Effect of different amphiphiles and their monolayers on the crystallization of CuSO4·5H2O†

Abstract

The crystallization of CuSO₄·5H₂O under a series of monolayers, 9-hexadecylimino-4,5-diazafluorene (hidf), 5-hexadecyliminomethyl-8-hydroxyquinoline (hihq), 8-hexadecyloxyquinoline-2-carboxylic acid (hqa) and stearic acid (sa) has been studied. The results demonstrate that the selection of the amphiphile for controlling oriented crystallization is very important. The hidf monolayer is the best template for oriented nucleation and growth of CuSO₄·5H₂O as its lattice structure can match the (010) face of CuSO₄·5H₂O perfectly. Furthermore, between CuSO₄·5H₂O and Na₂SO₄·7H₂O, only the hidf monolayer can choose CuSO₄·5H₂O to nucleate under it. The selection of a suitable phase of each monolayer for controlling the oriented crystallization is also a key factor in the induced crystallization. For example, when a hqa monolayer is in the gas or liquid phase its ability to induce oriented crystallization of CuSO₄·5H₂O is poor and the best state is not the most condensed one, rather a liquid–solid state. This is attributed to the co-ordination effect and the lattice matching between the inorganic and organic interfaces. The relationship between the surface pressure and area per molecule (π vs. A curves) and the monolayers’ ability to control crystallization is also discussed.