Date of Award

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Materials Science and Engineering

Advisor

Dr. Igor Luzinov

Committee Member

Dr. Stephen H. Foulger

Committee Member

Dr. O. Thompson Mefford

Committee Member

Dr. Scott M. Husson

Committee Member

Dr. Ruslan Burtovyy

Abstract

Anchoring thin polymer films to metal surfaces allows us to alter, tune, and control their biocompatibility, lubrication, friction, wettability, and adhesion, while the unique properties of the underlying metallic substrates, such as magnetism and electrical conductivity, remain unaltered. This polymer/metal synergy creates significant opportunities to develop new hybrid platforms for a number of devices, actuators, and sensors. This present work focused on the synthesis and characterization of polymer layers grafted to the surface of metal objects. We report the development of a novel method for surface functionalization of arrays of high aspect ratio nickel nanowires/micronails. The polymer 'grafting to' technique offers the possibility to functionalize different segments of the nickel nanowires/micronails with polymer layers that possess antagonistic (hydrophobic/hydrophilic) properties. This method results in the synthesis of arrays of Ni nanowires and micronails, where the tips modified with hydrophobic layer (polystyrene) and the bottom portions with a hydrophilic layer (polyacrylic acid). The developed modification platform will enable the fabrication of switchable field-controlled devices (actuators). Specifically, the application of an external magnetic field and the bending deformation of the nickel nanowires and micronails will make initially hydrophobic surface more hydrophilic by exposing different segments of the bent nanowires/micronails. We also investigate the grafting of thin polymer films to gold objects. The developed grafting technique is employed for the surface modification of Si/SiO2/Au microprinted electrodes. When electronic devices are scaled down to submicron sizes, it becomes critical to obtain uniform and robust insulating nanoscale polymer films. Therefore, we address the electrical properties of polymer layers of poly(glycidyl methacrylate) (PGMA), polyacrylic acid (PAA), poly(2-vinylpyridine) (P2VP), and polystyrene (PS) grafted to the Si/SiO2/Au microprinted electrodes. The polymer layers insulated under normal ambient conditions can display a significant increase in conductivity as the environment changes. Namely, we demonstrate that the in-plane electrical conductivity of the grafted polymer layers grafted to Au and SiO2 surfaces can be changed by at least two orders of magnitude upon exposure to water or organic solvent vapors. The conductive properties of all the grafted polymer films under study are also significantly enhanced with temperature increase. The observed phenomenon makes possible the chemical design of polymer nanoscale layers with reduced or enhanced sensitivity to anticipated changes in environmental conditions. Finally, we show that the observed effects can be used in a micron-sized conductometric-transducing scheme for the detection of volatile organic solvents. This research also includes the study of nanoscale-level actuation with grafted polymer films and polymer/gold nanoparticles systems-grafted composites. First, we investigate the nanoscale-level actuation with polymer films. To this end, we use 'grafting to' approach to synthesize PGMA thin polymer film (80-200 nm). Then, film is swollen in a good solvent and freeze-dried until the solvent is sublimated, thereby creating grafted polymer nanofoam that exhibits shape memory properties. We demonstrate nanoscale actuation using the developed system. In addition, we show that the modification of the PGMA nanofoam with low molecular weight polystyrene allows response tuning of the porous polymer film. Furthermore, we incorporate gold nanoparticles (5 nm) into a thin PGMA layer (80 nm) to fabricate a PGMA/gold nanoparticles grafted composite film. The PGMA/gold nanoparticles grafted nanofoam is synthesized following the same procedure developed for the fabrication of the PGMA nanofoam. We demonstrate the shape-memory properties and nanoscale-level actuation of the developed system. Moreover, we investigate the change in the optical signal of the developed system as a function of temperature arising from the localized surface plasmon resonance and plasmon coupling effects of the gold nanoparticles. We envision that the change in optical properties upon actuation can be utilized to develop platforms for new off-line sensing devices.

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