Influence of solvent-headgroup interactions on the formation of lyotropic liquid crystal phases of surfactants in water and nonaqueous protic and aprotic solvents

Auvray, X.; Perche, T.; Petipas, C.; Anthore, R.; Marti, M. J.; Rico, I.; Lattes, Armand

doi:10.1021/la00047a017

Cited by 37 publications

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“…[41] Simultaneously, the diffusion of ethanol into the CTAB micelles reduces the interaction of the alkyl tails, which increases the hydrophobic volume of the micelles and lowers their curvature. [42,43] Furthermore, the presence of ammonia facilitates the formation hydrogen bonds between the adjacent CTAB micelles and silicate oligomers, which also favors the formation of parallel mesochannels to reduce the curvature energy of the micelles. Owing to these three factors, the CTAB-silicate composites undergo a structure transition from spherical to…”

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Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

et al. 2012

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Surfactant-templated synthesis [1,2] has been a focus of materials science, because it provides a unique means to prepare a variety of ordered mesostructured materials with high surface areas and large, uniform pores. These materials have shown great promise for applications in physics, chemistry, and biology. [3][4][5][6][7][8][9] Different morphologies of mesoporous materials, such as spheres, films, monoliths, rods, and fibers, can all be controllably synthesized. [10,11] Among these, mesoporous thin films have attracted significant attention owing to their unique structures and functions. [12][13][14][15] Previously, ordered mesoporous silica films have been synthesized by selfassembly of silica precursors with surfactant templates at air-water [16] or water-oil interfaces, [17] or by using the evaporation-induced self-assembly (EISA) approach.[18] As the surfactant micelles tend to orient parallel to substrates to reduce the surface energy at interfaces, the mesochannels obtained are always oriented parallel to the film surfaces. [3,[19][20][21] Continuous mesoporous films with perpendicularly aligned channels have recently been prepared by guiding the self-assembly of block copolymers or gemini surfactants with organosilica. [22][23][24][25] However, the thermal and mechanical stability of the films are low, as the pore walls consist of polymers and organosilica. Substrate-templating growth strategies for controlling mesopore orientation based on pp or hydrophilic-hydrophobic interactions have been reported. [26][27][28][29][30] However, these methods require special substrates, such as pyrolytic graphite, anodic alumina with conical holes, or block polymer modified glass, and the alignment of the mesophases at their interface is generally of mixed orientation. Furthermore, perpendicular mesochannels have also been prepared by magnetic-field or electrochemically assisted methods. [31,32] However, these methods often require special equipment and complex processes, and the obtained films have poor regularity and low levels of mesochannel alignment. To date, the synthesis of films with mesopore channels perpendicular to a substrate is still a major challenge.The Stçber approach is a facile and effective method for the synthesis of uniform mesoporous silica nanospheres by a self-assembly process using silica precursors with surfactant templates in an aqueous ethanol solution.[33] The ordered mesochannels in these mesoporous silica nanospheres are often oriented radially to the particle surfaces, [34][35][36] which is an ideal pore arrangement for applications such as catalysis and selective adsorption. Herein, we demonstrate a simple Stçber-solution growth method for the synthesis of mesoporous silica thin films with continuous 2D-ordered mesochannels perpendicular to the substrate. This is accomplished by immersing the substrate into a Stçber solution containing cetyltrimethylammonium bromide (CTAB), tetraethoxysilane (TEOS), ethanol, and ammonia. Moreover, a new type of sandwichlike mesoporous silica film, w...

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Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

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“…At low concentrations, these free silicate species are preferentially deposited at the junction between the spherical micelles and the substrate, which is expected to screen the intra‐micelle electrostatic repulsion among adjacent head groups 41. Simultaneously, the diffusion of ethanol into the CTAB micelles reduces the interaction of the alkyl tails, which increases the hydrophobic volume of the micelles and lowers their curvature 42. 43 Furthermore, the presence of ammonia facilitates the formation hydrogen bonds between the adjacent CTAB micelles and silicate oligomers, which also favors the formation of parallel mesochannels to reduce the curvature energy of the micelles.…”

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Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

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“…In our opinion, Evans et al did not observe aggregation because they worked at a too low temperature. We have been able to detect liquid crystalline phases in the binary system hexadecylpyridinium bromide/3-methylsydnone by optical microscopy and small angle X-ray diffraction: we observed two phases, the first one at 45.4 °C and the second at 55 °C [18]. Our conclusion was: surfactant self aggregation can thus occur in 3-methylsydnone and therefore in an aprotic solvent.…”

Section: -Methylsydnone: a New Mesoionic Liquid Solventmentioning

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Zwitterionic and mesoionic liquids: Molecular aggregation in 3-methylsydnone

2010

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Ionic liquids are green solvents with interesting properties: displaying low melting points and high boiling points. They offer a new approach applicable in many instances. Nevertheless, the presence of free ions can be a matter in some cases, e.g. for the study of nucleophilic reactions, in electrochemistry, and in each situation where there is a competition between counter ions, as in micellization of ionic surfactants. Neutral compounds having formal unit electrical charges of opposite sign, and the same physical properties than ionic liquids would be a nice alternative to these latter solvents. There are two classes of chemical compounds having these characteristics: zwitterionic liquids (with no uncharged canonical representation) and mesoionic liquids (in which the negative and the positive charges are delocalized). In that last class we have chosen to work with 3-methylsydnone in order to examine, in this aprotic solvent, if it was possible to observe aggregation of surfactants in the same manner as in water. With all kinds of surfactants studied (ionic, zwitterionic and mesoionic) we have been able to demonstrate the formation of direct micelles: hydrogen bonding is thus not mandatory for molecular aggregation. Comparison of the behavior in water and in formamide showed that solvophobic interactions were qualitatively comparable but with a lower intensity.

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Influence of solvent-headgroup interactions on the formation of lyotropic liquid crystal phases of surfactants in water and nonaqueous protic and aprotic solvents

Cited by 37 publications

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Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

Zwitterionic and mesoionic liquids: Molecular aggregation in 3-methylsydnone

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