Multifunctional Parylene-C Microfibrous Thin Films

摘要

Towards sustainable development, multifunctional products have many advantageous over single-function products: reduction in number of parts, raw material, assembly time, and cost involved in a product's life cycle. My goal for this thesis was to demonstrate the multifunctionalities of Parylene-C microfibrous thin films.;To achieve this goal, I chose Parylene C, a polymer, because the fabrication of periodic mediums of Parylene C in the form of microfibrous thin films (muFTFs) was already established. A muFTFs is a parallel arrangement of identical micrometer-sized fibers of shapes cylindrical, chevronic, or helical. Furthermore, Parylene C had three existing functions: in medical-device industries as corrosion-resistive coatings, in electronic industries as electrically insulating coatings, and in biomedical research for tissue-culture substrates.;As the functionalities of a material are dependent on the microstructure and physical properties, the investigation made for this thesis was two-fold: (1) Experimentally, I determined the wetting, mechanical, and dielectric properties of columnar muFTFs and examined the microstructural and molecular differences between bulk films and muFTFs. (2) Using physical properties of bulk film, I computationally determined the elastodynamic and determined the electromagnetic filtering capabilities of Parylene-C muFTFs.;Several columnar muFTFs of Parylene C were fabricated by varying the monomer deposition angle. Following are the significant experimental findings: 1. Molecular and microstructural characteristics: The dependence of the microfiber inclination angle on the monomer deposition angle was classified into four regimes of two different types. X-ray diffraction experiments indicated that the columnar muFTFs contain three crystal planes not evident in bulk Parylene-C films and that the columnar muFTFs are less crystalline than bulk films. Infrared absorbance spectra revealed that the atomic bonding is the same in all columnar muFTFs and bulk films. The static hydrophobicity of columnar muFTFs was found to be anisotropic and can be maximized by a proper choice of monomer deposition angle. In contrast, the hydrophobicity of bulk film is isotropic. 2. Mechanical properties: Dynamic storage and loss moduli of columnar muFTFs were determined in the 1 to 80 Hz frequency range for temperatures between --40 °C and 125 °C in one of two orthogonal directions lying wholly in the substrate plane: either (i) normal or (ii) parallel to the morphologically significant plane of the muFTF. The storage and loss moduli for normal loading did not exceed their counterparts for parallel loading. All columnar muFTFs were found to be softer than a bulk film. In both bulk and columnar forms, Parylene C was found to be rheologically not simple. 3. Relative permittivity: The charge-storage and absorption properties measured for the columnar muFTFs in the 100 Hz--1 MHz frequency range over temperatures between --40 °C and 125 °C were lower than the bulk film. Internal surfaces of the columnar muFTFs were found to increase the charge-storage capacity. The lower charge-storage capability of columnar muFTFs suggests their possible applications as interlayer dielectrics. The frequency dependence of the relative permittivity of the columnar muFTFs was identified in terms of the Hashin-Shrtikmann model.;The elastodynamic bandgaps of Parylene-C muFTFs as phononic crystals were computationally determined for the columnar, chevronic, and chiral muFTFs. Microfibers were arranged either on a square or a hexagonal lattice with the host medium as either water or air. Following are the significant findings: 1. All bandgaps were observed to lie in the 0.01--162.9-MHz regime. The upper limit of the frequency of bandgaps was the highest for the columnar muFTFs and the lowest for the chiral muFTFs. More bandgaps were found to exist when the host medium is water than air. The presence of complete bandgaps suggests their use as bulk-acoustic-wave and surface-acoustic-wave filters. The softness of the Parylene-C muFTFs makes them mechanically tunable, and their bandgaps can be exploited in multiband ultrasonic filters.;An investigation was made to demonstrate Parylene-C muFTFs as circular-polarization filters. 1. The relative permittivity of bulk Parylene C was determined as a function of frequency between 15 THz and 149 THz. Potential application of chiral muFTFs as reflectors of thermal energy was identified. The circular Bragg regime for chiral muFTFs of Parylene C was identified as 31.8--35.2 THz, making them useful as circular-polarization band-rejection filters.