• S K Sit

Articles written in Pramana – Journal of Physics

• Relaxation phenomena of polar non-polar liquid mixtures under low and high frequency electric field

Simultaneous calculation of the dipole moment μj and the relaxation time τj of a certain number of non-spherical rigid aliphatic polar liquid molecules (j) in non-polar solvents (i) under 9.8 GHz electric field is possible from real ε′ij and imaginary ε″ij parts of the complex relative permittivity ε*ij. The low frequency and infinite frequency permittivities ε0ij and ε∞ij measured by Purohitet al [1,2] and Srivastava and Srivastava [3] at 25, 35 and 30°C respectively are used to obtain static μs. The ratio of the individual slopes of imaginary σ″ij and real σ′ij parts of high frequency (hf) complex conductivity σ*ij with weight fractionswjatwj → 0 and the slopes of σ″ij— σ′ij curves for differentwjs [4] are employed to obtain τjs. The former method is better in comparison to the existing one as it eliminates polar-polar interaction. The hf μjs in Coulomb metre (C m) when compared with static and reported μs indicate that μs s favour the monomer formations which combine to form dimers in the hf electric field. The comparison among μs shows that a part of the molecule is rotating under X-band electric field [5]. The theoretical μtheos from available bond angles and bond moments of the substituent polar groups attached to the parent molecules differ from the measured μjs and μs to establish the possible existence of mesomeric, inductive and electromeric effects in polar liquid molecules.

• Dielectric relaxation of binary polar liquid mixture measured in benzene at 10 GHz frequency

The dielectric relaxation times $\tau_{jk}$'s and dipole moments $\mu_{jk}$'s of the binary ($j_{k}$) polar liquid mixture of N,N-dimethyl acetamide (DMA) and acetone (Ac) dissolved in benzene (i) are estimated from the measured real $\sigma_{ijk}^{'}$ and imaginary $\sigma_{ijk}^{''}$ parts of complex high frequency conductivity $\sigma_{ijk}^{*}$ of the solution for different weight fractions $w_{jk}$'s of 0.0, 0.3, 0.5, 0.7 and 1.0 mole fractions $x_{j}$ of Ac and temperatures (25, 30, 35 and 40°C) respectively under 9.88 GHz electric field. $\tau_{jk}$'s are obtained from the ratio of slopes of $\sigma_{ijk}^{''} - w_{jk}$ and $\sigma_{ijk}^{'} - w_{jk}$ curves at $w_{jk} \rightarrow 0$ as well as linear slope of $\sigma_{ijk}^{''} - \sigma_{ijk}^{'}$ curves of the existing method (Murthy et al, 1989) in order to eliminate polar-polar interaction in the latter case. The calculated 𝜏's are in excellent agreement with the reported 𝜏's due to Gopalakrishna's method. $\mu_{jk}$'s are also estimated from slopes 𝛽's of total conductivity $\sigma_{ijk} - w_{jk}$ curves at $w_{jk} \rightarrow 0$ and the values agree well with the reported 𝜇's from G.K. method. The variation of $\tau_{jk}$'s and $\mu_{jk}$'s with $x_{j}$ of Ac reveals that solute-solute molecular association occurs within $0.0-0.3x_{j}$ of Ac beyond which solute-solvent molecular association is predicted. The theoretical dipole moments $\mu_{\text{theo}}$'s are calculated from bond angles and bond moments to have exact 𝜇's only to show the presence of inductive, mesomeric and electromeric effects in the substituent polar groups. The thermodynamic energy parameters are estimated from ln($\tau_{jk}T$) against $1/T$ linear curve from Eyring's rate theory to know the molecular dynamics of the system and to establish the fact that the mixture obeys the Debye-Smyth relaxation mechanism.

• Dielectric behaviour of some amides and formamides dissolved in nonpolar solvents under static electric ﬁeld

Structural and associational aspects of polar amides (𝑗) like formamide, acetamide, Nmethyl acetamide (NMA), N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMA) and acetanilide dissolved in the nonpolar solvent (𝑖) benzene or 1,4-dioxan have been estimated from the measured static relative permittivity $\varepsilon_{0ij}$ and high-frequency permittivity $\varepsilon_{\infty ij}$ at different weight fractions $w_j$s of polar solute at 35°C under static electric ﬁeld using Debye model of polar liquid molecule. The static dipole moments $\mu_s$s are compared with $\mu_j$s reported from conductivity method and theoretical $\mu_{\text{theo}$s to get exact $\mu_{\text{cal}} \cdot \mu_{\text{theo}$s of the molecules are predicted from the available bond angles and bond moments where difference in electron afﬁnity exists between two adjacent atoms of a polar group due to inductive, mesomeric and electromeric effects in them. Solute–solute molecular association for NMA in benzene and solute–solvent association for other amides are ascertained to arrive at their conformational structures.

• Dielectric relaxation of ethanol and 𝑁-methyl acetamide polar mixture in C6H6 at 9.90 GHz

Debye relaxation times $(\tau_{jk})$ and dipole moments $(\mu_{jk})$ of binary ($jk$) polar mixtures of ethanol (EtOH) and 𝑁-methyl acetamide (NMA) dissolved in benzene(i) are studied by studying conductivity of solution at 9.90 GHz for different temperatures, different mole fractions ($x_j$) of ethanol and different weight fractions $(w_{jk})$ of the mixtures, respectively. The variation of $\tau_{jk}−x_j$ from linear slope of imaginary ($\sigma''_{ijk}$) against real ($\sigma'_{ijk}$) part of total conductivity ($\sigma^{\ast}_{ijk}$) curve reveals solute–solute (dimer) or solute–solvent (monomer) molecular associations up to $x_j$ = 0.0−0.3 and thereafter, solute–solvent molecular associations. $\tau_{jk}$s from the ratio of slopes of $\sigma''_{ijk}$−w_{jk}$and$\sigma'_{ijk}$−w_{jk}$ curves exhibit solute–solvent molecular association for all $x_j$s which are consistent with the $\mu_{jk}−x_j$ curves at all temperatures except at 35°C. This signifies the validity of both the proposed methods in estimating 𝜏 and 𝜇. The molecular dynamics of the polar mixture are ascertained from Eyring rate theory. Theoretical dipole moments from bond angles and bond moments ($\mu_{\text{theo}}$) are also calculated to predict associational aspects.

• # Pramana – Journal of Physics

Volume 95, 2021
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