Slow solvent evaporation

Using two different procedures, based, respectively, on slow solvent evaporation[14] and on coprecipitation, a new proprietary method was developed during the fulfillment of a research project funded by the European Community (EC) under the Brite-EuramProgram[15,16], were tested for the preparation of microspheres. 

The slow solvent evaporation technique afforded milky nanosphere dispersions. No effect of the polymer/protein/lipid weight ratios on the dispersion stability was detected, at least in the investigated range. 

Figure 1 Size distribution of a particle dispersion prepared by slow solvent evaporation. 

By taking into account the difficulties connected to the slow solvent evaporation technique, a new procedure for nanoparticle preparation by co-precipitation was set up. This technique does not use chlorinated solvents and energetic mixing, which are both known to cause appreciable protein denaturation[17,18]. 

Two methods, annealing and film-casting by slow solvent evaporation, have been used effectively to develop maximum crystallinity in PVDF blends. The... 

Finally, our group reported on gold nanoparticles decorated with bent-core liquid crystals showing pattern formation on TEM grids after slow solvent evaporation (18 in Fig. 22). These particles showed interesting self-assembly effects in different bent-core liquid crystal hosts (SmCPA and Colr) and slightly improved electro-optic effects such as shorter response time, x, and unaltered spontaneous polarization in the SmCPA host, but no mesophase formation [547]. 

Compared with the solution absorption, the film sample prepared by spin-coating a dichlorobenzene solution using a slow solvent evaporation process showed pronounced peak broadening and a significant shift of —100 nm of the absorption edge. 

Samples for the viscoelastic experiments were prepared by a conventional slow-solvent-evaporation technique (1) followed by vacuum drying. For ease in handling in certain experiments, some samples were lightly cured using a 30-MRad dose of electrons other experiments were carried out on uncured materials. Transmission electron microscopy (Phillips Model 200) was used to investigate possible morphological features in the block polymers and blends. Details of the various staining techniques used are presented elsewhere (1,11,12,13). 

Solvents or thinners control paint consistency and application properties. Slow solvents evaporate slowly and leave the film open (workable) for longer periods than fast solvents, which evaporate rapidly in water-thinned paints, water is the thinner and there is no control over rate of evaporation. 

FIGURE 2.8. Some methods for growing crystals from solution, (a) Slow solvent evaporation, primarily used for small molecules, (b) Vapor diffusion, (c) The hanging drop method, primarily used for macromolecules, (d) A crystallization plate used for hanging drops there are slightly different crystallization conditions in each well, varied systematically with respect to, for example, pH and ionic strength. 

Slow solvent evaporation is a valuable method for producing crystals of high quality it is used primarily for small molecules. The rate of growth is manipulated by adjusting conditions (initial concentration, temperature, evaporation rate) so that crystals are obtained in a few days, not months or minutes. The rate of evaporation can be adjusted by covering the solution with a watch glass or a piece of film (aluminum or Parafilm ) with a number of small holes punched in it. The solution is then left to stand undisturbed. 

Of course, the first task in any study is acquisition of a pure compound. For coordination chemistry, this is often a non-trivial task, as several stable compounds may form during a synthesis. Separation, by chromatography and/or crystallization, is often required (Table 7.1). Crystal growth through slow solvent evaporation, dilution with another solvent, lowering temperature or addition of other counter-ions is a common task in coordination chemistry, although it is now possible to define compounds reasonably well in solution. 

Peptization of mineral precipitates in a suitable pH range is a method to obtain colloidal particles in aqueous solution [43]. Gelation is sometimes possible by a slow solvent evaporation [44]. Monolithic materials are obtained if the drying step is carefully controlled. Usually drying requires a very long time. Moreover, the monolithic ceramics are frequently hydroxides, and monolithicity is rarely conserved during the further thermal treatments because of the chemical or crystalline transformations that take place [45]. 

This was dissolved in CH2CI2. Slow solvent evaporation from the golden yellow solution resulted in yellow crystals in 38% yield. Recrystallization from toluene affords the compound containing a toluene of crystallization mp 161-162°C crystals are completely black before melting IR (Nujol) P-H 2360cm ... 

The volatiles are removed from the mixture under vacuum. The product is dissolved in 20 ml of CH2CI2 and then anaerobically filtered. Slow solvent evaporation in an inert atmosphere results in large yellow crystals. The crystals are often covered with a brown tarry residue which is readily removed by washing the crystals with a small amount of 2 1 hexane/CH2Cl2 mixture. (Yield 60% mp 103-114°C (sealed tube). Anal. Calcd for C22H2oFioFe06 C, 42.19 H, 3.22 ... 

The behaviour of the modified fabrics when wet with the two organic solvents shown in Table 5.2 and Fig. 5.5 and 5.6 (95% ethanol and acetone, respectively) differed from those wet with aqueous media in three fundamental aspects (1) maximum tension took longer to achieve with these solvents than those wet with aqueous media (2) the tension developed was also less than those exposed to aqueous media and (3) the reversal of load and pressure occurred over relatively short time periods due to the high vapour pressure and accompanying evaporation of solvent. Fabrics wet with ethanol took about 450-550 seconds to reach maximum stress (138 psi generated), then reversed this effect due to slow solvent evaporation (Fig. 5.5). Fabrics wet with acetone reach maximum tension more rapidly (150 seconds with a corresponding load of 1.61b and 56 psi), but rapidly reversed back to zero load after 250 seconds due to the complete evaporation of the solvent (Fig. 5.6). 

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