Langmuir’s principle

Using Langmuir s principle of independent surface action, make qualitative calculations and decide whether the polar or the nonpolar end of ethanol should be oriented toward the mercury phase at the ethanol-mercury interface. 

Surface Area and Permeability or Porosity. Gas or solute adsorption is typicaUy used to evaluate surface area (74,75), and mercury porosimetry is used, ia coajuactioa with at least oae other particle-size analysis, eg, electron microscopy, to assess permeabUity (76). Experimental techniques and theoretical models have been developed to elucidate the nature and quantity of pores (74,77). These iaclude the kinetic approach to gas adsorptioa of Bmaauer, Emmett, and TeUer (78), known as the BET method and which is based on Langmuir s adsorption model (79), the potential theory of Polanyi (25,80) for gas adsorption, the experimental aspects of solute adsorption (25,81), and the principles of mercury porosimetry, based on the Young-Duprn expression (24,25). 

Theoretical models based on first principles, such as Langmuir s adsorption model, help us understand what is happening at the catalyst surface. However, there is (still) no substitute for empirical evidence, and most of the papers published on heterogeneous catalysis include a characterization of surfaces and surface-bound species. Chemists are faced with a plethora of characterization methods, from micrometer-scale particle size measurement, all the way to angstrom-scale atomic force microscopy [77]. Some methods require UHV conditions and room temperature, while others work at 200 bar and 750 °C. Some methods use real industrial catalysts, while others require very clean single-crystal model catalysts. In this book, I will focus on four main areas classic surface characterization methods, temperature-programmed techniques, spectroscopy and microscopy, and analysis of macroscopic properties. For more details on the specific methods see the references in each section, as well as the books by Niemantsverdriet [78] and Thomas [79]. 

Physisorption arises from the van der Waals forces, and these forces also condense gas molecules into their liquid state. Thus, in principle, there is no reason to stop upon completion of a monolayer during physisorption. Indeed, the formation of multi-layers, which are basically liquid in nature, is very common in physisorption experiments. Brunauer, Emmett and Teller developed a theory in 1938 to describe physisorption, where the adsorbate thickness exceeds a monolayer, and this isotherm equation is known by the initials of the authors (B.E.T.). The original derivation of the B.E.T. equation is an extension of Langmuir s treatment of monolayer adsorption from kinetic arguments. Later, in 1946, Hill derived this equation from statistical mechanics. In the B.E.T. isotherm, it is assumed that ... 

Indeed, these surface areas could in principle be determined from the Langmuir equation, provided the interaction between the substrate and the adsorbed molecules was considerably stronger than the interaction between the adsorbed molecules themselves. If one kept the pressure well below the vapor pressure, then Langmuir s curve should apply and the adsorbed quantity would be directly proportional to the surface. 

FIGURE 8.8 Langmuir s extended cubical atom models. From E.W. Washburn, Introduction to the Principles of Physical Chemistry, 2nd ed., McGraw-Hill, New York, 1921, p. 470. 

In principle, the FIAM does not imply that the measured flux. / s should be linear with the metal ion concentration. The linear relationship holds under submodels assuming a linear (Henry) isotherm and first-order internalisation kinetics [2,5,66], but other nonlinear functional dependencies with for adsorption (e.g. Langmuir isotherm [11,52,79]) and internalisation (e.g. second-order kinetics) are compatible with the fact that the resulting uptake is a function (not necessarily linear) of the bulk free ion concentration cjjjj, as long as these functional dependencies do not include parameters corresponding with the speciation of the medium (such as or K [11]). 

Niels Bohr s 1913 hydrogen atom paper demonstrates the traditional interest of some physicists in placing the facts and laws of chemistry within a broader framework of foundational principles laid out by physicists. During the course of the next two decades, a number of physicists who became known as quantum physicists developed physical theories and mathematical techniques that they claimed would create a mathematical and theoretical chemistry. However, few of them had much chemical knowledge beyond a general understanding of the periodic table of the elements and familiarity with the Lewis-Langmuir theory of the electron duplet and octet. 

Ruthven DM (1984) Principles of Adsorption and Adsorption Processes, Wiley-lnterscience, New York Sahouli, B, Blacher, S andBrouers, F (1997) Langmuir 13,4391 Sen-Levy, A and Avnir, D (1993) Langmuir 9,2523 SingKSW (1973) In Colloid Science I, The Chemical Society, London, p 30 SmgKSW (1979) In Characterization of Porous Solids (S J Gregg, KSW Sing and HF Stoeckli, eds), Society of Chemical Industry, London, p 98... 

This approximation gives an exact solution only at a measurement temperature near the absolute zero. At room temperature and over it, this approximation fails completely. To overcome this difficulty, a lot of other approximations were proposed and reviewed by Nederlof et al. [30]. Among them, for Langmuir local isotherm, the Rudzinski-Jagiello s method [31] allows, in principle, to compute the actual distribution function according to Equation (14) ... 

The work done by Adam Langmuir on monolayers has had many repercussions. Not least was that it was from these two great men that I drew the concepts which enabled me to develop the basic principles of cell membrane structure in the 1930 s. These defined cell membranes has having a lipid bilayer as their continuous phase, sandwiched between two protein layers, and penetrated by hydrophobic proteins. There are now some thousands of biologists studying these membranes, and the source of concepts remains in the work of Adam and Langmuir. I wish we knew as much about the protein components as we do about the lipids. 

The principle of thermionic conversion derives from Edison s discovery in 1885 that current could be made to flow between two electrodes at different temperatures in a vacuum. The analysis and ejqrerimental investigation of thermionic emission from a hot electrode were performed by O. W. Richardson in 1912. W. Schlichter in 1915 recognized this means of converting heat to electricity. A patent was submitted on this topic in 1923.1. Langmuir and his associates characterized the electron and ion emission from cesium-adsorbed films on tungsten in the 1920s. 

---