Rubber-to-glass adhesion between a rigid sphere and a shape memory polymer substrate of finite thickness

TL;DR

This study investigates the fundamental mechanics of rubber-to-glass adhesion in shape memory polymers, combining experiments, simulations, and models to enhance understanding of their adhesion strength and design parameters.

Contribution

It introduces analytical models for R2G adhesion in SMPs, revealing the influence of substrate thickness and providing design insights for smart adhesives.

Findings

Analytical solutions for contact radius and adhesion force

Critical thickness-to-contact-radius ratio of around 5

Thickness significantly affects adhesion performance

Abstract

Shape memory polymers (SMPs) are emerging as innovative smart adhesive materials with broad application potential. Compared to conventional elastomeric adhesives, SMP adhesives are distinguished by the so-called rubber-to-glass (R2G) adhesion, which involves contact in the rubbery state followed by detachment in the glassy state. This process, through a shape-locking effect, enhances adhesion strength by more than an order of magnitude compared to conventional adhesive contact. Here, we investigate the fundamental problem of a rigid sphere undergoing R2G adhesion with an SMP substrate of finite thickness through experiments, finite element (FE) simulations, and theoretical modeling. It is demonstrated that during press-in, the contact problem can be modeled as a rigid oblate spheroid contacting an infinite substrate, while the pull-off process can be described by a modified ball-and-socket model. These equivalent models yield practically useful analytical solutions for the contact radius during press-in and the R2G adhesion force during pull-off. A critical thickness-to-contact-radius ratio of around 5 is identified, below which the thickness effect becomes significant. These insights provide valuable guidance for the design and application of SMP-based smart adhesives.