Structural study of poly (N-isopropylacrylamide) microgels interpenetrated with polypyrrole

Abstract

Thermosensitive cross-linked poly(N-isopropylacrylamide)[poly(NIPAM)] microgels in D₂O present a continuous volume phase transition from swollen to deswollen states at a temperature within 32–34 °C and the process is thermoreversible without hysteresis. The poly(NIPAM) microgels with 0.25% (w/w) cross-linker content were used as a matrix to entrap polypyrrole. Pyrrole was dissolved in the colloidal microgel dispersion and polymerisation was performed at three selected temperatures: 20 °C in the swollen state of the microgel, at 37 °C having the microgel collapsed and at 32.5 °C corresponding to the beginning of the volume phase transition of the microgel. Dynamic light scattering, differential scanning calorimetry, small angle neutron scattering and transmission electron microscopy have been used to study the structural modifications induced by polypyrrole in these microgels. The small angle neutron scattering pattern was analysed using an expression that consists of solution-like concentration fluctuations given by an Orstein–Zernike type function, a solid-like concentration fluctuations described by a Gauss function and a contribution arising from the surface of the colloidal microgel. It seems that polymerisation of pyrrole, when the microgel particles are in the swollen state (20 °C), results in a uniform distribution of polypyrrole within the particles. However, when the polymerisation is carried out at the beginning of the volume phase transition (32.5 °C) an outer shell of polypyrrole could be formed. Finally, polymerisation of pyrrole at 37 °C produced non-stable colloidal particles.