T. A. Litovitz

On the Relative Roles of Free Volume and Activation Energy in the Viscosity of Liquids

The rate‐theory approach of Eyring and the free‐volume theory of Cohen and Turnbull for liquid viscosities have been reconsidered. The rate theory has been reformulated using the Cohen and Turnbull expression for the probability of finding a vacant site and yields an equation of the form η=A0exp[Ev*/RT+γV0/Vf]. This result has been applied to many liquids ranging from fused silica to liquid argon and including polyatomic van der Waals as well as hydrogen‐bonded liquids.Consistent fits to both temperature and pressure dependence of viscosity were obtained. A significant conclusion is that the free volume of liquids is considerably higher than that suggested by the WLF and Cohen and Turnbull equations.

Raman Scattering: Orientational Motions in Liquids

A systematic study of reorientational motions by Raman scattering is undertaken for 10 liquids. The theory of orientational broadening of Raman lines is presented with emphasis on the use of symmetry of molecular vibrations to obtain information of reorientational motions about different axes. The rotational diffusion tensor of benzene was obtained and found to be approximately isotropic. The time for reorientation of the major molecular axis was measured for nine liquids and the mechanism for reorientation for these liquids discussed. Liquids are classified according to whether reorientation is determined by structural dynamics or collisional motions. Finally it was possible to obtain the time between collisions for liquids in which reorientation is collision limited and occurs in small angular steps.

Analysis of Orientational Broadening of Raman Line Shapes

A systematic investigation of orientational broadening of Raman vibrational lines is undertaken and measurements of line shapes are made for 19 liquids. The problem of separating orientational broadening from the intrinsic vibrational lineshape is discussed in detail and a method of analysis is presented. The advantages and limitations of this method are considered and compared to an earlier method proposed by Rakov [Tr. Fiz. Inst. Akad. Nauk SSSR 27, 111 (1964); Opt. Spectrosc. 7, 128 (1959)]. The intrinsic width is determined for each line studied and removed from the spectrum to give the orientational broadening. It is noted that the intrinsic line shape, measured from polarized Raman spectra, may be used to correct infrared vibrational spectra which suffer from the same problems. It is shown that neglect of intrinsic width can lead to significant errors in the interpretation of the infrared data.

Rayleigh Scattering: Collisional Motions in Liquids

Measurements of light scattered in the Rayleigh wing were made over the range from 5 to 500 cm−1 in CCl4, C6H12, C5H12, CH3OH, C2H5OH, H2O, NH3, and CHCl3. These data when compared with earlier data on Ar, Xe, and SnBr4 indicate that in all of these liquids there is present the essentially exponential frequency dependence typical of collision induced effects. A calculation of the spectrum for large frequency shifts based on a binary interaction picture employing a Lennard‐Jones potential and a short range electronic overlap distortion model agrees well with the experimental results in liquid argon. Further, assuming that molecular frame distortion is proportional to the interaction force, a similar calculation yields excellent agreement for the molecular systems. It is concluded that isolated binary interactions are mainly responsible for the spectral density in the wings of the Rayleigh spectrum.

Depolarized Rayleigh scattering and hydrogen bonding in liquid water

Depolarized Rayleigh scattering spectra have been obtained for water over essentially its entire liquid range at atmospheric pressure. Three principal components of the Rayleigh line were identified and these were described in terms of molecular reorientation of the molecules, the formation and breaking of hydrogen bonds between molecules, and polarizability anisotropies resulting from the collisions or interactions among several molecules. For the region of the spectrum 0 to 50 cm−1, the most intense component of the spectrum is that which we have ascribed to hydrogen bond kinetics; from it we have determined the mean lifetime of a hydrogen bond in water as a function of temperature.

Dielectric Relaxation in Associated Liquids

The dielectric properties of the associated liquids butanediol 1,3, 2‐methyl pentanediol 2,4, glycerol, and hexanetriol 1,2,6 have been measured over the temperature range —20° to +10°C, and over a frequency range of 0.01 to 1200 Mc/sec. Dielectric relaxation times and their distributions have been determined and indicate the following: (a) All four liquids exhibit an asymmetric distribution of relaxation times of the Davidson—Cole form. (b) With the exception of hexanetriol 1,2,6, the distribution of relaxation times becomes narrower with increasing temperature. It is proposed that groups (regions of appreciable order) exist in these liquids, and that dielectric orientation is closely related to the structural breakup of these groups, this breakup being a necessary condition for dipole reorientation. It is further proposed that the structural breakup is a cooperative process which does not proceed exponentially, therefore giving rise to a nonexponential decay of dielectric polarization. This concept offers an explanation for the observed distribution of relaxation times. The temperature dependence of the width of the distribution is explained by assuming that the group‐size decreases with increasing temperature, and that as the groups become smaller, the structural‐decay process becomes more exponential.

ROLE OF MODULATION ON THE EFFECT OF MICROWAVES ON ORNITHINE DECARBOXYLASE ACTIVITY IN L929 CELLS

The effect of 835 MHz microwaves on the activity of ornithine decarboxylase (ODC) in L929 murine cell was investigated at an SAR of approximately 2.5 W/kg. The results depended upon the type of modulation employed. AM frequencies of 16 Hz and 60 Hz produced a transient increase in ODC activity that reached a peak at 8 h of exposure and returned to control levels after 24 h of exposure. In this case, ODC was increased by a maximum of 90% relative to control levels. A 40% increase in ODC activity was also observed after 8 h of exposure with a typical signal from a TDMA digital cellular telephone operating in the middle of its transmission frequency range (approximately 840 MHz). This signal was burst modulated at 50 Hz, with approximately 30% duty cycle. By contrast, 8 h exposure with 835 MHz microwaves amplitude modulated with speech produced no significant change in ODC activity. Further investigations, with 8 h of exposure to AM microwaves, as a function of modulation frequency, revealed that the response is frequency dependent, decreasing sharply at 6 Hz an 600 Hz. Exposure with 835 MHz microwaves, frequency modulated with a 60 Hz sinusoid, yielded no significant enhancement in ODC activity for exposure times ranging between 2 and 24 h. Similarly, exposure with a typical signal from an AMPS analog cellular telephone, which uses a form of frequency modulation, produced no significant enhancement in ODC activity. Exposure with 835 MHz continuous wave microwaves produced no effects for exposure times between 2 and 24 h, except for a small but statistically significant enhancement in ODC activity after 6 h of exposure. Comparison of these results suggests that effects are much more robust when the modulation causes low-frequency periodic changes in the amplitude of the microwave carrier.

Rayleigh Scattering: Orientational Relaxation in Liquids

A systematic investigation of orientational relaxation in liquids has been initiated employing the technique of Rayleigh scattering. The experimental results are interpreted based on an approximate theory which is developed and justified. Scattering spectra from 15 different liquids, including the homologous alkyl bromides and polyethylene glycols as well as glycerol, 1,3‐butanediol, and n‐octyl alcohol, were obtained as a function of temperature using a 6328‐A Ne–He laser source and a Fabry–Perot interferometer. All spectra were found to have approximately Lorentzian form symmetric about the source frequency, which implies molecular reorientation is a relaxational process. Also, the width of these Lorentzian lines (which is reciprocally related to the orientational relaxation time) increased with increasing temperature in such a way that an effective orientational activation enthalpy was determined. In both the alkyl bromide and polyethylene glycol series, increased molecular size resulted in increased r...

Comparison of Dielectric and Mechanical Relaxation in Associated Liquids

A comparison is made of existing dielectric and ultrasonic shear and compressional relaxation data in several associated liquids including glycerol, hexanetriol 1,2,6, butanediol 1,3, 2‐methyl pentanediol 2,4, and n‐propyl alcohol. The data show that the pressure and temperature dependences of the dielectric time τD and the volume relaxation times τv are very similar indicating a close connection between the two processes. It is proposed here that cooperative effects cause the distribution of mechanical relaxation times in these liquids as well as the non‐Arrhenius behavior of the temperature dependence of the shear and volume viscosities. It is further suggested that structural relaxation is a rate‐determining step in the dielectric relaxation process and that the origin of the distribution of dielectric times is the distribution of structural relaxation times.

Determination of Electrolyte Apparent Molal Compressibilities at Infinite Dilution Using a High‐Precision Ultrasonic Velocimeter

Using a newly designed high‐stability sing‐around circuit ultrasonic velocities in aqueous salt solutions down to concentrations of 2 × 10−4mole/liter have been measured. Adiabatic apparent molal compressibilities at infinite dilution, and where possible standard molal compressibilities, have been determined for some aqueous solutions of tetra‐alkylammonium bromides, alkali‐metal chlorides and sulfates, and MgSO4. The determination of these quantities from precise sound velocity, volumetric, and calorimetric measurements is discussed. The practice of obtaining φKs0 from empirical extrapolation of φKs data is shown to be unreliable and unnecessary.