Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 102, Issue 40, Pages 14191-14196Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0500664102
Keywords
liquid crystal; chirality; screw dislocation; helix
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Funding
- NHLBI NIH HHS [R01 HL051177-16, R01 HL051177-14, R01 HL051177] Funding Source: Medline
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Study of a diverse set of chiral smectic materials, each of which has twist grain boundary (TGB) phases over a broad temperature range and exhibits grid patterns in the Geandjean textures of the TGB helix, shows that these features arise from a common structure: giant smectic blocks of planar layers of thickness I-b > 200 nm terminated by GBs that are sharp, mediating large angular jumps in layer orientation between blocks (60 degrees < Delta < 90 degrees), and lubricating the thermal contraction of the smectic layers within the blocks. This phenomenology is well described by basic theoretical models applicable in the limit that the ratio of molecular tilt penetration length-to-layer coherence length is large, and featuring GBs in which smectic ordering is weak, approaching thin, melted (nematic-like) walls. In this limit the energy cost of change of the block size is small, leading to a wide variation of block dimension, depending on preparation conditions. The models also account for the temperature dependence of the TGB helix pitch.
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