No abstract

ABSTRACT:The fluorescence behavior of 1,1Ј-dimethyl-2,2Ј-carbocyanine and p-N,Ndimethylamino-styryl-2-ethylpyridinium was investigated in several epoxy systems. Time-correlated single photon counting was used for all fluorescence measurements to obtain the rate constant for viscosity or mobility-dependent nonradiative processes of the probe. Microviscosity effects were discussed on the basis of a model describing the microfriction between matrix and probe molecules. The probes investigated are able to detect the glass-transition temperature of the materials investigated. These compounds also show a dependence on the mobility in the glassy state. The probes applied in this work also can be used to monitor the crosslinking process of several epoxy systems containing 4,4Ј-diaminodiphenylmethane (DDM) as curing agent. The epoxides used for the crosslinking process were 2,2Ј-[(1-methylethylidene)bis(4,1-phenyleneoxymethylene)bis-oxiranemethaneamine] [common name, diglycidyl ether of bisphenol A (DGEBA)], N-oxiranylmethyl-N-phenyl-oxiranylmethane [common name, diglycidyl aniline (DGA)], and epoxy novolacs of different functionality. The networks obtained have a different morphology, which was studied by the fluorescence probe technology. The structure of the epoxy compound has an important influence on the probe behavior because both network density and size of the free volume influence the photochemical behavior of the probe.

No abstract

No abstract