Regensburg 2007 – scientific programme

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SYPE: Symposium Polyelectrolytes

SYPE 1: Polyelectrolytes Poster

SYPE 1.6: Poster

Wednesday, March 28, 2007, 16:00–18:30, Poster B

Diffusion and binding of phenol in sub-micron polyelectrolyte capsule dispersions measured using PFG-NMR — •Rudra Prosad Choudhury and Monika Schönhoff — Institute of Physical Chemistry and Graduate School of Chemistry, WWU Münster, Germany

The distribution and dynamics of phenol molecules in colloidal dispersions of sub micron hollow polymeric capsules is investigated by pulsed field gradient NMR (PFG-NMR). The capsules are prepared by self-assembly of polyelectrolytes onto silica particles, followed by dissolution of the silica core in HF. Here, diffusion echo decays are single exponentials, proving the fast exchange of phenol between a free site and a capsule-bound site. However, apparent diffusion coefficients extracted from the echo decays depend on the diffusion time, which is typically not the case for the fast exchange limit. We attribute this to the presence of a particular regime, where apparent diffusion coefficients are observed, which are influenced by an ultrafast spin relaxation in the bound site. Indeed, relaxation rates of phenol are strongly enhanced in the presence of capsules, indicating binding to the capsule wall rather than encapsulation in the interior. We present an analysis in terms of a combined diffusion-relaxation model, where exchange times can be determined from diffusion and spin relaxation experiments even in this particular regime, where the exchange is fast. Based on the ultrafast relaxation in the bound site, the apparent diffusion coefficients become sensitive to the diffusion time. The results show an increase of exchange rates with phenol concentration.