Fatty acid on water

The clearest results were obtained with the normal, saturated fatty acids and alcohols. These formed stable films, which would stand considerable compression laterally, and (at room temperature on distilled water) gave a very clearly marked critical area at which the surface pressure first appeared, this point being of course Pockels s critical point of the first diminution of surface tension. As the area was reduced from large initial areas no surface pressure could be detected until the area had reached about 22 sq. A. per molecule and at 20 5 sq. A. the pressure increased very rapidly indeed with further increase of pressure. The curve I of Fig. 15 shows the relation between surface pressure and area per molecule, which is obtained with accurate apparatus for the fatty acids on water curve III is that obtained with the alcohols.3... 

The composition of the films deposited,1 in the case of fatty acids on water, is pure fatty acid if the solution is rather strongly acid, and soap, almost always the soap of a divalent metal (present in traces in the water), if the solution is fairly alkaline. At intermediate acidities the films consist of various proportions of acid and divalent soap the presence of potassium and sodium salts also influences the composition of the films. 

Actually, Stewart and Morrow have observed interferences in liquid fatty acids and paraffins (see later, p. 191), which point to the existence of bundles. The fundamental researches of Adam and Langmuir showed some time ago that film formation of fatty acids on water surfaces is due to the fact that the carboxyl groups cleave to the surface of the water while the lipoid hydrocarbon chains, in consequence of their strong molecular cohesion, form a relatively stable surface film which, itself, has a very low surface tension on account of the small secondary valence effect of the end methyl groups. If we calculate the surface tension of such a film in absolute energy units from molecular cohesion, we obtain values between 10 and 50 dynes/cm, which agree satisfactorily in order of magnitude with values determined experimentally. 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

In situ observation of monolayers of fatty acids on the water surface by a Brewster angle microscope. 

The results of this test demonstrated that the diamides of the Ci4 and higher saturated fatty acids were water repellents. On the other hand, the unsaturated oleic acid derivatives enhanced hydrophilicity. 

The term lipid includes all compounds that release fatty acids on digestion, so that this definition is more extensive than that of fat. Compounds which are insoluble in water, soluble in organic solvents but not derived from fatty acids have been termed non-saponifiable lipids. They include steroids, terpenes and ubiquinone. 

The rates of evaporation of water through unimolecular fi has been examined by Hedestrom and by the writer. It is foi that the rate of evaporation of water through unimolecular fi of fatty acids on the surface of water is relatively slow in compari to the high rate of evaporation calculated with the aid of Herz-Knudsen equation. The rate is approximately inveri proportional to the surface film pressure F as is indicated fi the following figures. 

The implicit assumption made in deriving equation (7.4) is that an adsorbed gas on a solid surface behaves similarly to a thin film of fatty acid on the surface of water. 

Chen and Frank [356] studied the adsorption of a series of fatty acids on to both aluminium oxide and clean glass. In particular they studied the variation of appropriate peaks in the infrared absorption spectra as a function of time in order to monitor the kinetics of adsorption. They also studied the variation of contact angle of both water and hexadecane with time allowed for adsorption. 

With the fatty acids on distilled water the very steep curve I continues almost down to zero pressure. On dilute acid solutions, however, this steep curve only occurs above about 17 dynes per cm., and below this pressure there is a second, nearly straight portion of the curve (see curve III), cutting the abscissa at about 25 sq. A. Both the upper and lower parts of these curves are very little changed when the number of carbon atoms in the acid is altered from 14 to 22 carbon atoms the steep curve always tends to an area within 1 sq. A. of 20 5 the lower part on acid solutions tends to 25 sq. A. for the medium-chain aoids, about 16 carbons, and to very slightly smaller areas for longer chain acids (24 for the 22... 

First report on the separation of underivatized fatty acids using water in carbon dioxide with FID Petrochemicals Simulated distillations for the characterization of oil fractions Metals Study of metal ions related to nuclear industry... 

Engblom, J., Engstrbm, S. and Fontell, K. The effect of the skin penetration enhancer Azone on fatty-acid soap-water mixtures. Journal of Controlled Release 33 299-305, 1995. 

Biodiesel is produced on the industrial scale by methanolysis of vegetable oUs (usually rape or soybean) or waste fat, particularly using frying oils. Methanolysis proceeds with modest amounts of base catalyst, provided the levels of free fatty acid and water in the oil are low (24, 25). The fatty acid content may be reduced by physical or chemical treatment before methanolysis but for waste fats, alternative processes that do not use base catalysis may be preferred. Lipase catalyzed methanolysis is less sensitive to fatty acid and water in the oil and has been tested in batch (26) and fixed-bed reactor (27) conversion of waste oil and grease to biodiesel. 

The water-insoluble fatty acids on the filter paper are washed, dissolved in ethyl alcohol, and titrated with 0.10 A sodium hydroxide. Polenske value = B — S where B = titer of blank in mL and S = titer of insoluble fatty acids in mL. 

The term lipid applies to a class of compounds that are soluble in organic solvents and nearly insoluble in water. Chemically, lipids are either compounds that yield fatty acids on hydrolysis or complex alcohols that combine with fatty acids to form esters. Some lipids are more complex, containing nonlipid groups, such as sialic, phosphoryl, amino. 

Our own study examined the effects of a mixture of fatty acids on cortisol and cholesterol levels in laboratory stress situations. (Yehuda, al el, 2000). A compound of free nonesterified unsaturated fatty acids a-linolenic and linolenic acids in a ratio 1 4 was administered for 3 wk prior to injection of cortisone (10 mg/kg) or prior to immersion of rats in a 10°C saline bath. The results confirmed the expected elevation of cortisol and cholesterol level in stress, but, more importantly, the treatment prevented elevation of blood levels of cortisol and cholesterol and protected against deficits in the Morris water maze learning that usually accompany such stressful conditions. Differences from con-... 

For coal hquefaction wastewater, phenol and o-, m- and p-cresol were removed from the wastewater but no removal was observed for acetate or propionate. The results of this study could be used to design an effective extraction system for the removal of short-chain fatty acids, which have been shown to inhibit anaerobic biodegradation of different types of waste-waters [93]. This is desirable to avoid the inhibitory effect ofthe short-chain fatty acids on the course of the treatment process. 

In 1887, Pade described a piece of apparatus that enabled researchers to determine precisely the absolute densities of coffees and to detect coffee frauds involving manipulation of green coffees and watering of roast coffees. In this connection he mentions and comments on a fraudulent method whereby products released during roasting are condensed and reinserted into the coffee beans. After a summary analysis he deduces that this concentrated liquid contains caffeine, ammonia, amines, ammonia salts, acrid bases near pyridinic compounds and fatty acids. By watering down the still-hot coffee with this mixture, 14 to 15% of the lost weight can be fraudulently restored to it. 

---