Monolayers mixed alcohol

Shah, D. O. and Shiao, S. Y. (1975). The chain-length compatibility and molecular area in mixed alcohol monolayers. In Goddard, E. D., ed. Monolayers, Advances in Chemistry Series 144 Am. Chem. Soc., Washington, DC, pp. 153-164. 

The ex-situ investigation with the sampled monolayers did not always reflect the original monolayers at the air/water interface in analyzing adsorption of cadmium ions. It was newly observed by the in-situ method that the adsorptivity of cadmium ions to acidic monolayers could be abruptly reduced when the inactive alcohols were mixed into at more than 20% in composition. 

Mixed Monolayers. Figure 1 shows the excess area/molecule when C g alkyl alcohol was mixed with alkyl alcohols of various chain lengths. In this figure, A g represents the molecular area at surface pressure of 20 dynes/cm, whereas A and A represent the area/molecule at zero surface pressure in the condensed and expanded states of the mixed monolayers. The excess area/molecule is the difference between the experimentally measured area/molecule in the mixed monolayers and that expected from the simple additivity rule ( T7). The comparison of the results of area/molecule in pure and mixed monolayers indicates that the mixed alkyl alcohols of different chain lengths form a... 

The Chain-Length Compatibility and Molecular Area in Mixed Alcohol Monolayers... 

Figure 1 shows the surface pressure—area curve of stearyl alcohol monolayer at pH 2.0 and 25 °C, where Ae is the area/molecule in the expanded state at zero surface pressure, Ac is the area/molecule in the condensed state at zero surface pressure, and A2o is the area/molecule at surface pressure of 20dynes/cm. Figure 2 shows the values of Ae, Ac, and A2o for various alkyl alcohols. From this diagram the average area per molecule in mixed monolayers was calculated using simple additivity rule. Figure 3 shows the excess molecular area when Ci6 alkyl alcohol... 

It has been shown that mixed monolayers of oleic acid and cholesterol exhibit the minimum rate of evaporation at a 1 3 molar ratio of oleic acid to cholesterol. This is shown in mixed monolayers of oleic acid and cholesterol in Fig. 7 as a function of surface pressure [11]. In has further been shown that a 1 3 molar ratio in mixed fatty acid and fatty alcohol monolayers, one observes the maximum foam stability, minimum rate of evaporation, and maximum surface viscosity in these systems [12]. 

The adsorbed layer at G—L or S—L surfaces ia practical surfactant systems may have a complex composition. The adsorbed molecules or ions may be close-packed forming almost a condensed film with solvent molecules virtually excluded from the surface, or widely spaced and behave somewhat like a two-dimensional gas. The adsorbed film may be multilayer rather than monolayer. Counterions are sometimes present with the surfactant ia the adsorbed layer. Mixed moaolayers are known that iavolve molecular complexes, eg, oae-to-oae complexes of fatty alcohol sulfates with fatty alcohols (10), as well as complexes betweea fatty acids and fatty acid soaps (11). Competitive or preferential adsorption between multiple solutes at G—L and L—L iaterfaces is an important effect ia foaming, foam stabiLizatioa, and defoaming (see Defoamers). 

It has been shown (Friberg, 2003 Birdi, 2002, 2008) that there exists a correlation between foam stability and the elasticity [E] of the film (i.e., the monolayer). In order for E to be large, surface excess must be large. Maximum foam stability has been reported in systems with fatty acid and alcohol concentrations well below the minimum in y. Similar conclusions have been observed with -C12H25S04Na [SDS] + -C12H25OH systems that give minimum in y versus concentration with maximum foam at the minimum point (Chattoraj and Birdi, 1984). Because of mixed mono-layer formation it has been found that SDS + C12H25OH (and some other additives) make liquid-crystalline structures at the surface. This leads to a stable foam (and liq-... 

Various inert compounds such as fatty acids, fatty alcohols, and lipids behave as two-dimensional diluents for Chi monolayers and lead to the formation of homogeneously mixed monolayers (20). These diluents have facilitated the study of Chl-Chl energy transfer within a two-dimensional plane as a function of the intermo-lecular Chi separation (26,27). In sufficiently dilute mixed monolayers, a majority of the Chi molecules are thought to exist in the monomeric state, with their mutual aggregations effectively suppressed within the geometrically controlled, ordered configuration. Multilayers (built-up monolayers) of Chi a have also been studied (23) and utilized for photovoltaic studies (see the next section). The molecular orientation in such Chi a multilayers has been ascertained from the observed dichroism in spectropolarization measurements with respect to absorption (23) and emission (28). 

The importance of selecting gravimetry instead of volumetry to measure liquid amounts in the pharmaceutical industry of liquid dosage forms is well illustrated by the volume contraction of water-ethanol and volume expansion of ethyl acetate-carbon disulfide liquid mixtures as well as a CS2-ethyl acetate system. The National Formulary (NF) diluted alcohol is a typical example of the volume nonadditivity of liquid mixtures [29], This solution is prepared by mixing equal volumes of alcohol [U.S. Pharmacopeia (USP)] USP and purified water (USP). The final volume of this solution is about 3% less than the sum of the individual volumes because of the contraction due to the mixing phenomenon [1], In addition, molecular interactions of surfactants in mixed monolayers at the air-aqueous solution interface and in mixed micelles in aqueous media also cause some contraction of volume upon mixing [30],... 

Following such treatment, the cultured cells in monolayer are washed with phosphate-buffered saline and extracted in 4 ml 0.5% Triton X-100 in saline/EDTA (100 mM NaCl, 10 mM EDTA, pH 8.0) for 2 min at room temperature. This releases most of the cytoplasmic material whilst the nuclei remain attached to the culture dish. 0.5% sodium dodecyl sulphate and 40 //g/ml pancreatic RNAse (preincubated at 80°C for 10 min, to inactivate DNAse) in saline/EDTA (above) is then added and the mixture incubated for 20 min at 37°C. One volume of chloroform/isoamyl alcohol (20 5, v/v) is then added and the phases mixed gently. The aqueous phase is separated by centrifugation and extracted again with chloroform/isoamyl alcohol. DNA is precipitated from the aqueous phase with 2 vol 95% ethanol and resuspended in 0.01 M Tris, pH 7.5. Alkaline sucrose density gradients (5-20%) are prepared in 0.1 M NaCl, 0.1 M NaOH with a final volume of 4.1 ml. Samples of DNA (max 3 fig) are layered on the top of these gradients and spun at 32 000 rpm at 20°C in a SW.50.1 Beckman rotor for 120 min. Fractions are collected and the [3H]DNA precipitated... 

Compounds used to form Langmuir monolayers were stearic acid (>99.9%) and stearyl alcohol (>99.9%) purchased from Aldrich. Stearic acid known to bind with cadmium ions (CdCh, >99.9%, Aldrich) were mixed with stearyl alcohol at varying compositions from 100 0 to 50 30. Each solution was at the concentration of ImM in chloroform (>99%, Fluka). 

Figure 1. Tcansmissiun FTlk results on the mixed monolayers spread on pure water with varying monolayer composition (stearic acid streaiyl alcohol) (a) and the peak area of the carbonyl band at various composition (b). The peak areas were normalized with respect to that of pure straric acid case (100 0).

Contrary to the case of Q3P, cholesterol only slightly disordered the structure of the film in the mixed monolayers with DPPC or SM. No brightly expressed phase separation was found despite of essential variations (from 60 to 20%) in molar ratio of the alcohol in DPPC/CHL or SM/CHL mixtures. 

Serpinet, using the inverse gas chromatography method, demonstrated the existence of oriented monolayers of long-chain hydrocarbons on silica gel surface [13], on the other hand Untz [31] showed that hydrocarbons also form solid condensed and liquid expanded monolayers on glycerol but not on the water surface. However, the addition of some amount of amphiphilic molecules to the hydrocarbon provokes the mixed monolayer formation on the water surface. The phase transition in such a monolayer occurs at the temperature higher than the melting point of bulk hydrocarbon. It also appeared that the monolayers characterized by 1 1 ratio of hydrocarbon to alcohol molecules were particularly stable [41]. 

It can be predicted that the properties of mixed monolayers composed of hydrocarbon and alcohol molecules deposited on the water, glycerol and silica gel surfaces will be different despite a common feature of these surfaces which are the hydroxyl groups. The reason for these differences is t he localized adsorption of alcohol molecules on silica gel and the heterogeneity of its surface. In Fig. 5 the results of investigation of mixed monolayers... 

The experiments on mixed monolayers were carried out using alkyl alcohols (Ci6, Ci8, C20, C22). These surfactants were obtained from Supelco, Inc. (Bellefonte, Pa.) with purity greater than 99+%. The C22 alcohol was purchased from the Applied Science Laboratories, Inc. (State College, Pa.). The solutions of all pure alkyl alcohols were prepared (concentration 0.004 M) in a mixture of chloroform, methanol, and... 

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