Hydrogen-Bonding-Induced Complexation of Polydimethylsiloxane-<i>graft</i>-poly(ethylene oxide) and Poly(acrylic acid)-<i>block</i>-polyacrylonitrile Micelles in Water

Abstract

Polydimethylsiloxane-<i>graft</i>-poly(ethylene oxide) (PDMS-<i>g</i>-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-<i>block</i>-polyacrylonitrile (PAA-<i>b</i>-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (<i>r</i>) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of <i>r</i>. At <i>r</i> < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-<i>b</i>-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-<i>g</i>-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < <i>r</i> < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-<i>b</i>-PAN micelles absorbed onto the initial PDMS-<i>g</i>-PEO micelles. At <i>r</i> > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.