Epifluorescence Studies and Secondary Relaxation Processes in Immiscible Blends of Polybutadiene-Poly(2-vinyl naphthalene) by Fluorescence Spectroscopy M. C. P. CRUZ, F. M. CASSIOLA, T. D. Z. ATVARS Instituto de Quı ´mica, Caixa Postal 6154, CEP 13083-970 Campinas, SP, Brazil Received 27 February 2001; accepted 5 June 2001 Published online 6 March 2002 ABSTRACT: The development of the morphology of polybutadiene/poly(2-vinyl naphtha- lene) blends in five proportions by mass (5, 10, 50, 90, and 95%, w/w) is studied by epifluorescence and scanning electron microscopy (SEM) techniques. The phase sepa- ration process of these immiscible polymers produces a primary morphology that is formed by dispersed droplets in a continuous matrix. In the sequence a secondary phase separation inside the primary domains is detected by epifluorescence microscopy of the intrinsically fluorescent domains. Secondary phase separation is confirmed by SEM fracture surface analysis. The relative size of the droplets and the matrix composition depend on the proportion of the components of the blends. The mechanism of the phase separation process is preferentially by nucleation growth for either primary or second- ary phase separation processes. Secondary relaxation processes involving the poly(2- vinyl naphthalene) phase are studied by fluorescence spectroscopy. The profile of the steady-state excimer fluorescence of poly(2-vinyl naphthalene) with the temperature in the blend differs from that of the isolated homopolymer and is explained by the contribution from the interface to the radiationless deactivation. The Arrhenius plot for the temperature dependence exhibits slope changes that are related to the polymer relaxation processes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1637–1649, 2002; DOI 10.1002/app.10389 Key words: epifluorescence microscopy; polybutadiene; poly(2-vinyl naphthalene); relaxation processes; scanning electron microscopy INTRODUCTION Studies of polymer blends may be considered from different viewpoints. In some cases optimization of properties is the main interest and in others compatibilization of the phases or preparation of a miscible material is emphasized. Regardless of the aim of the work, the final properties and mor- phology of the material are controlled by the in- terfacial properties. Nevertheless, the determina- tion of the interfacial properties in microhetero- geneous materials, including polymer blends, is still difficult, regardless of whether we consider theoretical models or experimental methodology. The main reasons for these difficulties reside in the width of the interface and in the absence of precise thermodynamic models describing the gradient of composition throughout the interfacial cross section. 1–5 In immiscible polymer blends the interfacial tension increases with the molecular weight of each homopolymer and linearly decreases with the increase of the temperature. 4 Direct study of polymer interfaces is a very difficult task, and measurements of composition Correspondence to: T. D. Z. Atvars (tatvars@iqm. unicamp.br). Contract grant sponsor: FAPESP. Journal of Applied Polymer Science, Vol. 84, 1637–1649 (2002) © 2002 Wiley Periodicals, Inc. 1637