Enhanced salt thickening effect of the aqueous solution of peaked-distribution alcohol ether sulfates (AES)

Abstract

Alcohol Ether Sulfates (AES) are emerging as a potent category of surfactant in consumer product industry owing to their much better hard water resistance, foaming/wetting ability, and less irritating than alkyl sulfate. These excellent performances are attributed to the presence of oxyethylene (EO) chain between the hydrophilic and the hydrophobic portions which endows AES the combined advantages of both nonionic and anionic surfactants. Most strikingly, addition of NaCl would considerably enhance the viscosity of the aqueous solution of AES, which is very important for a better retention of the surfactant to the interacting substrate. Recent study shows that the number distribution of EO groups considerably affects this salt-thickening performance, yet its mechanism is not clear. We report in this work that the narrower number distribution of the EO groups in the AES chains would generate an order alignment of the stretched EO chains, which can then bind with Na+ efficiently to form supramolecular crown ethers. In contrast, as the EO numbers are polydispersed, it is hard for them to align orderly, resulting in poor supramolecular crown ether formation ability with Na+. As a result, the wormlike micelles formed in the AES with narrower EO number distribution has much pronounced salt-thickening effect. This finding may help people in relating fields to create products with desired performance.