Static adsorption surface excess

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. 

As an example of a membrane model, phospholipid monolayers with negative charge of different density were used. It had already been found ( ) and discussed O) that the physical and biological behavior of phospholipid monolayers at air-water interfaces and of suspensions of liposomes are comparable if the monolayer is in a condensed state. Two complementary methods of surface measurements (using radioactivity and electrochemical measurements), were used to investigate the adsorption and the dynamic properties of the adsorbed prothrombin on the phospholipid monolayers. Two different interfaces, air-water and mercury-water, were examined. In this review, the behavior of prothrombin at these interfaces, in the presence of phospholipid monolayers, is presented as compared with its behavior in the absence of phospholipids. An excess of lipid of different compositions of phos-phatidylserine (PS) and phosphatidylcholine (PC) was spread over an aqueous phase so as to form a condensed monolayer, then the proteins were inject underneath the monolayer in the presence or in the absence of Ca. The adsorption occurs in situ and under static conditions. The excess of lipid ensured a fully compressed monolayer in equilibrium with the collapsed excess lipid layers. The contribution of this excess of lipid to protein adsorption was negligible and there was no effect at all on the electrode measurements. 

The adsorption-desorption energies, AG, were calculated by means of and AG =-RTlnCk /k ). They are listed in Table 1. The obtained values, however, cannot be referred to the literature ones by the static methods, since the surface excess near the CMC increases appreciably with c. Then, the effective adsorption-desorption energy near the CMC was computed by means of Szyszkowski s equation it is listed in Table 1. The values of AG obtained are in good agreement with the calculated ones. This also suggests that the proposed mechanism is reasonable. 

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... 

In prefilled syringes, silicone oil is available in two forms with which a protein can interact surface bound and free. Surface bound silicone oil provides a static interface with water in a device. Free sificone oil is present because of the application of excess sificone oil, poor coating process, or product mishandling [102], which may leach into the bulk. The leached sificone oil results in an increase in the interfacial area available for protein adsorption and it also presents a problem from a regulatory perspective because of enhanced particulate load in the drug solution. 

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