Steady state and time-resolved fluorescence spectroscopic techniques have been used to explore the Stokes’ shift dynamics and rotational relaxation of a dipolar solute probe in molten mixtures of acetamide (CH3CONH2) with sodium and potassium thiocyanates (Na /KSCN) at T ∼ 318 K and several other higher temperatures The dipolar solute probe employed for this study is coumarin 153 (C153) Six different fractions (f) of KSCN of the following ternary mixture composition, 075CH3CONH2 + 025[(1 − f)NaSCN + fKSCN], have been considered The estimated experimental dynamic Stokes’ shift for these systems ranges between 1800 and 2200 cm−1 (±250 cm−1), which is similar to what has been observed with the same solute probe in several imidazolium cation based room temperature ionic liquids (RTIL) and in pure amide solvents Interestingly, this range of estimated Stokes’ shift, even though not corresponding to the megavalue of static dielectric constant reported in the literature for a binary mixture of molten CH3CON

Fluorescence spectroscopic studies of (acetamide + sodium/potassium thiocyanates) molten mixtures: composition and temperature dependence.

Time-resolved fluorescence Stokes shift and anisotropy measurements using a solvation probe in [0.78CH(3)CONH(2) + 0.22{f LiBr + (1-f) LiNO(3)}] melts reveal a strong decoupling of medium dynamics from viscosity. Interestingly, this decoupling has been found to occur at temperatures ∼50-100 K above the glass transition temperatures of the above melt at various anion concentrations (f(LiBr)). The decoupling is reflected via the following fractional viscosity dependence (η) of the measured average solvation and rotation times ( and , respectively): ∝ (η∕T)(p) (x being solvation or rotation), with p covering the range, 0.20 than for , indicating a sort of translation-rotation decoupling. Multiple probes have been used in steady state fluorescence measurements to explore the extent of static heterogeneity. Estimated experimental dynamic Stokes shift for coumarin 153 in these mixtures lies in the range, 1000 < Δν(t)/cm(-1) < 1700, and is in semi-quantitative agreement with predictions from our semi-molecular theory. The participation of the fluctuating density modes at various length-scales to the observed solvation times has also been investigated.

Medium decoupling of dynamics at temperatures ~100 K above glass-transition temperature: a case study with (acetamide + lithium bromide/nitrate) melts.

Solubility of n-alkanols (C16, C18, C20) in binary solvent mixtures

Measurement and correlation of the solubility of n-alkanols (C18, C20) in n-alkanes (C7–C16)

Measurement and correlation of the solubility of 1-alkanols (C14, C16), in n-alkanes (C7C16)

This paper presents a final discussion on studies of solutions of electrolytes in molten acetamide. These studies deal with cryoscopic and ultrasonic (by shear waves) techniques and reveal the complexity of the behaviour of these systems due to strong ion-solvent interactions.

Supercooling phenomena in the binary systems: Acetamide-electrolytes

The liquid — liquid and liquid — solid equilibrium temperatures are taken for the binary systems octadecanol + A (A=dicarboxylic acids, biphenyl or (K, Na) stearate). The results are discussed and a relation connecting the composition of the eutectics with the thermodynamic properties of fusion of the components is derived from the ideal equation and compared with the experimental one.

The phase equilibria in some binary systems containing stearic alcohol

The characteristics of the eutectic points and of the miscibility gaps are submitted for binary systems composed of margaric, palmitic or pentadecanoic acid as one component and succinic, glutaric or adipic acid as the other.

The miscibility gaps in monocarboxylic-dicarboxylic aliphatic acid mixtures

The characteristics are submitted of the crystallization curves of binary systems composed of sodium or potassium stearate as one component and succinic, glutaric, adipic, pimelic, suberic or azelaic acid as the other.

The liquid-liquid and liquid-solid equilibria in some binary systems containing alkali metal stearates

The liquid-liquid equilibrium regions in binary systems, one component of which is a dicarboxylic aliphatic acid, are examined by the linear equation in (x1/x′1)=a+bT Theb term is plottedvs the difference of polar character and one graph is obtained for the different systems

G. Gioia Lobbia

Papers

Supercooling phenomena in the binary systems: Acetamide-electrolytes

The phase equilibria in some binary systems containing stearic alcohol

The miscibility gaps in monocarboxylic-dicarboxylic aliphatic acid mixtures

The liquid-liquid and liquid-solid equilibria in some binary systems containing alkali metal stearates

A correlation between the extension of the miscibility gaps and the nature of the components in some binary systems