pH control of transport through a porous membrane self-assembled with a poly(acrylic acid) loop brush

Side chains of poly(acrylic acid) (PAA) were conjugated with cysteamines for self-assembly on a gold-coated membrane. The self-assembly of the cysteamine-modified PAA on the membrane was monitored by surface plasmon resonance spectroscopy. It was found that the amount of assembled polyelectrolytes significantly depended on the concentration of the polyelectrolytes, the content of cysteamine in the polyelectrolyte, solution pH and ionic strength. Transport through porous membranes gold-coated and subsequently self-assembled with the polyelectrolyte was investigated. Water permeability through the membrane was reversibly regulated by pH and ionic strength. The permeability was high at low pH and low at high pH, and an increase in ionic strength increased the permeability at high pH. It wits suggested that at low pH the polyelectrolyte was protonated which caused the brushes to shrink and opened the pores. At high pH, the opposite process took place. The ionic strength reduced the electrostatic repulsion between the ionized polyelectrolytes that shrank the opening of the pores. These phenomena depended on the state of the self-assembled polyelectrolytes. Filtration of water solutions of ionic (oligodeoxyribonucleotide) and nonionic (poly(ethylene glycol)) polymers through the modified membrane was also studied. pH-responsive permeability depended on the molecular weight of the solutes.