Structural and dielectric behaviour of non-aqueous lyotropic mixtures: influence of amphiphile chain lengths and counter ions

This study highlights the effects of amphiphile chain length and counter ions on the self-assembly and dielectric behaviour of non-aqueous lyotropic liquid crystals. Two-dimensional hexagonal mesophase is seen for short-chain length sodium dodecyl sulphate, while lamellar and multiwall lamellar mesophases are noticed for long-chain length cetyltrimethylammonium bromide and polyoxyethylene (20) sorbitan monolaurate amphiphiles in the non-aqueous domains of ethylene glycol. A strong influence of amphiphile counter ions is seen on static dielectric constant, loss factor, relaxation frequency and relaxation time of these lyotropic mixtures. Refractive indices of these lyotropic phases are also highlighted.     

Synthesis,thermal and lyotropic liquid crystalline properties of protic ionic salts

A series of protic ionic salts were synthesised by a simple acid–base reaction from various pyridine derivatives and dodecylbenzenesulfonic acid in a common organic solvent and characterised in terms of their thermal and lyotropic liquid crystalline properties using various experimental techniques. All of them exhibited lyotropic liquid crystalline phases in toluene, methanol, acetonitrile, dimethyl sulfoxide and water. Their critical concentrations for the formation of biphasic solutions and concentrations for the formation of lyotropic solutions were quite broad depending on the dielectric constants of the solvents. Their lyotropic phases were identified as lamellar phases, since their textures exhibited bâtonnets, oily streaks and mosaic textures. They can potentially be used for many organic transformations, which may have implications in green chemistry.     

层状溶致液晶中磁性纳米粒子掺杂的研究

选择非离子表面活性剂十二烷基(4)聚氧乙烯醚(C₁₂E₄)与H₂O构成的溶致液晶(LLC)层状模板, 掺杂油酸铵包覆的Fe₃O₄亲水性磁性纳米粒子, 构建稳定的有机/无机杂合体. 用透射电镜(TEM), X射线粉末衍射(XRD), 偏光显微镜(POM), 小角X射线散射(SAXS)和振动探针式磁强计(VSM)等对粒子及掺杂前后的层状液晶相结构变化进行表征. 结果表明, 粒子掺入使LLC模板的层间距产生了改变, 同时增强了体系有序性．通过对杂合体表征结果的分析, 阐述了模板与粒子间相互作用的机理.     

Effect of quenching on the structural and dynamic properties of non-aqueous lyotropic mesophases

We focused to highlight the effect of quenching on the development and ordering of non-aqueous lyotropic liquid crystalline phases. Lyotropic mesophases are prepared from binary mixtures of sodium dodecyl sulphate and ethylene glycol at varying concentrations 30:70 and 50:50 wt%. The obtained self-assembled phases are characterised by X-ray diffraction, polarisation optical microscopy, differential scanning calorimetry and dielectric spectroscopy to evaluate the structural, optical, thermal and dielectric behaviours. Structural and textural measurements confirmed mesomorphic and crystalline phases for both mixtures. Calorimetric study gives insight about the growth of new phases at ≈335 K and isotropic temperatures of these mixtures. Both the mixtures are quenched from 335 K to the 303 K to analyse the effect of quenching on the structure and ordering of mesophases. We noticed well-defined hexagonal liquid crystalline mesophases for both concentrations after quenching at 303 K. Dielectric and relaxation behaviours of quenched mesophases were also examined. Higher capacitance and dielectric strength are noticed for quenched mixtures. The application prospective of such phases is also discussed.     

Effect of ZnO nanoparticles doping on structural,dielectric and interfacial behavior of polyoxyethylene (20) sorbitan/ethylene glycol lyotropic phases

ABSTRACT

We are reporting on the interaction of zinc oxide (ZnO) nanoparticles (NPs) with the lyotropic phase comprises of Polyoxyethylene (20) sorbitan monolaurate and protic solvent ethylene glycol. The concentration of the NPs has been varying from 0.05 to 0.5 wt%. Multiwall lamellar and inverse phases have been observed at lower and higher concentration of ZnO NPs doping. Interestingly, the organization of ZnO NPs on the periphery and inside the periphery of ring-like structures has been observed at lower and higher concentration of the dopant, respectively. Such organization of the NPs can be explained considering interfacial interaction amid host and dopant and may also attribute to the adsorption mechanisms of surfactant. Effects of NPs doping on the dielectric dynamics has also been examined. About 32.6% decrease in the dielectric permittivity has been noticed at higher NPs doping. Such decrement in permittivity could be a result of the screening of the ZnO NPs dipole moment by the adsorption of surfactant molecules on their surface. Relaxation and optical parameters of the non-doped and doped mixtures have also been discussed.     

掺杂聚合物对溶致液晶结构的影响

利用聚合物大分子作构建组分,将其掺杂到不同类型表面活性剂构成的溶致液晶中,考察对液晶相结构的影响．利用小角X射线散射及偏光显微镜对聚合物掺杂前后液晶的结构进行表征,并讨论了聚合物与液晶模板间的相互作用．对阴离子型表面活性剂琥珀酸二异辛酯磺酸钠(AOT)／水液晶体系,聚合物的嵌入使层间距d增大;而对非离子表面活性剂十二烷基聚氧乙烯醚(C12EO4)／水体系,除小分子量的聚乙二醇PEG400外,其它聚合物嵌入使d减小,表明聚合物分子类型、大小及浓度对溶致液晶的结构参数甚至组装方式有不同的影响机制．     

Rheological properties of lyotropic liquid crystals encapsulating curcumin

This study constructed new curcumin-loaded lyotropic liquid crystals containing pharmaceutically accepted oil, and ethyl oleate (EtOL). Three liquid crystalline phases including lamellar, hexagonal, and cubic phases were identified by means of the polarized optical microscopy and rheology method. By analyzing the shear viscosity (η_0.1), the viscosity of curcumin-liquid crystals is smaller than those without curcumin. Dynamic rheological results show that: Dissolved curcumin in EtOL can make the elastic modulus of hexagonal and cubic phase increase compared with that without curcumin, while the elastic modulus of lamellar phase decreases. Dissolved curcumin in Brij 97 can lead to the decreasing of the elastic modulus for cubic and lamellar phases, whereas it has little influence on hexagonal phase. When the curcumin is solubilized in both EtOL and Brij 97, the elastic modus of hexagonal phase increase, the elastic modus of lamellar and cubic phases decrease compared with that without curcumin. Furthermore, three temperature turning points were identified by the change in the slope of tanδ (G″/G′) for curcumin-hexagonal liquid crystal. These studies might be a help to study the storage of drug carrier and in vitro release properties of lyotropic liquid crystals containing curcumin.     

层状溶致液晶中电沉积铂纳米线

以非离子表面活性剂四氧乙烯基正十二烷基醚与氯铂酸水溶液构建层状溶致液晶, 通过电沉积技术制备了金属铂纳米线. 分别采用偏光显微镜、小角X射线散射对液晶进行结构分析, 通过透射电镜和能量弥散X射线谱分析观测产物形貌并确定其组成. 结果表明, 相对于饱和甘汞电极, 沉积电势在0.05～0.20 V范围内, 金属铂沿表面活性剂双分子层膜生长, 反应前后液晶相的长程周期性结构无明显变化; 在0.10 V沉积电势下, 随反应时间从960 s延长至3840 s, 去除表面活性剂后沉积产物分别为层状纳米粒子、层状纳米线以及长度达十几微米且致密的纳米线. 讨论了层状液晶对沉积产物的结构导向作用.     

溶致液晶中金属纳米粒子的掺杂及其作用机制研究

在用琥珀酸二异辛酯磺酸钠(AOT)构建的具有长程有序结构的层状溶致液晶内, 用不同方式导入预制的亲油或亲水贵金属纳米粒子, 可得到纳米粒子分布在不同介观空间内的无机/有机杂合体. 依据小角X射线散射和偏光显微镜结果, 通过分析掺杂纳米粒子与液晶模板的相互作用, 对掺杂前后体系结构的变化及制得杂合体的稳定性进行了表征. 结果表明, 除考虑掺杂粒子与层状模板空间的匹配外, 体系中静电斥力、范德华引力和Helfrich涨落力之间的平衡是维持液晶结构稳定的基本条件.     

Novel Amphiphilic Block Copolymers for the Formation of Stimuli-Responsive Non-Lamellar Lipid Nanoparticles

Non-lamellar lyotropic liquid crystalline (LLC) lipid nanoparticles contain internal multidimensional nanostructures such as the inverse bicontinuous cubic and the inverse hexagonal mesophases, which can respond to external stimuli and have the potential of controlling drug release. To date, the internal LLC mesophase responsiveness of these lipid nanoparticles is largely achieved by adding ionizable small molecules to the parent lipid such as monoolein (MO), the mixture of which is then dispersed into nanoparticle suspensions by commercially available poly(ethylene oxide)–poly(propylene oxide) block copolymers. In this study, the Reversible Addition-Fragmentation chain Transfer (RAFT) technique was used to synthesize a series of novel amphiphilic block copolymers (ABCs) containing a hydrophilic poly(ethylene glycol) (PEG) block, a hydrophobic block and one or two responsive blocks, i.e., poly(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl acrylate) (PTBA) and/or poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). High throughput small angle X-ray scattering studies demonstrated that the synthesized ABCs could simultaneously stabilize a range of LLC MO nanoparticles (vesicles, cubosomes, hexosomes, inverse micelles) and provide internal particle nanostructure responsiveness to changes of hydrogen peroxide (H₂O₂) concentrations, pH and temperature. It was found that the novel functional ABCs can substitute for the commercial polymer stabilizer and the ionizable additive in the formation of next generation non-lamellar lipid nanoparticles. These novel formulations have the potential to control drug release in the tumor microenvironment with endogenous H₂O₂ and acidic pH conditions.     

Lyotropic liquid crystalline phases formed in ternary mixtures of 1-cetyl-3-methylimidazolium bromide/p-xylene/water: a SAXS, POM, and rheology study

The phase behavior of ternary mixtures of 1-cetyl-3-methylimidazolium bromide (C(16)mim-Br)/p-xylene/water is studied by small-angle X-ray scattering (SAXS), polarized optical microscopy (POM), and rheology measurements. Two types of lyotropic liquid crystalline phases are formed in the mixtures: hexagonal and lamellar. The structural parameters of the lyotropic liquid crystalline phases are calculated. Greater surfactant content in the sample leads to denser aggregation of the cylindrical units in the hexagonal liquid crystalline phase. The increase in lattice parameter and thickness of the water layer in lamellar phase are attributed to the increase of water content, and the area per surfactant molecule at the hydrophobic/hydrophilic interface for lamellar phase is found to be larger than that for hexagonal phase. The structural parameters of the liquid crystalline phases formed from the cetyltrimethylammonium bromide (CTAB) system are larger than those for the C(16)mim-Br system. The rheological properties of the samples are also found to be related to the structure of the liquid crystalline phases.     

Doping silver nanoparticles in AOT lyotropic lamellar phases

The organic lyotropic liquid crystal with long-range structural order is used as template to assemble inorganic/organic hybrid by doping pre-fabricated Ag nanoparticles. The lamellar hybrid with both hydrophilic and hydrophobic particles doped simultaneously is realized for the first time. The change of template structure after doping and the stability origin of dual-doped system are characterized by small angle X-ray scattering and polarized optical microscopy. Results show that the interaction and space matching between surfactant bilayers and doped particles are key factors to obtain stable hybrid.     

表面活性剂溶致液晶的流变学性质

系统阐述了三种溶致液晶(六角状、立方状和层状液晶)的流变性质,概括了各自的流变性特点并给出了其理论模型,特别对立方相的流变学模型和层状相的剪切诱导转变作用进行了较详细的说明.讨论了因为这种转变而导致的囊泡的形成,并且在表面活性剂和嵌段共聚物中均可观察到剪切诱导的结构转变.     

Biomimetic Nucleation and Morphology Control of CaCO_3 in PAAm Hydrogels Synthesized from Lyotropic Liquid Crystalline Templates

Hydrogels have been thought to be the material which can provide appealing replacements of biological organisms. Pores of hydrogels synthesized from lyotropic liquid crystalline (LLC) templates were smaller in size and more uniform than those of traditional hydrogels. LLC poly‐acrylamide (PAAm) hydrogels were used as the growth media of CaCO₃. After copolymerized with acrylic acid and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), LLC hydrogels were modified with COOH and SO₃H, respectively. The effect of functional groups on the biomimetic mineralization of CaCO₃ was studied. Most of crystals from traditional hydrogels are rhombohedral and could not form aggregates. Only a few could aggregate and have a particular morphology with irregular orientation of subcrystal. Compared with crystals separated from traditional hydrogels, crystals growing in the LLC hydrogels were much more regulated and could form aggregates with particular morphology and regular orientation, that is, face (104) of rhombohedral subcrystals parallel to the surface of the macrocrystals. Modification of COOH and SO₃H groups made CaCO₃ subcrystal align more tightly. COOH had minor influences on the crystal orientation and small modification to the aggregate morphology. SO₃H groups could change the crystal orientation and morphology effectively. The aggregates are pseudo‐spherical and the face perpendicularity to the face (104) parallels to the surface of the aggregates.     

Preparation of silver nanoparticles in liquid crystalline systems

Silver nanoparticles preparation and the aggregation stability of the particles was investigated in lamellar liquid crystalline systems. A liquid crystal of HDTABr/pentanol/water was first prepared. The water content was next increased while keeping the mass ratio of HDTABr and pentanol constant. Silver nanoparticles were produced by replacing the aqueous phase by Ag sols of various concentrations (0.5–5×10^–3 mol/l) or by an in situ preparation method, i.e., interlamellar reduction of Ag⁺ ions in the liquid crystalline phase. The stability of the silver nanoparticles was monitored by UV-VIS spectroscopy and TEM. The particle size ranged from 5 to 44 nm. The kinetic of silver nanoparticle aggregation was investigated. The effect of nanoparticles on structural ordering in liquid crystals was studied by XRD measurements and it was established that the lamellar distance (d_L) was only slightly altered. Electronic Publication     

Preparation of a solution‐processable,nanostructured ionic polyacetylene

Polymerization of a self‐assembled 1‐dodecyl‐3‐propargylimidazolium bromide ionic liquid (IL) yields a nanostructured ionic polyacetylene. A 1:1 aqueous mixture of the amphiphilic IL produces an ordered lyotropic mesophase that adopts a hexagonal perforated lamellar structure. Rh (I)‐mediated polymerization of the assembled mixture yields a hexagonal modulated lamellar structured polymer. FTIR spectroscopy reveals that the polymer was self n‐doped. The polymer was fractioned into three components with the majority product, possessing an intermediate molecular weight that is soluble in polar organic solvents. In methanol, the optical band gap of the main fraction was determined to be 2.38 eV and was nonemissive. The solution‐processable polymer was airbrush sprayed onto glass substrates to give a liquid‐crystalline, lamellar structured semiconductive film (7.02 × 10^?5 S cm^?1). The polymer resisted oxidation (degradation) upon storage in air as monitored by vibrational spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1215–1227     

Structural,dielectric and conductivity behaviours of cetyltrimethylammonium bromide/ethylene glycol-based quenched lyotropic mesophases

The present study highlights the effect of quenching on the structural, textural and dielectric dynamics of cetyltrimethylammonium bromide/ethylene glycol binary mixtures of varying concentrations 30:70, 50:50 and 75:25 wt.%. No mesomorphism is seen in the as-prepared binary mixtures as X-ray diffraction and polarisation optical microscopy studies reveal the crystalline-like structures for the studied concentrations. With the effect of quenching, lyotropic hexagonal phase is obtained at 30:70, 50:50 wt.% concentration; however, mixture with higher 75:25 wt.% concentrations exhibit crystalline-like phase. The obtained hexagonal lyotropic phases restrain the mesomorphism up to ≈340 K and then show crystalline-like structures with the further increase in the temperature. Dielectric and relaxation behaviours of hexagonal lyotropic phases are presented in this study. The relaxation parameters of lyotropic phases are also discussed. Interestingly, the hexagonal lyotropic phases obtained for 30:70 and 50:50 wt.% concentrations exhibit ac conductivity of the order of 10^–5 S/m, which can be seen as a significant result of this study.     

New one-pot technique to introduce charged nanoparticles into a lyotropic liquid crystal matrix

We present a new method to incorporate hydrophilic charged nanoparticles into the lyotropic liquid crystal (LLC) template. This method is based on the effect of the polymer-induced phase separation (PIPS) and consists of two steps. In the first step, the nanoparticles are mixed with a surfactant micellar solution. In the second step, upon addition of polymer, phase separation is induced and the LLC phase doped with the nanoparticles is formed. Columnar hexagonal and lamellar LLC templates are obtained with the PIPS method. The ordering of the LLC phase can be controlled by the amount of polymer added to induce phase separation. The method works both for the system of nonionic surfactants and polymers and ionic surfactants and polyelectrolytes. We demonstrate that the PIPS method enables the fabrication of the LLC templates doped with positively or negatively charged nanoparticles as well as with a mixture of oppositely charged nanoparticles in arbitrary proportions.     

溶致液晶及其在纳米结构材料合成中的应用*

有序纳米结构材料是一类具有广泛应用前景的新材料,在分离、催化、传感器等领域的应用潜力巨大。近年来,利用溶致液晶模板合成纳米结构颗粒和薄膜材料的研究取得了一系列重要进展,包括新纳米结构金属和半导体材料的合成、由过渡金属水合物与表面活性剂构建的新液晶体系、溶致液晶与其它模板结合制备具有多级孔结构的新材料、影响液晶体系及纳米结构材料有序性与稳定性的关键因素、以及纳米结构形成机理等方面的内容。本文就上述几个方面的近期研究成果进行了总结与综述,并展望了利用溶致液晶模板合成纳米结构材料需要进一步深入开展的内容,有助于化学、化学工程和材料科学等领域的相关研究工作。