Adsorption static bulk

Static Bulk Adsorption versus Dynamic Core Flood... 

There are large differences between the level of static adsorption of HPAM and dynamically retained level in a core or pack (Lakatos et al., 1979). These differences are the result of changes in the specific surface area of consolidated and unconsolidated packs and also the accessibility of certain portions of the pore space. These differences also depend on the extent of mechaifical retention that is present in the dynamic core flood experiment. Polymer retention in consolidated porous media cannot be determined with static bulk adsorption (batch adsorption techniques) because the process of disaggregation to obtain... 

Data from Szabo (1979) in Table 5.10 show that the adsorption of silica flour (measured in static bulk adsorption) is 55 J,g/g, which is higher than that (3.3 (ig/g) of sand pack (dynamic flow test) because the surface area in the silica flour is higher than that in the sand pack. When the adsorption is defined in g/m, which takes into account the surface area, the adsorption data from the two types of measurements are almost the same (28 (ig/m versus 27 iig/rn ). 

The relationship between film thickness of hexadecane with the addition of cholesteryl LCs and rolling speed under different pressures is shown in Fig. 25 [50], where the straight line is the theoretic film thickness calculated from the Hamrock-Dowson formula based on the bulk viscosity under the pressure of 0.174 GPa. It can be seen that for all lubricants, when speed is high, it is in the EHL regime and a speed index 4> about 0.67 is produced. When the rolling speed decreases and the film thickness falls to about 30 nm, the static adsorption film and ordered fluid film cannot be negligible, and the gradient reduces to less than 0.67 and the transition from EHL to TFL occurs. For pure hexadecane, due to the weak interaction between hexadecane molecules and metal surfaces, the static and ordered films are very thin. EHL... 

The choice between the static methods (Wilhelmy plate method and the du Noiiy ring method) should primarily be based on the properties of the system being studied, in particular, the surfactant. As mentioned in UNITD3.5, the transport of surfactant molecules from the bulk to the surface requires a finite amount of time. Since static interfacial tension measurements do not yield information about the true age of the interface, it is conceivable that the measured interfacial tension values may not correspond to equilibrium interfacial tension values (i.e., the exchange of molecules between the bulk and the interface has not yet reached full equilibrium and the interfacial tension values are therefore not static). If the surfactant used in the experiment adsorbs within a few seconds, which is the case for small-molecule surfactants, then both the Wilhelmy plate method and the du Noiiy ring method are adequate. If the adsorption of a surfactant requires more time to reach full equilibrium, then the measurement should not be conducted until the interfacial tension values have stabilized. Since interfacial tension values are continuously displayed with... 

The time required to conduct an interfacial tension experiment depends largely on the properties of the surfactants and less on the chosen measurement method. A notable exception is the drop volume technique, which, due to the measurement principle, requires substantial ly more time than the drop shape analysis method. Regardless of the method used, 1 day or more may be required to accurately determine, e.g., the adsorption isotherm (unit D3.s) of a protein. This is because, at low protein concentrations, it can take several hours to reach full equilibrium between proteins in the bulk phase and those at the surface due to structural rearrangement processes. This is especially important for static interfacial tension measurements (see Basic Protocol 1 and Alternate Protocols 1 and 2). If the interfacial tension is measured before the exchange of molecules... 

In a liquid binary solution, this accumulation is accompanied by the corresponding displacement of another component (solvent) from the surface region into the bulk solution. At equilibrium a certain amount of the solute will be accumulated on the surface in excess of its equilibrium concentration in the bulk solution, as shown in Figure 2-6. Excess adsorption E of a component in binary mixture is defined from a comparison of two static systems with the same liquid volume Vo and adsorbent surface area S. In the first system the adsorbent surface considered to be inert (does not exert any surface forces in the solution) and the total amount of analyte (component 2) will be no = VoCo. In the second system the adsorbent surface is active and component 2 is preferentially adsorbed thus its amount in the bulk solution is decreased. The analyte equilibrium concentration Ce can only be measured in the bulk solution, so the amount VoCe is thereby smaller than the original quantity no due to its accumulation on the surface, but it also includes the portion of the analyte in the close proximity of the surface (the portion U Ce, as shown in Figure 2-6 note that we did not define V yet and we do not need to define... 

The laboratory unit used to define polymer retention, Cp, is in mass of polymer per unit mass of solid, usually in micrograms per gram of rock (itg/g). Sometimes (e.g., in UTCHEM), the unit is in grams per 100 milliliter (cm ) of pore volume (PV), g/100 mL PV, which is equivalent to weight percent (wt.%) if the solvent (water) density is 1 g/mL and the pore volume is filled up by the solvent (water) only. In bulk static adsorption, a more fundamental measure of adsorption is the mass of polymer per unit surface area of solid, which is referred to as the surface excess, Cps, usually in milligrams or micrograms per square meter (mg/m or (tg/m ). Sometimes, in field applications, the retention unit is in mass of polymer per unit volume of rock, usually in lb/ acre-foot. 

For instance, what model should be assumed for the atomic structure of a surface The simplest picture of a surface is a planar terrace, a static array of passive adsorption sites. For a crystal, such terraces are slices through the bulk stacking sequence, a cleavage of the bulk. Is the planar terrace a reasonable model Some unrelaxed bulk terminations are polar and thus inherently unstable (see below). But for non-polar surfaces, planarity is often favoured in order to minimise the surface energy (Section 3). Thus on the timescales of diffraction techniques, such as LEED and XAFS, many surfaces are indeed observed to be... 

The low rate at which equilibrium between the adsorption layer and the bulk is established is typical for high molecular weight surface active substances for which the surface tension gradually decreases with time. The measurement of the surface tension by static and semi-static methods (see Chapter I, 4) as a function of time during the formation of adsorption layers allows one to retrieve information on the kinetics of adsorption phenomena [11,12]. 

The interfacial tension may be determined to within about 1% accuracy with the spinning-drop method (127, 128). It is an absolute and static method that requires only small samples and, in contrast to most other methods, does not depend on the wettability of a probe, such as a ring or Wilhelmy plate. The stabilizing surfactant is commonly used at concentrations in the bulk continuous phase that are far above the critical micelle concentration (erne). This ensures that the concentration remains above the erne after adsorption on to the vastly extended interface has taken place, which is clearly needed to maintain emulsion stability. It is tempting, therefore, to assume that the interfacial tension in the finished emulsion equals that between the unemulsified bulk phases and that it remains constant when a mother emulsion is diluted with continuous phase in order to create a series of emulsions in which only O is varied (67). This may be a reasonable assumption when a pure surfactant is used, but there is evidence that this may not be so when impure commercial surfactants or surfactant mix-... 

The surface tension of surfactant solutions is the easiest accessible experimental quantity and hence the most frequently used method to study the adsorption process at liquid interfaces. As earlier shown the rate of adsorption is a function of surface activity and bulk concentration. This explains why a broad time interval has to be experimentally covered to study the large variety of surfactants. A single method cannot provide a sufficiently broad interval so that different complementary methods are needed. Some methods are particularly developed for the short adsorption times, such as the bubble pressure method providing data from less than 1 ms up to some minutes. On the contrary, so-called static methods like the Wilhelmy plate or drop and bubble shape methods give access to very large times, starting from few seconds and reaching up to hours and even days. Both techniques complement each other perfectly. 

Methods of evaluating such conditioned keratin (in particular, hair) are discussed in Chapter 12. While mechanisms are not fully understood, a very broad expectation might be that Iriction and static electrification would be influenced by surface adsorption, strength and bending modulus by bulk sorption, and abrasion resistance by both of the foregoing. 

The surface properties of supported Pt particles were examined by gas adsorption and X-ray photoelectron spectroscopy (XPS) with Shimadzu ESCA-750. The uptake of Hj and CO was measur by a static volumetric method at 292 K and an equilibrium pressure of about 25 kPa. In XPS, the catalysts were exposed to air on the introduction into the system, and the spectra for Pt and other species were collected after Ar sputtering. Tlie bulk structure of the particles was examined by extended X-ray absorption fine structure (EXAFS). Pt L -edge EXAFS spectra were measured at room temperature at the BL-lOB station of Photon Factory in the National Laboratory for High Energy Physics (Proposal No.93G147). In addition, the supported Pt was extracted by immersing the catalysts in a mixed acid of HCl and HNO3 at room temperature for 24 h and the amounts of Pt extracted were measured by AAS. 

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