Surfactant precursor solutions

Self-assembly of the precursor components in the EISA process starts after evaporation of part of the volatile solvent, which progressively enriches the solution with respect to surfactant, precursor, and water. When their concentration in the deposited him achieves a certain critical level, mesostructure formation takes place. The latter is in equilibrium with the processing atmosphere. So the relative humidity, as well as the temperature during him deposition, represent some of the most important parameters influencing the mesostructure formation. 

The thermal stability of mesoporous frameworks substantially increases with an increase in the wall thickness and pore size, which can be varied even for the same template by changing the processing conditions. Ozin et al.55 developed a way to prepare crystalline titania films with a 2D-hexagonal architecture by replacement of ethanol in the Pluronic-containing precursor solution with more hydrophobic butanol-1. The latter promotes phase separation at low surfactant-to-titania ratios, resulting in thicker pore walls, which are more compatible with the crystal growth during subsequent calcination. 

A variation of this method was used to control the surface properties of aluminum oxide particles, particularly the surface density of Lewis acid sites. Instead of using a long-chain amine surfactant, the solution of aluminum alkoxide precursor was mixed with a small amine to convert the alkoxide dimer (or oligomer in general) into monomeric alkoxide-amine adduct. Controlled hydrolysis of this adduct produces an aluminum oxyhydroxide in which the surface A1 ions are coordinated to amine... 

These results suggest that interactions between silicate species and surfactant micelles are weak in the precursor solution. The absence of any organization in the system prior to precipitation seems to indicate that the most important step in the process is the formation of siliceous prepolymers. The interaction of these prepolymers with surfactants could be responsible for micelle growth and subsequent reorganization of the silica/micelle complexes into ordered mesoporous structures. Such a hypothesis might be confirmed by preliminary potentiometric measurements using a bromide ion-specific electrode the amount of free bromide anion increasing at pH around 11 when the polymerization of silica starts. 

Figure 18.6 Fabrication of polymer-silica mesostructured materials through a self-assembly process by (a) addition of reactive monomers to the precursor solution, followed by postdeposition polymerization (b) addition of a polymerizable surfactant and (c) direct addition of a soluble polymer to the synthesis solution.

The synthesis of mesoporous silica films typically begins with the preparation of precursor solutions. These solutions contain a silica source (typically an alkoxide, although chloride and colloidal precursors can be used), a surfactant molecule used to template the mesostructure, an acid or base catalyst, and solvents. The nanoscale structure is then formed by a cooperative self-assembly of monomeric or partially... 

Typically, silica precursor solutions and surfactant solutions are prepared separately where the alkoxide precursors in the silica solution are allowed to hydrolyze for some period before mixing with a surfactant solution to form the coating solution. Likewise, the surfactant solution is allowed to equilibrate before the mixing. 

A precursor solution was prepared from R complex salt (M), surfactant (S), resorcinol (R), formaldehyde (F), Na2C03, ethanol (EtOH) and deionized water. Pluronic PI23 was used as a surfactant. Pt complex salt (Hydrogen hexachloro platinate(IV) hexahydrate H2PtCl6 6H20) was used as a Pt source. All the chemicals were purchased from Wako Pure Chemical Industries, Ltd. 

Precursor solutions were prepared by mixing tetraethoxysilane (TEOS), ethanol, HaO and hydrochloric acid in a molar ratio of 1 20 4 0.004 [6]. The PEO-h-PDMS diblock copolymer surfactant (1 to 20 wt%) was added to the sol, the mixture was stirred until a homogeneous solution was obtained and films were deposited on silicon wafers by dip coating [7]. 

According to the work of Sharma et al. [30], to obtain a-Al203, a precursor solution was prepared dissolving AICI3 in water, in the presence of a surfactant and an aqueous ammonium hydroxide solution (pH > 10). After stirring this... 

This article describes the preparation, properties (including characterization techniques), and potential applications of mesoporous materials. The article begins by examining the chemistry of surfactant/inorganic precursor solutions and discusses its application to the synthesis of mesoporous materials. The most common methods of characterization and the properties of the materials are described and finally potential applications are mentioned. This article is therefore intended to provide a general overview of the synthesis, formation mechanisms, characterization, properties, and applications of mesoporous molecular sieves. 

Multiwalled carbon nanotubes (MWCNT) are relatively easy to synthesize and cheaper compared to either double-walled or single-walled carbon nanotubes. Hence they have been investigated for incorporation into BC. The electrical conductivity of BC-MWCNT composite depends on various factors such as 1) average length of MWCNT 2) their concentration in the precursor solution 3) type of surfactant used for dispersing the nanotubes and 4) immersion time for dispersing the nanotubes in the BC matrix. Yoon et al. [57] studied the effect of these variables on the overall electrical conductivity by using two surfactants. Cetyl trimethylammonium bromide (CTAB)... 

An example of the preparation of a precursor solution for a thick PZT film based on this considerations is seen in the report by Tsurami et al. (2003). It begins with the dissolution of PZT (Zr/Ti = 53/47) alkoxide solution in hexane along with ethanol, followed by adding PZT fine powders of about 0.2 /itm in diameter and a surfactant (sorbitan monooleate) to give a good dispersion of the powders. The PZT fine powders... 

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