Investigation of aqueous foam stability containing pigment colorant using polyoxyethylene nonionic surfactant

Abstract

To improve foam stability in pigment foaming dispersions, a series of fatty alcohol polyoxyethylene ether (CmEOn) with different alkyl chain and ethylene oxide (EO) chain length (m = 12, 14, 16 and n = 5, 7, 9) were used as foam stabilizer to select the most superior structure for stabilizing foam. The effects of CmEOn on surface tension were investigated which revealed that the CMC of CmEOn in the pigment foaming dispersion decreased with the increase of surfactant hydrophobicity or the decrease of hydrophilicity. Compared to the alkyl chain, EO chain length influenced foam more significantly. C14EO5 in the pigment foaming dispersion showed lowest CMC and equilibrium surface tension. The presence of wormlike micelles and lamellar liquid crystal of SDS and C14EO5 endowed the C14EO5 pigment foaming dispersion with highest viscosity which was distinctly different with other CmEOn. C14EO5 showed the most superior stabilization effects with foam half-life of 172.9 min at 9 wt%. To further analyze the stabilization mechanism of C14EO5, the foam volume and bubble diameter change were observed with a digital microscope. The results demonstrated that the superior stabilization effects of C14EO5 were closely related to its high viscosity, which mainly resulted in the decrease of foam drainage and gas permeability. C14EO5, the optimal CmEOn structure for stabilizing foam, shows excellent foam stabilization capability in pigment foaming dispersions, which is a promising tool to realize pigment foam coloring.