Enhance understanding of rhythmic crystallization in confined evaporating polymer solution films: from environment to solution film and then to one period

It has been shown that rhythmic-crystallization-caused concentric ringed spherulites in polymer solution films can only be observed upon a confined slow evaporation. Here, by analysing the physical principle of evaporative crystallization, the special effects of experimental conditions on such rhythmic crystallization in a confined environment are explored via optical microscopy and atomic force microscopy observations. It is unveiled that the coupling of the confined conditions and extra solvent provides a suitable and stable solvent partial pressure that ensures the generation and continuation of rhythmic crystal growth. By slanting the substrate, the unusual dependences of radial growth rate and ring periodicity upon the film thickness are also illustrated. Finally, the growing front evolution and the melt-like growth in the induction time before the next period are demonstrated. These present findings significantly enhance our understanding of the rhythmic crystallization in evaporating polymer solution films.