Increasingly, surfactants with multifunctional performance benefits are desired to not only lower the surface tension of waterborne formulations but also to reduced foam, and low HLB, non-ionic Gemini-type surfactants are commonly utilized for this reason. As legislation has required coatings with increasingly lower VOCs (volatile organic compounds) and, consequently, lower coalescent levels, the ability of Gemini surfactants to lower the minimum film formation temperature (MFFT) of emulsion polymers has garnered interest as a means to enable formulation of lower VOC coatings. This paper describes the MFFT reduction imparted by Gemini-type surfactants for a wide variety of emulsion polymers. Atomic force microscopy (AFM) showed that films prepared using an alkyl ester (AE) surfactant were generally smoother than films not containing the AE surfactant. While enabling low-VOC formulating, these surfactants were found to have minimal effect on coating performance. Lower HLB surfactants were found to be the most effective coalescents. A simple model whereby these surfactants preferentially adsorb onto the surface of the polymer particles is introduced to explain their efficiency.
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