(347e) Adhesion and Detachment Mechanisms of Polymer Thin Films

The transient deformations and flows during both detachment and attachment (coalescence or spreading) of two viscoelastic polymer films were studied using a surface forces apparatus (SFA). In the case of detachment, liquid columns thin then snap, while solids crack. By studying the way liquids, viscoelastic polymers, glassy and brittle solids detach when pulled apart over a large range of pulling forces, pulling rates, temperatures, and material properties, we find that there is a continuous transition between these two very different modes of failure. It is found that the deformations of the columns or necks of materials as they break apart are very complex, exhibiting irregular transient fingering patterns as well as internal cavities; but that the transition nevertheless seems to vary in a continuous way from simple neck thinning, to inward liquid-like fingering, to sharp solid-like cracking.

The dynamics of adhesion (coalescence or spreading) of polymer melt surfaces and films has also been studied in detail. A new type of self-organized periodic transient surface fingering pattern and instability was found to generally exist during the adhesive contact and coalescence of two polymer films, which eventually disappeared, leaving smooth polymer-air interfaces. The life-times of the transient well-ordered patterns mainly depend on the viscosities and film thickness of the polymers. Such transient fingering instabilities may also generally exist in biological surface interactions such as lipid vesicle-vesicle adhesion and coalescence, bilayer and biomembrane interactions, cell-solid adhesion/binding, and cell-cell coalescence, which could be important to fully understand the mechanisms of these biological surface interactions.