Nandhibatla V. Sastry

Aggregation behavior of pyridinium based ionic liquids in water--surface tension, 1H NMR chemical shifts, SANS and SAXS measurements.

The aggregation behavior of short alkyl chain ionic liquids (ILs), namely 1-butyl, or 1-hexyl or 1-octylpyridinium and 1-octyl-2-, or -3-, or -4-methylpyridinium chlorides, in water has been assessed using surface tension, electrical conductance, (1)H NMR, small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) measurements. Critical aggregation concentrations (CACs), adsorption (at air/water interface) and thermodynamic parameters of aggregation have been reported. The values of CAC and area per adsorbed molecule decrease with the number of carbon atoms in the alkyl chain. The aggregation process is driven by both favorable enthalpy and entropy contributions. An attempt was made to examine the morphological features of the aggregates in water using SANS and SAXS methods. SANS and SAXS curves displayed diffuse structural peaks that could not be model fitted, and therefore, we calculated the mean aggregation numbers from the Q(max) assuming that IL molecules typically order into cubic type clusters.

Densities, viscosities, sound speeds, and excess properties of binary mixtures of methyl methacrylate with alkoxyethanols and 1-alcohols at 298.15 and 308.15 K

The densities, viscosities, and sound speeds were measured for six binary mixtures of methyl methacrylate (MMA)+2-methoxyethanol (ME), +2-ethoxyethanol (EE), +2-butoxyethanol (BE), +1-butanol (1-BuOH), +1-pentanol (1-PeOH), and +1-heptanol (1-HtOH) at 298.15 and 308.15 K. The mixture viscosities were correlated by Grunberg–Nissan, McAllister, and Auslander equations. The sound speeds were predicted by using free length and collision factor theoretical formulations, and Junjie and Nomoto equations. The excess viscosities and excess isentropic compressibilities were also calculated. A qualitative analysis of both of these functions revealed that structure disruptions are more predominant in MMA+1-alcohol than in MMA+alkoxyethanols mixtures. The estimated relative associations are found to become less in MMA+alcohol mixtures than in pure alcohols. The solvation numbers derived from the isentropic compressibility of the mixtures, considering MMA as a solvent, showed that structure making interactions are also present in MMA + alkoxyethanols in addition to the structure disruptions.

Thermodynamics of acrylic esters containing binary liquid mixtures. I. Excess volumes and isentropic compressibilities of alkyl methacrylates +n-hexane, +n-heptane, + carbon tetrachloride, + chlorobenzene, ando-dichlorobenzene at 303.15 K

Excess volumes and isentropic compressibilities of 15 binary liquid mixtures containing methyl methacrylate (MMA). ethyl methacrylate (EMA), and butyl methacrylate (BM) andn-Hexane,n-heptane, carbon tetrachloride chlorobenzene ando-dichlorobenzene are derived from the measured densities and speeds of sound at 303.15 K. The dependence of the excess volumes and the isentropic compressibilities both on the alkyl chain length and on the nature of the solvent shots the dominance of dispersing interactions in the mixtures of aliphatic hydrocarbons and specific interactions im the chlorinated solvent mixtures. The speeds of sound of binary mixtures of MMA were found to be reasonably predicted by free length and collision factor theories. An attempt is also made to estimate the individual contributions of interactional. free volume andP* effects to the overall excess volumes of binary mixtures containing MMA. The results indicate that the three factors are equally responsible for the observed values.

Thermodynamics of acrylic ester-organic solvent mixtures. V. viscosities and excess viscosities of alkyl acrylates-1-alcohol binary mixtures at 298.15 and 308.15 K

The viscosities for 12 binary mixtures of methyl acrylate (MA), ethyl acrylate (EA), and butyl acrylate (BA)-1-heptanol-1-octanol,-1-decanol, and-1-dodecanol were measured at 298.15 and 308.15 K. The excess viscosities were calculated from the results. The typical variations in the viscosities and excess viscisities of the mixtures as a function of ester mole fractions were explained in terms of structure-breaking dispersion and ester-ester-like interactions. The viscosities can be reasonably correlated in terms of Grunberg-Nissan, McAllister, and Auslander equations.

Molecular interpretation of water structuring and destructuring effects: Hydration of alkanediols

Molecular electrostatic potential (MESP) guidelines are employed for understanding the reactivity and hydration patterns in alkanediol molecules. The deeper oxygen lone pair MESP minima indicate stronger basicity of 1,n-diols and 2,4-pentanediol (2,4-PeD) as compared to that of vicinal diols. The existence and strength of the intramolecular hydrogen bond in diols are gauged in terms of the electron density at the bond saddle points. A model named electrostatic potential for intermolecular complexation (EPIC) is used for generating the structures of hydrated complexes, which are subsequently subjected to ab initio calculations at Møller-Plesset second-order perturbation level of theory. Further, the nature of water...water as well as diol...water interactions is appraised employing many-body energy decomposition analysis. It is seen that water...water interactions are more favorable in vicinal diol...6H(2)O than those in 1,n-diol...6H(2)O (n=3, 4, 5,...) complexes. Exactly opposite trends are shown by diol...water interaction energies. Thus vicinal diols, being more effective at strengthening water...water network, are expected to act as water structuring agents, whereas the non-vicinal diols are expected to be water destructuring agents.

Ultrasonic behaviour of methyl methacrylate+hydrocarbon mixtures at 298.15 and 308.15 K

Abstract The excess isentropic compressibilities, KsE for seven binary mixtures of methyl methacrylate+benzene, +o-xylene, +m-xylene, +p-xylene, +toluene, +ethylbenzene and +cyclohexane were estimated from the measured densities and speeds of sound at 298.15 and 308.15 K. The KsE values were large and positive for MMA+cyclohexane and +m-xylene, while they were negative for other mixtures. A qualitative analysis of KsE values was made in terms of molecular interactions. The speeds of sound of all the mixtures were also predicted from the free length theory (FLT) and collision factor theory (CFT).

Viscosities, speeds of sound and excess isentropic compressibilities of binary mixtures of alkyl alkanoate-hydrocarbons at 308.15 K and 318.15 K

Abstract The viscosities and speeds of sound of 15 binary mixtures of alkyl alkanoate (methyl- or ethyl propanoate and butanoate)–hydrocarbons ( n -heptane, benzene, chlorobenzene and 1,1,2,2-tetrachloroethane) have been measured at 308.15 K and 318.15 K. The mixture viscosities were correlated by Grunberg–Nissan, Hind and Auslander equations. The speeds of sound of all the mixtures were also predicted by free length theory (FLT) and collision factor theory (CFT) at 308.15 K. The excess isentropic compressibilities were calculated. The qualitative analysis of the excess isentropic compressibilities shows that disruption in dipolar associates of ester species by n -heptane in ester- n -heptane and the specific interactions of n – π and -O⋯⋯Cl-types in ester–benzene, -chlorobenzene and -1,1,2,2-tetrachloroethane mixtures are predominant.

Small Angle Neutron Scattering and Viscosity Measurements on Silicone, Ionic, and Nonionic Surfactant Mixed Systems in Aqueous Solutions

The structural features of mixed micelles of a silicone surfactant (SS-1) with a comb-like structure, and three hydrocarbon surfactants (HS), sodium dodecyl sulfate, SDS, tetradecyl trimethylammonium bromide, DTAB, and t-octylphenoxy polyethoxyethanol, TX-100 in water were investigated using dilute solution phase characteristics, small angle neutron scattering (SANS) and solution viscosity measurements. The surfactants interact with the SS-1 micelles leading to the formation of highly hydrophilic complexes. The enhanced hydrophilicity shifts the unimer ↔ micelle in favor of former. The reduced viscosities of the mixed systems of SS-1—ionic surfactants in the very low SS-1 concentrations were high and show a curvature suggesting strong repulsive interactions among the complexes. The intrinsic viscosity of mixture solutions are more than the SS-1 micellar solutions indicating enhanced hydration. The hydrophilicity increased the cloud points of SS-1 in simple surfactants.

Thermophysical Properties of Nonelectrolyte Mixtures. Densities, Viscosities, and Sound Speeds of Binary Mixtures of Methyl Methacrylate+Branched Alcohols (Propan-2-ol, 2-Methylpropan-1-ol, Butan-2-ol, and 2-Methylpropan-2-ol) at T=298.15 and 308.15 K

Measurements of the densities, viscosities, and sound speeds at T=298.15 and 308.15 K for the binary mixtures of methyl methacrylate+propan-2-ol, +2-methylpropan-1-ol, +butan-2-ol, and +2-methylpropan-2-ol are made over the complete composition range. From the measured data, excess isentropic compressibilities have been calculated. The mixture viscosities have been correlated by the Grunberg–Nissan, McAllister, and Auslander equations, while the sound speed in binary mixtures has been analyzed using free length and collision factor theories, and Junjie and Nomoto equations. The excess isentropic compressibilities, κEs are fitted to a third degree polynomial equation. The qualitative analysis of κEs have been made in terms of bulk molecular interactions. The conclusions drawn were supplemented by examining the variation of relative association and solvation numbers over the complete composition range.

Effect of Surfactants on Association Characteristics of Di- and Triblock Copolymers of Oxyethylene and Oxybutylene in Aqueous Solutions: Dilute Solution Phase Diagrams, SANS, and Viscosity Measurements at Different Temperatures

◦C in the copolymer micelles but also destabilize them and even suppress the micelle formation at high surfactant loading. DTAB destabilizes the copolymer micelles more than SDS. TX-100, being nonionic, however, forms stable mixed micelles. The block copolymer-surfactant complexes are hydrophilic in nature and are characterized by high turbid and cloud points. Triblock copolymer micelles got easily destabilized than the diblock copolymer ones, indicating the importance of the interaction between the hydrophilic E chains and surfactants. The effects of destabilization of the copolymer micelles are more dominating than the micellar growth at elevated temperatures, which is otherwise predominant in case of copolymer micelles alone.