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 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This article reports data supporting that the hydroxypropyl cellulose-methyl methacrylate (HCMMA) hydrophobically modified polymer studied is surface-active at the air-water interface due to its amphiphilic nature. Surface tension measurements of diluted solutions point to the formation of a complex between this copolymer and a polyoxyethylene nonylphenyl ether non-ionic surfactant of high HLB. Conversely, no indications of specific interactions were found either with a polyoxyethylene nonylphenyl ether non-ionic surfactant of intermediate HLB or with an anionic surfactant such as sodium dodecyl sulfate (SDS). The physical stability of such dispersions depended on the surfactant used. The HCMMA/SDS systems studied showed phase separation shortly after preparation, while the dispersions with the non-ionic surfactant of higher HLB exhibited at least short-term stability and Newtonian behaviour. Foam-like dispersions of HCMMA-surfactant systems with intermediate HLB presented long-term stability, underlying the important role of hydrophobic interactions in these systems. One of the latter dispersions and the corresponding continuous phase were rheologically characterised by small amplitude oscillatory shear and flow curve experiments and exhibited a high Newtonian viscosity up to a critical shear stress followed by a shear thinning as well as weak-gel viscoelastic properties. The results obtained support that (a) the continuous phase presents a complex microstructure, which required the use of a serrated sensor system to avoid the occurrence of wall depletion phenomena, (b) it controls the rheology of the whole dispersion and (c) the latter showed both physical stability and rheological properties suitable for applications as controlled release systems in pharmacy or cosmetics.
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PMID:Surface tension and rheology of aqueous dispersed systems containing a new hydrophobically modified polymer and surfactants. 1769 44

Rheological measurements of dense calcium caseinate and sodium caseinate dispersions (> or =15%) provided insight into the factors determining shear-induced structure formation in caseinates. Calcium caseinate at a sufficiently high concentration (30%) was shown to form highly anisotropic structures during shearing and concurrent enzymatic cross-linking. In contrast, sodium caseinate formed isotropic structures using similar processing conditions. The main difference between the two types of caseinates is the counterion present, and as a consequence, the size of structural elements and their interactions. The rheological behavior of calcium caseinate and sodium caseinate reflected these differences, yielding non-monotonic and shear thinning flow behavior for calcium caseinate whereas sodium caseinate behaved only slightly shear thinning. It appears that the intrinsic properties of the dense caseinate dispersions, which are reflected in their rheological behavior, affect the structure formation that was found after applying shear. Therefore, rheological measurements are useful to obtain an indication of the structure formation potential of caseinate dispersions.
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PMID:Importance of intrinsic properties of dense caseinate dispersions for structure formation. 1792 72

The behaviour of wetting films of sodium hyaluronate (NaHA) saline solutions, at physiological conditions, is investigated using interferometry. Concentrations in the range of dilute and semi-dilute regimes were chosen to assess the role of bulk molecular interactions on the surface forces. The transition from dilute to semi-dilute solutions is known to occur at c*=0.59 mg mL(-1). Dilute solutions form stable films whose behaviour is explained by van der Waals interactions. For semi-dilute solutions, the disjoining pressure vs film thickness isotherms show branches attributed to stepwise thinning or film stratification, which is interpreted in terms of a network as predicted by the theory of semi-dilute polyelectrolyte solutions. The distance between branches is 16 nm for the NaHA concentration of 2 mg mL(-1) and 12 nm for the concentration of 3.5 mg mL(-1), in agreement with the calculated correlation lengths of the polymeric network. Since no experimental evidence exists for the presence of a stable network in the bulk, this tendency for self-association should be the result of the liquid confinement. To our knowledge, the existence of oscillatory disjoining pressure isotherms in the presence of excess salt was never observed for other polyelectrolyte solutions.
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PMID:Behaviour of wetting films of sodium hyaluronate saline solutions. 1795 Mar 5

The aim of the study was to evaluate the cardioprotective and antiarrhythmic effects of intravenous Na+/H+ blockers (cariporide and SM-20550) in a rat model of ischemia and a long period reperfusion (14 days). This model allowed study of the role of Na+/H+ exchanger against late myocardial infarct expansion and left ventricular dysfunction. Each compound was administered 5 min before ischemia. Cariporide (from 0.16 mg/kg) and SM-20550 (from 0.04 mg/kg) significantly and dose-dependently reduced the number of ventricular premature beats during ischemia. The duration of ventricular tachycardia was importantly shortened in the presence of cariporide (0.63 mg/kg) and SM-20550 (0.16 mg/kg). Furthermore, cariporide (0.63 mg/kg) and SM-20550 (from 0.04 mg/kg) significantly reduced the infarct expansion: 43 +/- 2% in the cariporide group and 42 +/- 2% at 0.16 mg/kg SM-20550 versus 48 +/- 1% in the vehicle group. Cariporide and SM-20550 significantly prevented the left ventricular free wall thinning associated with the thickness ratio, suggesting a significant reduction of the ventricular dilation. Cariporide and SM-20550 significantly improved the negative dP/dtmax, suggesting a partial restoration of the cardiac relaxation. Collectively, Na+/H+ blockers administered before ischemia reduced arrhythmias and also prevented the remodeling process of the heart during postinfarction.
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PMID:Effects of SM-20550 against myocardial infarction-induced arrhythmias, late infarct expansion, and left ventricular dysfunction. 1803 67

This report describes a patient who developed a corneal melt after the use of nepafenac, a nonsteroidal antiinflammatory drug. An 82-year-old woman with chronic cystoid macular edema after cataract extraction and intraocular lens implantation in the left eye, which was clinically controlled with a topical nonsteroidal antiinflammatory drug, was initially treated with diclofenac sodium 0.1% before being treated with nepafenac 0.1%. After 5 months of nepafenac use, the patient complained of pain, a foreign body sensation, and decreased vision in her left eye. The left eye showed a peripheral corneal ulcer with no stromal cell infiltration. The corneal ulcer was scraped and cultured to show epithelial cells and neutrophils with no growth of microorganisms. The nepafenac was discontinued, and a topical antibiotic and lubrication were used. After 2 months, the patient's visual acuity improved, and she had an intact epithelium and stable corneal thinning. To the authors' knowledge, this is the first case report of a corneal melt after the prolonged use of nepafenac to treat cystoid macular edema.
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PMID:Corneal melting after use of nepafenac in a patient with chronic cystoid macular edema after cataract surgery. 1832 52

Mesophase separation has been identified in a polycation/anionic-nonionic mixed micelle system formed by the coacervation of poly(diallyldimethylammoniumchloride)/sodium dodecylsulfate-Triton X-100 in 0.40 M NaCl. The resultant dense, optically clear fluid was studied by turbidity, dynamic light scattering (DLS), and rheology. The presence of two diffusion modes in DLS points to microscopic heterogeneity: coexistence of micelle-rich (dense) domains with micelle-poor (dilute) domains. With an increase in temperature above 20 degrees C, the turbidity rises rapidly along with the intensity of the slow mode. The concomitant decrease in the diffusivity of the slow mode signals an increase in the effective viscosity of the dense domain. With further increase in temperature, dramatic shear thinning is observed, and finally, macroscopic phase separation can be identified by centrifugation. At a temperature near that for quiescent phase separation, we observe shear-induced phase separation. We propose a mechanism to explain the connection between temperature- and shear-induced mesophase separation.
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PMID:Mesophase separation in polyelectrolyte-mixed micelle coacervates. 1838 41

We carried out pointwise local velocity measurements on 40 mM cetylpyridinium chloride-sodium salicylate (CPyCl-NaSal) wormlike micellar solution using high-frequency ultrasound velocimetry in a Couette shear cell. The studied wormlike solution exhibits Newtonian, shear-thinning and shear-thickening rheological behavior in a stress-controlled environment. Previous rheology, flow visualization and small-angle light/neutron scattering experiments in the shear-thickening regime of this system showed the presence of stress-driven alternating transparent and turbid rings or vorticity bands along the axis of the Couette geometry. Through local velocity measurements we observe a homogeneous flow inside the 1mm gap of the Couette cell in the shear-thinning (stress-plateau) region. Only when the solution is sheared beyond the critical shear stress (shear-thickening regime) in a stress-controlled experiment, we observe inhomogeneous flow characterized by radial or velocity gradient shear bands with a highly sheared band near the rotor and a weakly sheared band near the stator of the Couette geometry. Furthermore, fast measurements performed in the shear-thickening regime to capture the temporal evolution of local velocities indicate coexistence of both radial and vorticity shear bands. However the same measurements carried out in shear rate controlled mode of the rheometer do not show such rheological complexity.
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PMID:Ultrasound velocimetry in a shear-thickening wormlike micellar solution: evidence for the coexistence of radial and vorticity shear bands. 1841 43

In Jordan, a growing industry has been established to produce different types of Dead Sea (DS) cosmetics that have DS salt (contains mainly NaCl, KCl, and MgCl(2)) in their formulas. In this work, the effect of DS salt on the rheology of hair shampoo containing the sodium lauryl ether sulfate as a main active matter was studied. The effects of DS salt and active matter concentration, and the temperature and time of salt mixing, on the rheological properties of hair shampoo were investigated. The salt-free shampoo showed a Newtonian behavior at 'low active matter' (LAM) and shear thinning at 'high active matter' (HAM). The presence of DS salt changed the rheological behavior of LAM shampoo from Newtonian (for the salt-free shampoo) to shear thinning. On the other hand, the behavior of HAM shampoo switched from shear thinning to Newtonian behavior in the presence of high concentration of DS salt. The addition of DS salt increased the apparent viscosity of shampoo to reach a maximum value that corresponded to a salt concentration of 1.5 wt.%. Further addition of DS salt led to a decrease in the shampoo viscosity to reach a value less than that of the salt-free sample at high salt concentration. Changing the mixing temperature (25-45 degrees C) and mixing time (15-120 min) of DS salt with shampoo has no significant influence on the rheological behavior. However, the mixing process increased the apparent viscosity of salt-free shampoo. The power law model fitted well the flow curves of hair shampoo with and without DS salt.
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PMID:Rheological characterization of hair shampoo in the presence of dead sea salt. 1849 21

In this study, diffusing wave spectroscopy (DWS) is used to investigate the effect of shear on a food-related aggregating emulsion. The principle of the method is validated using a nonaggregating, nearly monodisperse latex suspension. In general, with increasing shear rate the diffusive motion of the scatterers becomes negligible compared to the convective motion. This causes a decrease in the decay time of the autocorrelation curves and a change in the form of the autocorrelation curves from nearly exponential to Gaussian. This is reflected in the exponent of the mean square displacement that changes from 1 to 2. The effect of shear on the acidification of a sodium caseinate-stabilized emulsion was studied by DWS and by rheometry. The emulsion droplets in the food-related emulsion were uniformly dispersed at neutral pH. Upon acidification down to a pH of 5.2 +/- 0.05, the emulsion showed Newtonian behavior with constant viscosity over the whole pH range. At pH 5.17 +/- 0.05, independent of the applied shear rate during acidification, the viscosity suddenly increased. From this point on, the emulsion showed shear-thinning behavior. The photon-transport mean free path ( l*) was not influenced by the applied shear rate and did not change down to pH 5.2 +/- 0.05. Close to this pH, l* increased, and the decay of the autocorrelation curves shifted to longer correlation times when shear rates smaller than 1 s (-1) were applied. At lower pH (5.05 +/- 0.05), l* started to fluctuate, and the autocorrelation curves no longer decayed to zero, indicating that at these shear rates the system behaved nonergodicly. Assuming that the convective motion and the Brownian motion are independent of each other, the mean square displacement as a result of Brownian motion was determined. From this, the sol-gel point and the radius of the aggregates at this point as a function of the shear rate was determined. The results indicated that the radius of the aggregates at the sol-gel transition decreased with increasing shear rate and suggested that shear will result in a more open structure of the network formed by the aggregates.
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PMID:Diffusing wave spectroscopy used to study the influence of shear on aggregation. 1854 85

Sodium caseinate is derived from casein which is the major milk protein and forms small star-like aggregates in aqueous solution. The dynamic mechanical properties of dense sodium caseinate suspensions were studied by measuring the shear viscosity and the frequency dependent loss and storage shear modulus. The viscosity is shown to increase strongly above a concentration, C(c), due to jamming of the aggregates. C(c) depends little on the pH or on the ionic strength. The repulsion between the aggregates increases with decreasing temperature leading to jamming at lower concentrations. As a consequence the viscosity decreases strongly with increasing temperature for concentrated suspensions. The frequency dependent shear modulus of concentrated suspensions shows a solid like behaviour at high frequencies. Shear thinning is observed at Peclet numbers larger than unity.
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PMID:Structure and dynamical mechanical properties of suspensions of sodium caseinate. 1867 76


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