Thermocapillary and electrohydrodynamic manipulation of soft material in thin film and laminate device
Creators: name: Ma, Tianxing
Publisher: name: No Publisher Supplied
Year: 2021

description: With thin film materials applied more ubiquitously to industrial applications, the demand for scalable low-cost thin film devices has surged. Generally, a tradeoff between device cost, efficiency, and speed has to be made during the manufacturing processes. As a result, challenges exist in exploring new mechanisms that enable the scalable fabrication and examination of thin film devices.Among the non-cleanroom thin film manufacturing techniques, such as inkjet printing, gravure printing, and screen printing, most processes involve the manipulation of soft material in their liquid state. Due to the small scale of the material, capillary forces play an important role. The ability to control the capillary force using external fields is thus vital for these processes. With progress made on laser and electronic techniques, thermal and electrical methods to manipulate materials are on a higher technical readiness level. Specifically, this dissertation looks into applying extreme thermal and electrical field and the induced thermocapillary stress and electrocapillary stress to manipulate the flow of soft material in and out of plane for the synthesis, measurement of nanomaterials, and the design of scalable laminate device. Three aspects are investigated by this dissertation. (1) Focused laser spike (FLaSk) dewetting of gold thin film on glass substrate: Parametric study of overlapping laser scans on gold nanofilm deposited on glass/fused quartz is conducted to unveil the influence of numerical aperture, laser power, and substrate effect. Through FLaSk dewetting of a gold thin film on a meltable substrate, densely packed nanoparticle arrays are manufactured in and out of the plane via laser induced localized physical vapor deposition. (2) FLaSk thermocapillary dewetting based thin film rheology for soft material films that uses an optical microscope to characterize the thin film’s flow behavior under thermocapillary stress: FLaSk Thermocapillary dewetted hole radius is used as a metrics for studying the soft material nano film’s rheological properties. By designing a multilayer heating substrate, a top material-independent thermal field is established and calibrated by melting of crystal material. Dot-exposure type FLaSk dewetting on nanofilms with different material composition and thickness is conducted. The nonlinear radii size evolution is captured by a stretched exponential function and the decay time is used for probing the film’s viscosity. Extracted viscosities on different films demonstrate how FLaSk thermocapillary dewetting can be used for probing rheological properties of thin films. (3) Switchable electrohydrodynamic (EHD) capillary bridge oscillator: The behavior of microliter sized opposing sessile droplets in ~ kV/mm electric field in a parallel plate capacitor is investigated. Based on whether the droplets could be actuated into a stable capillary bridge in electric field that is unstable without the electric field, the motions are characterized into multiple phases. The mechanism is explained by free energy analysis and experimental testing of fluids with various physical properties in different electric field and gap size. The study has enabled using electrocapillary phenomena to control the morphology change of microliter-sized droplets in a simple configuration suitable for the design of a thin sheet device compatible with mass fabrication. Finite element method simulations are conducted in a combination of experimental results for the understanding of the physics. Progress made in each aspect of this dissertation could serve as the stepstone for the development of scalable ways of applying thermocapillary stress and electrocapillary effect for the rapid fabrication/characterization of low-cost thin-film devices.