TY - JOUR
T1 - Anion-dependence of fast relaxation component in Na-, K-halide solutions at low concentrations measured by high-resolution microwave dielectric spectroscopy
AU - Mogami, George
AU - Miyazaki, Takashi
AU - Wazawa, Tetsuichi
AU - Matubayasi, Nobuyuki
AU - Suzuki, Makoto
PY - 2013/6/13
Y1 - 2013/6/13
N2 - High-resolution microwave dielectric spectra of NaX, KX (X: F, Cl, Br, I) aqueous solutions of c = 0.05 and 0.1 M measured in the frequency range 0.2-26 GHz at 10 C are analyzed. The dielectric relaxation (DR) spectrum of each solution, which deviates slightly from the bulk-water spectrum, is mathematically divided into the bulk-water spectrum and the spectrum of solute particles covered with a water layer using a mixture theory by assuming the existence of continuous bulk-water phase. The solute spectra above 3 GHz are fitted with a linear series of pure water component (γ dispersion with DR frequency fw), fast Debye component-1 with DR frequency f1 (>fw), and slow Debye component-2 with DR frequency f2 (w). Component-2 is only found for the fluorides. The sum of dispersion amplitudes of γ and components -1 and -2 for NaX and KX are found to be almost irrespective of X and equal to the pure water level, indicating that components -1 and -2 are from the water modified by ions, thus denoted as "hypermobile water" and "constrained water" (not rigidly bound to ion), respectively. Below 3 GHz, sub-GHz dispersion component is detected and assigned as a relaxation response of counterion cloud. The resulting limiting-molar conductivities of NaX and KX are in good agreement with the literature data measured at much lower frequencies. The estimated number of hypermobile water molecules is found to increase from 9 to 31 for NaX and from 9 to 37 for KX with increasing anion size. Thus, except for the fluorides, it is reported that the modified water by salt ions exhibits only Debye component-1 other than γ dispersion, indicating the existence of a water-ions collective hypermobile mode in each solution.
AB - High-resolution microwave dielectric spectra of NaX, KX (X: F, Cl, Br, I) aqueous solutions of c = 0.05 and 0.1 M measured in the frequency range 0.2-26 GHz at 10 C are analyzed. The dielectric relaxation (DR) spectrum of each solution, which deviates slightly from the bulk-water spectrum, is mathematically divided into the bulk-water spectrum and the spectrum of solute particles covered with a water layer using a mixture theory by assuming the existence of continuous bulk-water phase. The solute spectra above 3 GHz are fitted with a linear series of pure water component (γ dispersion with DR frequency fw), fast Debye component-1 with DR frequency f1 (>fw), and slow Debye component-2 with DR frequency f2 (w). Component-2 is only found for the fluorides. The sum of dispersion amplitudes of γ and components -1 and -2 for NaX and KX are found to be almost irrespective of X and equal to the pure water level, indicating that components -1 and -2 are from the water modified by ions, thus denoted as "hypermobile water" and "constrained water" (not rigidly bound to ion), respectively. Below 3 GHz, sub-GHz dispersion component is detected and assigned as a relaxation response of counterion cloud. The resulting limiting-molar conductivities of NaX and KX are in good agreement with the literature data measured at much lower frequencies. The estimated number of hypermobile water molecules is found to increase from 9 to 31 for NaX and from 9 to 37 for KX with increasing anion size. Thus, except for the fluorides, it is reported that the modified water by salt ions exhibits only Debye component-1 other than γ dispersion, indicating the existence of a water-ions collective hypermobile mode in each solution.
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U2 - 10.1021/jp4012119
DO - 10.1021/jp4012119
M3 - Article
C2 - 23650875
AN - SCOPUS:84879038933
VL - 117
SP - 4851
EP - 4862
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 23
ER -