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Master of Science / Department of Mechanical and Nuclear Engineering / Amy R. Betz / The purpose of this research was to test if biphilic surfaces mitigate frost and ice formation. Frost, which forms when humid air comes into contact with a surface that is below the dew point and freezing temperature of water, hinders engineering systems such as aeronautics, refrigeration systems, and wind turbines. Most previous research has investigated increasingly superhydrophobic materials to delay frost formation; however, these materials are dependent on fluctuating operating conditions and surface roughness. Therefore, the hypothesis for this research was that a biphilic surface would slow the frost formation process and create a less dense frost layer, and water vapor would preferentially condense on hydrophilic areas, thus controlling where nucleation initially occurs. Preferential nucleation can control the size, shape, and location of frost nucleation. To fabricate biphilic surfaces, a hydrophobic material was coated on a silicon wafer, and a pattern of hydrophobic material was removed using photolithography to reveal hydrophilic silicon-oxide. Circles were patterned at various pitches and diameters. The heat sink was comprised of two parts: a solid bottom half and a finned upper half. Half of the heat sink was placed inside a polyethylene base for insulation. Tests were conducted in quiescent air at room temperature, 22 °C, and two relative humidities, 30% and 60%. Substrate temperatures were held constant throughout all tests. All tests showed a trend that biphilic surfaces suppress freezing temperature more effectively than plain hydrophilic or hydrophobic surfaces; however, no difference between pattern orientation or size was noticed for maximum freezing temperature. However, the biphilic patterns did affect other aspects such as time to freezing and volume of water on the surface. These effects are from the patterns altering the nucleation and coalescence behavior of condensation.

The overarching objective of the investigations discussed herein is the development of a model experimental system for surface-enhanced infrared absorption (SEIRA) spectroscopy, with potential applicability in higher order infrared spectroscopic techniques, specifically, surface-enhanced two-dimensional infrared (SE-2D IR) spectroscopy. Theoretical predictions that accurately predict the stability of functionalized nanoparticles enable guided design of their properties but are often limited by the accuracy of the parameters used as model inputs. Hence, first, such parameterization limitations for the extended DLVO (xDLVO) theory are overcome using a size-dependent Hamaker constant for gold, interfacial surface potentials, and tilt angles of self-assembled monolayers (SAMs), which collectively improves the predictive power of xDLVO theory for modeling nanoparticle stability. Measurements of electrical properties of functionalized gold nanoparticles validate the predictions of xDLVO theory using these new parameterizations illustrating the potential for this approach to improve the design and control of the properties of functionalized gold nanoparticles in various applications. Next, a series of experiments were conducted to elucidate the behavior of various infrared active molecules in the presence of spherical gold nanoparticles of average diameter ∼20 nm. Here, the spectroscopic anomalies, specifically the shifted vibrational frequency and the dispersive lineshape observed in the infrared spectra for SCN- in the presence of gold nanoparticles provide direct evidence of SIERA. Nevertheless, it was evidenced that nanomaterial with plasmonic properties that extends into the infrared wavelengths are imperative in observing efficient infrared enhancements. Hence, nanomaterial indicating plasmonic properties extending into the infrared wavelengths were synthesized via a straightforward, seedless, one-pot synthesis. The gold nanostars prepared here indicated plasmonic behavior clearly extending into the near infrared, with simple plasmonic tunability via changing the buffer concentration used during synthesis. The systematic understanding achieved here in terms of theoretical prediction of nanoparticle stability, origin of infrared spectral anomalies in the presence of nanomaterials, and the preparation of infrared plasmonic material, collectively provides a resilient framework for the further investigation of surface-enhanced infrared spectroscopic techniques including SEIRA and SE-2D IR spectroscopies.

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