One-sided precipitation

In nature, asymmetry is achieved through membrane dissolved proteins. In lipid membrane systems without proteins, only monolayers made of bola-amphiphiles allow a totally asymmetric arrangement of head groups. The simplest asymmetry to be achieved is dependent on the one-sided precipitation of bolaamphiphiles. a,to-Dicarboxylic acids, for example, are often soluble at pH > 8 and spontaneously form vesicles upon acidification to pH 5. At a lower pH, all carboxyl groups become protonated and one usually observes ill-defined precipitates . 

The same behaviour can be observed for a,o)-bis(dipyridinium) salts, e.g. 2. The tetrabromide is easily soluble in water, but upon addition of 1-2 moles perchlorate or iodide, a one-sided precipitation occurs , meaning that the insoluble bipyridinium perchlorate head groups move together, whereas the bipyridinium bromide head groups stay more hydrated. The curvature of extremely uniform vesicle membranes is thus induced (Figure 4.5) and the perchlorate or iodide ions are entrapped within the vesicle. Vesicle formation... 

Figure 4.5 A small part of a monolayered vesicle membrane made by a one-sided precipitation of the given bipyridinium bolaamphiphile 2 with perchlorate.

Stripping of CO2 may also cause iron to precipitate, normally as iron hydroxide. That type of precipitation will also occur if an reduced type of water is entering the well from one side and an oxidized type from the other side. A third and obvious iron oxidation process will take place if reduced water gets in contact with oxygen. 

Figure 16-1 A cutaway view ofan electrostatic precipitator. The gas flows in one side and out the other.

To disintegrate the filter paper, the rinsed filter paper containing the precipitate is folded and placed into a preweighed porcelain crucible and the crucible is heated, first cautiously with a cooler Bunsen burner flame, so as to dry and char the filter paper, and then with the full heat of a Meker burner. For this final ignition step, the crucible should be tilted to one side and partially covered with the crucible lid so that the burner flame can be directed to the bottom of the crucible, thus avoiding engulfing the... 

Coaxial intergrowth is a paragenetic relation that describes crystals of two different species growing with a common axis the misfit ratios between the two crystals in the direction of the common axis are small, without exception. The formation of coaxial intergrowth can be understood to be one crystal conjunct to the other in an epitaxial relation, where both continue to grow. If a liquid of eutectic A-B component is solidified from one side (unidirectional solidification), crystals of the two phases A and B precipitate in dotted, columnar or lamellar (with common axis) form, and show unique textures for unidirectional solidification. This is a well known phenomenon in metallurgy. 

Figure 23.4 Prismatic dislocation punching at spherical precipitate, (a) A dislocation dipole loop is generated in the interface. One side expands into the matrix while the other remains in the interface, (b) Segments of the loop in the matrix glide downward to form additional loop length in the interface, (c) The loop in (b), which is partially in the interface and partially in the matrix, pinches together at its lowest point and splits into two loops, with one remaining in the interface and the other gliding into the matrix. From Porter and Easterling [4],...

NaOH (dropwise) until the solution becomes colorless. Keep the test tubes in the warm water bath for 5 min. Remove the test tubes from the water, let cool, and look for a light yellow precipitate. Record your observations on the Report Sheet (3). The formation of the yellow precipitate tends to be slow. Put these test tubes to one side and make your observations when all the other tests are completed. 

T)his last misdeed had a decisive effect upon him it rushed across the chaos of his Intellect and dissipated it, set the light on one side and the dark clouds on the other, and acted upon his soul... as certain chemical reagents act upon a turbid mixture, by precipitating one element and producing a clear solution of the other. 

The relationship between chemical equilibrium and the electromotive force of galvanic cells was first recognised by van t Hoff in 1886. It was not until much later, however, that a cell in chemical equilibrium was investigated experimentally, as it is not easy to find cells in which the equilibrium is not entirely to the one side or the other. In most cells the reaction and the production of current proceed until one of the reacting substances has disappeared almost entirely (e.g. the precipitation of copper by zinc in the Daniel cell). At the instigation of Bredig, Kniipffer investigated a cell made up as follows ... 

Most UF membranes are asymmetric, having a thin separating layer or skin layer with small pores on one side of the membrane, and a much thicker layer with larger pores below the membrane which provides structural support with minimum flow resistance. Asymmetric membranes are manufactured by wet phase inversion casting. In this process, a casting solution of a polymer in a water-miscible solvent is spread in a thin layer onto a flat surface and then immersed in water. The water causes extraction of solvent and precipitation of the polymer as a porous flat sheet. The skin layer is formed on the upper surface that was in direct contact with water, and the underlying... 

The most widely used sampler in the United States networks today is comprised of two buckets, and a rain-activated switch to operate a movable cover. During non-precipitating periods, the cover remains tightly sealed on one bucket. Precipitation falling on the sensitive switch completes an electrical circuit activating a motor which lifts the cover from one side and places it on the opposite bucket. The sampler thus provides a dry sample as well as a wet sample. This is the standard instrument used throughout the NADP/NTN network. 

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