The drying of industrially relevant latex dispersions designed for use as pressure-sensitive adhesives (PSAs) was followed using Forster resonance energy transfer (FRET) and scattering intensity as indicators for the progress of film formation. FRET and scattering intensity report the state of polymer interdiffusion and of particle deformation, respectively. Because the exciting UV-radiation only penetrated a few micrometers deep into the film, FRET measurements undertaken from the top and the bottom yielded different results. The combination of the two evidenced skin formation. Particle deformation occurs in two steps. There is a significant, but incomplete, decrease in turbidity because of skin formation. Only after the drying front has propagated to the substrate, the top layer turns fully clear. This second step is interpreted as coalescence, meaning the breakup of lamellae separating particles. Coalescence is followed by a sharp increase in interdiffusion. Further aspects studied included crosslinking, hydroplasticization, and tackifying resins.

Förster resonance energy transfer (FRET) was employed to study polymer interdiffusion in drying latex dispersions designed for application as pressure-sensitive adhesives. The materials differed in the degree of chain branching, where branching was controlled by the addition of styrene as a retarder. The FRET efficiency, ΦET, quantifies the degree of interdiffusion between particles. A plot of log (ΦET) versus log (time) showed an upturn after a drying time of a day or more. This increased slope can be explained in the frame of the Rouse model and reptation. ΦET(t) showed a step at the time of first contact between particles, the height of which increased with increased branching. Branches delayed interdiffusion in the later stages of drying. Presumably, these two effects are linked to short-chain branching and long-chain branching, respectively. As adhesion tests on these samples show, their tackiness is the largest when they contain an intermediate amount of retarder.