Cone motion viscosity and optical second harmonic generation of ferroelectric liquid crystalline dendrimers

Citation
J. Ortegren et al., Cone motion viscosity and optical second harmonic generation of ferroelectric liquid crystalline dendrimers, LIQ CRYST, 28(6), 2001, pp. 861-868
Citations number
38
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
LIQUID CRYSTALS
ISSN journal
0267-8292 → ACNP
Volume
28
Issue
6
Year of publication
2001
Pages
861 - 868
Database
ISI
SICI code
0267-8292(200106)28:6<861:CMVAOS>2.0.ZU;2-U
Abstract
We report second harmonic generation in a ferroelectric liquid crystalline trimer and ferroelectric liquid crystalline dendrimers of first, second and third generation. Thin cells were filled with the compounds by capillary f orces at elevated temperature, and cooled from the surface stabilized ferro electric state to below the glass transition temperature, while kept in an electric field. The cone motion viscosity and the threshold electric field for unwinding of the helix axis of the chiral tilted smectic mesophases wer e studied separately at elevated temperature, and these data were used to o ptimize the preparation of the films. The measured response time was betwee n 0.3 and 3 ms, which corresponds to a cone motion viscosity between 0.5 an d 50 Pa s. Second harmonic generation was studied both at elevated temperat ure with an electric field and at room temperature with and without electri c field. The first generation dendrimer exhibited a strong increase in the second order non-linear optical response with time at room temperature. The d(23)-coefficient of this dendrimer was approximately four times larger th an for the other macromolecules and was 0.045 pm V-1. The relatively large d-coefficient of the first generation dendrimer is ascribed to crystallizat ion, which improved the orientation of the molecular dipoles.