Role of Thickeners

As mentioned above, thickeners reduce creaming or sedimentation by increasing the residual viscosity //(o), which must be measured at stresses compared to those exerted by the droplets or particles (mostly less than 0.1 Pa). At such low stresses, / (o) increases very rapidly with increase in thickener concentration  

It can be seen that the limiting residual viscosity increases rapidly with increase in EHEC concentration. A plot of sedimentation rate for 1.55 pm PS latex particles versus rj o) is shown in Eigure 21.7 which shows an excellent correlation [2], in which case a value of rj o) 10 Pa-s is sufficient for reducing the rate of sedimentation to 0. 

For the above purpose, some model emulsions were prepared using mixtures of oils and commercial surfactants. The oil phase of the emulsion consisted of 10 

Two emulsifier systems were used for the preparation of O/W emulsions. The first emulsifier was Synperonic PEE 127, an A-B-A block copolymer of poly(ethylene oxide), PEO (the A chains, were about 100 EO units each) and propylene oxide PPO (the B chain was about 55 PO units), supplied by UNIQEMA. The second emulsifier system was Arlatone V-100 (supplied by UNIQEMA), a nonionic emulsifier system composed of a blend of Steareth-100 (stearyl alcohol with 100 EO units), Steareth-2 (stearyl alcohol with 2 EO units), glyceryl stearate citrate, sucrose, and a mixture of two polysaccharides, namely mannan and xanthan gum (Keltrol F, supplied by Kelco). In some emulsions, xanthan gum was used as a thickener. AH emulsions contained a preservative (Nipaguard BPX). 

The rate of creaming and cream volume was measured using graduated cylinders. The creaming rate was assessed by comparing the cream volume with that of the maximum value obtained when the emulsion was stored at 55 C. The time tj j taken to reach a value of V /V = 0.3 (i.e., 30% of the maximum rate) was calculated [4]. 

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We now consider the role of lamellar thickening on the relation between Tc and Tm- At Tc, the initial thickness of the virgin lamella is given by Eq. (1.32) as... 

A.C. Newby, Dual role of matrix metalloproteinases (matrixins) in intimal thickening and atherosclerotic plaque rupture. Physiol. Rev. 85 (2005) 1-31. 

Currie BS, Rowley DB, Tabor NJ (2005) Middle Miocene paleoaltimetry of southern Tibet Implications for the role of mantle thickening and delamination in the Himalayan orogen. Geology 33 181-184 Cyr A, Currie BS, Rowley DB (2005) Geochemical and stable isotopic evaluation of Fenghuoshan Group lacustrine carbonates, north-central Tibet Implications for the paleoaltimetry of Late Eocene Tibetan Plateau. J Geol 113 517-533... 

Results from in vitro experiments, catalytic properties, and tissue localization are all compatible with the role of SCCE in the degradation of intercellular cohesive structures in the stratum corneum as part of the events leading to remodeling of the tissue and eventually to desquamation. Increased expression of SCCE in the epidermis of transgenic mice leads to impaired barrier function with increased transepidermal water loss. The transgenic animals have a thickened epidermis and a marked hyperkeratosis, possibly reflecting compensatory reactions.47-48 There are also other proteases... 

The level of oxidative protein modifications may indicate oxidative stress in normal and pathological conditions. Increased content of carbonyl groups was found in diffusely thickened intima (neointima) of arterial walls in arteriosclerotic tissues (M19). Comparison of oxidatively modified amino acids content in normal intima and in human carotid plaque samples revealed an increased content of 3-chlorotyrosine, DOPA, o-tyrosine, m-tyrosine, hydroxyleucine, hydroxyva-line, and especially, dityrosine (F17, H13). These plaques are indicative of the role of protein oxidative damage in the formation of atherosclerotic plaques. Postmortem studies revealed that the content of dityrosine is increased in the stage of advanced lesions. However, the o-tyrosine and m-tyrosine are not elevated in plaque proteins (H13, LI 1). The question of 3-nitrotyrosine level in atherosclerotic plaques remains unresolved, the reported data being contradictory (E6, L10, M24). 

Azam, F. (1998). Microbial control of oceanic carbon flux The plot thickens. Science 280, 694. Azam, F., Fenchel, T., Field, J. G., Gray, J. S., Meyer-Reil, L. A., and Thingstad, F. (1983). The ecological role of water-column microbes in the sea. Mar. Ecol. Prog. Ser. 10, 257—263. 

Role of Particles in Shear-Thickening Non-Food Dispersions... 

DeYoreo J. J., Lux D. R., and Guidotti C. V. (1989) The role of crustal anatexis and magma migration in the in the thermal evolution of regions of thickened crust. In Evolution of Metamorphic Belts, Special Publications 43 (eds. J. S. Daly, R. A. Cliff, and B. W. D. Yardley). Geological Society of London, London, England, pp. 187 -202. 

At present there are a number of competing lines of evidence in support of the TTG being formed by remelting at the base of thickened crust, and in the subducted slab. Support for the subduction model is reviewed by Martin (1995), whereas evidence for the role of... 

These are high-molecular-weight polymers, either natural or synthetic, such as xanthan gum, hydroxyethyl cellulose, alginates, and carrageenans. In order to understand the role of these thickeners, the gravitational stresses exerted during creaming or sedimentation should be considered ... 

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