This work reports
a simple approach to form, study, and utilize rough coatings that
prevent the adhesion of gallium-based liquid metal alloys. Typically,
liquids with large interfacial tension do not wet nonreactive surfaces,
regardless of surface topography. However, these alloys form a surface
oxide “skin” that adheres to many substrates, even those
with low surface energy. This work reports a simple approach to render
closed channels and surfaces, including soft materials, to be “oxide-phobic”
via spray-coating (NeverWet, which is commercially available and inexpensive).
Surface spectroscopic techniques and metrology tools elucidate the
coatings to comprise silica nanoparticles grafted with silicones that
exhibit dual length scales of roughness. Although prior work shows
the importance of surface roughness in preventing adhesion, the present
work confirms that both hydrophobic and hydrophilic rough surfaces
prevent oxide adhesion. Furthermore, the coating enables reversible
actuation through submillimeter closed channels to form a reconfigurable
antenna in the gigahertz range without the need for corrosive acids
or bases that remove the oxide. In addition, the coating enables open
surface patterning of conductive traces of liquid metal. This shows
it is possible to actuate liquid metals in air without leaving neither
metal nor oxide residue on surfaces to enable reconfigurable electronics,
microfluidics, and soft electrodes.
This paper describes surface functionalization of poly(ethylene terephthalate) (PET) films by transamidation of the ester groups with primary amines. The use of water as a solvent improves tremendously the reaction rate and yield compared to conventionally used alcohols. In this study, PET films were exposed to an aqueous solution of 3-aminopropyltriethoxysilane (APTES), which resulted in ester-to-amide reactions on the surface of the film. Hydrolysis of the resulting ethoxy moieties in APTES creates hydroxyl groups that can be used as anchoring points for further modification of PET films. This scheme offers an alternative approach to modify polyesters using water as the solvent.
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