An analysis of a polymer additive for calcium carbonate crystallization - a small-angle neutron scattering investigation by applying contrast variation

The role of the double-hydrophilic block copolymers (poly(ethylene glycol)-block-poly(methacrylic acid)) on the morphogenesis of calcium carbonate (CaCO₃) was studied by applying contrast variation small-angle neutron scattering (SANS). The scattering function for ternary systems can be expressed by only partial scattering functions of the single species, as derived on the assumption of incompressibility. We demonstrate the feasibility of this formula by means of contrast variation SANS, and the decomposed partial scattering functions give their detailed information. Especially the partial scattering function of polymer shows a Q^-2.7 monotonic slope at low Q (0.002 Å < Q < 0.02 Å; Q is the modulus of the scattering vector), which is a clear evidence that the distribution of the polymer in CaCO₃ has a mass fractal dimension. This result is confirmed by time-resolved SANS experiments with CaCO₃ contrast, where a Q^-2.5 slope was observed at the early stage of the reaction in the same Q range.