Main-chain Chiral Smectic Polymers Showing a Large Electroclinic Effect in the SmA* Phase

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Chemistry of Materials

DOI:https://doi.org/10.1021/cm0606373· OSTI ID:930254

Walba, D; Yang, H; Shoemaker, R; Keller, P; Shao, r; Coleman, D; Jones, C; Nakata, M; Clark, N

The synthesis and characterization of a main-chain smectic liquid-crystalline polymer system designed for development into electromechanical actuators is described. The chemical structure is chosen to provide a large electroclinic effect in the SmA* phase, with large concomitant layer shrinkage (a rare combination). The polymers are prepared by acyclic diene metathesis polymerization (ADMET) of liquid-crystalline ,-dienes. Oligomers with a degree of polymerization of {approx}10-30 are obtained using Grubbs first-generation catalyst, while oligomers with a degree of polymerization of {approx}200 are obtained using Grubbs second-generation catalyst. All polymer samples show the following phase sequence: I - SmA* - SmC* - Glass. X-ray analysis of polymer powder samples demonstrates the desired layer shrinkage at the SmA* - SmC* transition. The polymers form well-aligned fibers by pulling from the isotropic melt, and X-ray analysis of fibers in the SmA* phase shows that in the bulk of the fiber the layers are oriented perpendicular to the fiber axis, while at the surfaces there appears to be a thin sheath where the layers are parallel to the fiber/air interface. The desired layer shrinkage with tilt at the SmA* - SmC* transition in these fibers is seen as well, and in the SmC* phase the fibers exhibit an interesting conical chevron layer structure. Electro-optic investigation of aligned thin films of the polymer, prepared from quenched fiber glasses using a novel technique, exhibit a large electroclinic effect, with substantial degradation of alignment quality upon field-induced tilt. This degradation in alignment quality, coupled with the layer shrinkage at the SmA* - SmC* transition demonstrated by X-ray scattering, strongly suggests the desired layer shrinkage with electroclinic tilt is in fact occurring in the polymer films.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 930254
• Report Number(s): BNL--80946-2008-JA
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Vol. 18; ISSN CMATEX; ISSN 0897-4756
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTUATORS
ELECTRO-OPTICAL EFFECTS
FIBERS
LIQUID CRYSTALS
ORIENTATION
PHASE TRANSFORMATIONS
POLYMERS
SHRINKAGE
SYNTHESIS
THIN FILMS
national synchrotron light source