While most commercial soft adhesives are based on hydrophobic components, this is no longer true for the specific application of skin adhesives. Due to their low toxicity and ready absorption of moisture, hydrophilic gels are often used. The requirement of hydrophilicity implies the presence of polar components and often of hydrogen bonding. Furthermore properties of such gels are highly dependent on water content. Although the mechanical and adhesive properties of hydrophobic adhesives have been extensively investigated, much less is known of their hydrophilic counterparts. It is expected that the presence of a network of hydrogen bonds will greatly alter the deformation properties of such an adhesive both in small and large strains. Adhesion tests performed with a probe method showed an uncharacteristically high sensitivity to the velocity of removal of the probe, with a sharp transition from detachment by fibril formation at low probe velocity to brittle fracture at high probe velocity. Furthermore the small strain storage part of the elastic modulus G', was close to 1 MPa, in the frequency regime where significant pressure-sensitive-adhesion was observed, result in blatant disagreement with the well-known Dahlquist's criterion.
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