(303d) Hierarchical Structures of PDMS-PU Copolymer and Particles for Hydrophobic Coatings

Development of durable functional coatings is a key focus for many industries. Tighter environmental regulations on the use of fluorinated compounds open a new avenue for green approaches to synthesize high performance, superhydrophobic coatings. To prepare such coatings both chemical and physical properties must be addressed. By combining hydrophobic properties of polydimethylsiloxane (PDMS) with those of mechanically robust polyurethane (PU) we have designed a durable hydrophobic polymer. The individual monomers were first linked into a copolymer using isocyanate and hydroxyl groups followed by dispersing the polymer in water. We used dip coating and layer-by-layer deposition approaches to coat cotton fabrics with this PDMS-PU polymer dispersion.

We assessed the effects of monomer molecular weight, particle size and hydrophobic particle effect to fabric coatings. Variation in molecular weight of individual PDMS and PU monomer units had a direct effect on the contact angle of the polymer coating. Lower molecular weight of the hydrophilic PU increased the water contact angle by ca. 20 °, while higher molecular weight of PDMS raised the contact angle by ca. 10 °. Addition of as low as 0.1 wt% of hydrophobized silica particles into the formulation also increased water contact angle by 10 ° and further increase was observed with additional silica content. Antisolvent precipitation of the polymer produced particles with different sizes, which allowed us to achieve hierarchical structure on the coated substrates. Controlling water addition rate enabled us to obtain different particle sizes, ranging from 70 nm to ~3 µm. Narrow particle size distributions allowed to establish a link between the particle size and water contact angle. The versatility of this polymer allows deposition of environmentally friendly hydrophobic coatings on many different substrates for various industries.