Mediation of a phase transition in hyaluronate films by the counterions Li, Cs, Mg and Ca as observed by infrared spectroscopy, optical microscopy, and optical birefringence

Infrared (IR) spectroscopy and optical microscopy have been performed as a function of relative humidity (rh) on wet-spun oriented films of hyaluronat e (HA) prepared with various counterions. Complete swelling measurements ha ve been obtained through optical microscopy for films of Cs-, Mg-, and CaHA . IR spectroscopy of Cs-, Mg-, Ca-, and LiHA films was performed for skelet al vibrations (800-1000 cm(-1)) and for vibrational modes (1150-1300 cm(-1) ) attributed to C-C and C-O stretching modes and C-C-H and C-O-H bending mo des. These techniques reveal evidence of a counterion-dependent phase trans ition occuring at high relative humidities. Optical birefringence measureme nts on the polycrystalline samples showed order before and disorder after t he transition from lower to higher humidity.