(322c) Rheology, Adhesion, and Debonding of Lightly Cross-Linked Polymer Gels

Lightly cross-linked polymer gels are soft, sticky materials with tunable properties making them ideal for use as pressure-sensitive adhesives.  Here, the viscoelastic and adhesive properties of fluorosilicone gels of varying equilibrium modulus are examined.  The commercially available material manufactured by Dow Corning is a mixture of fluorosilicones that, when heated, undergoes a platinum catalyzed reaction to form a lightly cross-linked gel swollen by long chain fluorosilicone polymers which are not covalently bound into the gel network.  In each case, the sol fraction of the gel is about 50%.  The rheology and adhesion properties of the resulting gel can be tuned by varying material parameters such as crosslink density, sol fraction, and polymer molecular weight of the cross-linked polymers or the polymer sol.  Here, we first discuss the rheology of three different fluorosilicone gels which vary only in their equilibrium modulus.  This basic rheological characterization then provides a fundamental basis for discussing the differences in adhesion properties exhibited by the gels.

Adhesive properties such as peak adhesive force, work of adhesion and strain to failure are also measured using a typical probe tack test and correlations to the gel rheology are made.  Further, adhesive bond failure mechanisms such as bulk cavitation and interfacial cavitation are explored in relation to initial strain rate, confinement and gel material properties.  We show a clear transition in debonding mechanisms from being dominated by surface effects at low initial strain rates and degrees of confinement to being dominated by bulk cavitation at high initial strain rates or degrees of confinement.  The effects of gel rheology and equilibrium modulus on the observed debonding behavior are also elucidated. 

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.