Guest-Host Materials

IV Behavior and Properties of Side Group Thermotropic Liquid Crystal Polymers 

The polar alignment that was induced in this system was shown to be stable for long periods of time. However, several complexities in the poling process were uncovered in this study. It was found that the induced SHG dropped precipitously as Tg was approached from below. This was speculated as being due to the establishment of a mono- 

In addition to this SCLCP host, MCLCPs have also been used. Li et al. [ 168] dissolved molecules of an oligomeric fragment of po-ly(p-phenylenebenzobisthiazole) 10, which was terminated by opposing nitro and di-methylamino groups, in the polymer itself. The resultant material has a value of 6x10 esu. Stupp et al. [169, 170] carried out a careful analysis of the system of Disperse Red 1 (11) dissolved in a chemically aperiodic nematic polymer containing the following three structural units (12). 

The trade-off between concentration and P limits the applicability of guest-host materials for useful devices. The higher P molecules tend to be larger and less soluble in the hosts. Exceptionally high concentrations of up to 20 mol% of 4-hydroxy-4 -ni-trostilbene (13) have been achieved in the polymer 14 without destroying the LC for- 

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Fig. 6. Measurement of photostability of two polymeric electro-optic materials as carried out by researchers at IPITEK (TACAN) Corporation. The data represented by the solid line correspond to the LRD-3 DEC material of Dalton and co-workers [138] while the data represented by open circles correspond to a diaminonitrostilbene chromophore/poly(methyl methacrylate) guest/host material produced by IBM Almaden Laboratories. The dramatic improvement observed for the DEC material can be associated with increased lattice hardness from the chromophore coupling to adjacent polymer chains...

Kaino and co-workers [255] have investigated the effect of polymer polydis-persity on electro-optic materials properties. No dependence on polydispersity was observed for guest host materials but for Disperse Red chromophores covalently attached to monodisperse polystyrene weaker absorption tails were observed. This result suggests that chromophore-chromophore interactions are modified by the polymer host. 

The advent of the apparently superior White and Taylor device retarded the development of better guest-host materials and mixtures for this device type. 

Electro-optic activity in guest-host materials can be quantified in terms of the electro-optic coefficient, which can be expressed as... 

Barto, R.R., Jr., P.V. Bedworth, C.W. Frank, S. Ermer, and R.E. Taylor. 2005. Near-infrared optical-absorption behavior in high-beta nonlinear optical chromophore-polymer guest-host materials. II. Dye spacer length effects in an amorphous polycarbonate copolymer host. J Chem Phys 122 234907 1-14. 

Zou J, He HY, Dong JP, Long YC (2004) A guest/host material of LiCl/H-STI (stilbite) zeolite assembly preparation, characterization and humidity-sensitive properties. J Mater Chem 14 2405-2411... 

The conventional crystal structure refinement method by means of the Rietveld method suffers from considerable uncertainty largely because of the unfavorable data-to-parameter ratios. The complexity of the problem generally depends on the number of atoms located in the asymmetric unit. For nonstoichiometric guest-host materials, the difficulty in structural determination of crystalline powders lies in how to determine dynamical disorder and partial... 

Fig. 3.6 The effect of atmosphere on corona poling. Intensity of second harmonic signal is shown as a function of time for a guest-host material (DRl in PMMA) poled in air and in dry nitrogen atmosphere...

Makowska-Janusik, M., Kassiba, A., Failleau, G., Boucl, J. (2006). Interface effects on the NLO properties of guest-host materials. Materials Science, 24, 891-900. 

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