Effect of growth conditions on the structure of two-dimensional latex crystals: experiment

Abstract

The growth kinetics and structure of two-dimensional crystals of fine latex particles on solid substrates have been studied using a variety of microscopic techniques: optical microscopy, surface plasmon resonance microscopy, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. A circular-shaped crystal is grown from a thin layer of a latex suspension by a two-step mechanism: nucleation and crystal growth. Here we report an experimental study of the factors influencing the crystallization process, especially focusing on the water evaporation rate, the liquid meniscus at the crystal boundary, the particle size and concentration, the substrate, etc. Crystals of good quality and structure are grown at a high evaporation rate (low humidity) favoring a convection-dominated influx of particles from the suspension. The particle diffusion plays a role at suppressed evaporation thus causing an increase in the number of crystal defects. The dynamics of the meniscus slope leads to growth instability resulting in a sequence of multilayer rings. A hexagonal lattice prevails in the final crystal whereas a square lattice is observed in the transition regions between two different hexagonal multilayers. These general trends of the crystallization process are the same for different particle diameters (19 nm, 55 nm, 144 nm and 1.696 μm), volume fractions (0.001–0.01) and substrates (bare and metal-coated glass and mica).