Formation and properties of composites based on microgels of a responsive polymer and TiO2 nanoparticles

Organic-inorganic composites were prepared with titanium dioxide (TiO2) nanoparticles embedded within colloidal particles of a cross-linked, thermally responsive polymer. To promote the incorporation of unaggregated nanoparticles of TiO2, temperature responsive microspherical gels (microgels) of N-isopropylacrylamide (NIPAM) with interpenetrating (IP) linear chains of poly(acrytic acid) (PAAc) were synthesized. Dynamic light scattering (DLS) measurements revealed that these microgels reversibly shrink and swell in diameter from 300-400 nm to 600-800 nm with temperature. Two types of nanoparticles of TiO2 were immobilized within the IP-microgels-tine TiO2 nanoparticles synthesized by the hydrolysis of titanium(IV) isopropoxide and commercially available Degussa P25. Characterization of the composite was conducted using transmission electron microscopy (TEM) and UV-vis absorption spectroscopy from which it was determined that the extent of loading of the TiO2 within the colloidal particles can be easily manipulated from a low value of 10% (weight) to a value as high as 75%. The TiO2 nanoparticles were in a dispersed state within the microgels and the composites showed rapid (similar to minutes) sedimentation, which is useful for gravity separations. By using turbidometry to characterize the settling behavior of the organic-inorganic composites, it was found that the settling time decreases as the content of TiO2 increases within the particles. (c) 2007 Elsevier Inc. All rights reserved.