Mixtures, spreading

The deposition, exposure, and removal of resists involve quite a few issues of chemistry and transport that benefit from the chemical engineering perspective. For example, resists are typically deposited by a spin-on process, in which the polymer is dissolved in a solvent and poured onto a rapidly spinning wafer. With the addition of suitable viscosity thinners and careful choice of spinning speed, this mixture spreads uniformly over the wafer with simultaneous evaporation of the solvent. Detailed modeling of the simultaneous flow and evaporation presents a nontrivial transport problem. Chemical issues make their appearance during optical exposure. Positive resists contain... 

Heat the slide on a hotplate ( 40°C) for a few seconds and shear the mixture (spread thinly) in a single direction across the surface of the slide using another clean borosilicate slide. 

Chromatography Chromatography is a technique that separates the components of a mixture (called the mobile phase) based on the ability of each component to travel or be drawn across the surface of another material (called the stationary phase). Usually, the mobile phase is a gas or a liquid, and the stationary phase is a solid, such as chromatography paper. The separation occurs because the various components of the mixture spread through the paper at different rates. Components with the strongest attraction for the paper travel slower. 

Figure 6 H— isotherms for asphaltene/resin mixtures spread from pure 20/80 toluene/hexane on pure water (bulk concentration of asphaltenes = 4 mg/ml).

Mohammed et al. (144, 145), in a series of studies, examined several aspects of emulsion films with and without demulsifiers as well as their chemistries. Using the Langmuir balance for studying the air/ crude/water interface, they examined the sinface pressme n-area isotherm for monolayers of Buchan crude s asphaltenes and resins and their mixtures, spread on distilled water at pH 6.2 and 25°C. They found that the asphaltenes upon compression formed solid films, that could withstand pressures up to 45 mN m" in contrast to the resin films at 7 mN m which thereafter collapsed. The asphaltenes formed highly stable emulsions in contrast to the resins alone, which formed the least stable emulsions. They found that film compressibility and emulsion stability decreased as resin content increased. Temperature increases caused no significant effects on asphaltene monolayer compressibility as was observed earlier by Reis-berg and Doscher (126) for natural crude oil films. 

Vaporization from the surface occurs without vigorous agitation of bubbles, unlike the case of nucleate boiling, where bubbles are formed and agitated at the heating surface. The liquid mixture spreads over the heating surface becoming a thin film of constant thickness. 

Lee et al. used the Langmuir film balance technique to determine the hydrolytic kinetics of stereo-complex monolayers formed from PLLA/PDLA mixtures spread at the air-water interface. The hydrolysis of the mixture monolayers under basic conditions is slower than that of individual PLLA or PDLA monolayers, depending on the composition or the degree of com-plexation. In the presence of proteinase K, the hydrolysis rate of mixture monolayers with >50 mol% PLLA is much slower than that of the singlecomponent PLLA monolayer. The monolayers formed from mixtures with <50 mol% l-PLA do not show any degradation. It is concluded that the slower hydrolysis of mixture monolayers is mainly due to the strong interaction between PLLA and PDLA chains, which prevents the penetration of water or enzyme into the bulk. In an in vivo study on the biocompatibility of PLLA and stereo-complexed nanofibres by subcutaneous implantation in rats, Ishii et al. also observed that stereo-complexed nanofibres exhibit slower degradation than PLLA. ... 

In the coarse mixing phase of the problem, the melt enters the water and falls to the bottom of the water chamber. Heat transfer between the hot melt and the surrounding water is limited by film boiling. The melt fragments and mixes with the surrounding water-steam mixture, spreading out radially as it falls. 

Preparation of the layers according to [46] 30 g kieselguhr G (Firm 88) + 0.05 g sodium diethyldithiocarbamate are carefully stirred into a mixture of 45 ml water and 15 g polyethylene glycol and the mixture spread on to 5 plates using the standard method these are... 

Figure 5 Fourier transform of the derivative (with respect to time) of the interfacial pressure obtained through compressing (at a rate of 9.1 mm /s) a 1 1 behenic acidxholesterol mixture spread on water. (Reproduced from Ref. 24. Collegium BasUea, 2008.)...

Figure 9 Pressure-area isotherms of nucleobase amphiphUe monolayers (a) mixed monolayers spread on pure water subphase (b) 1 1 mixture spread on various polynucleotide subphases (c) schematic illustration of triplex formation at the air-water interface.

Method 2. Mix 1 0 g. of 3 5-dinitrobenzoic acid with 1 5 g. of phosphorus pentachloride in a small, dry test-tube. Warm the mixture gently over a small smoky fiame to start the reaction when the reaction has subsided (but not before), boil for 1-2 minutes or until the solid matter has dissolved. Pour the mixture while still liquid on a dry watch glass (CAUTION the fumes are irritating to the eyes). When the product has solidified, remove the liquid by-product (phosphorus oxychloride) by transferring the pasty mixture to a pad of several thicknesses of filter paper or to a small piece of porous tile. Spread the material until the liquid has been absorbed and the residual solid is dry. Transfer the 3 5 dinitrobenzoyl chloride to a test-tube, add 0-5-1 ml. of the alcohol, and continue as in Method 1. 

Drying oils. Place 3 ml. of hnseed oil in a test-tube, add about 01 g. of Utharge and boil the mixture gently for 10 minutes. When cold, pour a httle of the product on a watch glass and spread the oil into a thin film with the aid of a smah piece of paper. Pour a little of the untreated hnseed oil on another watch glass and spread it out as a thin film. Compare the times taken for the films to become dry. 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

Cholestenone. Place a mixture of 1 0 g. of purified cholesterol and 0-2 g. of cupric oxide in a test-tube clamped securely at the top, add a fragment of Dry Ice in order to displace the air by carbon dioxide, and insert a plug of cotton wool in the mouth of the tube. Heat in a metal bath at 300-315° for 15 minutes and allow to cool rotate the test-tube occasionally in order to spread the melt on the sides. Warm with a few ml. of benzene and pour the black suspension directly into the top of a previously prepared chromatographic column (1) rinse the test-tube with a little more benzene and pour the rinsings into the column. With the aid of shght suction (> 3-4 cm. of mercury), draw the solution into the alumina column stir the top 0 -5 cm. or so with a stout copper wire to... 

Equip a 500 ml. three-necked flask with a dropping funnel, a mechanical stirrer and a reflux condenser. Place a solution of 72 g. (65 ml.) of redistilled phenylhydrazine (Section IV,89) CAUTION poisonous) in 300 ml. of ether in the flask, stir vigorously, and add 33 g. (26 ml.) of A.R. carbon disulphide slowly during about 30 minutes. A precipitate is formed immediately upon the addition of the carbon disulphide, the mixture becomes warm and the temperature soon approaches the boiling point maintain the temperature just below the b.p. by cooling with ice water if necessary. When the addition is complete, stir for a further 30 minutes, then filter the precipitate at the pump, wash it with about 25 ml. of ether, and spread it upon filter paper for 20 minutes to permit of the evaporation of the ether. The yield of the salt (I) is 92 g. 

For burning oil (or organic solvents), do not use water as it will only spread the fire a mixture of sand and sodium bicarbonate is very effective. 

The fungus responsible for Dutch elm disease is spread by European bark beetles when they burrow into the tree Other beetles congregate at the site attracted by the scent of a mixture of chemicals some emitted by other beetles and some coming from the tree One of the compounds given off by female bark beetles is 4 methyl 3 heptanol Suggest an efficient synthesis of this pheromone from alcohols of five carbon atoms or fewer... 

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