Latex Imaging by Environmental STEM: Application to the Study of the Surfactant Outcome in Hybrid Alkyd/Acrylate Systems

Abstract

Among other uses, latexes are a successful alternative to solvent-borne binders for coatings. Efforts are made to produce hybrid nanostructured latexes containing an acrylic phase and an alkyd phase. However, after the film-forming process, the surfactant used to stabilize these latexes remains in the film, and its location can have a drastic effect on the application properties. Among the processing parameters, the alkyd hydrophobicity can strongly influence this location. This article aims at the imaging of these surfactant molecules in two hybrid latexes with different hydrophobicity level of the alkyd resin. A first part of this paper is dedicated to the understanding of the contrast provided by the surfactant in environmental STEM imaging of latexes. Then, the influence of surfactant-polymer affinity on the surfactant location after film-forming of those hybrid alkyd/acrylate latexes is studied by this technique. It is shown that in the hybrid latex with an alkyd shell (obtained with the most hydrophilic resin), the surfactant molecules tend to remain buried in the alkyd phase. Conversely, in the hybrid latex with an acrylate shell (in the case of the most hydrophobic resin), the surfactant molecules tend to gather into islands like in pure acrylate latex films.

Study of the surfactant role in latex–aerogel systems by scanning transmission electron microscopy on aqueous suspensions

“…It is thus attributed to Triton, in agreement with the observations of Faucheu et al . () on other latex formulations. From the measurement on 233 particles, the median value of the distance between centroids is equal to 237 nm, which is also similar to the value measured on SBA alone, the slight difference being possibly attributed to a slightly different local concentration of latex particles.…”

“…The SBA particles are surrounded by a uniform bright layer. The existence of such a shell has been previously reported and can be assigned to PMMA (Faucheu et al ., ), although such contrast could not be modelled by Monte Carlo simulations (not shown). By image analysis on 127 particles, it has been found that the diameter of the SBA core – without the PMMA shell – follows a Gaussian distribution; see the blue curve in Figure , with an average value of 171 ± 4 nm.…”

“…Alternatively, the interpenetration can be explained by a possible migration of the Triton molecules onto the SBA surface, allowed by the weak Triton–SBA interaction. The migration and outcome is observed during dehydration, in agreement with previous observations (Evanson & Urban, ; Faucheu et al ., ), and leads to the formation of either a relatively homogeneous film or a nonuniform distribution (Tzitzinou et al ., ). Zhao & Urban () also showed that upon dehydration, surfactant desorption occurred with the latex particle deformation.…”

Environmental Tomography of Liquid Latex Suspensions in STEM

“…The SBA particles has already included 3% PMMA shell playing the role of steric surfactant. Some other surfactants can also be introduced to further stabilize the latex for some special applications [4].In this work, we show series of tilted images that are acquired during in situ hydration / dehydration experiments with our improved device. Reconstructed volumes are obtained using the image processing software Etomo and ImageJ (see Figure 1), and the resolution is calculated using Fourier Shell Correlation (FSC).…”

“…The SBA particles has already included 3% PMMA shell playing the role of steric surfactant. Some other surfactants can also be introduced to further stabilize the latex for some special applications [4].…”