Drying dissipative structures of nonionic surfactants in aqueous solution.

Abstract

Macroscopic and microscopic dissipative structural patterns form in the course of drying a series of aqueous solutions of polyoxyethylenealkyl ethers. The shift from the single round hill with accumulated surfactant molecules to the broad ring patterns of the hill in a macroscopic scale occurs as the HLB (hydrophile-liophile balance) of the surfactant molecules increases. The patterns correlate intimately with the HLB values of the surfactants. Microscopic patterns of small blocks, starlike patterns, and branched strings are formed. The size and shape of the surfactant molecules themselves influence the drying patterns in part. The pattern area and the time to dryness have been discussed as a function of surfactant concentration and HLB of the surfactants. The convection flow of water accompanying the surfactant molecules, the change in the contact angles at the drying frontier between solution and substrate in the course of dryness, and interactions among the surfactants and substrate are important for the macroscopic pattern formation. Microscopic patterns are determined in part by the shape and size of the molecules, translational Brownian movement of the surfactant molecules, and the electrostatic and hydrophobic interactions between surfactants and/or between the surfactant and substrate in the course of solidification.