Effect of silica particles on hydrophobicity

In order to further improve the surface roughness of the coating, additives were added to the PDMS-PU coating formula. Control samples coated with 0.1wt%FS dispersion only absorbed water instantaneously in polymer-free isopropyl alcohol. As shown in the chart and digital image in Figure 4(a), the WCA of fabrics coated only with PDMS-PU(excluding FS) was 132°, and the WCA of fabrics (142°) increased by 10° when the FS content was 0.1wt%. The WCA of the fabric was further improved (145°) when coated with 0.5wt% FS. On the other hand, when the FS content of fabrics coated only with FS(without PDMS-PU) increased from 0.5wt% to 2.5wt%, the WCA increased from about 50° to 60°. In contrast, when the FS content in PDMS-PU dispersion was 2.5wt%, the fabric became superhydrophobic with an apparent WCA of 160°.

At low concentrations, FS could not completely cover the cotton fiber, and the water droplets were adsorbed on the fabric by capillary force. However, moderate hydrophobic PDMS-Pu particles may develop non-covalent interactions with cotton via hydrogen bonding, while FS may easily develop hydrophobic-hydrophobic interactions between its -CH3 group and PDMS-PU layer. FTIR studies of coated fabrics compared to FS and raw cotton showed that while there was no evidence of new covalent bonds between cotton, FS and polymer, strong hydrogen bonds were formed between polymer and fabric, The FS layer is also bound to the polymer by hydrophobic - hydrophobic interaction between methyl groups on both sides and hydrogen bond between the -OH group of FS and the polar group of the polymer (-NH or C-O-C).

In this study, a series of fluorine-free PDMS-PU structures were successfully synthesized and their water-based dispersions were used for superhydrophobic, mechanically strong, water-based and air-permeable coatings on mercerized cotton fabrics. Compared with polymer particle coatings of random size, the surface water contact Angle of the dispersion size and multilayer PDMS-PU particle coatings has better water repellant performance. In order to enhance the hydrophobicity of PDMS-PU coating, commercial hydrophobic gas phase silica particles were added to PDMS-PU coated cotton as a second coating, which were integrated through covalent bonds during polymer synthesis. A superhydrophobic, wet-resistant, mechanically strong coating can be obtained by coating the polymer coated cotton with gaseous silica particles as a second layer. Hydrophobicity did not change significantly even after 1000 wear cycles using standard wear test procedures. This work has shown that water-based, mechanically strong, breathable, and superhydrophobic coatings can be produced without the use of fluoridation. The layered coating method provides a new perspective for fine-tuning the hydrophobicity, air permeability and robustness of coating materials. We anticipate that these durable PDMS-PU polymer coatings can also be used to enhance a variety of surfaces, such as paper, polyester, and water-based dispersions for a variety of uses