Design and Engineering of Slippery Liquid-Infused Porous Surfaces by LbL Technique for Icephobic Surfaces and Hydrodynamic Cavitation
Sheibani Aghdam, Araz (2020) Design and Engineering of Slippery Liquid-Infused Porous Surfaces by LbL Technique for Icephobic Surfaces and Hydrodynamic Cavitation. [Thesis]
In this thesis a phenomenon that had been observed in nature and has been explained by fluid dynamics and surface engineering, was mimicked to study its properties and potential applications. The slippery liquid-infused porous surfaces (SLIPS) technology, which is inspired by pitcher plant, has been developed using Layer-by-Layer (LbL) assembly technique. The roughness of the surface was provided by deposition of a thin film of silica nanoparticles on a substrate and then the porosities of the surface was filled by a lubricant to have a non-stick, ultra-repellent, self-healing, icephobic and hydrophobic SLIPS. The charged silica nanoparticles with a diameter range of 40 to 80nm were synthesized using Stöber method and their size and surface charge were adjusted by controlling the TEOS/Ammonia ratio. The synthesized silica nanoparticles were deposited on the surface of the substrate using LbL assembly technique via dip coating and fluidic coating methods. The SEM, AFM, UV-Vis and ellipsometry results confirmed the deposition of a rough coating with root mean square roughness of 30 to 15nm, young modules of 5.3Gpa, 98% transparency in visible region and thickness of 100 to 200 nm. The icephobic porosities of the assembled thin films, which were filled by a lubricant were evaluated using a homemade ice adhesion strength measurement setup in an environmental chamber. The ice adhesion strength of the prepared SLIPS was measured as less than 5kPa. The cycling and aging tests, which were carried out on the SLIPS showed 35% reduction in the icephobicity of the SLIPS after 100 days and the ice adhesion strength of the coatings was about 5 times lower than untreated samples even after 50 icing deicing cycles. Surface topography and properties have an important influence on the generation of cavitating flow in microscale. For studying the effect of SLIPS and the surface roughness on the cavitating flow, the designed SLIPS structure was layer-by-layer assembled using fluidic method on the hydrodynamic cavitation microchips with various hydraulic diameters. The microfluidic devices were exposed to upstream pressures varying from 1 to 7.23 MPa and it has been observed that the inception of the cavitating flow and supercavitation condition have been occurred at much lower pressures in comparison with non-treated microfluidic devices. Introducing the cellulose nanofiber-stabilized perfluoropentane droplets to the SLIPS assembled micro channels, reduced the upstream pressure down to 1.7 MPa for generation of the supercavitation flow pattern within the device. The cellulose nanofibers were assessed by AFM after the cavitation process and it was observed that they were left undamaged during the cavitation process due to the lower upstream pressure, which in turn, increased the regeneration potential of the droplets for closed-loop applications.
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