SURFACE ANALYSIS OF TEMPLATED POLYACRYLAMIDE GELS BY ATOMIC FORCE MICROSCOPY. D. H. Van Winkle, M. Chakrapani, S. J. Mitchell, and P. A. Rikvold, Department of Physics and Center for Materials Research and Technology, Florida State University, Tallahassee, FL 32306-4350

Using atomic force microscopy AFM, we have imaged the mountainous surface of templated polyacrylamide (pAAm) gels. Polyacrylamide gels are composed of a network of cross-linked acrylamide fibers separated by aqueous buffer. These are formed by polymerizing monomer acrylamide and N',N'-methylene-bisacrylamide (bis) in buffer. AFM on normal polyacrylamide gels shows surfaces smooth on a 10 nm length scale. This is expected, since the polymer fibers are on average separated by about 1.0 nm. Templated gels are formed in the presence of 3.5 nm diameter micelles of tetra-decyl-trimethyl-ammonium bromide (TTAB) surfactant. The surfactant is removed from the gels by soaking against buffer. As the surfactant diffuses out of the clear gels, the gels become turbid. For high surfactant concentration, the resulting templated gels become opaque and white. Structures as high as 300 nm, separated by about 500-1000 nm are observed in AFM on the white surfaces. The surface roughness is analyzed as a function of initial surfactant concentration.

Standard methods of characterizing the surface roughness show an exponential increase in certain parameters with concentration. A self-affine scaling analysis of the surfaces as a function of concentration shows that normal gels are self-affine over the entire range of image length scales measured. High concentration templated gels show self-affine behavior for small image sizes, but a crossover to a surface with a characteristic length for large images.