Solvent Evaporation Times

Drug release may be affected by a number of process parameters such as drug loading, polymer molecular weight, polymer composition, initial concentration of the polymer in the organic phase of the emulsion, amount of emulsifier, stirring speed, vacuum pressure, solvent evaporation time and temperature. These parameters were kept constant and only the amount of NaOH was varied. Therefore, changes in the in vitro release curves should reflect only the effect of NaOH in various concentrations. ... 

Fig. 2. Volume fluxes of water (—) and dye solution (x—x) versus solvent evaporation time at 0.06 MPa (1) 0.12 MPa (2) and 0.18 MPa (3) for membranes cast from 15 wt. % PS solution. Temperature of casting solution 298 K...

Fig. 9. Volume flux of dye solution versus membrane operation time at 0.18 MPa for two seleeted membranes (A and B) east from 12..5 wt. % PS solution. Temperature of casting solution 298 K solvent evaporation time 0 s...

There are two widely used standard solvents -diethyl ether and butyl acetate - against which other solvents evaporation times can be compared. Somewhat confusingly, a low rate of evaporation on the ether scale corresponds to a high number (i.e. the time it takes to evaporate is many times the time ether takes), while on the butyl acetate scale a low rate of evaporation corresponds to a low number (i.e. the rate of evaporation is lower than that of butyl acetate). 

Fang, Y., Pham, V.A., Matsuura, T., Santerre, J.P. and Narbaitz, R.M. 1994. Effect of surface-modifying macromolecules and solvent evaporation time on the performance of polyethersulfone membranes for the separation of chloroform/water mixtures by per-vaporation.. 7. Ami. Polvm. ScL 54 1937-1943. 

The most interesting result from the present study is that it is possible to prepare membranes with different levels of free volume and, consequently, with different physical aging stability, by choosing the most suitable operating conditions (solvent, evaporation time, etc.). 

Macrovoids formation can be avoided by delayed demixing, and increasing polymer and/or nonsolvent concentration in the polymeric dope. Other studies suggested to introduce solvent into the coagulation bath [21-23], to increase solvent evaporation time [24], to work with a S-NS pair with low miscibility [25] or to use organic additives such as polyvinylpyrrolidone (PVP) [26,27]. 

For the surface composition of copolymers, many studies have been reported [47-49] that revealed that the surface composition of copolymers can differ greatly from that of the bulk owing to difference in the solid-state surface tension of the contained polymers, the solvent from which the films were cast, and the casting conditions. From these studies it was apparent that the solvent evaporation time, one of the casting conditions, strongly influenced the surface compositions of PAS. These findings were important for preparing many other PAS composites. 

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