1. Presented By: Dr. Debashis Das Department of Chemistry
Van der Waals clusters detection through the activation of viscous flow derived properties in isobutyric acid + water binary mixtures near and far away from critical temperature.
Subject:
Presented By: Dr. Debashis Das
Department of Chemistry
Dinhata College
Dinhata, Cooch Behar,

2. INTRODUCTION
Among the physico-chemical properties viscosity is a valuable tool for developing new theoretical models to understand the molecular interactions in the binary solvent system. Recently, the derivation of different thermodynamic parameters from experimental values of various physical properties and their meaningful correlations with one another introduces a new framework of scientific research on binary liquid mixtures. In this presentation values of different thermodynamic properties along with excess partial molar properties were deduced from various methods and was found that structural order is not much destroyed by the activation process, and consequently bonds are not so much broken between the associated molecules to form smaller clusters (IBA:8 W). er

3. Description of the solvent
Table I. Comparison of Experimental Densities ρ (10−3 kg·m−3) and Viscosities η (10−3 Pa·s) with the Literature Data for Pure Components at Different Temperatures from T = ( to )K
Water Isobutyric acid
ρ (10−3 kg·m−3) η (10−3 Pa·s) ρ(10−3 kg·m−3) η (10−3 Pa·s)
T (K) Exptl Lit. (1) Lit. (2) Exptl Lit. (2) Exptl Lit.(1) Exptl Lit.(1)
Experimental Procedure:
Density : Ostwald-Sprengel type Pycnometer,
Volume 25 cm3 , Diameter 1mm
Viscosity: Suspended level Ubbelohde Viscometer,
Water thermostat controlled to ±0.01K
1.A.K.Covington, T.Dickinson,Phy. Chem of Organic Solvent System, Plenum Press,
New York, 1973, chapter-I
2. R. C. Weast and M. J. Astle, in CRC Handbook of Chemistry and Physics, 60th edn. (CRC Press,Boca Raton, FL, 1980).

4. Excess viscosity : Δη = ηmix − (x1η1 + x2η2) (1)
∆η vs x1 shows that the maximum value of ∆ η is obtained in the mole fraction region of 0.10–0.45 with a critical region centered around xc =
Fig. 1. Viscosity deviation (η) for isobutyric acid + water mixtures versus the mole fraction x1 of IBA at the temperatures: (◊) K; (◦) K; (■ ) K; (□) K and ( ∆) K.
3. N. Ouerfelli, M. Bouanz, Journal of Solution Chemistry, Vol. 35, No. 1, January 2006

5. Correlation between the Arrhenius activation energy Ea (kJ·mol-1) of viscosity and the logarithm of the Arrhenius entropic factor (lnAs) for isobutyric acid (1) + water (2) mixtures in the temperature range (302.15–313.15) K.
ln h = lnAs + Ea/RT (2)
The pre-exponential entropic factor (As), equivalent to the viscosity at infinite temperature, is very closely related to the viscosity of the same system in the vapor phase at the normal boiling temperature and at the same pressure. It can also be compared with the viscosity of the fluid in the ideal state for pure components as well as their mixtures.
Fig. 2 (filled square), experimental data points; (solid line), linear least squares fit of Eq 2
Conclude that there are two association-type structures in two distinct ranges separated by the critical composition around xC = , where the Arrhenius activation energy Ea(x1) and the logarithm of the Arrhenius entropic factor
Rln(AS) take their maximum values (Fig. 2).
4. M. Dallel, D. Das, E.S.Hmida, N. Al-Omair, A. Al-Arfaj, N. Ouerfelli. Phys. & Chem. of Liquids, 52, (3), 2014, 442–451.

6. absolute reaction rate theory
In case of liquid phase Eyring et al. [5] and Ali et al. [3] relates viscosity with the free energy (DG*) of activation of viscous flow:
(3)
The temperature dependence of (DG*) leads us to determine the enthalpy DH* and entropy DS* of activation of viscous flow :
DG* = DH* - T DS* (4)
Inspection of the Ea values and those of the enthalpy (ΔH*) of activation of viscous flow shows that the Ea and Δ H* values are very closely related
Δ H* = Ea - δH* (5)
the entropy of activation of viscous flow (ΔS*) that is closely correlated with the difference between the Arrhenius entropic factor (-RlnAS) and an entropy increment (Δ S*)
DS* = - Rln As + δS * (6)
Considering the quasi-equality between the Arrhenius activation energy Ea and the enthalpy of activation of viscous flow ∆H*, and between logarithm of the Arrhenius entropic factor -Rln(As) and the entropy of activation of viscous flow ∆S* we can assume that Ea(x1) is approximately a thermodynamic function, then we can define the partial molar quantities Y1 and Y2 for IBA (1) and W(2), respectively, through the following equations
5. H. Eyring and M.S. John, Significant liquid structure. (Wiley, New York 1969).
6. A. Ali, A.K.Nain, S.Hyder, J. Indian Chem. Soc. 5, , 1998.
7. D. Das, A. Messandi, Z. Barhoumi, N.Ouerfelli, J. Solution Chem. 41,1555–1574,(2012).

7. Variation of ∆G*E with x1 of IBA
shows that in the water-rich region and near the critical composition (from x1 = 0 to xc ≈ ) the ∆G∗ values exponentially increase with x1 which is an effect on ∆G∗ resulting from the strong correlation between the water and isobutyric acid molecules in the vicinity of xc. For a fixed temperature and away from xc, the mole fraction has no significant influence on the ∆G∗ values.
Fig. 3. Gibbs energies of activation (∆G∗E) for isobutyric acid + water mixtures
versus the mole fraction x1 of IBA at the temperatures:(◊) K;
(◦) K; (■) K; (□) K and (∆) K.
3. N. Ouerfelli, M. Bouanz, Journal of Solution Chemistry, Vol. 35, No. 1, January 2006

8. Variation of ∆H* & ∆S* with x1 of IBA:
By assuming that the activation parameters ∆H* and ∆S* are independent of temperature, we can obtain values of these parameters for each mixture composition (x1, x2) by plotting ln (ηmixV/hNA) vs 1/T,
Slope = ∆H*/R & Intercept= -∆S*/R
both exponentially increase with the mole fraction x1 of IBA at the critical composition xc and then decrease
smoothly to the ∆H1* and ∆S1*of the pure IBA.
Fig. 4. The enthalpy (∆H*) and entropy (∆S*) of activation of viscous flow for isobutyric acid + water mixtures versus the mole fraction x1 of IBA at the temperatures: (◊) K;
(◦) K; (■) K; (□) K and (∆) K.
3. N. Ouerfelli, M. Bouanz, Journal of Solution Chemistry, Vol. 35, No. 1, 2006

9. Correlation between the entropy and enthalpy
The negative values of ∆S∗ suggest that structural order is not destroyed much by the activation process, in as much as bonds are not broken between the associated
molecules to form smaller units. These distinct behaviors are clearly shown when the correlation between disorder and order is plotted in Fig. 5.
Fig. 5. Correlation between the entropy (∆S*) and enthalpy (∆H*) of activation of viscous flow for isobutyric acid + water mixtures versus the mole fraction x1 of IBA.
3. N. Ouerfelli, M. Bouanz, Journal of Solution Chemistry, Vol. 35, No. 1, 2006

10. excess molar properties were correlated by the Redlich–Kister equation :
where Qj (j=1,2,3…..) denotes the shear viscosity deviation
The concordance with experimental data requires more parameters (n in Eq. (7)), especially for ∆η. For the mixtures that show a critical behavior, the correlation fails. This is not surprising, considering that the R–K model does not consider all the possible interactions occurring in the studied mixtures, such as the critical behavior around xc∼ mole fraction and the dissociation of IBA by water in the very dilute region.
Fig. 6. The Redlich–Kister function f2(x1) for the ratio η/(x1(1− x1)) of the viscosity deviation for isobutyric acid + water mixtures versus the mole fraction x1 of IBA at the temperatures: (◊) K; (◦) K; (■) K; (□) K and (∆) K

11. Partial Molar Activation Energy
(6)
(7)
Where Yi represents the partial molar activation energy Ea1 and Ea2 or the partial molar quantity relative to the entropic factor of Arrhenius –R·ln(Asi).
Ea value increases with x1 of IBA shows maximum at resulting strong interaction between W and IBA. This fact suggests that the structural order is not much destroyed by the activation process, and consequently most bonds are not broken between the associated molecules to form smaller clusters (IBA:8 W).
Figure 7 Arrhenius activation energy Ea /(kJ·mol-1) and partial molar activation energies of viscosity (Eqs. 6,7) Eai /(kJ·mol-1) for {isobutyric acid (1) + water (2)} mixtures as a function of the mole fraction of isobutyric acid (x1) over the temperature range ( to ) K. (filled triangle), Ea(x1); (filled circle), Ea1(x1); (open circle), Ea2(x1)

12. Excess partial molar enthalpy:
Figure.8. The excess partial molar enthalpy (∆H*) / kJ·mol-1 of activation of viscous flow of IBA (1) and W (2) respectively for the system of (IBA-W) mixtures versus mole fraction x1 in the temperatures range (from to ) K.

13. Correlation between the partial molar Arrhenius activation energies
The very dilute region can be associated with the thermodynamic dissociation equilibrium. In fact, in the dissociation α that is not negligible (0.05<α<1) highly dilute region (0<x1<0.02 and molar concentration C1 less than 1 mol L-1), we must take into account the ionization of IBA and the fractional ,
(CH3)2CH2COOH ↔ (CH3)2CH2COO- + H+
α = (CH3)2CH2COO- / C1 = 10-pH / C1
where the IBA molarity is C1<0.15 mol L-1 which corresponds to mole fraction x1< We add that this acid dissociation region is clearly delimited in Fig. 9.
Fig. 9. Correlation between Ea1(x1) and Ea2 (x1) for {isobutyric acid (1) + water (2)} mixtures over the temperature range (302.15–313.15) K
8. D.Das, H.Salhi, M. Dallel, Z. Trabelsi, A.A. Al-Arfaj, N. Ouerfelli, J. Solution Chem, 44, 54-66, 2015.

14. Conclusions:
The changes in curvature were found for all the studied thermodynamic and excess properties in the very dilute region of the IBA solutions. Distinguishing behaviors are observed, especially near the critical temperature, limited by the critical composition.
In fact, in the highly dilute region, isobutyric acid is weakly dissociated by water and the negative values of ∆S∗ suggest that structural order is not destroyed much by the activation process, inasmuch as bonds are not broken between the associated molecules to form smaller units.
If we neglect the observed anomaly from IBA dissociation occurring in water at high dilution (x1 < 0.02), we can conclude that there are two association-type structures limited by the critical composition xc ≈ (corresponding approximately to one IBA molecule + eight water molecules to form small clusters)
From an analysis of the results, it is clear that the complexity of the critical mixtures and the acid dissociation of IBA are reflected in the reduced excess functions. It is obvious that the structure of water is very much affected by
IBA and this phenomenon is more pronounced at the critical composition in
a larger temperature range, even far away from the critical temperature.

15. ACKNOWLEDGEMENT:
The author is grateful to Prof. N. Ouerfelli (Université de Tunis El Manar, Laboratoire de Biophysique et Technologies Médicales, LR13ES07, Institut Supérieur des Technologies Médicales de Tunis, 9 Avenue Dr. Zouhaier Essafi 1006 Tunis, Tunisia) and his research scholars for some calculations made by their computer programmes and helpful suggestions.

16. Our contributions:
D. Das,N. Ouerfelli , The Relative Reduced Redlich-Kister and Herráez Equations for Correlating Excess Properties of N,N-Dimethylacetamide + Formamide Binary Mixtures atTemperatures from K to K. Journal of Solution Chemistry 41(8), , 2012
D. Das*, A. Messaâdi 2, Z. Barhoumi 2, N. Ouerfelli 2,3 The Relative Reduced Redlich-Kister Equations for Correlating Excess Properties of N,N-Dimethylacetamide + Water Binary Mixtures at Temperatures from K to K. Journal of Solution Chemistry, 41(9), , 2012
D. Das*, Z. Barhoumi and N.Ouerfelli, The relative reduced Redlich–Kister equations for correlating excess properties of N,N-dimethylacetamide + 2-methoxyethanol binary mixtures at temperatures from K to K., Physics and Chemistry of Liquids,Vol. 50, No. 3, 346–366, 2012,
D. Das,*, Z. Barhoumi, N. Ouerfelli, The reduced Redlich-Kister equations for correlating volumetric and viscometric properties of N,N-dimethylacetamide + dimethylformamide binary mixtures at temperatures from K to K., Physics and Chemistry of Liquids, Vol. 50, No. 6, 712–734, 2012.
D. Das*, A. Messaâdi, N. Dhouibi, N. Ouerfelli., Investigations of the Reduced Redlich-Kister Equations for Correlating Excess Properties of N,N-Dimethylacetamide + 2-Ethoxyethanol Binary Mixtures at Temperatures from K to K., Physics and Chemistry of Liquids, Vol. 50, No. 6, 773–797, 2012
A. Messaâdi, N. Ouerfelli*, D. Das, H. Hamda, M.A. Hamzaoui , Correspondence between Grunberg-Nissan, Arrhenius and Jouyban-Acree Parameters for Viscosity of Isobutyric Acid + Water Binary Mixtures from K to K., Journal of Solution Chemistry, Vol 41, 2186–2208, 2012.

17. Our contributions continued
7. D. Das *, A. Messaâdi, N. Dhouibi, N. Ouerfelli, A.H.Hamzaoui, Viscosity Arrhenius activation energy and derived partial molar properties in N,NDimethylacetamide + Water Binary Mixtures at Temperatures from K to K., Physics and Chemistry of Liquids, Vol. 51, No. 5, 677–685, 2013.
8. M. Hichri, D. Das*, A. Messaâdi, E.S. Bel Hadj Hmida, N. Ouerfelli, I. Khattech, Viscosity Arrhenius activation energy and derived partial molar properties in of N,N-Dimethylacetamide + 2-Ethoxyethanol Binary Mixtures at Temperatures from K to K. Physics and Chemistry of Liquids, Vol. 51, No. 6, 721–730, 2013.
9. M. Dallel*, D.Das, E.S. Bel Hadj Hmida, N.A. Al-Omair, A.A. Al-Arfaj & N. Ouerfelli , Derived partial molar properties investigations of viscosity Arrhenius parameters in formamide + N,N-dimethylacetamide systems at different temperatures, . Physics and Chemistry of Liquids, Vol. 52, (3), pp 442–451, 2014.
10. N. Ouerfelli, D. Das*, H. Latrous, M. Ammar, J. Oliver, Transport behaviour of the lanthanide 152Eu(III), Gd(III) and 170Tm(III) and transplutonium element 254Es(III), 244Cm(III), 241Am(III),249Cf(III) and 249Bk(III) ions in aqueous solutions at 298 K, Journal of Radioanalytical and Nuclear Chemistry, Vol 300 issue 1 pp, , 2014.
11. Z. Trabelsi , M. Dallel , H. Salhi, D. Das*, N.A. Al-Omair, N. Ouerfelli , On the viscosity Arrhenius temperature for methanol + N,N-dimethylformamide binary mixtures over the temperature range from K to K. Physics and Chemistry of Liquids, Accepted, 2014
12. N. Dhouibi*, M. Dallel, D. Das, M. Bouaziz, N. Ouerfelli, A.H. Hamzaoui, Notion of Viscosity Arrhenius temperature for N,N-dimethylacetamide with N,Ndimethylformamide binary mixtures and its pure components, Physics and Chemistry of Liquids, Accepted, 2014
13. D. Das *, H. Salhi, M. Dallel , Z. Trabelsi, A.A. Al-Arfaj, N. Ouerfelli, Viscosity Arrhenius activation energy and derived partial molar properties in isobutyric acid + water binary mixtures near and far away from critical temperature from K to K., Journal of Solution Chemistry, Accepted, 2014.

18. Thank You all