Showing papers by "John Bechhoefer published in 1997"
TL;DR: In this paper, the in-plane diffusion constant increases in agreement with a hydrodynamic theory outlined here for free-standing smectic films as thin as two layers and for films four or more layers.
Abstract: Using laser-induced photobleaching of a fluorescent tracer molecule, we study diffusion in free-standing smectic films as thin as two layers. For films four or more layers thick, the in-plane diffusion constant increases in agreement with a hydrodynamic theory outlined here. Two- and three-layer films show different behavior.
21 citations
TL;DR: In this article, growth morphologies during solidification of a liquid crystal (10 OCB) were studied and sharp transitions analogous to equilibrium phase transitions were seen between the growth modes.
Abstract: We have studied growth morphologies during solidification of a liquid crystal (10 OCB). As the undercooling is varied, sharp transitions analogous to equilibrium phase transitions are seen between the growth modes. We identify three types of morphology transitions: strongly first order, where the growth velocity is discontinuous at the transition; weakly first order, where the velocity curve, but not its derivative, is continuous and the morphology changes discontinuously; and second order, with continuous changes in the growth properties and pretransitional effects.
16 citations
TL;DR: In this article, the authors investigated the smectic-to-crystal phase transition of the liquid crystal 1O OCB and observed six different solidification modes, each characterized by a distinct micro-and meso-structure.
Abstract: We have investigated the smectic-to-crystal phase transition of the liquid crystal 1O OCB The smectic plays the role of a viscous liquid, and the system shares essential characteristics with the freezing of polymers, viscous liquids, and liquid metals The 10 OCB material has the advantage of convenient time scales: “rapid”-solidification effects occur at freezing velocities of 10–100 μm/s, versus 10 μm/h for polymers and 1 m/s for metals We observe six different solidification modes, each characterized by a distinct micro- and meso-structure In addition, each mode is correlated with a separate branch of the front-velocity versus undercooling curve This curve has a discontinuity in the slope at mode transitions In one case, the velocity curve itself is discontinuous A suggested morphology-selection hypothesis — “the fastest mode wins” — is explicitly ruled out
12 citations
TL;DR: In this article, the nematic-smectic-A (NA) phase transition in liquid crystals has been studied using an extremely sensitive optical method, and it has been shown that the NA transition in the liquid crystal 8CB is clearly first order.
Abstract: We present a new, extremely sensitive optical method to study the nematic-smectic-A (NA) phase transition in liquid crystals. In this new technique, we monitor nematic director fluctuations as a function of temperature as we approach the NA transition. We show that the NA transition in the liquid crystal 8CB (which has a small nematic range) is clearly first order, well within the resolution of the experiment. This is contrary to previous calorimetric measurements but confirms an earlier dynamical measurement. We characterize the strength of the phase transition by a dimensionless, technique-independent quantity t 0 = (T NA - T*)/T NA. For 8CB, we measure t 0 = (6 ± 2) × 10−6.
6 citations