Ionic fluorinated polyphosphazenes (FPs) were used in all-aqueous layer-by-layer (LbL) assemblies to control the hydrophobicity of ultrathin polymer coatings over a wide range, ultimately reaching a contact angle (CA) &gt;120° on flat surfaces. In this work, we focus on the self-assembly conditions of carboxylated FPs with polyamines, showing that control over both the surface morphology and chemistry is achieved by varying the degree of FP fluorination (up to 77%), polyamine structure, and deposition pH. Importantly, atomic force microscopy revealed well-defined microphase domains whose formation is likely driven by the hydrophobicity of the fluorinated groups and further assisted by neutralization of charges during assembly. The CA was governed by the parameters of the phase-separated domains and ionization of FP carboxyl groups; however, the CA hysteresis was consistently &gt;100° on flat surfaces, demonstrating the highly adhesive nature of the coating. Depositing as few as five bilayers (~25 nm) on a microstructured, rather than flat, silicon substrate resulted in a superhydrophobic surface (CA &gt;150°) with an attenuated CA hysteresis dependent on both the deposition conditions and structural dimensions. Lastly, we demonstrate pH-selective droplet transfer between surfaces with either different microstructure or deposition pH. The demonstrated capability of hydrophobic FP LbL coatings to have programmable adhesion and transfer of water droplets between surfaces can be used in droplet-based microfluidics and water collection/harvesting.

Highly hydrophobic, pH-responsive, nanostructured layer-by-layer coatings from anionic fluorinated polyphosphazenes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.