Soft Condensed Matter Physics

Blue-phase templated fabrication of three-dimensional nanostructures for photonic applications

by Flynn Castles

Published in 'Nature Materials'

F. Castles, F. V. Day, S. M. Morris, D-H. Ko, D. J. Gardiner, M. M. Qasim, S. Nosheen, P. J. W. Hands, S. S. Choi, R.... more F. Castles, F. V. Day, S. M. Morris, D-H. Ko, D. J. Gardiner, M. M. Qasim, S. Nosheen, P. J. W. Hands, S. S. Choi, R. H. Friend, and H. J. Coles

Official link: http://dx.doi.org/10.1038/nmat3330

A promising approach to the fabrication of materials with nanoscale features is the transfer of liquid-crystalline structure to polymers. However, this has not been achieved in systems with full three-dimensional periodicity. Here we demonstrate the fabrication of self-assembled three-dimensional nanostructures by polymer templating blue phase I, a chiral liquid crystal with cubic symmetry. Blue phase I was photopolymerized and the remaining liquid crystal removed to create a porous free-standing cast, which retains the chiral three-dimensional structure of the blue phase, yet contains no chiral additive molecules. The cast may in turn be used as a hard template for the fabrication of new materials. By refilling the cast with an achiral nematic liquid crystal, we created templated blue phases that have unprecedented thermal stability in the range −125 to 125 °C, and that act as both mirrorless lasers and switchable electro-optic devices. Blue-phase templated materials will facilitate advances in device architectures for photonics applications in particular.

Flexoelectric and elastic coefficients of odd and even homologous bimesogens

by Flynn Castles

Published in 'Physical Review E' [copyright (2012) American Physical Society].

Katie L. Atkinson, Stephen M. Morris, Flynn Castles, Malik M. Qasim, Damian J. Gardiner, and Harry J. Coles
more Katie L. Atkinson, Stephen M. Morris, Flynn Castles, Malik M. Qasim, Damian J. Gardiner, and Harry J. Coles

Official link: http://link.aps.org/doi/10.1103/PhysRevE.85.012701
PDF: http://www.eng.cam.ac.uk/~fc252/PRE_85_012701_2012.PDF

It is known that bimesogenic liquid crystals exhibit a marked “odd-even” effect in the flexoelastic ratio (the effective flexoelectric coefficient to the average elastic coefficient), with the ratio being higher for the “odd-spaced” bimesogens (those with an odd number of alkyl groups in the spacer chain) than their neighboring even-spaced counterparts. To determine the contribution of each property to the flexoelastic ratio, we present experimental results on the flexoelectric and elastic coefficients of two homologous nonsymmetric bimesogens which possess odd and even alkyl spacers. Our results show that, although there are differences in the flexoelectric coefficients, there are substantially larger differences in the effective elastic coefficient. Specifically, the odd bimesogen is found to have both a low splay elastic coefficient and a very low bend elastic coefficient which, when combined, results in a significantly lower effective elastic coefficient and consequently a higher flexoelastic ratio.

DNA closed nanostructures: a structural and Monte Carlo simulation study

by Marco Lagi

A two-species model of a two-dimensional sandpile surface: a case of asymptotic roughening

by Anita Mehta

Published in Granular Matter online , DOI 10.1007/s10035-012-0350-3 (2012).

Oscillatory settling in wormlike-micelle solutions: bursts and a long time scale

by Nitin Kumar

Nitin Kumar, Sayantan Majumdar, Aditya Sood, Rama Govindarajan, Sriram Ramaswamy and A.K. Sood

Soft Matter, 2012, 8, 4310-4313
DOI: 10.1039/C2SM25077B

Preprint available here:
http://arxiv.org/pdf/1203.2130.pdf

We study the dynamics of a spherical steel ball falling freely through a solution of entangled wormlike-micelles. If... more We study the dynamics of a spherical steel ball falling freely through a solution of entangled wormlike-micelles. If the sphere diameter is larger than a threshold value, the settling velocity shows repeated short oscillatory bursts separated by long periods of relative quiescence. We propose a model incorporating the interplay of settling-induced flow, viscoelastic stress and, as in M. E. Cates, D. A. Head and A. Ajdari, Phys. Rev. E, 2002, 66, 025202(R) and A. Aradian and M. E. Cates, Phys. Rev. E, 2006, 73, 041508, a slow structural variable for which our experiments offer independent evidence.

Fast-switching phase gratings using in-plane addressed short-pitch polymer stabilized chiral nematic liquid crystals

by Flynn Castles

Published in 'Applied Physics Letters' [copyright (2011) American Institute of Physics].

S. M. Morris, D. J. Gardiner, F. Castles, P. J. W. Hands, T. W. Wilkinson, and H. J. Coles

Official link:... more S. M. Morris, D. J. Gardiner, F. Castles, P. J. W. Hands, T. W. Wilkinson, and H. J. Coles

Official link: http://dx.doi.org/10.1063/1.3670041
PDF: http://www.eng.cam.ac.uk/~fc252/APL_99_253502_2011.PDF

We demonstrate a fast-switching (sub-millisecond) phase grating based upon a polymer stabilized short-pitch chiral nematic liquid crystal that is electrically addressed using in-plane electric fields. The combination of the short-pitch and the polymer stabilization enables the diffraction pattern to be switched “on” and “off” reversibly in 600 µs. Results are presented on the far-field diffraction pattern along with the intensity of the diffraction orders as a function of the applied electric field and the response times.

Liquid-Liquid Phase Separation in Protein Solutions Controlled by Multivalent Salts and Temperature

by Christos Christodoulou

Poster

Solutions of most globular proteins are charge-stabilized. Charge screening, salting-in and salting-out behavior via... more Solutions of most globular proteins are charge-stabilized. Charge screening, salting-in and salting-out behavior via addition of salts are available ways controlling the phase behavior of the solutions. However, multivalent salts have been found to induce even more complex effects in protein solutions. In particular, reentrant condensation is observed for several globular proteins in the presence of multivalent salts (1, 2), i.e. the protein solution is stable at low and high salt concentration but phase-separates at intermediate salt concentration. As conclusive explanation, specific ion binding to the protein residues and pH effects cause an inversion of the protein global charge.
Importantly, besides the expected amorphous aggregation at low charge-stabilization, also a liquid-liquid phase separation occurs for several proteins at intermediate salt concentration. The full phase diagram of the protein solution extends to three control parameter – temperature, protein and salt concentration. Considering the protein-ion complexes as effective particles with short-range attractions whose strength varies with the
protein charge, the full phase behavior can be explained. Interestingly, the observed lower critical solution point suggests an inportant role of hydration to the free energy of the protein solution.

Stretching and relaxation of vesicles

by Beatriz Burrola Gabilondo

Investigating the fundamental effects of high frequency ultrasound upon biomacromolecular vibration and sub-cellular systems (2010)

by Michael Butler

PhD Report (midway point)

The broad motivation of this project is to investigate the role of acoustic waves within systems of soft matter,... more The broad motivation of this project is to investigate the role of acoustic waves within systems of soft matter, specifically in systems of molecular cell biology. The individual elements and structures involved in the dynamics of biological systems occur at various levels, from nanometre sized molecular dynamics to micron sized cells to millimetre sized tissue architectures. An understanding of the fundamental effects of acoustic energy upon biological systems could therefore take into account dynamics and structures up many orders of magnitude. The project presented is aiming to access the least complex, although also least accessible, structures; those at the molecular level corresponding to nanometre sized wavelengths and GHz frequency. Although we currently cannot produce ultrasonic devices that probe these systems directly[1], we can push classical piezoelectric technology toward its upper frequency limit in order to study molecular assemblies and sub-cellular structures. Therefore, the primary focus of the project has been to design and fabricate high frequency ultrasonic transducers that could be used to test the effects of high frequency on model chemical and biological systems. However, the initial focus of the project was to provide a solid, interdisciplinary theoretical basis for this experimental work and further investigations.

Cubic crystals from cubic colloids

by Laura Rossi

We have studied the crystallization behavior of colloidal cubes by means of tunable depletion interactions. The... more We have studied the crystallization behavior of colloidal cubes by means of tunable depletion interactions. The colloidal system consists of novel micron-sized cubic particles prepared by silica deposition on hematite templates and various non-adsorbing water- soluble polymers as depletion agents. We have found that under certain conditions the cubes self-organize into crystals with a simple cubic symmetry, which is set by the size of the depletant. The dynamic of crystal nucleation and growth is investigated, monitoring the samples in time by optical microscopy. Furthermore, by using temperature sensitive microgel particles as depletant it is possible to fine tune depletion interactions to induce crystal melting. Assisting crystallization with an alternating electric field improves the uniformity of the cubic pattern allowing the preparation of macro- scopic (almost defect-free) crystals that show visible Bragg colors.

Stretching and migration of DNA by solvent elasticity in an oscillatory flow

by Wei-Chang Lo

Wei-Chang Lo, H. C. Hong, H. J. Choi, Pik-Yin Lai and C. K. Chan; Physical Review E 84, 021802 (2011).

A model with solution viscoelasticity is proposed to explain the ratchetlike stretching of DNA by a symmetric ac... more A model with solution viscoelasticity is proposed to explain the ratchetlike stretching of DNA by a symmetric ac electric field in polymer solutions. In this model, DNA is stretched by the interaction between the fluid elasticity and the oscillatory flow induced by DNA. Predictions of the model are confirmed by DNA stretching experiments performed in various polymer solutions and the corresponding rheological measurements of the solutions. In particular, experiments have verified that a net migration of stretched DNA in polymer solutions can be induced by a zero-mean asymmetric ac electric field. This last finding cannot be explained by other existing models.

Local ordering of polymer-tethered nanospheres and nanorods and the stabilization of the double gyroid phase

by Christopher Iacovella

Christopher R. Iacovella, Mark A. Horsch, and Sharon C. Glotzer
JOURNAL OF CHEMICAL PHYSICS , 129, 044902, 2008

We present results of Brownian dynamics simulations of tethered nanospheres and tethered nanorods. Immiscibility... more We present results of Brownian dynamics simulations of tethered nanospheres and tethered nanorods. Immiscibility between tether and nanoparticle facilitates microphase separation into the bicontinuous, double gyroid structure (first reported by Iacovella et al. [Phys. Rev. E 75, 040801(R) (2007) ] and Horsch et al. [J. Chem. Phys. 125, 184903 (2006)] , respectively). We demonstrate the ability of these nanoparticles to adopt distinct, minimal energy local packings, in which nanospheres form icosahedral-like clusters and nanorods form splayed hexagonal bundles. These local structures reduce packing frustration within the nodes of the double gyroid. We argue that the ability to locally order into stable structures is key to the formation of the double gyroid phase in these systems.

Phase behavior of ditethered nanospheres

by Christopher Iacovella

Christopher R. Iacovella and Sharon C. Glotzer
SOFT MATTER , 5, pp 4492 - 4498, 2009

We report the results from a computational study of the self-assembly of amphiphilic ditethered nanospheres using... more We report the results from a computational study of the self-assembly of amphiphilic ditethered nanospheres using molecular simulation. We explore the phase behavior as a function of nanosphere diameter, interaction strength, and directionality of the tether–tether interactions. We predict the formation of seven distinct ordered phases. We compare these structures with those observed in linear and star triblock copolymer systems.

Characterizing Structure Through Shape Matching and Applications to Self Assembly

by Christopher Iacovella

Aaron S. Keys, Christopher R. Iacovella, and Sharon C. Glotzer
ANNUAL REVIEW OF CONDENSED MATTER PHYSICS, 2, pp 263-285, 2011

Structural quantities such as order parameters and correlation functions are often employed to gain insight into the... more Structural quantities such as order parameters and correlation functions are often employed to gain insight into the physical behavior and properties of condensed matter systems. Although standard quantities for characterizing structure exist, often they are insufficient for treating problems in the emerging field of nano- and microscale self-assembly, wherein the structures encountered may be complex and unusual. The computer science field of shape matching offers a robust solution to this problem by defining diverse methods for quantifying the similarity between arbitrarily complex shapes. Most order parameters and correlation functions used in condensed matter apply a specific measure of structural similarity within the context of a broader scheme. By substituting shape matching quantities for traditional quantities, we retain the essence of the broader scheme, but extend its applicability to more complex structures. Here we review some standard shape-matching techniques and discuss how they might be used to create highly flexible structural metrics for diverse systems such as self-assembled matter. We provide three proof-of-concept example problems applying shape-matching methods to identifying local and global structures and tracking structural transitions in complex assembled systems. The shape-matching methods reviewed here are applicable to a wide range of condensed matter systems, both simulated and experimental, provided particle positions are known or can be accurately imaged.

Structural Relaxation in Nanometer Thin Layers of Glycerol

by Simone Napolitano

Investigation of structural relaxation and surface modification of ultrathin films of poly (ethylene terephthalate)

by Simone Napolitano

Structural relaxation and dynamic fragility of freely standing polymer films

by Simone Napolitano

The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale

by Simone Napolitano

published on nature Communications 2, 260
visit my website http://web.me.com/simone.napolitano
and send me a mail for a reprint

Monitoring the impact of annealing on the dynamic glass transition of nanometres-thick polymer layers provides new... more Monitoring the impact of annealing on the dynamic glass transition of nanometres-thick polymer layers provides new insights into the mechanisms behind the tremendous changes in the performance of macromolecular materials in close proximity to an interface. Here we present results revealing a correlation between deviations from bulk behaviour, manifesting in changes to the glass transition temperature, the reduction of dielectric strength and the growth of an irreversibly adsorbed layer (Guiselin brushes). The non-universal behaviour of polymers under confinement could be explained in terms of a dimensionless number given by the ratio between the timescale of adsorption and the annealing time. In particular, in the case of slow adsorption kinetics, such as for polystyrene on aluminium, deviations from bulk behaviour correspond to metastable states with an extremely long lifetime.

Dynamics of the Crystal to Plastic Crystal Transition in the Hydrogen Bonded N-Isopropylpropionamide

by Simone Napolitano

Unusual Deviations from Bulk Behavior in Ultrathin Films of Poly (tert-butylstyrene): Can Dead Layers Induce a Reduction of T g?

by Simone Napolitano