Surface elastic modulus of latex films studied with atomic force microscopy (AFM) and its correlation with dirt pick-up resistance (DPUR) performance

•Surface elastic moduli of coating films acquired by AFM are found to be probing rate dependent.•AFM and DMS results can be qualitatively compared by considering relative locations of the glassy and rubbery region.•AFM can obtain data on specimens that are not robust enough for DMS analysis.•Surface mechanical properties by AFM correlate with the DPUR performances of the coating films. The surface mechanical properties of coatings have strong relationship with many performance attributes such as its dirt pick-up resistance (DPUR), scratch resistance, etc. Despite this important surface contribution most of the mechanical property measurements are carried out on the macroscopic scale using tensile tests or dynamic mechanical spectroscopy (DMS), which cannot provide surface mechanical property information. Moreover, some low glass transition temperature (Tg) coatings are not robust enough for bulk testing techniques. In this report, the surface mechanical properties of a series of latex films with different DPUR performances were studied with AFM (Atomic Force Microscopy) based force spectroscopy (FS). Through the study, we were able to measure surface elastic moduli of these films and found them to be probing rate dependent. This dependence is influenced by materials glass transition temperature and probing frequency in accordance with the viscoelastic nature of the latex materials. Results of the AFM FS study were compared to the bulk DMS data. The correlation between surface properties and DPUR performance was explored. The results showed the surface elastic modulus had good correlation with the DPUR performance. AFM FS may have the potential to predict DPUR performance of coating products and shorten the evaluation cycle time.