I Harkins

The three general states of monolayers are illustrated in the pressure-area isotherm in Fig. IV-16. A low-pressure gas phase, G, condenses to a liquid phase termed the /i uid-expanded (LE or L ) phase by Adam [183] and Harkins [9]. One or more of several more dense, liquid-condensed phase (LC) exist at higher pressures and lower temperatures. A solid phase (S) exists at high pressures and densities. We briefly describe these phases and their characteristic features and transitions several useful articles provide a more detailed description [184-187]. 

Equation 17.26, derived by Harkins and Jura(15) may be plotted as In (P/To) against I / V2 to give a straight line. The slope is proportional to A2. The constant of proportionality may be found by using the same adsorbate on a solid of known surface area. Since the equation was derived for mobile layers and makes no provision for capillary condensation, it is most likely to fit data in the intermediate range of relative pressures. 

Another piece of information was necessary before one arrives at a periodic table which is close to the modern view. This is the whole number rule which states that the masses of atoms on the 160 scale (i.e. mass of the major isotope of oxygen is 16.00) tend to have close to integer values. This information was provided by W. D. Harkins (vide infra) and F. W. Aston (Historical Vignette 1.2). 

There is anecdotal material that W. D. Harkins, whose career at the University of Chicago started around the time of World War I, felt that his scientific contributions were not adequately recognized by the community. It is indeed correct that he is not well known for his contributions to the Whole Number Rule . 

Harkins, I., and S. W. Nkksic. Studies on the role of sulfur dioxide in visibility reduction. J. Air Pollut. Control Assoc. 15 218-221, 1%5. 

The molecules that are situated at the interfaces (e.g., between gas-liquid, gas-solid, liquid-solid, liquid,-I iquid2, and sol id,—sol id 2) are known to behave differently from those in the bulk phase (Adam, 1930 Aveyard and Hayden, 1973 Bakker, 1926 Bancroft, 1932 Partington, 1951 Davies and Rideal, 1963 Defay etal., 1966 Gaines, 1966 Harkins, 1952 Holmberg, 2004 Matijevic, 1969 Fendler and Fendler, 1975 Adamson and Gast, 1997 Chattoraj and Birdi, 1984 Birdi, 1989, 1997, 1999, 2002, 2009 Miller and Neogi, 2008 Somasundaran, 2006). Typical examples are... 

Connolly A, Dalgleish WH, Harkins P, Keat R, Porte AL, Raitt I, Shaw RA (1978) J Magn Reson 30 439... 

In our final case study we shall focus on the photoinduced mer to fac isomerization reaction recently observed by Harkins and Peters (109). We have investigated this system in detail (110), and it provides a nice example of a general conical intersection in an inorganic photochemical problem, i.e., one that is not imposed by symmetry via a Jahn-Teller degeneracy. 

Vinylidene chloride and chloroprene (Figures 7 and 8) under the given conditions produce curves which more or less resemble the styrene curve. Vinylidene chloride especially shows a long period of a rather constant reaction rate. By the theory of Harkins and Smith-Ewart this would be interpreted as a period of constant particle number and of constant monomer concentration at the reaction site—i.e., the monomer-polymer particles. The first assumption seems justified (15). The second assumption of constant monomer concentration at the reaction site can be true only in a modified sense because poly (vinylidene chloride) is insoluble in its monomer, and the monomer-polymer particles in this system therefore have a completely different structure as compared with the monomer-polymer particles in the styrene system. 

Although it may give satisfactory values for Asp, the Harkins-Jura equation leaves something to be desired at the molecular level. For example, the linear 7r versus o equation of state —the starting point of the derivation of the Harkins-Jura isotherm —represents the relatively incompressible state of the surface phase (i.e., 6 = 0.7 in Fig. 9.6b). (This equation is obtained in analogy with the approximately linear ir versus a equation for insoluble mono-layers discussed in Chapter 7.) However, in most instances of physical adsorption, no satura-... 

On Harkins, see R.S. Mulliken, William Draper Harkins, 1873-1951, Biographical Memoirs of Members of the National Aca-damy of Science 47 (1975) 49-81 and G. B. Kauffman, William Draper Harkins (1873-1951) A controversial and neglected physical chemist, Journal of Chemical Education 62 (1985) 758-761. In a letter to Bertram Boltwood of February 28, 1921, Rutherford described Harkins as moderately sound and a man of intelligence, but added that I wish he did more experimenting and spent less time in theorising and in endeavouring to cover every possible idea. Quoted in L. Badash (ed.), Rutherford and Boltwood Letters on Radioactivity (New Haven, 1969), 343. 

Harkins and Langmuir at one time considered that the total surface energy (Chap. I, 13). ... 

The adsorption of oleic acid from benzene solution, assumed to be uni-molecular with an area per molecule of 20 sq. A., i.e. with the molecules closely packed and arranged perpendicular to the surface, is taken by Harkins and Gans1 as a measure of the area of titania or silica powders. 

In Fig. 8 the calorimetric curve of a typical miniemulsion polymerization for 100-nm droplets consisting of styrene as monomer and hexadecane as hydrophobe with initiation from the water phase is shown. Three distinguished intervals can be identified throughout the course of miniemulsion polymerization. According to Harkins definition for emulsion polymerization [59-61], only intervals I and III are found in the miniemulsion process. Additionally, interval IV describes a pronounced gel effect, the occurrence of which depends on the particle size. Similarly to microemulsions and some emulsion polymerization recipes [62], there is no interval II of constant reaction rate. This points to the fact that diffusion of monomer is in no phase of the reaction the rate-determining step. 

First, allow me to impart to you some of my present thoughts on the BET theory (3, 4) for whatever they are worth. [Reference (3) is a continuation and extension of the BET theory. Some authors refer to it as the BDDT theory others call both papers together the BET theory.] Probably there are very few among you who have never made a BET plot, and many of you have made quite a few. I suppose, it will surprise no one among you if I say that I made the first BET plot. I did not know at that time that it was a BET plot, because that name did not exist yet. I tried to give a name to the theory that the three of us had developed, and I called it the multimolecular adsorption theory, which was probably not a very good name, but it was the best I could think of. Fortunately, somewhat later Professor Harkins invented the colorful name BET theory, and that name has stuck. 

Harkins and Boyd found by heat of emersion experiments that the value of E1 — EL was 5.2 kcal. per mole, whereas the C constant of the BET plot gave a value of only 2.6 kcal. per mole. Clampitt and German calculated the third energy term in C, and showed that with their interpretation of C the value of E1 — EL obtained from the BET plot was 4.3 kcal. per mole, which is much closer to the experimental value. If we combine the two explanations I have discussed, the discrepancies between experimental and theoretical values practically disappear. 

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