Film Formation of Pressure-Sensitive Adhesives (PSAs) Studied with Förster Resonance Energy Transfer (FRET) and Scattering Intensity

Abstract

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.

Interdiffusion during film formation of ionically cross‐linked acrylics investigated with Förster resonance energy transfer (FRET)

“…Details about the instrument as well as the sample preparation and measurement are provided in Ref. . FRET studies were carried out on 1/1 ( m / m ) blends of donor‐ and acceptor‐labeled dispersions (“DA”) with otherwise identical properties.…”

“…In films from polymer dispersions, interdiffusion is initially dominated by chains with low molecular weight due to their higher mobility compared with the chains with high molecular weight which diffuse much slower . Irreversible, covalent cross‐linking prevents interdiffusion . Also, interdiffusion of polymers which can undergo a cross‐linking reaction after drying starts has been investigated (post‐cross‐linking) .…”

“…It has been shown by differential scanning calorimetry (DSC) measurements that polymer films made from dispersions have a reduced glass transition temperature, T g , when water is dissolved in their matrix (hydroplasticization) . FRET studies have shown that hydroplasticization accelerates polymer interdiffusion . Recent studies addressed polymer interdiffusion in film forming water‐borne PSA dispersions .…”

“…FRET studies have shown that hydroplasticization accelerates polymer interdiffusion . Recent studies addressed polymer interdiffusion in film forming water‐borne PSA dispersions . Because of the low T g of the polymers, interdiffusion at room temperature is fast to the extent that is almost finished immediately after the polymer particles deform and come into contact .…”

“…Recent studies addressed polymer interdiffusion in film forming water‐borne PSA dispersions . Because of the low T g of the polymers, interdiffusion at room temperature is fast to the extent that is almost finished immediately after the polymer particles deform and come into contact . Furthermore, blends of industrially relevant dispersions of linear polymers blended with the ionic cross‐linker aluminum acetylacetonate have been studied .…”