Nanoscale alumina/protein gel composite films with 10-50 wt% filler were subjected to scratch testing and compared to micron-scale alumina/protein gel composites. Atomic force microscopy (AFM) was employed to examine the width, depth, and morphology of the as-produced scratches. The results show that the scratch depth in gelatin films and the tearing within the scratch decrease dramatically with the addition of the nanoscale (average particle size, 13 nm) alumina fillers. It was found that refining the particle size distribution of the Al_2O_3 powder (average particle size, 10 nm, with no particles larger than 70 nm) further reduced the scratch depth and width, while improving the dimesnional integrity and surface roughness of the nanocomposites. Aging of the gelatin films improved the intrinsic scratch resistance of both filled and unfilled gelatin films. In comparison, micron-size Al_2O_3 filler not only increased the scratch width, but also resulted in poor particle dispersion and low transparency of the films. The optical clarity of the nanofilled composites was much igher than that of the composites with micron-size filler.
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