Effects of latex and thickener polarities on rheology and phase stability of latex–HEUR mixtures

Tailoring Waterborne Coating Rheology with Hydrophobically Modified Ethoxylated Urethanes (HEURs): Molecular Architecture Insights Supported by CG-MD Simulations

“…Latex is a colloidal system in which small hydrophobic polymer particles are dispersed in water. In such system, the hydrophobic segments of HEUR tend to associate with the hydrophobic surface of the latex particles, whereas the hydrophilic segments remain in the aqueous phase. ,, When the latex surface is not saturated by surfactants with higher affinity and given sufficient thickener concentration, HEUR molecules can bridge latex particles by adsorbing their hydrophobic segments. The strength of these interactions depends on the chemistry of both the HEUR and latex surface. ,,− Previous studies have identified various association mechanisms of HEUR with latex particles. ,,,,, These include a single hydrophobe adsorbed on a latex particle with another bridged on a HEUR micellar cluster, adsorption on different latex particles forming bridges, or adsorption to the same latex particle forming loops. ,,,,, The favored interactions depend on several factors including latex surface polarity, thickener hydrophobicity, temperature, and the concentration of latex and thickener.…”

“…In such system, the hydrophobic segments of HEUR tend to associate with the hydrophobic surface of the latex particles, whereas the hydrophilic segments remain in the aqueous phase. 6 , 8 , 12 When the latex surface is not saturated by surfactants with higher affinity and given sufficient thickener concentration, HEUR molecules can bridge latex particles by adsorbing their hydrophobic segments. The strength of these interactions depends on the chemistry of both the HEUR and latex surface.…”

“…Research on the rheological behavior of HEURs in waterborne systems has mostly focused on investigating the rheology of HEURs in aqueous media, both in the absence and in the presence of surfactants. − These studies aim to assess the effect of various factors, such as the size of hydrophilic and hydrophobic segments, temperature, concentration, and molecular weight distribution of HEUR and the interaction with surfactants. Further, relevant research activity has been extended to examine the rheology and stability of latex emulsions thickened with HEURs, focusing on the effect of latex monomer composition, particle size distribution, surface charge, and hydrophobicity. ,,− Bridging mechanisms and associations between HEURs and latex particles have also been studied, particularly focusing on the adsorption of hydrophobic segments, interparticle bridging, and loop formation. ,, Despite this extensive research, only few studies have transitioned these findings to waterborne paint formulations; ,,, therefore, a comprehensive analysis linking the HEUR rheological behavior across aqueous solutions, latex-based emulsions, and paint formulations is missing. At the same time, the methods for optimizing rheological properties in waterborne dispersions in the industry rely almost exclusively on trial-and-error processes and the experience of formulators, underscoring the necessity for more standardized approaches.…”

“…In this context, rheology modifiers (or viscosity thickeners) exert significant influence on the rheological properties of waterborne dispersions despite their relatively low concentration in the paint formulation (1 to 3 wt %). − ,− Among various rheology modifiers, hydrophobically modified ethoxylated urethanes (HEURs) constitute a specific class of nonionic associative thickeners. They are extensively employed in waterborne paints, inks, emulsions, and coatings due to their superior performance attributes, including excellent flow, leveling, spatter and water resistance, and pH insensitivity.…”

“…Further, relevant research activity has been extended to examine the rheology and stability of latex emulsions thickened with HEURs, focusing on the effect of latex monomer composition, particle size distribution, surface charge, and hydrophobicity. 6 , 13 , 30 − 37 Bridging mechanisms and associations between HEURs and latex particles have also been studied, particularly focusing on the adsorption of hydrophobic segments, interparticle bridging, and loop formation. 12 , 38 , 39 Despite this extensive research, only few studies have transitioned these findings to waterborne paint formulations; 2 , 3 , 9 , 40 therefore, a comprehensive analysis linking the HEUR rheological behavior across aqueous solutions, latex-based emulsions, and paint formulations is missing.…”