Soft Matter Blog

Stimuli-responsive materials have received much attention recently because of their ability to switch their physical and chemical properties in response to external environmental conditions such as irritation with light, temperature or pH. Layer-by-layer multilayer films have been studied because they can be quite sensitive to external stimuli such as pH, temperature and ionic strength. Most studies have focussed on the formation of multilayer films on supporting porous templates or deposition with micro-sized pores. Nano-sized cylindrical porous membranes with tunable pore diameters by external stimuli are important in understanding molecular translocation through membranes by stimuli-responsive porous membranes.

In this hot paper, Char and colleagues from Seoul National University deposited pH sensitive multilayer films on the sidewalls of pores with diameter sub-100 nm. The authors carefully control the molecular weight of the polyelectrolytes during the deposition and use multivalent salts. It is suggested that this approach can be applied to stimuli-driven gating devices that mimic living membranes.

Layer-by-layer assembled stimuli-responsive nanoporous membranes
Soft Matter, 2012, 8, 10271.  DOI: 10.1039/c2sm26562a (free to read for a short time)

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Ionic liquid crystals (ILCs) are closely related to ionic liquids. They have one key different feature compared to ionic liquids in that they consist of at least one long alkyl chain. This also differentiates them from liquid crystals where the alkyl chains are usually short and must contain a rigid core. The applications of ILCs tend to exploit their anisotropic ion conductivity, and they have been used as ordered reaction media or templates for the synthesis of mesoporous materials. A clear understanding of the many molecular factors influencing the ionic mesophases from experimental efforts is lacking.

In this hot paper, Saielli uses molecular dynamics stimulations (coarse-grained force fields) to give a semi-quantitative description of the mesomorphic behaviour of 1-hexadecyl-3-methylimidazolium nitrate. The author shows that coarse-grained force fields can be tuned to better reproduce the thermal range of stability of the mesophase.

MD simulation of the mesomorphic behaviour of 1-hexadecyl-3-methylimidazolium nitrate: assessment of the performance of a coarse-grained force field
Soft Matter, 2012, 8, 10279.  DOI: 10.1039/c2sm26376a (free to read for a short time)

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The dynamics in protein folding on the slower and larger length scale are facilitated by atomic fluctuations in the pico- and nano-second time scale. To understand the complexity of biomacromolecular materials the details of the structure-dynamics-function relationships at these scales must be analysed.

In this hot paper communication Telling and colleagues report the systematic study of macromolecular dynamics in green fluorescent protein, superoxide dismutase and insulin. The authors use neutron spectroscopy as a non-destructive and selective technique in the study, specifically elastic fixed window scattering and the newly developed technique of inelastic fixed window scattering. They find that the proteins show very different structures, but have similar methyl group compositions.

Lyophilised protein dynamics: more than just methyls?
Soft Matter, 2012, 8, 9529.  DOI: 10.1039/c2sm26540k (free to read for a short time)

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Pickering emulsions are currently a ‘hot topic’ in the field because of their applications in cosmetics, foodstuffs, waste-water treatment and energy. Emulsification is regulated by two fundamental steps: coalescence and fragmentation. Emulsions can be stabilised by solid particles which impede coalescence.

This hot paper by the Striolo group from the University of Oklahoma, describes the coalescence of droplets stabilised by solid particles. The authors use dissipative particle dynamics simulations to study water (oil) droplets dispersed in oil (water) in the presence of various nanoparticles. The droplets are forced to coalesce and the process is observed at the molecular level. The results could be used to help design more stable Pickering emulsions.

Mechanistic study of droplets coalescence in Pickering emulsions
Soft Matter, 2012, 8, 9533.  DOI: 10.1039/c2sm26416a (free to read for a short time)

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This review by Marcel Utz, Jan G. Korvink and colleagues describes the use of the common analytical technique, nuclear magnetic resonance (NMR) spectroscopy in connection with soft matter research. The authors discuss the developments in the technique comparing the performance of various microscale NMR detectors. Applications of microscale NMR in soft matter research are also described.

Microscale nuclear magnetic resonance: a tool for soft matter research
Soft Matter, 2012, 8, 10583.  DOI: 10.1039/c2sm26065d (free to read for a short time)

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Droplet-based microfluidics is an effective tool for the miniaturisation and automation of biological assays in many applications. For reliable function, the droplets must be stable against coalescence; must be biocompatible and their components must remain encapsulated. These conditions are all controlled by the surfactant molecules. Understanding the transport of molecules between dispersed microcontainers is highly relevant for many encapsulation systems such as drug delivery systems and applications related to emulsion polymerisation or cell physics.

This hot paper by Taly, Baret and colleagues, addresses the dynamics of molecular exchange between droplets in a mixed emulsion. The authors link microscope exchange between two adjacent droplets and macroscopic kinetics of experimentally measured relaxation of concentration differences in an emulsion. The system uses droplets with two different concentrations of a fluorescent dye.

This article features on the front cover of the Soft Matter principles of microfluidics themed issue.

Dynamics of molecular transport by surfactants in emulsions
Soft Matter, 2012, 8, 10618.  DOI: 10.1039/c2sm25934f (free to read for a short time)

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Biomolecular motors can be found everywhere in nature from the rotary motor enzyme ATP synthase to kinesin and dynein motor proteins. In recent decades, scientists have been able to produce a wealth of synthetic molecular machines such as switches, shuttles, gears, wheels and artificial muscles.

This Review by Lensen and Elemans from the Institute for Molecules and Materials at Radboud University surveys the study of synthetic molecular rotors and motors on surfaces using scanning tunnelling microscopy (STM). This technique allows imaging at the atomic scale and in recent years, has enabled visualisation of molecular motion.

Artificial molecular rotors and motors on surfaces: STM reveals and triggers
Soft Matter, 2012, 8, 9053.  DOI: 10.1039/c2sm26235e (free to read for a short time)

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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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