Low-Foaming Nonionic Gemini Surfactants Containing Hydrophilic Poly(oxyethylene) Chain and Hydrophobic Di-<i>tert</i>-pentylbenzenes Groups

Low-foaming nonionic gemini surfactants have a wide range of applications in industrial cleaning and photoresist development. In this study, three low-foaming nonionic gemini surfactants (S1, S2, and S3) with different poly(oxyethylene) chain lengths have been synthesized by using methoxy poly(ethylene glycol) and 2,5-di-<i>tert</i>-pentylhydroquinone. The chemical structures of the novel surfactants are confirmed by ¹H NMR, Fourier transform infrared, and gel permeation chromatography (GPC), and their properties such as surface tension, wetting properties, emulsifying properties, and foaming properties are investigated. The surface tension values of S1, S2, and S3 at the critical micelle concentration are 40.29, 37.14, and 41.64 mN/m, exhibiting good surface activity. When the surfactant concentration is higher than 2 mM, the contact angles of S1 and S2 no longer change and can maintain 62 and 64°, showing good wetting properties. In addition, S3 can keep an emulsion state for 2 months at high concentrations, exhibiting good emulsion stability. Furthermore, all the prepared surfactants show good low-foaming properties. The initial foaming volumes of S1 are very low, less than 0.1 mL at various concentrations, less than 2% of the conventional surfactant sodium dodecyl sulfate. For S2, the initial foaming volumes at the concentration of 0.1, 1, 2, and 3 g/L are 1, 0.5, 0.55, and 0.45 mL, respectively. For S3, the initial foaming volumes show a general trend of increasing with concentration. The surfactants with longer poly(oxyethylene) chains possess more initial foaming volumes at the same concentration, which is because the greater cohesion between the surfactant molecules can increase the elasticity of the bubble film. Our study enriches the design rationales for low-foaming surfactants and motivates researchers to develop more advanced surfactants for industrial cleaning and photoresist development.