The effects of some factors on the rheological properties of the lyotropic liquid crystals formed in Brij97/NaDC/IPM/water system: compositions,temperature and polyphenols

In this paper, interaction between Brij97 and NaDC in mixed micelles was studied by surface tension method. Phase behavior for Brij97/NaDC/IPM/H₂O system was investigated at the desire molar ratio of α_NaDC?=?0.42 and the human body temperature of 37?°C. Hexagonal and cubic liquid crystal were found in this system analyzed by small angle x-ray scattering (SAXS). some factors were changed to affect the rheological properties of liquid crystal. Rheological investigations showed: The higher content of water and lower experimental temperature favored the greater values of shear viscosity and viscoelastic modulus; The sample was closer to the plastic fluid and was more likely to recover from disturbed state to equilibrium state at lower ratio of NaDC; The curcumin and TP can influence the shear viscosity, viscoelastic properties and phase transition temperature, even change the structure of liquid crystal. This supplies a way to adjust rheological properties, structure and even phase transition by altering those factors.     

Hexagonal liquid crystalline phases formed in ternary systems of Brij 97-water-ionic liquids

Phase diagrams of two ionic liquids: hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF(6)) and relatively hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF(4)) in aqueous solutions of Brij 97 were determined at 25 degrees C. Two hexagonal liquid crystalline phases formed in bmim-PF(6)- and bmim-BF(4)-containing ternary systems were investigated by means of small-angle X-ray scattering (SAXS) and rheological techniques, with comparison of composition and temperature effects. From analysis of the SAXS data, bmim-PF(6) is dominantly penetrated between the oxyethylene chains of surfactant molecules, whereas bmim-BF(4) is mainly located in the water layer of hexagonal phases. The strength of the network of hexagonal phase formed in the Brij 97/water/bmim-BF(4) system is appreciably stronger than that of the Brij 97/water/bmim-PF(6) system, indicated by the smaller area of the surfactant molecule at the interface and the higher moduli (G', G' '). Temperature has a converse effect on the lattice parameters of the two hexagonal phases.     

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.     

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.     

Microstructure and rheological properties of polybutadienes

The viscosities, rubbery deformations, densities, and their dependence on temperature have been measured for several series of polybutadienes with molecular weights ranging from 5,000 to 400,000 and differing in proportions of cis and trans structures (cis content from 40 to 95%). On the basis of the viscosity measurements the critical molecular weight M_c has been determined, corresponding to a sharp change in the nature of the viscosity versus molecular weight dependence. Rubbery deformations are displayed pronouncedly in specimens with M > M_c and are closely related to the appearance of non-Newtonian flow. The value of M_c depends on the relative content of cis and trans forms. When M > M_c, the initial viscosity is a parameter sensitive to the microstructure of polybutadienes, so that with at a single molecular weight, depending on the ratio of cis and trans units, the viscosity may vary over a more than tenfold range. The glass transition temperature and activation energy of viscous flow rise regularly with increasing trans content in the polymer chain, these parameters becoming independent of the molecular weight for specimens with M > M_c within a series of polybutadienes of equal microtacticity. Thermomechanical investigations of polybutadienes also made it possible to define more accurately the boundaries of the crystallization region and the dependence of the melting point on the microtacticity. The results obtained are discussed on the basis of modern ideas of polymer structure.     

Optical and rheological properties of the dibutyl phthalate-decalin binary liquid system

The flow birefringence method, diffusometry, and viscosimetry were used to study optical and rheological properties of dibutyl phthalate-decalin liquid mixtures of various compositions. The molecular refraction was demonstrated to obey the additivity rule, while the Maxwell constant was observed to deviate slightly from this rule. The nonmonotonic dependence of the molecular mobility of the medium on its composition was revealed and examined. The effects observed were interpreted. According to the diffusiometry and viscosimetry data obtained, the mean size of the mobile units in the system attains its maximum value at a dibutyl phthalate mole fraction of 0.2.     

Synthesis of 3,5-disubstituted 1,2,4-oxadiazoles and their behavior of liquid crystallines

The synthesis of 3,5-disubstituted 1,2,4-oxadiazoles by the cyclocondensation of amidoximes with trifluoroacetic anhydride or benzoic acid derivatives in moderate to high yields is described. The study on the phase transition behavior has disclosed that some of the synthesized oxadiazoles show smectic or nematic phases depending on their structures, which have the high potential application as liquid crystalline monomers.     

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.     

Effect of ethoxylated nonyl-phenols on interfacial rheological properties of oil/water systems

 Interfacial rheological properties of different Hungarian crude oil/water systems were determined in wide temperature and shear rate range and in presence of ethoxylated nonyl-phenols with ethoxy group number between 10 and 40. The fundamental conclusion of the experimental results is that the interfacial viscosity, the non-Newtonian flow behavior and the activation energy of the viscous flow drastically decrease in presence of non-ionic surfactants. Modification of these interfacial rheological properties increase with decreasing ethoxy group number and increasing tenside concentration and temperature. The most radical change was observed in presence of NPEO₁₀. As a summary it was evidenced that the interfacial rheology is an efficient and powerful detection technique, which may enhance our knowledge on formation, structure, properties and behavior of interfacial layers formed in oil/water systems. Thus, similar studies will probably accelerate the progress significantly not only in oil recovery but also in all areas of colloid science and technology. Received: 10 August 1996 Accepted: 29 November 1996     

Self-assembly and physicochemical and rheological properties of a polysaccharide-surfactant system formed from the cationic biopolymer chitosan and nonionic sorbitan esters

The natural cationic polysaccharide chitosan was mixed with the nonionic surfactants sorbitan monolaurate, sorbitan monooleate, or sorbitan triooleate to produce a biopolymer-surfactant system with unique properties. The mixtures of chitosan and surfactant formed emulsion-like solutions and/or creams. The known properties of the components were considered (i.e., hydrophile-lipophile balance, molecular weight, structure, and density), and various physicochemical and rheological properties of the mixtures were measured. Specifically, the critical micelle concentration of the sorbitan esters in a chitosan solution was measured using both surface tension and fluorescence-based methods. The concentration-dependent morphologies of the aggregates within the chitosan-surfactant solutions were evaluated by optical microscopy and dynamic light scattering. A schematic depicting the possible molecular arrangement of chitosan and surfactant within the various formulations was produced from consideration of the experimental findings. The degree of interaction between chitosan and the individual surfactants was assessed by FTIR analysis. The rheological properties of the chitosan-surfactant emulsions were also investigated and found to be related to the observed morphologies. Overall, clear composition-property relationships were established for these chitosan-surfactant systems which have potential applications in the food and pharmaceutical industries.     

The rheological properties of model liquid n-hexane determined by non-equilibrium molecular dynamics

Molecular dynamics computer simulation has been used to study a dense liquid composed of model molecules resembling n-hexane under steady-state she     

High magnification microscopic system focusing on transparent liquid/liquid interface formed in thin-layer two-phase microcell.

A thin-layer two-phase microcell was fabricated without an adhesive, which showed no fluorescence and resisted acids. The lower hollow of the microcell was thin (0.18 mm), which was in the range of the working distance of the used objective of high magnification (60x) and high numerical aperture (1.2). A reflection method using probe light was newly employed for focusing the objective on a transparent dodecane/water interface strictly with an inverted microscope. The system was applied to in situ fluorescence microscopic measurements of the dynamics of single DNA molecules (165600 base pairs) at the dodecane/water interface.     

Structural properties of liquid water

Monte Carlo simulations of molecular configurations of liquid water in theNVT-ensemble atT=298 K using unit cells containing 125 and 1000 molecules were, carried out. Comparison of experimental and calculated radial distribution functions suggests the existence of two types of spatial ordering in water. Structural properties of low-energy molecular clusters and associates of closed cycles of H-bonds were determined. The properties of the network of H-bonds can be described by a set of fundamental constants and one free parameter,viz., the probability of bond formation. The existence of long-range correlations in spatial arrangement of both the molecules and the cycles of bonds was established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 841–851, May, 1999.     

Quantitative determination of alpha-tocopherol distribution in a tributyrin/Brij 30/water model food emulsion

Until recently, determining the distribution of antioxidants, AOs, between the oil, interfacial and aqueous regions of opaque emulsions has not worked well because the concentrations of AOs in interfacial regions cannot be determined separately from their concentrations in the oil and water phases. However, our novel kinetic method based on the reaction between an arenediazonium ion and vitamin E, or alpha-tocopherol, provides the first good estimates for the two partition constants that describe alpha-tocopherol distribution between the oil/interfacial and water/interfacial regions of tributyrin/Brij 30/water emulsions without physical isolation of any phase. The reaction is monitored by a new derivatization method based on trapping unreacted arenediazonium ion as an azo dye and confirmed by linear sweep voltammetry, LSV. The results by both derivatization and LSV methods are in good agreement and show that alpha-tocopherol distributes strongly in favor of the interfacial region when the oil is tributyrin, e.g., ca. 90% when the surfactant volume fraction is Phi I=0.01. The second-order rate constant for reaction in the interfacial region is also obtained from the results. Our kinetic method provides a robust approach for determining antioxidant distributions in emulsions and should help develop a quantitative interpretation of antioxidant efficiency in emulsions.     

The rheological properties of concentrated cetyltrimethylammonium bromide-salicylic acid solutions in water

Data on the rheological properties of the hexadecyl-trimethylammonium salicylate system (CTAB-SA) in water are reported. Three concentrations were used (0.1, 0.01, and 0.001 M). For the highest concentration, the effect of temperature on the rheology was studied in detail.The rheology of the 0.1 M CTAB-SA solution indicates a very uniform micellar size. By contrast with concentrated polymethyl methycrylate dispersions studied by the author, there was a strong divergence between the viscosity-shear rate and viscosity-frequency data, although the plateau low shear rate and frequency values agreed over a wide range of temperature. This effect could be explained by a shear rate dependent diffusion constant. The large temperature variation of the plateau viscosity and elasticity modulus values could be explained by a combination of micellar number concentration and flexibility changes as the temperature varies.At lower concentrations, the rheological data shows evidence of polydispersity in micellar size. Strong shear thickening and extensional viscosity effects are also evident, probably due to micellar overlap and cluster formation in strong shear fields and the alignment of the very long micelles in elongational flow. The shear thickening effects take some 200 s to relax (0.01 M solution). Recovery of the elasticity after shearing the 0.1 M solution is rapid (a few hundred milliseconds).     

Composition of heteroassociates formed in an HF-diethyl ketone liquid binary system

The IR spectra and solution densities in a binary liquid system (BLS) HF-diethyl ketone were measured for the first time upon variation of the component molar ratio from 1: 12 to 12: 1 and to 27: 1, respectively. Analysis of the concentration dependences of normalized (to the total number of moles of BLS components in 1 L) optical density and excess density of the solutions revealed the presence of 1: 1, 4: 1, and ∼12: 1 heteroassociates (HAs). For each associate, the concentration range in which it forms in the HF-(C₂H₅)₂CO binary mixture was estimated. It was shown that, at component molar ratios from 2: 1 to 9: 1, all three types of HAs are present simultaneously.     

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.     

Silver nanoplates formed at the air/water and solid/water interfaces

Silver nanoparticles and nanoplates were prepared at the air/AgNO₃ aqueous solution interfaces under poly(9-vinylcarbazole) (PVK) monolayers when illuminated by UV-light at room temperature and elevated temperatures, respectively. When the illuminated films at the air/water interfaces were covered by carbon-coated copper grids, nanoplates were formed even at room temperature, and the size of the nanoplates was much larger than those formed at the air/water interface under the same experimental conditions, indicating that copper took part in the formation of Ag nanoplates through the galvanic displacement reaction between Cu and Ag⁺ ions with the help of carbon layer to conduct electrons. It was found that the basal plane of these nanoplates is the (1 1 1) face of a face-centered cubic (fcc) Ag crystal. Although platelike structure can be formed at the carbon-coated copper grid/AgNO₃ aqueous solution interface without PVK film, it shows different features from those with PVK films, indicating that PVK film plays an important role in the formation of regular large nanoplates. Further observations indicate that special restrained microenvironment, adsorption of PVK molecules on a specific crystal face, anisotropic growth and attachment of the nanoparticles are responsible for the formation of the nanoplates.     

Phase behavior and rheological properties of a salt-free catanionic surfactant TTAOH/LA/H2O system

Conventional cationic and anionic (catanionic) surfactant mixtures tend to form precipitates at the mixing molar ratio of the cationic and anionic surfactant of 1:1 because of the excess salt formed by their counterions. By using OH- and H+ as the counterions, however, excess salt can be eliminated, and salt-free catanionic systems can be obtained. Here, we report the detailed phase behavior and rheological properties of salt-free catanionic surfactant system of tetradecyltrimethylammonium hydroxide (TTAOH)/lauric acid (LA)/H2O. With the variation of mixing molar ratio of LA to TTAOH (rho=nLA/nTTAOH), the system exhibits much richer phase behavior induced by growth and transition of aggregates. Correspondingly, the rheological property of the system changes significantly. Take the series of samples with fixed total surfactant concentration (cT) to be 15 mg.mL(-1), the system only forms a low viscous L 1 phase with a Newton fluid character at the TTAOH-rich side. With increasing rho, first a shear-thickening L1 phase region is observed at 0.70or=1.05, and finally, at rho>or=1.13, the excess LA will separate from the bulk solution and form a white top layer. Investigations were also carried out by varying c T at fixed rho and by changing temperature, respectively. It was found micelle growth would be greatly suppressed at higher temperatures. However, the vesicle phases showed a considerable resistance against temperature rise.