Author

Manish Giri

Date of Award

8-2001

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Computer Engineering

Advisor

William N. Unertl

Second Committee Member

Douglas W. Bousfield

Third Committee Member

Vincent Caccese

Abstract

Nan0 to microscale deformation behavior of different carboxylated styrene-butadiene co- polymer Latexes were investigated using a commercial nanoindentation device. The latexes dif- fered primarily in their glass transition temperature (Tg). The bulk dynamic rheological properties, as determined from a rheometer, dictate the axismmetric deformation behavior of the latexes. Results from dynamic tests performed on latexes were analyzed using the theories in contact and fracture mechanics. Two theories of linear viscoelastic fracture mechanics (LVEFM) were employed to model the adhesion hysteresis (loading-unloading cycle) curves to obtain meaningful cohesive zone (fracture process zone) parameters and a stress intensity functional (KI(t)) for an entire cycle. The stress intensity functional, extracted from the deformation behavior, is inde- pendent of the loading history and was shown to depend only on the crack propagation velocity, (dddt), for the entire cycle. The quantitative values of stress intensities were then discussed in the light of polymer molecular phenomenon’s such as viscous chain desorption. Nanoindetation was developed as a tool for systematically investigating both the bulk as well as the cohesive zone properties of viscoelastic polymers. Effect of plastic deformation on the deformation behavior of high pigment volume concentration (PVC) coatings was also analyzed. Polystyrene plastic pigment, CaC03 and Clay pigments were used to form the coatings layers. High PVC coatings are viscoelastic due to the latex present but also contain air, the third phase, which could explain the plastic deformation if a certain critical yield stress is exceeded. At PVC’s greater than 70%, the coatings showed significant plastic (permanent) deformation, which has to be accounted for in modeling the hysteresis curves. The residual plastic deformation was confirmed by imaging the indent over a period of time. Modeling the curves resulted in a compressive yield stress (σγ) value, which is an important parameter in predicting the calendaring performance of these coatings.

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