十二烷基苯磺酸钠在联苯类分子液晶传感器中传感过程的分子动力学模拟

本文采用分子动力学模拟,通过建立了液晶5CB/真空,液晶5CB/水,表面活性剂SDS/水溶液和液晶5CB/SDS水溶液界面来研究基于竞争包合的液晶传感器中传感分子的工作原理。研究表明,5CB液晶在真空下会自发的变为一维有序的排列,当和水作用时液晶分子5CB取向为趋于与液体表面水平,当与表面包含SDS的溶液相互作用时分子取向为垂直液面。本动力学模拟反映了以SDS作为探针分子的竞争包合类液晶传感器中的传感过程。     

丝状液晶5CB与铁(Ⅲ)卟啉之间的轴向配位作用

通过考察掺杂配位性质不同的两种铁(Ⅲ)卟啉的丝状液晶5CB在磁场下的行为以及UV-Vis光谱,研究了液晶5CB与铁(Ⅲ)卟啉的轴向配位作用.结果表明,弗雷德里克兹转变阈值的降低和Soret带随着液晶5CB含量增大而红移是液晶5CB与五配位Fe(TPCl发生轴向配位的结果.     

一种新型的氢键自组装液晶光控取向膜

报道了一种新型的以氢键为驱动力的液晶自组装光控取向膜, 研究了薄膜的制备方法与光敏特性. 通过聚(4-乙烯基吡啶)中的吡啶基团与光敏聚丙烯酰氧基肉桂酸间的氢键作用制备了LBL(layer-by-layer)型的自组装多层膜, 制备过程的紫外-可见光谱表明, 该组装过程为逐层、均匀沉积过程. 傅里叶变换红外光谱表明, 多层膜的成膜驱动力为氢键. 用线性偏振紫外光辐照该薄膜, 多层膜中与光矢量方向匹配的光敏基团发生[2+2]环加成反应, 形成表面张力各向异性的薄膜. 用该薄膜作为向列相液晶的取向膜制成平行液晶器件, 在偏光显微镜下观察, 发现获得了均一、稳定的取向效果.     

聚合物分散液晶PMMA-5CB的制备及电光性能

以聚合引发相分离的方法制备了聚甲基丙烯酸甲酯(PMMA)基聚合物分散液晶(PDLC).通过差示量热扫描仪(DSC)、偏光显微镜(POM)对不同液晶5CB(4-氰基-4'-戊基联苯)含量的PDLC热力学行为和液晶分散状态进行了表征.在电压为0～30 V、波长为633 nm处,用紫外可见分光光度计(UV-Vis)对PDLC的电光性能进行了研究.结果表明当w(5CB)达到20%以上时,PDLC发生相分离现象;当w(5CB)=30%时,液晶的分散状态最佳,电光效应最强.     

液晶聚合物的单层与Langmuir-Blodgett膜

系统研究了手性液晶聚硅氧烷和光致变色液晶聚硅氧烷两个毓的侧链液晶聚合物在空气/水界面的单层行为和Langmuir-Blodgett(LB)膜沉积特性,对LB膜结构与存在的聚集现象进行了系统的表征,并初步探讨了LB膜中液晶聚合物表现的功能性。     

松果状纳米氧化铁对液晶电光性能的影响

液晶材料被广泛应用于液晶显示器(LCD)中,但是由于液晶中杂质的存在,导致液晶的应用电压变大,增加了能耗。 为了降低应用中的阈值电压和饱和电压,通常向液晶中添加纳米颗粒来提高电光性能。 本文采用简单的化学沉淀法制备了形貌均一,大小尺寸均匀的松果状氧化铁(P-Fe₂O₃)纳米颗粒。 将其掺杂到向列相液晶4-氰基-4'-戊基联苯(4-cyano-4'-pentylbiphenyl,5CB)中,结果表明,掺杂质量分数为0.5%时,电光性能达到最优,阈值电压和饱和电压分别降低24.8%和45.2%,对比度增大46%,响应时间降低至17.6 ms,此性能优于相同条件下掺杂普通Fe₂O₃纳米颗粒的向列相液晶5CB,其阈值电压和饱和电压分别降低15%和16%。 这归因于松果状Fe₂O₃纳米颗粒可以在向列相液晶5CB中均匀分散,其粗糙的表面吸附了液晶中的杂质离子,减少了杂质离子的屏蔽效应,从而提高了电光性能。     

氢键稳定的苯并菲盘状液晶的合成及介晶性

盘状液晶分子能自组装成高度有序的六方柱状介晶相. 其各向异性的载流子高速迁移率使其成为较理想的有机光电子材料. 采用分子间氢键锚定柱状相, 获得介晶相温度范围宽、有序度高的苯并菲盘状液晶是本研究的目的. 本文通过分子设计, 合成了3个系列, 共18个有两种不同软链的苯并菲盘状液晶化合物C₁₈H₆(OR)₅(OCH₂COOEt), C₁₈H₆(OR)₅(OCH₂COOBu)和C₁₈H₆(OR)₅(OCH₂CONHBu), 其中R＝C_nH_2n＋1, n＝4～9. 化合物的纯度和结构通过¹H NMR和元素分析确证. 化合物热稳定性通过热重分析(TGA)测定, 并显示出较高的热稳定性. 通过偏光显微镜(POM)和差示扫描量热法(DSC)对这些化合物的热致液晶性进行了研究. 结果显示对于分子中含有酰胺基的苯并菲液晶化合物C₁₈H₆(OR)₅(OCH₂CONHBu), 与具有同样软链长度的分子中不含酰胺键的化合物系列C₁₈H₆(OR)₅(OCH₂COOBu)相比较, 前者由于柱内分子间氢键的形成, 具有更高的熔点和清亮点.     

新型聚氨酯基液晶光定向层材料的合成与性能研究

设计并合成了一种新的二醇单体 5 羟基 1 ,3 间苯二甲酸二 (2 羟基 )乙酯 [Di(2 hydroxyethyl) 5 hydroxylisophthalate,DHHI],并用各种手段对其进行了表征 .DHHI与二苯基甲烷 4 ,4′ 二异氰酸酯 (MDI)溶液聚合得到一种侧链含有酚羟基的先驱聚合物PU OH ,通过肉桂酰氯的功能化反应制备出新型光敏聚氨酯 (PU CI) .用示差扫描量热分析 (DSC) ,红外光谱 (FT IR) ,紫外可见光谱 (UV Vis)等对PU CI进行了表征 .研究表明 ,PU CI在紫外光的照射下可发生环 (2 +2 )加成反应 .PU CI经线性偏振光聚合技术 (LPP)处理制成液晶光定向层 ,采用向列型液晶 5CB组装成液晶盒 ,在偏光显微镜下可以观察到均匀的液晶取向 ,表明该聚合物膜具有很好的液晶定向能力 ,是一类具有潜在应用价值的新型液晶光定向层材料     

含Gemini表面活性剂的PVA分散液晶的微结构与性能

采用N,N'-二(十二烷基)-N,N,N',N',N″-五甲基-1,4,7-三氮杂双碘化氨为Gemini表面活性剂,液晶为4-正戊基-4'-氰基联苯(5CB),通过微胶囊法制备了聚乙烯醇(PVA)分散液晶薄膜,着重研究Gemini表面活性剂对PVA分散液晶薄膜的微结构、电光特性的影响.结果表明,加入Gemini表面活性剂仅略微增加了PVA与5CB液晶的相容性,PVA分散液晶仍保持较高的相分离程度,但是Gemini表面活性剂使液晶微滴尺寸明显变小,液晶相均匀分散地于PVA基体中,液晶指向矢构型由两极型变化为径向型,PVA分散液晶薄膜的对比度和响应速度明显提高,同时保持较低的驱动电压.     

侧链液晶聚硅氧烷langmuir膜的原子力显微镜观察

通过原子力显微镜观测了含手性基团侧链液晶聚硅氧烷在空气/水界面上的单层膜,观测了成膜物在界面形成微畴结构以及表面压力升高时微畴聚集、重排过程,分析了纳米级微畴形成、聚集和重排的机理和规律。     

Influence of simple electrolytes on the orientational ordering of thermotropic liquid crystals at aqueous interfaces

We report orientational anchoring transitions at aqueous interfaces of a water-immiscible, thermotropic liquid crystal (LC; nematic phase of 4'-pentyl-4-cyanobiphenyl (5CB)) that are induced by changes in pH and the addition of simple electrolytes (NaCl) to the aqueous phase. Whereas measurements of the zeta potential on the aqueous side of the interface of LC-in-water emulsions prepared with 5CB confirm pH-dependent formation of an electrical double layer extending into the aqueous phase, quantification of the orientational ordering of the LC leads to the proposition that an electrical double layer is also formed on the LC-side of the interface with an internal electric field that drives the LC anchoring transition. Further support for this conclusion is obtained from measurements of the dependence of LC ordering on pH and ionic strength, as well as a simple model based on the Poisson-Boltzmann equation from which we calculate the contribution of an electrical double layer to the orientational anchoring energy of the LC. Overall, the results presented herein provide new fundamental insights into ionic phenomena at LC-aqueous interfaces, and expand the range of solutes known to cause orientational anchoring transitions at LC-aqueous interfaces beyond previously examined amphiphilic adsorbates.     

Influence of specific anions on the orientational ordering of thermotropic liquid crystals at aqueous interfaces

We report that specific anions (of sodium salts) added to aqueous phases at molar concentrations can trigger rapid, orientational ordering transitions in water-immiscible, thermotropic liquid crystals (LCs; e.g., nematic phase of 4'-pentyl-4-cyanobiphenyl, 5CB) contacting the aqueous phases. Anions classified as chaotropic, specifically iodide, perchlorate, and thiocyanate, cause 5CB to undergo continuous, concentration-dependent transitions from planar to homeotropic (perpendicular) orientations at LC-aqueous interfaces within 20 s of addition of the anions. In contrast, anions classified as relatively more kosmotropic in nature (fluoride, sulfate, phosphate, acetate, chloride, nitrate, bromide, and chlorate) do not perturb the LC orientation from that observed without added salts (i.e., planar orientation). Surface pressure-area isotherms of Langmuir films of 5CB supported on aqueous salt solutions reveal ion-specific effects ranking in a manner similar to the LC ordering transitions. Specifically, chaotropic salts stabilized monolayers of 5CB to higher surface pressures and areal densities (12.6 mN/m at 27 ?(2)/molecule for NaClO(4)) and thus smaller molecular tilt angles (30° from the surface normal for NaClO(4)) than kosmotropic salts (5.0 mN/m at 38 ?(2)/molecule with a corresponding tilt angle of 53° for NaCl). These results and others reported herein suggest that anion-specific interactions with 5CB monolayers lead to bulk LC ordering transitions. Support for the proposition that these ion-specific interactions involve the nitrile group was obtained by using a second LC with nitrile groups (E7; ion-specific effects similar to 5CB were observed) and a third LC with fluorine-substituted aromatic groups (TL205; weak dipole and no ion-specific effects were measured). Finally, we also establish that anion-induced orientational transitions in micrometer-thick LC films involve a change in the easy axis of the LC. Overall, these results provide new insights into ionic phenomena occurring at LC-aqueous interfaces, and reveal that the long-range ordering of LC oils can amplify ion-specific interactions at these interfaces into macroscopic ordering transitions.     

Liquid crystal-based sensors for the detection of heavy metals using surface-immobilized urease

In this study, a new method for the detection of heavy metals in aqueous phase was developed using liquid crystals (LCs). When UV-treated nematic LC, 4-cyano-4'-pentyl biphenyl (5CB) that was confined in the urease-modified gold grid was immersed in a urea solution, an optical response from bright to dark was observed under a polarized microscope, indicating that a planar-to-homeotropic orientational transition of the LC occurred at the aqueous/LC interface. Since urease hydrolyzes urea to produce ammonia, which would be ionized into ammonium and hydroxide ions, the main product of the photochemically degraded 5CB, 4-cyano-4'-biphenylcarboxylic acid (CBA), was deprotonated and self-assembled at the interface, inducing the orientational transition in the LC. Due to the high sensitivity and rapid response of this system, detection of heavy metal ions was further exploited. The divalent copper ion, which could effectively inhibit the activity of urease, was used as a model heavy metal ion. The optical appearance of the LC did not change when urea was in contact with the copper nitrate hydrate-blocked urease. After the copper-inhibited urease was reactivated by EDTA, a bright-to-dark shift in the optical signal was regenerated, indicating an orientational transition of the LC. This type of LC-based sensor shows high spatial resolution due to its optical characteristics and therefore could potentially be used to accurately monitor the presence of enzyme inhibitors such as heavy metal ions in real-time.     

Ordering transitions triggered by specific binding of vesicles to protein-decorated interfaces of thermotropic liquid crystals

We report that specific binding of ligand-functionalized (biotinylated) phospholipid vesicles (diameter = 120 ± 19 nm) to a monolayer of proteins (streptavidin or anti-biotin antibody) adsorbed at an interface between an aqueous phase and an immiscible film of a thermotropic liquid crystal (LC) [nematic 4'-pentyl-4-cyanobiphenyl (5CB)] triggers a continuous orientational ordering transition (continuous change in the tilt) in the LC. Results presented in this paper indicate that, following the capture of the vesicles at the LC interface via the specific binding interaction, phospholipids are transferred from the vesicles onto the LC interface to form a monolayer, reorganizing and partially displacing proteins from the LC interface. The dynamics of this process are accelerated substantially by the specific binding event relative to a protein-decorated interface of a LC that does not bind the ligands presented by the vesicles. The observation of the continuous change in the ordering of the LC, when combined with other results presented in this paper, is significant, as it is consistent with the presence of suboptical domains of proteins and phospholipids on the LC interface. An additional significant hypothesis that emerges from the work reported in this paper is that the ordering transition of the LC is strongly influenced by the bound state of the protein adsorbed on the LC interface, as evidenced by the influence on the LC of (i) "crowding" of the protein within a monolayer formed at the LC interface and (ii) aging of the proteins on the LC interface. Overall, these results demonstrate that ordering transitions in LCs can be used to provide fundamental insights into the competitive adsorption of proteins and lipids at oil-water interfaces and that LC ordering transitions have the potential to be useful for reporting specific binding events involving vesicles and proteins.     

Use of liquid crystal to study the interactions of alkyl polyglycosides with gelatin and bovine serum albumin

In this study, liquid crystal (LC) was used to study the interactions of alkyl polyglycosides (APG) with gelatin and bovine serum albumin (BSA) at the LC-aqueous interface. The LC easily undergo an orientational transition from a homeotropic to a planar state after proteins were in contact to the LCaqueous interface decorated with APG, thus inducing an optical change from dark to bright. The optical image analysis reveals that the rearrangement rate of APG monolayer is tightly dependent on the concentration and chemical structure of the protein of interest. For example, the rearrangement rate of APG monolayer increases with an increasing gelatin concentration. We also find that the chemical structure of the proteins has a significant impact on the difference in the growth behavior of bright domains in LC.     

Insertion of the Liquid Crystal 5CB into Monovacancy Graphene

Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by defects that are introduced, either by design or as a byproduct of fabrication processes. Herein, we present density functional theory (DFT) calculations of the LC mesogen 4-cyan-4′-pentylbiphenyl (5CB) on graphene in the presence of a monovacancy (MV-G). We find that the monovacancy strengthens the binding of 5CB in the planar alignment and that the structure is lower in energy than the corresponding homeotropic structure. However, if the molecule is able to approach the monovacancy homeotropically, 5CB undergoes a chemical reaction, releasing 4.5 eV in the process. This reaction follows a step-by-step process gradually adding bonds, inserting the 5CB cyano group into MV-G. We conclude that this irreversible insertion reaction is likely spontaneous, potentially providing a new avenue for controlling both LC behavior and graphene properties.     

A Simple Quantitative Method to Study Protein–Lipopolysaccharide Interactions by Using Liquid Crystals

The interaction of proteins with endotoxins has divergent effects on lipopolysaccharide (LPS)‐induced responses, which serve as a basis for many clinical and therapeutic applications. It is, therefore, important to understand these interactions from both theoretical and practical points of view. This paper advances the design of liquid crystal (LC)‐based stimuli‐responsive soft materials for quantitative measurements of LPS–protein binding events through interfacial ordering transition. Micrometer‐thick films of LCs undergo easily visualized ordering transitions in response to proteins at LPS–aqueous interfaces of the LCs. The optical response of the LC changes from dark to bright after aqueous solutions of hemoglobin (Hb), bovine serum albumin (BSA), and lysozyme proteins (LZM) are in contact with a LPS‐laden aqueous–LC interface. The effects of interactions of different proteins with LPS are also observed to cause the response of the LC to vary significantly from one to another; this indicates that manipulation of the protein–LPS binding affinity can provide the basis for a general, facile method to tune the LPS‐induced responses of the LCs to interfacial phenomena. By measuring the optical retardation of the 4′‐pentyl‐4‐cyanobiphenyl (5CB) LC, the binding affinity of the proteins (Hb, BSA, and LZM) towards LPS that leads to different orientational behavior at the aqueous interfaces of the LCs can be determined. The interaction of proteins with the LPS‐laden monolayer is highest for LPS–Hb, followed by LPS–BSA, and least for LPS–LZM; this is in correlation with their increasing order of binding constants (LPS‐Hb>LPS‐BSA>LPS‐LZM). The results presented herein pave the way for quantitative and multiplexed measurements of LPS–protein binding events and reveal the potential of the LC system to be used as quantitative LC‐based, stimuli‐responsive soft materials.     

LC Determination of Mono-Substituted Phenols in Water Using Liquid–Liquid–Liquid Phase Microextraction

A simple liquid–liquid–liquid microextraction device of new design was used to pre-concentrate phenols from water samples before liquid chromatographic (LC) analysis. Extraction was induced by the pH difference inside and outside an organic phase located at the interface. The pH of the donor phase outside the organic phase was adjusted to 1 with HCl whereas the acceptor phase was a basic solution at pH 13. On stirring neutral phenols were extracted into the organic solvent then back-extracted into 1 μL of basic acceptor solution suspended from the tip of a micro syringe. The acceptor phase was then withdrawn into the micro syringe and injected directly into the LC. The technique uses a low-cost disposable extraction ‘device’ and is very convenient to operate. Up to 230-fold enrichment of analytes could be achieved. This procedure could also serve as a sample clean-up step because neutral and basic compounds were not extracted into the acceptor phase. The RSD (n = 5) was better than 6.2% and the linear calibration range was from 1 to 1000 µg–L⁻¹ with r ² ≥ 0.992.Optimization of experimental conditions (rate of stirring, ionic strength of the sample solution, concentration of reagents, time of extraction, and organic solvent volume) were also examined. The method was applied to the determination of phenols in tap and well waters.Revised: 14 February and 29 March 2005     

Water effect on the o-h dissociation enthalpy of para-substituted phenols: a DFT study

The effect of water on the O-H bond dissociation enthalpy (BDE) of para-substituted phenols has been investigated by means of DFT calculations. It is shown that the experimental BDE values are fairly well-reproduced by simple B3LYP/6-31G* calculations carried out on the phenol/phenoxyl-water complexes taking into account only hydrogen-bonding (HB) interactions of water molecules with molecular sites (HB model). On the contrary, the BDE values computed with the polarizable continuum model (PCM/B3LYP/6-31G*)8 are overestimated by about 3-4 kcal/mol. Discrepancy between theory and experiment increases using the PCM method in addition to the HB model. Calculations show that, in general, the HB interaction with water molecules decreases the BDE of phenols bearing electron-releasing groups while increasing the BDE of phenols bearing electron-withdrawing substituents. This opposite effect is explained by considering the resonance structures with charge separation both in phenols and in phenoxyl radicals. With electron donors, the phenoxyl radical is preferentially stabilized by the HB acceptor interaction with two water molecules, while with electron acceptors the phenol is preferentially stabilized by the HB donor interaction with one water molecule.     

Photoluminescence of a 5CB liquid crystal–organomontmorillonite nanoparticle heterocomposite

Photoluminescence (PL) of a heterocomposite, consisting of the nematic liquid crystal (LC) 4-pentyl-4´-cyanobiphenyl (5CB) and anisometric nanoparticles of montmorillonite (MMT) clay, modified by cetyltrimethylammonium bromide (CTAB) has been investigated at 4.2 and 300 K. The incorporation of this organoclay (B4) to 5CB decreases the emission intensity by 7–8 times due to efficient resonant quenching of the exciting energy by the organoclay. The spectrum shifts to a long-wave region, with this effect being considerably larger at low temperatures. Graphical separation of complex bands, corresponding to the bulk 5CB and 5СВ?+?В4 heterosystem at both temperatures revealed that the presence of the organoclay resulted in a significant growth of LC dimer quantity, shifting spectra towards longer wavelengths. Changes in the 5CB luminescence under organoclay influence can be explained by quite strong interphase interactions specified earlier by infrared spectroscopy between the MMT surface and LC, and by a realisation of more flat conformations of 5CB molecules. Confinement effects prevent full crystallisation of 5CB in the 5CB?+?B4 composite, and LC dimer structures located in the organoclay near-surface layers on the outer surface of the nanoparticles and inside its galleries remain in a larger amount, at low temperature, when compared to bulk 5CB. The remaining LC crystallises and photoluminescence from the 5CB monomers becomes intense.