Gel network incorporation into single-crystals: effects of gel structures and crystal–gel interaction

Gel-grown single-crystal composites where gel networks are incorporated inside single-crystals have been reported in an increasing number of studies, with the composite structure similar to that of the biogenic biomacromolecule-incorporated single-crystals. However, the mechanisms of the gel incorporation are still not clear. In this work, we examined the growth of four types of crystals (NaF, NaCl, KBr and potassium dihydrogen phosphate (KDP)) in both silica gels and agarose gels to assess the effects of the crystal–gel interaction and the gel structure on the gel incorporation. In all of the eight crystal–gel pairs, single-crystals were obtained by single-crystal X-ray diffraction analysis. Dissolution of the crystals revealed that all of the four types of crystals grown from the agarose gels incorporated the gel networks during crystallization. In contrast, NaF and KDP crystals incorporated the silica gel networks but NaCl and KBr did not when grown from silica gels. The discrepancies among the eight crystal–gel pairs suggest that crystal–gel interaction (hydrogen bond) and fibre-like gel structure with large gel strength favour the gel incorporation. This work may facilitate understanding of the formation mechanisms of single-crystal composites.