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Morphology transitions in nonionic surfactant adsorbed layers near their cloud points
Annabelle Blom1, Gregory G Warr, Erica J Wanless
1School of Chemistry, The University of Sydney, NSW, Australia.
Langmuir : the ACS Journal of Surfaces and Colloids
|December 1, 2005
Summary
The structure of nonionic surfactants on silica and graphite changes with temperature. Surfactant layers form distinct patterns like meshes on silica and hemicylinders on graphite, even above their cloud points.
Area of Science:
- Surface science
- Colloid and interface science
- Materials science
Background:
- Nonionic surfactants, such as polyoxyethylene alkyl ethers (C(n)E(m)), are widely used in various industrial applications.
- Understanding the adsorption behavior of these surfactants on different surfaces is crucial for optimizing their performance.
- The cloud point phenomenon in nonionic surfactants is related to changes in their hydration and aggregation states.
Purpose of the Study:
- To investigate the structural evolution of adsorbed nonionic surfactant layers on silica and graphite surfaces.
- To correlate the observed structures with temperature and proximity to the surfactant cloud point.
- To elucidate the differences in adsorption behavior between silica and graphite substrates.
Main Methods:
- Atomic force microscopy (AFM) was employed to image the adsorbed surfactant layers.
- Experiments were conducted across a range of temperatures, up to and beyond the cloud points of the surfactants.
- Several types of polyoxyethylene alkyl ether (C(n)E(m)) nonionic surfactants were studied.
Main Results:
- On silica, adsorbed surfactant layers transformed from globular structures to rods, and finally to a mesh-like network with increasing temperature.
- This mesh structure persisted even when the temperature exceeded the cloud point, indicating stable layer formation.
- On graphite surfaces, all studied surfactants consistently formed straight, parallel hemicylindrical structures at all examined temperatures.
- A specific surfactant, C(12)E(3), was observed to form a laterally unstructured bilayer on silica.
Conclusions:
- The morphology of adsorbed nonionic surfactant layers is highly dependent on the substrate (silica vs. graphite) and temperature.
- The cloud point plays a significant role in the structural transitions observed on silica surfaces.
- The formation of stable mesh structures above the cloud point suggests unique interfacial properties of these surfactant layers.
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