Influence of Alkylpyridinium Cation Length on the Sorption Properties of Template-Containing Mesoporous Molecular Sieves

Mesoporous MSM-41 molecular materials containing alkylpyridinium templates are shown to have the properties of microporous sorbents. Characteristic energy of the sorption in micropores of these materials decreases as the surfactant hydrocarbon radical lengthens, irrespective of a sorbate type. The sorption volume of the pores of template-containing MSM-41 sieves accessible to water and methanol vapors decreases with the lengthening of the hydrophobic radical of a template. This dependence has an extremal pattern for the sorption of propanol-2 and hexane vapors. A conclusion is drawn that, under the chosen synthesis conditions of the mesophase materials, the packing density of surfactant molecules in encapsulated micelles increases with the lengthening of the alkyl radical. It is assumed that the differences in the packing densities of surfactant molecules substantially explain the characteristic sorption properties and the perfection of the hexagonal structure of prepared MSM-41 mesophase materials.     

Synthesis,liquid crystalline properties and fluorescence of polycatenar 1,3,4‐oxadiazole derivatives

A series of hexacatenar liquid crystals containing the 1,3,4‐oxadiazole group as rigid core, i.e. 1,4‐bis[(3,4,5‐trialkoxyphenyl)‐1,3,4‐oxadiazolyl]‐ benzene (P‐P‐oxd‐n), were designed and synthesised. Based on a detailed study of their thermotropic phase behaviour and mesophase structures, it was revealed that columnar phases are generated in these materials. Furthermore, combination of experimental and calculated results enabled a proposal for the molecular packing in the mesophase. The photoluminescent properties of these materials were examined using P‐P‐oxd‐8 as an example. A strong blue light emission (λ_max = 456 nm) was observed in P‐P‐oxd‐8 and a higher quantum yield was obtained in dilute chloroform solution.     

ABC copolymer silicone surfactant templating for biomimetic silicification

Using the ABC copolymer silicone surfactant polydimethylsiloxane (PDMS)-graft-(polyethylene oxide (PEO)-block-propylene oxide (PPO)) (PSEP, Scheme 1a) as a template and tetraethoxysilane (TEOS) as a silica source, silica particles with various structures and morphologies (i.e., disordered spherical micellar aggregation, two-dimensional p6mm mesostructure, asymmetric multi-layer non-equilibrium vesicles and symmetric monolayer vesicles) were synthesized by changing the synthesis temperature from 30 to 80 °C. Increasing the hydrophobicity of the surfactant by increasing the temperature resulted in an increase in the surfactant packing parameter g, which led to the mesophase transformation from micellar to cylinder and later to a lamellar structure. The good compatibility between the PDMS and the TEOS, the different natures of the hydrophobic PDMS and PPO segments, and the hydrolysis and condensation rates of TEOS enabled the variation of silicification structures. This novel silicone surfactant templating route and a new type of materials with highly ordered mesostructures and asymmetric morphologies provide a new insight into the molecular factors governing inorganic-organic mesophase and biosilicification for fabricating functionalized materials.     

Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers

Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.     

The effect of the counteranion on the formation of mesoporous materials under the acidic synthesis process

The presence of various counteranions at the interfacial region of the silicate-surfactant mesophase introduces opportunities for manipulation of the phase structure. Well-ordered 3D-hexagonal P63/mmc, cubic Pmn, 2D-hexagonal p6mm, and cubic Iad mesoporous materials have been synthesized with the same surfactant, cetyltriethylammonium bromide, in the presence of various acids. The counteranions of acidic media have resulted in increasing the surfactant packing parameter g in the order SO42- < Cl- < Br- < NO3-, which leads to the different time course of formation of mesostructures. The effect of counteranions on the formation of mesostructures is explained in terms of not only the adsorption strength on the headgroups of the surfactant micelle but also the rate of silica condensation affecting the charge density matching between the surfactant and silica. It has been found that the mesophase is always transformed from the larger g parameter into the smaller one. The distinct morphologies of the 3D-hexagonal P63/mmc mesophases have been rationally explained by supposing this particular mesostructure. The cubic Iad phase has been first synthesized under acidic conditions.     

Synthesis and thermotropic behaviour of liquid crystals containing tolane-based mesogenic units

Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain.     

Liquid crystals derived from 2-phenylisoindoles: synthesis and characterization

2-Phenylisoindole was investigated as the rigid core unit in a series of asymmetric mesogenic molecules. When the 2-phenylisoindole core was terminated with a hexyl tail, no mesophase formation could be observed. When 4- n -(tridecafluorohexyl) was used, however, both monotropic and enantiotropic phase behaviour were observed. It was found that most functionalities at the anhydride 5-position results in the formation of smectic A (SmA) phases in the temperature range 70-180°C. Functionalities at the anhydride 4-position suppress mesophase formation. Large substituents (-Br, -NO2) and symmetric substitution patterns (5,6-dichloro, 4,7-dichloro and 4,5,6,7-tetrachloro) on the anhydride moiety increase the melting point and destabilize the mesophase. Temperature dependent X-ray diffraction experiments suggest an interdigitated SmA packing for this family of compounds.     

Synthesis and thermotropic behaviour of liquid crystals containing tolane-based mesogenic units

Abstract

Tolane-based liquid crystal materials with three different terminal groups: trifluoromethyltolanes, cyanotolanes, and nitrotolanes, and with different chain lengths of alkenyloxy groups, have been synthesized. The phase behaviour of these liquid crystal materials has been characterized by differential scanning calorimetry, optical polarized light microscopy and X-ray diffraction. The mesophase behaviour of the materials was shown to be significantly influenced by the polarity of the terminal groups. The trifluoromethyltolanes exhibit an enantiotropic smectic E mesophase and the cyanotolanes exhibit a monotropic nematic mesophase. The most polar among the three types of liquid crystal material; the nitrotolanes do not display any liquid crystalline phases, except for the homologue with an eleven methylene unit chain.     

The self-ordering properties of novel phthalocyanines with out-of-plane alkyl substituents

Two novel homologous series of phthalocyanines were prepared from 2,2-dialkylindane and 2,2-dialkyl-1,3-benzodioxole precursors. It was anticipated that attaching alkyl chains to five-membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out-of-plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket-fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2-dialkyl-1,3-benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin-coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2-dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single-crystal X-ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out-of-plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron-donating oxygen atoms directly attached to the ring.     

Influence of silver nanoparticles on the phase behavior of side-chain liquid crystalline polymers

The synthetic approach to the new class of mesomorphous nanocomposite polymer systems was developed. It is based on the in situ reduction of silver ions in the liquid crystalline (LC) polymer matrix leading to the formation of nanoparticles with typical sizes in the range of 5-30 nm. The influence of silver nanoparticles on the phase state of the LC composites, i.e., type and temperature interval of the mesophase, was studied. Regardless of chemical structure of the LC polymer matrix, an increase in the metal concentration is accompanied by a decrease of clearing temperature due to adsorption of macromolecules on the nanoparticle's surface. In the case of an LC copolymer with cyanobiphenyl side mesogenic fragments, the complete disruption of mesophase is observed below 2 wt% content of silver. This phenomenon is, most likely, a result of chemosorption of terminal cyano groups on the nanoparticles with the formation of sigma complexes that disturb packing of the mesogenic units.     

Liquid-crystalline symmetric triblock copolymers

Symmetric fully liquid-crystalline triblock copolymers of various structures containing optically active mesogenic groups are for the first time synthesized via pseudoliving radical reversible addition-fragmentation chain-transfer polymerization. Their phase behavior and physicochemical and optical properties are studied. It is shown that, depending on composition, at low temperatures block copolymers can form at temperatures phase-separated structures caused by microsegregation of blocks of different chemical natures and that, with an increase in temperature, these structures can mix to form a cholesteric mesophase characterized by a helical supramolecular structure. A model illustrating the molecular packing of block copolymers with a phase-separated lamellar structure is advanced. The effect of the molecular structure of the block copolymers on their optical properties is discussed.     

Physicochemical Properties of Mesoporous Mesophase Silicate Materials Formed via the Electrostatic S+I– Mechanism

The formation of the structure of a highly organized silicate mesoporous mesophase material (MMM) with hexagonal packing via the S⁺I^–reaction pathway and MMM-based aluminosilicates (Al,Si)-MMM and titanosilicates (Ti,Si)-MMM with different concentrations of the elements are considered. The structural, textural, and catalytic properties of the materials are studied.     

Studies of the thermotropic mesophase behaviour exhibited by a highly asymmetric tetrabenzotriazaporphyrin derivative

The thermotropic mesophase behaviour of an asymmetrically shaped and highly substituted tetrabenzotriazaporphyrin (TBTAP) derivative has been studied by optical microscopy, DSC and X-ray diffraction. The TBTAP macrocycle differs from the more common phthalocyanine ring system by the substitution of a methine for a nitrogen at one meso-position. The TBTAP core was substituted with a single heptadecyl chain at this meso-position and four neopentyl groups were statistically distributed around the peripheral benzene rings. In contrast to an earlier study of this system which described the structure of the mesophase as discotic lamellar, detailed X-ray diffraction study indicates that the TBTAP derivative forms a disordered hexagonal columnar mesophase (Col hd ), with a weak tendency towards antiparallel orientation of neighbouring molecules observed in the form of a weak pseudo-centred rectangular packing.     

Chirality Synchronization of Hydrogen‐Bonded Complexes of Achiral N‐Heterocycles

2,4‐Diamino‐6‐phenyl‐1,3,5‐triazines carrying a single oligo(ethylene oxide) (EO) chain form an optically isotropic mesophase composed of a conglomerate of macroscopic chiral domains with opposite sense of chirality even though the constituent molecules are achiral. This mesophase was proposed to result from the helical packing of hydrogen‐bonded triazine aggregates, providing long‐range chirality synchronization. The results provide first evidence for macroscopic achiral symmetry breaking upon conglomerate formation in an amorphous isotropic phase formed by hydrogen‐bonded associates of simple N‐heterocycles that are related to prebiotic molecules.     

Self-organization of amphiphilic liquid-crystalline dendrimers in bulk and at the interface

A comparative analysis of the structure and phase behavior of synthesized carbosilane amphiphilic LC dendrimers of the third generation containing mesogenic phenyl and oligo(ethylene glycol) fragments is performed. When phenol groups are replaced with oligo(ethylene glycol) moieties, the temperature interval of the existence of the LC phase in the mesogen-containing dendrimers decreases. The chemical nature of hydrophilic terminal groups is found to control the organization of dendrimers in the smectic mesophase. Structural models for their packing are proposed. Amphiphilic dendrimers are shown to form stable Langmuir films at the water/air interface. Surface-pressure-surface area-isotherms are constructed. The effect of the chemical nature of hydrophilic groups on the formation of a monolayer at the interface and on the packing density of dendrimer molecules in the monolayer is discussed.     

Mesophase structure of low‐wetting liquid crystalline polyacrylates with new perfluoroalkyl benzoate side groups

The synthesis, thermal behavior, bulk microstructure, and wettability of new polyacrylates carrying spaced 4‐perfluorohexylpropyl benzoate and 4‐perfluorooctylpropyl benzoate units in the side groups were investigated. X‐ray diffraction analysis proved the formation of different smectic mesophases (SmI₂, SmF₂, and SmC₂) and the evolution of their structures and lattice parameters with temperature. The mesophase polymorphic behavior depended on the length of the perfluorinated chain segment in the repeat unit. The electron density profiles along the smectic layer normal were drawn and provided a deeper insight into the packing of the side chains in a tilted, double layer structure. Thin polymer films were cast from solution, and their low wettability was established by measurements of contact angles with different probing liquids. We suggest that the hydrophobicity and lipophobicity of the films are enhanced by the mesophase surface structure which is mediated by the high‐order, mesophase bulk structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4128–4139, 2010     

Aliphatic Liquid Crystals with Positive Dielectric Anisotropy

Cyanothyl-subsituted cylohexyl cyclohexanoates, bi(cyclohexanes) and phenyl cyclohexanes were synthisized. Their mesmorphic behaviour is compared to that of the corresponding cyano derivatives. (Cyanoethyl)cyclohexyl cyclohenxanoates show mesmorphic properties in contrast to the corresponding cyano derivative. Separation of the cyano substituent from the rigid core of an anisotropic aliphatic compound by methylene groups enhances the thermodynamic stability of the mesophase. In aromatic compound, the cyanoethyl group leads to lower clearing points. These phenomena are attributed to teh influence of steric effects on the packing density and to the dependence of the clearing point on molecular association.     

Interactions of surfactants in nonionic/anionic reverse hexagonal mesophases and solubilization of α-chymotrypsinogen A

In an attempt to form H_II mesophases at room temperature we prepared lyotropic liquid crystals with two surfactants of the same lipophilic tails (glycerol monooleate, GMO, and oleyl lactate, OL) but differing in the size and charge of the headgroups.Increasing OL concentration significantly affected the hydration of the headgroups and subsequently the lipids packing. At low OL content the cubic mesophase was formed, while at higher OL contents the formation of hexagonal mesophase was favored. It was assumed that OL competed on the water binding, tuning the headgroups’ curvature and the packing parameter inducing the formation of reverse hexagonal mesophase. It was detected that cubic mesophase transformed upon heating to hexagonal structures. The hexagonal mesophases, which were formed both immediately after preparation and after aging, remained stable at elevated temperatures.α-Chymotrypsinogen was solubilized into the obtained LLCs at relatively high concentration (up to 1 wt%). The lattice parameter of the host LLCs exhibited a decrease as a function of the protein content. This process was assigned to partial dehydration of the GMO polar moieties in favor to CTA hydration.Generally speaking, the present study indicated that adding anionic to nonionic lipid is highly beneficial to gain additional compositional and structural characteristics of LLCs.     

Crystallization of the mesomorphic form and control of the molecular structure for tailoring the mechanical properties of isotactic polypropylene

The combination of the control of the concentration of stereodefects in isotactic polypropylene using metallocene catalysts and the crystallization via the mesophase is a strategy to tailor the mechanical properties. Stiff materials, flexible materials, and thermoplastic elastomers can be produced depending only on the concentration of rr stereodefects. Modulus, ductility, and strength can be modulated through the crystallization of α and γ forms or of the mesophase. Different morphologies are observed depending on the stereoregularity and conditions of crystallization. Crystals of the mesomorphic form always exhibit a nodular morphology, accounting for the similar good deformability of all quenched samples, whatever the concentration of stereodefects. The mesophase transforms by thermal treatments into the α form preserving the nodular morphology, with increase of strength while maintaining the ductility typical of the mesophase. Annealing of the mesophase permits a precise adjustment of crystallinity and size of nodular crystals offering additional options to modify the mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 677–699