Filamentous Viruses


Viruses with Variable Flexibility and Chirality

We have demonstrated that a single point mutation in the major coat protein of fd virus changes its bending rigidity by fourfold and inverts the chirality of the system. Unlike fd wt, the mutant fd is essentially a rigidity rod and allows us for the first to test the Onsager theory of the isotropic-nematic phase transition for rigid rods. These results are described by Barry et al. Soft Matter  5 (2009),  2563-2570.

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Fluctuations of wild type and mutant fd virus

Self-assembly of Nonamphiphilic Colloidal Membranes

We have demonstrated that a simple suspension of hard rods in the presence of attractive interactions assembles into 2D membranes. The continuum fluctuations of these membranes are equivalent to those of lipid bilayers. However, unlike heterogeneous amphiphiles which assembly into lipid bilayers, the building blocks of colloidal membranes are homogenous hard rods. The mechanism that leads to formation of colloidal membranes and the analysis of their fluctuations at continuum and molecules fluctuations have been described in a publication recently submitted to PNAS.

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Fluctuations of colloidal membranes

Surface Freezing

In most materials the melting of bulk material is preempted by surface melting. There are very few materials that exhibit the reverse behavior where the surface freezes before its bulk. We demonstrate that in fd virus suspension the 2D smectic phase forms on the surface of the isotropic-nematic interface. This surface layer plays an important role in the kinetics of the isotropic-smectic phase transition. These results are described by Dogic, PRL  91 (2003),  165701.

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2D smectic located at isotropic-nematic interface

Melting of Lamellar Phase

A drawback of most colloidal systems is that they are athermal, thus making it difficult to study kinetics of various samples. We prepare a mixture of rods and thermosensitive polymer NIPA, whereby changing the temperature allows us to tune the strength of attractive interactions. This allows us to study the kinetics of how lamellar phase melts into nematic liquid crystals.  These results are described by Alsayed et. al., PRL 93 (2004), 057801.

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Melting of lamellar phase into nematic droplet

Twist Penetration in Single-layer Smectics

In the 1970's, deGennes discussed the fundamental geometry of smectic liquid crystals and established an analogy between the smectic A phase and superconductors. It follows that smectic layers expel twist deformations in the same way that superconductors expel magnetic field. We make a direct observation of the penetration of twist at the edge of a single isolated smectic A layer. These results are described by Barry et. al. J. Phys. Chem. B  113 (2009),  3910-3913.

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PolScope image of a smectic membrane

Single Molecule Diffusion in Liquid Crystals

We directly visualize the anisotropic diffusion of fluorescently labeled tracer particles in the nematic liquid crystals. When compared to isotropic phase, the diffusion along the director is enhanced in the nematic. These results are described by Lettinga et al. EPL  71 (2005),  692-696.

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Anisotropic diffusion in nematics