Combining the pH measurement with the solids fraction measurements (Fig. 6), we are then able to establish the solids fraction when crosslinking is favored. The figure shows that the pH decreases below 7 when a solids content of approximately 68 wt% is achieved. Depending on the particular packing of the particles, this solids content would correspond to the point of contact between particles. (For mono-size hard particles, the maximum solids fraction at close packing is 74 vol%.) The gas chromatography data clearly showed that the chemical reaction rate increases substantially below a pH of 7. Therefore, crosslinking in the film is favorable only near and after the point of close packing. Polymer interdiffusion likewise cannot occur until particles have made physical contact, of course. Thus, interdiffusion and