Dip-coating crystallization on a superhydrophobic surface: a million mounted crystals in a 1 cm2 array

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Superhydrophobic surfaces exhibit extreme water repellency.
• Fabrication of micro-scale structures is crucial for various applications.
• Understanding liquid behavior on superhydrophobic surfaces is key.

Purpose of the Study:

• To investigate the behavior of superhydrophobic surfaces upon withdrawal from aqueous solutions.
• To explore the potential of this technique for controlled crystallization.
• To demonstrate the formation of micro-scale liquid droplets and crystalline arrays.

Main Methods:

• Photolithography was used to pattern silicon wafers with specific post dimensions and arrays.
• Vapor phase reaction with tridecafluorooctyldimethylchlorosilane created superhydrophobic surfaces.
• Dip-coating with aqueous sodium chloride solutions of varying concentrations was performed.

Main Results:

• Superhydrophobic surfaces emerged from water seemingly dry but retained sessile droplets.
• Dip-coating crystallization produced NaCl crystals of controlled sizes (∼1 μm and ∼500 nm) using different solution concentrations.
• The technique allows for the preparation of arrays of micro-scale liquid drops or crystalline substances.

Conclusions:

• Superhydrophobic surfaces retain femtoliter-scale water droplets upon withdrawal from liquids.
• Dip-coating crystallization is a viable method for fabricating controlled arrays of micro-scale crystals.
• This technique offers a simple approach for generating micro-scale liquid drops and crystalline structures.