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Modified Scanning Probes for the Analysis of Polymer Surfaces

Barrios, Carlos A.
http://rave.ohiolink.edu/etdc/view?acc_num=akron1249315424

Abstract Details

2009, Doctor of Philosophy, University of Akron, Polymer Science.
Scanning probe microscopies (SPMs) allow the observation and measurement of surface properties on a highly local level based on the interaction between a very sharp probe and the surface. Interaction stability and probe integrity, at least during the scanning time, are necessary, but still a challenge. Conventional scanning probes have been used for revealing morphological features connected with macroscopic properties of complex latex films. These films, when dry, are sufficiently hard to be studied with minimal distortion of the surface by the probe. By comparing formulations with various fluorosurfactant concentrations, it was demonstrated how the fluorosurfactant, which is known heuristically to improve leveling, gives the system more mobility before drying. Specifically, in styrene-butadiene copolymer formulations, sub-micrometer differences in surface morphology, observed as a function of fluorosurfactant concentration, correlated with differences in gloss. In some cases, surfaces are too soft or too adhesive to be studied by conventional probes. Modification of scanning probes with hydrophobic layers having methyl or fluorinated end groups has been used to weaken the probe-surface interaction to study model adhesive surfaces. Acrylic block copolymers with well-defined molecular weight and composition were synthesized by controlled radical polymerization to create models of pressure sensitive adhesives to evaluate performance after aging or humidity exposure.Macroscopically, tack measurements demonstrated that blending a triblock copolymer with a homopolymer of the midblock polymer can be used to tailor the tack value. Microscopically, force-penetration curves of the acrylic blends showed a superficial phase separation into two mixed phases as homopolymer content was increased. Hydrophobic modification made it possible to measure these surfaces that would otherwise be too adhesive to study with conventional probes. Modification of scanning probes has also been used to bring robustness to high resolution chemical imaging. Addition of a 2-3 nm Al2O3 protective layer on silver-coated scanning probes dramatically reduced degradation of the probes with time, without sacrificing initial probe efficiency. In addition, the protective layer improved markedly the wear resistance of the probes. The surface morphology of the silver structure was not altered and the signal enhancement decay was completely stopped. These results agree with the conjecture that an ideal dielectric coating shifts the epicenter of the electromagnetic field enhancement in plasmonic structures, a behavior previously simulated, but not demonstrated. New types of plasmonic structure fabrication were also explored as means to surpass currently available signal enhancements by controlled size and shape, increased roughness or higher crystallinity. A single metal nano-pillar deposited by electron beam induced deposition (EBID), crystalline dendritic structures deposited by metal replacement reactions, and layers with sharper asperities deposited by ion sputtering were all fabricated on conventional scanning probes. The last produced a significant enhancement. In addition, strong signal fluctuations in Raman band intensity (“blinking”), similar to those seen in single molecule surface enhanced Raman spectroscopy, were also observed. This approach opens exciting new possibilities.
Mark Foster (Advisor)
174 p.
Analytical Chemistry; Materials Science; Optics; Physics; Polymers
scanning probe microscopy; SPM; AFM; modified probe; tip enhanced Raman spectrocopy; TERS; nanoRaman; plasmonics; ultrathin; dielectric; SERS; acrylic block copolymer; surface segregation; latex films; fluorosurfactant; SAM; scanning probes

Recommended Citations

Citations

  • Barrios, C. A. (2009). Modified Scanning Probes for the Analysis of Polymer Surfaces [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1249315424

    APA Style (7th edition)

  • Barrios, Carlos. Modified Scanning Probes for the Analysis of Polymer Surfaces. 2009. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1249315424.

    MLA Style (8th edition)

  • Barrios, Carlos. "Modified Scanning Probes for the Analysis of Polymer Surfaces." Doctoral dissertation, University of Akron, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1249315424

    Chicago Manual of Style (17th edition)

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© 2009, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.