Morphology Transitions in Nonionic Surfactant Adsorbed Layers near Their Cloud Points

Abstract

The structure of adsorbed layers of several polyoxyethylene alkyl ether (C(n)E(m)) nonionic surfactants on silica and graphite surfaces has been imaged using atomic force microscopy as a function of temperature up to their cloud points. For all surfactants with a cloud point within the experimentally accessible range, the adsorbed layer morphology on silica evolved from globules at low temperatures first into rods and then a mesh with increasing temperature. This mesh structure was retained even when the solutions were heated above their cloud points into the two-phase coexistence region. Only C(12)E(3) was observed to form a laterally unstructured bilayer. On graphite, all surfactants formed straight, parallel hemicylinders at all temperatures examined.

Clouding behaviour in surfactant systems

“…The transition of morphology during the clouding of several polyoxyethylene alkyl ether (CnEm) nonionic surfactants with CP ≤ 40°C, was studied from Fourier transform atomic force microscopic images of adsorbed layers of aqueous solution of those surfactants on silica and graphite surfaces at temperatures below and near CP [194]. The adsorption morphology of the surfactants changes from initial globules to rod with the rise in temperature and finally to a mesh structure near cloud point.…”

Laterally nanostructured adsorbed layers of surfactant/surfmer mixtures before and after polymerisation

“…3 might be that the film morphology changes from rods to globules, and then a bilayer with increasing MEDDAB content, as a mesh structure does not look dissimilar to an adsorbed layer of globular aggregates under the AFM. However this progression is unlikely as the film would have to first increase in curvature and then change to a planar conformation with further addition of MEDDAB [24,25]. Another means of distinguishing a deflection image of globules from that of a mesh is that the periodicity of the mesh is usually larger [24].…”

“…A wealth of AFM studies of surfactant self-assembly on various substrates have revealed the existence of globular [20], cylindrical [16,17], mesh [24,25] and bilayer [17,26] structures. The effects of factors such as alkyl chain length [15], headgroup structure and charge [18,20], counterion type [20] and electrolyte concentration [27,28] all been found to mirror the structural trends observed in bulk self-assembly.…”

Dynamic and static radiation scattering in a microemulsion as a function of dispersed phase concentration

“…Among these non-ionic surfactants, polyethoxylated alkyl ones (C n E m , where n is the number of carbons of the hydrophobic and saturated linear chain, and m is the number of ethoxy groups in the polar head) [12] are one of the most useful surface-active substances, attracting the interest of the scientific community, due to their remarkable and unique properties [13][14][15]. In the oil industry, they have been used in metalworking fluids [16], drilling fluid formulations [17] as well as systems with biocide activity [18].…”