Nonlinear materials 3 polymers

In this chapter we deal primarily with experimental results that have been reported dealing with parametric interactions in nonlinear poled polymers, i.e. mostly on second harmonic generation in phase-matched configurations. Because the theoretical analysis associated with these processes has been known for some time and has been independently reviewed many times, we will only briefly overview these basics. Also, the polymeric materials developed for similar applications are reviewed in another section of this book and we refer the reader to that for details. 

R. A. Schapery, On the Characterization of Nonlinear Viscoelastic Materials, Polymer Engineering and Science, 9, 295-310 (1969). 

The previous discussion illustrates the difficulties in crystal engineering as an approach to the development of new nonlinear materials. With polymers, the situation is, conceptually at least, straightforward, and the problems that must be overcome are subject to analysis. The approach is to apply an external alignment field to polymer (or prepolymer) in a softened state and to fix the orientation with one of a variety of processing approaches. This approach is illustrated schematically in Figure 6.5, which shows how... 

As discussed earlier, while the scale of the fillers is substantially different, nanocomposite materials concepts and technology are very similar to those of conventional composite materials. This is clearly demonstrated in the case of new thermosets for nonlinear optical (NLO) applications, " " where nanocomposite of liquid crystalline thermosets, IPNs, and simple filled thermosets are evaluated. Tripathy et al. discussed four different ways to prepare nonlinear optical polymers. (1) The polymer matrix is doped with NLO moieties in a guest/host system (2) In side-chain polymer systems, NLO polymers with active moieties are covalently bonded as pendant groups (3) In the main chain polymer, the chromo-phores are incorporated as parts of the main polymer backbone to enhance the temporal stability of the NLO properties and (4) Stability of the optical noninearity in sol-gel-based thermosets is related to... 

Keywords Elastohydrodynamic interactions Glass transition Linear viscoelasticity Nonlinear rheology Polymer-colloid materials Shear-thinning Wall slip... 

Fullerene has important properties as a nonlinear material, particularly as an optical limiting material with applications in device fabrication. The poor solubility of this material and the processing difficulties associated with it severely limit its direct application, however. One possibility of overcoming these disadvantages involves binding polymers on to Ceo to obtain fullerene-based polymeric materials with peculiar physical and/or chemical properties and good processability. 

In fact, contrary to the accepted mechanism at the time, this spacer is not necessary, and the motion of such side groups with short or no spacers was becoming obvious from the study of polymer materials for nonlinear optics. Polymers with higher Tg were proposed and actually used in the poling process, where a polar alignment is achieved with the help of an electric field. 

Grote, J.G., J.S. Zetts, R.L. Nelson, EK. Hopkins, J.B. Huddleston, P.P. Yaney, C.H. Zhang, W.H. Steier, M.-G. Oh, H.R. Fetterman, A.K. Jen, and L.R. Dalton. 2001. Advancements in conductive cladding materials for nonlinear-optic-polymer-based optoelectronic devices. Proc SPIE4470 10-19. 

A huge number of other applications exist, where the chemical and physical requirements are totally different. These applications include reflectors, temperature measurement with thermochromic materials, nonlinear optics, polymer materials, SAMs (self-assembled mono-layers) and LB (Langmuir-Blodgett) Aims, the use of liquid crystals in template synthesis of porous materials, drug delivery, and many more. 

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