Study on the formation and rheological properties of sucrose stearate lamellar liquid crystals

The phase diagrams of S1570–Brij 97/oleic acid/water system at two different S1570/Brij 97 mass ratios of 1/1 (system S) and 7/3 (system P) were determined at 37°C, respectively. The microstructures and rheological properties of liquid crystals at constant surfactants/water mass ratio of 1/1 were studied with increase in oil content. Small-angle x-ray scattering measurements showed that system S exhibited a typical lamellar liquid crystals and the repeat distance (d) decreased as oil content increased. While for system P, two couples of scattering peaks were observed when oil content reached 28 wt%. This indicated that adding oil content may give rise to a multilamellar structures in the higher S1570/Brij 97 mass ratio system. The rheological tests indicated that a transition from elastic gel-like properties to viscoelastic liquid-like properties appeared in both system S and P when oil content reached 20 wt%, corresponding to the polarizing optical microscopy textures changing from oily streak to cruciate flower. This supplies a way to adjust structure, rheological properties, and even phase transition by altering the S1570/Brij 97 mass ratio and oleic acid content in system.     

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.     

Lamellar Liquid Crystals of Brij 97 Aqueous Solutions Containing Different Additives

Lamellar liquid crystals of Brij 97 aqueous solutions were investigated by means of rheological techniques and SAXS at 25 °C, in the presence of various additives including isopropyl myristate, oleic acid, ionic liquid bmim-PF₆ and bmim-BF₄. The lamellar phases show high elasticity as indicated by their mechanical and discrete relaxation spectra, which is expected to be an advantage when they are used as drug delivery vehicles. It is noted that in comparison with other systems, the lamellar phase formed in the Brij 97/water/IPM system has the lowest storage and loss moduli, implying that it has a weak network strength and less stable internal structure. The Brij 97/water/oleic acid system is the most shear resistance, whereas the Brij 97/water/bmim-PF₆ system exhibits fluid-like viscoelastic properties to some extent. These differences are analyzed through SAXS data for the different location of the additive in the lamellar phase.     

Phase Behavior and Rheological Properties of Concentrated Lecithin Aqueous Solutions with Additives

The phase behavior and rheological properties of the concentrated lecithin aqueous solutions were investigated at 37°C. When adding Isopropyl myristate (IPM) to lecithin solutions, besides an anisotropic liquid crystal (LC) phase, an isotropic liquid (L₂) region and an isotropic viscous (I) phase are found. By continuously adding Brij 97, the LC region shifts towards higher water content and the L₂ region is extended to the area of lower IPM concentration, meanwhile the I phase disappears. By analyzing the shear rate (η_γ=0.1) and yield stress (σ₀), adding IPM to lecithin solutions increases the values of η_γ=0.1 and σ₀, and after further adding Brij 97, the η_γ=0.1 and σ₀ decrease dramatically. Notably, different from the lecithin/DDAB/water system studied by Youssry and Montalvo, in lecithin/Brij 97/IPM/H₂O system, at the relatively higher water content area of the LC phase, the water content has little effect on the critical stress. It is also found that the change of dynamic storage modulus (G′) is similar with that of η_γ=0.1 and σ₀ parameters when adding IPM and Brij 97. Maxwell model fitting results show that in the LC phase, the relaxation of the water molecule is prolonged by adding IPM and Brij 97 to lecithin solutions.     

Curcumin-Encapsulated Hexagonal Liquid Crystalline Formed by Brij 97/NaDC Mixtures

The phase diagram of a five-components Brij 97-NaDC/IPM-PEG 400/H₂O system was determined at 25°C. The hexagonal liquid crystalline phase (H₁) was found in this system. By use of small-angle x-ray scattering (SAXS), polarization microscopy, and rheology techniques, the influence of composition, temperature, and addition of curcumin on H₁ phase was studied. It is shown that: 1) the investigated hexagonal liquid crystals exhibit a strong shear thinning behavior and viscoelasticity and the strength of the network of H₁ phase becomes weaker with increasing oil content; 2) the frequency-dependent moduli of H₁ samples decreases as the temperature increases and the steady-state limiting viscosity of the hexagonal samples shows an Arrhenius-like dependence on temperature; and 3) samples in H₁ phase containing curcumin retained their organized hexagonal structure. The SAXS results show that the curcumin molecules may be solubilized both into the apolar core of cylinders together with IPM and in the polar domain coexisting with PEG 400 between the cylinders. When curcumin is encapsulated in samples with low oil content, there is a significant decrease in the frequency-dependent moduli. The tendency of frequency behavior for samples incorporating curcumin as a function of temperature is weakened.     

Effect of temperature on dynamic rheological behavior of discontinuous cubic liquid crystal

The dynamic rheological properties of discontinuous cubic liquid crystal, formed by nonionic surfactant C(12-14)E(12), were investigated in the discrete and continuous patterns of raising temperature. In the discrete pattern, the discontinuous cubic phase appears in two types of viscoelastic behaviors under the melting points of cubic phase: elastic gel and viscoelastic liquid. When the discontinuous cubic phase begins to melt, it has the weak polymer-like viscoelasticity. Temperature and shear frequency have completely different effects on the ratio of viscous and elastic components of samples in these three states. At low temperature, the samples dominate in elasticity and temperature and shear frequency has hardly any effect on viscoelasticity. At moderate temperature, its ratio of viscous and elastic components increases with increasing temperature and decreasing shear frequency. At the vicinity of the melting point of cubic liquid crystal, the cubic liquid crystal appears to have almost equaled viscous and elastic component; shear has obvious effect on the ratio of viscoelasticity at low frequency. The results from the continuous pattern of raising temperature are consistent with those from the discrete pattern.     

Lyotropic Liquid Crystal Formed in Oleyl Polyoxyethylene Solutions by Adding Different Additives: NaDC,Tween 80, Alkyl Esters

Lyotropic liquid crystalline of oleylpolyoxyethylene(20)(AEO₂₀)/oil/water system was investigated at 25°C. The phase behavior, microstructure, and rheological properties of liquid crystalline were investigated by rheological techniques and polarizingoptical microscopy in the presence of various additives including Tween 80, sodium deoxycholate (NaDC), isoamylacetate, butyl acetate, isopropyl myristate. Diagrams show that cubic phase transforms to hexagonal phase when a shorter chain length oil is applied or NaDC or Tween 80 is added to the system.Flow experiments indicate the shear-thinning properties and a plastic behavior. The turning points of flow curves of the system AEO₂₀ and system AEO₂₀/NaDC were found. The dynamic modulus increase with increase in water content however the tendency is weaken by adding NaDC. Frequency dependence of experimental G ′ and G ′ were fitted using the multiple Maxwell model the cubic LLCs described by three relaxation times while hexagonal LLCs described by 5–8 elements. When AEO₂₀ mixes with Tween 80, the hexagonal have a monotonic decrease distribution of relaxation times without valleys.     

Formation of liquid crystal/gel emulsions to nano-emulsions constructed by polyalkoxylated fatty alcohol (PAFA)-based mixed surfactant systems

In the construction of ternary phase diagrams, the polyalkoxylated fatty alcohol (PAFA)-based mixed surfactant systems including PAFA-AS (alkyl sulfonate), PAFA-CB (cocamidopropyl betaine) and PAFA-APG (alkyl polyglucosides) were used to develop self-standing liquid crystal/gel emulsions containing rapeseed oil methyl esters (ROME) and water. The formation of liquid crystal/gel emulsions are observed at semi-dilute regions of the phase diagrams. A pre-emulsion was chosen from each of PAFA-AS, PAFA-CB and PAFA-APG systems for minor modification with sodium silicate. Upon aqueous dilution of the modified pre-emulsions to weight fractions (Φ_w) of 0.8 and 0.6 and with an isothermal shaker agitation, the samples demonstrate dramatic increases in apparent viscosity with flow resistance and shear thinning behaviour. In oscillatory amplitude study, the emulsions show linear viscoelastic (LVE) plateau (G’>G”) and strain softening region (G”>G’) indicating the samples promote a viscoelastic behaviour. Further affirmation by Cole-Cole plots reveal the emulsion samples behave as a Maxwell fluid. The optical microscope study verifies the emulsions of PAFA-AS, PAFA-CB and PAFA-APG systems comprising of multilamellar vesicles, bicontinuous cubic phase and multilamellar phase, respectively. Upon aqueous dilution of the liquid crystal/gel emulsions with an isothermal agitation, the formation of nano-emulsion droplets is confirmed by transmission electron microscopy (TEM) and dynamic light scattering studies. The nano-emulsions display spherical and elliptical shapes with mean droplet sizes are in the range of 158.37 to 206.43?nm and zeta potential values are in the range of –12.07 to –32.79?mV.     

Studies on the phase properties of lyotropic liquid crystals of Brij35/sodium oleate/oleic acid/water system: By means of polarizing microscope, SAXS, 2H-NMR and rheological methods

The pseudo-quaternary phase diagram of Brij35/sodium oleate/oleic acid/water systems has been investigated, and the liquid crystal area has been identified, which covers about two thirds of the whole phase diagram. The liquid crystal structure and behavior have been also studied by using polarizing texture, small angle X-ray scattering, ²H-NMR and rheometer etc. The result shows that when the composition of the system changes along the line of AA’ in this large liquid crystal region, the structural change is cubic→cubic/lamellar→lamellar→lamellar/hexagonal→hexagonal. Meanwhile, we made the first attempt of systematic study of the rheological properties of the above system. The lattice constants of cubic and hexagonal liquid crystals are 10.53 and 5.68 nm, respectively.     

Lyotropic liquid crystalline phases formed by phyosterol ethoxylates in room-temperature ionic liquids

The phase behaviors of four phytosterol ethoxylates surfactants (BPS-n, n = 5, 10, 20, and 30) with different oxyethylene units in room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), have been studied. The polarized optical microscopy and small-angle X-ray scattering techniques are used to characterize the phase structures of these binary systems at 25 °C. The structure and ordering of the liquid crystalline (LC) phases in such BPS-n/[Bmim]BF₄ systems are found to be influenced by BPS-n concentration and the temperature. Due to the bulky and rigid cholesterol group, the phytosterol ethoxylates surfactants exhibit different properties and interaction mechanism from the conventional C_nEO_m type nonionic surfactant systems. The rheological measurements indicate a highly viscoelastic nature of these lyotropic LC phases and disclose a lamellar phase characteristic with a rather strong rigidity at high surfactant concentrations. The control experiment with Brij 97(polyoxyethylene (10) oleyl ether)/[Bmim]BF₄ system and the FTIR measurements help to recognize that the solvophobic interaction combining with the hydrogen bonding are the main driving forces for the LC phases formation.     

Studies on the phase properties of lyotropic liquid crystals of Brij35/sodium oleate/oleic acid/water system:By means of polarizing microscope,SAXS,~2H-NMR and rheological methods

The pseudo-quaternary phase diagram of Brij35/sodium oleate/oleic acid/water systems has been investigated, and the liquid crystal area has been identified, which covers about two thirds of the whole phase diagram. The liquid crystal structure and behavior have been also studied by using polarizing texture, small angle X-ray scattering, 2H-NMR and rheometer etc. The result shows that when the composition of the system changes along the line of AA′ in this large liquid crystal region, the structural change is cubic→cubic/lamellar→lamellar→lamellar/hexagonal→hexagonal. Meanwhile, we made the first attempt of systematic study of the rheological properties of the above system. The lattice constants of cubic and hexagonal liquid crystals are 10.53 and 5.68 nm, respectively.     

Non-covalent intermolecular interactions of colloidal nematic liquid crystals doped with graphene oxide

Graphene oxide (GO) was doped to eutectic uniaxial nematic liquid crystals (NLCs) (E_5CN7) with different percentages to improve the physiochemical properties of NLCs effectively. GO shifts the N-I phase transition temperature to higher values. It has been observed that increasing GO concentration up to 0.75% increases the N-I phase transition temperature substantially while further increase of GO concentration results in an inverse trend. The GO/E_5CN7 non-covalent interactions change the N-I phase transition. The contribution of several terms such as anchoring and polarisation effects on N-I phase transition was quantified as well. The results suggest that the size is an important contributor to GO and liquid crystal interaction. The results show that E_5CN7@GO composites may act as promising candidates to enhance the efficiency of room temperature devices.     

Microstructure and rheological properties of liquid crystallines formed in Brij 97/water/IPM system

The phase diagram of Brij 97/water/IPM systems was determined at 25 degrees C. Rich liquid crystalline phases including Lalpha, H1, and cubic Fd3m phases were identified by means of small angle X-ray scattering (SAXS). Microstructure transitions of liquid crystals with changes in surfactant concentration and oil content are explained qualitatively by the surfactant packing parameter (vL/aSlc). Dynamic rheological results indicate that all three kinds of liquid crystals investigated show high elasticity. The lamellar, Lalpha, phases formed in Brij 97/water with two different oils, oleic acid and geraniol, were also studied in comparison with those of Brij 97/water/IPM systems. The strength of the network of lamellar phases formed in Brij 97/water/oleic acid and Brij 97/water/geraniol systems are appreciably stronger than for Brij 97/water/IPM systems, indicated by the smaller area of surfactant molecules at the interface and the higher moduli (G' and G').     

A rheological and morphological study of a copolyester liquid crystal/polypropylene blend system

The effects of composition and shear rate on the rheology and morphology of blends of LC–3000, a thermotropic liquid crystalline polymer consisting of 60/40 of hydroxybenzoic acid and poly(ethylene terephthalate), with polypropylene were studied. It was found that the rheological properties depend in a complex manner on composition and applied shear. Both positive and negative deviations from the log-additivity rule were observed at low shear rates. Significant viscosity reduction was measured when the dispersed phase was a nematic TLCP. The accompanying microstructural transitions were characterized a posteriori, and it was found that the state of dispersion of the TLCP phase also influences the viscosity reduction phenomenon. A nematic, fibrillar TLCP phase shows a viscosity reduction of the order of fourfold with respect to the viscosity of the matrix. Another important finding was that the stability of these fibers would not be expected from work on other non-TLCP-containing immiscible blends. This suggests that the unique rheology of the TLCP minor phase is relevant to the formation of stable fibers. © 1996 John Wiley & Sons, Inc.     

热致性液晶共聚酯的拉伸流动行为

采用入口收缩流动的实验方法研究了改性PET/ 80PHB液晶共聚酯LCP80的拉伸流动行为 ,考察了拉伸速率、温度等对其拉伸粘度、Trouton比的影响 .实验结果表明 ,LCP80的入口压降值很大 ,其中由拉伸引起的入口压降是主要的 .在该文实验条件下LCP80均表现出拉伸稀化现象 ,并且Trouton比值都远大于 3 .根据流动中液晶织态结构的变化解释了实验现象 ,并对入口收缩流动的实验数据处理方法作了改进 ,比Beery的方法更为合理 ,也具有更广的适用性 .     

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.     

Lyotropic Liquid Crystals Formed by Brij 97/PEO‐PPO‐PEO Mixtures

The phase diagrams of Brij 97/(PEO)_m(PPO)_n(PEO)_m/water/IPM quaternary systems (A L‐64: m=13, n=30; A L‐62: m=7, n=32; A L‐61: m=3.5, n=31) were determined at 25°C. The liquid crystalline phases (lamellar L_αand hexagonal H₁) were investigated by means of small angle x‐ray scattering (SAXS) and rheological techniques, with comparison of composition and component effects. The lamellar phases formed in Brij 97/A L‐64 and Brij 97/A L‐62 systems array more orderly than that of Brij 97/A L‐61 system, indicated by the stronger intensity of the second reflection peak in the SAXS patterns and the higher moduli (G′ and G″) in the dynamic rheograms. In Brij 97/A L‐64/water/IPM system, all L_α phases exhibit elastic rheograms, moreover the viscous property get increased with increase in water content. On the other hand, with this change, the H₁ phases show Maxwell and gel‐like rheograms in order, in which the latter shows mechanical and relaxation spectra typical of highly structured materials.     

含氰基离子液体的合成、表征及流变性质研究

摘要合成、 表征了一系列新的含氰基咪唑类离子液体. 测定了该离子液体的密度、 熔点及溶解性等物理性质, 研究了其在稳态、 瞬态和动态条件下的流变行为. 结果表明, 当剪切速率在0.1～50 s^-1范围内时, 其粘度不随剪切速率的变化而变化, 但随温度升高而降低, 粘流活化能随取代基长度变化呈现规律性变化. 对于1-丁基-3-氰乙基咪唑六氟磷酸盐离子液体, 维持剪切速率不变时, 其剪切应力和粘度均不随时间变化, 且随着温度的升高而降低; 在动态条件下, 在线性粘弹区, 复合粘度和损耗模量G″ 随温度升高而降低. 关键词     

笼形倍半硅氧烷修饰的金纳米粒子对4-正戊基4'-氰基联苯液晶性能的影响

为有效降低液晶器件的开启电压,获得具有低功耗特性的液晶显示器件。本文采用巯基功能化的笼形倍半硅氧烷(POSS)作为修饰配体,硼氢化钠为还原剂,采用一步法还原氯金酸制备出粒径约为5 nm的金纳米粒子。将该金纳米粒子以不同质量分数掺杂到向列相液晶4-正戊基4'-氰基联苯(5CB)中,研究了其对液晶黏度、阈值电压、相变温度的影响。结果表明,POSS修饰的金纳米粒子可以使液晶材料5CB的黏度降低、阈值电压减小。该金纳米粒子的掺入,拓宽了液晶材料的相变温度范围。     

Influence of pressure on the B2I phase transition of a banana-shaped liquid crystal

Employing a phenomenological mean field theory, we analyse the effect of high pressure on the B₂I phase transition properties of a bent-core liquid crystal. The basic idea of the work is to explain the phase transition behaviour of system by assuming that certain Landau coefficients associated with the order parameters coupling terms of the free-energy density expansion are pressure dependent. We observe excellent agreement between the theoretical and experimental results of mesogen PHDBB and that the B₂I transition remains first order even at the elevated pressures.