Applications of Liquid Crystal - Block Copolymers

It is our belief that block copolymers containing LC segments are materials with novel and unencountered properties which will offer great opportunities for developing high performance materials. Here we would like to give two examples. One example is a microphase stabilized ferroelectric liquid crystal (MSFLC) [109] for potential flat panel display applications, while the other is a material for stable, low surface energy [110] application. 

4 Block Copolymers Containing Liquid Crystalline Segments 

---

The phase behaviour of rod-coil block copolymers is already known to be much richer than that of coil-coU block copolymers, because the rod block can orient into liquid crystal structures [1]. The rod block may be analogous to a biomacromolecule, for example /7o/y(benzyl glutamates) [44,45] and po/y(peptides) [46] forming heUcal rodlike blocks have been incorporated in block copolymers. Possible applications of these materials arising from their biocompatibility are evident. 

The main state-of-the-art of presented work is based on development of new strategy of preparation of thermo-responsive materials in which, amphiphilic block copolymers are used as both a nanostructured agent for epoxy network and as a dispersing agent for low molecular liquid crystals. These novel materials can find application in the field of liquid crystals which possess nematic-isotropic transition and allow the designing of materials which can switch from the opaque... 

At the time of this writing, the most immediate application for the surfaces discussed in this section is to provide models for viscous isotropic phase liquid crystals and certain phase-segregated polymer blends and block copolymers. In this subsection, we show how to calculate diffraction peak intensities from a class of model structures based on these surfaces. The method applies to scattering-density profiles (electron densities for x-ray scattering) determined by ... 

Ferroelectric liquid crystals (FLC) are of great interest due to their fast electro-optical response which is about 1,000 times faster than conventional twisted nematic cells [131]. The geometry used is called a surface stabilized FLC cell which utilizes a very thin gap (=2 pm) to unwind the FLC supramolecular pitch (=1-2 pm) since the bulk FLC materials do not show macroscopic polarization. This very thin gap, however, leads to difficulties in manufacturing large panels and very poor shock resistance. Researchers have proposed the concept of microphase stabilized FLC [79,109, 130] using FLC-coil diblock copolymers for electro-optical applications as shown in Fig. 15. This concept takes advantage of ferroelectric liquid crystallinity and block copolymer microphase separation since the block... 

Various liquid-crystal structures have been observed in many amphiphilic systems, such as block copolymers in selective solvents [1, 2], membrane hpids [3], and surfactants in aqueous solution [4]. These structures have found widespread application in the preparation of mesoporous templates [5], the colloidal structure design of nanomaterials, including semiconducting assemblies [6], and the formation of micro structured polymeric gels [7] and vesicles for drug delivery [8],... 

One type of gel which has been extensively investigated in relation to pharmaceutical applications is that formed by certain PEO-PPO-PEO block copolymers (153). These systems are particularly interesting since even a concentrated polymer solution is quite low-viscous in nature at low temperature, whereas a very abrupt gelation (liquid crystal formation (25, 187, 188)) occurs on increasing the temperature. The precise value of the transition temperature depends on the polymer molecular weight, composition and concentration, the concentration and nature of the drug, etc., but by... 

Because of the various technological applications of polymer thin films, ranging from multicolor photographic printing to flat panel and liquid crystal displays, it is important to understand thin film and polymer surface characteristics in order to improve performance or to develop entirely new applications or processing methodologies. Polymer and block copolymer thin films and surfaces thus enjoy continued research interest from both a technological and fimdamental perspective. 

In certain high molecular weight materials (e.g. deformed elastomers, amorphous regions in semicrystalline polymers, and phase-separated block copolymers) some characteristics of the mesomorphic state are observed, namely local orientational order in the absence of translational order. In some instances researchers have tried to describe the deviation from isotropy observed on a local scale in these materials with the vocabulary used for liquid crystals. Indiscriminate applications... 

---