Stress-free production and effective medium model of colloidal crystals

Abstract

Colloidal crystals of silica spheres functionalized with N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride have been formed by the Langmuir–Blodgett methodology (LB). Monolayers at the air/water interface of functionalized silica spheres have been characterized by surface pressure–area and surface potential–area isotherms and by Brewster angle microscopy (BAM). In order to control and optimize the production of such a colloidal crystal we have measured the diameter and order of spheres in the films, their defects and the density of spheres in each film. Morphologies of the Langmuir–Blodgett films were analyzed by scanning probe ellipsometric microscopy (SPEM) and by scanning electron microscopy (SEM). The results of SPEM are in agreement with the SEM results. The density distribution of colloidal crystals was evaluated using the ellipsometric data by means of the three-layer Brueggemann effective medium approach. The Langmuir–Blodgett methodology was successful for the synthesis of colloidal crystals without cracks.