Nacre is a multilayered film material consisting of alternating layers of aragonitic tablets and organic membranes (OMs). However, at this time, no authors have discussed the growth mode of nacre from the perspective of the science of typical film materials. Here, for the first time, we focus on measuring the contact angles of the nacre growth surface (GS) using the contact angle meter. Additionally, we also investigate the GS's structure and phases using field emission scanning electron microscopy and X-ray diffractometer, respectively. We firstly found that: (1) The contact angles of the GS are always greater than 90°, with a maximum value of 113° and minimum value of 91°, indicating that the GS is hydrophobic. (2) The growth mode of GS is similar to the island growth mode (V-W) of the typical films. (3) The hydrophobicity of OMs plays an important role in the nucleation and growth of nacre. This research may provide new insights into the mechanism underlying nacre formation. In the field of thin-film, this conclusion will provide a new direction for the preparation and research of hydrophobic substrates, and a new idea for the development of thin-film technology.

Nacre has long served as a research model in the field of biomineralization and biomimetic materials. It is widely accepted that its basic components, aragonite biocrystals, namely, tablets, are formed by the nanoparticle-attachment pathway. However, the details of the nanoparticle morphology and arrangement in the tablets are still a matter of debate. Here, using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), we observed the nanostructure of the growing tablets at different growth stages and found that: (1) the first detectable tablet looked like a rod; (2) tablets consisted of subhedral nanoparticles (i.e., partly bounded by crystal facets and partly by irregular non-crystal facets) that were made of aragonite single crystals with a width of 160–180 nm; and (3) these nanoparticles were ordered in orientation but disordered in position, resulting in unique subhedral and jigsaw-like patterns from the top and side views, respectively. In short, we directly observed the growth of nacre biocrystals by the self-assembly of aragonite nanoparticles with a novel subhedral morphology.

The hydrophobic substrate has an effect on the non-classical crystallization of nacreous aragonite crystals.