It is well known that the addition of non-adsorbing polymers to a dispersion of hard sphere like (HS) colloidal particles introduces short range attraction to the system. This so called depletion attraction can be used to study flocculation or the phase-behaviour of colloidal systems with short range attraction. Beside this polymer-induced (PI) attraction in some cases a PI repulsion can be observed. So far a (re-)stabilisation of a flocced phase by PI repulsion could only be observed in stericaly stabilised particles having thick stabilisation layers. Whether restabilisation can be realised in a true HS system is not yet known. Recently Semenov et al. published theoretical work on colloid-polymer-mixtures[1], where they predicted restabilisation in a HS system in the case of large particles and much smaller polymers, but these predictions have not yet been tested experimentally. To gain experimental access to the influence of PI interactions on particle interactions, we study the osmotic compressibility of HS systems using turbidimetry. So far similar experiments where only carried out on rather small particles, where PI repulsion is of no importance.[2] Thus we are extending the method towards larger particle sizes to check whether the PI stabilisation described by Semenov is able to give a more satisfying description of the data than the classic approaches.
[1] A. A. Shvets, A.N. Semenov, J. Phys. Chem., 139 054905, (2013).
[2] S. Ramakrishnan, M. Fuchs, K. S. Schweizer, C.F. Zukuvski, Langmuir, 18, 1082-1090 (2002).
