Lupu Alexandru

Deposition of ultrathin films by a withdrawal method

Abstract Ultrathin polymer coatings of styrene-hexylmethacrylate, with thicknesses ranging from less than 100A to 1 μm, were prepared on glass and aluminized Mylar substrates using a simple withdrawal method. The thickness of the polymer coatings could be controlled by choosing an appropriate combination of the speed of withdrawal of the substrate from the polymer solution and the concentration of polymer in the solvent. Electrical resistivity measurements, surface roughness measurements and thin section electron micrographs showed that the polymer coatings were uniform and continuous. These results show that the coating dries fast enough during withdrawal that a uniform thin film is produced. A simplified solution of the Navier-Stokes equation was successfully applied to describe the withdrawal process as a function of the coating parameters in the range of very low capillary numbers.

Suspension polymerization processes

Several processes can be employed for manufacturing of polymer materials. Each process presents some intrinsic features that lead to production of resins with peculiar structural and morphological characteristics that define the final polymer properties and the end-use application of the obtained polymer material. Suspension polymerization processes are extensively used because of their many advantages, including easy separation of the polymer particles, easy removal of the heat of reaction, easy temperature control, and low levels of impurities and additives in the final polymer resin. For this reason, suspension polymerization processes are suitable for production of polymer resins intended for many distinct applications, including biotechnological, medical, and dental applications. The main objective of this article is to discuss the fundamental aspects of suspension polymerization processes, focusing upon the effects of the main process variables on the performance of suspension polymerizations. Representative types of suspension polymerization (eg, pearl, precipitation, suspension-emulsion, reverse, microsuspension, and seeded polymerizations), copolymerization, determination of reactivity ratios, and typical operation conditions practiced in commercial processes are also discussed. Keywords: suspension polymerization; polymer; particle; monitoring; copolymerization