Control of mesostructure and morphology of surfactant-templated silica in a mixed surfactant system

Abstract

Mixed cationic surfactants were used in the synthesis of MCM-41 materials. Synthetic conditions for controlling the nanometer-scale channels size and micrometer-scale morphology in mixed alkyltrimethylammonium halides systems (n \ 8È18 ; X \ Cl or Br) were studied. The spacing (C n TMAX) d 100 of MCM-41 synthesized using the system decreases linearly with increase in the C 18 TMABrÈC 14 TMABr molar fraction. Such linearity was also reproduced in other systems with some deviation at high C 14 TMABr molar fractions of short chain length surfactants (n \ 14). The morphology in mixed system can be C n TMABr changed from particle form to a tubules-within-tubule (TWT) structure by adjusting the average surfactant chain length. It was found that the optimum average chain length for preparing a TWT structure is 15È16 for the mixed system and 16È17 for the mixed system. A high yield TWT morphology also C n TMABr C n TMACl can be prepared by adding the cosolvent acetone to a suitable value of the hydrophobicÈlipophilic balance (HLB). The change in morphology of the products with respect to average chain length, counter ions and cosolvents are explained by the principle of hydrophilicÈhydrophobic (lipophilic) balance (HLB).

Control of morphology in synthesizing mesoporous silica

“…During the early stage, where the liquid crystalline surfactant/silicate assembly is still very soft, one could form many structures in the micron scale by various methods, including phase transformation between mesophases [19] and cosolvent control [22]. We will discuss them separately in the following sections.…”

Fabrication and Size‐Selective Bioseparation of Magnetic Silica Nanospheres with Highly Ordered Periodic Mesostructure

“…It has been demonstrated that the nanometer-scale structures of the mesoporous materials synthesized by longer carbon chain surfactants are more highly ordered than those prepared by the shorter chain surfactants under the same conditions. [50,51] This is expected because the higher hydrophobicity can lead to longer cylindrical micelles and a well-ordered hexagonal phase. In contrast, the shorter chain surfactants cannot easily aggregate to form long micelles and the micellar surface becomes rough, which leads to worsened packing and poor order in the mesostructure.…”

“…In contrast, the shorter chain surfactants cannot easily aggregate to form long micelles and the micellar surface becomes rough, which leads to worsened packing and poor order in the mesostructure. [50,51] L. Zhang et al / Mesoporous Magnetic Silica Nanospheres Sol-gel processing temperature plays an important role in the self-assembly of surfactant/silica complexes because the hydrophobic interactions change relative to temperature and the micellization is largely affected by these interactions. For MSNs-C 14 synthesis, a low temperature (30 8C) makes C 14 TAB more hydrophobic which may favor a tight aggregation of the surfactant in a micelle and the formation of highly ordered hexagonal phase.…”

Synthesis,Mechanisms and Different Applications of Mesoporous Materials Based on Silica and Alumina

“…Generally, tailoring the pore sizes of OMMs can be achieved either by using surfactants with various chain lengths, or by adding swelling agents, such as 1, 3, 5-trimethylbenzene (TMB), amines, and decane and/or hydrothermal treating under different temperatures. Very recently, Chang and co-workers (11) used a blend of cationic-cationic surfactants, and Ryan and co-workers (12) used the mixed triblock copolymer surfactants to tailor the pore morphology. Lee et al (13) utilized the hexadecyl-ether-type surfactant and CTAB as co-surfactant to tailor the pore size of OMMs.…”