher throughput at high count rates. When applied to a 16-tube detector module, the system achieved an average position resolution of 3.63 mm (FWHM) at the central region and 4.03 mm at the end regions. Furthermore, with a pusle width of 0.6 μs, the 96-tube detector array is promised to sustain a count rate over 1 Mcps.

In-situ SANS study on spatial evolution of coal nanoporosity during pyrolysis at elevated temperatures

The nanopore evolution in coal during pyrolysis is vital for optimizing heat and mass transfer in coal conversion processes. Therefore, small-angle neutron scattering (SANS) was utilized to examine the in-situ changes in the nanopore structures of two subbituminous Chinese coal samples during pyrolysis. The nanopore structures were examined in terms of average pore size, pore volume distribution, fractal dimension by SANS at elevated temperatures. Throughout the pyrolysis process, a consistent enlargement of the average size of nanoscale pores was noted as temperatures escalated, with an expansion ranging from 5.3 to 8.2 nm. Particularly during the devolatilization phase (300–500 °C), there was a marked surge in the volume of large pores, exhibiting a growth rate of about 88.1–150.5%. High-temperature (600–800 °C) conditions facilitated the formation of new and smaller pores. While the surface roughness of nanopores experienced a slight reduction throughout the pyrolysis, the directional growth of the pores maintained an isotropic distribution.

Morphology evolution of lipid nanoparticle discovered by small angle neutron scattering

The structure of mRNA lipid nanoparticles (LNPs) is still under debate, with different studies presenting varying morphological characteristics, significantly hindering their biomedical potential. A typical formulation process of mRNA LNPs involves three steps: initial rapid mixing of lipids in an ethanol phase and mRNA in an acidic aqueous phase, followed by the swift removal of ethanol, and finally adjusting the solution to a neutral environment. In this study, we utilize Small Angle Neutron Scattering (SANS) with contrast matching to reveal the kinetic pathway-dependent of mRNA LNPs morphology. We find that the formulation process of the Moderna COVID-19 vaccine is controlled by a competition between aggregation and microphase separation, dictating the diverse morphologies observed in mRNA LNPs. The first step leads to the formation of polydisperse spherical droplets with an average diameter of 42±6.0 nm in an acidic ethanol aqueous solution. Ethanol removal initiates both aggregation and internal microphase separation, resulting in a polydisperse core-shell structure with an average diameter of 48±3.7 nm. Heptadecan-9-yl 8-((2-hydroxyethyl) (6-oxo-6-(undecyloxy) hexyl) amino) octanoate (SM-102) binds to mRNA via electrostatic interaction to form a reverse-wormlike micelle structure inside. The 1,2-Distearoyl-sn‑glycero-3-phosphocholine (DSPC) and PEG-lipid are just in the shell and cholesterol acting as a filler throughout the core-shell structure. Upon transitioning to a neutral environment, SM-102 loses its charge and neither the periphery nor the reverse-wormlike micelle can maintain their stabilities, leading to further aggregation and microphase separation. The average diameter of core-shell structure turns to be 66±5.2 nm. In the actual formulation process of the Moderna COVID-19 vaccine, steps 2 and 3 occur simultaneously, and the competition between aggregation and microphase separation determines the final morphology. These findings offer crucial insights into optimizing the morphology of mRNA LNPs, thereby facilitating advancements in vaccine development and mRNA vaccine delivery technologies.

The Influence of SC-CO2 on the Nanopore Structures of Different Types of Shales Based on Small-Angle Neutron Scattering and Multifractal Methods

The Influence of SC-CO₂ on the Nanopore Structures of Different Types of Shales Based on Small-Angle Neutron Scattering and Multifractal Methods

Molecular Insights into the Conformational and Binding Behaviors of Human Serum Albumin Induced by Surface-Active Ionic Liquids.

Extensive research has been carried out to investigate the stability and function of human serum albumin (HSA) when exposed to surface-active ionic liquids (SAILs) with different head groups (imidazolium, morpholinium, and pyridinium) and alkyl chain lengths (ranging from decyl to tetradecyl). Analysis of the protein fluorescence spectra indicates noticeable changes in the secondary structure of HSA with varying concentrations of all SAILs tested. Helicity calculations based on the Fourier transform infrared (FTIR) data show that HSA becomes more organized at the micellar concentration of SAILs, leading to an increased protein activity at this level. Small-angle neutron scattering (SANS) data confirm the formation of a bead-necklace structure between the SAILs and HSA. Atomistic molecular dynamics (MD) simulation results identify several hotspots on the protein surface for interaction with SAIL, which results in the modulation of protein conformational fluctuation and stability. Furthermore, fluorescence resonance energy transfer (FRET) experiments with the intramolecular charge transfer (ICT) probe trans-ethyl p-(dimethylamino) cinnamate (EDAC) demonstrate that higher alkyl chain lengths and SAIL concentrations result in a significantly increased energy transfer efficiency. The findings of this study provide a detailed molecular-level understanding of how the protein structure and function are affected by the presence of SAILs, with potential implications for a wide range of applications involving protein-SAIL composite systems.

5-Fluoro uracil mediated transformation of surface-active ionic liquid based micellar nanoaggregates into pH-responsive vesicular nanoaggregates as promising drug delivery vehicle

Surface-active ionic liquids (SAILs) are poised as significant contenders in sustained and targeted drug delivery due to their membrane-like structures and their ability to transport drug molecules regardless of their polarity. In order to design a simple system that an encapsulate the anticancer drug and release it in a sustained manner, herein we designed vesicular nano-aggregates through synergistically interacting chemotherapeutic drug 5-Fluoro Uracil (5-FU) with the biocompatible SAILs, Choline Oleate ([Ch][Ol]) and Tetramethyl guanidine Oleate ([TMG][Ol]). The intention for designing the system is to offers less complexity and improved drug loading efficiency and targeted and sustained release. The molecular interactions have been proven by computational approach and the size of the nanoaggregates was determined using techniques such as Dynamic Light Scattering (DLS), Förster Resonance Energy Transfer (FRET) and Small-Angle Neutron Scattering (SANS). SANS fitting data and TEM images confirmed the transition of prolate ellipsoid micelles at [5-FU] = 0 mM to uni-lamellar ([5-FU] = 1 mM) and multi-lamellar vesicles ([5-FU] = 2 mM). These vesicular nano-aggregates are studied for their stability against temperature, pH-response and ionic strength of solution, revealing stability up to 60 °C, robust at physiological pH 7.4 and remain stable to exposure to Na+ and Ca2+ ions at concentrations up to 180 mM and 50 mM, respectively. The vesicular nano-aggregates ([Ch][Ol]/5-FU and [TMG][Ol]/5-FU) when exposed to physiological pH (i.e., 7.4) released 64.8 % and 61.2 % drug release whereas when the same systems were exposed to cancerous pH (5.2 and 6.7) released 95.9 % and 84.5% (pH 5.2 and 6.7) and 94.8 % and 81.2 % (pH 5.2 and 6.7) for the [Ch][Ol]/5-FU and [TMG][Ol]/5-FU systems, respectively. Results for the studied system encompasses them as a promising candidate for drug release at specific sites. The anticipated research might pave the way for the development of a biocompatible and stimuli-responsive drug carrier that would allow for the localized delivery of an anticancer drug.

Learning from virtual experiments to assist users of Small Angle Neutron Scattering in model selection

In this work, we combine the advantages of virtual Small Angle Neutron Scattering (SANS) experiments carried out by Monte Carlo simulations with the recent advances in computer vision to generate a tool that can assist SANS users in small angle scattering model selection. We generate a dataset of almost 260.000 SANS virtual experiments of the SANS beamline KWS-1 at FRM-II, Germany, intended for Machine Learning purposes. Then, we train a recommendation system based on an ensemble of Convolutional Neural Networks to predict the SANS model from the two-dimensional scattering pattern measured at the position-sensitive detector of the beamline. The results show that the CNNs can learn the model prediction task, and that this recommendation system has a high accuracy in the classification task on 46 different SANS models. We also test the network with real data and explore the outcome. Finally, we discuss the reach of counting with the set of virtual experimental data presented here, and of such a recommendation system in the SANS user data analysis procedure.

New processing routes for Zr-based ODS ferritic steels

In this work, Zr addition is proposed to refine the nanoparticle dispersion in an ODS RAF steel of composition Fe-14Cr-2W-0.3Zr-0.24Y (wt.%). Three batches of material are obtained using pre-alloyed atomized powder, where yttrium is directly introduced in the melt, and manufactured through three different processing routes. First route is based on the newly developed STARS route that aims to avoid subsequent mechanical alloying. The second route explores the impact of mechanical alloying in pre-oxidized powders. The third route uses mechanically alloyed powders without the pre-oxidation process. The ODS-powders were individually consolidated by hot isostatic pressing and later hot rolled. The obtained materials were characterized by small-angle neutron scattering (SANS) and X-ray absorption spectroscopy (XAS) techniques. SANS and XAS analysis point out the absence of oxide nanoparticles in the material based on the STAR route. SANS analysis confirms that the mechanically alloyed materials do exhibit the presence of nanoparticles. These are identified as Zr-O-rich nanoprecipitates by XAS and the calculated A-ratio by SANS is linked with the phase Y2Zr2O7. Their radii are in the range of 3–3.6 nm. XAS results show that mechanical alloying minimizes the initial differences regarding the oxidation state between the ODS powders with and without pre-oxidation.

The porous system of a reverse osmosis membrane − operando studies with small-angle neutron scattering

This manuscript deals with operando small-angle neutron scattering (SANS) on a reverse osmosis (RO) thin film composite (TFC) membrane, which was exposed to salt-free water at a transmembrane pressure of 25 bar and a transverse flow rate of 18 L/h. Permeate flux and electric conductivity were detected in parallel to SANS. The relevant objects of investigation are macro- and nanopores in the range of μm and nm, which were investigated with two SANS diffractometers covering a scattering vector Q between 10-4 and 0.3 Å−1. Salt-free water isotopes of H2O and D2O and their mixtures were used for the purpose of contrast matching, thereby determining the size of pores in the membrane layers. Macropores of the order of μm dimension were found in the nonwoven polypropylen (PP) layer showing a decline in size between 2 and 2.5 % over the experimental time of 7 to 17 h. The macropores of the polysulfone layer (PSU) have a size of about 0.4 μm. Nanopores with an average total diameter of (23.7 ± 0.5) Å of volume fraction of the order of 2 % vol are found exclusively in the PSU layer. The pore morphology was compared with the results of local methods such as SEM and TEM tomography, showing the complementarity of these methods and their necessity for a more complete picture of membrane morphology. A correlation between permeate flux and SANS parameter is discussed.

Effect of Micellar Morphology on the Temperature-Induced Structural Evolution of ABC Polypeptoid Triblock Terpolymers into Two-Compartment Hydrogel Network.

We investigated the temperature-dependent structural evolution of thermoreversible triblock terpolypeptoid hydrogels, namely poly(N-allyl glycine)-b-poly(N-methyl glycine)-b-poly(N-decyl glycine) (AMD), using small-angle neutron scattering (SANS) with contrast matching in conjunction with X-ray scattering and cryogenic transmission electron microscopy (cryo-TEM) techniques. At room temperature, A100M101D10 triblock terpolypeptoids self-assemble into core-corona-type spherical micelles in aqueous solution. Upon heating above the critical gelation temperature (T gel), SANS analysis revealed the formation of a two-compartment hydrogel network comprising distinct micellar cores composed of dehydrated A blocks and hydrophobic D blocks. At T ≳ T gel, the temperature-dependent dehydration of A block further leads to the gradual rearrangement of both A and D domains, forming well-ordered micellar network at higher temperatures. For AMD polymers with either longer D block or shorter A block, such as A101M111D21 and A43M92D9, elongated nonspherical micelles with a crystalline D core were observed at T < T gel. Although these enlarged crystalline micelles still undergo a sharp sol-to-gel transition upon heating, the higher aggregation number of chains results in the immediate association of the micelles into ordered aggregates at the initial stage, followed by a disruption of the spatial ordering as the temperature further increases. On the other hand, fiber-like structures were also observed for AMD with longer A block, such as A153M127D10, due to the crystallization of A domains. This also influences the assembly pathway of the two-compartment network. Our findings emphasize the critical impact of initial micellar morphology on the structural evolution of AMD hydrogels during the sol-to-gel transition, providing valuable insights for the rational design of thermoresponsive hydrogels with tunable network structures at the nanometer scale.

Detecting Shape of Hybrid Polymer/Surfactant Micelles: Cryo-Transmission Electron Microscopy, Small-Angle Neutron Scattering and Dynamic Light Scattering Study

In-depth study of shape of hybrid micelles in the micellar solutions of anionic surfactant potassium oleate, containing hydrophobic polymer poly(4-vinylpyridine) (P4VP) was conducted via cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS) and dynamic-light scattering of visible light (DLS). Direct visualization of the solutions with cryo-TEM evidenced the coexistence of polymer-free spherical micelles and branched rodlike hybrid micelles with mean length of 200 nm and radius of 2 nm, governed by contour length of solubilized P4VP and length of hydrophobic “tail” of potassium oleate, respectively. The formation of branches in the hybrid micelles was explained by attaching the thermodynamically unfavorable end-caps of micelles to their polymer-loaded cylindrical fragments. By SANS it was shown that the cylindrical local shape and the radius of the micelles are independent of the concentration of embedded P4VP. Relaxation processes in the solutions were investigated with DLS. Three relaxation modes were observed for hybrid micelles, similar to polymer-free wormlike micelles. Fast and medium relaxation modes were attributed to diffusion of entangled micellar chains and their segments, respectively. The slow mode was related to electrostatic repulsion between similarly charged hybrid micelles.