STRUCTURE STUDIES OF MICELLE-ENHANCED POLYELECTROLYTE MICROCAPSULES

Abstract

Hybrid calcium carbonate particles,synthesized in the presence of block copolymer polystyrene-b-poly-(acrylic acid)(PS-b-PAA),were used to fabricate polyelectrolyte(PE) such as polylallyamine hydrochloride)/(poly(strene) sulfonate sodium)(PAH/PSS) and poly(diallyldimethyl ammonium chloride)/poly(styrene sulforate sodium)(PADH/PSS) capsules by layer-by-layer(LbL) technique.Novel micelle-enhanced polyelectrolyte(PE) capsules were thus obtained.The structure of the micelle-enhanced PE microcapsules was studied in this article.Due to the presence of a large amount of negatively charged micelles inside PE capsule interior,which were liberated from templates,the capsule wall was tightly re-constructed.Different from the wall properties of the conventional PE capsules,the wall of the micelle-enhanced PE capsules showed stability under an extensive pH range from 1 to 14,but the micelled enhanced capsules showed dented morpholog in solutions with high NaCl concentration such as 0.5 mol/L and 1 mol/L.The state of the block copolymer in the capsules was investigated in dialysis bag by simulating the solution condition of the capsule interior after the template being removed.It was found that the micelle size of the block copolymer in solution of templates dissolution was tens of nanometers after the solution was dialyzed for(24 h.)With the dialysis time increasing up to at least 72 h,the block copolymer began to precipitate onto the dialysis bag from the solution.The interaction between the 2-D polyelectrolyte multilayer film and micelles formed by block copolymer in templates solution was studied by UV-Vis measurements as well.It was found that PE multilayer could interact with micelles via electrostatic force.At the same time,the block copolymer remained in the capsules interior could be precipitated onto the PE multilayer via dialyzing in deionized water for a long time(pH～6).A micelle-related layer was formed which was stabilized by the "bridge effect" of calcium ions.That is,the wall of the micelle-enhanced PE capsules had a bilayer structure and was formed by the polyelectrolyte multilayer and micelle-related layer.It seemed that the two layers with different properties clung to each other via electrostatic force.The formation mechanism of the bilayer structure was well illuminated on the aforementioned studies.This is a key property of the micelle-enhanced PE capsules with which all the properties of the capsules were linked.Based on the bilayer structure of the capsules,the morphology changes of the capsules in solutions with different conditions such as high NaCl concentrations could be elucidated well.However,more direct proofs and further studies were needed to completely resolve the fine structure of the micelle-enhanced PE capsules.