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Title: High-Resolution X-ray Scattering Study of the Effect of Quenched Random Disorder on the Nematic-Smectic-A Transition

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930537
Report Number(s):
BNL-80591-2008-JA
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review E: Stat. Phys., Plasmas, Fluids; Journal Volume: 75
Country of Publication:
United States
Language:
English
Subject:
national synchrotron light source

Citation Formats

Ramazanoglu,M., Larochelle, S., Garland, C., and Birgeneau, R. High-Resolution X-ray Scattering Study of the Effect of Quenched Random Disorder on the Nematic-Smectic-A Transition. United States: N. p., 2007. Web. doi:10.1103/PhysRevE.75.061705.
Ramazanoglu,M., Larochelle, S., Garland, C., & Birgeneau, R. High-Resolution X-ray Scattering Study of the Effect of Quenched Random Disorder on the Nematic-Smectic-A Transition. United States. doi:10.1103/PhysRevE.75.061705.
Ramazanoglu,M., Larochelle, S., Garland, C., and Birgeneau, R. Mon . "High-Resolution X-ray Scattering Study of the Effect of Quenched Random Disorder on the Nematic-Smectic-A Transition". United States. doi:10.1103/PhysRevE.75.061705.
@article{osti_930537,
title = {High-Resolution X-ray Scattering Study of the Effect of Quenched Random Disorder on the Nematic-Smectic-A Transition},
author = {Ramazanoglu,M. and Larochelle, S. and Garland, C. and Birgeneau, R.},
abstractNote = {},
doi = {10.1103/PhysRevE.75.061705},
journal = {Physical Review E: Stat. Phys., Plasmas, Fluids},
number = ,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Using high-resolution x-ray scattering, the effect of quenched random disorder (QRD) on the second-order nematic-smectic-A (N-SmA) phase transition in butyloxybenzilidene-octylaniline (4O.8) has been studied. 4O.8 is a nonpolar liquid crystal (LC) with a monomeric smectic-A phase. The QRD is created by aerosil nanoparticles which gelate to form a three-dimensional network, confining the LC. The QRD caused by the aerosil gel generates quenched random fields acting on both the nematic and smectic-A order parameters. This results in the destruction of the quasi-long-range order of the smectic-A phase. The x-ray scattering data are modeled with a structure factor composed of two terms,more » one thermal and one static, corresponding to the connected and disconnected susceptibilities, respectively. Unlike previous studies, the two parts of the structure factor are decoupled by allowing different thermal and static correlation lengths. Our fitting procedure involves temperature-dependent and temperature-independent (global) variables. The amplitude and the parallel correlation length for the thermal part of the line-shape show critical-like behavior both above and below the transition temperature. Detailed analysis reveals that the thermal correlation length does not truly diverge at the phase transition. This effect is discussed on the basis of a cutoff for the divergence caused by the random fields generated by the aerosil network confining the liquid crystal. The intensity of the static term in the line-shape behaves like the order parameter squared at a conventional second-order phase transition. The effective order parameter critical exponent shows an evolution with increasing aerosil gel density ranging from the Gaussian tricritical value to the 3D-XY value. The results of a pseudocritical scaling analysis are compared to an analysis of 4O.8+aerosil heat capacity data and discussed using a phenomenological correlation between the nematic range of pure liquid crystals and the aerosil mass density, {rho}{sub s}.« less
  • We have studied the effects of quenched random disorder created by dispersed aerosil nanoparticle gels on the nematic to smectic- A (N- SmA ) and smectic- A to reentrant nematic ( SmA -RN) phase transitions of thermotropic liquid-crystal mixtures of hexyloxycyanobiphenyl (6OCB) and octyloxycyanobiphenyl (8OCB). These effects are probed using high-resolution synchrotron x-ray diffraction techniques. We find that the reentrant characteristics of the system are largely unchanged by the presence of the aerosil gel network. By comparing measurements of the smectic static structure amplitude for this 8OCB- 6OCB+aerosil system with those for butyloxybenzilidene-octylaniline (4O.8)+aerosil gels, we find that the short-rangemore » smectic order in the smectic- A phase is significantly weaker in the reentrant system. This result is consistent with the behavior seen in pure 8OCB-6OCB mixtures. The strength of the smectic ordering decreases progressively as the 6OCB concentration is increased. Detailed line shape analysis shows that the high- and low-temperature nematic phases (N and RN) are similar to each other.« less
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