Soft Matter Blog

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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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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