Date of Award

Fall 12-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

James W. Rawlins

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Robson Storey

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Derek Patton

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

Robert Lochhead

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Sergei Nazarenko

Committee Member 5 School

Polymer Science and Engineering

Abstract

“Adhesion” can be considered either a mechanical or chemical phenomenon. The mechanical interpretation describes the difficulty of separating surfaces and is useful for quantifying performance within applications that depend on bulk and interfacial properties. Chemical adhesion describes interfacial resistance to chemical attack and does not depend on bulk properties. Predicting chemical failure through mechanical measurement is confounded by the influence of bulk properties. However, the prospect is attractive because of the robust tolerance for sample geometries, allowing experiments to resemble an end-use system. The present work's primary goal was to elevate mechanical methods to provide a detailed interfacial characterization of industrially relevant samples.

Bulk mechanical property effects on 90° peel tests were addressed by leveraging mechanical properties' predictability relative to the Tg. Characterization of peel forces of three epoxy-amine coatings with various Tgs at four test temperatures demonstrated the extent of the temperature dependence of adhesion. Framing the results relative to each coating’s Tg uncovered a universal peel force maximum at Tg-20°C and identified that chain mobility is as vital to interfacial strength as functional group compatibility.

Pull-off adhesion results can be difficult to interpret from the minimal information provided by peak stress values. One quantity represents the entire pull-off testing procedure. Performing pull-off on a load frame provides stress-strain curves with each pull to describe how a coating responds to the tensile load and what defects are present that can lead to peak stress data sets with high variation. This analysis technique was applied to deciding on an appropriate adhesive and scoring method for the present coating-substrate system.

Predicting adhesion is an important step toward predicting coating performance. A model describing pull-off peak stress as a function of coating thickness was found to be inaccurate for a number of literature examples. A critical modulus was defined where coating film yielding occurred at lower stresses than interfacial failure leading to increases in pull-off peak stress with thickness, in contrast to predictions. Similar effects were induced through solvent trapping. These findings are essential for defining relationships between mechanical test results and interfacial parameters to understand coating performance.

ORCID ID

0000-0003-0827-7488

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