Detection of local density distribution of isolated silanol groups on planar silica surfaces using nonlinear optical molecular probes

Crystal Violet has been used as a nonlinear optical molecular probe for the detection of local density distribution of isolated silanol groups on planar silica surfaces. Because of its large size (similar to 120 Angstrom(2)) and nearly hat adsorption geometry, Crystal Violet has successful separated the truly isolated silanol groups (i.e., the silanol groups that cannot form a hydrogen bond with their neighbors by any means, similar to 9.3 x 10(13) cm(-2)) into two major classes. The first class includes those isolated silanol groups; each is surrounded by a large empty surface area (greater than or equal to 120 Angstrom(2)) in which a Crystal Violet cation can be placed. The surface density of this type of silanol groups is similar to 1.1 x 10(13) cm(-2). The second class includes the rest of the isolated silanol groups with a surface density of 8.2 x 10(13) cm(-2).