Permeability of polyamide microcapsules toward ions and the effect of water structure

Abstract

Permeability coefficients for sodium, potassium, and rubidium hydroxide in poly(1,4-terephthaloylpiperazine) and poly(1,6-hexamethylenesebacamide) microcapsules were determined in order to examine the effect of water structure on the permeation of ions through microcapsule membranes. p]The results show that, with increasing proportion of cyclohexane in the mixed solvent used in the preparation of the microcapsules, the membrane thickness of the microcapsules increases and the permeability coefficient decreases. The difference between the permeability of poly(1,4-terephthaloylpiperazine) and poly(1,6-hexamethylenesebacamide) microcapsules was clearly demonstrated. The permeability was measured using three alkali hydroxides (NaOH, KOH, and RbOH). Potassium hydroxide permeated through the microcapsules about three times faster than sodium hydroxide and about an order of magnitude faster than rubidium hydroxide, under comparable conditions. The water structure was determined from the thermal behavior of aqueous microcapsule suspensions, which was studied by differential scanning calorimetry. The thermal behavior of the suspensions and the permeability of the microcapsules were found to change when urea was added to the suspensions. It was concluded that the ion permeation closely related to the water structure in and around the microcapsule membrane.