Spinodal Decomposition in a Model Colloid-Polymer Mixture in Microgravity
Original Entry by Michelle Borkin, AP225 Fall 2009
A. E. Bailey, W. C. K. Poon, R. J. Christianson, A. B. Schofield, U. Gasser, V. Prasad, S. Manley, P. N. Segre, L. Cipelletti, W. V. Meyer, M. P. Doherty, S. Sankaran, A. L. Jankovsky, W. L. Shiley, J. P. Bowen, J. C. Eggers, C. Kurta, T. Lorik, Jr., P. N. Pusey, and D. A. Weitz, Physical Review Letters 99, 205701 (2007).
A quenched colloid-polymer mixture was prepared in a microgravity environment to study the mixtures evolution from spinodal decomposition to interfacial tension driven coarsening. The experiment was conducted on the International Space Station (ISS) as part of NASA's "Physics of Colloids in Space" project. The sample was imaged with the project's light scattering instrumentation and direct digital imaging cameras. The mixture was composed of polymethylmethacrylate particles and polystyrene. The liquid after total separation was 45%:55% by volume liquid and gas phases. On Earth, this separation took ~2 hours, whereas in the microgravity environment it took ~30 times longer and was able to be studied is far greater detail. Microgravity also resulted in larger density differences between the final phases as well as an ultralow interfacial tension. Also, it was observed that the evolution over time of the deep quenching follows the same evolutionary function as in binary liquids. This implies variations in the characteristic length scale of colloidal gels depend on the rate of coarsening.
For more information about this experiment and others from the "Physics of Colloids in Space" project, go to:
This paper focuses on studying the properties of a colloid-polymer mixture. These mixtures are composed of colloidal particles with non-absorbing polymers. The colloidal particles will attract and push away the polymers (such depletion interactions are driven by osmotic pressure) and the unbalanced system will result in the coarsening of the sample so the colloidal particles will bunch together. These colloid-polymer mixtures are commonly studied to investigate phase change behavior since as the colloids attract they will form a "colloid rich liquid" while the rest of the solution will become a "colloid poor gas" exhibiting spinodal decomposition.