Adhesion and particle deformation of submicron-sized latex particles on hydrophobically modified solid substrates at room temperature

Two- and three-dimensional colloid arrays were fabricated using three different kinds of monodisperse poly(styrene/sodium p-styrenesulfonate) (poly(St/NaSS) (i.e., high- and low-charged un-cross-linked, and low-charged cross-linked poly(St/NaSS) particles) on 3-aminopropyltrimethoxysilane (APTMS)-modified glass substrates at 20 °C. The array patterns were investigated by field-emission scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-vis spectroscopic analyses. The adhesive force measured by AFM analysis revealed negligible attractive force between APTMS and the poly(St/NaSS) particles. The adhesion force measured between a 3-aminopropyltrimethoxysilane (APTMS)-modified SiN_x tip and the self-assembled particle arrays was in good agreement with the attractive force calculated using the Lifshitz theory with the appropriate Hamaker constants. The cross-linked poly(St/NaSS) particles on the APTMS-modified glass substrate showed mainly hexagonal and square-lattice-free patterns without any crevices, in stark contrast to that of the cleaned, bare glass substrate. The APTMS layer provided the necessary "free-slipping" condition in which nuclei of scattered pinnings of particles in the colloidal crystal were absent. As a consequence, dense fee (or hcp) packing densities (high-charged un-cross-linked: 0.80; low-charged un-cross-linked: 0.76; low-charged cross-linked: 0.76) and narrower stop bands were obtained.