Relaxations and nano-phase-separation in ultraviscous heptanol-alkyl halide mixture

Abstract

To gain insight into the effects of liquid-liquid phase separation on molecular relaxation behavior we have studied an apparently homogeneous mixture of 5-methyl-2-hexanol and isoamylbromide by dielectric spectroscopy over a broad temperature range. It shows two relaxation regions, widely separated in frequency and temperature, with the low-frequency relaxation due to the alcohol and the high-frequency relaxation due to the halide. In the mixture, the equilibrium dielectric permittivity s of the alcohol is 41% of the pure state at 155.7 K and s of isoamylbromide is ϳ86% of the pure state at 128.7 K. The difference decreases for the alcohol component with decreasing temperature and increases for the isoamylbromide component. The relaxation time of 5-methyl-2-hexanol in the mixture at 155.7 K is over five orders of magnitude less than in the pure state, and this difference increases with decreasing temperature, but of isoamylbromide in the mixture is marginally higher than in the pure liquid. This shows that the mixture would have two T g 's corresponding to its of 10 3 s, with values of ϳ121 K for its 5-methyl-2-hexanol component and ϳ108 K for its isoamylbromide component. It is concluded that the mixture phase separates in submicron or nanometer-size aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own s and decrease markedly.

Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture

“…1 for the temperature range 109.2-140.3 K in which the dispersion and absorption features due to each component are clearly distinct. As seen in our study of 5-methyl-2-hexanol-iso-amylbromide mixture, 26 and as was observed previously by Denney 17 for the 1-propanol-isoamylbromide mixture, the spectra show two dispersion regions in Ј and two peaks corresponding to these dispersions in Љ. The lower frequency dispersion and the Љ peak correspond to Brownian diffusion of 1-propanol while the higher frequency peak is associated with the isoamylbromide molecules.…”

“…26 This is the opposite of the change in observed for 1-propanol-isoamylbromide mixture. 17,24 In view of the interpretation of the Debye-type spectra in terms of the relaxation by hydrogen bond breaking and reforming, [1][2][3][11][12][13][14]27,28 and our findings for the 5-methyl-2-hexanol mixture, 26 we have restudied the dielectric behavior of 1-propanol-isoamylbromide mixture in detail and have examined its crystallization behavior in real time by using broad band spectroscopy. Studies on their pure liquid states have been reported in earlier papers, 16,22 and are used for comparison.…”

“…26 For brevity, the homogeneous solution of 1 mol of 1-propanol with 4 mol of isoamylbromide ͑i.e., a 20 mol % solution of the 1-propanol in isoamylbromide͒ studied here is referred to as the mixture.…”

“…The effect of such aggregation on the features of ␣-relaxation process behavior was recently reported by studying a mixture of a long chain alcohol, 5-methyl-2-hexanol, with a slightly shorter molecule, isoamylbromide. 26 It was found that in the nanophase separated mixture, of the alcohol was shorter than the value measured for the pure liquid, 26 while of the isoamylbromide was slightly longer than measured for the pure liquid. 26 This is the opposite of the change in observed for 1-propanol-isoamylbromide mixture.…”

“…26 It was found that in the nanophase separated mixture, of the alcohol was shorter than the value measured for the pure liquid, 26 while of the isoamylbromide was slightly longer than measured for the pure liquid. 26 This is the opposite of the change in observed for 1-propanol-isoamylbromide mixture. 17,24 In view of the interpretation of the Debye-type spectra in terms of the relaxation by hydrogen bond breaking and reforming, [1][2][3][11][12][13][14]27,28 and our findings for the 5-methyl-2-hexanol mixture, 26 we have restudied the dielectric behavior of 1-propanol-isoamylbromide mixture in detail and have examined its crystallization behavior in real time by using broad band spectroscopy.…”