Hair-Inspired
Crystal Growth of HOA in Cavities of Cellulose Matrix via Hydrophobic–Hydrophilic
Interface Interaction
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Abstract
As one of the most ordinary phenomena
in nature, numerous pores on animal skins induce the growth of abundant
hairs. In this study, cavities of a cellulose matrix were used as
hard templates to lead the hair-inspired crystal growth of 12-hydroxyoctadecanoic
acid (HOA) through hydrophobic–hydrophilic interface interaction,
and short hair-like HOA crystals with a smooth surface were formed
on cellulose films. In our findings, by using solvent evaporation
induced crystallization, hydrophobic HOA grew along the hydrophilic
cellulose pore wall to form regular vertical worm-like and pillar-like
crystals with an average diameter of about 200 nm, depending on the
experimental conditions and HOA concentration. The formation mechanism
of the short hair-like HOA crystals as well as the structure and properties
of the cellulose/HOA submicrometer composite films were studied. The
pores of the cellulose matrix supplied not only cavities for the HOA
crystals fixation but also hydrophilic shells to favor the vertical
growth of the relatively hydrophobic HOA crystals. The cellulose/HOA
submicrometer composite films exhibited high hydrophobicity, as a
result of the formation of the solid/air composite surface. Furthermore,
4-(1,2,2-triphenylethenyl) benzoic acid, an aggregation-induced emission
luminogen, was used to aggregate on the cellulose surface with HOA
to emit and monitor the HOA crystal growth, showing bifunctional photoluminscence
and self-cleaning properties. This work opens up a novel one-step
pathway to design bio-inspired submicrometer materials by utilizing
natural products, showing potential applications in self-cleaning
optical devices