Soft Solid Materials Research Articles

Polymer Electrolytes for Supercapacitors.

Because of safety concerns associated with the use of liquid electrolytes and electrolyte solutions, options for non-liquid materials like gels and polymers to be used as ion-conducting electrolytes have been explored intensely, and they attract steadily growing interest from researchers. The low ionic conductivity of most hard and soft solid materials was initially too low for practical applications in supercapacitors, which require low internal resistance of a device and, consequently, highly conducting materials. Even if an additional separator may not be needed when the solid electrolyte already ensures reliable separation of the electrodes, the electrolytes prepared as films or membranes as thin as practically acceptable, resistance may still be too high even today. Recent developments with gel electrolytes sometimes approach or even surpass liquid electrolyte solutions, in terms of effective conductance. This includes materials based on biopolymers, renewable raw materials, materials with biodegradability, and better environmental compatibility. In addition, numerous approaches to improving the electrolyte/electrode interaction have yielded improvements in effective internal device resistance. Reported studies are reviewed, material combinations are sorted out, and trends are identified.

Crack tip stress intensification in strain-induced crystallized elastomer

Natural rubber (NR) exhibits strain-induced crystallization (SIC), enhancing tearing strength and crack resistance. However, the reinforcement mechanism along with nonuniform strain around a crack tip remains unclear. We reveal the nonuniform stress field around a crack tip using the DIC-based deformation field data and a hyperelasticity approach. A hyperelastic strain energy density function (W) is derived to be able to replicate stress-strain data across various deformations, encompassing equal and unequal biaxial, uniaxial, and pure shear stretching. These data cover the full range and magnitude of deformations around the crack tip. SIC significantly impacts the singular behaviors of strain and stress near the crack tip, causing a pronounced stress increase and strain decrease within the SIC zone that extends up to approximately 100 μm away from the crack tip. This results in a distinct crossover in singularity power-law index between the SIC zone and the fully amorphous zone. With increasing crack opening, the stress upturn intensifies, and the crossover shifts away from the crack tip due to SIC zone enlargement and local crystallinity increase. These findings deepen our understanding of the physics of SIC near crack tips and its reinforcement mechanism in strain-induced crystallizable soft solid materials.

Effect of combined treatments of hydrolysis and succinylation on the solubility and emulsion stability of rennet casein and micellar casein

Casein is the most abundant protein in milk with good emulsifying properties and bioavailability. However, the tight micellar structure of casein results in poor solubility. In the case of soft solid materials such as processed cheese, imitation cheese, yoghurt and protein-based oil-in-water emulsions, poor solubility directly affects the homogeneity and stability of the texture structure of such products, leading to a poor user experience. In this study, two protein modification techniques, hydrolysis and succinylation, were combined to improve the solubility of casein and the stability of its emulsions. The individual and combined effects of enzymatic hydrolysis and succinylation modification approaches on the stability of rennet casein (RC) and micellar casein (MC) emulsions were further explored. After double-treatment of casein with enzymatic hydrolysis and succinylation, the solubility of RC and MC was up to about 95 %, which was superior to that of single-treatment. Fourier transform infrared spectroscopy showed that the characteristic wave signals of the double-treated samples were located between the two single-treated samples, and that there may be an opposite effect between the two modifications. After 21 days of storage, the emulsions prepared from double-treated caseins still remained stable. The salt ionic stability and freeze-thaw stability were significantly improved, and the physical stability of MC was increased by nearly three times. The results explained the effects of enzymatic hydrolysis and succinylation on the functional properties of casein, provided a reference for the development of food systems based on oil-in-water emulsions, and offered a new idea for the wide application of succinylated casein.

Functionalizing Surfaces by Physical Vapor Deposition To Measure the Degree of Nanoscale Contact Using FRET.

Adhesion between solid materials is caused by intermolecular forces that only take place if the adhering surfaces are at nanoscale contact (NSC) (i.e., 0.1-0.4 nm. To study adhesion, NSC can be evaluated with Förster Resonance Energy Transfer (FRET). FRET uses the interaction of compatible fluorescence molecules to measure the nanometer distance between bonded surfaces. For this, each surface is labeled with one fluorescence dye, named the Donor or Acceptor. If these molecules are in NSC, a nonradiative Donor-Acceptor energy transfer will occur and can be detected using FRET spectroscopy. Here, for the first time, we introduce an innovative concept of a FRET-based NSC measurement employing dye-nanolayer films prepared by a physical vapor deposition (PVD). The dye nanolayers were prepared by PVD from the vaporization of the Donor and Acceptor molecules separately. The selected molecules, 7-Amino-4-methyl-cumarin (C120) and 5(6)-Carboxy-2',7'-dichlor-fluorescein (CDCF), present high quantum yields (QY, QYD = 0.91 and QYA = 0.64) and a low FRET distance range of 0.6-2.2 nm, adequate for the study of NSC. The produced dye-nanolayer films exhibit a uniform dye distribution (verified by atomic force microscopy) and suitable fluorescence intensities. To validate the NSC measurements, FRET spectroscopy experiments were performed with bonded dye-nanolayer films prepared under different loads (from 1.5 to 140 bar), thus creating different degrees of NSC. The results show an increase in FRET intensity (R 2 = 0.95) with the respective adhesion energy between the films, which is directly related to the degree of NSC. Hence, this work establishes FRET as an experimental technique for the measurement of NSC, and its relation to surface adhesion. Additionally, thanks to the FRET dye-nanolayer approach, the method can be employed on arbitrary surfaces. Essentially, any sufficiently transparent substrate can be functionalized with FRET compatible dyes to evaluate NSC, which represents a breakthrough in contact mechanics investigations of soft and hard solid materials.

Crack-insensitive fracture of elastomer-based soft network materials under monotonic and cyclic loads

In various applications of stretchable electronics and soft robots, soft materials are subjected to long-term load-bearing conditions, requiring them to possess good extreme mechanical properties such as highly stretchable, strong, fracture-resistant and anti-fatigue. Conventional soft materials with a single polymer network typically exhibit relatively low fracture resistance, while commonly employed toughening method involves introducing mechanical dissipation into original polymer networks often require complicated chemical synthesis and result in significant hysteresis under cyclic loads. Designing soft solid materials into soft network materials with periodic lattice structure paving another effective route to improve the fracture-resistant performance of soft materials, which has not been reported in the literature. This work provides a combined experimental and computational study on the mechanical properties and fracture behaviors of elastomer-based soft network materials with/without a precut crack under monotonic and cyclic loads, aiming to present a structural design strategy for fracture-resistant soft materials. The elastomer-based soft network materials are proven to be crack-insensitive, low-hysteresis and anti-fatigue. The nonlinear finite element analysis (FEA) is employed to reveal the underlying mechanism of crack-insensitivity in elastomer-based soft network materials. Both the mechanical properties and deformed configurations of soft network materials with/without a precut crack are accurately predicted by the FEA method. The effect of microstructure geometry and network topology on the mechanical properties of soft network materials is systematically studied. Under various amplitudes of cyclic applied strain, the elastomer-based soft network materials can survive even after individual microstructures ruptured, and the fatigue fracture process slows down as the applied strain amplitude decreases. In contrast to the behavior observed in monotonic loads where fracture initiates at the microstructure located ahead of the crack tip, fatigue fracture initiation in soft network materials with a precut crack exhibits a random distribution.

Protein-Stabilized Emulsion Gels with Improved Emulsifying and Gelling Properties for the Delivery of Bioactive Ingredients: A Review.

In today's food industry, the potential of bioactive compounds in preventing many chronic diseases has garnered significant attention. Many delivery systems have been developed to encapsulate these unstable bioactive compounds. Emulsion gels, as colloidal soft-solid materials, with their unique three-dimensional network structure and strong mechanical properties, are believed to provide excellent protection for bioactive substances. In the context of constructing carriers for bioactive materials, proteins are frequently employed as emulsifiers or gelling agents in emulsions or protein gels. However, in emulsion gels, when protein is used as an emulsifier to stabilize the oil/water interface, the gelling properties of proteins can also have a great influence on the functionality of the emulsion gels. Therefore, this paper aims to focus on the role of proteins' emulsifying and gelling properties in emulsion gels, providing a comprehensive review of the formation and modification of protein-based emulsion gels to build high-quality emulsion gel systems, thereby improving the stability and bioavailability of embedded bioactive substances.

Mixed-Matrix Ion Gel Membranes for Gas Separation

The potential of ionic liquid materials to improve membrane-based gas separation processes has been realized during the past few years, through the exploitation of diverse configurations, chemical functionalities, and properties. Nowadays, one of the most recent trends on this field is the development of mixed-matrix ion gels, an emerging family of ionic soft-solid materials, in which fillers are embedded into polymer/IL matrices. This review aims at presenting an overview on the latest developments and advances on ion gel membranes containing a third component, such as zeolites, metal organic frameworks, silica, graphene oxide, metal salts, and nanoparticles, for gas separation processes. We provide an analysis of this building system and highlight the diverse type of mixed-matrix ion gels hitherto reported, for which the impact of the different fillers on the ion gels’ overall properties is discussed in detail. The main challenges on their preparation, as well as their transport mechanism and how it can be influenced by the different fillers, are also addressed. Finally, technological aspects, perspectives, and opportunities to pursue this topic are discussed from a critical point of view.

Dynamic mechanical analysis with torsional rectangular geometry: A critical assessment of constrained warping models

Dynamic mechanical oscillatory shear measurements with torsional rectangular geometry are widely carried out in order to determine the mechanical properties of soft solid materials in a quick and practical way. This technique has the advantage of avoiding slip effects, thus being particularly attractive for testing stiff elastomers such as vulcanized rubber compounds. However, one of its drawbacks is the clamping system required to keep the specimen edges in place. Since it imposes a constraint to warping deformations (i.e., out-of-plane cross-section distortions about the torsional axis), a certain increase of dynamic moduli with respect to their values in simple shear is observed and considered as an experimental artifact (i.e., de Saint-Venant's assumption of primary torsion of the specimen is no longer valid). The increase of dynamic moduli in torsion depends on the specimen's cross-section geometry and relative dimensions. We test here the capability of different torsion models to describe the constrained warping effect for an industrial rubber with rectangular specimen cross section using a wide range of different geometric parameters (length-to-width p ratio and width-to-thickness u ratio). We compare two theoretical models (Vlasov's model and Timoshenko's approach) and a phenomenological model (based on finite element simulations by Diani and Gilormini) with our experimental data set. We propose a slight modification of Vlasov's model to obtain realistic predictions of torsion over a wider parameter range. It is shown to be particularly useful in soft rubber testing, and the limitations in the choice of specimen geometry to obtain sufficient torque signal are overcome.

Synthesis and Characterization of Cationic Dendrimer‐PDMS Hybrids

A modular strategy for the synthesis of dendron-linear polymer hybrids comprised of a flexible polydimethylsiloxane (PDMS) midblock with cationic 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendron end groups is developed. The invention of a scalable methodology to access quaternary ammonium carboxylate building blocks and their direct use in esterification chemistry enables rapid access to cationic bis-MPA dendrons. The convergent click coupling of highly charged dendrons to hydrophobic PDMS chain-ends gives a 12-membered family of hybrids that are comprised of different dendron generations (G1-3) and quaternary ammonium alkyl chain lengths (C4 , C8 , C12 , C16 ). This provides a library of materials with variable hydrophobicity, charge density, and chain-end valency. The physical behavior of the dendron-linear PDMS hybrid copolymers significantly changes after introduction of the cationic dendron end-groups and leads to soft-solid materials as a result of inhibited chain mobility. These PDMS-dendron hybrids are expected to behave as surface-active antimicrobial additives in bulk cross-linked silicone systems.

Rheology of Emulsion-Filled Gels Applied to the Development of Food Materials.

Emulsion-filled gels are classified as soft solid materials and are complex colloids formed by matrices of polymeric gels into which emulsion droplets are incorporated. Several structural aspects of these gels have been studied in the past few years, including their applications in food, which is the focus of this review. Knowledge of the rheological behavior of emulsion-filled gels is extremely important because it can measure interferences promoted by droplets or particle inclusion on the textural properties of the gelled systems. Dynamic oscillatory tests, more specifically, small amplitude oscillatory shear, creep-recovery tests, and large deformation experiments, are discussed in this review as techniques present in the literature to characterize rheological behavior of emulsion-filled gels. Moreover, the correlation of mechanical properties with sensory aspects of emulsion-filled gels appearing in recent studies is discussed, demonstrating the applicability of these parameters in understanding mastication processes.

МЕМБРАННЫЕ МОДЕЛИ И АНЗАЦ ГРАФЕНА КАК АГЕНТНОГО МЕМБРАНОМИМЕТИКА

Since the pioneering works of the founder of membrane mimetic chemistry Janos H. Fendler it is known that a number of atomic or molecular clusters and films (including nanoscale ones) are capable of mimicking the membrane functions. Membrane mimetic materials can be either soft matter or solid state materials. Conducting films (including those with magnetic properties) and semiconductors are also known to possess membrane mimetic properties. If we consider the agent exchange through the membrane in the operator form, the chemical composition of the membranes and their models, as well as the difference between the atomic and molecular clusters or layers become not so essential, and hence, membrane mimetic chemistry of nano- and mesostructures do not differ significantly within the agent-based approach. This invited review containing several parts reflects the main aspects of the author's report at the conference "Graphene: a molecule and 2D-crystal" (September 8-12, 2015, Novosibirsk, Russia) and considers various aspects of the similarity between the graphene nanostructures, membranes and bionic membrane-like nanomaterials.

Modelling and animation of impact and damage with Smoothed Particle Hydrodynamics

In this paper we present a unique procedure for extending the method of Smoothed Particle Hydrodynamics (SPH) to allow for the simulation of permanently deformable soft-solid materials. SPH has previously been shown to be a computationally and visually effective method for fluid dynamics simulations and recently for modelling the deformation of elastic soft solids. By incorporating new parameters into the procedure, the current research is able to demonstrate a range of visually appealing plasticity and damage scenarios. As SPH is a mesh-free Lagrangian method, data can be manipulated to allow for parallelisation using nVidia's CUDA platform, as is shown here where simulations are capable of performing at real-time rates.

Nanocomposite polymer electrolytes comprising PVA-graft-PEGME/TiO2 for Li-ion batteries

Abstract

Cubically non-linear effects of plane waves in isotropic soft solid materials

In this paper we analyze mathematical properties of an isotropic soft solid model which is characterized by three elastic constants. The model was proposed to interpret measurements of weakly non-linear shear waves in gel-like and tissue-like media. In our analysis we are particularly interested in third order non-linear terms. We present for the first time the full equations of elastodynamics, as well as the equations for plane waves for this model, with cubically non-linear terms. Next, the interaction coefficients for non-linear interactions of three plane waves to produce the fourth wave are explicitly calculated. These coefficients show which of the three waves interact with each other and determine how strong the effect of interaction is on the produced fourth wave. It turns out that these coefficients are expressed in terms of some combinations of three elastic constants. The obtained results can be helpful in experimental determination of elastic constants which describe the model.

Stress Enhancement in the Delayed Yielding of Colloidal Gels

Networks of aggregated colloidal particles are solidlike and can sustain an applied shear stress while exhibiting little or no creep; however, ultimately they will catastrophically fail. We show that the time delay for this yielding decreases in two distinct exponential regimes with applied stress. This behavior is universal and found for a variety of colloidal gel systems. We present a bond-rupture model that quantitatively describes this behavior and highlights the role of mesoscopic structures. Our result gives new insight into the nature of yielding in these soft solid materials.

Bijel Capsules: Novel, Robust, and Versatile Bijels of Nitromethane, Ethanediol, and Colloidal Silica: Capsules, Sub‐Ten‐Micrometer Domains, and Mechanical Properties (Adv. Funct. Mater. 11/2011)

Bicontinuous, interfacially jammed emulsion gels (bijels) are a class of soft solid materials in which interpenetrating domains of two immiscible fluids are stabilized by an interfacial colloidal monolayer. Bijel capsules, as presented by Joe W. Tavacoli and co-workers on page 2020, may find application in controlled release. They contain bicontinuous liquid domains where internal and external interfaces are stabilized by (different) colloidal particles. The image shows a fluorescence confocal microscopy image of such a capsule.

Novel, Robust, and Versatile Bijels of Nitromethane, Ethanediol, and Colloidal Silica: Capsules, Sub‐Ten‐Micrometer Domains, and Mechanical Properties

AbstractBicontinuous, interfacially jammed emulsion gels (bijels) are a class of soft solid materials in which interpenetrating domains of two immiscible fluids are stabilized by an interfacial colloidal monolayer. Such structures form through the arrest of the spinodal decomposition of an initially single‐phase liquid mixture containing a colloidal suspension. With the use of hexalmethyldisilazane, the wetting character of silica colloids, ranging in size and dye content, can be modified for fabricating a novel bijel system comprising the binary liquid ethanediol–nitromethane. Unlike the preceding water‐lutidine based system, this bijel is stable at room temperature and its fabrication and resultant manipulation are comparatively straightforward. The new system has facilitated three advancements: firstly, we use sub 100 nm silica particles to stabilize the first bijel made from low molecular weight liquids that has domains smaller than ten micrometers. Secondly, our new and robust bijel permits qualitative rheological work which reveals the bijel to be significantly elastic and self healing whilst its domains are able to break, reform and locally rearrange. Thirdly, we encapsulate the ethanediol–nitromethane bijel in Pickering drops to form novel particle‐stabilized bicontinuous multiple emulsions that we christen bijel capsules. These emulsions are stimuli responsive – they liberate their contained materials in response to changes in temperature and solvency, and hence they show potential for controlled release applications.

EVOLUTION OF NEEDLE-FREE MICRO-INJECTION TO THE SOFT SOLID MATERIAL FOR MEDICAL DELIVERY

The evolutions and mechanisms of micro-jet penetration into the solid soft material are described in this paper. The diameter of the micro injector is 300µm. We use the gelatin gel as the solid soft material and water as the injection fluid. Experimental results show that the penetration processes can be described by three phases. I. Induction phase: this phase covers the penetration process of the skin layer. This period lasts only a very short time depending on the power of the micro jet. II. Break phase: This phase covers the penetration process of the inner layer. The volume of jet penetration grows dramatically in this period. III. Saturation phase: The saturation condition was attained when the penetration depth was found to be fixed with time. It is also found that the penetration rate increased linearly with the injection power. It can be fitted in a line with slope of 0.04. It indicates that the stress work of the soft solid is proportional to the injection power. The characteristics can be used to determine the strength of the soft solid materials by jet injection. These data are useful in the needle-free injection for the drug delivery with the endoscope system.

Bijels Containing Magnetic Particles: A Simulation Study

Bicontinuous, interfacially jammed emulsion gels (bijels) represent a class of soft solid materials in which interpenetrating domains of two immiscible fluids are stabilized by an interfacial colloidal monolayer. Such structures can be formed by arrested spinodal decomposition from an initially single-phase colloidal suspension. Here, we explore by lattice Boltzmann simulation the possible effects of using magnetic colloids in bijels. This may allow additional control over the structure, during or after formation, by application of a magnetic field or field gradient. These effects are modest for typical parameters based on the magnetic nanoparticles used in conventional ferrofluids, although significantly larger particles might be appropriate here. Field gradient effects, which are cumulative across a sample, could then allow a route for controlled breakdown of bijels as they do for particle-stabilized droplet emulsions.

CHARACTERIZATION OF THE PULSED NEEDLE-FREE MICRO-INJECTOR IN THE MEDICAL DELIVERY SYSTEM

This paper describes the development of the needle-free injection with a pulsed micro-injector. The novel injection system consists of a micro-injector, a solenoid valve with an electron-control system and a high pressure liquid supply system. The diameters of the orifice are 200µm~ 300µm. The performance of both pulsed and continuous injections is characterized. Results show that the mass flow rate is increased linearly for the liquid pressure ranging from 50bar to 125bar. The jet velocity increases from 50.6m/s to 104m/s as the liquid pressure increases from 50bar to 125bar. Penetration test to the soft solid materials shows that the penetration depth is increased from 2mm to 7mm depending on the injection power under single pulsed injection. It is believed that the technique will be useful for the drug delivery as well as the localized tumor treatment.