Search results for " thinning"
showing 10 items of 32 documents
Shear-thinning fluids for gravity and anisotropy mitigation during soil remediation in the vadose zone
2018
Abstract Surfactant foam has been proposed as an effective treatment fluid for in situ environmental remediation of soils. In the vadose zone, it could improve treatment homogeneity, but its use remains challenging. To better understand and predict foam formation and propagation in vadose zone, we studied them in 24 soils with wide range of properties (including permeability: 2 10−12 to 3.3 10−9 m2). Foam rheology showed to be complex and mostly influenced by soil permeability and grading. Below 2 10−11 m2, foam propagation velocity was not influenced by permeability. Conversely, slight shear thinning to Newtonian behavior was observed for higher permeabilities. Benefits for remediation in …
Rheological and Flocculation Analysis of Microfibrillated Cellulose Suspension Using Optical Coherence Tomography
2018
A sub-micron resolution optical coherence tomography device was used together with a pipe rheometer to analyze the rheology and flocculation dynamics of a 0.5% microfibrillated cellulose (MFC) suspension. The bulk behavior of the MFC suspension showed typical shear thinning (power-law) behavior. This was reflected in a monotonously decreasing floc size when the shear stress exceeded the yield stress of the suspension. The quantitative viscous behavior of the MFC suspension changed abruptly at the wall shear stress of 10 Pa, which was reflected in a simultaneous abrupt drop of the floc size. The flocs were strongly elongated with low shear stresses. With the highest shear stresses, the flocs…
Interrelation between the thermodynamic and viscometric behaviour of aqueous solutions of hydrophobically modified ethyl hydroxyethyl cellulose
2000
Abstract Aqueous solutions of a commercial sample of hydrophobically modified ethyl hydroxyethyl cellulose (HC, Mw=100 kg/mol, nonylphenol substitution ca. 1.7 mol%) were studied with respect to their demixing behaviour and flow characteristics. Phase separation temperatures were measured turbidimetrically and by determining the first discernible macroscopic phase separation. In some cases demixing was also monitored viscometrically. Phase volume ratios yielded a critical polymer concentration of 1.87 wt.% HC (displaced considerably out of the minimum of the demixing curve towards higher polymer concentrations) and a lower critical solution temperature of 47°C. Model calculations of the spi…
Retinal and choroidal vasculature changes associated with chronic kidney disease
2018
Retinal and choroidal microvascular changes can be related to renal impairment in hypertension and chronic kidney disease (CKD). The study examines the association between retinochoroidal parameters and renal impairment in hypertensive, non-diabetic patients. This is a cross-sectional study on Caucasian patients with systemic arterial hypertension with different levels of renal function. All subjects were studied by blood chemistry, urine examination, microalbuminuria and blood pressure. Complete eye examination was completed with swept source optical coherence tomography (SS-OCT) and optical coherence tomography angiography (OCTA) scans of macular region. Patients were divided in groups: L…
Thixotropic Behavior of Salad Dressings Stabilized with Modified Starch, Pectin, and Gellan Gum. Influence of Temperature
2008
The thixotropy of low‐oil salad dressing has been analyzed at different temperatures (8–26°C). The usual formulation containing modified starch (4%) was compared with others in which part of the starch had been substituted by pectin (0.5%) or different concentrations of gellan (0.1 and 0.5%). Up and down flow curves were measured, showing in all cases shear thinning behavior and fitting the Herschel‐Bulkley model. Thixotropic areas enclosed by the up curve and the corresponding different down curves, STh, were obtained. With the aim of establishing comparative results, and since the viscosities were quite different, the parameter considered was relative thixotropic area, SR (%)=100 (STh/Sup…
1983
The viscosity of solutions of poly(decyl methacrylate)s, PDMA, in 1-pentanol (thermodynamically poor solvent) and in toluence or isooctane (good solvents) was measured up to shear rates of 3 · 104s−1 by means of rotational viscosimeters. The observed pronounced shear thinning is for all solutions well described by the theory of Graessley, with the extension, introduced by Ito. Two parameters, resulting from the evaluation of the flow curves on the basis of the above theory, are discussed: τ0, a characteristic relaxation time of the polymer chain, is found to be in the range of ms. ηfric, a frictional parameter, independent of shear rate, amounts upto 50% of the zero-shear viscosity for the …
Cellulose ether emulsions as fat source in cocoa creams: Thermorheological properties (flow and viscoelasticity)
2019
Flow behaviour and viscoelastic properties at three different temperatures (20, 45 and 70 °C) of cocoa filling creams have been studied. These creams were composed of cocoa, starch, sugar, skimmed milk powder and non-digestible cellulose ether emulsions as fat source. Two types of methylcelluloses, MC, and two types of hydroxypropyl methylcelluloses, HPMC, with different chemical substitution degrees were employed. Results showed important differences in zero shear viscosity and shear thinning character at room temperature, due to the different internal structure revealed by the viscoelastic moduli spectra. Temperature sweeps of storage modulus showed different temperature gelation dependin…
Effetti dei diradamenti sulle caratteristiche ecologiche e selvicolturali dei rimboschimenti di pino d’Aleppo nei Monti Sicani (Sicilia occidentale)
2014
I rimboschimenti di conifere mediterranee sono, in Sicilia, una delle tipologie forestali più rappresentative, sia per la superficie che occupano sia per l’eterogeneità ambientale dei contesti territoriali dove sono stati realizzati. Scopo principale della presente indagine è stato quello di effettuare una valutazione degli impatti dei diradamenti sulle caratteristiche ecologiche e selvicolturali dei rimboschimenti di pino d’Aleppo. L’indagine è stata condotta in tre differenti siti localizzati nell’area dei Monti Sicani caratterizzati dalla stessa tipologia forestale (Pineta a pino d’Aleppo) e da simili caratteristiche stazionali. Inoltre, tutti e tre i siti sono stati interessati da inter…
RHEOLOGICAL BEHAVIOUR OF MICROCRYSTALLINE CELLULOSE HYDROGELS
1992
ABSTRACT An extensive study was made of the rheological behaviour of microcrystal1ine cellulose-sodium carboxymethyl cellulose (MCC-NaCMC) gels at six different concentrations. The effect of agitation time, storage time, shear rate and temperature on the viscosity of these thixotropic gels was analysed, over 7200 resulting values of being available to this effect The pseudoplastic and thixotropic characteristics of the gels was established and a progressive decrease in gel viscosity with increasing storage time was observed, although retaining stability. On the other hand, constant agitation for five minutes was found to reduce gel viscosity by 40 to 50%, regardless of concentration.