Dynamic measurements of humidity attack on polymer/ glass interfaces under stress

Abstract

A simple, compact apparatus has been constructed for simultaneous tensile testing and optical microscopy in a time-resolved fashion of small adhesive droplets subjected to rapid variations in humidity. We utilize this system to study the 'attack' of humidity on the bonding of a polybutadiene rubber (PBR) and an isoprene-based pressure-sensitive adhesive (PSA) to soda lime glass. In the PBR, interfacial failure in humid air begins at a well-defined threshold stress; nevertheless, the rate of subsequent interfacial crack growth is a complex function of the sample history (stress and humidity). In PSA, interfacial failure in humid air begins soon after fibril formation (accompanying meniscus instabilities around the circumference of the adhesive drop). When humid air is introduced after fibril formation, interfacial failure begins promptly. Fibril formation produces stress concentrations which render the interface very susceptible to water attack - even at relatively low applied stresses. Although fibril formation enhances energy dissipation in PSA tested in dry air (due to fibril elongation), it limits energy dissipation in humid air (by inducing premature interfacial failure).

Keywords:

• Adhesion
• interfacial failure
• polymer/glass interface
• humidity effects
• fibril formation
• meniscus instabilities