Polystyrene/Sn–Pb Alloy Blends. II. Effect of Alloy Particle Surface Treatment on Dynamic Rheological Behavior Xiang-Wu Zhang, 1 Yi Pan, 2 Qiang Zheng, 1 Xiao-Su Yi 3 1 Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China 2 Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China 3 National Key Laboratory of Advanced Composites, P.O. Box 81-3, Beijing 100095, People’s Republic of China Received 12 June 2001; accepted 9 April 2002 Published online 3 October 2002 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/app.11352 ABSTRACT: The effect of filler surface treatment on the dynamic rheological behaviors of polystyrene filled with Sn–Pb alloy particles was tested below and above the melt- ing temperature (T m ) of the alloy. The mechanical relaxation relevant to the T m of the alloy in the composite was dimin- ished by the filler surface pretreatment. In the whole tem- perature range of interest, there existed a secondary plateau of the storage modulus at low frequencies. The effect of alloy particle surface treatment on the plateau was related to the matter-state change (from solid to liquid) of the alloy. Above the T m of the alloy, the surface treatment of the alloy affected the secondary plateau, but below the T m , it did not. The analyses of Cole–Cole diagrams of the systems suggested that untreated and pretreated alloy fillers all retarded the relaxation processes in the molten state of polystyrene below the T m of the alloy and that the relaxation process was separated into the high-frequency relaxation of the phases and the low-frequency relaxation of the droplets above the T m . The surface treatments of the alloy filler further en- hanced this action. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3173–3179, 2002 Key words: surfaces; rheology; composites; alloys; melting point INTRODUCTION The rheological behavior of filled polymer composites has become of great interest because of the increasing applications of the polymer composites. Compared with the rheological behavior of the pure polymer matrix, polymer composites generally exhibit pro- nounced elastic properties and long relaxation times. 1–4 The rheological behavior of a filled polymer composite is governed first by the properties of both the polymer matrix and incorporated fillers and is then influenced by the volume fraction and agglom- erations of the filler particles and the interfacial adhe- sion between the filler and matrix. 5–8 On the other hand, dynamic rheological measure- ment is an effective method to characterize the mor- phological and structure of the multicomponent and/or multiphase polymer composites. 9 –16 The rheo- logical property change of a polymer matrix induced by filler incorporation are thought to be caused by two factors. One is the mechanical coupling between filler and polymer matrix, 7,8 The other one is the interface morphological structure depending on the interfacial adhesion or adsorption between the phases. 6,7,15,16 Be- sides the previously mentioned causes, the matter state (solid or liquid) of fillers also has a significant influence on the rheological behavior of composites; little attention was paid to this behavior until recently. In previous research, 17–20 rigid particles, such as min- eral fillers, and deformable droplets, such as rubber fillers, softeners, and lubricants, have been two main kinds of fillers. Rigid particles are the reinforcements of composites, but deformable droplets usually act as a polymer processing promoters. In processing tem- peratures of the previous systems, however, matter- state changes did not occur. Incorporation of a filler in a polymer matrix often brings about some important properties to the com- posite. An example of academic and application im- portance is the positive temperature coefficient (PTC) composites made of electrical conductive particles and a polymer matrix by blending. These kinds of com- posites, exhibiting a remarkable increase in electrical resistance in a narrow range during a temperature increase, have been successfully used as thermistors, or temperature-dependent resistors. 21,22 However, a neg- ative temperature coefficient (NTC) effect following the PTC transition limits the applications of such com- Correspondence to: Q. Zheng (zhengqiang@cmsce.zju. edu.cn). Contract grant sponsor: Special Funds for Major State Basic Research Projects; contract grant number: G1999064800. Contract grant sponsor: National Natural Science Foun- dation; contract grant number: 59683003. Contract grant sponsor: National Science Fund for Distin- guished Young Scholars; contract grant number: 50125312. Journal of Applied Polymer Science, Vol. 86, 3173–3179 (2002) © 2002 Wiley Periodicals, Inc.