Soft Matter Blog

Graphene is considered as the ultimate membrane material because it is atomically flat and extremely tough, but at the same time it can be very flexible. Solubilising graphene layers will be an important process for future applications. One route to do this has been to use graphite intercalation compounds which have been shown to be soluble in organic solvents such as NMP. However, NMP has a high boiling point and is highly toxic.

In this hot paper, Pénicaud and colleagues show that the graphite intercalation compound KC₈ is soluble in low boiling point and less toxic solvents such as ethers like THF. The authors study the graphene in solution, focussing on the crumbling of the 2D layers using light scattering and molecular dynamic simulations. Nanodroplets of solvent are thought to trigger graphene folding.

Solutions of fully exfoliated individual graphene flakes in low boiling point solvents
Soft Matter, 2012, 8, 7882.  DOI: 10.1039/c2sm25960e (free to read for a short time)

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Generating solids from liquid and gases via crystallisation is an important process both theoretically and technologically. In this hot paper, scientists from Harvard University in the group of George Whitesides, describe a model system for studying the self-assembly processes important in crystallisation. In particular they study millimeter-sized objects in systems in which charge-charge interactions dominate. The authors find that self-assembly is robust. Closely-packed crystalline structures are formed under many distinct experimental conditions. At least three classes of structure can be formed during self-assembly: crystals, chains and rosettes.

A simple two-dimensional model system to study electrostatic-self-assembly
Soft Matter, 2012, 8, 9771.  DOI: 10.1039/c2sm26192h (free to read for a short time)

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This tutorial review by members of The Polymers and Soft Matter Research Group (in the Material Physics Centre – Joint Centre of the University of the Basque Country and the Spanish Scientific Research Council) focuses on the combined use of molecular simulations and neutron scattering as a powerful tool to investigate structure and dynamics in polymers. The tutorial review describes several examples of how this strategy has been the right one to investigate the structural and dynamic features of linear homopolymer melts. The authors suggest that this approach will be important in addressing problems in more complex polymer systems such as biomacromolecules.

Neutron scattering and molecular dynamics simulations: synergetic tools to unravel structure and dynamics in polymers
Soft Matter, 2012, 8, 8257.  DOI: 10.1039/c2sm26061a (free to read for a short time)

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Disclination lines are microscopic objects in nematic liquid crystals that mediate forces between dispersed objects and modify the optical response of the medium. These are interesting properties for the production of complex materials and micro devices. Colloidal particles are often introduced to nematic liquid crystals as a way of increasing the number of disclination lines. Colloidal dispersions in chiral nematics have been shown to undergo spontaneous entanglement to give complex disclination networks.

In this hot paper, scientists in Ljubljana study the stability of theoretically predicted tangles in chiral nematic cells. Colloidal dimers in π-twisted chiral nematic cells are used as a model system. The authors developed a method that uses an analytical approximation arrangement of the disclination and found that the stability of a structure results from the individual stability of each tangle.

Stability and rewiring of nematic braids in chiral nematic colloids
Soft Matter, 2012, 8, 8595. DOI: 10.1039/c2sm25952d (free to read for a short time)

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The role of adsorbed particles on interfaces between immiscible fluids is important in many applications such as the stabilisation of droplets in Pickering emulsions in foods, cosmetics and oil recovery. They are also fundamentally interesting, particularly in materials science, in studies on the formation of functional membranes from monolayers of nano- or micro-particles. The geometry of the fluid interface must be considered as it is not always planar.

This hot paper by Dinsmore and colleagues analyses the adsorption of one or more spherical particles on a fluid interface that is initially curved in an anisotropic shape. The authors study the effect of interfacial curvature on the binding energy and on the associated capillary force exerted on the particles. The paper reports that the binding energy of one particle on a curved interface depends on the interface shape for the particle and not the local shape. Conversely, the binding energy for two particles depends only on the local shape.

Capillary interactions among spherical particles at curved liquid interfaces
Soft Matter, 2012, 8, 8582. DOI: 10.1039/c2sm25871d (free to read for a short time)

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Effect of lipid architecture on cubic phase susceptibility to crystallisation screens

Many therapeutics for diseases such as Alzheimer’s disease and Parkinson’s disease target membrane proteins. Structural characterisation of the proteins is required to produce better drugs, but growing high quality crystals for X-ray diffraction analysis can be a challenge. In this hot paper (front cover of Soft Matter Issue 26), Conn and co-workers report on the structural characterisation of four different lipids. The lipids were successfully used in the growth of membrane protein crystals, the structures of which were studied using SAXS and WAXS.

Soft Matter, 2012, 8, 6884-6896

Swelling-induced long-range ordered structure formation in polyelectrolyte hydrogel

In this hot paper (front cover of Soft Matter Issue 31), Gong and co-workers describe a strategy for introducing long-range ordered structure in amorphous hydrogels using dynamic mechano-complexation coupling in a non-equilibrium process. They report the swelling of a hydrogel consisting of poly(2,20-disulfonyl-4,40-benzidine terephthalamide) (PBDT). The mechanism of non-equilibrium structure formation is discussed and may provide insights into the formation of biomacromolecules, such as the growth of biological organs.

Soft Matter, 2012, 8, 8060-8066

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Simulation of fusion-mediated nanoemulsion interactions with model lipid bilayers

Coarse-grain simulations have been used to model atomistic structures of biological emulsions such as lipoproteins. This hot paper by Baker and co-workers presents a new coarse-grained perfluorooctylbromide (PFOB) model. The paper focuses on the initial step of the contact-facilitated delivery mechanism. This work could be used in new studies to understand the delivery mechanism of cargo molecules to target cells trough membrane fusion.

Soft Matter, 2012, 8, 7024–7035

Biomimetic fabrication of genetically engineered collagen peptide-assembled freestanding films reinforced by quantum dot joints

The biomimetic fabrication of nanomaterials is very important in many applications. Biomimetic films using a molecular self-assembly approach can be fragile and have a Young’s modulus less than 10 GPa. In this hot paper, Matsui and co-workers describe the preparation of freestanding films using collagen peptides and quantum dots. The films have a Young’s modulus of ~20 GPa and other interesting mechanical properties. The new films could potentially be applied to substrate-free electronics, ultrafast filtration and tissue engineering.

Soft Matter, 2012, 8, 6871-6875

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Ion electrodiffusion governs silk electrogelation

The formation of biocompatible medical adhesives based on silk hydrogels can be controlled by electric fields.  The elongation of the silk fibres is dependent on factors such as the value of the applied DC current, pH and silk fibroin concentration.  In this hot paper, Kaplan and co-workers describe a model which describes the transition of silk fibroin solution to a gel sate whereby the silk elongation can be mediated by a local change of the pH. The model was confirmed experimentally suggesting it could be used to calculate the amount of current needed for desired gel state growth under various conditions.

(Soft Matter, 2012, 8, 6897-6905 )

Interfacial viscoelasticity controls buckling, wrinkling and arrest in emulsion drops undergoing mass transfer

Oil droplets in emulsions are widely used for foods, consumer products and pharmaceutical applications. The mass transfer and ripening processes in emulsions with complex, non-Newtonian interfaces is little studied. In this hot paper, Erni and co-workers present a detailed study of the effect of interfacial rheological properties on compositional ripening in emulsions. The results are expected to have applications in the design and engineering of delivery systems in pharmaceuticals, phytochemicals, and flavour or fragrance compounds.

(Soft Matter, 2012, 8, 6958-6967)

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Double network hydrogels are tough synthetic gels consisting of two-interpenetrating networks. The recoverability of double network hydrogels from loading and unloading is improved in this hot paper by synthesising hydrogels using an ionically cross-linked network and a covalently cross-linked network. The authors prepare hydrogels consisting of ionically cross-linked Gellan gum (a naturally occurring anionic polysaccharide) and covalently cross-linked poly(acrylamide). The new hydrogel shows improved mechanical properties and can almost completely recover from subsequent loading-unloading cycles with respect to the second compressive cycle.

(Soft Matter, 2012, DOI: 10.1039/C2SM26745D, Advanced Article). Read for free until October 12^th.

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