About: Lamellar structure is a(n) research topic. Over the lifetime, 14658 publication(s) have been published within this topic receiving 351300 citation(s). The topic is also known as: microstructures.
Papers published on a yearly basis
TL;DR: In this paper, a family of highly ordered mesoporous (20−300 A) structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media.
Abstract: A family of highly ordered mesoporous (20−300 A) silica structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media. Periodic arrangements of mescoscopically ordered pores with cubic Im3m, cubic Pm3m (or others), 3-d hexagonal (P63/mmc), 2-d hexagonal (p6mm), and lamellar (Lα) symmetries have been prepared. Under acidic conditions at room temperature, the nonionic oligomeric surfactants frequently form cubic or 3-d hexagonal mesoporous silica structures, while the nonionic triblock copolymers tend to form hexagonal (p6mm) mesoporous silica structures. A cubic mesoporous silica structure (SBA-11) with Pm3m diffraction symmetry has been synthesized in the presence of C16H33(OCH2CH2)10OH (C16EO10) surfactant species, while a 3-d hexagonal (P63/mmc) mesoporous silica structure (SBA-12) results when C18EO10 is used. Surfactants with short EO segments tend to form lamellar mesost...
12 Feb 1996-Macromolecules
TL;DR: In this article, a mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented, which traverses the weak- to strong-segregation regimes, is free of traditional approximations.
Abstract: A mean-field phase diagram for conformationally symmetric diblock melts using the standard Gaussian polymer model is presented. Our calculation, which traverses the weak- to strong-segregation regimes, is free of traditional approximations. Regions of stability are determined for disordered (DIS) melts and for ordered structures including lamellae (L), hexagonally packed cylinders (H), body-centered cubic spheres (QIm3m), close-packed spheres (CPS), and the bicontinuous cubic network with Ia3d symmetry (QIa3d). The CPS phase exists in narrow regions along the order−disorder transition for χN ≥ 17.67. Results suggest that the QIa3d phase is not stable above χN ∼ 60. Along the L/QIa3d phase boundaries, a hexagonally perforated lamellar (HPL) phase is found to be nearly stable. Our results for the bicontinuous Pn3m cubic (QPn3m) phase, known as the OBDD, indicate that it is an unstable structure in diblock melts. Earlier approximation schemes used to examine mean-field behavior are reviewed, and compa...
01 Jan 1964-Journal of Molecular Biology
TL;DR: The negative-staining technique was applied to the study of lipid phase structures in the electron microscope and lecithin dispersions were shown to be progressively disrupted after mixing with lysolecithin in water.
Abstract: The negative-staining technique was applied to the study of lipid phase structures in the electron microscope. Lecithin dispersions were seen to contain spherulites composed of concentric lamellae. The width of the lipid layer was estimated to be 44 A. Rod-shaped elements were also observed and interpreted as being groups of lipid molecules arranged at right angles to the long axis of the lamellae. Preparations of lecithin-cholesterol of equal molar proportions were described as being basically the same as lecithin alone. Saponin modified the lamellar structure of lecithin-cholesterol in such a way as to produce an array of perforations with a centre-to-centre spacing of 120 A and with a diameter of 85 A. Separated rings together with helical structures estimated to be 220 A in diameter with an axial hole of 68 A were described. The helical structures showed a well-defined periodicity of 58 to 59 A along the axis. Lecithin dispersions were shown to be progressively disrupted after mixing with lysolecithin in water. Beading of the lamellae was a pronounced feature. Lecithin progesterone dispersions in water produced a line structure of about 20 to 22 A across.
TL;DR: Model Q230 proposed by Mariani and his co-workers satisfactorily fits the x-ray data collected on the cubic mesostructure material and suggests that the silicate polymer forms a unique infinite silicate sheet sitting on the gyroid minimal surface and separating the surfactant molecules into two disconnected volumes.
Abstract: A model is presented to explain the formation and morphologies of surfactant-silicate mesostructures. Three processes are identified: multidentate binding of silicate oligomers to the cationic surfactant, preferential silicate polymerization in the interface region, and charge density matching between the surfactant and the silicate. The model explains present experimental data, including the transformation between lamellar and hexagonal mesophases, and provides a guide for predicting conditions that favor the formation of lamellar, hexagonal, or cubic mesostructures. Model Q(230) proposed by Mariani and his co-workers satisfactorily fits the x-ray data collected on the cubic mesostructure material. This model suggests that the silicate polymer forms a unique infinite silicate sheet sitting on the gyroid minimal surface and separating the surfactant molecules into two disconnected volumes.
TL;DR: In this article, a solgel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate is presented, which can be used for membrane-based separations, selective catalysis and sensors.
Abstract: Thin films of surfactant-templated mesoporous materials1,2 could find applications in membrane-based separations, selective catalysis and sensors. Above the critical micelle concentration of a bulk silica–surfactant solution, films of mesophases with hexagonally packed one-dimensional channels can be formed at solid–liquid and liquid–vapour interfaces3,4,5. But this process is slow and the supported films3,5 are granular and with the pore channels oriented parallel to the substrate surface, so that transport across the films is not facilitated by the pores. Ogawa6,7 has reported a rapid spin-coating procedure for making transparent mesoporous films, but their formation mechanism, microstructure and pore accessibility have not been elucidated. Here we report a sol–gel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate. The influence of the substrate generates film mesostructures that have no bulk counterparts, such as composites with incipient liquid-crystalline order of the surfactant–silica phase. We are also able to form mesoporous films of the cubic phase, in which the pores are connected in a three-dimensional network that guarantees their accessibility from the film surface. We demonstrate and quantify this accessibility using a surface-acoustic-wave nitrogen-adsorption technique. We use fluorescence depolarization to monitor the evolution of the mesophase in situ, and see a progression through a sequence of lamellar to cubic to hexagonal structures that has not previously been reported.
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