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Nanoscale Viscoelastic Characterization of Emerging Engineering Materials
The atomic force microscope (AFM) has developed into a critical instrument that allows for nanometer length scale investigation for a multitude of materials. To date, there are numerous AFM modes that can be used to quantify a variety of properties. By combining multiple AFM modes, such as quasi-static force mapping (FM-AFM), nano-infrared AFM (nanoIR), and contact-resonance AFM (CR-AFM), comprehensive, localized characterization is possible. In this dissertation, the robust capabilities offered by AFM are used to examine three distinctly different materials on the nanoscale: construction materials, semi-crystalline polymers, and energy harvesting materials. Ordinary Portland cement (OPC) and a greener construction material, geopolymer, are first investigated to obtain the nanomechanical properties of the reaction products—calcium silicate hydrates (C-S-H) and sodium alumino silicate hydrates (N-A-S-H), respectively. An innovative method to create samples with sub-micron roughness without the need for polishing is described: surface morphology optimization for optical and topographical homogeneity (SMOOTH), The SMOOTH fabrication method allows the reaction products of OPC to be studied in their native condition. Geopolymer samples are examined using a combination of three different AFM modes. This approach, denoted Tri-force microscopy (TFM), allows the distinct polymerization states to be quantified in spite of the misleading evidence offered by the sample topography. The CR-AFM technique is then coupled with a constant heating element, thermal CR-AFM (TCR-AFM), to investigate the crystallinity and glass transition temperature, Tg, of the semi-crystalline polymer polyether ether ketone (PEEK). The local TCR-AFM measurements reveal the change in polymer organization with respect to temperature. Finally, two energy harvesting materials, diisopropylammonium bromide (DIPAB) and poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFe)], are examined with respect to specific fabrications approaches. The goal of this study is to quantify confinement effects that may result. In particular, the influence of nano-imprinting lithography is investigated. Experiments show that confinement can have a dramatic effect on the elastic and viscoelastic properties. The results will allow improvements to be made in the fabrication of new devices based on these materials.
Nanoscience|Mechanical engineering|Materials science
Nguyen, Charles C, "Nanoscale Viscoelastic Characterization of Emerging Engineering Materials" (2019). ETD collection for University of Nebraska - Lincoln. AAI27667104.