Polymer and Separations (PolySep) Research Laboratory

Last update:

01/04/2004

B.S. California Institute of Technology, 1996

Research Interests

Surface-polymer science and applications in membrane technology.

Current Project

My research project deals with the study of grafted polymer surfaces and the application to the synthesis of pervaporation membranes. The molecular polymer layers prepared by the present approach have been shown to be effective in reducing protein-surface interactions in ultrafiltration of proteins and oil-in-water emulsions (e.g., using silica-PVP membrane) and also in the synthesis of a new class of pervaporation membranes.

Surface modification by graft polymerization onto inorganic oxide substrates is a unique method of tailoring and manipulating interfacial properties for use in various applications such as biocompatibility, chromatography and the creation of composite ceramic-polymer membranes. Graft polymerization is a process consisting of the following two steps: (1) surface activation with a suitable organo-silane; and (2) a subsequent polymerization reaction to covalently graft a thin polymeric layer of terminally anchored chains onto the substrate surface. The chemical and physical properties of the polymeric layer essentially determine the macroscopic properties of the resulting material.

In the present study inorganic oxide surfaces (e.g., silica and zirconia particles and silicon wafer) are activated by vinyl silylation using vinyltrimethoxysilane (VTMS) in xylene. VTMS is used to replace existing hydroxyl groups on the substrate surface with vinyl silane groups. These covalently bonded vinyl groups provide the attachment points for the graft polymerized chains. Surface conditions can be manipulated to promote additional reactions between VTMS alkoxy groups leading to a network of polysilanes coverage. Subsequent free-radical graft polymerization of vinyl acetate or vinylpyrrolidone is carried out to form the active polymer layer. The polymerization is initiated with an appropriate initiator. For example, graft polymerization with vinylpyrrolidone is accomplished with hydrogen peroxide as the initiator. 

Previous studies of graft polymerization have shown that reaction conditions such as monomer concentration and temperature profoundly affect the macroscopic polymer graft yield. Therefore, in the present study, we are investigating the surface morphology, surface roughness and mass distribution of silylated and polymerized layers by AFM analysis (tapping mode) using modified (silylated and grafted) silicon wafers. We are also imaging porous tubular silica membranes to assess the effects of morphological features on the performance of polymer-modified silica membranes.

The results, to date, have demonstrated that although the grafting process resulted in a complete surface coverage, there appears to be a lateral distribution of grafted mass due to the agglomeration of large polysilanes during the silylation step and a distribution of chain heights expected for free-radical polymerization. The distribution and nonuniformity of the silylation and the resulting polymerization is therefore being characterized using statistical analysis methods. The effects of the various reaction conditions on the surface structure are then compared in terms of uniformity and roughness. In addition, we are estimating the average polymer graft heights and effects of the surface structure on membrane materials.

Publications & Presentations

1. Yoshida, W. H and Y. Cohen, "Topological AFM Characterization of Graft Polymerized Silica Membranes", J. Membrane Science, submitted.
2. Yoshida, W. and Y. Cohen, "Ceramic-Supported Polymer Membranes for Pervaporation of Binary Organic/Organic Mixtures",  in press (2002).
3. Nguyen, V., W. Yoshida,  and Y. Cohen, "Graft Polymerization of Vinyl Acetate onto Silica", in press, J. Appl. Polym. Sci. (2002).
4. Nguyen, V., W. Yoshida,  J-D. Jou and Y. Cohen, "Kinetics of Free-Radical Graft Polymerization of 1-vinyl-2-pyrrolidone onto Silica," Journal of Polymer Science Part A: Polymer Chemistry, Volume 40, Number 1, 26-42 (2002).
5. Cohen, Y., W. Yoshida, V. Nguyen, N. Bei and J-D Jou, "Surface Modification of Oxide Surfaces by Graft Polymerization," in "Oxide Surfaces", J. A. Wingrave (editor), Marcel Dekker, New York (2001).
6. Yoshida, W, Castro, R. P., Jou, J. D. and Cohen, Y., "Multilayer alkoxysilane silylation of oxide Surfaces," Langmuir, 17, 5882-5888 (2001).
7. Cohen, Y., J. Deng-Jeng, W. Yoshida, "Pervaporation with Ceramic-Supported Polymer Membranes", J. Membrane Sci., 162, 269-284 (1999).
8. Wayne Yoshida and Tony Jou, accomplishments of their research on CSP membranes , presented at the DOE First Annual Environmental Management Science Program Scientific Workshop, Rosemont, IL, July 27-30, 1998.
9. Cohen, Y., W. Yoshida and Jend-Deng, J., "CSP Membranes", invited poster presentation, DOE First Annual Environmental Management Science Program Scientific Workshop, Rosemont, IL, July 27-30, 1998.
10. Yoshida, W., Y. Cohen and Jeng-Deng J., "Graft Polymerization and Application to ceramic Supported Polymer Pervaporation Membranes for VOC Removal",AICHE Annual Meeting, Miami Beach, FL, November 15-20, 1998.
11. Cohen, Y., W. Yoshida, Jeng-Dung Jou, Hiroyoshi Ohya, Nianjiong Bei "Ceramic-supported Polymer (Csp) Membranes for Pervaporation Separation of Organic/aqueous and Organic/organic Mixtures", International Conference on Membranes (ICOM), June 12-18, 1999, Toronto, Ontario, Canada.

Personal home page:
www.polysep.ucla.edu/wayne
Currently a picture gallery of photographs I have taken

Address

5531 Boelter Hall
Chemical Engineering Department
UCLA, Los Angeles
CA-90095, USA
PH:  (310) 2061297; Fax: (310)206 4107

Phone

Lab:  (310) 206-1297

Email
Wayne Yoshida <archon@ucla.edu>