Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

Abstract

Dewetting is a spontaneous phenomenon that occurs when unstable thin liquid films break apart on a non-wettable substrate, driven by unfavorable intermolecular forces at the interface. The Neto group has used dewetting of polymer films extensively in the last decade to generate patterned surfaces for a range of applications, including atmospheric water capture and cell patterning. [16][17][18][19][20][21] Dewetting of metastable thin polymer films (≈100 nm) occurs when the polymer is brought above its glass transition temperature (T g ), by either thermal or solvent annealing, to enable sufficient mobility of the polymer chains. During dewetting, holes appear in the initially uniform film, then grow with time, until eventually all the polymer is accumulated in isolate droplets on the substrate. When the polymer film is brought below its T g , the pattern is frozen in and preserved. [22][23][24][25][26] Spatially controlled alignment of the droplets or confinement of the dewetted areas can be induced by external stimuli such as stamp or probe, or by using prepatterned substrates. [14,[27][28][29] Sol-gel films are much more robust than polymer films as they are mostly inorganic in nature, so can withstand high working temperature and UV irradiation, are harder, and their refractive index and electronic properties can be modulated. [30][31][32][33] In the sol-gel process, inorganic polymers and ceramics are obtained starting from liquid precursors though hydrolysis and condensation reactions that lead the formation of a network structure called "gel.". This gel is then converted into a dense "xerogel" during the drying through expulsion of solvent and collapse of the porous network and eventually converted into a dense ceramic through calcination at high temperature (if required). [34,35] So far, the dewetting of sol-gel films has been studied only in a couple of papers. [36,37] In this paper, we investigated for the first time the dewetting of bilayers of sol-gel films: the top film is hydrophilic (silica) and the bottom one hydrophobic (CH 3silica), with the objective of producing silicate patterns that are both chemical and topographical in nature. The control of the wettability of the surface is obtained by chemical modification of the sol-gel network by using organic-modified silicon precursors with hydrophobic groups. [38,39] The produced patterns, hydrophilic bumps on a hydrophobic background, mimic the exoskeleton of the Namib desert beetle (which has ≈500 µm hydrophilic bumps on a waxy background), [17,40] and could facilitate the nucleation of water droplets via condensation Dewetting of thin polymer films has been extensively investigated as a way to generate patterned surfaces. In this paper, the controlled dewetting of sol-gel thin films induced by solvent annealing is reported. The key factors that control the dewetting process are identified and patterns with tunable diameter between 5 and 80 µm and tunable height between 1 and 10 µm are fabricated on a large scale. By changing the chemistry of the s...

Optimization of Hybrid Sol-Gel Coating for Dropwise Condensation of Pure Steam

“…When methyl group is introduced in the silica film, IR spectra exhibit some typical vibrations coming from the organic groups, especially in the range 3000-2800 cm −1 and 1300-1200 cm −1 . In particular, the clearest peak is the one centered at 1270 cm −1 , not present in the pure silica film spectra, and coming from the vibration of the methyl attached to Si [20,25,[27][28][29]. Other bands related to Si-CH 3 vibrations are less visible because they are partially overlapped and characterized by lower intensity, e.g., around 2950 cm −1 , the -CH 3 vibrations are overlapped by the board peak in the 3500-3000 cm −1 range, related to the O-H stretching of the physisorbed water and to the unreacted Si-OH stretching; around 780 cm −1 the C-H vibration is overlapped by the broadband of the Si-O-Si bond vibration [20,30].…”

Tailoring Materials with Specific Wettability in Biomedical Engineering

“…[ 59 , 60 ] With the development of science and technology, many advanced methods have been put forward to prepare materials especially biomaterials with specific wettability such as superwetting materials and SLIPS. [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 ,…”

“…So far, the popular chemical methods for surface modification include sol–gel method, layer‐by‐layer technique, self‐assembly, and chemical vapor deposition (CVD). [ 2 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 ] With decades of development, these methods have achieved great progress in fabricating various wettability materials in precise and controllable manner, paving the way for further application of these materials.…”

“…[ 97 , 98 ] In addition to fabricating surfaces with uniform wettability performance, sol–gel method is also suitable for manufacturing materials with composite wettability. [ 99 ] Layer‐by‐layer (LBL) technique has evolved into a relatively mature method for fabricating multilayered films with specific wettability, which depends on the electrostatic interaction among different layers such as polyanion and polycation. [ 100 , 101 , 102 ] To be specific, the positively and negatively charged layers are alternately deposited on the substrates until reaching the desired thickness.…”

Dewetting of Thin Lubricating Films Underneath Aqueous Drops on Slippery Surfaces

“…Thin polymer film used as the lubricating fluid in slippery surfaces often becomes unstable (dewetting) on solid surfaces due to its interaction with the substrate and test liquid by long-range interaction, short-range polar interaction, and other molecular forces [14,15]. Despite the * kcharya@iitk.ac.in large applications of the system when drop floats, instability pattern arises by rupturing of the film when the drop sinks, used in many applications like protein patterning, cell culture, contact lens production, and water harvesting [16][17][18][19][20][21][22][23][24].…”