Surface pressure measurements

A static bottom hole pressure survey (SBHP) is useful for determining the reservoir pressure near the well, undisturbed by the effects of production. This often cannot be achieved by simply correcting a surface pressure measurement, because the tubing contents may be unknown, or the tubing contains a compressible fluid whose density varies with pressure (which itself has an unknown profile). 

Langmuir-Blodgett was the first technique to provide a practical route for the constmction of ordered molecular assembhes. These monolayers, which provide design dexibiUty both at the individual molecular and at the material levels, are prepared at the water—air interface using a hiUy computerized trough (Fig. 1). Detailed discussions of troughs (4) and of surface pressure, 7T, and methods of surface pressure measurements are available (3,6). 

FIG. 17 Schematic illustration of the setup for a tip-dip experiment. First glycerol dialkyl nonitol tetraether lipid (GDNT) monolayers are compressed to the desired surface pressure (measured by a Wilhehny plate system). Subsequently a small patch of the monolayer is clamped by a glass micropipette and the S-layer protein is recrystallized. The lower picture shows the S-layer/GDNT membrane on the tip of the glass micropipette in more detail. The basic circuit for measurement of the electric features of the membrane and the current mediated by a hypothetical ion carrier is shown in the upper part of the schematic drawing. 

The surface pressure-area (tc-A) isotherm measurements and LB film transfer were performed with the use of a KSV 5000 minitrough (KSV Instrument Co., Finland) operated at a continuous speed for two barriers of 10 cm2/min at 20°C. The buffer used in the present work was composed of 10 mM MES, 2 mM ascorbic acid sodium salt, and a given concentration of salt or polymers (pH =7.0). The accuracy of the surface pressure measurement was 0.01 mN/m. Monolayers of the PS I were transferred at 10 mN/m on hydrophobic substrate surface by horizontal lifting method. 

Stine KJ et al (2006) Interaction of the glycoalkaloid tomatine with DMPC and sterol mono-layers studied by surface pressure measurements and brewster angle microscopy. J Physical Chem B 110 22220... 

The molecules will have an average kinetic energy, that is, 1/2 kB T, for each degree of freedom, where k is the Boltzmann constant (=1.372 10 16 erg/T), and T is the temperature. The surface pressure measured would thus be equal to the collisions... 

The water for the substrate was distilled from a Stokes still and foamed in a 600-ml. medium porosity sintered glass funnel the foam was removed several times by sweeping the surface. The water gave adequately stable base line readings for both the surface potential and surface pressure measurements. 

The following surface pressure measurements were obtained for a film of haemoglobin spread on 0.01 mol dm-3 HC1 (aq.) at 25°C ... 

The interfacial properties of HM - PNIPAM, including the formation and the compression - expansion reversibility of the monolayers, at different subphase temperatures were more recently studied by using the Langmuir film balance technique [90], The stability and dynamic nature of the HM - PNIPAM monolayers were also further studied by the time - dependent surface pressure measurements. All results have suggested a compression - promoted temperature - and rate - dependent conformational rearrangement of the polymer on the water surface. Increasing the level of hydrophobic modifications progressively improved the monolayer compressibility and stability, and reduced the hysteresis. 

Exact experimental methods. Surface-pressure measurements. Nearly all the methods in use at present are modifications of Langmuir s method, of directly measuring the outward force exerted on a light floating barrier which divides the film-covered surface from a clean surface and for the manipulation of the films, and adjustment of the area available for them, modifications of Pockels s barriers are almost always used. Ths essential points requiring attention for accuracy are as follows ... 

In Langmuir s original instrument, and Adam s first modification of it, leakage of the film past the ends of the float was prevented by leaving narrow gaps, closed by jets of air. These are effective if carefully adjusted, but disturb the float slightly so that delicate surface-pressure measurements are not possible. 

The spectra clearly show that the adsorption of charged surfactants at the CCLj/H20 interface at nanomolar aqueous phase surfactant concentrations results in a significant modification of the interfacial water behaviour. Wilhelmy balance surface pressure measurements [89] show that at these concentrations (headgroup areas of >4000 molecule ), the water molecules responsible for the observed spectral... 

A mixed monolayer consisting of stearic acid (9.9%), palmitic acid (36.8%), myristic acid (3.8%), oleic acid (33.1%), linoleic acid (12.5%), and palmitoleic acid (3.6%) produces an expanded area/pressure isotherm on which Azone has no apparent effect in terms of either expansion or compressibility (Schuckler and Lee, 1991). Squeeze-out of Azone from such films was not reported, but the surface pressures measured were not high enough for this to occur. The addition of cholesterol (to produce a 50 50 mixture) to this type of fatty acid monolayer results in a reduction of compressibility. However, the addition of ceramide has a much smaller condensing effect on the combined fatty acids (ratio 55 45), and the combination of all three components (free fatty acids/cholesterol/ceramide, 31 31 38) produces a liquid condensed film of moderate compressibility. The condensed nature of this film therefore results primarily from the presence of the membrane-stiffening cholesterol. In the presence of only small quantities of Azone (X = 0.025), the mixed film becomes liquid expanded in nature, and there is also evidence of Azone squeeze-out at approximately 32 mN m. ... 

The viscosity of the solutions was measured using the Cannon-Fenske viscometer. The foam tests were done by the conventional cylinder shake test In which a fixed amount of the solution Is shaken vigorously for a minute and the foam height Is monitored with time. The surface pressure measurements were carried out using a conventional Langmuir trough set-up, again with a platinum plate sensor. See text for further details. 

Abrahamson et at (34) observed a similar departure from the latter sequence of calcium and magnesium in their reaction with a phosphatidic acid dispersion at pH 7. Shah and Schulman (35) also found a higher tendency of Ca2+ than Mg2+ to interact with a monolayer of dicetyl phosphate at pH 5.6 as judged by surface pressure measurements although surface potential measurements indicated little difference between the two ions as did potential measurements on phosphatidyl serine mem-... 

Chemical Activities by the Surface Vapor Pressure Method. Surface pressure measurements in the transition region between the condensed and gaseous monolayer states of a single lipid component spread as a monolayer on water yield a value of ir which is independent of the surface area. This value—the surface vapor pressure, irv—is analogous to the vapor pressure of a liquid in equilibrium with its vapor. When a second lipid component is in the surface, the limits of miscibility in the condensed phase may be determined on the basis of the surface vapor pressure dependence on the mole fraction in the condensed phase (8). 

Monolayer studies were done on a polyester resin-impregnated fiber glass Langmuir trough, 15.1 X 85 cm and 5 mm deep, coated with paraffin. This arrangement was mounted on a lathe bed equipped with a variable speed motor with a tachometer feedback control which drove the Teflon sweeps at 0.65 cm/min, 1%. Surface pressure measurements were made with a platinum Wilhelmy plate coupled to a Cahn RG Electro-... 

To compensate for any additivity effects of the surfactants and gliadin we spread surfactant solutions, in the amounts used in the experiments, on the film balance. No significant surface pressure was observed over the entire compression range, indicating that the surfactants did not contribute directly to the surface pressure measurements. 

The compression or decompression of bovine serum albumin monolayers spread on an aqueous substrate at a pH near the isoelectric point can effect surface tension. The surface pressure changes depend on the distance between the position of the surface pressure measuring device and the compression barrier. This effect is minimal at a pH above or below the isoelectric point and undetected for small molecules (myristic acid and eicosyl sodium sulfate) even when the substrate contains substituted alkyl amines. A theory is proposed which attributes the above observation to surface drag viscosity or the dragging of a substantial amount of substrate with the BSA monolayer. This assertion has been experimentally confirmed by measuring the amount of water dragged per monolayer using the technique of surface distillation. 

Figure 2. Effect of pH on surface pressure measured at various distances from the compression barrier. Measurements taken after compressing at 1.96 X 10 2 cm/sec for 60 sec. Initial pressure 5 dynes/cm.

Nevertheless, no matter how one interprets the theory, the implications of this experiment are far more important and should be understood and used for future work on macromolecular monolayer systems. We urge the use of an additional variable—the distance that the surface pressure measuring device is from the point of perturbation this must be included in future work to ensure accuracy and reproducibility of mono-layer studies. 

The water was distilled twice from glass (initially from alkaline permanganate). It was subsequently twice distilled from quartz. Surface areas at most pressures were reproducible within 0.5 A2/molecule however, at low pressures, for gaseous isotherms, the error was somewhat greater. Surface potentials were also obtained but are not reported here. Surface potential values, however, confirm observations made with surface pressure measurements (8). 

Surface pressure, measured by an apparatus already described (8, 9, 10), was 0.05 dyne/cm the surface area was 0.02 m2/mg. All isotherms were constructed by points after each area reached a constant surface pressure to guarantee that surface equilibrium was attained. All isotherms were obtained at various surface concentrations to ensure repro-... 

Surface pressure measurements conducted in Langmuir film balance showed that at a constant area per molecule the attachment of... 

It was confirmed that Ca increases the adsorption, but it was found that even in the absence of Ca , prothrombin interacts with phospholipids. Consequently, besides the electrostatic interactions, some Ca - independent interactions, which might be hydrophobic, are also involved. The observation that prothrombin and some of its fragments penetrated the layer is in accordance with this idea. This implies that fragments other than Fragment 1 might be involved in the interaction. It must be noticed, that penetration could not be obtained by the less sensitive technique of surface pressure measurements ( ). 

Abstract The miscibility of two phospholipids dipalmitoyl-phosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) possessing both a choline head group, with per-(6-dodecanoylamino-6-deoxy) j8-cyclodextrin (CnCONH-/ -CD) and poly(ethylene oxide)-bearing lipid (PEO-lipid), respectively, has been assessed by surface pressure measurements of binary monolayers under dynamic conditions. Although the four studied amphiphiles had similar hydrophobic moieties constituted of hydrocarbon units with the number of carbons ranging from 12 to 16, PEO-lipid markedly differed from other amphiphiles due to its bulky poly(ethylene oxide) chain containing 13 ethylene oxide units totally immersed in the aqueous subphase. The additivity rule applied to these binary mixtures clearly showed that molecular areas for both systems deviated from linearity. For... 

Figure 5.6 shows surface excess data for the adsorption of pentaerythritol obtained from surface pressure measurements by the application of Equation... 

Surface pressure measurements at the air-water interface showed that the lipid molecules begin to associate at low monoglyceride monomer concentration (typically 10 mol dm for mono-olein), forming a cubic structure. Monoglycerides of saturated fatty acids associate to form lamellar liquid crystalline phases at low concentrations. These condensed layers form at the oil-water interface at and above the critical temperature which is the temperature used for emulsification. These liquid crystalline phases play a major role in emulsion stabilisation (see Chapter 6). As discussed before, lamellar liquid crystalline phases form at the O/W interface, providing a barrier against coalescence. These multilayers signifi-... 

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