Investigating wetting characteristics on microstructured surfaces for superhydrophobicity and metal microcasting

superhydrophobic;superhydrophobicity;ultrahydrophobic;ultrahydrophobicity;micromolding;Nanoimprint lithography (NIL)

Cannon, Andrew H.

关键词: superhydrophobic;    superhydrophobicity;    ultrahydrophobic;    ultrahydrophobicity;    micromolding;    Nanoimprint lithography (NIL);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/14748/Cannon_Andrew.pdf?sequence=2&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The engineering of liquid behavior on surfaces is important for infrastructure, transportation,manufacturing, and sensing. Surfaces can be rendered superhydrophobic by microstructuring,and superhydrophobic devices could lead to practical corrosion inhibition, self-cleaning, fluidflow control, and surface drag reduction. To more fully understand how liquid interacts withmicrostructured surfaces, this dissertation introduces a direct method for determining dropletsolid-liquid-vapor interfacial geometry on microstructured surfaces. The technique performsmetrology on molten metal droplets deposited onto microstructured surfaces and then frozen.Unlike other techniques, this visualization technique can be used on large areas of curved andopaque microstructured surfaces to determine contact line. This dissertation also presentsmeasurements and models for how curvature and flexing of microstructured polymers affectshydrophobicity. Increasing curvature of microstructured surfaces leads to decreased slide anglefor liquid droplets suspended on the surface asperities. For a surface with regularly spacedasperities, as curvature becomes more positive, droplets suspended on the tops of asperities aresuspended on fewer asperities. Curvature affects superhydrophobicity because microscopiccurvature changes solid-liquid interaction, pitch is altered, and curvature changes the shape ofthe three phase contact line. This dissertation presents a model of droplet interactions withcurved microstructured surfaces that can be used to design microstructure geometries thatmaintain the suspension of a droplet when curved surfaces are covered with microstructuredpolymers. Controlling droplet dynamics could improve microfluidic devices and the shedding ofliquids from expensive equipment, preventing corrosion and detrimental performance. Thisdissertation demonstrates redirection of dynamic droplet spray with anisotropic microstructures.Superhydrophobic microstructured surfaces can be economically fabricated using metalembossing masters, so this dissertation describes casting-based microfabrication of metalmicrostructures and nanostructures. Low melting temperature metal was cast into flexiblesilicone molds which were themselves cast from microfabricated silicon templates. Theflexibility of the silicone mold permits casting of curved surfaces, which this dissertationdemonstrates by fabricating a cylindrical metal roller with microstructures. The metalmicrostructures can be in turn used as a reusable molding tool. This dissertation also describesan industrial investment casting process to produce aluminum molds having integratedmicrostructures. Unlike conventional micromolding tools, the aluminum mold was large and hadcomplex curved surfaces. The aluminum was cast into curved microstructured ceramic moldswhich were themselves cast from curved microstructured rubber. Many structures weresuccessfully cast into the aluminum with excellent replication fidelity, including circular, square,and triangular holes. This dissertation demonstrates molding of large, curved surfaces havingsurface microstructures using the aluminum mold. This work contributes a more fullunderstanding of the phenomenon of superhydrophobicity and techniques for the economicfabrication of superhydrophobic microstructures.