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Query: UMLS:C0851184 (thinning)
 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Constant shear and shear dependent viscosity measurements are reported in aqueous systems of co- and terpolymers of acrylamide (AM), N-n-alkylacrylamide (C10, C12, and C14 alkyl groups), and acrylic acid (AA) with added anionic surfactant sodium dodecyl sulfate (SDS). The results are presented as three-dimensional plots of viscosity vs surfactant concentration and pH at constant shear rate or viscosity vs shear rate and surfactant concentration at constant pH. For terpolymers incorporating AA, a strong viscosity maximum is observed at intermediate pH values (pH 4-6) where the AA groups are partially ionized and at SDS concentrations close to the critical micelle concentration. At high pH, all AA incorporating terpolymer solutions with SDS are strongly shear thinning, but at pH 3-4 the systems of terpolymers with SDS are strongly shear thickening at low shear, followed by a shear-thinning region at high shear. These results are explained in terms of surfactant-mediated network formation with polymer coil expansion and hydrogen bonding between partially ionized AA groups as additional factors.
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PMID:Rheology of hydrophobically modified polyacrylamide-co-poly(acrylic acid) on addition of surfactant and variation of solution pH. 1598 42

Brief ischemia was reported to protect retinal cells against injury induced by subsequent ischemia-reperfusion with de novo protein synthesis, and this phenomenon is known as late ischemic preconditioning. The aims of the present study were to determine whether nitric oxide synthase (NOS) was involved in the mechanism of late ischemic preconditioning in rat retina using pharmacological tools. Under anesthesia with pentobarbital sodium, male Sprague-Dawley rats were subjected to 60 min of retinal ischemia by raising intraocular pressure to 130 mm Hg. Ischemic preconditioning was achieved by applying 5 min of ischemia 24 hrs before 60 min of ischemia. Retinal sections sliced into 5 microm thick were examined 7 days after ischemia. Additional groups of rats received NG-nitro-L-arginine and NG-monomethyl-L-arginin, non-selective NO synthase inhibitors, 7-nitroindazole, a neuronal NOS inhibitor, and aminoguanidine and L-N6-(1-iminoethyl) lysine, inducible NO synthase (iNOS) inhibitors before preconditioning, and were subjected to 60 min of ischemia. In the non-preconditioned group, cell loss in the ganglion cell layer and thinning of the inner plexiform and inner nuclear layer were observed 7 days after 60 min of ischemia. Ischemic preconditioning for 5 min completely protected against the histological damage induced by 60 min of ischemia applied 24 hrs thereafter. Treatment of rats with aminoguanidine and L-N6-(1-iminoethyl) lysine, but not NG-nitro-L-arginine, NG-monomethyl-L-arginine or 7-nitroindazole, wiped off the protective effect of ischemic preconditioning. The inhibitory effect of aminoguanidine was abolished by L-arginine, but not D-arginine. The results in the present study suggest that NO synthesized by iNOS is involved in the histological protection by late ischemic preconditioning in rat retina.
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PMID:Inducible nitric oxide synthase inhibitors abolished histological protection by late ischemic preconditioning in rat retina. 1619 35

When dissolved in aqueous solutions, sodium hyaluronate substituted with low amounts of alkyl chains [amphiphilic hyaluronate (HA)] can give rise to hydrogels thanks to intermolecular reversible hydrophobic interactions, leading to a three-dimensional (3D) network. Such hydrogels possess shear-thinning properties and can thus be injected in cartilage defect to promote chondrocyte proliferation and cartilage repair. However, these hydrogels are only physically crosslinked and can progressively loose their 3D structure when they are in contact with aqueous fluids. To overcome this drawback, HA derivatives substituted with dodecyl chains were chemically crosslinked by a difunctional reagent, tetraethylene glycol ditosylate (TEG-diOTs). To preserve the shear-thinning properties of amphiphilic HA, small amounts of TEG-diOTs were used so as to obtain a low chemical crosslinking ratio. After optimization of the synthesis parameters, aqueous solutions of the HA derivatives, crosslinked both physically and chemically, were obtained, with rheological properties improved compared to the amphiphilic polymers. As the hydrogels are aimed to cartilage repair, they were sterilized by wet heating; the effect of this treatment on the polymer characteristics was analyzed by different techniques. A similar study was carried out on HA derivatives stored under conditions mimicking physiological ones.
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PMID:New physically and chemically crosslinked hyaluronate (HA)-based hydrogels for cartilage repair. 1627 Mar 49

The rheology of dense suspensions of beta-casein micelles is investigated at pH 6. For a given temperature, the viscosity increases dramatically at a critical concentration (Cc) of about 100 g/L due to jamming of the micelles. For a given concentration close to and above Cc, the viscosity of dense suspensions decreases strongly with increasing temperature because Cc increases. The suspensions show weak shear thickening followed by strong shear thinning. At lower pH, that is, closer to the isoelectric point, spontaneous gelation is observed, which is favored by lowering the temperature and addition of sodium polyphosphate. The gelation process is studied at pH 5.5 by rheology and light scattering.
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PMID:Jamming and gelation of dense beta-casein micelle suspensions. 1628 34

Experiments have been conducted to understand the mechanism by which the ultrasonic vibration at the gas liquid interface causes the atomization of liquid. For this purpose, aqueous solutions having different viscosities and liquids showing Newtonian (aqueous solution of glycerin) and non-Newtonian behavior (aqueous solution of sodium salt of carboxy methyl cellulose) were employed. It has been found that the average droplet size produced by the pseudo-plastic liquid is less than that produced by the viscous Newtonian liquid having viscosity equal to zero-shear rate viscosity of the shear thinning liquid. The droplet size was found to increase initially with an increase in the viscosity up to a certain threshold viscosity after which the droplet size was found to decrease again. Also droplet size distribution is found to be more compact (uniform sizes) with an increasing viscosity of the atomizing liquid. The presence of the cavitation and its effect on the atomization has been semi quantitatively confirmed using energy balance and by the measurement of the droplet ejection velocities and validated on the basis of the decomposition of the aqueous KI solution. A correlation has been proposed for the prediction of droplet size for aqueous Newtonian fluids and fluids showing non-Newtonian behavior based on the dimensionless numbers incorporating the operating parameters of the ultrasonic atomizer and the liquid phase physico-chemical properties.
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PMID:Ultrasonic atomization: effect of liquid phase properties. 1632 16

Stratification of a foam liquid film drawn from aqueous solutions of sodium naphthenate at relatively high concentration is likely due to a lamellar liquid crystal-like structure within the film. Film stratification, resulting in stepwise thinning, has been observed in foam films formed from systems containing either moderate to high concentrations of surfactant or in films formed from solutions containing solid particles. At moderate surfactant concentrations, film stratification is likely due to layers of ordered spherical micelles as postulated in Wasan and Nikolov's model of film stratification. At high surfactant concentrations, stepwise thinning of the films and occurrence of domains of uniform color within the film suggest a lamellar liquid crystal-like structure within the film, potentially up to hundred or more oriented layers. The LLC-like structure inside the film can occur at concentrations below the lower limit of the LLC existence as a bulk phase.
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PMID:Aqueous foam films stabilized by sodium naphthenates. 1656 15

We used molecular dynamics (MD) simulations to investigate the structures and properties of Newton black films (NBF) for several surfactants: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (C16TAB), and surfactin using film thicknesses up to 10 nm. By calculating the interface formation energy for various packing conditions on the surface pressure-area isotherm, we found that the most probable surface concentration is approximately 42 A(2)/molecule for SDS and C16TAB and approximately 170 A(2)/molecule for surfactin. We then used this most probable concentration of each surfactant to simulate NBF with various film thicknesses. From analyzing the disjoining pressure-film thickness isotherms with the density profiles and the solvation coordination number, we found that the increase of the disjoining pressure during the film thinning was coupled with the change in inner structure of the NBF (i.e., density profile and the solvation of ionic entities). In the range of film thicknesses less than approximately 30 A, the disjoining pressures for the SDS and C16TAB were found to be larger than that of the surfactin. We predicted the Gibbs elasticity (175 dyn/cm for surfactin; 109 dyn/cm for C16TAB; 38 dyn/cm for SDS) required to assess the stability of NBF against surface concentration fluctuations, and the shear modulus (6.5 GPa for the surfactin; 6.1 GPa for the C16TAB; 3.5 GPa for the SDS) and the yield stress (approximately 0.8 GPa for surfactin; approximately 0.8 GPa for C16TAB; approximately 0.4 GPa for the SDS) to assess the mechanical stability against the externally imposed mechanical perturbation.
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PMID:Structures and properties of Newton black films characterized using molecular dynamics simulations. 1661 Aug 99

The shear-thickening behavior of an equimolar semidilute aqueous solution of 40 mM/L cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 degrees C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range as well as the effect of boundary conditions and time of flow on the creation and destruction of shear-induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear-thickening behavior and the dynamics of the SIS but are not distinguished by pure rheometrical measurements. A rich-in-details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear-thickening. The fourth and fifth regimes in the flow curve were separated by a spurtlike behavior, and they clearly evidenced the existence of shear-thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. The presence of apparent slip at the wall of the rheometer provides an energy release mechanism which leads to breakage of the SIS, followed by their further reformation during the stick part of the cycles. In addition, PIV measurements allowed the detection of apparent slip at the wall, as well as mechanical failures in the bulk of the fluid, which suggests an extra contribution of the shear stress field to the SIS dynamics. Increasing the residence time of the fluid in the flow system enhanced the shear-thickening behavior. Finally, the flow kinematics is described in detail and the true flow curve is obtained, which only partially fits into the scheme of existing theoretical models for shear-thickening solutions.
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PMID:Rheometry-PIV of shear-thickening wormlike micelles. 1661 40

Identifying the mechanisms responsible for the interaction of peptides with cell membranes is critical to the design of new antimicrobial peptides and membrane transporters. We report here the results of a computational simulation of the interaction of the 13-residue peptide indolicidin with single-phase lipid bilayers of dioleoylphosphatidylcholine, distearoylphosphatidylcholine, dioleoylphosphatidylglycerol, and distearoylphosphatidylglycerol. Ensemble analysis of the membrane-bound peptide revealed that, in contrast to the extended, linear backbone structure reported for indolicidin in sodium dodecyl sulphate detergent micelles, the peptide adopts a boat-shaped conformation in both phosphatidylglycerol and phosphatidylcholine lipid bilayers, similar to that reported for dodecylphosphocholine micelles. In agreement with fluorescence and NMR experiments, simulations confirmed that the peptide localizes in the membrane interface, with the distance between phosphate headgroups of each leaflet being reduced in the presence of indolicidin. These data, along with a concomitant decrease in lipid order parameters for the upper-tail region, suggest that indolicidin binding results in membrane thinning, consistent with recent in situ atomic force microscopy studies.
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PMID:Molecular dynamics simulations of indolicidin association with model lipid bilayers. 1741 17

Under normal conditions, the cornea absorbs the majority of UVB (ultraviolet B, 280-320 nm) rays, which is very important for the protection of the inner eye against their damaging effect. Our previous studies have shown that repeated irradiation of the rabbit cornea with UVB rays for 5 days (daily dose of 1.01 J cm(- 2)) caused photokeratitis accompanied by swelling (hydration) of the corneal stroma, thinning of the corneal epithelium and decrease in antioxidants. The purpose of this study was to examine the light absorption properties of such damaged rabbit cornea. Results of both spectrophotometry of the whole corneal buttons and corneal tissue dissolved in sodium hydroxide show that because of above mentioned disturbances, UVB-irradiated cornea absorbs more light throughout the whole measurable UV-VIS spectral range than the normal cornea. Increased corneal thickness (result of hydration), changes of corneal transparency (the cornea becomes grayish) and some increase in protein content all contribute to the increased light absorption of UVB irradiated corneas. We suggest that the UVB-irradiated cornea, although damaged and nearly without antioxidants, might actually through its higher UV absorbance protect the inner eye against further damage from UVB rays.
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PMID:Light absorption properties of the rabbit cornea repeatedly irradiated with UVB rays. 1757 75


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