The rheological properties of hydrogenated castor oil crystals

The present study focuses on the rheological performance of a surfactant-rich aqueous suspension containing hydrogenated castor oil (HCO) crystals. HCO can be typically crystallized in five distinct shapes: spherically shaped, irregularly shaped, star-shaped (also called rosettes), short needles, and thick or thin fibers. The effect of the differences in shape on the rheological performance is studied, and the rheological properties are compared to the behavior of other triacylglycerol’s (TAG) suspensions. A suspension of TAG crystals usually behaves as a colloidal gel wherein a colloidal gel is defined as a network of flocs, with each floc being an aggregate of smaller subunits. All of these surfactant-rich aqueous suspensions of HCO crystals behaved according to a colloidal gel in the transient regime, independent of the studied crystal shapes, except the long thin fibers at a concentration above 0.1 wt% HCO transitioning from a heterogeneous fractal rod network to a homogeneous rod network, shifting from a colloidal gel to a glass.     

Phase equilibrium, structure, and rheological properties of the carboxymethyl cellulose-water system

The phase transitions, structure, and rheological properties of the carboxymethyl cellulose-water system were studied via the turbidity-point method, viscometry, polarization microscopy, and the turbidityspectrum method as well as with a polarization photoelectric unit. The regions of existence of the isotropic and anisotropic phases, the gel point, and the concentration dependence of the supramolecular-particle size were determined. Magnetic-field application results in a gain in the viscosities of carboxymethyl cellulose solutions.     

Structural and rheological properties of hydrophobically modified alkali‐soluble emulsion solutions

Scattering and rheological experiments were carried out on hydrophobically modified alkali‐soluble emulsion solutions at pH ～ 7.3 as a function of the polymer concentration. The light scattering experiments revealed the existence of a liquidlike order for concentrations below approximately 0.1 × 10^?2g cm^?3 corresponding approximately to the close packing of microgels particles. Above this concentration, the zero‐shear viscosity rose sharply, whereas the ordering disappeared progressively. The results are discussed within the framework of gelation models of associating polymers. Diffusing wave spectroscopy experiments provided estimates of the high‐frequency modulus. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1985–1994, 2002     

Composition, structure, and properties of pharmacologically active silicon dimethylglycerolates

¹H and ²⁹Si NMR spectroscopy showed that the product of the reaction of dimethyldiethoxysilane with glycerol in the molar ratio 1: 2 is an equilibrium mixture of dimethyldiglyceroxysilane and low-molecular-weight condensation products. The change of viscosity of silicon dimethylglycerolates, synthesized using different excesses of glycerol, versus time was studied by viscosimetry. Composition of products of hydrolysis and condensation of silicon dimethylglycerolates is determined by their concentration in the starting aqueous solutions.     

Crosslinked oligoethylene glycols: Correlation between their structure and some rheological properties

Six oligoethylene glycols were crosslinked with triphenylmethane triisocyanate, and polymers with systematically changing network chain lengths were obtained and investigated. The 10-sec. torsion moduli versus temperature, glass transition temperatures, and cohesive energy densities of the polymers were determined and studied. The 10-sec. torsion modulus versus temperature plots show that all six polymers have a glassy transition and rubbery region of rheological behavior. The front factor calculated from the equation for the torsion modulus in the rubbery region when measured values of the modulus were used was compared with the front factor computed from equations that take into consideration molecular structures of the rubbery networks. With the exception of the case of crosslinked diethylene glycol the agreement in all the other cases between the values obtained for the front factor in both ways was good. In the investigated range of temperatures the polymers have below the glass transition temperature another transition point. The solubility parameters of the polymers, calculated from swelling experiments, were with the exception of the first member in the series almost identical.     

Relationship between rheological properties and one-step W/O/W multiple emulsion formation

Formation of a normal (not temporary) W/O/W multiple emulsion via the one-step method as a result of the simultaneous occurrence of catastrophic and transitional phase inversion processes has been recently reported. Critical features of this process include the emulsification temperature (corresponding to the ultralow surface tension point), the use of a specific nonionic surfactant blend and the surfactant blend/oil phase ratio, and the addition of the surfactant blend to the oil phase. The purpose of this study was to investigate physicochemical properties in an effort to gain a mechanistic understanding of the formation of these emulsions. Bulk, surface, and interfacial rheological properties of adsorbed nonionic surfactant (CremophorRH40 and Span80) films were investigated under conditions known to affect W/O/W emulsion formation. Bulk viscosity results demonstrated that CremophorRH40 has a higher mobility in oil compared than in water, explaining the significance of the solvent phase. In addition, the bulk viscosity profile of aqueous solutions containing CremophorRH40 indicated a phase transition at around 78 ± 2 °C, which is in agreement with cubic phase formation in the Winsor III region. The similarity in the interfacial elasticity values of CremophorRH40 and Span80 indicated that canola oil has a major effect on surface activity, showing the significance of vegetable oil. The highest interfacial shear elasticity and viscosity were observed when both surfactants were added to the oil phase, indicating the importance of the microstructural arrangement. CremophorRH40/Span80 complexes tended to desorb from the solution/solution interface with increasing temperature, indicating surfactant phase formation as is theoretically predicted in the Winsor III region. Together these interfacial and bulk rheology data demonstrate that one-step W/O/W emulsions form as a result of the simultaneous occurrence of phase-transition processes in the Winsor III region and explain the critical formulation and processing parameters necessary to achieve the formation of these normal W/O/W emulsions.     

Biodegradable systems: Thermodynamics, rheological properties, and biocorrosion

Systems based on starch and chitosan blends with synthetic polymers and cellulose derivatives (poly(ethylene oxide) and methyl cellulose of various molecular masses, PA, and ethylene-vinyl acetate copolymers containing different amounts of vinyl acetate groups) have been studied. The thermodynamic characteristics of the formation of blends have been determined. The rheological properties characterizing formation of blends from melts have been investigated. The biocorrosion ability of the blends after their use has been estimated by various methods. The concentration dependences of the thermodynamic functions of mixing of components (change in the Gibbs energy, enthalpy, and entropy) change sign in a wide composition range, indicating the complexity of mixing of rigid-chain natural polysaccharides with synthetic polymers. The rheological study of blends in which starch or chitosan plays the role of a biodegradation modifier shows that they are non-Newtonian fluids. The absolute values of viscosity and the activation parameters of melts increase with the content of polysaccharide in the system. The values of viscosity correspond to those typical for commercially processable polymers. The blends under study are biodegradable in a wet and water-soil medium with the content of the natural component being in the range 15–30 wt %.     

Complexes of a cationic polymer with oxidized anionic liposomes: Composition,structure, and properties

Formation of complexes obtained by the adsorption of a cationic polymer, poly(N-ethyl-4-vinylpyridium bromide), with a degree of polymerization of 600 on the surface of 50-nm bilayer vesicles (liposomes) formed from neutral phosphatidyl choline, anionic diphosphatidyl glycerol (cardiolipin), and a surfactant with one alkyl radical, such as electroneutral n-hexadecylphosphocholine, palmitic acid, or heptanoic acid, is studied. The incorporation of these surfactants into the liposomal membrane stimulates the appearance of oxidized forms of lipids in it. The incorporation of n-hexadecylphosphocholine into the membrane of n-hexadecylphosphocholine and palmitic acid with the alkyl radical, whose length is comparable with the length of alkyl radicals in a lipid molecule, has no effect on the permeability of the membrane. However, these liposomes lose integrity upon the adsorption of polycation; as a result, complexation becomes irreversible. Electroneutral and anionic surfactants with long hydrocarbon chains may accumulate in a cellular membrane owing to the oxidative degradation of unsaturated radicals in lipid molecules. This finding may be used in the design of polymeric therapeutic means specifically interacting with damaged cells.     

Effects of ascorbic acid on the physiochemical,rheological, and antioxidant properties of citrus essential oil-based emulsion stabilized by pectin

The present study was conducted to enhance the peel of Citrus sinensis (sweet orange) by using their essential oils (EOs) as a potential source of natural bioactive molecules. EOs were obtained by hydrodistillation and their chemical profile was determined through GC-MS analysis. O/W EO emulsions were prepared using pectin as biopolymer emulsifier at different proportions, including different amounts of ascorbic acid (0, 0.5, and 1% w/w). The effect of pectin and ascorbic acid concentrations on the stability and rheological behavior of emulsions was investigated. It was found that adding ascorbic acid to the appropriate concentration of pectin enhances the interfacial membranes surrounding the oil droplets and decreases the droplet sizes. As a result both the viscoelastic modules and the resulting viscosity of emulsions increase leading to an improvement of their stability. Antioxidant activity of orange EO emulsion in combination with ascorbic acid was found significantly higher than that without ascorbic acid, and higher than that of individual components. Overall, this study would be helpful in developing more effectives systems with promising physical and antioxidant characteristics for the preservation of foods.     

Influence of aggregation of asphaltenes on the rheological properties of oil

Photon correlation spectroscopy was used to determine the threshold concentrations of n-heptane for phase transitions of asphaltenes in model systems for two types of oil. The rheological properties exhibited by high-paraffin oil in the asphaltene aggregation process were analyzed. It was shown that the presence of resin and paraffi n fractions in oil prevents phase transition of asphaltenes at the threshold concentration of n-heptane for the model system, so that a higher precipitant concentrations is required for aggregation of asphaltenes and formation of oil sludge.     

Effect of molecular structure on rheological and crystallization properties of polyethylenes

This article describes the development of reliable techniques to measure the isothermal crystallization rates (ICR) under quiescent as well as under small amplitude, oscillatory shear conditions. Quiescent crystallization rates were obtained using a differential scanning calorimeter. Those under small amplitude shear were obtained using Rheometrics rheometers. It is shown how a small amount of long-chain branching in high-density polyethylene homopolymer (HDPE) dramatically influences rheological properties and enhances ICR. For these HDPEs, the rate increases with the increase in long-chain branching. The general application of isothermal crystallization studies, however, should be done with great caution. This is because the fundamentals of isothermal crystallization require that it be done on the basis of a fixed undercooling with respect to the equilibrium melting temperature. Such a temperature is ill-defined for the commercial polymers having broad molecular weight distribution (MWD). Nonetheless, a practical procedure is outlined wherein the melting curve of a previously isothermally crystallized sample is used as a substitute for judging the equilibrium melting point and in deciding the selection of a proper crystallization temperature. Even this new procedure may not be applicable for polymers having heterogeneous short-chain branching distribution. © 1996 John Wiley & Sons, Inc.     

Correlation between rheological properties of zinc carboxylate liquids and molecular structure

Using Fourier transform infrared spectroscopy (FTIR), the viscosity of zinc 2-ethylhexanoate liquid has been found to correlate with the intensity of an asymmetric COO stretching resonance at 1632 cm-1. This is consistent with the presence of the zinc carboxylate polymer, catena-2-ethylhexanato-(O,O')-tri-micro-2-ethylhexanato-(O,O')-dizinc(II) as the origin of the viscosity, a conclusion that is further supported by theoretical predictions. Density functional theory has been used to assign the IR spectra of the zinc carboxylate dimer, catena-2-ethylhexanato-(O,O')-di-(tri-micro-2-ethylhexanato-(O,O')-dizinc(II)-formic) acid, and the model of the molecular liquid, micro-4-oxo-hexakis-(micro-2-ethylhexanato)-tetrazinc(II). The predicted spectra indicate that the decreased symmetry of the polymer relative to the zinc 2-ethylhexanoate liquid increases the intensity of the asymmetric carboxylate stretch at 1632 cm-1 and leads to the observed correlation.     

Alkali treatment of lignocellulosic fibers extracted from sugarcane bagasse: Composition,structure, properties

Lignocellulosic fibers extracted from sugarcane bagasse were treated with NaOH solutions of different concentration (0-40 wt%) to study the effect of alkali treatment on the composition, structure and properties of the fibers. Composition was determined by the van Soest method, structure was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while mechanical properties by tensile testing. Hemicellulose and lignin content decrease, while cellulose content goes through a maximum as a function of alkali concentration. Crystallinity changes only slightly and microfibril angle (MFA) remains constant thus structural effects and especially MFA are not the primary reasons for changing properties. The Young's modulus of the fibers shows a slight maximum at around 2-4 wt% NaOH content, while tensile strength goes through a much more pronounced one at around 5-8 wt%. Direct correlation between structure and mechanical properties was not found indicating that composition is more important in the determination of properties than structure. Regression analysis proved that the combination of several compositional variables determines mechanical properties in a non-linear manner. The improvement in fiber properties was explained with the dissolution of weak amorphous fractions and the relative increase of cellulose content.     

Cellulose ester-polyolefine binary blend: Morphological,rheological and mechanical properties

Binary blends of thermoplastic polymers, one being a polyolefin (high density polyethylene) and the other a bio-based polymer (cellulose acetate butyrate) were prepared with various components proportions. No compatibiliser was used. Depending on blend composition, different morphologies were obtained, from fine nodular to co-continuous. Blends viscoelastic and mechanical properties were studied in details in all range of compositions. The results obtained were interpreted using a careful analysis of the viscoelastic properties of the initial components and classical approaches developed for immiscible blends. Except the blends containing low amount of cellulose acetate butyrate finely dispersed in polyethylene, all other blends viscoelastic and mechanical properties follow the additive mixing rule.     

Effect of carbon dioxide on rheological properties and structure of polyacrylamide solutions

The effect of CO₂ on rheological properties and structure of polyacrylamide solutions was studied as a function of pressure, treating time, polymer type and presence of inorganic electrolytes and natural formation rocks. It was found that the serious deterioration of the solution viscosity can be attributed mostly to the change of the solution structure, while the actual molecular degradation plays negligible role in the process. The phenomena are explained by modification of the dissociation equilibrium of poly-electrolytes in presence of high hydrogen ion concentration. The experimental results may contribute significantly to elaboration of new stabilization concepts in special enhanced oil recovery technologies based on joint application of carbon dioxide and polymers.     

Effect of composition and structure on rheological properties of styrene-butadiene block copolymers

Styrene-butadiene copolymers of the S-B-S and S-B-S-B-S types, both unmodified and extended with paraffinic-naphthenic oil, were studied by dynamic mechanical spectroscopy and capillary rheometry. In the triblocks at low deformation rates, an increase in 1-vinylethylene unit content leads to an increase in complex dynamic viscosity |η*|. This may be explained by their different supermolecular structure with a higher proportion of long relaxation times. The pentablocks show a considerable effect of molecular parameters on their flow behaviour at low deformation rates. In all the systems, steady viscosity η shows no significant differences at higher shear rates. Obviously the supermolecular structure is disintegrated in these conditions and the effect of chemical structure is negligible. An expected decrease in viscosity in the whole range of deformation rates was observed with the oil-extended copolymer. The dependences of complex dynamic viscosity on angular frequency were compared with those of steady viscosity on shear rate but no unequivocal conclusion as regards the validity of the Cox-Merz rule could be reached.     

ABS blends with phenoxy: morphology,thermal, mechanical and rheological properties

Blends of ABS (acrylonitrile–butadiene–styrene) with phenoxy(poly(hydroxyether bisphenol A)) were prepared using a Branender single screw extruder. Scanning and transmission electron micrographs (SEM, TEM) showed a typical two-phase morphology; particle-in-matrix (90/10) (ABS/phenoxy by weight), 70/30, 10/90), island/sea (30/70) and co-continuous (50/50) morphologies. The glass transition temperature (T_g) of SAN was almost unchanged in the blends, while the T_g of phenoxy increased by about 5 °C in the blends. The synergistic effect of tensile modulus and strength was noted in ABS-rich blends, where a drastic drop of ductility was seen, and the results were interpreted in terms of rubber particle migration form SAN to phenoxy phase, which was visualized by TEM. Melt viscosity showed yield in ABS-rich blends, and generally followed the log additivity.     

Composition,properties, and structure of palladium(II) chlorides in aqueous solution

The composition, stability, and structure of palladium(II) chloride complexes in hydrochloric acid media have been determined using nuclear-magnetic relaxation, magnetochemical methods, and Rayleigh light scattering. The predominant form in solution for palladium(II) concentrations greater than 0.005 moles/liter is the octahedral Pd₆Cl₁₂ or Pd₆Cl₁₄ ^2–, which has antiferromagnetic properties in contrast with the paramagnetic properties of the mononuclear aquachloride. The polarizability anisotropy of Pd-Cl bonds with terminal and bridging chlorine atoms has been determined.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2473–2477, November, 1990.     

Aminonaphthalic anhydrides as red-emitting materials: electroluminescence, crystal structure, and photophysical properties

The red and orange emitters (ANA-1-3) consisting of a 4-amino-1,8-naphthalic anhydride group were synthesized. The lowest absorption band of these ANA molecules centered at approximately 450 nm is assigned to be a charge-transfer transition with emission at 514-536 nm in nonpolar solvents such as n-hexane and at approximately 590-640 nm in polar solvents such as THF and CH(2)Cl(2) and in the solid states. Emission lifetimes are measured with time-correlated single photon counting. Shorter lifetimes are observed for the ANA molecules when dissolved in polar solvents compared with those in nonpolar solvents. Strong dipole-dipole interaction of ANA molecules with solvents is indicated. At high concentrations the measured emission lifetimes, generally shortened from self-quenching, are found to remain about the same order of magnitude in ANAs. This implies that the exciton states of aggregates are formed and they exhibit a relatively long lifetime. Crystallographic data of 4-(phenyl antracen-9-yl) (ANA-2) and 4-(phenyl-2-naphthyl) amino-1,8-naphthalic anhydrides (ANA-3) show that the molecules exist as dimeric structures with antiparallel head-to-tail stacking of naphthalic anhydride planes in addition to other pi-pi stacking. The strong dipole-dipole interactions and the pi-pi stacking account for the observed red-shifted emissions of ANAs in the powders. For films prepared from vacuum sublimation, a structure similar to that in the crystal but with less crystalline order is expected based on the emission wavelength. Several electroluminescent devices based on these ANAs are reported here; they emit orange-red light at 602-628 nm with high brightness and steady external quantum efficiency.