Experimental study on the surface characteristics of polymer melts

With the dimensional reduction of micro-structure, the surface effects greatly influence the dimension precision and surface quality of micro-structure during micro-processing of thermoplastic materials. In this paper, the surface characteristics of several thermoplastic materials usually used in industry are investigated. The Axisymmetric Drop Shape Analysis (ADSA) method in nitrogen gas (N2) environment is adopted to measure the surface tensions of polymethylmethacrylate (PMMA), polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE) melt under different temperatures. The theoretical relationships between surface tension and temperature of polymer melts are obtained. The comparisons are made among different polymer melts according to the relationship of molecular dynamics. The static contact angles between polymer melts (PMMA, PS) and mold materials (silicon, nickel) under different temperatures are also measured in N2 environment using the ADSA method. The results indicate that the contact angle decreases with the increase of temperature and/or the increase surface energy of the mold material. This study provides relevant data to support for micro-injection molding and to optimize processing parameters.