Browsing by Subject "Micellization"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Synthesis of mesoporous silica particles controlling the CTABr-pluronic assembly
    (2009) Poyraz, Altuğ Süleyman
    In the synthesis of mesoporous silica materials, self-assembly of a charged surfactant (cetyltrimethylammoniumbromide, CTABr) and a pluronic (PEOx-PPOy-PEOx where PEO is CH2CH2O and PPO is CH(CH3)CH2O) into micelles have key. By controlling the hydrophilic-hydrophobic character of the CTABr-Pluronic micelles, mesoporous silica particles can be synthesized with different morphologies (sphere, wormlike, crystal-like etc.). The particles generally have 2D hexagonal mesostructure with a high surface area (as high as 800 m2 /g). Shape of the micelles as well as the morphology of the particles depend on the hydrophobic nature of the pluronic surfactant and the CTABr amount. The CTABr amount is carefully adjusted to control the morphology and structural order of the particles. The self-assembly of the CTABr-Pluronic micelles and silica species has been achieved by adjusting pH of the synthesis medium to 1.0 in order to produce mesoporous particles with a distinct morphology and mesostructure. Nature of the CTABr-Pluronic micelles can be influenced by adding organic and inorganic additives to the reaction media. The effect of the lyotropic (F- , SO4 2- and Cletc.) and hydrotropic (NO3 - , SCNetc.) anions on the micellization of P85 has been first investigated in the aquoues media using UV-Vis Spectroscopy and ethyl orange dye. Then these inorganics and organic (Benzene) additives, in the synthesis of mesoporous silica, have been used to control the micellization of the CTABr-P123 couples as well as the morphology and the pore structure of the silica particles. Highly ordered particles with larger pores and various pore structures have been synthesized using lyotropic anions in the CTABr-P123 system. Furthermore, the hydrotropic anions control the CTABr content of the CTABr-P123 micelles. Increasing CTABr amount in the CTABr-P123 micelles decreases the wall thickness of the silica particles. The hydrophobic character of the micelles can also be enhanced by adding water insoluble organic additives (benzene). The silica particles, synthesized using CTABr-P123-Benzene system, are well structured, where the higher order X-ray diffraction lines can also be observed. Finally, the catalytic role of Fions on the polymerization of the silica has been studied in the CTABr-Pluronic system. Addition of Fion to the reaction medium speeds up the formation process and producing spherical and uniform mesoporous particles less than 20 minutes. The effect of each of the reaction component, Fion, CTABr and P123 molecules, to the assembly rate has also been investigated by determining the turbidity point (due to the formation of silica particles) of the solutions. A correlation between the particle size and reaction rate has also been brought out. The mesoporous silica particles synthesized in this thesis have been characterized using PXRD, FT-IR and Raman Spectroscopy, SEM, TEM and N2 sorption measurements.
  • Thumbnail Image
    ItemOpen Access
    Synthesis of mesoporous silica particles using SDS-Pluronic couples
    (2010) Sayın, Mustafa
    Controlling the cooperative self assembly and micellization of pluronics and SDS (sodium dodecyl sulfate)are pivotal for the synthesis of mesoporous silica particles. The pH and temperature of the synthesis media, SDS/Pluronic mole ratio, TMOS (tetramethyl orthosilicate)amount, alkali salt amount of the synthesis solution are the parameters, which play significant roles on the micellization and self assembly of surfactants. The synthesis of mesoporous silica particles with distinct morphologies is possible with the precise optimizations of these parameters. In this thesis we have investigated the synthesis of mesoporous silica particles with a well defined morphology and structure using SDS-Pluronic couple as the template. The pore size can be tuned by changing the aggregation number of the surfactant molecules in the micelles, also by changing the pluronic type. The morphological control is achieved mainly by changing the pH and temperature of the synthesis media. At different temperatures and pHs, rods, spheres, muffin and ‘s’ shaped particles have been obtained. The addition of inorganic salts, such as NaNO3, NaCl, and KCl, has also effects on the morphology and meso-structure. Addition of a small amount of NaNO3 changes spherical particles to amorphous silica however, addition of large amount of NaNO3 gives well defined muffin shaped and worm-like particles. The concentration of nitrate ion also affects the pore size and wall thickness of the synthesized particles. The KCl or NaCl salts also have similar effects on the morphology of the silica particles, the morphological transitions have been observed but the role of Cl- ion is minor on the control of pore size. The SDS concentration has important effects on the micellization of pluronics, changing the SDS/Pluronic mole ratio (between 0.05 and 5.0) in the reaction media changes the structure of the mesoporous silica particles. Particularly the SDS concentration has important effects on the surface area of the synthesized particles. The surface area of the samples changes between 100 m2 /g and 700 m2 /g and the pore size of the particles changes between 3.0 and 6.0 nm by changing the SDS/Pluronic mole ratio. This ratio is also effective on the micropore amount of the samples together with mesopores. The tunable particle size (between 0.2µ to 1000µ) and morphology (spheres, rods, muffin and ‘s’ shaped.) can be achieved by changing the SDS concentration. Furthermore, the low reaction temperature (below RT) is essential for the synthesis of mesoporous silica particles in SDS-Pluronic system. However, the low temperature is a problem for micellization. This problem was overcome by using P123, which has low critical micellization concentration (CMC) and critical micellization temperature (CMT) values or by using Hofmeister ions to decrease the pluronic surfactant solubility and the CMC and CMT of the pluronics used. Decreasing solubility of the pluronics causes effective micellization of the surfactants. The well defined micelles are the templates for the synthesis of mesoporous silica particles. Overall , the effects of SDS/Pluronic mole ratio, pH and temperature of the synthesis solution, TMOS concentration, and the additives (alkali salts) have been investigated by synthesis of more than 300 samples that were analyzed using PXRD, SEM, TEM, POM, and N2 sorption techniques.