Class Of Soft Materials Research Articles

Polymers and its applications in agriculture

Graphical Abstract Abstract Polymers are a class of soft materials with numerous and versatile mechanical and chemical properties that can be tuned specific to their application. Agriculture is an expanding area due to the requirement for indispensable food to meet the demands of a growing global population. Consequently, development of technology to improve the quality of the soil and agriculture manages is still under development. Intelligent agricultural supplies (controlled or slow release agrochemicals and superabsorbents) and biosorbents contribute to an expanding niche using technology from polymers. This review elucidates the state-of-the-art and will discuss some important aspects of using polymers in intelligent fertilizers, as well as superabsorbent, biosorbent and biodegradation processes in agriculture that are environmentally, technically, socially, and economically sustainable.

Dynamics of Shape-Persistent Giant Molecules: Zimm-like Melt, Elastic Plateau, and Cooperative Glass-like

Giant molecules are a new class of soft matter having three-dimensional (3D) shapes and composed of chemically linked rigid molecular nanoparticles. Structurally, a 3D cluster of molecular nanoparticles can be one giant molecule or a few giant molecules associated together via specific interactions. The dynamics of clusters that are smaller than a critical diameter (∼5 nm) presents a power law relaxation exponent of 0.7 at the high frequency region corresponding to segmental dynamics. Such scaling is similar to the result of the Zimm model although those clusters are neither chain-like nor in solution. Clusters that are larger than this critical diameter and formed by the association of giant molecules exhibit an elastic plateau due to caging of individual giant molecules. We hypothesize that clusters of such a large size cannot move as a whole, even above the glass transition temperature of the sample. They thus are “cooperative glass-like”. A structural cluster of giant molecules could be abstracted as ...

Coupling the Leidenfrost effect and elastic deformations to power sustained bouncing

The Leidenfrost effect occurs when an object near a hot surface vaporizes rapidly enough to lift itself up and hover. Although well-understood for liquids and stiff sublimable solids, nothing is known about the effect with materials whose stiffness lies between these extremes. Here we introduce a new phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost effect. By dropping hydrogel spheres onto hot surfaces we find that, rather than hovering, they energetically bounce several times their diameter for minutes at a time. With high-speed video during a single impact, we uncover high-frequency microscopic gap dynamics at the sphere-substrate interface. We show how these otherwise-hidden agitations constitute work cycles that harvest mechanical energy from the vapour and sustain the bouncing. Our findings unleash a powerful and widely applicable strategy for injecting mechanical energy into soft materials, with relevance to fields ranging from soft robotics and metamaterials to microfluidics and active matter.

Scalable manufacturing of biomimetic moldable hydrogels for industrial applications.

Hydrogels are a class of soft material that is exploited in many, often completely disparate, industrial applications, on account of their unique and tunable properties. Advances in soft material design are yielding next-generation moldable hydrogels that address engineering criteria in several industrial settings such as complex viscosity modifiers, hydraulic or injection fluids, and sprayable carriers. Industrial implementation of these viscoelastic materials requires extreme volumes of material, upwards of several hundred million gallons per year. Here, we demonstrate a paradigm for the scalable fabrication of self-assembled moldable hydrogels using rationally engineered, biomimetic polymer-nanoparticle interactions. Cellulose derivatives are linked together by selective adsorption to silica nanoparticles via dynamic and multivalent interactions. We show that the self-assembly process for gel formation is easily scaled in a linear fashion from 0.5 mL to over 15 L without alteration of the mechanical properties of the resultant materials. The facile and scalable preparation of these materials leveraging self-assembly of inexpensive, renewable, and environmentally benign starting materials, coupled with the tunability of their properties, make them amenable to a range of industrial applications. In particular, we demonstrate their utility as injectable materials for pipeline maintenance and product recovery in industrial food manufacturing as well as their use as sprayable carriers for robust application of fire retardants in preventing wildland fires.

Intermolecular Interaction between Phosphatidylcholine and Sulfobetaine Lipid: A Combination of Lipids with Antiparallel Arranged Headgroup Charge.

Intermolecular interactions between lipid molecules are important when designing lipid bilayer interfaces, which have many biomedical applications such as in drug delivery vehicles and biosensors. Phosphatidylcholine, a naturally occurring lipid, is the most common lipid found in organisms. Its chemical structure has a negatively charged phosphate linkage, adjacent to an ester linkage in a glycerol moiety, and a positively charged choline group, placed at the terminus of the molecule. Recently, several types of synthetic lipids that have headgroups with the opposite charge to that of phosphatidylcholine have emerged; that is, a positively charged ammonium group is present adjacent to the ester linkage in their glycerol moiety and a negatively charged group is placed at their terminus. These types of lipids constitute a new class of soft material. The aim of this study was to determine how such lipids, with antiparallel arranged headgroup charge, interact with naturally occurring phosphatidylcholines. We synthesized 1,2-dipalmitoyl-sn-glycero-3-sulfobetaine (DPSB) to represent a reversed-head lipid; 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) was used to represent a naturally occurring phospholipid. The intermolecular interaction between these lipids was investigated using surface pressure-area (π-A) isotherms of the lipid monolayer at the air/water interface. We found that the extrapolated area and excess free energy of the mixed monolayer deviated negatively when compared with the ideal values from additivity. Moreover, differential scanning calorimetry of the lipid mixture in aqueous dispersion showed that the gel-to-liquid crystal transition temperature increased compared with that of each pure lipid composition. These results clearly indicate that DPSB preferably interacts with DPPC in the mixture. We believe that the attraction between the oppositely charged headgroups of these lipids reinforces the intermolecular interaction. Our results provide insight into the intermolecular interaction between phospholipids and reversed-head lipids, which may prove useful for the design of lipid-based materials in the future.

A shrinkable dendritic glutamic acid based supromolecular gel: From microscopic volume phase transition to functional applications

Supramolecular gel is an important class of soft materials formed through the self-assembly of low molecular weight molecules in water or organic solvents via various non-covalent interactions to immobilize the solvents. Supramolecular gels have attracted widespread attentions due to their structural and functional diversity. One of the important features of the gel materials is their responsiveness, which include the reversible gel-to-sol transition, macroscopic volume phase transition (shrinkage-swelling) and so on depending upon the external stimulus such as temperature, light, metal ions, electrical or magnetic field. Among these, volume phse transition is important since it can be used to develop various functions in drug release, biosensing, controlled microvalves, self-healing and so on. Although there are large amount of reports on the volume phase transition in polymer gels, there is fewer reproted on the supramolecualr gels due to the the inherent weak character of non-covalent interactions. Supramolecular hydrogels suffer the reality that the brittle 3D structures have difficulty in maintaining physical change such as folding and curling of the supramolecular chains as in polymer hydrogels to accordingly exhibit phase transition in volume (shrinkage-swelling) and shape (deformation- recovery). Among several shrinkable supramolecular gels, the dendritic glutamic acid amphiphile OGAc containing multi-carboxylic acid as the head group and a long alkyl chain appeared to be one of the good examples of such gels. This minireview focuses on the formation of the supramolecular hydrogel OGAc, the shrinkage-swelling transition, the stimuli-responsive together with such volume phase transition and the potential applications by utilizing the shrinkage/ swelling properties. The paper firstly introduces the unique reversible shrinking and swelling supramolecular gel triggered by divalent metal ions. Then the function of the various metal ions as the inducer for the gel shrinkage was discussed and a mechanism was proposed. Based on these discussions, the design concept for the shrinkable supramolecular gels was suggested. Secondly, the pH responsiveness of the OGAc-Mg2+ is discussed. Thirdly, in order to functionalize the supramolecular gels, charged organic compounds were introduced into the shrinkable gels. It was found that OGAc-AZOC2Py complex system also exhibited reversible shrinkage/swelling transition. Simultaneously, the gel showed a change in supramolecular chirality. Fourthly, the potential applications of the supramolecular assemblies by using the shrinkable gel are discussed, which mainly highlights the application in the efficient separation of the mixtures composed of positively and negatively charged dyes, visualized recognition of chiral amines based on OGAc- Mg2+-PIC system, the construction of dual reversible thermal and light-responsive chiroptical switches for OGAc-AZOC2Py hydrogel and controlled step-wise release of drug or biological substances in OGAc-Mg2+ gels. Finally, the future development and application of supramolecular shrinkable gel is outlooked. It is anticipated to design more sophisticated multi-functional materials based on reversible macroscopic volume phase transition and also to combine the advantage of the shrinkable polymer gels to develop new soft materials. It is expected that the shrinkable gels will find more applications in biological system and biotechnology.

Topological defects and electro-convective flows in anisotropic fluids: A microfluidic platform for nano-objects tunable structuring

Anisotropic fluids are a class of soft materials that offer wide possibilities for engineering a small scale laboratory; their physical properties can be manipulated on short length scale by appropriate confining conditions and external stimuli leading the systems across fascinating phenomena. In this work, two of these phenomena are combined to create a microfluidic platform for reconfigurable nanoparticles (NPs) patterning: the formation of topological defects and the electrically controlled convective flows. Here, the nanoscopic environments created by defects within liquid crystals have been used as linear nano-reservoirs of NPs. Afterwards, virtual channel flows that connect the linear reservoirs have been created by exploiting electro-convective rolls. The reported results reveal a strategy for managing nanometric objects based on anisotropic fluids and connected phenomena, proposing an unconventional microfluidic device characterized by switchable and contactless micro-channels.

Bottom-up Approach Design, Band Structure, and Lithium Storage Properties of Atomically Thin γ-FeOOH Nanosheets.

As a novel class of soft matter, two-dimensional (2D) atomic nanosheet-like crystals have attracted much attention for energy storage devices due to the fact that nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. Herein, atomically thin γ-FeOOH nanosheets with a thickness of ∼1.5 nm are synthesized in a high yield, and the band and electronic structures of the γ-FeOOH nanosheet are revealed using density-functional theory calculations for the first time. The rationally designed γ-FeOOH@rGO composites with a heterostacking structure are used as an anode material for lithium-ion batteries (LIBs). A high reversible capacity over 850 mAh g(-1) after 100 cycles at 200 mA g(-1) is obtained with excellent rate capability. The remarkable performance is attributed to the ultrathin nature of γ-FeOOH nanosheets and 2D heterostacking structure, which provide the minimized Li(+) diffusion length and buffer zone for volume change. Further investigation on the Li storage electrochemical mechanism of γ-FeOOH@rGO indicates that the charge-discharge processes include both conversion reaction and capacitive behavior. This synergistic effect of conversion reaction and capacitive behavior originating from 2D heterostacking structure casts new light on the development of high-energy anode materials.

In Situ Mechanical Testing of Nanostructured Bijel Fibers.

Bijels are a class of soft materials with potential for application in diverse areas including healthcare, food, energy, and reaction engineering due to their unique structural, mechanical, and transport properties. To realize their potential, means to fabricate, characterize, and manipulate bijel mechanics are needed. We recently developed a method based on solvent transfer-induced phase separation (STRIPS) that enables continuous fabrication of hierarchically structured bijel fibers from a broad array of constituent fluids and nanoparticles using a microfluidic platform. Here, we introduce an in situ technique to characterize bijel fiber mechanics at initial and final stages of the formation process within a microfluidics device. By manipulation of the hydrodynamic stresses applied to the fiber, the fiber is placed under tension until it breaks into segments. Analysis of the stress field allows fracture strength to be inferred; fracture strengths can be as high as several thousand Pa, depending on nanoparticle content. These findings broaden the potential for the use of STRIPS bijels in applications with different mechanical demands. Moreover, our in situ mechanical characterization method could potentially enable determination of properties of other soft fibrous materials made of hydrogels, capillary suspensions, colloidal gels, or high internal phase emulsions.

Perspective: Evolutionary design of granular media and block copolymer patterns

The creation of new materials “by design” is a process that starts from desired materials properties and proceeds to identify requirements for the constituent components. Such process is challenging because it inverts the typical modeling approach, which starts from given micro-level components to predict macro-level properties. We describe how to tackle this inverse problem using concepts from evolutionary computation. These concepts have widespread applicability and open up new opportunities for design as well as discovery. Here we apply them to design tasks involving two very different classes of soft materials, shape-optimized granular media and nanopatterned block copolymer thin films.

Numerical simulations of bijel morphology in thin films with complete surface wetting.

Bijels are a relatively new class of soft materials that have many potential energy and environmental applications. In this work, simulation results of bijel evolution confined within thin films with preferential surface wetting are presented. The computational approach used is a hybrid Cahn-Hilliard/Brownian dynamics method. In the absence of suspended particles, we demonstrate that the model accurately captures the rich kinetics associated with diffusion-based surface-directed spinodal decomposition, as evidenced by comparison with previous theoretical and simulation-based studies. When chemically neutral particles are included in the films, the simulations capture surface-modified bijel formation, with stabilized domain structures comparable with the experimental observations of Composto and coworkers. Namely, two basic morphologies - bicontinuous or discrete - are seen to emerge, with direct dependence on the film thickness, particle volume fraction, and particle radius.

Polymer-<I>Block</I>-Polypeptides and Polymer-Conjugated Hybrid Materials as Stimuli-Responsive Nanocarriers for Biomedical Applications

Stimuli-responsive nanocarriers are a class of soft materials that includes natural polymers, synthetic polymers, and polypeptides. Recently, modern synthesis tools such as atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, nitroxide-mediated radical polymerization, ring-opening polymerization of α-amino acid N-carboxyanhydrides, and various "click" chemistry strategies were simultaneously employed for the design and synthesis of nanosized drug delivery vehicles. Importantly, the research focused on the improvement of the nanocarrier targetability and the site-specific, triggered release of therapeutics with high drug loading efficiency and minimal drug leakage during the delivery to specific targets. In this context, nanocarriers responsive to common stimuli such as pH, temperature, redox potential, light, etc. have been widely used for the controlled delivery of therapeutics to pathological sites. Currently, different synthesis and self-assembly strategies improved the drug loading efficacy and targeted delivery of therapeutic agents to the desired site. In particular, polypeptide-containing hybrid materials have been developed for the controlled delivery of therapeutic agents. Therefore, stimuli-sensitive synthetic polypeptide-based materials have been extensively investigated in recent years. This review focuses on recent advances in the development of polymer-block-polypeptides and polymer-conjugated hybrid materials that have been designed and evaluated for various stimuli-responsive drug and gene delivery applications.

Synthesis and Characterization of Liquid Crystal Elastomer

The thermal and mechanical properties of Liquid Crystal Elastomers (LCEs) were characterized using various techniques for understanding of their physical behavior. The material used for investigation was synthesized by us, using Finklemann procedure, with proper cross linking density in nematic phase. The material is found to have unique coupling between anisotropicorder of liquid crystal component and elasticity of polymer network. The chemical structures were confirmed by Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). Fabry Perot Scattering Studies (FPSS), Thermo gravimetric Analysis (TGA) and Differential Scanning Calorimatory (DSC) were used to study thermal properties. The mechanical properties were studied using force sensor. Our investigation shows that this synthesized Liquid Crystal Elastomer has ability of spontaneous change as a function of temperature and mechanical force, which shows it as a unique class of soft material.

Influence of emulsifier concentration on nanoemulsion gelation.

Nanoemulsion gels are a new class of soft materials that manifest stronger elasticity even at lower dispersed phase volume fraction. In this work, gelation in 40 wt % canola oil-in-water nanoemulsions was investigated as a function of emulsifier type (anionic sodium dodecyl sulfate (SDS) or nonionic Tween 20) and concentration. It was observed that the liquid nanoemulsions transformed into viscoelastic gels at a specific concentration range of SDS, whereas no gelation was observed for Tween 20. The apparent viscosity, yield stress, and storage modulus of the nanogels increased with SDS concentration until 15 times critical micelle concentration (CMC), thereafter decreased steadily as the gelation weakened beginning 20 CMC. Three regimes of colloidal interactions in the presence of emulsifier were proposed. (1) Repulsive gelation: at low SDS concentration (0.5-2 times CMC) the repulsive charge cloud around the nanodroplets acted as interfacial shell layer that significantly increased the effective volume fraction of the dispersed phase (ϕ(eff)). When ϕ(eff) became comparable to the volume fraction required for maximal random jamming, nanoemulsions formed elastic gels. (2) Attractive gelation: as the SDS concentration increased to 5-15 times CMC, ϕ(eff) dropped due to charge screening by more counterions from SDS, but depletion attractions generated by micelles in the continuous phase led to extensive droplet aggregation which immobilized the continuous phase leading to stronger gel formation. (3) Decline in gelation due to oscillatory structural forces (OSF): at very high SDS concentration (20-30 time CMC), structural forces were manifested due to the layered-structuring of excess micelles in the interdroplet regions resulting in loss of droplet aggregation. Tween 20 nanoemulsions, on the other hand, did not show repulsive gelation due to lack of charge cloud, while weak depletion attraction and early commencement of OSF regime leading to liquid-like behavior at all concentrations. The nanogels possess great potential for use in low-fat foods, pharmaceuticals and cosmetic products.

Self-assembly of colloid-cholesteric composites provides a possible route to switchable optical materials.

Colloidal particles dispersed in liquid crystals can form new materials with tunable elastic and electro-optic properties. In a periodic 'blue phase' host, particles should template into colloidal crystals with potential uses in photonics, metamaterials and transformational optics. Here we show by computer simulation that colloid/cholesteric mixtures can give rise to regular crystals, glasses, percolating gels, isolated clusters, twisted rings and undulating colloidal ropes. This structure can be tuned via particle concentration, and by varying the surface interactions of the cholesteric host with both the particles and confining walls. Many of these new materials are metastable: two or more structures can arise under identical thermodynamic conditions. The observed structure depends not only on the formulation protocol but also on the history of an applied electric field. This new class of soft materials should thus be relevant to design of switchable, multistable devices for optical technologies such as smart glass and e-paper.

Electroformation of Janus and patchy capsules.

Janus and patchy particles have designed heterogeneous surfaces that consist of two or several patches with different materials properties. These particles are emerging as building blocks for a new class of soft matter and functional materials. Here we introduce a route for forming heterogeneous capsules by producing highly ordered jammed colloidal shells of various shapes with domains of controlled size and composition. These structures combine the functionalities offered by Janus or patchy particles, and those given by permeable shells such as colloidosomes. The simple assembly route involves the synergetic action of electro-hydrodynamic flow and electro-coalescence. We demonstrate that the method is robust and straightforwardly extendable to production of multi-patchy capsules. This forms a starting point for producing patchy colloidosomes with domains of anisotropic chemical surface properties, permeability or mixed liquid–solid phase domains, which could be exploited to produce functional emulsions, light and hollow supra-colloidosome structures, or scaffolds.

Graphene oxide dispersions: tuning rheology to enable fabrication

Ultra-large graphene oxide sheets exhibit unique viscoelastic properties, making them a new class of soft material. We provide fundamental insights enabling development of various fabrication techniques utilizing this 2D material.

Triphenylene-based discotic liquid crystals: recent advances

Since the early work of Chandrasekhar and his co-workers on hexaesters of benzene published in 1977, discotic liquid crystals (DLCs), in particular, triphenylene-based DLC materials have been investigated intensively, especially over the last decade. The first successful commercialisation of triphenylene-based DLCs has been accomplished in Fuji ‘Wide-View’ optical compensation films. DLCs represent a broad well understood class of soft matter which possess the ability to self-organise into highly anisotropic and ordered structures such as columns that function not only as organic anisotropic semiconductors, but also contribute to the development of new smart materials in the field of organic electronics for many device applications such as photovoltaic devices, light-emitting diodes, field-effect transistors, memory elements, and sensors. Over the last 35 years, more than 1000 triphenylene derivatives have been synthesised and investigated starting from structure-properties to structure-device performance relationships. The very first review by Cammidge and Bushby followed by Kumar summarised the chemistry and physical properties of triphenylene-based discotics up to 2003. In this review, progress in the research of triphenylene DLC materials since 2004 is comprehensively outlined.

Helium impurity nanocluster gels in superfluid helium

Rapid cooling of a helium impurity gas mixture to the superfluid helium temperatures allows us to prepare an impurity-helium condensate with jelly-like structure (impurity gel) in superfluid He-II. It is clear that the properties of these gels should be substantially different from those of a bulk impurity substance, constituting a new class of soft matter — quantum gel, where superfluid He-II filling the nanopores between the randomly connected impurity nanoclusters serves as the dispersion medium of the gel.

Self-assembly of diblock copolymers under confinement

Block copolymers are a class of soft matter that self-assemble to form ordered morphologies at nanometer scales, making them ideal materials for various applications. The self-assembly of block copolymers is mainly controlled by the monomer–monomer interactions, block compositions and molecular architectures. Besides these intrinsic parameters, placing block copolymers under confinement introduces a number of extrinsic factors, including the degree of structural frustration and surface–polymer interactions, which can strongly influence the self-assembled morphologies. Therefore confinement of block copolymers provides a powerful route to manipulate their self-assembled nanostructures. In this review, we discuss the relationship between confining conditions and the resulting structures, focusing on principles governing structural formation of diblock copolymers under two-dimensional and three-dimensional confinement. In particular, the effects of commensurability condition, surface–polymer interactions, and confining geometries on the self-assembled morphologies are discussed.