Abstract
Hollow polyelectrolyte microcapsules prepared by layer-by-layer assembly of polyelectrolytes onto colloidal particles and subsequent core removal are investigated concerning their uptake capacity and the exchange dynamics of aromatic alcohols, that is, hydroquinone and phenol. Diffusion coefficients of the alcohols in the dispersion are determined by pulsed field gradient (PFG) NMR spectroscopy. In addition, spin relaxation rates are determined, which characterize the molecular dynamics. Alcohol molecules in capsule dispersions occur as a bound fraction that is adsorbed to the wall and as a free fraction in the aqueous phase. According to a previously established procedure, from diffusion and relaxation data, population fractions and exchange times are calculated using a two-site model. The adsorbed amounts are well described by Langmuir isotherms, where for hydroquinone as compared to phenol the equilibrium constant is about a factor of 3 larger, and the maximum adsorbed amount about a factor of 3 lower. This indicates the relevance of H bonds for adsorption as well as size effects controlling the uptake capacity of the wall for small molecules.
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