Soft Materials Research Articles

Urea/Thiourea Imine Linkages Provide Accessible Holes in Flexible Covalent Organic Frameworks and Dominates Self‐Adaptivity and Exciton Dissociation

Unraveling the robust self‐adaptivity and minimal energy‐dissipation of soft reticular materials for environmental catalysis presents a compelling yet unexplored avenue. Herein, a top‐down strategy, tailoring from the unique linkage basis, flexibility degree, skeleton electronics to trace‐guest adaptability, is proposed to fill the understanding gap between micro‐soft covalent organic frameworks (COFs) and photocatalytic performance. The thio(urea)‐basis‐dominated linkage within benzotrithiophene‐based COFs induce the framework contraction/swelling (intralayer micro‐flexibility) in response to tetrahydrofuran or water. Adaptability of micro‐flexible thiourea‐COF with pore hydrophilicity not only contributes to the favorable mass transfer, but also enhances the accessible redox active sites, culminating in nearly 100% removal of micropollutant with low‐energy dissipation in wastewater. The incorporating urea/thiourea into imine linkage facilitates polarization reduction and exciton dissociation within skeleton wall, inducing strong localization for holes. This transformation facilitates interchain charge transport and unbalanced distribution conducive to oxidative holes‐mediated micropollutant decomposition.

Urea/Thiourea Imine Linkages Provide Accessible Holes in Flexible Covalent Organic Frameworks and Dominates Self-Adaptivity and Exciton Dissociation.

Unraveling the robust self-adaptivity and minimal energy-dissipation of soft reticular materials for environmental catalysis presents a compelling yet unexplored avenue. Herein, a top-down strategy, tailoring from the unique linkage basis, flexibility degree, skeleton electronics to trace-guest adaptability, is proposed to fill the understanding gap between micro-soft covalent organic frameworks (COFs) and photocatalytic performance. The thio(urea)-basis-dominated linkage within benzotrithiophene-based COFs induce the framework contraction/swelling (intralayer micro-flexibility) in response to tetrahydrofuran or water. Adaptability of micro-flexible thiourea-COF with pore hydrophilicity not only contributes to the favorable mass transfer, but also enhances the accessible redox active sites, culminating in nearly 100% removal of micropollutant with low-energy dissipation in wastewater. The incorporating urea/thiourea into imine linkage facilitates polarization reduction and exciton dissociation within skeleton wall, inducing strong localization for holes. This transformation facilitates interchain charge transport and unbalanced distribution conducive to oxidative holes-mediated micropollutant decomposition.

Whey protein-based bigels for co-encapsulation of curcumin and gallic acid: Characterization, stability and release kinetics

Bigels are a class of soft matter systems with great promise for the food industry as food analogs or as enhanced ingredient substitutes. This work aimed to improve the curcumin (CUR) and gallic-acid (GA) stability, antioxidant capabilities, and controlled release by co-encapsulating them within bigels. This delivery system included a bigel made by whey protein isolate (WPI) aggregates-based oleogel and WPI-based hydrogel in equivalent amounts (50:50). The following techniques were used to evaluate how different bigels affected the chemical stability of CUR and GA: X-ray diffraction (XRD), thermogravimetric analysis (TGA), 1H-nuclear magnetic resonance (1H-NMR), and Fourier infrared (FTIR) spectroscopy. As a result of the protein's ligand-binding abilities, some components may co-adsorb to oil droplet surfaces. Next, it was determined how well the bigels performed as a carrier and looked at their physicochemical stability, digestion, and performance. Examining the release rate of CUR and GA during digestion showed that bigel had a slower release rate (6–15%) than oleogel (16%) and hydrogel (34%), and CUR had a lower release (50%) due to its higher molecular weight and greater entanglement than GA (70%). The stability of bigel (against heat and light) was also higher than oleogel and hydrogel due to having a higher solid component that requires more stress to be applied to the system. CUR and GA had more antioxidant activity in bigel (96.24%) than oleogel (77.71%) and hydrogel (77.34%); which can be attributed to the formation of ultra-fine colloidal dispersions by bigel, allowing more CUR and GA to interact with free radicals by creating more contact surface. The multi-functional bigels showed great potential for delivering antioxidants to the intestine while enhancing their stability. Hydrophobic interactions and hydrogen bonding between WPI and CUR-GA were validated by FTIR analysis, that kept bigels stable. Overall, our findings demonstrated that WPI-based bigels with intriguing UV light, color, and thermal stability could be developed. This would increase the use of bigels in innovative food products with high nutritional value.

Polyvinyl fluoride: Predicting polarization in a complex soft matter system

We use first-principle density functional theory (DFT) to predict properties for semicrystalline polyvinyl fluoride (PVF) and compare with polyvinylidiene fluoride. We note that the crystalline regions of PVF are complex in the sense that we lack a complete experimental characterization of the detailed atomic organization. We therefore turn to DFT to predict both the structure and associated materials properties, illustrating a possible work flow for complex soft-matter modeling. We rely on the nonempirical consistent-exchange van der Waals density functional version [K. Berland and P. Hyldgaard, ] and identify plausible ground-state and excited-state motifs. From there we predict the elastic response of the crystalline motifs, and an upper limit estimate of the PVF polarization at room temperature. Published by the American Physical Society 2024

Research on Adhesion Pull-Off Behavior of Rigid Flat Punch and Viscoelastic Substrate

Interfacial adhesion is one of the key factors affecting the reliability of micro–nano systems. The adhesion contact mechanism is still unclear as the time-dependent viscoelasticity of soft materials. To clarify the adhesion interaction, the pull-off detachment between the rigid flat punch and viscoelastic substrate is explored considering the viscoelasticity of soft materials and rate-dependent adhesion. Taking the Lennard-Jones (L-J) potential characterizing interfacial adhesion and the Prony series defining the viscoelasticity of materials as references, the bilinear cohesion zone model (CZM) and standard Maxwell model are employed, and an adhesion analysis framework is established by combining finite element technology. The influence laws of the loading and unloading rates, material relaxation coefficients and size effect on adhesion pull-off behavior are revealed. The results show that the pull-off force is independent of the material relaxation effect and related to the unloading rate. When v^ ≥ 50 or v^ < 0.01, the pull-off force has nothing to do with the unloading rate, but when 0.01 < v^ < 50, the pull-off force increases with the increasing unloading rate. Also, it is controlled by the size effect, and the changing trend conforms to the MD-n model proposed by Jiang. The energy required for interfacial separation (i.e., effective adhesion work) is a result of the comprehensive influence of unloading rates, material properties and the relaxation effect, which is consistent with Papangelo1’s research results. In addition, we derive the critical contact radius of the transition from the Kendall solution to the strength control solution. This work not only provides a detailed solution for the interfacial adhesion behavior but also provides guidance for the application of adhesion in Micro-Electro-Mechanical Systems (MEMSs).

Structural Properties of [N1888][TFSI] Ionic Liquid: A Small Angle Neutron Scattering and Polarizable Molecular Dynamics Study.

In this study, we investigate the quaternary ammonium-based ionic liquid (QAIL), methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N1888][TFSI], utilizing small angle neutron scattering (SANS) measurements and polarizable molecular dynamics (MD) simulations to characterize the short- and long-range liquid structure. Scattering structure factors show signatures of three length scales in reciprocal space indicative of alternating polarity (k ∼ 0.44 Å-1), charge (k ∼ 0.75 Å-1), and neighboring or adjacent (k ∼ 1.46 Å-1) domains. Excellent agreement between simulation and experimental scattering structure factors validates various simulation analyses that provide detailed atomistic characterization of the different length scale correlations. The first solvation shell structure is illustrated by obtaining radial, angular, dihedral, and combined distribution functions, where two dominant spatial motifs, N+···N- and N+···O-, compete for optimal packing around the polar head of the [N1888]+ cation. Intermediate and long-range structures are governed by the balance between local electroneutrality and octyl chain networking, respectively. By computing the charge-correlation structure factor, SZZ, and the spatial extent of the octyl chain network using graph theory, the bulk-phase structure of [N1888][TFSI] is characterized in terms of electrostatic screening and apolar domain formation length scales.

Review of the Anti-Candida albicans Activity and Physical Properties of Soft Lining Materials Modified with Polyene Antibiotics, Azole Drugs, and Chlorohexidine Salts.

This review examined the current state of knowledge on the modifications of commercial soft lining materials (SLMs) with a variety of antifungal compounds: (i) polyene antibiotics, including nystatin and amphotericin B, (ii) azole drugs, including fluconazole, itraconazole, clotrimazole, ketoconazole, and miconazole, and (iii) antiseptics, including chlorhexidine salts to give them anti-Candida albicans properties. The effect of such modifications on the SLMs' physical properties, such as drug release, water sorption, surface properties, bond strength, tensile strength, and hardness, was also analyzed. In effect, this study provided a unique compilation of research results obtained for numerous properties of SLM modified with antifungal compounds that differ in their chemical structure and mechanism of antifungal action. These results might also be useful for prosthetic dentistry, where SLMs are used to prevent and treat candidiasis, the most common disease among denture wearers.

Grazing-incidence small-angle neutron scattering at high pressure (HP-GISANS): a soft matter feasibility study on grafted brush films

Grazing-incidence small-angle neutron scattering (GISANS) under pressure (HP-GISANS) at the solid (Si)–liquid (D2O) interface is demonstrated for the pressure-induced lateral morphological characterization of the nanostructure in thin (<100 nm) soft matter films. We demonstrate feasibility by investigating a hydrophobic {poly[(2,2,3,3,4,4,5,5-octafluoro)pentyl methacrylate]} (POFPMA)–hydrophilic {poly[2-(dimethylamino)ethyl methacrylate]} (PDMAEMA) brush mixture of strong incompatibility between the homopolymers, anchored on Si, at T = 45°C for two pressures, P = 1 bar and P = 800 bar. Our GISANS results reveal nanostructural rearrangements with increasing P, underlining P-induced effects in tethered polymer brush layers swollen with bulk solvent.

Soft matter mechanics of baseball’s Rubbing Mud

Researchers looking for sustainable materials with optimal mechanical properties may draw inspiration from a baseball tradition. For nearly 100 y, a mysterious mud harvested from an undisclosed river site in New Jersey (USA) has been the agent of choice in the USA's Major League Baseball for "de-glossing" new baseballs. It is unclear, however, what makes this "Rubbing Mud" work. Here, we perform a multiscale investigation of the rheology and tribology of this mud material under baseball-relevant conditions and identify three mechanisms by which the mud alters the surface properties of the baseball. First, the mud creates a more uniform baseball surface by filling in pores in the leather; this is possible because of its relatively high cohesion (clays and organics) making the material remarkably shear thinning. Second, the residue of cohesive particles coating the baseball effectively doubles contact adhesion. Third, a sparse population of angular sand grains are bonded to the baseball by clay-sized particles, leaving a studded surface that enhances friction. The proportions of cohesive, frictional, and viscous elements in Rubbing Mud conspire to create a soft material with an unusual mix of properties, that could find other applications in the development of sustainable geomaterials. Our improved understanding of the flow and friction of natural muds may also find use in modeling natural hazards such as mudslides and for locomotion in muddy environments.

Thermally Bisignate Anion Responsive Supramolecular Gel and In Situ Generation of a Conductive Hybrid-Gel Nanocomposite.

Understanding the structure-function relationship is a significant challenge in designing supramolecular soft materials such as supramolecular gels. To address this challenge, we report on two urea-based dipodal ligands, PY-NAP and PY-CF3, with different terminal substituents influencing their gelation properties. The terminal substituents play a crucial role in the gelation abilities. The gel formed from PY-NAP exhibited notably high thermal stability and displayed a unique "thermally bisignate" behavior. Both ligands contain urea and amide units, allowing them to encapsulate the SO42- anion in their pincer cavities in the solid state. The solid-state anion recognition principle is used to construct a selective anion-responsive supramolecular gel. Additionally, the gel was used to sequester precious metal salts from aqueous solutions, achieving an uptake efficiency of over 90%, followed by in situ reduction to form nanoparticles. This concept was then applied to create a conductive supramolecular hybrid gel nanocomposite with significantly high conductivity, holding significant implications for industrial and environmental applications.

Photochemical Patterning and Characterization of Mechanical Properties on Soft Materials

AbstractAlthough different chemistries for the spatio‐temporal localization of molecules and gradients of chemical signals within soft materials are now available, the achievement of spatio‐temporal patterns of mechanical properties in such materials and their characterization remain considerable challenges. This study presents the syntheses of two novel photo‐sensitive and thermoresponsive hydrogel systems, a photo‐stiffening and a photo‐softening hydrogel. Their potential for fabricating soft materials with patterned mechanical properties is then demonstrated by fabricating an actuator whose higher‐order bending properties can be switched on with light, and by encoding mechanical properties for digital information encryption and storage. Microindentation and a custom‐made data analysis software are essential for the characterization of all the materials. From a general perspective, this work opens a route to the fabrication of soft materials with patterned mechanical properties, addressing an important emerging challenge in soft materials science with applications in soft robotics and information encryption and storage.

Toughening of thick bonded interfaces through architected crack-arresting features

This research investigates the application of additively manufactured crack-arresting features (CAFs), designed from tough and soft polymers, in enhancing the performance of thick glass fiber-reinforced polymer composite-epoxy adhesive joints found in wind turbine rotor blades. Mode I fracture and fatigue behaviors of these joints are assessed through double-cantilever beam experiments and compared against pristine joints. In pristine joints, cracks consistently deviate from the adhesive bondline into the composite adherend, causing a sudden increase in strain energy release rate. Finite element models based on linear elastic fracture mechanics are employed to provide insight into this behavior. Experimental results demonstrate that joints with architected CAFs achieved higher strain energy release rates, more stable failure mechanisms, and minimized damage to the composite adherend. Under fatigue loading, joints featuring tough CAF material exhibit slower fatigue crack growth compared to both pristine joints and those with soft CAF material.

A simulation study of microstructure and dynamics of dual-functionalised imidazolium based ionic liquids (DFILs)

ABSTRACT We studied the liquid structures and dynamics of a series of dual-functionalised ionic liquids (DFILs) by Md simulations. The studied DFILs consist of functionalised imidazolium cations with a nitrile group and varying lengths of ether side chains, paired with bis(trifluoromethyl sulfonyl) imide anions, denoted as [C2CNIm(EtO)nMe][Tf2N]. We instigated distribution functions, Voronoi tessellation, and cluster analysis, to probe the liquid structures. Furthermore, we explored dynamic properties such as mean-square displacements (MSD), self-diffusivity coefficients, hydrogen bonding, ion pairing, and ion cage effects. Our findings revealed a correlation between the length of the ether side chains and the density of the studied DFILs when the longer side chains lead to a decreased density. Calculated partial radial distribution functions (PRDF) of ether side chains of the cations demonstrated a tendency for self-aggregation as the chain length increased. The combined distribution functions diagrams show that the hydrogen bond between ions is more pronounced for cations with smaller side chains. Anions displayed higher diffusivity than the cations, and among the cations, [C2CNIm(EtO)6Me]+ has the lowest diffusion coefficient. Various methods evaluated the micro-heterogeneity dynamics of DFILs.

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]+ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

Machine learning-assisted screening of efficient ionic liquids for catalyzing CO2 cycloaddition reaction

The catalysis of CO2 cycloaddition reactions by ionic liquids holds significant promise in addressing environmental and chemical synthesis challenges. However, the design of effective ionic liquid catalysts is hindered by the sheer diversity of cation-anion combinations, leading to challenges in targeted catalyst development. This study addresses these issues by utilizing experimental data collected from literature on reactions involving epoxy compounds as substrates, conducted without solvents or co-catalysts, to establish a database for machine learning (ML). Simple descriptors derived from the ion pair structures of ionic liquids are employed as inputs for five ML classification algorithms to predict the yield of CO2 cycloaddition reactions. Subsequently, the highly accurate ML models are applied to forecast the catalytic performance of 1344 ionic liquids under ambient conditions. This approach identifies 13 cation structures and 8 anion structures that exhibit superior catalytic properties. Further refinement through density functional theory (DFT) calculations selects ion pair structures capable of catalyzing CO2 cycloaddition reactions at ambient temperature and pressure, demonstrating the efficacy of this method in guiding the design and development of ionic liquid catalysts for CO2 conversion reactions involving epoxy compounds.

Transmission of mobility via cooperative mechanisms in soft active matter

When supercooled, liquid's viscosity increases dramatically as the glass transition temperature is approached. Although the physical origin of this behavior is still not understood, it is now well established that the addition of a few activated particles is able to reverse that increase in viscosity. Here we further raise the question of a limit in that fluidization process and of the differences between the fluidized liquid and its viscous counterpart. The results show that a few percent active molecules are enough to trigger a phase transition leading to diffusion coefficients typical of liquids while the medium retains cooperative properties of the viscous phase. The similarity between cooperative properties of the active and non-active molecules suggests that the mobility of active molecules is transmitted to inactive ones via the medium's cooperative mechanisms, a result in agreement with facilitation theories. This result is then confirmed by the compared behavior of the distinct Van Hove correlation functions of most mobile active and non-active molecules. Interestingly enough, in our simulations, the cooperative mechanisms are not induced or related to a decrease in the excitation concentration.

Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic Materials

Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic Materials

Advanced Soft Magnetic Materials for the Development of High-Frequency Magnetic Core Used in Solid-State Transformers

Advanced Soft Magnetic Materials for the Development of High-Frequency Magnetic Core Used in Solid-State Transformers

Phonons reveal coupled cholesterol-lipid dynamics in ternary membranes

Experimental studies of collective dynamics in lipid bilayers have been challenging due to the energy resolution required to observe these low-energy phonon-like modes. However, inelastic x-ray scattering (IXS) measurements—a technique for probing vibrations in soft and biological materials—are now possible with sub-meV resolution, permitting direct observation of low-energy, phonon-like modes in lipid membranes. Here, IXS measurements with sub-meV energy resolution reveal a low-energy optic-like phonon mode at roughly 3 meV in the liquid-ordered (Lo) and liquid-disordered phases of a ternary lipid mixture. This mode is only observed experimentally at momentum transfers greater than 5 nm−1 in the Lo system. A similar gapped mode is also observed in all-atom molecular dynamics (MD) simulations of the same mixture, indicating that the simulations accurately represent the fast, collective dynamics in the Lo phase. Its optical nature and the Q range of the gap together suggest that the observed mode is due to the coupled motion of cholesterol-lipid pairs, separated by several hydrocarbon chains within the membrane plane. Analysis of the simulations provides molecular insight into the origin of the mode in transient, nanoscale substructures of hexagonally packed hydrocarbon chains. This nanoscale hexagonal packing was previously reported based on MD simulations and, later, by NMR measurements. Here, however, the integration of IXS and MD simulations identifies a new signature of the Lo substructure in the collective lipid dynamics, thanks to the recent confluence of IXS sensitivity and MD simulation capabilities.

Detailed analysis on primary and secondary break up characteristics of liquid fuel jet in crossflow using homogeneous mixture model and large eddy simulation

The detailed breakup characteristics of the liquid jet fuel, Jet-A, in crossflow to various ranges of momentum flux ratios and Weber numbers have been investigated using a high-fidelity compressible multi-phase numerical technique. Multi-phase large eddy simulation with adaptive mesh refinement and Eulerian to Lagrangian transformation are applied to the homogeneous mixture model. The liquid surface instabilities and their frequencies inside the injector orifice are observed and analyzed. Interactions between liquid jet and crossflow result in phenomena such as horse-shoe vortex formation, boundary separation, liquid trailing, and counter-rotating vortex pair. Liquid column breakup characteristics and wave structures are analyzed from both temporal and spatial viewpoints. The Sauter mean diameter distribution and cumulative distributions of droplets resulting from secondary breakup are presented, along with the droplet size distribution derived from the momentum flux ratio and Weber number. Several engineering models, including the instability frequencies, the breakup length, and the penetration depth, are proposed in terms of the momentum flux ratio and Weber number, providing valuable insights for injector and combustor design.