Self-Assembly of Chiral Menthol Molecules from a Liquid Film into Ring-Banded Spherulites

Abstract

We investigate the growth of spherulites in the wake of a solidification front in a thin film of liquid menthol. We observed that the two enantiomeric forms of menthol ((−)-menthol and (+)-menthol)) form ring-banded spherulites, in which needle-like crystals self-assemble into high-and low-density crystal regions. Interestingly, the racemic mixture produces nonbanded spherulites consisting of closely packed plate-like crystals. In the ring-banded spherulitic growth, we could clearly identify the curvature effect of the solidification front on the pattern formation on a millimeter spatial scale. We developed a numerical model based on the Cahn− Hilliard equation, which qualitatively describes the main features observed in experiments, namely, the formation of periodic ring-banded structures and the curvature effect of the propagating solidification front.

Features of L-Menthol Crystallization in Optically Active Medium Based on L- and D-Asparaginate Chitosan

“…We should also dwell on the difference in orientational ordering and supramolecular chirality of non-banded crystal structures obtained in this work in an optically active aqueous medium and in an achiral aqueous medium in Ref. [15]. Non-banded L-menthol spherulites during thermally induced phase separation (in the absence of a liquid medium) are formed due to the spatial growth of lamellar crystals or of whiskers during extraction crystallization in a chiral aqueous medium.…”

“…Depending on the conditions of phase separation (temperature gradient, cooling rate, substrate structure, solvent, and precipitating medium), it is characterized by a variety of morphostructures formed in this process. For example, ring-shaped spherulites are formed during thermally induced crystallization from a melt in an air atmosphere, in which acicular crystals (whiskers) of L-menthol selforganize into radially oriented periodic regions with high and low densities of the solid phase of the substance, or non-banded continuous spherulites, consisting of densely packed lamellar crystals [15]. Such rhythmic crystallization could be due to the chirality of L-menthol [16], as well as nonlinear diffusion of the substance during mass transfer [17,18] and the "unbalanced" surface energy of the system [19].…”

Large‐scale chiral spherulites with controllable circularly polarized luminescence in liquid crystal block copolymers film

“…[4] To achieve macroscopic chiral structures and their specific functions in biological systems, hierarchical chiral assembly has been developed to construct multidimensional large-scale chiral structures, [5][6][7][8][9] including helical fibres [10,11] or ribbons, [12] chiral flowers, [13,14] spiral tubes, [15] and chiral spherulites. [16][17][18] Then, multifunctional materials with chiral response have been prepared by introducing fluorescent molecules or other functional molecules in situ into the chiral structures, which exhibit significant applications in the fields of biological probes and signatures, [19] chiral metamaterials, [20,21] flexible film, [22,23] and 3D optical displays. [24,25] In particular, chiral spherulites (including band spherulites), as a common morphology of crystalline poly-mers, are extensively exploring credit to their diverse crystal morphology which has a tremendous impact on material properties.…”

Self-organization of nanoparticles and molecules in periodic Liesegang-type structures

“…The repetition of the precipitation process yields periodic precipitate bands. In the second group of experiments, periodic ring-type structures form in a system that initially has a spatially uniform distribution of components but undergoes phase separation or crystallization (15,16).…”