In situ characterization of polymer blend mixing

Currently there is great interest in the development of polymer blend morphology arising from processing to control the properties of blends. A non-destructive technique, non-radiative energy transfer (NRET), was utilized to investigate polymer blend mixing ex and in situ . Donor (naphthyl) labeled polymers and acceptor (anthryl) labeled polymers were segregated to either phase domain limiting NRET to the interphase, and therefore permitting superior spatial resolution than obtained by other techniques such as light scattering. Observed donor and acceptor fluorescence intensities were correlated to respective concentrations, sample geometry, and interphase volume using a fluorescence model derived from the Beer-Lambert Law and Förster\u27s description of NRET between a single donor-acceptor chromophore pair. Particular attention was devoted to the phenomena of direct chromophore excitation, NRET, and radiative energy transfer. ^ The model was used to interpret experiments on the two determinant attributes of polymer mixing: interphase thickness and interphase area. Relative interphase thickness comparisons via polymer interdiffusion in a miscible blend of donor-labeled polystyrene and acceptor-labeled polystyrene indicated increasing ratios of acceptor fluorescence to donor fluorescence resulting from (1) longer diffusion time and (2) higher temperatures. Interphase area effects in an immiscible donor-labeled poly(methyl methacrylate)/acceptor-labeled polystyrene blend revealed a linear relationship between interphase area and donor to acceptor fluorescence ratio. Further interphase area investigation revealed that as the ratio of interphase area to sample volume increases, the resulting donor to acceptor fluorescence ratio approaches that of a homogenous mixed sample of equivalent thickness and dye concentration. ^ The observed fluorescence ratio response to mixing was utilized to interpret two commercial applications: interphase contact and random immiscible blend mixing. Improved contact between a donor-labeled poly(methyl methacrylate) film and an acceptor-labeled polystyrene film were observed via significant increases in acceptor to donor fluorescence ratios that can only arise from NRET between donor and acceptor moieties in the interphase region. Acceptor to donor fluorescence ratio responses to random mixing of commercial polystyrene and poly(methyl methacrylate) in a commercial mixer indicate interphase area differences resulting from morphology changes.