Showing papers in "Soft Matter in 2012"
TL;DR: In this article, the differences and similarities between nanoemulsions and micro-mulsions in terms of their compositions, structure, fabrication, properties, and stability are discussed.
Abstract: Colloidal delivery systems based on microemulsions or nanoemulsions are increasingly being utilized in the food and pharmaceutical industries to encapsulate, protect, and deliver lipophilic bioactive components. The small size of the particles in these kinds of delivery systems (r < 100 nm) means that they have a number of potential benefits for certain applications: enhanced long-term stability; high optical clarity; and, increased bioavailability. Currently, there is considerable confusion about the use of the terms “microemulsions” and “nanoemulsions” in the scientific literature. However, these are distinctly different types of colloidal dispersions: a microemulsion is thermodynamically stable, whereas a nanoemulsion is not. It is therefore important to distinguish between them since this impacts the methods used to fabricate them, the strategies used to stabilize them, and the approaches used to design their functional attributes. This article reviews the differences and similarities between nanoemulsions and microemulsions in terms of their compositions, structure, fabrication, properties, and stability. It also attempts to highlight why there has been so much confusion in this area, and to clarify the terminology used to refer to these two kinds of colloidal dispersion.
1,201 citations
TL;DR: This review aims to highlight the range of injectable shear-thinning hydrogel systems being developed, with a focus on the various mechanisms of formation and shear -thinning and their use in biomedical applications.
Abstract: Injectable hydrogels are becoming increasingly important in the fields of tissue engineering and drug delivery due to their tunable properties, controllable degradation, high water content, and the ability to deliver them in a minimally invasive manner. Shear-thinning is one promising technique for the application of injectable hydrogels, where preformed hydrogels can be injected by application of shear stress (during injection) and quickly self-heal after removal of shear. Importantly, these gels can be used to deliver biological molecules and cells during the injection process. This review aims to highlight the range of injectable shear-thinning hydrogel systems being developed, with a focus on the various mechanisms of formation and shear-thinning and their use in biomedical applications.
698 citations
TL;DR: Some representative theoretical and numerical approaches aimed at modelling the onset of instabilities as well as the postbuckling evolution involving multiple bifurcations and symmetry breakings are discussed along with the main characteristics and some possible applications of this rich phenomenon.
Abstract: Morphological instabilities and surface wrinkling of soft materials such as gels and biological tissues are of growing interest to a number of academic disciplines including soft lithography, metrology, flexible electronics, and biomedical engineering. In this paper, we review some of the recent progresses in experimental and theoretical investigations of instabilities that lead to the emergence and evolution of surface wrinkling, folding and creasing under various geometrical constraints (e.g., thin films, sheets, fibers, particles, tubes, cavities, vesicles and capsules) and loading stimuli (e.g., mechanical forces, growth, atrophy, swelling, shrinkage, van der Waals interactions). Some representative theoretical and numerical approaches aimed at modelling the onset of instabilities as well as the postbuckling evolution involving multiple bifurcations and symmetry-breakings are discussed along with the main characteristics and some possible applications of this rich phenomenon.
655 citations
TL;DR: In this paper, the authors demonstrate experimentally and models computationally a novel and simple approach for self-folding of thin sheets of polymer using unfocused light, which is made of optically transparent, pre-strained polystyrene (also known as Shrinky-Dinks).
Abstract: This paper demonstrates experimentally and models computationally a novel and simple approach for self-folding of thin sheets of polymer using unfocused light. The sheets are made of optically transparent, pre-strained polystyrene (also known as Shrinky-Dinks) that shrink in-plane if heated uniformly. Black ink patterned on either side of the polymer sheet provides localized absorption of light, which heats the underlying polymer to temperatures above its glass transition. At these temperatures, the predefined inked regions (i.e., hinges) relax and shrink, and thereby cause the planar sheet to fold into a three-dimensional object. Self-folding is therefore achieved in a simple manner without the use of multiple fabrication steps and converts a uniform external stimulus (i.e., unfocused light) on an otherwise compositionally homogenous substrate into a hinging response. Modeling captures effectively the experimental folding trends as a function of the hinge width and support temperature and suggests that the hinged region must exceed the glass transition temperature of the sheet for folding to occur.
484 citations
TL;DR: The author hopes that the present discussion will reduce the danger of inappropriate use of the beauty of the instrument sometimes seduces an investigator to use it without any connection to the physical model.
Abstract: A particle's motion in crowded environments often exhibits anomalous diffusion, whose nature depends on the situation at hand and is formalized within different physical models. Thus, such environments may contain traps, labyrinthine paths or macromolecular structures, which the particles may be attached to. Physical assumptions are translated into mathematical models which often come with nice mathematical instruments for their description, e.g. fractional diffusion equations. The beauty of the instrument sometimes seduces an investigator to use it without any connection to the physical model. The author hopes that the present discussion will reduce the danger of such inappropriate use.
455 citations
TL;DR: This review highlights recent efforts in converting a naturally occurring polysaccharide to drug releasing hydrogel particles, and finally, complex and instructive macroscopic networks that are promising materials for tissue repair and regeneration.
Abstract: Hyaluronic acid (HA) is one of nature's most versatile and fascinating macromolecules. Being an essential component of the natural extracellular matrix (ECM), HA plays an important role in a variety of biological processes. Inherently biocompatible, biodegradable and non-immunogenic, HA is an attractive starting material for the construction of hydrogels with desired morphology, stiffness and bioactivity. While the interconnected network extends to the macroscopic level in HA bulk gels, HA hydrogel particles (HGPs, microgels or nanogels) confine the network to microscopic dimensions. Taking advantage of various scaffold fabrication techniques, HA hydrogels with complex architecture, unique anisotropy, tunable viscoelasticity and desired biologic outcomes have been synthesized and characterized. Physical entrapment and covalent integration of hydrogel particles in a secondary HA network give rise to hybrid networks that are hierarchically structured and mechanically robust, capable of mediating cellular activities through the spatial and temporal presentation of biological cues. This review highlights recent efforts in converting a naturally occurring polysaccharide to drug releasing hydrogel particles, and finally, complex and instructive macroscopic networks. HA-based hydrogels are promising materials for tissue repair and regeneration.
442 citations
TL;DR: In this paper, the corn protein zein was used as a representative of water-insoluble proteins for particle-stabilization of oil-in-water emulsions.
Abstract: Few fully natural and biocompatible materials are available for the effective particle-stabilization of emulsions since strict requirements, such as insolubility in both fluid phases and intermediate wettability, need to be met. In this paper, we demonstrate the first use of water-insoluble proteins, employing the corn protein zein as a representative of this family, as effective particle-stabilizers of oil-in-water emulsions of natural oils and water. For this purpose, we synthesized zein colloidal particles through an anti-solvent precipitation procedure and demonstrated their use in the formation of stable oil-in-water Pickering emulsions as a function of particle concentration, pH and ionic strength. We confirmed that the wetting properties of zein, studied as a function of pH and ionic strength, strongly favor interfacial particle adsorption with oil-in-water three-phase contact angles θow close to 90°. We found that unmodified zein colloidal particles can produce stable, surfactant-free o/w emulsions with droplet sizes in the range 10–200 μm under experimental mixing conditions (2 min with Ultra Turrax homogenizer at 13500 rpm) at pH above and below the isoelectric point of zein, for low to moderate ionic strengths (1–10 mM). Under conditions where the particle volume fraction is low (<0.2 wt%) or at low pH, the resulting emulsions are not stable against coalescence. At a higher ionic strength, the zein particles have a tendency to aggregate and the resulting emulsions flocculate, forming an emulsion–gel phase.
403 citations
TL;DR: In this article, a soft dielectric membrane is shown to be prone to snap-through instability, and the instability can be harnessed to achieve giant voltage-triggered deformation.
Abstract: A soft dielectric membrane is prone to snap-through instability. We present theory and experiment to show that the instability can be harnessed to achieve giant voltage-triggered deformation. We mount a membrane on a chamber of a suitable volume, pressurize the membrane into a state near the verge of the instability, and apply a voltage to trigger the snap without causing electrical breakdown. For an acrylic membrane we demonstrate voltage-triggered expansion of area by 1692%, far beyond the largest value reported in the literature. The large expansion can even be retained after the voltage is switched off.
374 citations
TL;DR: In this paper, the authors summarize the recent developments of superhydrophobic surfaces with unique structural and functional properties, including self-cleaning, icephobicity, anti-corrosion, drag reduction, transparency, antireflection, structural color, droplet transportation, anisotropy, oil-water separation, water supporting force, superamphiphobicity and responsive switching.
Abstract: The surface wettability control of solid materials has been considered as an essential aspect of surface chemistry. In the past decade, superhydrophobic surfaces have revealed a cornucopia of novel structural and functional properties, exhibiting considerable importance in both fundamental research and practical applications. In this review, we summarize the recent developments of superhydrophobic surfaces with unique structural and functional properties. Both the fabricative methods and the working performance of superhydrophobic surfaces with multidisciplinary functionalities including self-cleaning, icephobicity, anti-corrosion, drag reduction, transparency, anti-reflection, structural color, droplet transportation, anisotropy, oil–water separation, water supporting force, superamphiphobicity and responsive switching, have been discussed briefly. Finally, the current challenges and future prospects of this dynamic field are discussed based on our own opinion.
345 citations
TL;DR: In this paper, a systematic study has been conducted with rice leaves and butterfly wings, using a combination of actual and replica samples, in order to mimic the rice and butterfly wing effect, replica rice leaf and shark skin samples received a superhydrophobic and low adhesion nanostructured coating.
Abstract: Living nature is the inspiration for many innovations and continues to serve as an invaluable resource to solve technical challenges. We find that unique surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus (superhydrophobic and self-cleaning) effects, producing what we call here the rice and butterfly wing effect. A systematic study has been conducted with rice leaves and butterfly wings, using a combination of actual and replica samples. In order to mimic the rice and butterfly wing effect, replica rice leaf and shark skin samples received a superhydrophobic and low adhesion nanostructured coating. The data are compared to those of uncoated samples of fish scales and shark skin. Surface morphology characterization is conducted with SEM and optical profiler imaging using software analysis. Drag is determined with pressure drop measurements from replica lined rectangular duct flow channels (using water and air in laminar and turbulent regimes). The lotus effect is shown with self-cleaning, contact angle, and adhesion force measurements. Results are discussed and conceptual models shown describing the role of surface structures related to low drag, self-cleaning, and antifouling properties.
298 citations
TL;DR: In this paper, phase separation and complex coacervation of polypeptides are investigated using equal chain lengths of polycation and polyanion in order to isolate and highlight effects of the interactions of the charged groups during complexation.
Abstract: Mixing of oppositely charged polyelectrolytes in aqueous solutions may result in the formation of polyelectrolyte complexes (PEC). Phase separation and complex coacervation of polypeptides are investigated in this study. Polypeptides have identical backbones and differ only in their charged side groups, making them attractive model systems for this work. All experiments are conducted using equal chain lengths of polycation and polyanion in order to isolate and highlight effects of the interactions of the charged groups during complexation. Complex coacervation is strongly affected by the polypeptide mixing ratio (stoichiometry), ionic strength (salt concentration), total polymer concentration, pH, and temperature. To examine the effect of these parameters on complex formation we use sample turbidity as an indicator, and optical microscopy to discriminate between coacervate and precipitate. We establish phase diagrams as a function of polybase content and salt concentration using the critical salt concentrations required to reach the coacervate to solution boundary. Additionally, we examine the effect of molecular weight on the complex formation for the P(L-Lysine) (PLys)/P(L-Glutamic acid) (PGlu) system and establish a phase diagram. By determining the water content of the coacervate phase under various conditions we find that the salt content and stoichiometry of the mixed polyelectrolytes have a significant effect on the coacervate composition.
TL;DR: In this article, the authors review recent advances in the field of anisotropic particles at fluid interfaces, by focusing on particles in the micron and submicron range, and discuss capillary adsorption, orientation, migration, and self-assembly, on planar and curved interfaces, and the rheology of particle-laden interfaces.
Abstract: Micro and nanoparticle adsorption to and assembly by capillarity at fluid–fluid interfaces are intriguing aspects of soft matter science with broad potential in the directed assembly of anisotropic media. The importance of the field stems from the ubiquitous presence of multiphase systems, the malleability of fluid interfaces, and the ability to tune the interactions of the particles adsorbed on them. While homogeneous spherical particles at interfaces have been well studied, the behavior of anisotropic particles – whether the anisotropy originates from shape or chemical heterogeneity – has been considered only very recently. We review recent advances in the field of anisotropic particles at fluid interfaces, by focusing on particles in the micron and submicron range. We discuss capillary adsorption, orientation, migration, and self-assembly, on planar and curved interfaces, and the rheology of particle-laden interfaces. Prospects for future work and outstanding challenges are also discussed.
TL;DR: In this article, an interesting water diode film is fabricated by a facile electrospinning technique, which is a composite of hydrophobic polyurethane (PU) and hydrophilic crosslinked poly (vinyl alcohol) (c-PVA) fibrous layers.
Abstract: An interesting “water diode” film is fabricated by a facile electrospinning technique. The fibrous film is a composite of hydrophobic polyurethane (PU) and hydrophilic crosslinked poly (vinyl alcohol) (c-PVA) fibrous layers. By taking advantages of the hydrophobic–hydrophilic wettability difference, water can penetrate from the hydrophobic side, but be blocked on the hydrophilic side.
TL;DR: In this paper, the authors investigate the complex dynamics exhibited by various active carrier-cargo composites, focusing on the cases in which a single or a pair of Janus micro-motors is used as carrier.
Abstract: Catalytically active Janus micro-spheres are capable of autonomous motion and can potentially act as carriers for transportation of cargo at the micron-scale. Focusing on the cases in which a single or a pair of Janus micro-motors is used as carrier, we investigate the complex dynamics exhibited by various active carrier–cargo composites.
TL;DR: In this article, a voltage-induced deformation of a dielectric elastomer membrane was demonstrated under equal-biaxial and uniaxial forces, as well as on fiber-constrained membranes.
Abstract: A membrane of a dielectric elastomer deforms when a voltage is applied through its thickness. The achievable voltage-induced deformation is strongly affected by how mechanical loads are applied. Large voltage-induced deformation has been demonstrated for a membrane under equal-biaxial forces, but only small voltage-induced deformation has been observed for a membrane under a uniaxial force. This difference is interpreted here theoretically. The theory also predicts that, when the deformation of a membrane is constrained in one direction, a voltage applied through the thickness of the membrane can cause it to deform substantially in the other direction. Experiments are performed on membranes under equal-biaxial forces and uniaxial forces, as well as on fiber-constrained membranes of two types: a dielectric elastomer membrane with carbon fibers on both faces, and two dielectric elastomer membranes sandwiching nylon fibers. The experimental observations are compared with the theory.
TL;DR: This review describes the various in vitro strategies used to bring biocatalysts together in an artificial way, and non-specific, covalent co-immobilization as well as non-covalent encapsulation, scaffold-mediated co-localization and site-specific covalents conjugation strategies are discussed.
Abstract: In living cells enzymes catalyze a wide variety of metabolic processes, which involve multiple reaction steps. Efficient transfer of the intermediates from one catalytic site to the other is achieved by the formation of macromolecular enzyme complexes. This phenomenon, called metabolic channeling, has inspired researchers to bring biocatalysts together in an artificial way as well. This review describes the various in vitro strategies which have been exploited so far. A distinction is made based on the degree of control over the assembly process. Non-specific, covalent co-immobilization as well as non-covalent encapsulation, scaffold-mediated co-localization and site-specific covalent conjugation strategies are discussed.
TL;DR: The present review assembles investigations on lipid/polymer/nanoparticle interaction with the main focus directed towards model membrane systems published in the recent literature starting from ∼2005, providing a deeper and more thorough understanding of these complex interactions and their effects on membrane properties.
Abstract: Membranes can be fabricated either from lipid or polymer molecules, leading to the formation of liposomes or polymersomes. In all types of liposomal membranes, the issue of phase separation plays a central role not only in the membrane-formation itself, but also in the resulting structural features taking place within or at the surface of such membranes. When nanoparticles or polymers interact with lipid membranes, the final morphology is strongly determined by the charge, composition and size of the interacting components, which in turn induce phase separation processes. The present review assembles investigations on lipid/polymer/nanoparticle interaction with the main focus directed towards model membrane systems published in the recent literature starting from ∼2005, providing a deeper and more thorough understanding of these complex interactions and their effects on membrane properties.
TL;DR: In this article, a case study comparing literature data sets on hard-sphere viscosity and diffusion is presented, showing that systematic errors of ≳3% are probably unavoidable.
Abstract: Hard-sphere colloids are popular as models for testing fundamental theories in condensed matter and statistical physics, from crystal nucleation to the glass transition. A single parameter, the volume fraction (ϕ), characterizes an ideal, monodisperse hard-sphere suspension. In comparing experiments with theories and simulation, researchers to date have paid little attention to likely uncertainties in experimentally-quoted ϕ values. We critically review the experimental measurement of ϕ in hard-sphere colloids, and show that while statistical uncertainties in comparing relative values of ϕ can be as low as 10−4, systematic errors of ≳3% are probably unavoidable. The consequences of this are illustrated by way of a case study comparing literature data sets on hard-sphere viscosity and diffusion.
TL;DR: In this paper, a linear-elastic model incorporating an out-of-plane restoring force due to solid surface tension was recently shown to accurately predict the equilibrium shape of a thin elastic film due to a large sessile droplet.
Abstract: Young's law fails on soft solid and liquid substrates where there are substantial deformations near the contact line. On liquid substrates, this is captured by Neumann's classic analysis, which provides a geometrical construction for minimising the interfacial free energy. On soft solids, the total free energy includes an additional contribution from elasticity. A linear-elastic model incorporating an out-of-plane restoring force due to solid surface tension was recently shown to accurately predict the equilibrium shape of a thin elastic film due to a large sessile droplet. Here, we extend this model to find substrate deformations due to droplets of arbitrary size. While the macroscopic contact angle matches Young's law for large droplets, it matches Neumann's prediction for small droplets. The cross-over droplet size is roughly given by the ratio of the solid's surface tension and elastic modulus. On thin substrates at this cross-over, the macroscopic contact angle increases, indicating that the substrate is effectively less wetting. For droplets of all sizes, the microscopic behaviour near the contact line follows the Neumann construction giving local force balance.
TL;DR: In this article, a review of electrorheological fluid, a special type of suspension with controllable fluidity by an electric field, generally contains semiconducting or polarizable materials as electro-responsive parts.
Abstract: An electrorheological fluid, a special type of suspension with controllable fluidity by an electric field, generally contains semiconducting or polarizable materials as electro-responsive parts. These materials align in the direction of the applied electric field to generate a solid-like phase in the suspension. These electro-responsive smart materials, including dielectric inorganics, semiconducting polymers and their hybrids, and polymer/inorganic composites, are reviewed in terms of their mechanism, rheological analysis and dielectric characteristics.
TL;DR: In this article, the authors summarize the recent developments of extreme wettability in nature and biomimetic examples, and then focus on surface wetting behavior beyond nature, which means surfaces wetting properties that cannot be found in nature.
Abstract: In this critical review, we summarize the recent developments of extreme wettability in nature and biomimetic examples, and then we focus on surface wetting behavior beyond nature, which means surface wetting properties that cannot be found in nature. They are: switchable wettability between (super)hydrophobicity and (super)hydrophilicity, switchable water/oil droplet adhesion between superhydrophobic pinning states and superhydrophobic rolling states, superoleophobicity at the air–solid interface or even under vacuum, and self-healing (super)amphiphobicity at the air–solid interface.
TL;DR: In this paper, the formation of nanoscale structural elements by triglyceride molecules is the first step in forming a fat material as we know it, and it is shown that these microstructural elements assemble into colloidal aggregates with fractal character.
Abstract: Fat-structured food materials are an important component of our diet. The role that fat plays in material functionality, flavor perception, texture and health characteristics is due in large part to its physical properties. An understanding of these physical properties is relevant from scientific, technological and medical perspectives. The physical properties of fat materials, are, in turn, governed by a complex confluence of the various structural levels in a fat material beginning with triglyceride molecules. The formation of nanoscale structural elements by these molecules is the first step in the formation of a fat material as we know it. This review shows how these microstructural elements can be imaged and characterized. It is also shown that the formation of these nanocrystals is affected by the attendant crystallization parameters. Through simulation and a discussion of van der Waals forces, it is shown that these nanoscale elements assemble into colloidal aggregates with fractal character. The influence of microstructure on the mechanical properties of a fat material is explained using a variety of mechanical models. Lastly, this review examines methods by which the properties and characteristics of the various structural levels can be engineered. Shear has been shown to affect the polymorphism and phase transition kinetics of triglyceride crystals. As well, shear has been shown to modify the aggregation of nanocrystals, with consequences for the porosity and diffusivity of oil through the fat crystal network.
TL;DR: In this article, a photo-crosslinkable poly(N-isopropylacrylamide) copolymer patterned into thin rectangular strips divided into one high and one low swelling region is considered.
Abstract: The process by which spatial variations in growth transform two-dimensional elastic membranes into three-dimensional shapes is both a fundamentally interesting mechanism of shape selection and a powerful tool for the preparation of responsive materials. From the perspective of lithographic patterning of thin gel sheets, it is most straightforward to prepare materials consisting of discrete regions with different degrees of swelling. However, the sharp variations in swelling at the boundaries between such regions make it impossible for the sheet to adopt a configuration that is free of in-plane stresses everywhere. Thus, the deformation of such materials is not well understood. Here, we consider the geometrically simple case of a photo-crosslinkable poly(N-isopropylacrylamide) copolymer patterned into thin rectangular strips divided into one high- and one low-swelling region. When swelled in an aqueous medium at 22 °C, the sheet rolls into a three-dimensional shape consisting of two nearly cylindrical regions connected by a transitional neck. Heating to 50 °C leads to fully reversible de-swelling back to a flat configuration. We propose a scaling argument based on a balance between stretching and bending energies that relates the curvature of the 3D shape to the width and thickness of the strip, find good agreement with experimental data and numerical simulations, and further demonstrate how this simple geometry provides a powerful route for the fabrication of self-folding stimuli-responsive micro-devices.
TL;DR: In this article, the authors describe recent progress and examples in the synthesis and application of mesoporous carbon materials based on soft-templating approaches and highlight the fundamental principles of self-aggregation, highlight proposed synthesis mechanisms and present means of controlling pore size.
Abstract: Mesoporous carbons synthesized via a soft-templating approach have attracted much attention due to their easy synthesis and facile control over the derived pore structure. In analogy to soft-templating approaches for mesoporous metal oxides, their synthesis is based on a sequence of forming supramolecular arrangements of precursor molecules with the soft templates, stabilization of the precursor framework by polymerization and finally the removal of the templates. Using micelles of amphiphilic block-copolymers as templates, facile control over the morphology and size of mesopores can be achieved by e.g. controlling size, composition, and concentration of the template polymers or composition and degree of polymerization of the precursor. Moreover, soft templating approaches can be extended to obtain also carbon materials with hierarchical meso- and macroporosity. The additional macroporosity either can result from templating by polymer latex or is induced via macrophase separation. In this review, we describe recent progress and examples in the synthesis and application of mesoporous carbon materials based on soft-templating approaches. Moreover, we reiterate fundamental principles of self-aggregation, highlight proposed synthesis mechanisms and present means of controlling pore size, also in hierarchical meso–macroporous carbon materials.
TL;DR: In this paper, the authors present a review of available crystallization techniques and discuss their scope and limitations, in order to provide just the right method for the next experiment, and discuss the limitations of these techniques.
Abstract: Take polymer colloids—simple to make and ubiquitously available—let them self-assemble into a monolayer and you have, readily engineered, a sophisticated mask to create highly symmetric surface patterns with nanometre precision. Thirty years after its invention, this process, commonly referred to as colloidal lithography, is far from being old news and an ever-increasing range of scientists continues to use their creativity to come up with increasingly more complex surface patterns. As intriguing this technique is, the devil is in the details and it is far from trivial to achieve high order in a colloidal monolayer. This article reviews available crystallization techniques and discusses their scope and limitations in order to provide just the right method for your next experiment.
TL;DR: In this paper, the authors demonstrate the use of foam to divert flow from high permeable to low permeable regions in a PDMS heterogeneous porous microfluidic system.
Abstract: We demonstrate the use of foam to divert flow from high permeable to low permeable regions in a PDMS heterogeneous porous microfluidic system. Foam is generated using a flow-focusing microfluidic device with co-flowing gas and aqueous surfactant streams. Foam quality (gas fraction) is modulated by adjusting the flow rate of the aqueous surfactant solution while keeping the gas inlet pressure fixed. The foam is then injected into an aqueous-solution filled heterogeneous porous media containing a high and low permeable region and sweep of the saturated aqueous phase is monitored. Compared with 100% gas injection, surfactant-stabilized foam is shown to effectively improve the sweep of the aqueous fluid in both high and low permeable regions of the porous micromodel. The best performance of foam on fluid diversion is observed in the lamella-separated foam regime, where the presence of foam can enhance gas saturation in the low permeable region up to 45.1% at the time of gas breakthrough. The presented results are useful in understanding and designing foam injection in porous underground formations for aquifer remediation and enhanced oil recovery processes.
TL;DR: In this paper, the GAFF Lennard-Jones parameters for the simulation of acyl chains are corrected to allow the accurate and stable simulation of pure lipid bilayers, which is intended for combination with the new AMBER Lipid11 modular force field as part of ongoing attempts to create a modular phospholipid AMBER force field allowing tensionless NPT simulations of complex lipid bilayer.
Abstract: Previous attempts to simulate phospholipid bilayers using the General Amber Force Field (GAFF) yielded many bilayer characteristics in agreement with experiment, however when using a tensionless NPT ensemble the bilayer is seen to compress to an undesirable extent resulting in low areas per lipid and high order parameters in comparison to experiment. In this work, the GAFF Lennard-Jones parameters for the simulation of acyl chains are corrected to allow the accurate and stable simulation of pure lipid bilayers. Lipid bilayers comprised of six phospholipid types were simulated for timescales approaching a quarter of a microsecond under tensionless constant pressure conditions using Graphics Processing Units. Structural properties including area per lipid, volume per lipid, bilayer thickness, order parameter and headgroup hydration show favourable agreement with available experimental values. Expanding the system size from 72 to 288 lipids and a more experimentally realistic 2 × 288 lipid bilayer stack induces little change in the observed properties. This preliminary work is intended for combination with the new AMBER Lipid11 modular force field as part of on-going attempts to create a modular phospholipid AMBER force field allowing tensionless NPT simulations of complex lipid bilayers.
TL;DR: In this paper, the authors investigated the underlying physical mechanisms for these observed shape memory behaviors and the associated energy storage and release by using a theoretical modeling approach, which is similar to the generalized standard linear solid model of viscoelasticity.
Abstract: Shape memory polymers have attracted increasing research interest due to their capability of fixing a temporary shape and associated deformation energy then releasing them later on demand. Recently, it has been reported that polymers with a broad thermomechanical transition temperature range can demonstrate a multi-shape memory effect (m-SME), where shape recovery and energy release occur in a stepped manner during free recovery. This paper investigated the underlying physical mechanisms for these observed shape memory behaviors and the associated energy storage and release by using a theoretical modeling approach. A multibranch model, which is similar to the generalized standard linear solid model of viscoelasticity, was used for a quantitative analysis. In this model, individual nonequilibrium branches represent different relaxation modes of polymer chains with different relaxation times. As the temperature was increased in a staged manner, for a given temperature, different numbers of branches (or relaxation modes) became shape memory active or inactive, leading to the observed m-SME. For energy release during free recovery, under a tensile deformation of the SMP, stored energy in individual nonequilibrium branches was first transferred into a compressive deformation energy, then gradually declined to zero. Energy release during recovery was a complicated process due to the involvement of multiple relaxation modes.
TL;DR: In this article, the shape-memory effect (SME) mechanism was investigated in an elastomeric thermoplastic polyurethane (TPU) matrix with a cellulose nano-whisker percolation network.
Abstract: We report a new phenomenon in which the reversible formation and disruption of a cellulose nano-whisker (CNW) percolation network in an elastomeric thermoplastic polyurethane (TPU) matrix leads to an unprecedentedly rapidly switchable shape-memory effect (SME) that may be activated by water The materials have been fully characterized to investigate the SME phenomenon using a number of different experimental techniques including cyclic tensile deformation, dynamic mechanical analysis, FTIR and polarized Raman spectroscopy A model is developed in which it is shown that exposure to water allows breakup of the CNW percolation network so that the flexible elastomer matrix can be deformed to the desired shape The CNW percolation network reforms after drying to provide a fixing force for the temporary shape The entropy elasticity of the TPU matrix then enables rapid shape recovery when the CNW percolation network is disrupted again during wetting This completely athermal water-sensitive SME mechanism is totally different from traditional ones, in which the water or other solvents are used as plasticizers to lower the glass transition temperature of shape memory polymers, so as to allow triggering of the shape recovery at room temperature or lower The reported work provides a novel and effective strategy to achieve rapidly switchable shape recovery in a material by a simple wetting process and fixing through an easily applicable programmed drying process
TL;DR: In this paper, a super-tough double-network (DN) composite hydrogels with grafted silica nanoparticles was developed, which do not fracture upon loading up to 73 MPa and a strain above 0.98.
Abstract: We have successfully developed hydrogels with high compressive toughness by reinforcing the double-network structure (PAMPS/PAAm) with grafted silica nanoparticles. Silica nanoparticles grafted with vinyl end groups were used as macro-crosslinkers to copolymerize with AMPS, yielding a nanocomposite first network. Subsequent introduction of a secondary PAAm network resulted in super-tough double-network (DN) composite hydrogels, which do not fracture upon loading up to 73 MPa and a strain above 0.98. The compressive strength, swelling behavior, and morphology of the silica-grafted DN hydrogels were investigated as functions of nanoparticle content and particle size, in comparison with silica nanoparticle-filled DN gels without covalent bonding to the polymer network. Maximal reinforcement of the DN gels was achieved at around 1 wt% (weight percent) of grafted silica nanoparticles with respect to AMPS. Unique embedded micro-network structures were observed in the silica-grafted DN gels and accounted for the substantial improvement in compressive toughness. The fracture mechanism is discussed in detail based on the yielding behavior of these covalently composited hydrogels.