Characterization of self assembled surfactant systems for their applications in templated materials synthesis
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Description
The goal of this research is to characterize surfactant based self-assembled systems that have potential applications in templated nano-materials synthesis. Three different surfactant based systems have been identified and investigated Rheological response and shear induced alignment has been studied for an optically clear, crystalline, rigid mesophase that is formed by the addition of water to a micellar solution consisting of a mixture of 0.85M anionic surfactant bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and 0.42M zwitterionic surfactant phosphatidylcholine (lecithin) in isooctane. At 25°C and water to AOT molar ratio of 70, the system has a columnar hexagonal microstructure with randomly oriented domains. The shear induced orientation, and subsequent relaxation was investigated via rheological and small angle neutron scattering (SANS) measurements. The rheological response and the shear SANS results indicate that the domains align under shear. The aligned domains remain aligned for several hours after cessation of shear. This alignment is retained as the temperature is increased to 57°C, indicating the potential to conduct templated polymer and polymer-ceramic composite materials synthesis in aligned systems Direct entrapment of aromatic molecules within cationic micelles to ultimately fabricate tailored, functional mesoporous silica/polymer composites is investigated. Specifically, the influence of 4-ethylphenol (dopant) on the shape of cetyltrimethylammonium bromide (CTAB) micelles is investigated. SANS indicates that the dopant affects the micellar size and shape. The micellar structure has been further investigated with Cryo-TEM (Transmission electron microscopy) technique. A systematic transition from globular micelles-to-elongated micelles-to-vesicles is observed. This understanding of the relation between dopant concentration and the micellar shape, provides very useful insights into effect of the dopant-to-surfactant molar ratio on the structure of surfactant-templated mesoporous silica The microstructural evolution in an organogel formed upon adding p-chlorophenol to the dry reverse micelles of AOT in isooctane has been investigated. This microstructural evolution has been studied through a combination of light scattering, small angle neutron scattering (SANS), NMR, and rheology. The dry micelles of AOT in isooctane do not undergo any detectable structural change up to a certain p-chlorophenol concentration. Upon a very small increment in the concentration of p-chlorophenol beyond this 'threshold' concentration, large aggregates are observed. Two alternative mechanisms for this structural evolution have been proposed