A biomimetic in situ synthesis of CdS in PEO has been devised, which produces composites in which the inorganic phase displays uniformity of size, morphology, phase, and crystallographic orientation. Such regularity is displayed in thin composite firms (<300 nm thick); in analogous thick films (approximate to 200 mu m thick) only amorphous CdS is produced. Molecular level solvation, matrix preorganization, and strong binding of the inorganic reagents have been shown to be critical for matrix mediation. Solvation or relaxation of the matrix leads to loss of control over crystallization. Addition of a surfactant, AOT, to the reaction system has been shown to effect uniformity of CdS crystal orientation, size, and morphology in thin films.