Template surfactant, Brij

Figure 9.4. Characterization of mesoporous Si02 films with cylindrical mesopores (ca. 3nm in diameter) templated using Brij 58 surfactant TEM image a), 2D GISAXS pattern with crystallographic indexation b), and SRSAXS/XRR analysis c).The experimental data in c) thus correspond to a detailed scan along the sz axis in b), using a suitable diffractometer. The films were prepared according to Ref. 39 and analyzed by the methods described therein.

Furthermore, aggregates of nonionic surfactants like polyoxyethylene alkyl/aryl ethers of the Tergitol, Triton, and Brij series were used as templates for the formation of mesoporous silica materials in neutral or acidic media. The pore diameters of the materials that can be obtained with these surfactants are restricted to around 5.5 nm. The advantages of these surfactants over triblock copolymers are that they are cheap, nontoxic, and biodegradable. An overview of the most commonly used SDAs is compiled in Table 3.1. 

Figure 13.12. UV/visible spectra of Brij 56-templated TSUA-modified nanoporous films, (a) After surfactant removal, reflection mode, (i) As-prepared, (ii) after UV irradiation of sample (i) for 30 min, and (iii) after heating sample (ii) at 100°C for 5 min. (b) Before surfactant removal, reflection mode, (i) As-prepared, (ii) after UV exposure of sample (i) for 20 min, and (iii) after room light exposure of sample (ii) for 60min. (c) After surfactant removal, transmission mode, (i) Before UV exposure, (ii) UV exposure for 5 min.

However, more details would be desirable. It is possible to express the architecture of an amphiphilic molecule by the number of units in the molecular chain. For instance, would denote the number of CH2 atoms, and AI7J would denote the number of ethylene oxide units in so-called Brij surfactants (see Fig. 2f). It is then possible to relate the size of the pores to the molecular architecture of the template molecules for a row of compositions (see Fig. 2g). Interestingly, the pore size depends on the size of both blocks. Classically (Fig. 3b), a microphase separation of the hydrophilic parts and hydrophobic parts into separate domains is expected. In this case, the pore-size dependence on both molecular parts is impossible. A "one-phase" scenario as depicted in Fig. 3a can also be excluded due to many reasons, which will not be further discussed here. ... 

As mentioned above, several types of PMO were synthesized using different templates and different reaction conditions. So, surfactant molecules are an important factor for the synthesis of PMOs and their numerous apphcations. The surfactants employed can be divided as shown in Figure 3.8. Ionic surfactants generally include C12-C18 alkyl chains with trimethylammonium head groups such as CTAB and octadecyltrimethylammonium chloride (OTAC). Nonionic surfactants consist of alkyl polyether type molecules such the Brij surfactants and the triblock copolymers such as Pluronic PI23 and FI27. 

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