Structure of weakly bonded PPG-silica nanocomposites

The structure of silica-polypropyleneglycol (PPG) nanocomposites with weak physical bonds between the organic (PPG) and inorganic (silica) phase, prep ared by the sol-gel process, was investigated by small angle X-ray scatteri ng (SAXS). These nanocomposite materials are transparent, flexible, have go od chemical stability and exhibit high ionic conductivity when doped with l ithium salt. Their structure was studied as a function of silica weight fra ction x (0.06 less than or equal to x less than or equal to 0.29) and [O]/[ Li] ratio (oxygens being of ether-type). The shape of the experimental SAXS curves agrees with that expected for scattering intensity produced by frac tal aggregates sized between 30 and 90 Angstrom. This result suggests that the structure of the studied hybrids consists of silica fractal aggregates embedded in a matrix of PPG. The correlation length of the fractal aggregat es decreases and the fractal dimension increases for increasing silica cont ent. The variations in structural parameters for increasing Li+ doping indi cate that lithium ions favor the growth of fractal silica aggregates withou t modifying their internal structure and promote the densification of the o ligomeric PPG matrix.