A fluorescence method to estimate the distribution of stresses in polymer materials

It is very important to control the distribution of stresses in order to prevent catastrophic failures during working life of polymer materials. At the present moment, there are several methods to test the distribution of stresses in materials. In the last years, many numerical methods have been proposed, but they have limitations. On the other hand, experimental methods are difficult to perform in all cases, for example when “in situ” determinations are required. In the present work, the use of environmentally sensitive fluorescence molecules (fluorophores) to estimate the tensile state in polymers is discussed. Pyrene, p-quaterphenyl, 1,6-diphenyl-1,3,5-hexatriene (DPhHT), 1,4-bis(5-phenyloxazol-2-yl)benzene and dansyl derivatives, whose fluorescences are sensitive to different types of changes (polarity, microviscosity, etc.), were immersed in one epoxy mixture. After that, the epoxy mixture was cured in a mould to prepare size controlled samples. The specimens were uniaxially loaded. In most of the cases the fluorescence suffers small variations with the epoxy deformation. To evaluate these changes, two photophysical parameters were used: (i) the integrated intensity and (ii) the first moment in the wavenumber of the emission band, 〈ν〉. Related to the fluorescence intensity, the dansyl moiety seems to be the most sensitive; however, for 〈ν〉 the DPhHT showed the highest changes.