Gas-Solid Coexistence in Highly Charged Colloidal Suspensions

摘要

Aqueous suspensions of highly charged polystyrene particles with differentvolume fractions have been investigated for structural ordering and phasebehavior using static light scattering (SLS) and confocal laser scanningmicroscope (CLSM). Under deionized conditions, suspensions of high chargedensity colloidal particles remained disordered whereas suspensions ofrelatively low charge density showed crystallization by exhibiting iridescencefor the visible light. Though for unaided eye crystallized suspensions appearedhomogeneous, static light scattering measurements and CLSM observations haverevealed their inhomogeneous nature in the form of coexistence of voids withdense ordered regions. CLSM investigations on disordered suspensions showedtheir inhomogeneous nature in the form coexistence of voids with densedisordered (amorphous) regions. Our studies on highly charged colloids confirmthe occurrence of gas-solid transition and are in accordance with predictionsof Monte Carlo simulations using a pair-potential having a long-rangeattractive term [Mohanty and Tata, Journal of Colloid and Interface Science2003, 264, 101]. Based on our experimental and simulation results we argue thatthe reported reentrant disordered state [Yamanaka et al Phys. Rev. Lett. 1998,80, 5806 and Toyotama et al Langmuir, 2003, 19, 3236] in charged colloidsobserved at high charge densities is a gas-solid coexistence state.