Polyelectrolyte Multilayer-Coated Colloids: Hydration, Internal Properties and Interactions

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The hydration water in layered polyelectrolyte complexes will be investigated: Multilayers formed by stepwise self-assembly of polyions of alternating charge will be prepared on colloidal surfaces, using particles as templates (team 1). Employing dispersions of such coated particles, volume techniques can be applied to the study of polyelectrolyte multilayers. Polyelectrolyte multilayers form a 2-dimensionally stratified network structure, comparable to a strongly crosslinked gel. Interesting questions are the influence of the layered arrangement on local properties on a molecular scale: The local heterogeneity is a key parameter for a number of important macroscopic properties, such as permeability for small molecules. NMR spin relaxation experiments deliver information about the average water mobility and structure in coated colloid dispersions. The spin relaxation rate of 2H in deuterated aqueous dispersions will be employed, where previous experiments showed a high sensitivity (team 1). It can be expected that water in the layers exists in different sites, therefore freezing experiments will be performed to investigate the fraction and relaxation rate of the liquid water component at temperatures just below the freezing point. Additional DSC data can confirm the shift of the freezing point, and can further contribute to a separation of water sites. In addition, the hydration of multilayers can be controlled by equilibrating them at defined osmotic pressures (team 2). The equilibrium distance can be determined by structural techniques, and is a function of the internal hydration/ swelling of the multilayers, as well as of the steric arrangement of the terminating polymer layer. The combination of such volume methods studying water in PEMs, such as spin relaxation, osmotic pressure equilibration and DSC measurements is expected to give insight into details of the hydration properties of PEMs.