Melting of homogeneously superheated colloidal susensions: processes and their kinetics

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Up to recently, the phenomenology of the melting process was thought to be quite well understood. However, with the advent of laser pulse heating and increase in computing power, investigations of strongly superheated solids became feasible. Their results raised a number of interesting fundamental questions concerning the mechanisms and the kinetics of melting under conditions of homogeneous superheating. Here, we suggest to study the phenomenolgy of melting and to quantify its kinetics utilizing colloidal model suspensions. We will exploit the excellent optical accessibility due to the colloid specific time and length scales and use state of the art optical methods. In addition to polarization and Bragg microscopy we will employ Differential Dynamic Microskopie and time resolved Static Light Scattering. We will focus on two classes of electrostatically interacting aqueous suspensions, and we will vary their interaction in a controlled way by established experimental procedures: binary eutectic mixtures and thermosensitive particle-surfactant mixtures. In the latter case, the interaction strength and range can be adjusted using the temperature dependent adsorption equilibrium of the surfactants. In our preliminary studies we found a rich variety of different melting scenarios for both system classes. In the first funding period we plan to obtain a comprehensive overview and classification of the observable phenomena in their dependence on superheating as well as a quantitative determination of the corresponding nucleation, growth and coalescence kinetics. Later we will also address the microscopic mechanisms of melting using high resolution microscopy. The long term goal of our studies - taking a complementary view on melting under homogeneously superheated conditions - is a substantial contribution to a deepened, possibly quantitative understanding of the involved processes.