Interface micelle-silica

Most probably the sulfonic groups interact with the cationic heads of the surfactant molecules via electrostatic interactions. When the synthesis is carried out in basic conditions, as in the present case, in the surfectant/silica mesophase the cationic parts of the surfectant molecules interact with the negatively charged silica surface [14]. Thus it can be assumed that in CR-MCM-41 the sulfonic groups of the CR molecule are located at the interface surfectant-silica, whereas the rest of the molecule, i. e. aromatic rings, amino groups and azo groups, is embedded in the micelle. 

In the last years large attention was devoted to the synthesis and characterization of SBA-16 material focusing the interest on the formation mechanisms of copolymer micelles which drive the organization of the final siliceous mesostructure. In this framework, the physico-chemical properties at the interface between silica and triblock E0106P070E0106 co-polymer in a SBA-16 material were investigated. In particular, the combination of IR spectroscopy with SS NMR allowed to obtain complementary information on how the surfactant co-polymer interacts with the SBA-16 surface silanols in the presence or absence of physisorbed water and to follow the evolution of the structural organization of the co-polymer, which depends on the hydration degree of the SBA-16 sample. 

TABLE 1 Shape of CTA Micelles Adsorbed onto the Interface Between Silica and Aqueous Salt Solution as a Function of Counterion Polarizability... 

Some surfactants aggregate at the solid-liquid interface to form micelle-like structures, which are popularly known as hemimicelles or in general solloids (surface colloids) [23-26]. There is evidence in favor of the formation of these two-dimensional surfactant aggregates of ionic surfactants at the alumina-water surface and that of nonionic surfactants at the silica-water interface [23-26]. 

Hirai T, Okuho H, Komasawa 1 (2001) Incorporation of CdS nanoparticles formed in reverse micelles into mesoporous silica. J Colloid Interface Sci 235 358-364... 

Fig. 3 Mechanism for the synthesis of a hexagonal silica thin film by dip coating. This is zoomed in at the substrate-bulk solution interface. The dotted line indicates the second critical micelle concentration, above which the micelles form cylindrical micellar rods. These rods then begin to assemble at the air-liquid interface and the liquid-substrate interface. (From Ref. l)...

Galameau, A. et al., Kinetics of formation of micelle-templated silica mesophases monitored by electron paramagnetic resonance, J. Colloid Interface Set, 201, 105, 1998. 

According to Milliken et al., the aluminum ions at the interface of 7-alumina and silica micelles are believed to be in a three-coordinated structure corresponding to the anhydride of the acid, HA102. An anhydride of this structure is a potential acid of the Lewis type (see above example of Lewis acid structure), and this is believed to be the only type of acid which is present in the silica-alumina catalyst at cracking temperatures (500°C.). 

An alternative approach to surface imprinting of silica was recently introduced [36,37]. The process is based on a sol-gel reaction inside reverse micelles (Fig. 18a). The template molecule acts as the headgroup of a surfactant. After mixing with a nonionic surfactant, cyclohexane, water and ammoniated ethanol, a water-in-oil microemulsion is formed. The co-condensation is then started by addition of Si(OEt)4 and amine-, dihydroimidazole- and carboxylate-terminated trialkoxysi-lanes to give silica particles with a diameter between 400 and 600 nm. Since the stemplate molecule was located at the interface of the micelle during the condensation reaction, the resulting imprints are formed at the surface of the particle. 

Harada et al. [271] report formation of silica in reverse micelles involving didodecyldimethylammonium bromide (DDAB), cyclohexane and TEOS, in which TEOS was supposed to be hydrolyzed at the interface of the reverse micelles (leading to condensation and network formation). 

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