Free volume, adhesion, and viscoelastic properties of model nanostructured pressure-sensitive adhesive based on stoichiometric complex of poly(N-vinyl pyrrolidone) and poly(ethylene glycol) of disparate chain lengths

Positron annihilation lifetime spectroscopy was used to characterize the size and content of subnanoscopic free volume in a model pressure-sensitive adhesive based on a stoichiometric hydrogen-bonded network complex of poly(N-vinyl pyrrolidone) (PVP) and oligomeric poly(ethylene glycol) (PEG). Adhesive properties were examined with peel and probe tack tests, and mechanical properties were studied with tensile test. Nonequimolar stoichiometry and the structure of PVP-PEG model pressure-sensitive adhesive blends were found to be determined by the length of PEG short chains. The size and number density of free volume domains in the PVP-PEG blends were determined as functions of blend composition and relative humidity of the surrounding atmosphere, which controls the amount of absorbed water. Correlating the free volume, adhesion behaviors, and tensile properties of the blends, the range of free volume favoring pressure-sensitive adhesion in examined compositions was established.