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.     

A Comprehensive Study on Lyotropic Liquid–Crystalline Behavior of an Amphiphile in 20 Kinds of Amino Acid Ionic Liquids

We examined the self‐organization behavior of a designed amphiphilic molecule in 20 kinds of amino acid ionic liquids composed of 1‐butyl‐3‐methylimidazolium cation and natural amino acid anion ([C4mim][AA]). Addition of [C4mim][AA], regardless of their anion species, to the amphiphile provided homogeneous mixtures showing lyotropic liquid–crystalline (LC) behavior. Upon increasing the component ratio of [C4mim][AA] in the mixtures, a successive change of the mesophase patterns from inverted hexagonal columnar, in some case via bicontinuous cubic, to layered phases was observed. By examining the LC properties at various temperatures and component ratios, we constructed lyotropic LC phase diagrams. Interestingly, the appearance of these phase diagrams is greatly different according to the selection of [AA]. Through comparison, we found that the self‐organization behavior of an amphiphile in ionic liquids can be tuned by controlling their ability to form hydrogen‐bond, van der Waals, and π‐π interactions.     

Ordered 2-D and 3-D nanostructured amphiphile self-assembly materials stable in excess solvent

Amphiphile lyotropic liquid crystalline self-assembly materials are being used for a diverse range of applications. Historically, the most studied lyotropic liquid crystalline phase is probably the one-dimensional (1-D) lamellar phase, which has been employed as a model system for biomembranes and for drug delivery applications. In recent years, the structurally more complex 2-D and 3-D ordered lyotropic liquid crystalline phases, of which reversed hexagonal (H(2)) and reversed cubic phases (v(2)) are two prominent examples, have received growing interest. As is the case for the lamellar phase, these phases are frequently stable in excess water, which facilitates the preparation of nanoparticle dispersions and makes them suitable candidates for the encapsulation and controlled release of drugs. Integral membrane protein crystallization media and templates for the synthesis of inorganic nanostructured materials are other applications for 2-D and 3-D amphiphile self-assembly materials. The number of amphiphiles identified as forming nanostructured reversed phases stable in excess solvent is rapidly growing. In this article, different classes of amphiphiles that form reversed phases in excess solvent are reviewed, with an emphasis on linking phase behavior to amphiphile structure. The different amphiphile classes include: ethylene oxide-, monoacylglycerol-, glycolipid-, phosphatidylethanolamine-, and urea-based amphiphiles.     

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.     

Effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases

Lyotropic quaternary mixtures of potassium alkanoates (KCx) and sodium alkyl sulphates (NaCxS), where x is the number of carbon atoms in their alkyl chains, were prepared to investigate the effect of the surfactant alkyl chain length on the stabilisation of lyotropic nematic phases. The lyotropic mixtures investigated were formed by the dissolution of KCx (NaCxS) surfactants in the mixture of Rb₂SO₄/1-decanol/water (Na₂SO₄/1-decanol/water), separately. The uniaxial-to-biaxial nematic phase transitions were identified from the temperature dependence of the birefringences of the nematic phases by means of laser conoscopy. The micelle dimensions were obtained from small-angle X-ray scattering measurements. It was observed that the increase in the surfactant alkyl chain length causes the micellar growth in the plane perpendicular to the main amphiphile bilayer. The surfactant alkyl chain length plays a key role on the shape anisotropy of micelles, which triggers the orientational fluctuations that are responsible for the stabilisation of the different lyotropic nematic phases.     

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 of sponge-like polymer dispersions via polymerization of bicontinuous microemulsions

Polymer gels with high water content are made by polymerization of hydrophilic/hydrophobic monomer mixtures in bicontinuous microemulsions. These structures can be described as a heterophasic, bicontinuous polymer colloid-in-water structure, the characteristic length of which is only indirectly influenced by the original microemulsion mixture.The structure formation and phase changes throughout the polymerization reaction are followed with rheology, polarization microscopy, and scanning and transmission electron microscopy. It is shown that already the very first formed polymer changes disturb the bicontinuous phase structure and nucleate a vesicular phase; with further consumption of the monomer mixture, at least three other phase transitions can be detected, ending with a simple globular surfactant structure.Although direct templating of the original mesomorphous structure does not occur, the existence of the diverse lyotropic phases influences the final structure. It is shown that simple dilution changes the characteristic length of the network elements from about 2 m down to 50 nm. This is explained by a combination of a nucleation-and-growth mechanism with the influence of a restricted colloidal stability in anisometric lyotropic phases.     

Shear-induced phase transitions in sucrose ester surfactant

The behavior of a commercial sucrose stearate blend has been examined by means of various experimental techniques (differential scanning calorimetry, light polarization and electron microscopy, and rotational rheometry). A partial phase diagram in water has been established. It shows that the binary system forms a lamellar lyotropic mesophase and that the melting behavior is characterized by a lamellar gel-lamellar liquid crystalline phase transition. The identification of the liquid crystalline phase has been carried out from textural observation using polarization microscopy and freeze-fracture electron microscopy. At low surfactant concentrations, the phase transition has been followed through rheological experiments. Furthermore, a shear-induced transition, from the lamellar phase (sheets of surfactant bilayers including a few large multilamellar vesicles) to an onion phase, has been observed above a critical temperature of 43 degrees C. The vesicles so obtained did not relax over more than 3 weeks. The presence of a small ratio of distearate in the sugar ester blend seems to be the key to vesicle formation at low surface-active material concentration.     

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．     

两亲分子聚集相的扫描隧道显微镜研究

用最近发展起来的局域探测手段－扫描隧道显微镜（ＳＴＭ）及其相伴的方法如局域功函数等，对具有十分丰富局域结构的两亲分子和水的两系统的聚集相作了初步研究，以期为两亲分子研究及局域化学的发展添砖加瓦，结果表明由ＳＴＭ可以真实对反映出各种聚集相的不同形貌，而且加上局域功函数像还可以揭示两亲分子的头尾取向，这对有机分子系统的局域结构的研究有普遍意义。     

Phase Behavior of Poly(Oxyethylene)–Poly(Oxypropylene)–Poly(Oxyethylene) Block Copolymer in Water and Water–C12EO5 Systems

Abstract

The binary phase diagram of a triblock copolymer poly(oxyethylene) (PEO) poly(oxypropylene) (PPO) poly(oxyethylene) (PEO), (PEO)₃₇(PPO)₅₈(PEO)₃₇ or P105 in water and the ternary system of P105, water, and pentaoxyethylene dodecyl ether (C₁₂EO₅) has been studied to understand the miscibility of a small amphiphile, C₁₂EO₅ and a copolymer, as well as the mixing effect on the formed liquid crystalline structures. Phase diagrams, small angle x‐ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to characterize these systems. The phase diagram of the binary system is presented together with the characteristic parameters for founded phases, namely, cubic, hexagonal, and lamellar phases. In the ternary system it was found that the small amphiphile and the block copolymer, despite having very different chain lengths are essentially miscible forming single phases. A large amount of C₁₂EO₅ can be solubilized in the P105 aggregates whereas P105 is most difficult to dissolve in the C₁₂EO₅ aggregates because of the difference in the molecular size. The copolymer is practically insoluble in the lamellar phase of C₁₂EO₅ due to the packing constraint. Hence, two lamellar phases coexist in a surfactant‐rich region, at W _s  = 0.66, where W _s is the weight fraction of the total amphiphile in the system. This indicates that the thickness of the lipophilic part of the C₁₂EO₅ lamellar phase is too small to allocate the large lipophilic chain of the P105 triblock copolymer.     

Phase behavior and polymerization of lyotropic phases. II. A series of polymerizable amphiphiles with systematically varied critical packing parameters

A group of polymerizable amphiphiles, with their critical packing parameters systematically varied, were studied with respect to the phase behavior and immobilization of their lyotropic liquid‐crystalline phase structures. Small‐angle X‐ray scattering and polarized light microscopy were used to study their liquid‐crystalline phases before and after photopolymerization. The liquid crystallinity of the amphiphiles depended on the contents of both oil and water in the ternary systems. Through photopolymerization, hexagonal phases could generally be immobilized, with the structural order reduced to various degrees. However, the cubic phases evolved with polymerization into another structural pattern, which was possibly related to the lamellar structure. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5887–5897, 2006     

Mixtures of branched non-ionic oligo-oxyethylene surfactants in aqueous solutions — the effect of molecular geometry on LC phase behaviour 4

The LC phase behavior of ternary mixtures of the two corresponding branched non-ionic surfactants 1,3-bis-(methoxy-tetraoxyethylene)-2-propoxy-tetradecane (Y-surfactant) and 1,3-bis-(heptyloxy)-2-propoxyoctaoxyethylene mono-methyl ether (V-surfactant) and water were studied by polarizing microscopy. The two branched surfactants, which have different molecular geometries but nearly the same hydrophilic-lipophilic volume ratio, exhibit extremely different phase behavior in binary surfactant/water systems. For the ternary mixtures of Y- and V-surfactant and water we found-according to established packing models-a continuous stabilization of the cubic and hexagonal phases and a destabilization of the lamellar phase with increasing amount of Y-surfactant. On the other hand, we observed a thermal stabilization of the lamellar phase. The maximal transition temperatures of the lamellar phase pass a maximum with increasing amount of Y-surfactant.     

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.     

Shapes of Micelles and Molecular Geometry Synthesis and Studies on the Phase Behaviour, Surface Tension and Rheology of Rigid Rod-Like Surfactants in Aqueous Solutions

Amphiphiles with rigid rod-like hydrophobic moieties have been synthesized in order to investigate the effect of the packing restraints of such moieties on the micellar association behaviour of amphiphiles in aqueous solution. Investigations of the phase behaviour of amphiphile/water mixtures reveal that liquid-crystalline phases exist in defined temperature and concentration regimes and that they are all lamellar, regardless of the hydrophilic-hydrophobic balance of the amphiphile. For these lyotropic liquid-crystalline phases a polymorphism is observed which is similar to the polymorphism of thermotropic smectic liquid crystals. Surface tension measurements indicate critical micelle concentrations of the amphiphiles in dilute solutions which are similar to those of conventional surfactants. From rheological measurements it can be assumed that the variation of temperature and/or concentration of the solution does not influence the micellar shape. This is in contrast to the behaviour of non-ionic surfactants having a flexible hydrophobic group.     

Phase behaviour of n-alkyl- and bi-alkylbenzenesulphonates. Nematic lyotropics from double chain surfactants

The lyotropic mesophases in binary systems of surfactants in water: n-alkylbenzenesulphonates (C₈-C₁₂), two chain C₁₂-surfactants, and dodecyl-benzenesulphonic acid, were investigated. The micellar properties were examined by conductometry and viscosimetry. The phase diagrams were determined using crossed polarizers, ²H NMR spectroscopy and polarization microscopy. Besides lamellar and inverse cubic phases, new nematic lyotropic phases have been found, presenting precursors for the lamellar phases, and exhibiting very fast alignment in a magnetic field.     

Lyotropic liquid crystalline phase behaviour of a monomeric and a polymeric monosaccharide amphiphile in aqueous solution

Monomeric and polymeric amphiphiles were synthesized which exhibit lyotropic liquid crystalline phases in aqueous solution. The hydrophobic group of the monomeric surfactant is a dodecane-group esterified with acrylic acid. The hydrophilic unit is a monosaccharide derivative. By radical polymerization the monomer (N-D(-)-gluco-N-methyl-(12-acryloyloxy)-dodecane-l-amide) is converted into the corresponding polymeric surfactant. The monomer as well as the polymer exhibit a lyotropic 1.c. phase of lamellar structure. Owing to the polymerization the regime of the lamellar phase is greatly enlarged for the polymer, compared to the monomeric sufactant. These results confirm earlier investigations on non-ionic ethylene-glycol surfactants.     

Formation of Lamellar Silica from Lyotropic Liquid Crystals of Dodecyl Benzene Sulfonic Acid

The formation of lamellar mesostructured silica by a neutral route in dodecylbenzene sulfonic acid (DBSA)/aminoalkoxysilane/water systems was investigated by phase study and Small Angle X‐ray Scattering (SAXS). Initially, two lamellar lyotropic phases are found, one corresponding to the DBSA and other corresponding to the DBSA‐aminoalkoxysilane salt. With the hydrolysis and condensation of siloxane groups, the DBSA‐aminoalkoxysilane lyotropic phase disappears and lamellar silica is formed. The lyotropic phase does not act as a true template but as a source of amphiphilic molecules, hence synthesis takes place via a phase separation mechanism. This synthesis route provides an easy way to prepare amino functionalized lamellar silica.     

Heat‐Triggered Crystallization of Liquid Crystalline Macrocycles Allowing for Conductance Switching through Hysteretic Thermal Phase Transitions

A polymesomorphic thermal phase‐transition of a macrocyclic amphiphile consisting of aromatic groups and oligoethylene glycol (OEG) chains is reported. The macrocyclic amphiphile exists in a highly‐ordered liquid crystal (LC) phase at room temperature. Upon heating, this macrocycle shows phase‐transition from columnar‐lamellar to nematic LC phases followed by crystallization before melting. Spectroscopic studies suggest that the thermally induced crystallization is triggered by a conformational change at the OEG chains. Interestingly, while the macrocycle returns to the columnar‐lamellar phase after cooling from the isotropic liquid, it retains the crystallinity after cooling from the thermally‐induced crystal. Thanks to this bistability, conductance switching was successfully demonstrated. A different macrocyclic amphiphile also shows an analogous phase‐transition behavior, suggesting that this molecular design is universal for developing switchable and memorizable materials, by means of hysteretic phase‐transition processes.