P(AAm-co-MAA) semi-IPN hybrid hydrogels in the presence of PANI and MWNTs-COOH: improved swelling behavior and mechanical properties.

A highly pH-sensitive hybrid hydrogel with semi-interpenetrating networks (semi-IPN)composed of co-polymer networks of acrylamide-methacrylic acid (P(AAm-co-MAA)) and polyaniline (PANI)/carboxyl-functionalized multi-walled carbon nanotubes (MWNTs-COOH) was designed and synthesized by a cross-linking co-polymerization route in the presence of N,N-methylene bisacrylamide (BIS) and ammonium persulfate (APS). The structural and morphological characterization and mechanical properties of the gels were investigated using a Equinx55 FT-IR spectrometer, an environmental scanning electron microscope and a dynamical viscoelasticity analyzer, respectively. Swelling capability of the hybrid hydrogels was examined under the conditions of various pH buffer solutions (1.35, 6.95 and 12.86) at a temperature of 27 degrees C. P(AAm-co-MAA) co-polymer hydrogels were discussed as a control sample at the same time. The experimental results indicated that the prepared P(AAm-co-MAA) co-polymer hydrogels showed a high equilibrium swelling ratio in distilled water, pH-responsive characteristics and excellent strain recoverability. After having incorporated the polyelectrolyte PANI and MWNTs-COOH into the above-mentioned network, the P(AAm-co-MAA)/PANI/MWNTs-COOH semi-IPN hybrid hydrogels obtained possessed an even higher sensitivity to pH environments, good swelling reversibility, higher ultimate compressive strength and good strain recoverable ability. Swelling experimentations in buffer solutions of different pH revealed that the semi-IPN hybrid hydrogels possessed higher tensile strengths at a lower pH than at a higher pH value. All the excellent properties may primarily be attributed to the formation and weakening or disappearance of a repulsive force based on hydrogen bonds, as well as appearance of attractive forces of pole-pole interactions between PANI chains at different pH values.