Interfacial crystallization in the polyhedral liquid marbles

Abstract

Hypothesis: We hypothesized that interfacial crystallization occurring within evaporated polyhedral liquid marbles may be controlled by hydrophilization of the polymer plates coating the marbles. The hypothesis was tested with polyhedral marbles coated with hydrophobized and cold plasma-hydrophilized PET (Polyethylene terephthalate) plates.

Experiments: Interfacial crystallization within polyhedral liquid marbles was investigated experimentally. Two types of polyhedral marbles filled with saturated saline were prepared: i) liquid marbles coated with hydrophobized PET plates (Marbles A); ii) liquid marbles coated with Janus PET plates, one facet of which was plasma hydrophilized and the other hydrophobized (Marbles B). The hydrophobized side of the PET plate was in contact with the saline solution, whereas, the hydrophilized facet contacted air. Crystallization occurring within the marbles under their evaporation was monitored in situ.

Findings: It was established that for both kinds of marbles, NaCl crystallization was initiated at the edges of the plates. NaCl crystallization on the hydrophobized PET surfaces was not registered. When Marbles B were evaporated, the outer hydrophilic side of the PET plates was coated by the saline creep process. For both kinds of marbles the process resulted in the formation of hollow shells built of PET plates and NaCl crystals. The thermodynamic explanation of the observed phenomena is suggested.

Keywords: Interfacial crystallization; Janus marbles; Plasma hydrophilization; Polyhedral liquid marbles; Saturated saline.