Showing papers by "Anand Yethiraj published in 2007"

Tunable colloids: control of colloidal phase transitions with tunable interactions

Abstract: Systems of spherical colloidal particles mimic the thermodynamics of atomic crystals. Control of interparticle interactions in colloids, which has recently begun to be extensively exploited, gives rise to rich phase behaviours as well as crystal structures with nanoscale and micron-scale lattice spacings. This provides model systems in which to study fundamental problems in condensed matter physics, such as the dynamics of crystal nucleation and melting, and the nature of the glass transition, at experimentally accessible lengthscales and timescales. Tunable control of these interactions provides reversible control. This will enable quantitative studies of phase transition kinetics as well as the creation of advanced materials with switchability of function and properties.

NMR determination of smectic ordering of probe molecules.

Abstract: The NMR spectra of the three solutes ortho-, meta-, and para-dichlorobenzene in the nematic and smectic A phases of the liquid crystals 8CB and 8OCB are analyzed to yield two orientational order parameters for each solute. Extrapolation of the asymmetry in the energy parameters that describe the orientational ordering in the nematic phase are used to provide estimates of the strength of the nematic potential in the smectic A phase. The experimentally determined asymmetry of the orientational order parameters in the smectic A phase is then used in conjunction with Kobayashi−McMillan theory applied to solutes to give information about the smectic A layering and the nematic/smectic A coupling. In both smectic A solvents, the solute smectic coupling constant, τ, is negative (with the origin fixed at the center of the smectic layer) for all solutes. The signs and relative values of τ indicate that the ortho and para solutes favor the interlayer region while the meta solute is more evenly distributed throughout...

Recent Experimental Developments at the Nematic to Smectic-A Liquid Crystal Phase Transition

Abstract: Continuous phase transitions are characterized by universality: thermodynamic observables that diverge with power-law exponents whose values are governed by symmetry considerations and are insensitive to other details of the materials [1, 2] The nematic-smectic-A (NA) transition, where an ordered liquid acquires additional one-dimensional periodicity is one of the outstanding unsolved problems in this field of study [3, 4] Here the critical behaviour appears non-universal The order of the transition has been a matter of debate The complexity of the NA transition arises from an intrinsic coupling between two order parameters Indeed, even the direct determination of mean-field parameters has been a matter of recent study Due to this complexity, there are still unresolved issues after more than three decades of research The subtleties involved have been addressed theoretically via different approximations, leading to a rich addition to the phase transitions literature Experimentally, these subtleties have inspired precise high-resolution experiments This article focuses on experimental developments in the last decade that address aspects of the nature of the NA transition