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Relaxation dynamics of poly(methyl methacrylate) (PMMA) and doped PMMA systems are investigated as a function of processing temperature and frequency. Polymer relaxations and changes in local mobility are responsible for chromophore reorientation and lead to a loss in second-order nonlinear optical (NLO) properties. Studying polymer relaxations enables the temporal and thermal stability of the NLO polymer systems to be more accurately and readily predicted. The polymer dynamics are studied by correlating mechanical and dielectric relaxations to polymer and chromophore relaxations that occur during chromophore reorientation in second harmonic generation experiments. Dielectric and mechanical relaxation techniques enable polymer relaxation dynamics to be observed over a broad frequency range. The plasticization effect of the NLO chromophores on the polymer relaxation dynamics is also investigated.
Much effort has been put into improving the temporal stability of electric field-induced chromophore alignment in molecularly doped or functionalized polymers for second order nonlinear optical device applications. Characterization of the alignment decay in electric field-poled films is complicated by charge injection during poling. In order to optimize poling schemes and to accurately determine the orientational mobility of the chromophores it is necessary to develop methods to measure the spatial extent and time-dependence of any residual fields in the polymer films. Such Measurements will also be important for the development of polymer-based electro-optic devices, and in fact for any guided wave application in these materials since the residual field may induce a spatial dependence in the refractive index.
Poly (arylene ether)s can be designed to be amorphous, optically clear materials with excellent hydrolytic and thermal stability as well as good electrical, Mechanical and fire resistant properties. As a result, the use of these macromolecules in second order nonlinear optical (NLO) applications are being investigated. Typically, polymeric systems with doped chromophores result in a signigicant decrease in Tg. Methods were investigated to functionalize the polymer backbone with NLO chromophores, resulting in increased Tg.
A new class of high temperature polymeric materials capable of second order nonlinear optical effects has been developed and characterized. These polymers, Bisphenol A-poly (arylene ether) phosphine oxides (Bis A-PEPO), F6 Bis A-PEPO, phenolphthalein•PEPO (PP-PEPO), and phenolphthaIein-anilide•PEPO (PP-PEPO), doped with nonlinear optical chromophores are being examined using second harmonic generation. Corona poling is used to orient the chromophores into the noncentrosymmetric structure required to obtain the second harmonic signal. These high glass transition temperature (>200°C) polymers have strong hydrogen bonding sites that can interact with the chromophores. This work describes the basic polymer physics including local Mobility, chromophore/polymer interactions, and polymer steric effects that control the thermal and temporal stability of chromophore orientation in these guest-host polymeric systems.
The dynamics of the gas phase photopolymerization of acrolein on aluminum (Al), nickel (Ni), and gold (Au) substrates were studied in-situ and in real time using surface second harmonic generation (SSHG) and monitoring vapor pressure decay. The Al and Ni substrates had a significant effect on the apparent rate of polymerization. A dark reaction after irradiation occurred in the absence of metal (Al or Ni) substrates, but no dark reaction was observed when the metal substrates were present. The significant differences in the metal/monomer interactions during photopolymerization are indicated by SEMs of the polyacrolein, as well as evidence from FTIR-ATR spectra. The SSHG intensities from the Au, Al, and polyacrolein surfaces were obtained.
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