Correlating Particle Deformation with Water Concentration Profiles during Latex Film Formation: Reasons That Softer Latex Films Take Longer to Dry

Abstract

During the past two decades, an improved understanding of the operative particle deformation mechanisms during latex film formation has been gained. For a particular colloidal dispersion, the Routh-Russel deformation maps predict the dominant mechanism for particle deformation under a particular set of conditions (evaporation rate, temperature, and initial film thickness). Although qualitative tests of the Routh-Russel model have been reported previously, a systematic study of the relationship between the film formation conditions and the resulting water concentration profiles is lacking. Here, the water Published in Langmuir (2014), vol, 30, pp 9672-9681 2 distributions during the film formation of a series of acrylic copolymer latexes with varying glass transition temperature, T g (values of 22, 11, 4 and 19 ºC) have been obtained using GARField nuclear magnetic resonance profiling. A significant reduction in the rate of water loss from the latex copolymer with the lowest T g was found, which is explained by its relatively low polymer viscosity enabling the growth of a coalesced skin layer. The set of processing parameters where the drying first becomes impeded occurs at the boundary between the capillary deformation and the wet sintering regimes of the Routh-Russel model, which provides strong confirmation of the model's validity. An inverse correlation between the model's dimensionless control parameter and the dimensionless drying time is discovered, which is useful for the design of fast-drying waterborne films.

Drying Mechanisms in Plasticized Latex Films: Role of Horizontal Drying Fronts

“…This model is in good agreement with various literature results. 14,38 Recently, it was further validated experimentally by Carter et al, 8 with the extrapolation of rheological data using the Williams−Landel−Ferry (WLF) The Journal of Physical Chemistry B Article equation. However, such an extrapolation may lead to differences in shear viscosities by several orders of magnitude.…”

“…They found significant differences between the predicted deformation mechanisms and the experimental results. Carter et al 8 and Simon et al 25 used NMR profiling techniques to measure the concentration of water in a film and to assess the deformation mechanisms. However, the results of Simon et al are globally less accurate (low spatial resolution and longtime measurements).…”

Watching paint dry; more exciting than it seems

“…After the rupture of the liquid film that separates two latex particles, the inner phases begin to mix. [25][26][27][28] With a typical resolution of approximately 10 micrometre, MRI profilometry does not give direct insight into particle deformation and coalescence at the single-particle scale. However, for aqueous paints, the latex particles are composed of a highly visco-elastic entangled polymer melt with a glass transition temperature T g at or around the relevant application temperature of the coating.…”

“…34 On a global scale, these effects can be ideally studied by for example water profilometry using MRI, 26,28 while insight into the phenomena on smaller scales requires the use of higher-resolution methods such as optical microscopy, including confocal microscopy, 35 and electron microscopy. The first film to rupture in a homogeneously compressed packing of equally sized droplets is a problem of symmetry breaking governed by thermal or external fluctuations.…”

In-Situ AFM and EIS Study of Waterborne Acrylic Latex Coatings for Corrosion Protection of Carbon Steel

“…The latex particle deformation by water increases their viscosity and enhances their ability to coalescent, which is important for the film formation from polymer dispersions. 39 In the case of SALH coating, probably the high Tg coalescence latex allowed sufficient interdiffusion, leading to densely packing of the nanoparticles.…”