Thermo- and pH-responsive polyelectrolyte complex membranes from chitosan-g-N-isopropylacrylamide and pectin

Non-stoichiometric polyelectrolyte complex membranes between chitosan-g-N-isopropylacrylamide (PNIPAm) and pectin were prepared and subjected to a thermal treatment by which ionic bonds were converted into amide bonds. Membranes are hydrophilic, with opaque appearance, but vitreous when dry. Swollen membranes undergo a sharp shrinking process with an inflexion point at 33.1 °C. Below LCST, NIPAm chains are hydrated and completely stretched. As temperature increases above LCST, NIPAm chains contract and water is expelled from the polymer matrix, giving rise to the phase transition that is associated to an endothermic peak and is fully thermoreversible. These membranes are not only sensitive to temperature, but also to the pH of the medium whose variation has no influence on LCST. Nevertheless, transition enthalpy decreases when pH increases within studied interval, showing the same trend as equilibrium swelling.