d ) Thin Film Instability and Patterning
I am also interested in the thin film instability and patterning. Here, I am utilizing the soft-lithography technique to transfer polyelectrolyte micro-patterned thin films directly on substrates, such as glass, silicon wafer, metal oxides, and gold for lithography purpose, in which a broad range of polymers can be used. Thin film morphology on surfaces has attracted great attention for its important applications in industry, such as coatings, adhesives, and opto-electronic display materials. As well as uniform layers on solid surfaces for practical purposes, functional or topographic, regular and irregular patterned surfaces have also gained a lot of interest. Non-uniform structures such as ramified structures are generally caused by non-equilibrium phenomenon with interfacial instability. Such irregular patterns of ramified structures on surfaces are also considered as a broad class of patterning processes on surfaces. Colloidal aggregation, dielectric breakdown, fractal hole growth in strained block copolymer films, dendritic crystal growth, electrodeposition, and viscous fingering in fluid flow, are all explained at both the micro and macroscopic levels, by fundamental concepts of materials structure and function, such as fractal growth and aggregation in diffusion limited aggregation of structure formation.
Figure 5. Optical micrographs of polycation (PDAC) stamped glass slides; (a) directed (to the right) fractal growth by directed polymer stamping, (b) isolated fractal growth of polymer thin film aggregation, (c) dark- field image (DLA), (d) after an careful washing with DI water (invisible), and (e) nickel stained micropatterns on glass for 10 seconds after washing step [ref 6].
For example, we demonstrate a direct polyelectrolyte micropattern transfer (PDAC) using µCP onto the oxygen-plasma-treated glass surfaces without multilayer coatings. A key feature of this work is the thin film morphology study of microcontact printed polyelectrolyte films on glass before and after the washing step. Before the washing step, it is observed that the direct polymer stamping on atomically flat glass surfaces caused a typical ramified structure formation of polyelectrolyte aggregation, The monolayer-like polyelectrolyte micropatterns on glass after the washing step, the samples were further modified to have functionality and topography with metals and colloids through selective metal plating and electrostatic colloidal-patterned polyelectrolyte interactions. We found out how to pattern a polyelectrolyte directly onto a glass surface.
. I. Lee, M. F. Rubner, P. T. Hammond, ¡°Diffusion Limited Aggregation in Polyelectrolyte Micropattern Transfer onto Oxygen Plasma Treated Glass Surfaces by Microcontact Printing,¡± Manuscript in preparation.
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