Liquid Crystals at Interfaces

The ordering in liquid crystals (LCs) can be influenced by an interface. Some of these molecules adsorbed at the air-water interface yield a stable Langmuir monolayer. They exhibit numerous surface phases, which are classified on the basis of intermolecular separation and ordering. These surface phases are governed by the molecular interactions and the ambient experimental conditions such as temperature, humidity, pH, and ion content of the subphase. In this article, the role of molecular interactions on the surface behavior of several rodlike LCs are discussed. The Langmuir monolayer of a cholesteric LC exhibits an interesting low density liquid (L_1′) phase with tilted molecules. Brewster angle microscopy reveals stripe patterns, which arise due to the precession of the tilted molecules. It is demonstrated that this molecular precession can be controlled by the relative humidity, presence of cations in the subphase, and incorporation of appropriate molecular species. The Langmuir monolayer and Langmuir-Blodgett films of a novel rod-disc hybrid LC are discussed.     

Molecular recognition of arginine by supramolecular complexation with calixarene crown ether based on surface plasmon resonance

Arginine plays an important role in cell division and the functioning of the immune system. We describe a novel method by which arginine can be identified using an artificial monolayer based on surface plasmon resonance (SPR). The affinity of arginine binding its recognition molecular was compared to that of lysine. In fabrication of an arginine sensing interface, a calix[4]crown ether monolayer was anchored onto a gold surface and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The interaction between arginine and its host compound was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Recognition of calix[4]crown monolayer was assessed by the selective binding of arginine. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of arginine under aqueous conditions.     

Langmuir and Langmuir‐Blodgett Asphaltene Films at Heptane‐water Interface

Monolayer characteristics of subfractions and unfractionated whole asphaltenes from Athabasca oil sands bitumen were studied at heptane‐water interface. The transferred Langmuir‐Blodgett films of asphaltenes were characterised with atomic force microscopy and contact angle measurements. Monolayers prepared from the three asphaltene samples are found to behave similarly at heptane‐water interface. The high molecular weight asphaltene monolayer is the most expanded one whereas the low molecular weight asphaltene monolayer is the most condensed one. An asphaltene monolayer behaves differently at an airwater interface to a heptane‐water interface. The presence of the bulk heptane phase renders the interfacial asphaltene monolayer more flexible as compared to that at air‐water interface.     

Structure and imidization of polyamic acid salt Langmuir–Blodgett films

Polyimide Langmuir‐Blodgett (LB) films were prepared with a Pyromellitic dianhydride‐4, 4′ oxydianiline precursor, and the properties of the polyamic acid salt monolayer characterized by different methods. The π‐A relationship revealed that the precursor monolayer exhibits anisotropy on the water surface, the Wilhelmy plate being more sensitive to pressure when it is perpendicular to the compression direction. FTIR results showed that polyamic acid salt LB films have lower imidization energy than the corresponding painting films and can be imidized at lower temperature. The molecular arrangement in the LB films was studied by X‐ray diffraction and polarized FTIR, showing that the polyamic acid salt LB film is of Y‐type, in which the molecules are highly oriented, with the main chain lying parallel to the substrate and the long fatty acid chains stretching out at a certain angle. © 2002 Society of Chemical Industry     

The langmuir-blodgett technique as a tool for homeotropic alignment of fluorinated liquid crystals mixed with arachidic Acid

Some fluoro-substituted liquid crystals mixed with arachidic acid in monolayers formed at air-liquid (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces were investigated. Molecular organization in Langmuir films was determined on the basis of the analysis of the shape of the surface pressure-mean molecular area isotherm and observations made by means of a Brewster angle microscope. It was found that in the compression process the liquid crystal molecules are pushed out towards the top of the first monolayer being in direct contact with the subphase. Langmuir films were transferred onto the quartz substrates at various surface pressures and mono- and multilayered Langmuir-Blodgett films were obtained. The films were characterized using electronic absorption measurements. The conditions for obtaining the homeotropic orientation of the liquid crystal molecules were determined.     

Para-carboxy modified amphiphilic calixarene, self-assembly and interactions with pharmaceutically-relevant molecules

The self-assembly properties of the amphiphilic 5,11,17,23-tetra-carboxy-25,26,27,28-tetradodecyloxycalix[4]arene have been investigated at the air-water interface as monomolecular Langmuir layers and in water. The interactions of this amphiphile with salicylic acid (SA), acetyl-salicylic acid (ASA) and acetaminophene (APAP) have been studied at the air-water interface by means of the Langmuir balance technique. It has been demonstrated that the calix-arene molecules, when self-assembled as Langmuir monolayers, have the ability to interact with all the tested compounds. While APAP causes a stabilization of the monolayer, ASA and SA cause a slight loss of stability and a drastic change of the compressibility of the monolayer. The study of the self-assembly properties of the title compound in water revealed that this amphiphile can be self-assembled as solid lipid nanoparticles (SLNs). The atomic force microscopy investigations of the colloidal suspension, spread on a solid surface and dried, revealed the coexistence of the SLNs with layered structures.     

Phase transitions in monolayer formed by hyperbranched polyester with alkyl-terminated branches at the air/water interface

Investigations of Langmuir and Langmuir–Blodgett molecular films of hyperbranched polyester with alkyl-terminated branches over a wide temperature range revealed an unusual phase transitions. The measured surface pressure–surface area isotherms clearly show that the hyperbranched polyester formed stable and well-defined monolayers at the air/water interface. At temperatures below 313 K ice floe-like structures of a condensed phase were formed already from very low surface pressures. On the increase of the surface pressure the floes of the condensed phase merged forming a uniform monolayer. Above 313 K a surface liquid phase was formed at the interface. It was shown that the phase transition from the surface liquid phase to the condensed phase occurred on temperature decrease. At lower temperatures the compression process was not reversible. The increase of temperature up to about 323 K made the compression process reversible. The monolayers were transferred from the air/water interface onto silicon and mica substrates using the Langmuir–Blodgett technique at different temperatures. The structure of the polyester monolayer formed at the substrates' surfaces was investigated.     

Simple Does Not Mean Trivial: Behavior of Phosphatidic Acid in Lipid Mono- and Bilayers

Phosphatidic acid (PA) is one of the simplest membrane phospholipids, yet it plays a crucial role in various biologically relevant processes that take place in cells. Since PA generation may be triggered by a variety of factors, very often of antagonistic character, the specific nature of physiological responses driven by PA is not clear. In order to shed more light on these issues, we carried out a systematic characterization of membranes containing one of the three biologically significant PA molecular species. The effect of these molecules on the properties of membranes composed of phosphatidylcholine and/or cholesterol was assessed in a multidisciplinary approach, including molecular dynamic simulations, flicker noise spectroscopy, and Langmuir monolayer isotherms. The first enables the determination of various macroscopic and microscopic parameters such as lateral diffusion, membrane thickness, and defect analysis. The obtained data revealed a strong interaction between unsaturated PA species and phosphatidylcholine. On the other hand, the behavior of saturated PA was greatly influenced by cholesterol. Additionally, a strong effect on mechanical properties was observed in the case of three-component systems, which could not be explained by the simple extrapolation of parameters of the corresponding two-component systems. Our data show that various PA species are not equivalent in terms of their influence on lipid mono- and bilayers and that membrane composition/properties, particularly those related to the presence of cholesterol, may strongly modulate PA behavior.     

植物提取物自组装膜在盐酸中对Q235钢的缓蚀作用

以铁线蕨植物提取物(ACE)为成膜物质,在Q235钢表面自组装得到缓蚀膜。通过极化曲线和电化学阻抗谱测试研究了该自组装膜对Q235钢在1 mol/L HCl溶液中的缓蚀性能。结果表明,该自组装膜对Q235钢的阴、阳极腐蚀反应均有抑制作用,可明显减缓Q235钢在盐酸溶液中的腐蚀,且缓蚀作用随ACE质量浓度的增大而增强。ACE分子在Q235钢表面的吸附遵从Langmuir和Frumkin吸附模型,为单分子层吸附,吸附分子之间存在横向吸引力。     

新型煤基吸附剂吸附硝基苯的机理研究

以神府煤为原料经过超细粉碎、化学处理、复合成型和后处理制得两种煤基超细复合吸附剂MMCA和AHCA,研究了二者对水溶液中硝基苯的吸附性能和吸附机理．结果表明,MMCA和AHCA对硝基苯的吸附过程符合二级吸附动力学模型,MMCA吸附硝基苯的过程由膜扩散控制,而AHCA吸附硝基苯过程由颗粒内扩散控制,求出了吸附速率常数和颗粒内有效扩散系数．MMCA和AHCA对硝基苯的吸附符合Langmuir吸附等温式,其单层饱和吸附量分别为109．89mg／g和229．57mg／g．     

Topography of collapsed triglyceride monolayers on glass

The stability and conformation of tripalmitin (TP) and triolein (TO) Langmuir‐Blodgett (LB) monolayers on glass were investigated using Atomic Force Microscopy (AFM). Compression isotherms revealed that TP reached the solid state at 15 mN m⁻¹, with a trident conformation. LB deposition of the monolayer on the glass surface was performed at the solid state (30 mN m⁻¹) with a transfer ratio close to 1. The TO monolayer collapsed in the liquid‐expanded phase at 13 mN m⁻¹. LB deposition was performed at 11 mN m⁻¹ with a transfer ratio of 1.4. The LB films were imaged by AFM (tapping mode). The TO monolayer collapsed in amorphous droplets. TP presented tiny amorphous drops plus crystalline shapes with unit layers of a thickness of 40—46 Å, corresponding to the long spacing of the β and α polymorphic forms. TP monolayer thus collapsed in aggregates to form crystalline structures. The thickness of the first step was mostly 86 Å, but sometimes 68 Å steps were observed, while the transferred monolayer generally reorganizes as a tuning fork in a regular crystalline unit, but can also remain as a trident, providing a hydrophobic support for upper layers. This findings supply backing for technical processes such as the interpretation of fat fractionation by microfiltration membranes, based on triglyceride/solid interaction statements.     

Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Molecular Sieve 13X

Abstract

Adsorption isotherms for acetaldehyde, propionaldehyde, and butyraldehyde on Davison molecular sieve 13X were determined gravimetrically at three temperatures. The isoteric heat of adsorption of acetaldehyde and propionaldehyde decreased initially with the increase in loading, then increased up to a certain point after which it decreased again. For butyraldehyde the heat of adsorption initially increased and then decreased with increased loading. The equilibrium adsorption data reduce to a single characteristic curve when correlated according to Polanyi's potential theory. Recently proposed isotherm equations for heterogeneous surfaces by Sircar and Hines et al. were used to correlate the isotherm data. The BET equation gave a good correlation of the data for a relative pressure range of 0.05 ≤ P/P, ≤ 0.25. The monolayer surface coverage and surface area were calculated by the Langmuir and the BET equations. The Langmuir equation consistently provided a larger estimate of the surface area than did the BET equation.     

Substituted Tobermorites: 27Al and 29Si MASNMR, Cation Exchange, and Water Sorption Studies

²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy revealed that the maximum amount of Al that can be substituted for Si in the tobermorite structure is 15 to 20 mol%. Powder X-ray diffraction and cation exchange studies corroborate the above finding. Anomalous tobermorite structures resulted in all cases, and hydrogarnet appeared beyond the 15 to 20 mol% Al substitution limit for Si. The sorption of water molecules by synthetic [Al³⁺+ Na⁺]-substituted tobermorites and their cation-exchanged forms heated at 200°C under vacuum (≥10⁻³ torr) was measured at 25°C in order to probe the nature of the ion-exchange cavity. Samples with ≤30 mol% of Al substitution for Si showed isotherms of Brunauer, Demming, Demming, Teller (BDDT) type I and gave better linearity with the Langmuir plot than with the BET plot. Samples with ≥35 mol% of Al substitution for Si showed BDDT type II isotherms and gave better linearity with the BET than with the Langmuir equation. The Langmuir monolayer capacity was found to depend on the Al content and on the cationic form. The Li⁺- and Na⁺-exchanged tobermorites with about 20 mol% of Al substitution for Si showed the highest Langmuir monolayer water sorption capacity. The Cs⁺-exchanged tobermorites showed a smaller capacity than the Li⁺- or Na⁺-exchanged samples, which can be ascribed to clogging of the ion-exchange cavity by the large Cs⁺ ions.     

Surface potential measurements of Langmuir films of azo dye/liquid crystal mixtures

Two-component films of a non-amphiphilic azo dye and a liquid crystal with strongly polar –CN group were studied at an air–water interface on the basis of the surface potential–mean molecular area dependence recorded simultaneously with the surface pressure–mean molecular area isotherm. Additionally, the morphology of the films was monitored with the aid of Brewster angle microscope. A conventional Langmuir technique was used to form dye/liquid crystal films during reduction and expansion of an area occupied by the molecules. From the surface potential value, the effective dipole moment in the first monolayer formed on the water was calculated. Moreover, the number of molecules with dipole moments directed from the water to the air with respect to those directed towards water was estimated. The influence of the two components' miscibilities upon the surface potential after addition of the dye to the liquid crystal was determined.     

Hierarchical structures of dendritic polymers

Dendritic polymers' highly specific and three‐dimensional architectures set them apart from linear and slightly branched polymers. Their unique properties also allow them to form hierarchical organizations, which can be classified as planar or non‐planar. The preparation of a planar hierarchy consisting of dendritic polymers can be achieved by conventional techniques of adsorption or Langmuir monolayer and Langmuir–Blodgett accumulation, and the resultant hierarchy is well ordered. Non‐planar hierarchies are built on non‐planar scaffolds, for example by self‐assembly. In this mini‐review, the practical/potential applications of dendritic polymers such as for electrical or optical devices, sensing systems, or medical diagnosis are also reviewed in association with their structures. Copyright © 2009 Society of Chemical Industry     

ZSM-5型分子筛对二氧化硫的动态吸附性能

采用ZSM-5型分子筛吸附脱除烟气中的二氧化硫,分析了其动态吸附过程的基本特性,以及硅铝物质的量比、温度、空速等影响因素.结果表明:ZSM-5型分子筛对二氧化硫的吸附符合Langmuir吸附等温线类型,属于单分子层物理吸附.用硅铝物质的量比为38的ZSM-5型分子筛,在温度为25 ℃、空速为700 h-1、入口二氧化硫体积分数为0.3%条件下,测量吸附饱和时间为180 min,饱和二氧化硫吸附容量为0.018 g/g.温度较低、硅铝物质的量比较小、空速较低的条件下,ZSM-5型分子筛对二氧化硫的吸附性能较好.     

Effect of Silica Microparticles on Interactions in Mono- and Multicomponent Membranes

Advancing our understanding of the mechanism of the interaction between inhaled pollutant microparticles and cell membrane components is useful to study the impact of fine particulate matter on human health. In this paper, we focus on the effect of cholesterol (Chol) molecules on the surface properties of a model membrane in the presence of silica microparticles (MPs). Mixed monolayers containing phospholipid-dipalmitoylphosphatidylcholine (DPPC), Chol and silica particle dispersions (MPs; 0.033% w/w, 0.33% w/w and 0.83% w/w) were formed and studied using the Langmuir monolayer technique complemented by Brewster Angle Microscopy (BAM) images. It was shown that Chol caused a condensation of the DPPC monolayer, which influenced the penetration of MPs and their interactions with the model membrane. The relaxation experiments of the lipid–MP monolayer proved that the presence of Chol molecules in the monolayer led to the formation of lipid and MP complexes. Strong interactions between Chol and MPs contributed to the formation of more stable monolayers. The presented results can be useful to better comprehend the interaction between particulate materials and the lipid components of biomembranes.     

交联氧化铝-壳聚糖新杂化吸附剂的制备及去除废水中Cu(Ⅱ)(英文)

A novel biosorbent was developed by coating chitosan,a naturally and abundantly available biopolymer,on to activated alumina based on oil shale ash via crosslinking.The adsorbent was characterized by various techniques,such as Fourier transform infrared spectroscopy,scanning electron microscopy,thermogravimetric-differential thermal analysis,and X-ray photoelectron spectroscope.Batch isothermal equilibrium adsorption experiments were condcted to evaluate the adsorbent for the removal of Cu(Ⅱ) from wastewater.The effect of pH and agitation time on the adsorption capacity was also investigated,indicating that the optimum pH was 6.0.The equilibrium adsorp-tion data were correlated with Langmuir and Freundlich models.The maximum monolayer adsorption capacity of chitosan coated alumina sorbent as obtained from Langmuir adsorption isotherm was found to be 315.46 mg·g-1 for Cu(Ⅱ).The adsorbent loaded with Cu(Ⅱ) was readily regenerated using 0.1 mol?L?1 sodium hydroxide solution.All these indicated that chitosan coated alumina adsorbent not only have high adsorption activity,but also had good stability in the wastewater treatment process.     

The synthesis of novel perylene-like dyes and their aggregation properties in Langmuir and Langmuir–Blodgett films

The synthesis of novel perylene-like dyes with different length and molecular structure of terminal chains substituted to the main perylene core is described. The dyes are able to form compressible and stable monolayers at the air–water interface (Langmuir films), which can be easily transferred onto solid substrates (Langmuir–Blodgett films). In the Langmuir and Langmuir–Blodgett films, the dye molecules show tendency to creation of self-aggregates, both in the ground and excited electronic states. The influence of the molecular structure of the substituents on the aggregation properties is observed and discussed.     

Thermo-induced Vesicular Dynamics of Membranes Containing Cholesterol Derivatives

Membrane structural organization is an intrinsic property of a cell membrane. Any changes in lipid composition, and/or any stimuli that affect molecular packing induce structural re-organization. It membrane dynamics provide a means by which changes in structure organization can be determined, upon a change in the membrane internal or external environment. Here, we report on the effect of thermo-stress on membranes containing cholesterol liquid crystal (LC) compounds cholesterol benzoate (BENZO) and oxidized cholesterols. We have (1) revealed that lipid vesicles containing this artificial cholesterol derivative (BENZO) is thermo-responsive, and that this thermo-sensitivity is significantly similar to naturally oxy-cholesterols (2) elucidated the mechanism behind the membrane perturbation. Using Langmuir monolayer experiments, we have demonstrated that membrane perturbation was due to an increase in the molecular surface area, (3) discussed the similarities between cholesterol benzoate in the cholesterol LC state and in lipid bilayer membranes. Last, (4) drawing from previously reported findings, our new data on membrane dynamics, and the discussion above, we propose that artificial cholesterol derivatives such as BENZO, open new possibilities for controlled and tailored design using model membrane systems. Examples could include the development of membrane technology and provide a trigger for progress in thermo-tropical liquid crystal engineering.