Physics of colloids in space plus (PCS+)

The Physics of Colloids in Space Plus (PCS+) experiment consists of light scattering and rheological measurements probing the essential features of the hard sphere disorder-order transition and the properties of the ordered solid phase that results. Several samples, in custom-designed cells at fixed volume fractions, will permit measurements from the disordered fluid phase, through the coexistence region, into the fully crystalline solid, and beyond toward random close packing. The dispersions will consist of monodisperse colloidal hard spheres 0.65-0.70 micron diameter with cores of poly(methylmethacrylate) and a comb-graft co-polymer stabilizer in a mixture of decalin and tetralin with an almost matching refractive index. The information obtained will answer fundamental questions in condensed matter physics regarding this most fundamental of transitions between liquid and solid phases. An extensive theoretical basis, from computer simulations and statistical mechanical theories, complements numerous experimental studies with similar model systems addressing one or more aspects of the phenomena. However, gravitational settling inevitably complicates the measurements and introduces ambiguities. With PCS+ we seek to sweep these aside in completing a comprehensive study capitalizing on the techniques and knowledge developed in the preceeding ground-based and flight experiments. With this space experiment we aim to • understand why glasses do not persist in microgravity, • correlate the visual appearance of dendrites with data on nucleation and growth from Bragg scattering, and •correlate depletion observed by low angle scattering with the visual appearance of dendrites.