A coloured ferroelectric side chain polymer

Abstract

Coloured ferroelectric liquid-crystalline side chain copolymers containing 5 per cent and 15 per cent of an azo dye were synthesized and characterized by DSC, GPC and optical microscopy. Order parameters, S, of the azo compound exceeding 0.8 were measured in the frozen smectic phase for the 5 per cent copolymer. The copolymers exhibit fast electrooptic switching in the range of a few hundred microseconds to milliseconds in the S$ phase. Both linear (i.e. electroclinic-like) and ferroelectric switching have been observed. Tilt angles of -19" and spontaneous polarization of -300nCcm-' have been recorded in the S$ phase. IntroductionResearch in ferroelectric liquid crystals has been intense over the past few years. One important advantage of ferroelectric displays compared with the well-known and widely used twisted nematic or supertwist nematic displays is the fast electrooptic switching which is in the range of microseconds. Recently the first examples of switchable ferroelectric liquid crystal side chain polymers have been reported [ 1-41. In favourable cases [3,4] we found response times in the range of some hundred microseconds. Because of the relatively poor anti-shock characteristics of surface stabilized low molar mass ferroelectric display devices fast switching ferroelectric liquid crystal polymers, which form robust films, may find future applications using various birefringent or absorption based electrooptic effects.Coloured liquid crystal displays applying the guest host effect of dichroic dyes dissolved in a nematic liquid crystal were developed some years ago [S]. Recently the guest host effect of dichroic dyes in a ferroelectric liquid crystal [6] and, for the first time, in ferroelectric liquid crystal polymers has been investigated [7]. One drawback to this effect is the poor solubility of dyes in both low molar mass and polymeric liquid crystal materials. By copolymerization of dye monomers a higher percentage of dye content has been achieved in nematic polymers [S]. Ferroelectric liquid crystal dye copolymers, hitherto unknown, might be expected to have both fast switching properties, associated with the ferroelectric phase, and high colour contrast in thin films, because of the higher order parameter and solubility of suitable dyes in the smectic S z layers.

Helical unwinding in polymer‐dispersed ferroelectric liquid crystals

“…2(b)), indicating that the azimuthal angle q reaches a maximum value which is equal to 28 for the case of complete helical unwinding. In addition to monomer systems, similar c p = -g -€ -c p = o -c p = + 9 (4 results have recently been obtained by G. Scherowsky et al [16] for the electro-optical behaviour of some ferroelectric liquid crystal polymers.…”

“…O n the other hand, smectic phases are known to be suitable for very fast switching devices, due to ferroelectric properties which occur in the presence of chiral molecules 16,71. In addition to the order of molecular orientation occurring in the nematic and cholesteric phase, the smectic phases exhibit a layer structure.…”

Ferroelectric liquid crystalline polyoxetanes bearing chiral dimesogenic pendants

“…We found that some of them formed incommensurate and twisted grain boundary (TGB) phases. 10,13,15,16 On the other hand, many side-chain liquid crystalline polymers (SCLCPs) based on poly(meth)acrylate, [18][19][20][21] polyoxetane, [22][23][24][25][26][27][28] and polysiloxane [29][30][31][32][33][34][35][36][37][38][39] backbones, with and without chiral centers, have been reported. In particular, some of the SCLCPs bearing chiral centers exhibit the chiral smectic C (Sc*) phase and, thus, ferroelectric properties.…”

“…In particular, some of the SCLCPs bearing chiral centers exhibit the chiral smectic C (Sc*) phase and, thus, ferroelectric properties. 21,26,28,29,31,32 Those derived from polysiloxanes appear to show high spontaneous polarization values and fast response times. One of the examples 31 was reported to reveal spontaneous polarization as high as 420 nC cm 22 .…”

Fast‐switching ferrolectric liquid crystalline polymers containing one or two centres of chirality in the side chain

“…The 5% dye containing copolymer has the same phase transition temperatures as the homopolymer: however, there is a significantly faster switching time, between 7 ms at 80°C and 400 ps at 120°C. The 15% dye containing copolymer switches even faster (2 ms at 80°C and less than 100 ps at 140°C) [35].…”