Relaxation of PLC networks

Several classes of crosslinked PLCs have been prepared  

Oriented PLC thermosets based on epoxy chemistry and with the mesogens in the backbone chain have been prepared by aligning an oligoether prepolymer either mechanically or in a magnetic field (13.5 T) prior to and during curing [135]. The temperature associated with a drop in order parameter increased with increasing crosslink density. Samples with few crosslinks showed a drop in order parameter at 130 C 

Polydiepoxide networks have lately received some attention owing to their superior thermal stability and adhesive properties compared to the polydiacrylates [136,137]. The polymers, prepared by photocrosslinking of surface-aligned monomer films, showed very high virgin order parameters (s 0.8) and it was concluded on the basis of refractive index measurements that the order parameter remained constant up to 140°C [136]. Jahromi et al [137] reported that postcuring of the PLC network further increased the thermal stability. 

Anisotropic PLC gels are blends of a PLC network and a miscible MLC, and the first reports appeared in the early 1990s [138-140]. Systems of this kind are also referred to as liquid crystal-liquid crystalline network composite systems. 

It is possible to align the MLC differently to the PLC network in an electric field which will cause the system to scatter light. When the electric field is switched off, the alignment of the MLC will adapt to the alignment of the PLC component. The size of the electric field strength required to realign the MLC component increases with increasing PLC content [138,140]. 

---