Critical Roles of Cationic Surfactants in the Preparation of Colloidal Mesostructured Silica Nanoparticles: Control of Mesostructure, Particle Size, and Dispersion

Abstract

Mesoporous silica nanoparticles are promising materials for various applications, such as drug delivery and catalysis, but the functional roles of surfactants in the formation and preparation of mesostructured silica nanoparticles (MSN-as) remain to be seen. It was confirmed that the molar ratio of cationic surfactants to Si of alkoxysilanes (Surf/Si) can affect the degree of mesostructure formation (i.e., whether the mesochannels formed inside the nanoparticles actually pass through the outer surface of the particles), the particle diameter, and the dispersibility of MSN-as. Wormhole-like mesostructures formed with low Surf/Si ratios; however, the mesopores did not pass through the outer surface of the particles completely. At high Surf/Si ratios, the mesostructures extended. The particle diameter was 100 nm or larger at low Surf/Si ratios, and the primary particle diameter decreased as the Surf/Si ratio increased. This was because the surfactants enhanced the dispersity of the alkoxysilanes in water and the hydrolysis rate of the alkoxysilanes became faster, leading to an increased nucleation as compared to the particle growth. Moreover, primary particles aggregated at low Surf/Si ratios because of the hydrophobic interactions among the surfactants that were not involved in the mesostructure formation but were adsorbed onto the nanoparticles. At high Surf/Si ratios, the surfactant micelles were adsorbed on the surface of primary particles (admicelles), resulting in the dispersion of the particles due to electrostatic repulsion. In particular, molar ratios of 0.13 or higher were quite effective for the preparation of highly dispersed MSN-as. Surfactants played important roles in the mesostructure formation, decreasing the particle diameters, and the dispersibility of the particles. All of these factors were considerably affected by the Surf/Si ratio. The results suggested novel opportunities to control various colloidal mesostructured nanoparticles from the aspects of composition, structure, and morphology and will also be useful in the development of novel methods to prepare nanomaterials in various fields.

Improved Performance of Lipase Immobilized on Tannic Acid-Templated Mesoporous Silica Nanoparticles

“…The hydrodynamic diameter is slightly higher than the particle size determined from SEM and TEM (ca. 195 ± 16 nm), which can be attributed to the existence of an extra hydration layer and diffuse electrical double layer [34][35][36][37]. These results are in agreement with Yamamoto et al and Fu et al [36,37].…”

Monodispersed mesoporous silica nanospheres based on pyridinium ionic liquids

“…Template with longer alkyl chain length will have a lower CMC value and hence more nuclei will be observed in the solution state. This leads to a smaller particles size as the nucleation dominates the reaction [20,41,43].…”

“…Bein et al reported on the use of triethanolamine (TEA) as the base for the reaction as it would act as the catalyst and encapsulator in developing monodispersed MSNs [17]. In the recent years, Yamada et al utilizes TEA in generating monodispersed MSNs while studying the effects of template amount, presence of alcohol, types of alcohols and alkyl chain length of the template on the synthesized MSNs [18][19][20]. All these researches used the common template which is cetyltrimethylammonium bromide or chloride (CTAB/CTACl).…”

Colloidal Mesoporous Silica Nanoparticles

“…78 In such high ratios, the micelles of surfactants are probably adsorbed on the outer surface of mesostructured silica nanoparticles, and act as dispersants. In fact, the surfactant/Si ratios of all of the preparative methods of colloidal mesostructured silica nanoparticles were higher than 1.2, as shown in Table 1.…”