Dielectric relaxation spectrometry of mixtures of water with isopropoxy- and isobutoxyethanol. Comparison to unbranched poly(ethylene glycol) monoalkyl ethers

At 25 degrees C the complex permittivity of mixtures of water with isopropoxyethanol (i-C(3)E(1)) and isobutoxyethanol (i-C(4)E(1)) has been measured as a function of frequency v (1 MHz less than or equal to v less than or equal to 55 GHz) and mole fraction x (0 less than or equal to x less than or equal to 1). Within the limits of experimental error the dielectric spectra of the liquids can be represented by a. variety of relaxation spectral functions. At low water content (x greater than or equal to 0.4) spectral functions reflecting an unsymmetrical continuous distribution of relaxation times, like the Davidson-Cole function or a restricted version of the Hill function, appear to be appropriate. Below x less than or equal to 0.4 the Hill function can also be used. The Davidson-Cole function, however, has to be complemented by an additional Debye relaxation term. These relaxation functions and their parameter values are compared to those for mixtures of water with unbranched C(i)E(7) chemicals and also with simple monohydric alcohols to extract the effects resulting from steric hindrance and the influence of the ether group of the ethylene glycol monoalkyl ethers, respectively. It is particularly found that the measured spectra of the i-C(4)E(1)/H2O mixtures largely agree with those of C(4)E(1)/H2O mixtures of similar concentration. This finding indicates that dielectric relaxation of these liquids reflects molecular motions other than ultrasonic relaxation since the latter exhibits significant differences between corresponding mixtures of the stereo isomers.