Membrane texture

Luscher, C., Sehluter, O., Knorr, D. (2005). High pressure-low temperature processing of foods Impaet on cell membranes, texture, color and visual appearance of potato tissue. Inn. Food Sci. Emerg. Technol., 6, 59-71. 

Finally it should be noted that the characterisation of membranes is more demanding than most other porous materials. Firstly, the membranes separation layer is generally thin and supported, which requires a sensitive technique capable of analysing a sample in such a form. The characterisation of a powder "equivalent" to the membrane carmot in all cases be considered as representative of the membrane texture. Secondly, the structure is frequently anisotropic and moreover often microporous. Assessment of the microporosity is much less advanced compared to meso- and macro-porosity, despite emphasis given to this in the recent lUPAC symposia [6-8]. The current and widespread interest in the characterisation of microporous matericds is well illustrated by the numerous and varied publications found in these symposia proceedings. These highlight recent developments in characterisation techniques, their applications and limitations. The particular features of importance in membrane studies will be considered in the light of the characterisation techniques to be described. 

Thermoporometry is a method which measures cavity sizes and not inlet sizes. It has been mainly used for the characterisation of organic mesoporous membrane texture [70-73] but has been also applied to inorganic alumina symmetric membranes [73] with a good reliability. However the solidification of water in small pores may sometimes damage the membrane structure due to the expansion of the condensate and consequently different results can be obtained after several runs [74]. 

B) there are much larger pores (about 50 nm). SEM images of a fractured, critical point dried membrane (Fig. 5.30) show robust, macrovoid structures. The top dense surface layer is clearly composed of a monolayer of densely packed, deformed particles, about 80 nm in diameter, packed so closely as to limit surface porosity. Less well packed particles form the more open bulk membrane texture. The structure shown confirms those hypothesized from earlier TEM replica studies of wet poly(amide-hydra-zine) and dry polyimide asymmetric membranes [157,158]. 

Figure 17.2 Manifestations of superstmctural aspects of DOPC bilayers, observed by cryo-TEM on surfaces of unilamellar vesicles that were prepared in pure water [26]. Left column linear isolated membrane bends or folds. They are found as deep notches as in heart-shaped vesicles and also as extended overhangs on flat membranes. (The cushion-like contours indicate the presence of passages (overpasses) on the membrane.) The constrictions on the branched tube may be envisaged as lines of saddles. Right column two-dimensional grainy membrane textures. The graininess was observed on small vesicles as well as on planar membranes and may even coexist with smooth bilayer portions.

Various dynamic situations induced by these reactions are described in Fig. 15. Note that the severance of a D-bridge such as shown in Fig. 15, b and c is the result of competition with monovalent cations M" or anions A . Under normal physiological conditions only a few D-bridges would be broken at any one time. Transient charges would arise from this interaction, with concomitant weakening of local subunit cohesion. A large increase in local M" " concentration would lead to extensive loosening of the membrane texture (Fig. 15, f,g) with attendant increase in conductance. Low pH (M" " = H" ) would result in appreciable decrease in intersubunit cohesion (Section III, B, 2). Other situations depicted in Fig. 15 are discussed below. 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Faser-gehalti m. fiber content (Paper) fiber yield, -gewebe, n. fibrous tissue fibrous texture, -gips, m. fibrous gypsum, -haut,/. (Anat.) fibrous membrane, faserig, a. fibrous, fibery, fillamentous, stringy. 

Stevens-Johnson syndrome fever, cough, muscular aches and pains, headache, and lesions of the skin, mucous membranes, and eyes. The lesions appear as red wheals or blisters, often starting on die face, in the mo util, or on the lips, neck, and extremities, stomatitis inflammation of die mo util striae lines or bands elevated above or depressed below surrounding tissue, or differing in color or texture subjective data information supplied by the patient or family sublingual under die tongue... 

Deutsch J, Motlagh D, Russell B, and Desai TA. Fabrication of micro textured membranes for cardiac myocyte attachment and. orientation. J Biomed Mater Res, 2000, 53(3), 267-275. 

The range of whey products that are used include, for example, ultra-filtered and dried WPC, which contains between 20% and 89% protein ion exchange and membrane filtered WPI, which contains at least 90-95% protein (Tunick, 2008) and other whey fraction-enriched products such as p-lactalbumin. These enriched protein whey products can be texturized and used in the manufacture of high-protein content puffed com products (Onwulata et al, 2010). 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

Pulsed electric field is another alternative to conventional methods of extraction. PEF enhances mass transfer rates using an external electrical field, which results in an electric potential across the membranes of matrix cells that minimizes thermal degradation and changes textural properties. PEF has been considered as a nonthermal pretreatment stage used to increase the extraction efficiency, increasing also permeability throughout the cell membranes. 

This transition produces an isomorphous phase and the resulting y-alumina has the same morphology and texture as its boehmite precursor. With increasing temperature and time the mean pore diameter increases gradually and other phases appear (S-, 6-alumina). Due to the broad XRD lines, the distinction between y- and S-alumina cannot be made 6-alumina occurs at about 900°C while the conversion to the chemically very stable a-alumina phase takes place at T> 1000°C. Some typical results for alumina membranes synthesized without binders are given in Table 2.4. When PVA was used as a binder, thermogravimetric analysis showed that, provided the appropriate binder type was used, the binder could be effectively removed at T > 400°C. The ash residue is of the order of 0.01 wt.%. Mean pore size and... 

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