• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1452-1458
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• 2009

The change in the electronic absorption and emission energy of 7-aminocoumarin derivatives in binary solvent mixtures has been studied. The electronic transition energy along with the Stokes' shift is correlated with the orientation polarizability of the solvent as well as the empirical solvent polarity parameters $E_T$ (30). It is observed that the emission peak shift traces the change of $E_T$ (30) value very closely in binary solvent mixtures. The emission transition more strongly depends on the solvent polarity than the absorption, which indicates the dipole moment gets larger on excitation. From the dependence of the Stokes’ shift of 7-aminocoumarins with the solvent polarity parameters and the ground state dipole moment obtained by the semi-empirical calculations, the excited state dipole moment was estimated. The fluorescence lifetime change of 7-aminocoumarins in binary solvent mixtures was measured and the results are explained in terms of molecular conformation and solvent polarity. The study indicates the empirical solvent polarity $E_T$ (30) is a good measure of microscopic solvent polarity and it probes in general the non-specific solvent interactions.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.613-620
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• 1992

The solvent-dependent photophysical properties of 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid(4BPCA), which have a pre-twisted conformation in the ground state, have been investigated. The fluorescence spectra of 4BPCA show vibrational structure with a non-mirror image to the absorption spectra in nonpolar solvent while those of 2BPCA show no structure even in nonpolar solvents. As the solvent polarity increases, the fluorescence spectra become diffuse and broad with a strong red shift resulting in the large Stokes shift. The large fluorescence Stokes shift of BPCA's in polar solvent is also partially due to an intramolecular charge transfer (ICT) interaction in the excited state, as demonstrated by the large dipole moment in the excited state (7.6-10.6 D). The fluorescence decay behaviors of BPCA's (decay-times and their pre-exponential factors) also depend on solvent polarity in agreement with the solvent-dependent properties of the steady-state fluorecence. The data have been discussed in terms of change in the excited-state potential energy surface with respect to change of the dihedral angle of biphenyl moiety.

• Korean Chemical Engineering Research
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• v.56 no.1
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• pp.14-23
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• 2018

The effect of dodecylbenzene sulfonic acid (DBSA) with different addition amount of DBSA ($M_{DBSA}$), temperatures and solvent-to-oil ratio (SOR, v/v) on asphaltene aggregation in a solvent deasphalting system was investigated. Increasing the $M_{DBSA}$ at SOR 10 and $55^{\circ}C$ caused the asphaltene removal ratio (ARR) to increase first, then maximize at 1 wt% of $M_{DBSA}$ and then decrease continuously. Based on the SARA (saturate, aromatic, resin, asphaltene) composition, the adsorption amount of DBSA on the asphaltene surface and the self-aggregation of the DBSA, the reason for the change in ARR with $M_{DBSA}$ was found due to the adsorption mechanism. In addition, the asphaltene-resin-DBSA colloidal size confirmed the change of adsorption behavior between the asphaltene and DBSA. Based on the results of this study, a hypothetical adsorption mechanism of DBSA on asphaltene aggregation in the solvent deasphalting system was conceived of and proposed.

• Applied Chemistry for Engineering
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• v.25 no.2
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• pp.209-214
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• 2014

In this paper, the rheological behaviors and non-Newtonian characteristics of maltenes which is effected by hydrocarbon solvent type, solvent mixing ratio, temperature and shear rate was measured and compared with oil sands bitumen. Maltenes was made by SDA (solvent deasphalting) method from oil sands bitumen. Oil sands bitumen had apparent viscosities of $800{\sim}150000mPa{\cdot}s$ measured at a shear rate of $50sec^{-1}$ in the range of $25{\sim}85^{\circ}C$ and showed yield stress of 0.1~0.3 Pa at the temperatures below $35^{\circ}C$. All the oil sands bitumen and maltenes exhibited a shear-thinning, i.e. pseudoplastic behavior and apparent viscosity of maltenes decreased with decreasing carbon numbers of hydrocarbon solvent. The change in apparent viscosity with temperature could be described by the simple Guzman-Andrade equation, and maltene viscosities were decreased as the mixing ratio of n-pentane was raised. Also, all maltenes approached to Newtonian fluid as temperature were increased. the degree of pseudoplasticity was enhanced with decreasing carbon number of solvent.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.615-621
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• 2013

Solvolyses of isobutyl chloroformate (4) in 43 binary solvent mixtures including highly aqueous media, water, $D_2O$, $CH_3OD$, 2,2,2-trifluoroethanol (TFE) as well as aqueous 1,1,1,3,3,3-hexafluoro-isopropanol (HFIP) solvents were performed at $45^{\circ}C$, in order to further investigate the recent results of D'Souza, M. $J^1$. et al.; solvolyses of 4 are found to be consistent with the proposed mechanism ($Ad_E$). The variety of solvent systems was extended to comprise highly ionizing power solvent media ($Y_{Cl}$ > 2.7 excepted for aqueous fluorinated solvents and pure TFE solvent) to investigate whether a mechanistic change occurs as solvent compositions are varied. However, in case of 18-solvent ranges having aqueous fluorinated solvent systems (TFE-$H_2O$ and HFIP-$H_2O$) and/or having $Y_{Cl}$ > 2.7 solvent systems, the solvent effect on reactivity for those of 4 are evaluated by the multiple regression analysis as competition with $S_N2$ - type mechanism. And in pure TFE and 97 w/w % HFIP solvents with high $Y_{Cl}$ and weak $N_T$, these solvolyses are understood as reactions which proceed through an ionization ($S_N1$) pathway.

• Bulletin of the Korean Chemical Society
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• v.8 no.1
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• pp.31-39
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• 1987

By using a complete rate constant($k_e$) which treats a solvent (water) as a reactant, and a conventional rate constant($k_c$), which ignores the solvent in describing the rate, the parameters ${\Delta}V^{\neq}_s,\;{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ were introduced. These quantities represent the volume change, the enthalpy change, and the entropy change accompanying the electrostriction which occurs when solvent molecules condense on the activated complex. The authors measured the rates of the solvolysis of benzoyl chloride in water-acetone mixtures at $15^{\circ}$ to $30^{\circ}C$ and 1 bar to 2500 bars. Applying the authors' theory to the experimental results, the parameters, ${\Delta}V^{\neq}_s,\;{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ were evaluated, and it was found that they are all negative, indicating that water dipoles condense on the activated complex. They also proposed the following equations: ${\Delta}H^{\neq}_c\;=\;{\Delta}H^{\neq}_e\;+\;{\Delta}H^{\neq}_s\;and\; {\Delta}S^{\neq}_c\;=\;{\Delta}S^{\neq}_e\;+{\Delta}S^{\neq}_s\;,\;where\;{\Delta}H^{\neq}_c\;and\;{\Delta}H^{\neq}_c\;and\;{\Delta}S^{\neq}_s $are the activation enthalpy change and the activation entropy change for the conventional reaction rate, respectively, and ${\Delta}H^{\neq}_e$ and ${\Delta}S^{\neq}_e$ are the corresponding quantities for the complete reaction rate. The authors proposed that for the $SN_1$ type, all the quantities, ${\Delta}V^{\neq}_s,\;{\Delta}S^{\neq}_s\;,{\Delta}H^{\neq}_s\;and\;{\Delta}S^{\neq}_s$ are comparatively large, and for the $SN_2$ type, these quantities are smaller than for the $SN_1$ type, and occasionally the case ${\Delta}S^{\neq}_e$ < 0 occurs. Using these criteria, the authors concluded that at high temperature, high pressure and for a high water content solvent, the SN_1$ type mechanism predominates whereas in the reversed case the $SN_2$M type predominates.

• Journal of the Korean Society of Clothing and Textiles
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• v.20 no.3
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• pp.467-480
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• 1996

Interactions between PET POY and solvents were estimated by the changes in microstructure and surface morphology. Changes in microstructure and surface morphology by the solvent treatments were: an increase in crystallite size, a decrease in interplanar spacing, a change in degree of orientation of crystalline region, a change in surface characteristics.

• Bulletin of the Korean Chemical Society
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• v.19 no.5
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• pp.561-564
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• 1998

Solvent effects on the reactions of DANSYL and BANSYL chlorides with substituted pyridines have been investigated using two parameters of Taft's solvatochromic correlation and four parameters of Kirkwood-Onsager, Parker, Marcus, Hildebrand equation. The acetonitrile molecules accelerate charge separation of the reactants and stabilize the transition state. The coefficient of the solvent parameters provide a good information to predict and to analyze the reaction mechanism. The nucleophilic substitution reaction of DANSYL and BANSYL chlorides with substituted pyridines are ruled by the contribution of the change in dipole moment term and polarity-polarizability term.

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1207-1210
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• 2003

The effect of solvent structure on the slope in the plot of ln K vs. solute carbon number was examined. It was found that the free energy of methylene group transfer from the gas phase into a solvent was always negative and that the absolute magnitude of interaction free energy between the methylene group and the solvent was always larger than the absolute magnitude of cavity formation free energy of the methylene group in the solvent. Thus, the slope in the plot of ln K vs. solute carbon number was always positive and its value decreases with increase of solvent polarity since the cavity formation energy of the CH₂ unit increases with increase of solvent polarity while the dispersive interaction energy of the CH₂ unit is virtually invariant. We also examined the effect of sequential addition of CH₂ unit to a solvent molecule upon ln K for three homologous series of solvents: n-alkanes, n-alcohols, and n-nitriles. Characteristic trends in the plots of ln K vs. solvent carbon number were observed for individual solvent groups. A decrease of ln K with solvent carbon number was observed for n-alkanes. An abrupt increase in ln K followed by levelling off was observed for n-alcohols while a final slight decrease in ln K after an abrupt increase followed by rapid levelling off was noted for n-nitriles. All of theses phenomena were found related to variation in cavity formation energy. It was clearly shown that a structural change of a polar solvent by sequential addition of CH₂ units causes an abrupt polarity decrease initially, then gradual levelling off, and finally, conversion to a virtually nonpolar solvent if enough CH₂ units are added.

• Macromolecular Research
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• v.16 no.7
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• pp.631-636
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• 2008

The intrinsic viscosities were determined for poly(DL-lactic acid) (PDLLA) solutions in 1,2-dialkyl phthalate at temperatures ranging from 30 to $60^{\circ}C$. A series of dialkyl phthalate, in which the alkyl group was changed from methyl to propyl, was used as the solvent to control the solvent quality systematically. The intrinsic viscosity of the PDLLA solution was higher in the better quality solvent, with a higher molecular weight of PDLLA, and at lower temperatures. The unperturbed dimensions of the PDLLA molecule and polymer-solvent interaction parameter of PDLLA in dialkyl phthalate were deduced using extrapolation methods based on the temperature-dependent intrinsic viscosities. Slight shrinkage in the unperturbed chain dimension was observed, which resulted from a change in polymer conformation with temperature. It was also observed that the polymer-solvent interaction became more favorable with the dialkyl phthalate containing a shorter alkyl chain.