Liquid crystals Network

Liquid crystalline polymers may be crosslinked to each other to form a network that retains the liquid crystal feature. The liquid crystal networks deform when a stress is applied as rubber does. They exhibit rubber elasticity. 

Now we return to liquid crystal networks. In addition to the above three postulates, we further assume (4) The total free energy of the network is comprised of elastic, nematic and external stress contributions, i.e.,... 

Apply the concept of liquid crystal networks crosslink the backbone of NLO side chain liquid crystalline polymers when they are in the liquid crystal phase. In the presence of a mechanical force the resultant sample may be well aligned because of the interaction between the network strands and the side groups. The mechanical effect is equivalent to the electric or magnetic field. The re-orientation response of the liquid crystal is a quadratic function of the applied electric field, but it is linearly proportional to the mechanical stress. Thus, the mechanical stress is more effective in aligning the liquid crystals and is expected to produce less defects and hence to promote the transparency of the sample. 

Hirschmann et al. (1991) synthesized a smectic liquid crystal network whose side chains contain NLO active groups. After the poling with the... 

In order to soften the network while preserving the memory of the template, the use of liquid-crystal networks should be a useful tool. In such systems, the... 

Mol GN, Harris KD, Bastiaansen CM, Broer DJ. 2005. Thermo mechanical responses of liquid crystal networks with a splayed molecular organization. Adv Funct Mater 15 1155 1159. 

C.L. Oosten, C.W.M. Bastiaansen, D.J. Broer, Printed artificial cilia from liquid-crystal network actuators modularly driven by light. Nature Mater. 8, 677-682 (2009)... 

The basic chemistry of liquid crystal elastomers is very similar to the chemistry of linear liquid crystal polymers. One can distinguish between main- and side-chain elastomers where the mesogenic units are either segments or side groups of the monomer imits of the macromolecular chain. The elastomers only differ from linear liquid crystal polymers by conventional crosslinking reactions. New aspects for chemistry appear when liquid crystal networks are required that spontaneously, and without any external fields, exhibit a macroscopically uniform orientation of the director. For these conditions, networks have to be sythesized where the chain conformation is consistent a priori with the uniform liquid crystal order [5]. 

The coupling between the properties of conventional polymer networks and the properties of chiral liquid crystalline phases results in interesting, new opto- and electromechanical effects of the chiral liquid crystalline elastomers, as demonstrated by theoretical considerations and experiments. Knowledge about these new materials is still in its infancy. But the properties analyzed so far for these elastomers indicate promising aspects for application and are the basis for the new syntheses of optimized chiral liquid crystal networks. 

The stiffest liquid crystal networks falling in this category are those created by crosslinking PBLG [279-281]. Here, the 3/1 helical rods of PBLG are stabilized by hydrogen bonds between every third peptide residue in the direction of the rod s axis, and crosslinking of the rods is effected by partial... 

A second interesting point is the fact that some of the thiophene-containing polydiacetylenes were shown to behave as lyotropic liquid crystals in concentrated solutions [627]. This observation may open the door to the creation of liquid crystal networks from such polymers by varying the level of interchain crosslinks. Such crosslinking can be effected either by heating the polymers neat or in solution, or by reacting them with reactive species such as primary diamines. On the other hand, exposure to heat of liquid crystal networks... 

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