Probing the jellium model with colloidal dispersions of charged liposomes

The structure factor, S(q), is measured for a set of dispersions that consist of liposome vesicles with differing numbers of ionizable surface groups. These systems allow us to probe the dependence of the local structure on the particle bare charge systematically. The height of the nearest neighbor peak in S(q), which is a direct measure of the spatial order of the vesicles, does not increase monotonically with the number of ionizable groups for a given volume fraction. On the contrary, it rather decreases. This feature cannot be explained by means of the classical renormalization scheme based on the cell model. We analyze our experimental data using a renormalization model based on the jellium approximation, which predicts the weakening of the spatial order for moderate and large particle charges and we find a qualitative agreement.