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The outstanding mechanical properties, light weight, and biodegradability of cellulose nanofibrils (CNFs) make them promising components of renewable and sustainable next-generation reinforced composite biomaterials and bioplastics. Manufacturing CNFs at a pilot scale requires disc-refining fibrillation of dilute cellulose fibers in aqueous pulp suspensions to shear the fibers apart into their nanodimensional forms, which is, however, an energy-intensive process. Here, we used atomistic molecular dynamics (MD) simulation to examine media that might facilitate the reduction of interactions between cellulose fibers, thereby reducing energy consumption in fibrillation. The most suitable medium found by the simulations was an aqueous solution with 0.007:0.012 wt.% NaOH:urea, and indeed this was found in pilot-scale experiments to reduce the fibrillation energy by ~21% on average relative to water alone. The NaOH:urea-mediated CNFs have similar crystallinity, morphology, and mechanical strength to those formed in water. The NaOH and urea act synergistically on CNFs to aid fibrillation but at different length scales. NaOH deprotonates hydroxyl groups leading to mesoscale electrostatic repulsion between fibrils, whereas urea forms hydrogen bonds with protonated hydroxyl groups thus disrupting interfibril hydrogen bonds. This suggests a general mechanism in which an aqueous medium that contains a strong base and a small organic molecule acting as a hydrogen-bond acceptor and/or donor may be effectively employed in materials processes where dispersion of deprotonable polymers is required. The study demonstrates how atomic-detail computer simulation can be integrated with pilot-scale experiments in the rational design of materials processes for the circular bioeconomy. [ABSTRACT FROM AUTHOR]

Salt hydrate-based phase-change materials are considered promising for future heat storage applications in residential heating/cooling systems. Smooth phase transition from the liquid to solid phase and vice versa is essential for effective heat exchanger; however, supercooling in salt hydrates delays the onset of liquid–solid phase transition. We investigate the molecular level mechanism of supercooling in sodium sulfate decahydrate (SSD). SSD is a complex salt hydrate whose properties are governed by electrostatic forces that include pure Coulombic interactions as well as hydrogen bonds. Experimentally, we examine the importance of a nucleator in reducing supercooling temperatures. We investigated the effect of various mass concentrations of a borax nucleator on a decrease of supercooling temperatures. Molecular dynamics simulation techniques are used to obtain a basic understanding of supercooling in SSD. We observe that by introducing borax as a nucleator, there is a decrease in the supercooling temperature before nucleation. Our molecular dynamics simulations show that long-range electrostatics between sodium and sulfate ion pairs and that with polar water molecules is responsible for delayed nucleation in SSD that results in supercooling, and also, dynamics of charged molecules slows down. The lack of crystallization leads to amorphous structures in supercooled SSD. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are used to understand the self-assembly and structural relaxation in ionomer melts containing less than 10% degree of ionization on the backbone. The self-assembly of charged sites and counterions shows structural ordering and agglomeration with a range of structures that can be achieved by changing the dielectric constant of the medium. The intermediate scattering function shows a decoupling of charge and counterion relaxation at longer length scales for only high dielectric constant and at shorter length scales for all dielectric constants. Overall, the slow structural decay of counterions in the strongly correlated ionomer system closely resembles transport properties of semi-flexible polymers. [ABSTRACT FROM AUTHOR]

The molecular structure and dynamics of water differ considerably at various interfaces. We compare the interfacial water structure–property relationship on three different carbon substrates, namely, amorphous carbon, compressed expanded natural graphite, and pure graphite by utilizing atomistic molecular dynamics simulations. The effect of different substrates on the structural and dynamical properties of water can readily be observed. The density distributions parallel and normal to the substrates show oblate droplet structures. The normal to the substrate water distribution shows a strong hydration layer at the interface that does not vary with substrates. However, the disparity in the structure and dynamics on three different substrates shows that the surface morphologies of the substrates are critical for determining nanoscale water properties. Furthermore, it is observed that the formation of an interfacial water layer or the hydration layer is a direct consequence of both water "confinement" at the nanoscale and "attraction" between water molecules and the carbon substrates. [ABSTRACT FROM AUTHOR]

The structural and dynamical properties of polymer nanocomposites are investigated using stochastic molecular dynamics simulations. For spherical nanoparticles dispersed in a polymer matrix, the results indicate that the polymer-nanoparticle interaction strength and the overall system temperature are primarily responsible for the type of dispersed state (clustering and homogeneous dispersion) achieved. A systematic study probing temperature, polymerization, and polymer-nanoparticle and nanoparticle-nanoparticle interaction strengths has been performed. In this paper, however, we focus the discussion on the results for varying polymer-nanoparticle interaction strengths at different temperatures. By examining the structure and dynamics, we show that there are two kinds of “clustering transitions:” one due to thermodynamic and another due to the dynamical response of the system. From these results, a representative phase diagram is developed that captures the entire simulated space and allows the easy identification of the highly dispersed and the clustered states. [ABSTRACT FROM AUTHOR]

Self-assembly and dynamics of a polyelectrolyte (PE)-surfactant complex (PES) are investigated using molecular dynamics simulations. The complexation is systematically studied for five different PE backbone charge densities. At a fixed surfactant concentration the PES complexation exhibits pearl necklace to agglomerated double spherical structures with a PE chain decorating the surfactant micelles. The counterions do not condense on the complex but are released in the medium with a random distribution. The relaxation dynamics for three different length scales, the polymer chain, segmental, and monomer, show distinct features of the charge and neutral species; the counterions are fastest followed by the PE chain and surfactants. The surfactant heads and tails have the slowest relaxation due to their restricted movement inside the agglomerated structure. At the shortest length scale, all the charge and neutral species show similar relaxation dynamics confirming Rouse behavior at monomer length scales. Overall, the present study highlights the structure-property relationship for polymer-surfactant complexation. These results help improve the understanding of PES complexes and should aid in the design of better materials for future applications. [ABSTRACT FROM AUTHOR]

Organic photovoltaics (OPVs) are a topic of extensive research because of their potential application in solar cells. Recent work has led to the development of a coarse-grained model for studying poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends using molecular simulations. Here we provide further validation of the force field and use it to study the thermal annealing process of P3HT:PCBM blends. A key finding of our study is that, in contrast to a previous report, the annealing process does not converge at the short time scales reported. Rather, we find that the self-assembly of the blends is characterized by three rate dependent stages that require much longer simulations to approach convergence. Using state-of-the-art high performance computing, we are able to study annealing at length and time scales commensurate with devices used in experiments. Our simulations show different phase segregated morphologies dependent on the P3HT chain length and PCBM volume fraction in the blend. For short chain lengths, we observed a smectic morphology containing alternate P3HT and PCBM domains. In contrast, a phase segregated morphology containing domains of P3HT and PCBM distributed randomly in space is found for longer chain lengths. Theoretical arguments justifying stabilization of these morphologies due to shape anisotropy of P3HT (rod-like) and PCBM (sphere-like) are presented. Furthermore, results on the structure factor, miscibility of P3HT and PCBM, domain spacing and kinetics of phase segregation in the blends are presented in detail. Qualitative comparison of these results with published small-angle neutron scattering experiments in the literature is presented and an excellent agreement is found. [ABSTRACT FROM AUTHOR]

Focuses on a one-dimensional plasma discharge under steady state conditions. Use of simple models for source and collisions; First-order differential equation obtained that simultaneously describes the bulk and presheath of the plasma; Analytic expressions obtained for profiles when collision frequency is assumed constant.

An ionomeric, leathery thermoplastic with high mechanical strength is prepared by a new thermal processing method from a soft, melt‐processable rubber. Compositions made by incorporation of equal‐mass lignin, a renewable oligomeric feedstock, in an acrylonitrile‐butadiene rubber often yield weak rubbers with large lignin domains (1–2 µm). The addition of zinc chloride (ZnCl2) in such a composition based on sinapyl alcohol‐rich lignin during a solvent‐free synthesis induces a strong interfacial crosslinking between lignin and rubber phases. This compositional modification results in finely interspersed lignin domains (<100 nm) that essentially reinforce the rubbery matrix with a 10–22 °C rise in the glassy‐to‐rubbery transition temperature. The ion‐modified polymer blends also show improved materials properties, like a 100% increase in ultimate tensile strength and an order of magnitude rise in Young's modulus. Coarse‐grained molecular dynamics (MD) simulations verify the morphology and dynamics of the ionomeric material. The computed result also confirms that the ionomers have glassy characteristics. [ABSTRACT FROM AUTHOR]

In this paper we present a self-consistent kinetic simulation of a diffusion dominated bulk plasma region. Collisions have been modeled by a velocity-dependent Krook collision operator. The technique is capable of handling large systems--the results presented here are for systems 100λ[sub mfp] in extent--yet retains the details of the edge physics present. The distribution functions for the trapped and the transiting orbits and their moments are obtained. The density and potential profiles inside the bulk shows overall agreement with ambipolar predictions. The kinetic equivalent of D[sub A] is obtained and compared to the fluid prediction. The validity of the code and the observed deviations from fluid treatments are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Liquid crystalline epoxy networks (LCENs) are a class of materials that combine the useful benefits of both liquid crystals and epoxy networks exhibiting fascinating thermal, mechanical, and stimuli-responsive properties. They have emerged as a new platform for developing functional materials suitable for various applications, such as sensors, actuators, smart coatings and adhesives, tunable optical systems, and soft robotics. This article provides an overview of LCENs and their composites as functional materials, including their synthesis and characterisation, focusing on structure-processing–property relationships. We provide objective analyses on how materials engineers can use these relationships to develop LCENs with desired functionalities for targeted applications. Emerging areas, including advanced manufacturing and multi-functional design of LCENs are covered to show the overall progress in this field. We also survey the forward-looking status of LCEN research in designing novel materials for future technologies. [ABSTRACT FROM AUTHOR]

Nanostructured thin films were synthesized using a silica-based sol-gel method. The morphology of the films was tailored by controlling the hydrolysis and crosslinking mechanisms of the tetraethyl orthosilicate precursor. Silica nanoparticle self-assembled structures and linear silica chains were crosslinked and formed monolithic nanostructured films. The self-assembly mechanism was investigated using coarse-grained molecular dynamic simulation. Three nanostructured configurations were synthesized and studied to optimize the surface features of the films and minimize the adhesion of sand particles. Surface microscopy imaging and adhesion force measurements using atomic force microscopy with an attached silica particle on the cantilever tip were performed to correlate the adhesion force and the surface structure. The solar specular reflectance of coated solar mirror samples was measured across the solar spectrum before and after the soiling test of the samples. The mechanical properties of the thin films were evaluated using nanoindentation measurements on coated substrates. The solution-derived thin film coatings can provide anti-soiling protection of solar glass in desert environments and increase the efficiency of photovoltaic and concentrated solar power installations. • A simple method to fabricate nanotextured monolithic silica thin film coating that exhibits anti-soiling behavior and enhanced durability. [ABSTRACT FROM AUTHOR]

We demonstrate a machine learning enabled low-cost acoustic detection of protease which may find application in assuring quality and safety of dairy products, drug screening, molecular profiling, and disease diagnostics. A hydrophilic SiO 2 -coated quartz crystal microbalance (QCM) acts as a substrate to assemble α-, β-, and ĸ-casein layers (protease reporters) and as a transducer for measuring changes in frequency as casein is removed by protease. We demonstrate that α-, β-, and ĸ-caseins can form stable assembly on SiO 2 from phosphate-buffered solution (PBS) solution. Exposure to protease results in cleaving of casein which changes the frequency of the 1st–11th odd harmonics of QCM. Monitoring β-casein cleavage allows ∼0.2 nM detection of trypsin and ∼0.5 nM detection of plasmin and enables differentiation between trypsin and plasmin after <2 min of protease exposure. The casein-coated QCM allows sub-nanomolar detection and classification of protease. [ABSTRACT FROM AUTHOR]

The outstanding mechanical properties, light weight, and biodegradability of cellulose nanofibrils (CNFs) make them promising components of renewable and sustainable next-generation reinforced composite biomaterials and bioplastics. Manufacturing CNFs at a pilot scale requires disc-refining fibrillation of dilute cellulose fibers in aqueous pulp suspensions to shear the fibers apart into their nanodimensional forms, which is, however, an energy-intensive process. Here, we used atomistic molecular dynamics (MD) simulation to examine media that might facilitate the reduction of interactions between cellulose fibers, thereby reducing energy consumption in fibrillation. The most suitable medium found by the simulations was an aqueous solution with 0.007:0.012 wt.% NaOH:urea, and indeed this was found in pilot-scale experiments to reduce the fibrillation energy by ~21% on average relative to water alone. The NaOH:urea-mediated CNFs have similar crystallinity, morphology, and mechanical strength to those formed in water. The NaOH and urea act synergistically on CNFs to aid fibrillation but at different length scales. NaOH deprotonates hydroxyl groups leading to mesoscale electrostatic repulsion between fibrils, whereas urea forms hydrogen bonds with protonated hydroxyl groups thus disrupting interfibril hydrogen bonds. This suggests a general mechanism in which an aqueous medium that contains a strong base and a small organic molecule acting as a hydrogen-bond acceptor and/or donor may be effectively employed in materials processes where dispersion of deprotonable polymers is required. The study demonstrates how atomic-detail computer simulation can be integrated with pilot-scale experiments in the rational design of materials processes for the circular bioeconomy., Competing Interests: Competing interests statement:The authors declare no competing interest.

Sodium sulfate decahydrate (SSD) is a low-cost phase-change material (PCM) for thermal energy storage applications that offers substantial melting enthalpy and a suitable temperature range for near-ambient applications. However, SSD's consistent phase separation with decreased melting enthalpy over repeated thermal cycles limits its application as a PCM. Sulfonated polyelectrolytes, such as dextran sulfate sodium (DSS), have shown great effectiveness in preventing phase separation in SSD. However, there is limited understanding of the stabilization mechanism of SSD by DSS at the atomic length and time scales. In this work, we investigate SSD stabilization via DSS using neutron scattering and molecular dynamics (MD) simulations. Neutron scattering and pair distribution function analysis revealed the structural evolution of the PCM samples below and above the phase change temperatures. MD simulations revealed that water from the hydrate structure migrates from the hydrate crystal to the SSD-DSS interfacial region upon melting. The water is stabilized at this interface by aggregation around the hydrophilic sulfonic acid groups attached to the backbone of the polyelectrolyte. This architecture retains water near the dehydrated sodium sulfate, preventing phase separation and, consequently, stabilizing SSD rehydration. This work provides atomistic insight into selecting and designing stable and high-performance PCMs for heating and cooling applications in building technologies., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

We investigate the effect of high-surface-area self-assembled TiO 2 :Cu 2 O nanostructures for CO 2 and relative humidity gravimetric detection using polyethylenimine (PEI), 1-ethyl-3-methylimidazolium (EMIM), and polyacrylamide (PAAm). Introduction of hierarchical TiO 2 :Cu 2 O nanostructures on the surface of quartz crystal microbalance sensors is found to significantly improve sensitivity to CO 2 and to H 2 O vapor. The response of EMIM to CO 2 increases fivefold for 100 nm-thick TiO 2 :Cu 2 O as compared to gold. At ambient CO 2 concentrations, the hierarchical assembly operates as a sensor with excellent reversibility, while at higher pressures, the CO 2 desorption rate decreases, suggesting possible application for CO 2 sequestration under these conditions. The gravimetric response of PEI to CO 2 increases by a factor of 3 upon introduction of a 50 nm TiO 2 :Cu 2 O layer. The PAAm gravimetric response to water vapor also increases by a factor of 3 and displays improved reversibility with the addition of 50 nm TiO 2 :Cu 2 O structures. We found that TiO 2 :Cu 2 O can be used to lower the detection limits for CO 2 sensing with EMIM and PEI and lower the detection limits for H 2 O sensing with PAAm by over a factor of 2. Coarse-grained and all-atom molecular dynamics simulations indicate the dissociative character of ionic liquid assembly on TiO 2 :Cu 2 O interfaces and different distributions of CO 2 and H 2 O molecules on bare and ionic liquid-coated surfaces, confirming experimental observations. Overall, our results show high potential of hierarchical assemblies of TiO 2 :Cu 2 O/room temperature ionic liquid and polymer films for sensors and CO 2 sequestration.

Understanding how additives interact and segregate within bulk heterojunction (BHJ) thin films is critical for exercising control over structure at multiple length scales and delivering improvements in photovoltaic performance. The morphological evolution of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blends that are commensurate with the size of a BHJ thin film is examined using petascale coarse-grained molecular dynamics simulations. Comparisons between two-component and three-component systems containing short P3HT chains as additives undergoing thermal annealing demonstrate that the short chains alter the morphology in apparently useful ways: they efficiently migrate to the P3HT/PCBM interface, increasing the P3HT domain size and interfacial area. Simulation results agree with depth profiles determined from neutron reflectometry measurements that reveal PCBM enrichment near substrate and air interfaces but a decrease in that PCBM enrichment when a small amount of short P3HT chains are integrated into the BHJ blend. Atomistic simulations of the P3HT/PCBM blend interfaces show a nonmonotonic dependence of the interfacial thickness as a function of number of repeat units in the oligomeric P3HT additive, and the thiophene rings orient parallel to the interfacial plane as they approach the PCBM domain. Using the nanoscale geometries of the P3HT oligomers, LUMO and HOMO energy levels calculated by density functional theory are found to be invariant across the donor/acceptor interface. These connections between additives, processing, and morphology at all length scales are generally useful for efforts to improve device performance.

Frustration in chain packing has been proposed to play an important role in thermodynamic and dynamic properties of polymeric melts and glasses. Based on a quantitative analysis using Voronoi tessellations and large scale molecular dynamics simulations of flexible and semi-flexible polymers, we demonstrate that the rigid polymer chains have higher averaged Voronoi polyhedral volumes and significantly wider distribution of the volume due to frustration in the chain packing. Using these results, we discuss the advantage of the rigid polymers for possible enhancement of transport properties, e.g. for enhancing ionic conductivity in solid polymer electrolytes.

We have synthesized linear ABC triblock terpolymers containing poly(1,3-cyclohexadiene), PCHD, as an end block and characterized their morphologies in the melt. Specifically, we have studied terpolymers containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the other blocks. Systematically varying the ratio of 1,2- /1,4-microstructures of poly(1,3-cyclohexadiene), we have studied the effects of conformational asymmetry among the three blocks on the morphologies using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and self-consistent field theory (SCFT) performed with PolySwift++. Our work reveals that the triblock terpolymer melts containing a high percentage of 1,2-microstructures in the PCHD block are disordered at 110 °C for all the samples, independent of sequence and volume fraction of the blocks. In contrast, the triblock terpolymer melts containing a high percentage of 1,4-microstructure form regular morphologies known from the literature. The accuracy of the SCFT calculations depends on calculating the χ parameters that quantify the repulsive interactions between different monomers. Simulations using χ values obtained from solubility parameters and group contribution methods are unable to reproduce the morphologies as seen in the experiments. However, SCFT calculations accounting for the enhancement of the χ parameter with an increase in the conformational asymmetry lead to an excellent agreement between theory and experiments. These results highlight the importance of conformational asymmetry in tuning the χ parameter and, in turn, morphologies in block copolymers.