Two-Phase Composite Adhesive with Viscoelastic Inclusion

Abstract

Platinum catalyst, used for cross-linking poly(dimethylsiloxane) (PDMS) gets poisoned by elements such as sulfur and nitrogen leading to incomplete curing of the elastomer. We used this effect to generate an elastomeric material embedded with viscoelastic inclusions. An aqueous solution of gelatin was dispersed as droplets within the continuous phase of the PDMS oligomer mixed with the cross-linking agent. Both these phases were cross-linked almost simultaneously forming an elastomeric network. Gelatin, however, contains sulfur (as sulfur dioxide preservative) and nitrogen (as part of amino acid in its backbone) which poison the platinum catalyst present in PDMS as a component of the curing agent. Consequently, the extent of cross-linking of the continuous phase diminished at the vicinity of gelatin drops, thereby generating viscoelastic domains within an otherwise elastic material. The viscoelastic effect increased with the volume fraction of the gelatin phase and/or the interfacial area between the two phases. However, because the individual phases were elastic, the material remained useable over repeated cycles of loading and unloading despite showing large hysteresis, as confirmed by adhesion tests. We expect the two-phase gel to be useful for applications requiring cyclic operations such as medical tapes, robotic hand grippers, soft dampeners-cum-joints, and so on.