Sustainable and Practical Superhydrophobic Surfaces via Mechanochemical Grafting

Abstract

contact angle (>150°) and readily roll off at low sliding angles. [1][2][3] Popularized by the discovery and elucidation of selfcleaning mechanism of lotus leaves, [4,5] superhydrophobic surfaces have attracted significant attention for practical applications such as self-cleaning solar cells, [6][7][8] corrosion inhibition layers on metal surfaces, [9,10] anti-icing coatings, [11,12] and oil/water separation membranes and meshes. [13][14][15] Superhydrophobic surfaces have been adopted in a number of niche applications such as blood-repellent garments, [16] anti-biofouling coatings, [17,18] and to concentrate molecules for bio-assay analysis and increase detection limit. [19,20] Superhydrophobic surfaces feature heterogeneous morphology with nanoscopic and microscopic roughness in the form of protrusions separated by air pockets and are generally fabricated by using low surface energy materials. [21] The combination of nano/micro-scale protrusions with low surface energy leads to diminished adhesion and improved droplet mobility.The excessive usage of solvents and toxic chemicals, long and tedious chemical processes, limited biocompatibility, and costly materials are challenges in the sustainable fabrication of superhydrophobic surfaces. A convenient and universal method, also adapted in commercialThe broad adoption of superhydrophobic surfaces in practical applications is hindered by limitations of existing methods in terms of excessive usage of solvents, the need for tedious and lengthy chemical processes, insufficient biocompatibility, and the high cost of materials. Herein, a mechanochemical approach for practical and solvent-free manufacturing of superhydrophobic surfaces is reported. This approach enables solvent-free and ultra-rapid preparation of superhydrophobic surfaces in a single-step without the need for any washing, separation, and drying steps. The hydrolytic rupture of siloxane bonds and generation of free radicals induced by mechanochemical pathways play a key role in covalent grafting of silicone to the surface of nanoparticles that leads to superhydrophobic surfaces with a water contact angle of >165° and a sliding angle of <2°. The direct use of industrially available and nonfunctional silicone materials together with demonstrated applicability to inorganic nanoparticles of varied composition greatly contribute to the scalability of the presented approach. The resulting superhydrophobic surfaces are highly biocompatible as demonstrated by fibroblast cells using two different assays. Monolith materials fabricated from silicone-grafted nanoparticles exhibit bulk and durable superhydrophobicity. The presented approach offers tremendous potential with sustainability, scalability, cost-effectiveness, simplicity, biocompatibility, and universality.

Mechanochemical Coupling of Alkylsilanes to Nanoparticles for Solvent-Free and Rapid Fabrication of Superhydrophobic Materials

“…Shown in Figure b is the TGA curve of the powders obtained using different amounts of alkylsilane. The small and gradual weight loss observed up to ∼450 °C is due to physically adsorbed molecules, while the sudden weight loss starting from 500 °C indicates the presence of grafted alkylsilane molecules. , The calculation reveals that when 400 μL of alkylsilane was used, approximately 0.94 alkylsilane molecules per nm were grafted onto the SiO 2 nanoparticle surface (refer to the Supporting Information for details). This grafting density is similar to the findings of a previous study .…”

“…Second, ball milling leads to local (a few hundred μm) and transient (tens of milliseconds) heating that can lead to the acceleration of the reaction. 51,60 The direct reaction of the alkylsilane with surface silanol groups cannot be ruled out.…”

“…Recently, we have shown mechanochemical grafting of poly(dimethylsiloxane) to metal oxide nanoparticles for the practical and sustainable preparation of superhydrophobic surfaces. 51 This work motivates the exploration of mechanochemical processes for grafting other hydrophobic molecules. Alkylsilanes, with their wide usage and strong hydrophobicity, are of significant interest in the preparation of superhydrophobic coatings.…”

“…49 This mechanochemical process is generally much faster than those carried out using traditional wet-chemistry methods. 50,51 In recent years, ball milling has been utilized for a variety of applications, including the solvent-free synthesis of drugs like dantrolene, catalytic ligands, graphene, nanoparticles, and modification of the surface properties of nanoparticles. 52−56 Therefore, ball milling has been proven to be a convenient, eco-friendly, rapid, and low-cost approach to processing chemical reactions.…”

“…Ball milling has recently re-emerged as a solventless technique for processing chemical reactions. − This process involves the use of a ball mill, which provides energy to drive chemical reactions in a solvent-free environment . This mechanochemical process is generally much faster than those carried out using traditional wet-chemistry methods. , In recent years, ball milling has been utilized for a variety of applications, including the solvent-free synthesis of drugs like dantrolene, catalytic ligands, graphene, nanoparticles, and modification of the surface properties of nanoparticles. − Therefore, ball milling has been proven to be a convenient, eco-friendly, rapid, and low-cost approach to processing chemical reactions. Recently, we have shown mechanochemical grafting of poly­(dimethylsiloxane) to metal oxide nanoparticles for the practical and sustainable preparation of superhydrophobic surfaces .…”