Monitoring of Colloidal Crystal Formation of Highly Charged Polystyrene and pH Sensing

Abstract

Colloidal crystals have been given a lot of attention in the scientific arena because of their versatility. Here we present a drop and slide technique that was adopted to fabricate a 3-D colloidal crystal array from an aqueous solution of monodispersed, highly charged polystyrene spheres. Bragg reflectance spectra were obtained for the array of colloidal crystal at 50% volume fraction of the colloids as a function of time. The time-resolved Bragg reflection spectra observed show a reflection peak maximum gradually moving towards higher energy state during the colloidal crystallization process. The path taken as the wavelength blue-shifts during drying has been hypothesized to be highly dependent on not only the ordering, but also the shape of the liquid-air interface. The study also highlights the crystallization process during drying. The pH effect on reflectance spectra was also studied on the crystal array by introducing various pH solutions into the system. The results of the pH investigation show that the reflectance spectra are blue-shifted as the pH decreases.