Rheology of poly(N-vinyl pyrrolidone)-poly(ethylene glycol) adhesive blends under shear flow

The rheological properties of adhesive miscible blends of high-molecular-weight poly(N-vinyl pyrrolidone) (PVP) with short-chain poly(ethylene glycol) (PEG) under oscillatory and steady-state shear flow have been examined with dynamic mechanical and squeezing-flow analysis. The latter allows the rheological characterization of adhesive blends under conditions modeling adhesive-bond formation as a fixed compressive force is applied to an adhesive film. The most adhesive PVP blend with 36 wt % PEG has been established to flow like a viscoplastic (yield stress) liquid with a power-law index of about 0.12. The study of the apparent yield stress as a function of the PVPPEG composition, content of sorbed water, molecular weight of PVP, and temperature shows that the occurrence of a yield stress in the blends results most likely from a noncovalent crosslinking of PVP macromolecules through short PEG chains by means of hydrogen bonding of both terminal OH groups of PEG to the complementary functional groups in PVP monomer units. A molecular mechanism of PVP-PEG interaction was established earlier by direct and independent methods. (c) 2006 Wiley Periodicals, Inc.