Lytropic Liquid Crystals Research Articles

Pt nanocrystallines/TiO2 with thickness-controlled carbon layers: Preparation and activities in CO oxidation

In this work, a series of Pt nanocrystallines (Pt NCs) supported on TiO2 substrate with controlled thickness of carbon layers (C-Pt/TiO2) were synthesized. Well-dispersed Pt NCs were facilely synthesized at room temperature by a photo-reduction process in lytropic liquid crystal (LCs). Surface tuning of the carbon layers on Pt/TiO2 catalysts was achieved by varying the calcination atmospheres (in argon, air, and oxygen) and characterized by XPS and HRTEM. The influence of the coated carbon layers on the catalytic activity of catalysts is investigated by CO oxidation reaction which presented the following ranks: C-Pt/TiO2-O2>C-Pt/TiO2-Air>C-Pt/TiO2-Ar. It is found that the carbon layer coating can stabilize the Pt NCs and enable them anti-sintering at high temperature. This finding provides new insight into understanding the C-Pt/TiO2 ternary system for tuning their catalytic performance.

Photoluminescent lyotropic liquid crystals formed by Tyloxapol and n-dodecyl tetraethylene monoether

Photoluminescent lytropic liquid crystals (LLCs) were prepared in aqueous solutions from n-dodecyl tetraethylene monoether (C12E4) and Tyloxapol, which is an oligomer of polyoxyethylene tert-octylphenyl ether (TX-100) with a polymerization degree below 7. The close packing of the seven benzene rings in Tyloxapol induces a strong π–π interaction, which makes Tyloxapol fluorescent. The Tyloxapol/C12E4 mixed system were characterized by polarized optical microscopy (POM) observations, small-angle X-ray scattering (SAXS), rheological and fluorescence measurements with close comparison to the TX-100/C12E4 mixture. It was found that the type of LLCs transfered gradually from lamellar phase to hexagonal phase with increasing mass ratio of Tyloxapol to C12E4, during which an enhanced photoluminescence was observed. Our results showed that encapsulation of fluorescent molecules into the matrix of traditional surfactants could be an effective way for the preparation of photoluminescent LLCs.

Interfacial Pressure/Area Sensing: Dual-Fluorescence of Amphiphilic Conjugated Polymers at Water Interfaces.

Exciton migration to emissive defects in π-conjugated polymers is a robust signal amplification strategy for optoelectronic sensors. Herein we report end-capped conjugated polymers that show two distinct emissions as a function of interpolymer distances at the air-water and hydrocarbon-water interfaces. Amphiphilic poly(phenylene ethynylene)s (PPEs) end-capped with perylene monoimides display two distinct emission colors (cyan from PPE and red from perylene), the relative intensity of which depends on the surface pressure applied on the Langmuir monolayers. This behavior produces a ratiometric interfacial pressure indicator. Relative quantum yields are maintained at the different surface pressures and hence display no sign of self-quenching of the excitons in an aggregated state. These polymers can be organized at the micelle-water interface in lytropic liquid crystals, thereby paving the way for potential applications of end-capped amphiphilic conjugated polymers in biosensors and bioimaging.

Structural changes in a cationic surfactant-water mixtures

Structure and structural changes in 3-tetradecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R14HTAB)/H2O mixtures have been studied by steady and dynamic shear rheology. The results showed that the self-aggregate undergo two transitions in shape from spherical to rod-like micelles to viscoelastic wormlike micelles and to the hexagonal lytropic liquid crystal in the investigated concentration range. The transition of spherical micelles into rod-like micelles takes place above 300 mmol kg−1. The overlap threshold micelle concentration is about 500 mmol kg−1, and the η0 and R14HTAB concentrations give relationship of the power law, i.e. . The microstructure of the formed micelles has been further ascertained by FF-transmission electronic microscopy. The deviations from Cox–Merz rule for the complex dynamic viscosity and the shear viscosity at above the critical shear rate mainly come from the formation of hydrogen bond.

ChemInform Abstract: Stereoselective Photochemical Reaction of Cyclohexyl Phenyl Ketone within Lytropic Liquid Crystals Formed by Chiral Ionic Liquids.

AbstractThe hexagonal liquid crystals composed of chiral (S)‐3‐hexadecyl‐1‐(1‐hydroxy‐propan‐2‐yl)‐imidazolium bromide (HLC), p‐xylene, and H2O can be used as a microreactor to achieve a stereoselective photochemical reduction.

Stereoselective Photochemical Reaction of Cyclohexyl Phenyl Ketone within Lytropic Liquid Crystals Formed by Chiral Ionic Liquids

AbstractIrradiation of cyclohexyl phenyl ketone (1) results in either intra‐ or intermolecular hydrogen abstraction to afford compounds 1‐phenylhept‐6‐en‐1‐one (2) and α‐cyclohexyl benzyl alcohol (3) as photoproducts, in which 3 has a pair of enantiomers. Herein, two types of chiral hexagonal liquid crystals were prepared to direct the enantioselective photochemical reaction of 1. One of the hexagonal liquid crystals is composed of 1‐tetradecyl‐3‐methylimidazolium bromide/p‐xylene/H2O with the modification by a chiral inductor. The other one is formed by chiral (S)‐3‐hexadecyl‐1‐(1‐hydroxy‐propan‐2‐yl)‐imidazolium bromide/p‐xylene/H2O. The product analysis shows that the latter one can be used as a microreactor to achieve stereoselective photochemical reaction, while the former one produced compound 3 with no enantioselectivity at all.

Fabrication and Characterizes of TiO<sub>2</sub> Nanomaterials Templated by Lyotropic Liquid Crystal

TiO2 nanomaterials were synthesized in lyotropic liquid crystal formed by nonionic surfactant TritonX-100 and TiOSO4 aqueous solution with NH3•H2O as precipitator. The lyotropic liquid crystals were characterized by means of POM and Low-angle XRD. FT-IR, TGA, XRD, TEM were used to characterize the TiO2 samples. It was found that all the lytropic liquid crystal were in lamellar liquid crysal phase and after casting the micro-structure of the LLC phase, the TiO2 samples were self-assemble to form lamellar, sphere and rod structures. According to the characterization results, possible formation mechanism was proposed.

Ordered Hierarchical Porous Platinum Membranes with Tailored Mesostructures

Swiss cheese or slices? A two-step method has been developed for the preparation of the title membranes from lytropic liquid crystals templated with poly(methyl methacrylate). The membranes have ordered mesopores and tunable macropore channels. The mesostructure of the membranes can be tailored by adjusting the concentration of the surfactant solution (see picture: 1=low, 2=high concentration).

Carbon-Supported Growth of Cross-Linked Platinum Nanowires by Surfactant Templating and Their Elecrochemical Characterization

Platinum/carbon (Pt/C) composite materials were prepared by the hydrazine reduction of H2PtCl6 confined to a mixed surfactant lytropic liquid crystal (LC)/C mixture with varying amounts of water. The reaction at relatively low water contents successfully yielded cross-linked Pt nanowires with wire-widths of 2-5 nm. The novel Pt nanostructure is believed to be from poorly hydrated hexagonal domains formed together with layered domains by the phase separation of the precursory LC mixture in the presence of carbon. Electrochemical measurements using cyclic volutammetry and membrane electrode assemblies revealed that the cross-linked nanowired Pt/C composite exhibits fairly high electrocatalytic activity for oxygen reduction reaction, as well as a high performance as the cathode material for polymer electrolyte fuel cells.

Aromatic azo-polyamide electrolyte with liquid crystal structure and photoelectrical properties

A dissoluble aromatic azo-polyamide electrolyte containing azobenzene derivatives in the main-chain is successfully prepared by ionizing amide nitrogens of poly( p-phenylene, 4,4′-azobenzene phthalamide) (Azo-PA) with the sodium methyl sulfinyl carbanion. The conductometric titration measurement shows that 95–98 mol.% of amide nitrogens were converted into anions. Orthogonal polarizing optical microscope images and UV–vis spectra reveal that this Azo-PA anion solution has formed a kind of lytropic liquid crystal structure in anhydrous dimethyl sulfoxide (DMSO) and represents great photoresponsive properties. The Azo-PA formed typical spherocrystal structure after precipitating from the solution when came across water. The photoelectrical properties are investigated by a precise digital conductance instrument and a ZF-7A UV-light examining lamp which can produce 365 nm UV-light. The results indicate that the conductivity value increases by a factor of 0.300–0.320 ms/cm upon UV irradiation and comes back to the initial value under visible light.

Polymerized lyotropic liquid crystals as contact lens materials

When an aqueous solution of a hydrophilic monomer such as 2-hydroxyethylmetharylate (HEMA) is mixed with a surfactant at the correct proportions, the components self-assemble into a lytropic liquid crystal comprising a highly ordered periodic microstructure, and polymerization of the monomer and removal of the surfactant results in a macroporous hydrogel of potential importance as a material for contact lenses and other prostheses. The two most important properties of these structured polymers as contact lens materials are: (1) unlike simple hydrogels which have irregular pores with a highly polydispersed size distribution, these new materials have an extremely well-characterized-in fact, triply periodic—network of pores of identical size, which can be preselected so as to allow for the transport of proteins, mucins, and other components of the pre-ocular tear film; and (2) this pore size can be selected independently of the polymer concentration and crosslink density, unlike simple hydrogels where large pores can only be obtained by reducing the crosslink density and along with it the shear modulus. The pore diameter can be selected in the range 20–400 Å and possibly higher. A wide variety of surfactant systems that have been shown to yield materials of this degree of precision and versatility is reviewed.

Lyotropic Liquisd Crystals

Abstract The importance of the atructure of solubilized molecules for the structure of lytropic liquid crystals is illustrated by examples form phase diagrams and NMR investigations of molecular mobility in th liquid crystal. When the Solubilization capacity is exceeded the liquid crystal is dispersed and a pronounced influence in the colloidal stability of the disperese system has been found. The basis for this stablization is discussed in terms of a strongly modified distance dependence of the Van der Waals attraction potential