https://doi.org/10.1140/epje/i2006-10022-4
Regular Article
Distortion and unwinding of the helical structure in polymer-stabilized short-pitch ferroelectric liquid crystal
1
Laboratoire de Thermophysique de la Matière Condensée, Equipe de l'UMR-CNRS 8024, Université du Littoral Côte d'Opale, 145, Avenue Maurice Schumann, 59140, Dunkerque, France
2
Laboratoire de Dynamique et Structure des Matériaux Moléculaires, UMR-CNRS 8024, Université des Sciences et Technologies de Lille, Bâtiment P5, 59655, Villeneuve d'Ascq Cedex, France
* e-mail: daoudi@univ-littoral.fr
Received:
13
February
2006
Accepted:
7
July
2006
Published online:
25
July
2006
We report the effect of an anisotropic polymer network formed from an achiral photoreactive monomer in a short-pitch chiral SmC* phase on the distortion and the unwinding of the helical structure of the ferroelectric phase. The electro-optical behaviour and ferroelectric properties were experimentally determined for films containing various polymer concentrations. The critical field, Eu, for the transition from the distorted structure to the homogeneous state was measured as a function of polymer concentration. A linear increase of Eu versus polymer concentration was observed, showing that the helical structure of the short-pitch SmC* phase was stabilized by the polymer network. This behaviour was expected to be a consequence of the increase of the apparent elastic constants of the ferroelectric liquid crystal stabilized by the anisotropic polymer network films. The polymer network morphology was investigated using atomic-force microscopy, revealing a twisted structure of the polymer fibers. This twisted structure was transferred onto a polymer network during the polymerization process within a short-pitch SmC* phase. The increase of the apparent elasticity can then be interpreted by a strong interaction between polymer network and the liquid-crystal molecules. From our experimental data, the coupling coefficient, Wp, characterizing this interaction was evaluated for all studied polymer concentrations.
PACS: 61.30.-v Liquid crystals – / 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions – / 61.41.+e Polymers, elastomers, and plastics – / 77.80.-e Ferroelectricity and antiferroelectricity-1 –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2006