Fast evaporation

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

Vorm, O. Roepstorff, P. Mann, M. Improved Resolution and Very High Sensitivity in MALDl-TOF of Matrix Surfaces Made by Fast Evaporation. Anal. Chem. 1994,66, 3281-3287. 

Solvents used here for a general liquid-liquid extraction method were selected from Snyders solvent selectivity triangle. As extraction liquids have to be composed of mixtures of three solvents which may enter into maximum interaction with the analyte, three solvents had to be selected that represent a wide variety of selective interactions. In addition, the solvents should be sufficiently polar to ensure quantitative extraction. Besides selectivity and polarity requirements, the solvents should also meet a few other criteria, mainly for practical reasons they should not be miscible with water, have low boiling points (for relatively fast evaporation procedures) and have densities sufficiently different from the density of water, for pure solvents as well as for selected binary or ternary mixtures of solvents. 

Nicola, A. J. et al.. Application of the fast-evaporation sample preparation method for improving quantification of angiotensin II by matrix-assisted laser desorption/ionization. Rapid Commun. Mass Spec., 9, 1164,1995. 

One should note, that in a real industrial process there are de-pressurization processes accompanied by fast intra-particle pressure drop, and the morphology of particles might be changed by stress created by fastly evaporating liquid gases stored in the pores and sorbed by the polymer. 

Vorm O, Roepstorff P, Mann M (1994) Improved resolution and very high sensitivity in MALDI TOF of matrix surfaces made by fast evaporation. Anal Chem 66 3218-3287... 

It must be pointed out, however, that the formation of rings and honeycomb pattern is a consequence of the instability of thin films to convection, caused by the fast evaporation of the solvent [290], It does not require complex shaped molecules or even depend on some molecular recognition process. 

Spray drying methods can also be used. Here, one first dissolves the reactants in a medium, preferably H2O. Small droplets are transported in a gas stream and heated, resulting in a very fast evaporation of H2O. As a result, an intimate reaction mixture is obtained. 

Bock has studied a number of systems in which different polymorphs were obtained under thermodynamic and kinetic conditions. (2-pyridyl)(2-pyrimidyl)amine 3-II is dimorphic. Modification I is readily crystallized thermodynamically from any solvent (toluene was actually used) while modification II is obtained kinetically by fast evaporation of an ethereal solution or by resolidification of the melt (Bock et al. 1997). 

Methyl ethyl ketone (fast evaporation rate) 32%... 

Pattern Development. The development of patterns exposed in thin films of PVTMSK was diflScult because of its high solubility in almost all organic solvents. Excessive thinning of the unexposed areas could be prevented by carrying out the development at low temperatures either by spray development with a 2-propanol mist while the wafer is spinning at 1000-2500 rpm or by dip development in 2-propanol at + 5 C. Spray development cooled the wafer to as low as 8-10 °C because of the fast evaporation of the solvent, but even at such low temperatures and short development times (5-15 s), a nonuniform thinning of the film occurred. 

Polycarbonate Solvent cementing is the most common method of bonding polycarbonate. Bonding can be carried out with specific solvents, mixtures of solvents, and mixtures of polycarbonate and solvents. Methylene chloride, when used by itself, has an extremely fast evaporation rate and is recommended for fast assembly of polycarbonate parts. A solution of 1-5% polycarbonate resin in methylene chloride has a decreased evaporation rate. Parts bonded with methylene chloride are usable at elevated temperatures after approximately 48 hours, depending on the bonding area. Ethylene dichloride is also used (5). 

The [Cr(OH)(OH2)x(Solv)]2+ ions (.v 0 3, Solv = MeOH or MeCN) have been detected by ESMS in the gas phase, on fast evaporation of solutions of [Cr(OH2)6](C104)3 in MeOH or MeCN.47 The [Cr(NH3)5(OH)]2+ complex promotes the phosphorylation (by ATP) of serine and threonine OH-residues in bovine serum albumin in vitro.511... 

Particles derived from the evaporation of solution droplets are spheroidal. Shape (primarily in surface features), density, and size control of particles can be achieved by the appropriate selection of the compound, the concentration of the solution, the size of the droplet generated, and the conditions for the evaporation of the droplets. Fast evaporation rates tend to produce less solid and rough-surface particles, but this is tempered by the chemical properties of the compound. Smooth, spherical particles call for compounds with high solubility and slow evaporation rates. These requirements were used by Vanderpool and Rubow [48] to produce solid, smooth spheres of up to 70 pm in diameter. The different types of particles that can be produced from the evaporation of solution droplets include solid spheres with surfaces that are smooth, cracked, or wrinkled hollow spheres, shells, and spheroidal particles that have a wrinkled surface like raisins porous-type particles that are perforated with holes, and single crystals and particles composed of several crystals, which may be angular or spheroidal in shape. 

Solution Filling. Solutions generally do not involve products subject to fast evaporation, such as chlorofluorocarbons, and therefore they do not require chilling and recirculation. Figure 12 shows a solution-filling system. 

A possibility is to saturate at different temperatures the reactants before they enter into the stack [33]. This approach can be accomplished by several procedures based on external dewpoint, external evaporation, steam injection with downstream condensers, or flash evaporation. High temperature values allow to absorb significant water amount in gas streams and then transport it inside the stack compensating the water losses due to internal fast evaporation. However, the main problem with external humidification is that the gas cools after the humidifier device, the excess of water could condense and enter the fuel cell in droplet form, which floods the electrodes near the inlet, thereby preventing the flow of reactants. On the other hand, internal liquid injection method appears preferable for example with respect to the steam injection approach because of the need of large energy requirement to generate the steam. 

Figure 5. Mortar deterioration due to salt crystallization in masonry. The mortar is more porous than the brick allowing for fast evaporation and concentration of the soluble salts.

A further refinement of the scale of phase separation was recently demonstrated by Xia and Friend using inkjet printing (IJP) and thereby doubhng the EQE [238]. As demonstrated by fluorescence and atomic force microscopies, this originates from a more rapid drying process of inkjet printed films as compared to spin cast ones (see Fig. 50). The small volume and hence the large surface to voliune ratio of each IJP droplet led to this fast evaporation and drying. 

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