Spontaneous formation of sinuous and wavy micropatterns with helical growth of CuSO ₄•5H ₂O in polymer matrix

Various 2-D patterns of copper sulfate pentahydrate (CuSO ₄•5H ₂O) were spontaneously formed through crystal growth in a thin gelatin matrix on a glass plate. The form of the grown crystal changes from polyhedrons to irregularly branching morphologies with increasing the polymer density in the matrix. Characteristic patterns, such as sinuous dendrites and wavy lattices, are obtained under specific intermediate conditions. The formation of periodically curving sinuous trunks is based on the helical growth with a pile of tilted units of CuSO ₄•5H ₂O. The wavy microlattices are produced with periodical branching of the sinuous trunks. The characteristic 2-D patterns with the curving trunks and branches are achieved with the controlled growth of the triclinic crystal under a diffusion-limited condition in the polymer matrix.