Recruiting physisorbed water in surface polymerization for bio-inspired materials of tunable hydrophobicity

Abstract

International audienceChemical grafting has been widely used to modify the surface properties of materials, especially surface energy for controlled wetting, because of the resilience of such coatings/modifications. Reagents with multiple reactive sites have been used with the expectation that a monolayer will form. The step-growth polymerization mechanism, however, suggests the possibility of gel formation for hydrolyzable moieties in the presence of physisorbed water. In this report, we demonstrated that using alkyltrichlorosilanes (trivalent [i.e., 3 reactive sites]) in the surface modification of a cellulosic material (paper) does not yield a monolayer but rather gives surface-bound particles. We infer that the presence of physisorbed (surface-bound) water allows for polymerization (or oligomerization) of the silane prior to its attachment on the surface. Surface energy mismatch between the hydrophobic tails of the growing polymer and any unreacted bound water leads to the assembly of the polymerizing material into spherical particles to minimize surface tension. By varying paper grammage (16.2–201.4 g m À2), we varied the accessible surface area and thus the amount of surface-adsorbed water, allowing us to control the ratio of the silane to the bound water. Using this approach, polymeric particles were formed on the surface of cellulose fibers ranging from $70 nm to a film. The hydrophobicity of the surface, as determined by water contact angles, correlates with particle sizes (p < 0.001, Student's t-test), and, hence, the hydrophobicity can be tuned (contact angle between 94 and 149). Using a model structure of a house, we demonstrated that as a result of this modification, paper-based houses can be rendered self-cleaning or tolerant to surface running water. In another application, we demonstrated that the felicitous choice of architectural design allows for the hydrophobic paper to be used for water harvesting

Waterproof, Breathable, and Antibacterial Self‐Powered e‐Textiles Based on Omniphobic Triboelectric Nanogenerators

“…The silanized textile fibers of the R F ‐TENGs do not show significant multi‐layer texturing artifacts since their silanization was completed in ≈10 min, at room temperature. Multi‐layer texturing is expected, however, when the reaction is performed at higher temperatures (95 °C) or for longer times (>30 min), due to the formation of small polymeric particles on the surface of the textile . We then sprayed a 5 wt% suspension of Ag nanoflakes (AgNFs) in toluene over the fabric through a laser cut Teflon stencil mask and let it dry in a desiccator at 36 Torr for 20 min.…”

Paper-based microfluidic devices by asymmetric calendaring

“…When such pressure is targeted/localized, and with the appropriate lubrication to mitigate fiber damage, a channel can be created (Figure 2(a)). We 28,29 and others 5,[30][31][32][33][34][35][36] have shown that paper can be rendered hydrophobic by treatment with alkyl trichlorosilanes (Figures 1(b) and 1(c); see details in the supplementary material Figure S1). 29 We, therefore, hypothesized that co-deposition of an appropriately functionalized silane during the asymmetric calendaring could lead to a channel with desired wetting properties.…”

Engineering tunable bio-inspired polymeric coatings for amphiphobic fibrous materials

“…This assumption hinges on the disproved notion that monolayers are formed when the paper is silanized. We, however, showed that silane molecules instead polymerizes to form cross-linked networks [33], an intuitive preposition considering that trihalosilanes and water are monomers with multiple reactive head groups. Thus, high grammage blotting paper treated with 1H,1H,2H,2H-trichloro (perfluorooctyl)silane was thermally degraded and the byproducts; i) gas, ii) solid, ii) liquid phases were analyzed.…”

“…For example, Belgacem [87] used trialkoxy silanes in either water or alcohol to modify cellulose-a mechanistic paradox since the reactive moiety on cellulose -OH, a moiety that is abundant in the medium of choice. The deposition of a perfluorosilane molecule onto the cellulose fibers in paper rapidly produces hydrophobic surfaces, [33] allowing the paper to be used as a substrate material for bio-analytical devices, microfluidics, self-cleaning surfaces, among others. [3,9,25,70,71,73,75,77,79,80,[88][89][90][91][92][93][94][95] We recently used trichlorosilanes to understand the underlying mechanisms and coupled it to the resulting materials properties, and expanded these reactions beyond pure cellulosic materials.…”

“…Countless ways to achieve surface modification of cellulosic material have been reported in literature. [25][26][27][28][29][30][31][32][33][34] Among them, the most common one is by functionalization with silanes. These molecules are well known for their ability to change the wetting properties of surfaces, without jeopardizing the mechanical properties of the substrate.…”