Soft Matter

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.

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.

Design of Surfaces for Liquid Crystal-Based Bioanalytical Assays

by Aaron M. Lowe

published in ACS Applied Materials & Interfaces (Lead Author)

Surface-induced ordering of liquid crystals (LCs) offers the basis of a label-free analytical technique for the... more Surface-induced ordering of liquid crystals (LCs) offers the basis of a label-free analytical technique for the detection of surface-bound biomolecules.  The orientation-dependent energy of interaction of a LC with a surface (anchoring energy of LC), in particular, is both sensitive to the presence of surface-bound molecules and easily quantified.  Herein we report a study that analyzes a simple model of twisted nematic LC systems and thereby identifies surfaces with LC anchoring energies in the range of 0.5 μJ/m^2 to 2.0 μJ/m^2 to be optimal for use with LC-based analytical methods.  Guided by these predictions, we demonstrate that analytic surfaces possessing anchoring energies within this range can be fabricated with a high level of precision (< 0.1 μJ/m^2) through formation of monolayers of organothiols (with -functional groups corresponding to oligoethyleneglycols and amines) on gold films deposited by physical vapor deposition at oblique angles of incidence.  Finally, by using the human epidermal growth factor receptor (EGFR) as a model protein analyte, we have characterized the influence of the anchoring energies of the surfaces on the response of the LC to the presence of surface-bound EGFR.  These results, when combined with 32P-radiolabeling of the EGFR to independently quantify the surface concentration of EGFR, permit identification of surfaces that allow use of LCs to report surface densities of EGFR of 70-90 pg/mm^2.  Overall, the results reported in this paper guide the design of surfaces for use in LC-based analytical systems.

Quantitative Methods Based on Twisted Nematic Liquid Crystals for Mapping Surfaces Patterned with Bio/Chemical Functionality Relevant to Bioanalytical Assays

by Aaron M. Lowe

Accelerated Article Featured on the Cover of Analytical Chemistry (Lead Author)

We report methods for the acquisition and analysis of optical images formed by thin films of twisted nematic liquid... more We report methods for the acquisition and analysis of optical images formed by thin films of twisted nematic liquid crystals (LCs) placed into contact with surfaces patterned with bio/chemical functionality relevant to surface-based assays. The methods are simple to implement and are shown to provide easily interpreted maps of chemical transformations on surfaces that are widely exploited in the preparation of analytic devices. The methods involve acquisition of multiple images of the LC as a function of the orientation of a polarizer; data analysis condenses the information present in the stack of images into a spatial map of the twist angle of the LC on the analytic surface. The potential utility of the methods is illustrated by mapping (i) the displacement of a monolayer formed from one alkanethiol on a gold film by a second thiol in solution, (ii) coadsorption of mixtures of amine-terminated and ethylene glycol-terminated alkanethiols on gold films, which leads to a type of mixed monolayer that is widely exploited for immobilization of proteins on analytic surfaces, and (iii) patterns of antibodies printed onto surfaces. These results show that maps of the twist angle of the LC constructed from families of optical images can be used to reveal surface features that are not apparent in a single image of the LC film. Furthermore, the twist angles of the LC can be used to quantify the energy of interaction of the LC with the surface with a spatial resolution of <10 μm. When combined, the results described in this paper suggest nondestructive methods to monitor and validate chemical transformations on surfaces of the type that are routinely employed in the preparation of surface-based analytic technologies.

Engineering of PDMS surfaces for use in microsystems for capture and isolation of complex and biomedically important proteins: Epidermal growth factor receptor as a model system

by Aaron M. Lowe

published in Lab on a Chip (Lead Author)

Elastomers based on poly(dimethylsiloxane) (PDMS) are promising materials for fabrication of a wide range of... more Elastomers based on poly(dimethylsiloxane) (PDMS) are promising materials for fabrication of a wide range of microanalytical systems due to their mechanical and optical properties and ease of processing. To date, however, quantitative studies that demonstrate reliable and reproducible methods for attachment of binding groups that capture complex receptor proteins of relevance to biomedical applications of PDMS microsystems have not been reported. Herein we describe methods that lead to the reproducible capture of a transmembrane protein, the human epidermal growth factor (EGF) receptor, onto PDMS surfaces presenting covalently immobilized antibodies for EGF receptor, and subsequent isolation of the captured receptor by mechanical transfer of the receptor onto a chemically functionalized surface of a gold film for detection. This result is particularly significant because the physical properties of transmembrane proteins make this class of proteins a difficult one to analyze. We benchmark the performance of antibodies to the human EGF receptor covalently immobilized on PDMS against the performance of the same antibodies physisorbed to conventional surfaces utilized in ELISA assays through the use of EGF receptor that was 32P-radiolabeled in its autophosphorylation domain. These results reveal that two pan-reactive antibodies for the EGF receptor (clones H11 and 111.6) and one phosphospecific EGF receptor antibody (clone pY1068) capture the receptor on both PDMS and ELISA plates. When using H11 antibody to capture EGF receptor and subsequent treatment with a stripping buffer (NaOH and sodium dodecylsulfate) to isolate the receptor, the signal-to-background obtained using the PDMS surface was 82 : 1, exceeding the signal-to-background measured on the ELISA plate (<48 : 1). We also characterized the isolation of captured EGF receptor by mechanical contact of the PDMS surface with a chemically functionalized gold film. The efficiency of mechanical transfer of the transmembrane protein from the PDMS surface was found to be 75–81%. However, the transfer of non-specifically bound protein was substantially less than 75%, thus leading to the important finding that mechanical transfer of the EGF receptor leads to an approximately four-fold increase in signal-to-background from 20 : 1 to 88 : 1. The signal-to-background obtained following mechanical transfer is also better than that obtained using ELISA plates and stripping buffer (<48 : 1). The EGF receptor is a clinically important protein and the target of numerous anticancer agents and thus these results, when combined, provide guidance for the design of PDMS-based microanalytical systems for the capture and isolation of complex and clinically important transmembrane proteins.

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.

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

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
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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.

Exploiting interfacial polarization to detect phase transitions in dilute solution: Crystallization and melting of P3HT in toluene down to ppm contents

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

Enhanced Mechanical Relaxation below the Glass Transition Temperature in Partially Supramolecular Networks

by Simone Napolitano

Distribution of Segmental Mobility in Ultrathin Polymer Films

by Simone Napolitano

Is the reduction in tracer diffusivity under nanoscopic confinement related to a frustrated segmental mobility?

by Simone Napolitano

Dynamics in ultrathin liquid films studied by simultaneous dielectric spectroscopy (DRS) and organic molecular beam deposition (OMBD)

by Simone Napolitano

Possible origin of thickness‐dependent deviations from bulk properties of thin polymer films

by Simone Napolitano

Deviation from bulk behaviour in the cold crystallization kinetics of ultrathin films of poly (3-hydroxybutyrate)

by Simone Napolitano

Molecular dynamics of atactic poly (propylene) investigated by broadband dielectric spectroscopy

by Simone Napolitano

Monitoring the cold crystallization of poly (3-hydroxy butyrate) via dielectric spectroscopy

by Simone Napolitano