Entrapped water volume

Figure 2.5.10 Typical dissolution pattern in the different regions of vesicle membranes the entrapped water volume 9 may contain an ionic dye, which can be separated from dyes in the bulk water phase by gel chromatography. The headgroups 3 and 7 may consist of redox systems, e.g., quinones in different oxidation states. The aqueous and membraneous surface regions 2,8 and 4,6 may enrich polar or charged compounds. Large and flat hydrophobic molecules (e.g., porphyrins) prefer the same regions. The central region 5 is thought take up some hydrophobic steroids and carotenoids.

With longer chain derivatives, the forces of attraction increase, the curvature decreases and micelles become oblate or form hexagonal (or columnar) phases. When the zero-curvature is reached, the flat oblate micelles can fold and close spontaneously, thus entrapping a volume of water and form vesicles that may contain one or several bilayers of the amphiphile. 

Assuming an average microvesicle with an outer diameter of 50 nm, a membrane thickness of 3 nm and a concentration of 10 M lipid molecules corresponding to a 10 M vesicle solution, one obtains volumes of around 3 mL each of entrapped water and hydrophobic lipid membrane per litre of bulk water. 

The entrapping of water-soluble compounds in the small internal water volume and their release within a period of several minutes or hours is evidently a relatively simple task as was demonstrated with the preceding examples. No domain formation or perforation is necessary here. Small cations, however, were only released in under a day in the case where the membrane was perforated or contained a dissolved carrier system. Before turning to these systems, we shall firstly introduce synkinetic domains. 

Consider a hydrated macromolecule containing d, grams of solvent per gram of dry macromolecular material. The specific volume Vq (volume per gram) of the entrapped water may be considerably different from that of pure solvent, vf. If V2 is the average specific volume of the macromolecular material, then the total hydrodynamic volume of the particle, V(, is... 

Perlite is a glassy volcanic rock with water trapped in its fine pores. The rock is pulverized and then heated to ca. 1000°C, whereupon the material melts and the entrapped water evaporates bloating the molten glass to many times its initial volume. 

It is important to address the physical interpretation of the UA-model. The parameter Ad is the concentration of dissolved excess air, but because the model assumes complete dissolution, it should also reflect the concentration of entrapped air in the soil of the recharge area. Values of Ad in units of cm STP air per g of water may therefore approximately be interpreted as volume ratios of entrapped air to water. Typical values are on the order of a few times 10 cm STP g. Assuming that such excesses originate from complete dissolution of entrapped air, they indicate that entrapped air initially occupies only a few per mil of the available pore space volume. This is in contrast to the literature about air entrapment in soils (Christiansen 1944 Payer and Hillel 1986 Stonestrom and Rubin 1989 Faybishenko 1995), in which entrapped air volume ratios ranging from a few percent up to several 10s of percent in extreme cases are reported. 

The model parameters Ag and F in the CE-model have a clear physical interpretation (Aeschbach-Hertig et al. 2000, 2001). Ag given in cm STP g approximately equals the initial volume ratio between entrapped air and water, whereas F describes the reduction of the gas volume by partial dissolution and compression. Correspondingly, F can be expressed as the ratio of two parameters v and q, where v is the ratio of the entrapped gas volumes in the final (Vg) and initial state (Vg ), and q is the ratio of the dry gas pressure in the trapped gas to that in the free atmosphere (P) ... 

Provided that Ptot > P, the following inequalities hold q > 1 and 0 < v, F < 1. Note that only the combined parameter F = v/q is needed to define the excess air component, not V and q individually. The parameters q, v, and Ag are coupled by the physical requirement that the sum of the partial pressures of all gases in the trapped volume equals Ptot. Any pair of the parameters Ag, F, q, and v fully determines the amount and composition of excess air, the most intuitive choice being Ag ( air / water volume ratio) and q pressure exerted on the entrapped air). The CE-model thus allows a direct physical interpretation of the excess air component. 

Vesicles enclose water volumes between 10 and 10 nm and they can be made so large (diameters from approximately 30 to 3000 nm) or concentrated (up to 10 M lipids) that up to a few percent of the bulk water volume becomes entrapped within the vesicle membrane. Biochemists also use the name hposome (fat particle) instead of vesicle, which is not very descriptive. Aggregation numbers are usually in the order of Ifr -lO molecules per vesicle. They are long-lived, have low critical... 

Vesicles can be used to entrap water-soluble compounds, which cannot pass the membrane within the inner water volume. Inorganic salts or organic polyelectrolytes are typical examples. Protic acids pass fluid membranes within a minute or so, and membranes containing 50% of cholesterol stabilize a pH gradient of two units for about 30 minutes. Hydrophobic compounds are dissolved within the membrane. Rigid or polar, poorly water-soluble compounds are mostly localized on the outer or inner surfaces of vesicles (Fig. 2.5.10). 

Hemoglobin and many enzymes are covalent polymers with a globular shape. This shape is enforced by the tendency of hydrophobic amino acids to form a hydrophobic droplet in aqueous solutions solubilized by hydrophilic side-chains around them. The same is true for synthetic block polymers made of hydrophobic and hydrophilic segments. " Spherical biopolymers thus usually appear as micelles, with a core made of organic material. Covalency allows the construction of fully organized micelles, e.g. dendrimeric spheres, where one half has a hydrophilic, the other a hydrophobic surface. Block polymers may not only form micelles, but they may also arrange to form vesicles which entrap a water volume. Such spheres have a thick polymer wall." Both the polymer micelles and vesicles can be removed from solution without collapsing. 

The amount of entrapped water was also estimated from volume considerations [9]. We find that either prolate or oblate ellipsoid give reasonable hydration values, (5=1-2 (3-7moles H20/mole ethylene-oxide unit). However, it is of interest to note that the degree of hydration decreases in the case of the oblate model, which is what one would expect as the temperature increases [6, 27, 29]. These data thus indicate that by both methods the oblate elliposid is the most reasonable shape for these micelles at a range of temperature. 

Incidentally, the water in the bucket is essential for generating the effect of theatrical smoke because the large volumes of CC>2(g) entrap minute particles of water (which forms a colloid see Chapter 10.2). This colloidal water is visible because it creates the same atmospheric condition known as fog, which is opaque. 

The recoverability of hydrocarbon from the subsurface refers to the amount of mobile hydrocarbon available. Hydrocarbon that is retained in the unsaturated zone is not typically recoverable by conventional means. Additional amounts of hydrocarbon that are unrecoverable by conventional methods include the immobile hydrocarbons associated with the water table capillary zone. Residual hydrocarbon is pellicular or insular, and is retained in the aquifer matrix. With respect to recoverability, residual hydrocarbon entrapment can result in volume estimate discrepancies as well as decreases in recovery efficiency. With increasing water saturation, such as when the water table rises via recharge or product removal, hydrocarbons essentially become occluded by a continuous water phase. This results in a reduction of LNAPL and product thickness as measured in the well at constant volume. When water saturation is decreased by lowering the water table (as during recovery operations), trapped hydrocarbons can remobilize, leading to increased recoverability. 

Dissolve dyes, if used, in 5 mL purified water and add to syrup with mixing. Adjust to pH 4.25 (range 4.0 to 4.5), if necessary, with hydrochloric acid or sodium hydroxide, q.s. to 1 L with purified water and and mix well. Allow product to stand overnight to let entrapped air escape. Readjust volume to 1 L. Add and mix 1.32 g of filter aid hyflo to the product. Circulate through a press until sparkling clear. 

Mix for 1 hour. Allow to stand overnight to eliminate entrapped C02 gas. Readjust volume to 1L with purified water. Mix for 1 hour. Filter by adding hyflo filter aid and mixing it, followed by passing through filter press. Do not allow temperature to exceed 30°C. Bubble C02 gas into clear filterate for 5 minutes. Then seal tank and hold product under C02 protection. 

Plating bath viscosity can be lowered by raising the solution s temperature. This will result in reduced process solution volumes entrapped on the workpiece, and thus, less dragout. Raising the bath temperature of a water-like solution from 100° to 140°F results in a viscosity reduction of 30%. Figure 8-3 illustrates that the drag-out reduction from this temperature increment is about 17% (Meltzer 1989). 

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