Monolayer surface area

Answer The conclusions are justified for dog erythrocytes but not for sheep or human erythrocytes. The table provides the total surface area of the lipid monolayer. To determine the monolayer surface area per cell, first calculate the total number of cells. For example, for dog erythrocytes, the number of cells is 8 X 106 per mm3 = 8 X 109 per cm3 (or per mb). In 40 mL, there is a total of (40 mb) (8 X 109 cells/mb) = 3 X 1011 cells. From the table, this number of cells yielded a monolayer surface area of 62 m2 = 6.2 X 10e cm2. Dividing the surface area by the number of cells gives... 

The deposition is usually monitored by the corresponding transfer ratio. During monolayer transfer, a further compression is required in order to maintain a constant surface pressure. The transfer ratio is defined as the ratio of the decrease in Langmuir monolayer surface area divided by the area of the solid support which has been coated. The user tries to adjust the experimental conditions such as the transfer speed, temperature and sub-phase composition (e.g. indifferent electrolytes) such that a transfer ratio close to one is achieved. The underlying assumption is that the Langmuir monolayer then serves as a simple building block which resembles the features of the pre-formed monolayer at the air-water interface. Repeated dipping cycles simply provide replicas of the monolayer and such monolayers thus allow the formation of stratified layer structures in the same manner as bricks are used to set up a wall in the... 

The automated pendant drop technique has been used as a film balance to study the surface tension of insoluble monolayers [75] (see Chapter IV). A motor-driven syringe allows changes in drop volume to study surface tension as a function of surface areas as in conventional film balance measurements. This approach is useful for materials available in limited quantities and it can be extended to study monolayers at liquid-liquid interfaces [76],... 

Estimate the specific surface area of the quartz powder used in Fig. X-1. Assume that a monolayer of C4H9OH is present at P/P = 0.2 and that the molecule is effectively spherical in shape. 

The central idea underlying measurements of the area of powders with high surface areas is relatively simple. Adsorb a close-packed monolayer on the surface and measure the number A of these molecules adsorbed per unit mass of the material (usually per gram). If the specific area occupied by each molecule is A then the... 

The saturation coverage during chemisorption on a clean transition-metal surface is controlled by the fonnation of a chemical bond at a specific site [5] and not necessarily by the area of the molecule. In addition, in this case, the heat of chemisorption of the first monolayer is substantially higher than for the second and subsequent layers where adsorption is via weaker van der Waals interactions. Chemisorption is often usefLil for measuring the area of a specific component of a multi-component surface, for example, the area of small metal particles adsorbed onto a high-surface-area support [6], but not for measuring the total area of the sample. Surface areas measured using this method are specific to the molecule that chemisorbs on the surface. Carbon monoxide titration is therefore often used to define the number of sites available on a supported metal catalyst. In order to measure the total surface area, adsorbates must be selected that interact relatively weakly with the substrate so that the area occupied by each adsorbent is dominated by intennolecular interactions and the area occupied by each molecule is approximately defined by van der Waals radii. This... 

Flere is the volume of gas required to saturate the monolayer, V the total volume of gas adsorbed, P the sample pressure, P the saturation vapour pressure and C a constant related to the enthalpy of adsorption. The resulting shape of the isothemi is shown plotted in figure Bl.26.6 for C = 500. A plot of P/V(P - Pq) against P/Pq should give a straight line having a slope (C - )/y C and an intercept The BET surface area is... 

The physical adsorption of gases by non-porous solids, in the vast majority of cases, gives rise to a Type II isotherm. From the Type II isotherm of a given gas on a particular solid it is possible in principle to derive a value of the monolayer capacity of the solid, which in turn can be used to calculate the specific surface of the solid. The monolayer capacity is defined as the amount of adsorbate which can be accommodated in a completely filled, single molecular layer—a monolayer—on the surface of unit mass (1 g) of the solid. It is related to the specific surface area A, the surface area of 1 g of the solid, by the simple equation... 

To obtain the monolayer capacity from the isotherm, it is necessary to interpret the (Type II) isotherm in quantitative terms. A number of theories have been advanced for this purpose from time to time, none with complete success. The best known of them, and perhaps the most useful in relation to surface area determination, is that of Brunauer, Emmett and Teller. Though based on a model which is admittedly over-simplified and open to criticism on a number of grounds, the theory leads to an expression—the BET equation —which, when applied with discrimination, has proved remarkably successful in evaluating the specific surface from a Type II isotherm. 

Surface heterogeneity is difficult to remove from crystalline inorganic substances, such as metal oxides, without causing large loss of surface areas by sintering. Thus in Fig. 2.14 in which the adsorbent was rutile (TiO ) all three adsorbates show a continuous diminution in the heat of adsorption as the surface coverage increases, but with an accelerated rate of fall as monolayer completion is approached. 

BET. This model (33) estimates the coverage corresponding to one monolayer of adsorbate and is used to measure the surface areas of soHds ... 

The external surface area of the filler can be estimated from a psd by summing the area of all of the equivalent spheres. This method does not take into account the morphology of the surface. It usually yields low results which provide Htde information on the actual area of the filler that induences physical and chemical processes in compounded systems. In practice, surface area is usually determined (5) from the measured quantity of nitrogen gas that adsorbs in a monolayer at the particle surface according to the BET theory. From this monolayer capacity value the specific surface area can be determined (6), which is an area per unit mass, usually expressed in m /g. 

Surface Area. The most important features influencing the performance of carbon blacks are aggregate size and surface area. Surface area is measured by gas- and Hquid-phase adsorption techniques, and depends on the amount of adsorbate required to form a surface monolayer. If the area occupied by a single-adsorbate molecule is known, a simple calculation will yield the surface area. A low temperature nitrogen absorption method, based on the original method of Bmnauer, Emmett, and Teller (BET) (30), has been adopted by ASTM as standard method D3037-86 (2). 

---