Influence of the surface charge of the substrate on the heat stability of electrostatic interactional colloidal crystals grown by heterogeneous nucleation

We studied the influence of the surface charge of the substrate on the heat stability of electrostatic interactional colloidal silica crystals grown through heterogeneous nucleation from the substrate by relative reflection spectroscopy and optical microscopy. During the crystal growth stage on a negatively charged substrate, a large blue shift of the reflection peak was observed in the reflection spectrum. On the other hand, during crystallisation on a positively charged substrate, the blue shift occurring on the negatively charged substrate was completely suppressed. This blue shift indicates a reduction in the lattice spacing when the crystals push each other during crystal growth. The melting behaviour of the crystal was also investigated in the case of heating from the substrate side. The melting point of the crystal on the positively charged surface was higher than that on the negatively charged surface. The blue shift in the spectrum of the crystals on the positively charged substrate was suppressed in the stage before melting; however, the blue shift increased when the crystal started to melt from the substrate surface. Colloidal crystals formed from heterogeneous nuclei on a positively charged substrate were stabilised by the interaction between the negatively charged colloidal particles in the substrate’s vicinity and the positively charged substrate surface.