Characterizing the Distribution of Nonylphenol Ethoxylate Surfactants in Water-Based Pressure-Sensitive Adhesive Films using Atomic-Force and Confocal Raman Microscopy

Abstract

Surfactant distributions in model pressure-sensitive adhesive (PSA) films were investigated using atomic force microscopy (AFM) and confocal Raman microscopy (CRM). The PSAs are water-based acrylics synthesized with n-butyl acrylate, vinyl acetate, and methacrylic acid and two commercially available surfactants, disodium (nonylphenoxypolyethoxy)ethyl sulfosuccinate (anionic) and nonylphenoxypoly(ethyleneoxy) ethanol (nonionic). The ratio of these surfactants was varied, while the total surfactant content was held constant. AFM images demonstrate the tendency of anionic surfactant to accumulate at the film surfaces and retard latex particle coalescence. CRM, which was introduced here as a means of providing quantitative depth profiling of surfactant concentration in latex adhesive films, confirms that the anionic surfactant tends to migrate to the film interfaces. This is consistent with its greater water solubility, which causes it to be transported by convective flow during the film coalescence process. The behavior of the nonionic surfactant is consistent with its greater compatibility with the polymer, showing little enrichment at film interfaces and little lateral variability in concentration measurements made via CRM. Surfactant distributions near film interfaces determined via CRM are well fit by an exponential decay model, in which concentrations drop from their highs at interfaces to plateau values in the film bulk. It was observed that decay constants are larger at the film-air interface compared with those obtained at the film-substrate side indicating differences in the mechanism involved. In general, it is shown here that CRM acts as a powerful compliment to AFM in characterizing the distribution of surfactant species in PSA film formation.

Comparison of Surfactant Distributions in Pressure-Sensitive Adhesive Films Dried from Dispersion under Lab-Scale and Industrial Drying Conditions

“…This indicates a nonuniform surfactant distribution, most likely due to agglomeration, as reported in other articles. 7,18,20,21 Since the measurement resolution is limited to 1−2 μm, potentially existing surfactant agglomerates can only be resolved if their size is above the resolution limit. All measurements showed comparable results in terms of lateral distribution, independent of adhesive and drying conditions.…”

“…Therefore, it is not surprising that the distribution of surfactants in films dried from film-forming dispersion has been intensively investigated with different methods. Raman spectroscopy, − ATR-FTIR, − Rutherford back scattering, AFM, , and XPS were used. One of the first studies that investigated the surfactant distribution and provided a distribution mechanism was made by Zhao et al They interpreted the surfactant enrichment at the interfaces as the result of the surfactants minimizing the interfacial energy.…”

Pressure-Sensitive Adhesive Joints

“…Acrylic PSAs, generally borne in an organic solvent, must possess correspondingly suitable 180° peel strength, high shear strength and appropriate tack for optical film applications. The adhesive properties of acrylic PSAs are critically determined by the monomer compositions, the initiators, the crosslinking agents and the tackifiers of acrylic PSAs [48][49][50].…”

The colloidal properties of alkaline‐soluble waterborne polymers

“…However, surfactants are also associated with various negative aspects such as reduced water resistance and adhesion problems . During drying, surfactants can migrate toward coating‐air, coating‐substrate, and/or particle‐particle interfaces . As a result, the surfactants can form separate phases and become locked in interstices between the particles in the coating during film formation .…”