Roughness as a measurement of random disorder

Abstract

We have studied the quenched random disorder (QRD) effects created by aerosil dispersion in octylcyanobiphenyl (8CB) liquid crystal (LC) using Atomic Force Microscopy (AFM) technique. Gelation process in the 8CB+aerosil gels yields a QRD network which also changes the surface topography. By increasing the aerosil concentration, the original smooth pattern of LC sample surfaces is suppressed by creating a fractal aerosil surface effect; these surfaces become more porous, rougher with more and bigger crevices. The dispersed aerosil also serves as pinning centers for the liquid crystal molecules. It has been observed that via the diffusion-limited-aggregation process, aerosil nano-particles yield a fractal like surface pattern for the less disordered samples. As the aerosil dispersion increases, the surface can be described by more aggregated regions which also introduce more roughness. Using this fact, we have shown that there is a net correlation between the short-ranged x-ray peak widths (-the results of previous x-ray diffraction experiments-) and the calculated surface roughness. In other words, we have shown that these QRD gels can also be characterized by their surface roughness values.

Geometric and chemical nonuniformity may induce the stability of more than one wetting state in the same hydrophobic surface

“…Most of the theoretical, numerical [9][10][11][12][13] and experimental [7,[14][15][16][17] studies approach this problem by varying the roughness via different geometrical parameters and assuming a regularity in the distribution of the textures and of the chemistry. However, real structures have some degree of disorder in its parameter [18][19][20] and in fact some simulations and experiments have used wetting dynamics to probe these irregularities [21,22]. Experimental studies have shown that strong spatial disorder have influence on the transition from the CB to W state [23], and it has been suggested that the phenomena is related to the negative curvature of the textures [24].…”