**5. References**


A nonlinear hook-type profile of rotational reorientation times of the probe as a function of viscosity is observed for all the dyes in binary mixtures, with the rotational reorientation times being longer in organic solvent rich zone, compared to the corresponding isoviscous point in water rich zone. This is attributed to strong hydrogen bonding between the solutes and DMSO or propanol molecules. Theoretical models mimic this trend qualitatively, though GW & DKS models invariably predict a reduced friction and illustrate a hairpin profile bending downwards. Thus they underestimate the friction experienced by the probe. The dual valuedness of τr at isoviscous points near the organic solvent rich zone were attributed to different contributions of dielectric friction at these compositions and to strong

In general, the theoretical models: hydrodynamic as well as those based on dielectric friction do not adequately and precisely describe the experimental observations. The theoretical description of solute-solvent interaction to explain the experimental observations is yet to evolve. The failure of the theoretical models, to explain the experimental results

The author acknowledges the encouragement and support of Profs. M.I. Savadatti and B.G. Mulimani. Thanks are also due to Dr. James R.M., K.H. Nagachandra and M.A. Shivkumar for their timely help and financial support from Council of Scientific & Industrial Research

Alavi, D.S., Hartman, R.S. & Waldeck, D.H., 1991a, A test of continuum models for dielectric

Alavi, D.S. & Waldeck, D.H., 1991b*,* Rotational dielectric friction on a generalized charge

Alavi, D.S., Hartman, R.S. & Waldeck, D.H., 1991c, The influence of wave vector dependent

Alavi, D.S. & Waldeck, D.H., 1993, Erratum: Rotational dielectric friction on a generalized

Anderton, R.M. & Kauffman, J.F., 1994, Temperature-Dependent Rotational Relaxation of

Anfinrud, P.A., C. Han, T. Lian and R. M. Hochstrasser, 1990, Evolution of the transient vibrational spectrum following short-pulse excitationJ. Phys. Chem. *94, 1180-84*  Backer, S.D., Dutt, G.B., Ameloot, M., Schryver, F.C.D., Müllen, K. & Holtrup, F., 1996,

tert-butylterrylene in Alkanes and AlcoholsJ. Phys. Chem. *100, 512-518*  Barbara, P.F. & Jarzeba, W., 1990, Ultrafast Photochemical Intramolecular Charge and

G.S. Hammond, K. Gollnick, John Wiley & Sons, Inc.,, USA

friction. Rotational diffusion of phenoxazine dyes in dimethylsulfoxide *J. Chem.* 

dielectric properties on rotational friction. Rotational diffusion of phenoxazine dyes

Diphenylbutadiene in n-Alcohols: A Test of the Quasihydrodynamic Free Space

Fluorescence Anisotropy of 2,5,8,11-Tetra-tert-butylperylene and 2,5,10,13-Tetra-

Excited State Solvation in *Adv. in Photochem.* Vol.15, pp. 1-68, Eds: D.H. Volman,

quantitatively in specific cases, calls for the formulation of molecular based theories.

hydrogen bonding.

**4. Acknowledgment** 

**5. References** 

and University Grants Commission, New Delhi.

distribution *J. Chem. Phys.* 94, 6196-6202

charge distribution *J. Chem. Phys.* 98, 3580-82

Model J. Phys. Chem. *98, 12117-12124*

*Phys.* 94, 4509-20

*J. Chem. Phys.* 95, 6770-83


Rotational Dynamics of Nonpolar and Dipolar

Molecules in Polar and Binary Solvent Mixtures 221

Dutt, G.B. & Raman, S., 2001, Rotational dynamics of coumarins: An experimental test of

Dutt, G.B. & Ghanty, T.K. 2003, Rotational Diffusion of Coumarins in Electrolyte Solutions:

Dutt, G.B. & Ghanty, T.K., 2004, Is molecular rotation really influenced by subtle changes in

Einstein, A., 1906, On the Theory of Brownian Motion (Zur Theorie der Brownschen

Eisenthal, K. B. 1975, Studies of chemical and physical processes with picosecond lasers Acc.

Elsaesser, T. & Kaiser, W., 1991, Vibrational and Vibronic Relaxation of Large Polyatomic

Evans, G.T., Cole, R.G. & Hoffman, D.K., 1982, A kinetic theory calculation of the

Evans, G.T. & Evans, D.R., 1984, Kinetic theory of rotational relaxation in liquids: Smooth

Fee, R.S. & Maroncelli, M., 1994, Estimating the time-zero spectrum in time-resolved emmsion measurements of solvation dynamics *Chem. Phys.* 183, 235-47 Fee, R.S., Milsom, J.A. & Maroncelli, M., 1991, Inhomogeneous decay kinetics and apparent

Felderhof, B.U., 1983, Dielectric friction on a polar molecule rotating in a fluid *Mol. Phys.* 48, 1269-81; Dielectric friction on an ion rotating in a fluid *Mol. Phys.* 48, 1283-88 Fleming, G.R., Morris, J.M. & Robinson, G.W., 1976, Direct observation of rotational

Fleming, G.R., Knight, A.E.W., Morris, J.M., Robbins, R.J. & Robinson, G.W., 1977,

Fleming, G.R., 1986, *Chemical Applications of Ultrafast Spectroscopy*, Oxford University Press:

Fox, F. & Whittingham, K.P., 1974, Component interactions in aqueous dimethyl sulphoxide

Garg, S.K. & Smyth, C.P., 1965, Microwave Absorption and Molecular Structure in Liquids.

Goulay, A.M., 1983, Rotational relaxation of OCS in n‐alkanes: Collective and collisional

Gustavsson, T., Cassara, L., Marguet, S., Gurzadyan, G., van der Meulen, P., Pommeret, S. &

Geirer, A. & Wirtz, K., 1953, Molecular theory of microfriction *Z. Naturforsch.* A8, 532-38 Gordalla, B.C. & Zeidler, M.D., 1986; Molecular dynamics in the system water-

Rotational diffusion of the mode-locking dye dodci and its photoisomer *Chem.* 

LXII. The Three Dielectric Dispersion Regions of the Normal Primary Alcohols *J.* 

dimethylsulphoxide *Mol. Phys.* 59*,* 817-28; 1991, NMR proton relaxation and chemical exchange in the system H16 2O/H17 2O-[2H6]dimethylsulphoxide, *Mol.* 

spherocylinder and rough sphere models *J. Chem. Phys.* 81, 6039-43 Evans, G.T., 1988, Translational and rotational dynamics of simple dense fluids *J.Chem. Phys.*

solvent relaxation at low temperaturesJ. Phys. Chem. *95, 5170-81* 

diffusion by picosecond spectroscopy *Chem. Phys.* 17, 91-100

orientational correlation time of a rotorlike molecule in a dense fluid of spheres *J.* 

dielectric friction theories *J. Chem. Phys.* 114, 6702-13

Molecules in Liquids Annu. Rev. Phys. Chem. *42, 83-107*

The Role of Ion Pairs *J. Phys. Chem B.* 107, 3257-64

molecular shape? *J. Chem. Phys.* 121, 3625-31

Bewegung) *Ann. Phys.* 19, 371-81

Chem. Res. 8, 118-24

*Chem. Phys.* 77, 3209-20

88, 5035-41

*Phys. Lett.* 49, 1-7

*Phys.* 74, 975-84

*J. Chem. Soc., Faraday Trans.*75, 1407-12

*Phys. Chem.* 69, 1294-1301

effects *J. Chem. Phys.* 79, 1145-53

Mialocq, J.–C., 2003, *Photochem. Photobiol. Sci.* 2, 329

New York


Chandra, A. & Bagchi, B., 1991, Molecular theory of solvation and solvation dynamics in a

Chandra, A., 1995, Ion solvation dynamics in binary dipolar liquids: theoretical and simulation results for mixtures of Stockmayer liquids *Chem. Phys. Lett.* 235, 133-39 Chandrashekhar, K., Inamdar, S.R., Patil, D.C. & Math, N.N., 1993, Orientational relaxation

Chapman, C.F., Fee, R.S. & Maroncelli, M., 1990, Solvation dynamics in N-methylamides

Chen, S.H., Katsis, D., Schmid, A.W., Mastrangelo, J.C., Tsutsui, T. & Blanton, T.N., 1999,

Chuang, J.T. & Eisenthal, K.B., 1971, Studies of effects of hydrogen bonding on orientational relaxation using picosecond light pulses *Chem. Phys. Lett.* 11, 368-70 Chuang, T.J. & Eisenthal, K.B., 1972, Theory of Fluorescence Depolarization by Anisotropic

Cole, R.H., 1984, in *Molecular Liquids-Dynamics and Interactions*, Eds: A. J. Barnes, W. J.

Courtney, S.H., Kim, S.K., Canonica, S. & Fleming, G.R., 1986, Rotational diffusion of stilbene in alkane and alcohol solutions J. Chem. Soc. Faraday Trans. *82, 2065-72*  Cowie, M.G. & Toporowski, P.M., 1961, Association in the binary liquid system dimethyl

Dahm, W.J.A., Southerland, K.B. & Buch, K.A. 1991, Direct, high resolution,

Day, T.J.F. & Patey, G.N., 1997, Ion solvation dynamics in binary mixtures *J. Chem. Phys*. 106,

De la Torre, J.C., 1983, Biological actions and medical applications of dimethyl sulfoxide

Demchenko, A.P., 2002, The red-edge effects: 30 years of exploration *Luminescence* 17, 19-42 Dote, J.L., Kivelson, D. & Schwartz, R.N., 1981, A molecular quasi-hydrodynamic free-space model for molecular rotational relaxation in liquids J. Phys. Chem. *85, 2169-80* Dutt, G.B., Doraiswamy, S., Periasamy, N. & Venkataraman, B., 1990, Rotational

Dutt, G.B. Konitsky, W. & Waldeck, D.H., 1995, Nonradiative relaxation of 2-phenylindene

Dutt, G.B., Singh, M.K. & Sapre, A.V., 1998, Rotational dynamics of neutral red: Do ionic and neutral solutes experience the same friction? *J. Chem. Phys.* 109, 5994-5603 Dutt, G.B., Srivatsavoy, V.J.P. & Sapre, A.V., 1999, Rotational dynamics of pyrrolopyrrole

Dutt, G.B. & Rama Krishna, G., 2000, Temperature-dependent rotational relaxation of

four‐dimensional measurements of the fine scale structure of Sc≫1 molecular

reorientation dynamics of polar dye molecular probes by picosecond laser

in solution and its implications for isomerization of stilbenes *Chem. Phys. Lett.* 245,

derivatives in alcohols: Does solute–solvent hydrogen bonding really hinder

nonpolar probes in mono and diols: Size effects versus hydrogen bonding *J. Chem.* 

Orville-Thomas and J. Yarwood, pp. 59-100, Reidel, Dordrecht

of aminocoumarins by time-resolved dichroism with picosecond pulses *Spectrosc.* 

Circularly polarized light generated by photoexcitation of luminophores in glassy

binary dipolar liquid *J. Chem. Phys.* 94, 8367-77

*Lett.* 28, 153-65

2782-91

437-40

*Phys.* 112, 4676-82

J.Phys.Chem. *94, 4929-35*

liquid-crystal films *Nature,* 397, 506

Rotational Diffusion *J. Chem. Phys.* 57, 5094-97

sulphoxide – water *Can. J. Chem.* 39, 2240-43

Debye, P., 1929, *Polar molecules*, Dover Publications, London

Ann. N.Y. Acad. Sci. 411, xi-xi

mixing in turbulent flows *Phys Fluids A*.3, 1115–1127

spectroscopic technique *J. Chem. Phys.* 93, 8498-8513

molecular rotation? *J. Chem. Phys.* 110, 9623-29


Rotational Dynamics of Nonpolar and Dipolar

Molecules in Polar and Binary Solvent Mixtures 223

Ito, N., Kajimoto, O.& K. Hara, 2000, Picosecond time-resolved fluorescence depolarization

Jarzeba, W., Walker, G.C., Johnson, A.E. & Barbara, P.F., 1991, Nonexponential solvation

Jiang, J. & Blanchard, G.J., 1994, Rotational Diffusion Dynamics of Perylene in n-Alkanes.

Jiang Y. & Blanchard, G.J., 1995, Vibrational Population and Orientational Relaxation

Kaatze, K., Pottel, R. & Schaefer, M., 1989, Dielectric spectrum of dimethyl sulfoxide/water

Karasso, P.S. & Mungal, M.G., 1997, PLIF measurements in aqueous flows using the

Kawski, A., Kuklinski, B. & Bojarski, P., 2005, Dipole moment of aniline in the excited S1

Koochesfahani, M.M. & Dimotakis, P.E., 1986, Mixing and chemical reactions in a turbulent

Krishnamurthy, M., Khan, K.K. & Doraiswamy, S., 1993, Rotational diffusion kinetics of polar solutes in hexamethylphosphoramide–water systems *J. Chem. Phys.* 98, 8640-47 Kubinyi, M., Grofcsik, A., Kárpáti, T. & Jones, W.J., 2006, Rotational reorientation dynamics

Kumar, P.V. & Maroncelli, M., 2000, The non-separability of "dielectric" and "mechanical" friction in molecular systems: A simulation study *J. Chem. Phys.* 112, 5370-81

Laitinen, E., Korppi-Tommola, J. & Linnanto, J., 1997, Dielectric friction effects on rotational reorientation of three cyanine dyes in n-alcohol solutions *J.Chem.Phys.* 107, 7601-12

Laria, D. & Skaf, M., 1999, Solvation response of polar liquid mixtures: Water-

Levitus, M, Negri, R.M. & Aramenda, P.F., 1995, Rotational Relaxation of Carbocyanines. Comparative Study with the Isomerization DynamicsJ. Phys. Chem. *99, 14231-39*  Lingle Jr. R., Xu, X., Yu, S.C., Zhu, H. & Hopkins, J.B., 1990, Ultrafast investigation of

electronic decay of the iodine A′ excited state *J. Chem. Phys.* 93, 5667-80 Luzar, A. & Chandler, D.,1993, Structure and hydrogen bond dynamics of water–dimethyl sulfoxide mixtures by computer simulations *J. Chem. Phys.,* 98, 8160-73

condensed phase chemical reaction dynamics using transient vibrational spectroscopy: Geminate recombination, vibrational energy relaxation, and

Lakowicz, J.R., 1983, *Principles of Fluorescence Spectroscopy*, Plenum Press, New York Lakowicz, J. R., 2006, Principles *of fluorescence spectroscopy*, Springer: New York

state from thermochromic effect on electronic spectra *Chem. Phys. Lett.* 415, 251-55 Kirov, A.S., Hurlbut, C., Dempsey, J.F., Shrinivas, S.B., Epstein, J.W., Binns, W.R., Dowkontt,

P.F. & Williamson, J.F., 1999, Radiation Therapy Physics: Towards two-dimensional brachytherapy dosimetry using plastic scintillator: New highly efficient water

of ionic dye solutes in polar solvents with the application of a general model for the

Observation of a Solvent Length-Dependent Change of Boundary ConditionJ. Phys. Chem. *98, 6436-40;* Vibrational Population Relaxation of Perylene in n-Alkanes. The Role of Solvent Local Structure in Long-Range Vibrational Energy Transfer*,* ibid, *9411-16:* Vibrational Population Relaxation of Perylene in Its Ground

Dynamics of 1-Methylpery lene in n-Alkanes. The Effective Range of Dipolar

of *p*-terphenyl at high pressures *Chem. Phys. Lett.* 318, 118-24

Energy Relaxation in SolutionJ. Phys. Chem. *99, 7904-12* 

mixtures as a function of compositionJ. Phys. Chem. *93, 5623-27* 

equivalent plastic scintillator materials *Med. Phys*. **26**, 1515-23

and Excited Electronic Statesibid*, 9417-21* 

Nd:YAG laser*Exp Fluids 23*, 382–387

liquid mixing layer *J Fluid Mech*. 170, 83–112

dimethylsulfoxide *J. Chem. Phys.* 111, 300-09

solvation shell *Chem. Phys.* 322, 247-54

dynamics of simple liquids and mixtures *Chem. Phys.* 152, 57-68


Hambir, S.A., Y. Jiang & Blanchard, G.J., 1993, Ultrafast stimulated emission spectroscopy of

Hartman, R.S., Alavi, D.S. and Waldeck, D.H., 1991, An experimental test of dielectric

Hartman, R.S., Konitsky, W.M., Waldeck, D.H., Chang, Y.J. & Castner, Jr, E.W., 1997,

Heilweil, E.J., Casassa, M.P., Cavanagh, R.R. & Stephenson, J.C., 1986, Population lifetimes

Heilweil, E.J., R. R. Cavanagh and J. C. Stephenson, 1987, Population relaxation of CO(*v* = 1 )

Heilweil, E.J., Casassa, M.P., Cavanagh, R.R. & Stephenson, J.C.1989, Picosecond Vibrational

Heilweil, E.J., Cavanagh, R.R. & Stephenson, J.C., 1989, CO(v=1) population lifetimes of metal– carbonyl cluster compounds in dilute CHCl3 solution *J. Chem. Phys.* 89, 230-39 Horng, M.-L., Gardecki, J.A. & Maroncelli, M., 1997, Rotational Dynamics of Coumarin 153:

Hu, C.M. & Zwanzig, R., 1974, Rotational friction coefficients for spheroids with the slipping

Hubbard, J.B. & Onsager, L., 1977, Dielectric dispersion and dielectric friction in electrolyte

Hubbard, J.B. & Wolynes, P.G., 1978, Dielectric friction and molecular reorientation *J. Chem.* 

Huppert, D., Ittah, V. & E. Kosower, 1989, Static and dynamic electrolyte effects on excited-

Huppert, D., Ittah, V. & Kosower, E., 1990, Static and dynamic electrolyte effects on excited large dipole solvation: high dielectric constant solvents *Chem. Phys. Lett.* 173, 496-502 Hynes, J.T., 1986, Chemical reaction rates and solvent friction *J. Stat. Phys.* 42, 149-168 and

Imeshev, G. & Khundkar, L.R., 1995, Inhomogeneous rotational dynamics of a rodlike probe

Inamdar, S.R., Chandrashekhar, K., Patil, D.C., Math, N.N. & Savadatti, M.I., 1995,

Inamdar, S.R., Nadaf, Y.F. & Mulimani, B.G., 2003, Ground and excited state dipole

Inamdar, S.R., Mannekutla, J.R., Mulimani, B.G. & Savadatti, M.I., 2006, Rotational dynamics

Inamdar, S.R., Gayathri, B.R. & Mannekutla, J.R., 2009, Rotational diffusion of coumarins in

Picosecond time-resolved laser emission of coumarin 102: Solvent relaxation,

moments of exalite 404 and exalite 417 uv laser dyes determined from solvatochromic shift of absorption and fluorescence spectra *J. Mol. Struct.*

9,10-disubstituted anthracenes *J. Chem. Phys.* 106, 7920-30

relaxation *J. Chem. Phys.* 98, 6075-82

solution *J. Chem. Phys.* 85, 5004-18

J. Phys. Chem. A *101, 1030-47* 

*Phys.* 69, 998-1006

references therein

boundary condition *J. Chem. Phys.* 60, 4354-57

Hubbard., J.B., 1978, Friction on a rotating dipole *J. Chem. Phys.* 69, 1007-09

solutions. I. *J. Chem. Phys.* 67, 4850-57

state behavior*Chem. Phys. Lett.* 159, 267-75

in 1‐propanol *J. Chem. Phys.* 103, 8322-28

aqueous DMSO *J. Fluoresc.* 19, 693-703

of nonpolar laser dyes *Chem. Phys. Lett.* 429, 141- 46

Pramana, J. Phys., 45, 279-290

(*Theochem*), 624, 47-51

Chem. *95, 7872-80* 

perylene in dilute solution: Measurement of ground state vibrational population

friction models using the rotational diffusion of aminoanthraquinones J. Phys.

Probing solute–solvent electrostatic interactions: Rotational diffusion studies of

of OH(v=1) and OD(v=1) stretching vibrations of alcohols and silanols in dilute

vibrations in solution phase metal carbonyl complexes *Chem. Phys. Lett.* 134, 181-88

Energy Transfer Studies of Surface AdsorbatesAnnu. Rev. Phys. Chem. *40, 143-71* 

Time-Dependent Friction, Dielectric Friction, and Other Nonhydrodynamic Effects


Rotational Dynamics of Nonpolar and Dipolar

Sphere *J. Chem. Phys.* 57, 2548-59

models *J. Chem. Phys.* 98, 3213-23

*Phys.* 83, 1298-1304

*Chem. Phys.* 30, 1-8

Press, New York

6197-6205

*Appl. Phys. Lett.* 26, 62-63

Study J. Phys. Chem. *100, 1357-67* 

mixtures J. Chem.Phys. *97, 1320-31* 

Stokes, G., 1856, *Trans. Cambridge Philos. Soc.* 9, 5

J. Phys. Chem. *89, 3238-43* 

J. Phys. Chem. *90, 2896-2900* 

*Chem. Phys.* 60, 1502-13

Molecules in Polar and Binary Solvent Mixtures 225

Qunfang, L. & Yu-Chun, H., 1999, Correlation of viscosity of binary liquid mixtures. *Fluid* 

Rice, S.A. & Kenney-Wallace, G.A., 1980, Time-resolved fluorescence depolarization studies

Rider, K.L. & Fixman, M., 1972, Angular Relaxation of the Symmetrical Top. II. The Rough

Roy, M. & Doraiswamy, S., 1993, Rotational dynamics of nonpolar solutes in different

Sanders, M.J. & Wirth, M.J., 1983, Evidence for solvation structural dependence of rotational

Safford, G.J., Schaffer, P.C., Leung, P.S., Doebbler, G.F., Brady G.W. & Lyden, E.F.X. 1969,

Selvaraju, C. & Ramamurthy, P., 2004, Excited-State Behavior and Photoionization of 1,8-

Shank, C.V. & Ippen, E.P., 1975, Anisotropic absorption saturation with picosecond pulses

Singh, M.K., 2000, Rotational Relaxation of Neutral Red in Alkanes: Effect of Solvent Size on

Skaf, M. & Ladanyi, B.M., 1996, Molecular Dynamics Simulation of Solvation Dynamics in

Soper, A.K. & Luzar, A., 1996, Orientation of Water Molecules around Small Polar and

Soper, A.K. & Luzar, A., 1992, A neutron diffraction study of dimethyl sulphoxide–water

Spears, K.G. and L. E. Cramer, 1978, Rotational diffusion in aprotic and protic solvents

Srivastava, A. & Doraiswamy, S., 1995, Rotational diffusion of rose bengal *J. Chem. Phys.* 103,

Steiner, R.F., 1991, *in Topics in Fluorescence Spectroscopy*, Vol. 2., J. R. Lakowicz (Ed.), Plenum

Templeton, E. F. G., Quitevis, E. L. & Kenney-Wallace, G. A., 1985, Picosecond

Templeton, E.F.G. & Kenney-Wallace, G.A., 1986, Picosecond laser spectroscopic study of

Titulaer, U.M. & Deutch, J.M., 1974, Analysis of conflicting theories of dielectric relaxation *J.* 

reorientational dynamics of resorufin: correlations of dynamics and liquid structure

orientational dynamics of probe molecules in the dimethyl sulfoxide-water system

Nonpolar Groups in Solution: A Neutron Diffraction and Computer Simulation

Dimethylsulphoxide and Dimethylsulphone *J. Chem. Phys.* 50, 2140-59 Shapiro, S.L. & Winn, K.R., 1980, Picosecond time-resolved spectral shifts in emission: dynamics of excited state interactions in coumarin 102 *Chem. Phys. Lett.* 71, 440-44 Sceats, M.G. & Dawes, J.M., 1985, On the viscoelastic properties of n‐alkane liquids *J. Chem.* 

solvents: Comparative evaluation of the hydrodynamic and quasihydrodynamic

Neutron Inelastic Scattering and X‐Ray Studies of Aqueous Solutions of

of rotational relaxation in viscous media *Chem. Phys.* 47, 161-70

*Phase Equilibria* 154, 153–163 and references therein

diffusion anisotropy *Chem. Phys. Lett.* 101, 361-66

Acridinedione Dyes in Micelles *Chem. Eur. J*. 10, 2253-62

Methanol−Water Mixtures *J. Phys. Chem.* 100, 18258-68

Probe Rotation *Photochem. Photobiol.* 72, 438-43


Madden, P. & Kivelson, D., 1982, Dielectric friction and molecular orientation *J. Phys. Chem.*

Mannekutla, J.R., Ramamurthy, P., Mulimani, B.G. & S.R. Inamdar, 2007, Rotational

Mannekutla, J.R., S. R. Inamdar, B. G. Mulimani and M. I. Savadatti, 2010, Rotational diffusion of coumarins: A Dielectric friction study *J Fluoresc.* 20, 797–808 Maroncelli, M., 1993, The dynamics of solvation in polar liquids*. J. Molec. Liq.* 57, 1-37

Maroncelli, M. & Fleming, G.R., 1987, Picosecond solvation dynamics of coumarin 153: The importance of molecular aspects of solvation *J. Chem. Phys.* 86, 6221-39 Martin, D. & Hanthal, H., 1975, *Dimethyl Sulfoxide;* John Wiley & Sons, Inc., New York McCarthy, P.K. & Blanchard, G.J., 1995, Vibrational Population Relaxation of Tetracene in n-

McCarthy, P.K. and Blanchard, G.J., 1996, Solvent Methyl Group Density Dependence of

McMahon, D.R.A., 1980, Dielectric friction and polar molecule rotational relaxation *J. Chem.* 

Millar, D.P., Shah, R. & Zewail, A.H., 1979, Picosecond saturation spectroscopy of cresyl

Moog, R.S., Ediger, M.D., Boxer, S. G. & Fayer, M.D., 1982, Viscosity dependence of the

Nadaf, Y.F., Mulimani, B.G., Gopal, M. & Inamdar, S.R., 2004, Ground and excited state

Nee, T.W. & Zwanzig, R., 1970, Theory of Dielectric Relaxation in Polar Liquids *J. Chem.* 

Nowak, E., 1983, Dielectric friction and energy dissipation in polar fluids *J. Chem. Phys.* 79,

Packer, K.J. & Tomlinson, D.J., 1971, Nuclear spin relaxation and self-diffusion in the binary

Pal, A. & Daas, G., 2000, Excess molar volumes and viscosities of binary mixtures

Papazyan, A. & Maroncelli, M., 1995, Rotational dielectric friction and dipole solvation:

Perrin, F., 1936, Mouvement brownien d'un ellipsoide (II). Rotation libre et depolarisation

Phillips, L.A., Webb, S.P. & Clark, J.H., 1985, High‐pressure studies of rotational reorientation dynamics: The role of dielectric friction *J. Chem. Phys.* 83, 5810-21 Porter, G., Sadkowski, P.J. & Tredwell, C.J., 1977, Picosecond rotational diffusion in kinetic and steady state fluorescence spectroscopy *Chem. Phys. Lett.* 49, 416-20

Organization in Branched Alkanes J. Phys. Chem. *100, 5182-87* 

transient grating experimentsJ. Phys. Chem. *86, 4694-4700* 

polarity parameters *J. Mol. Struct*. (*Theochem*) 678, 177-81

dynamics of UVITEX-OB in alkanes, alcohols and binary mixtures *Chem. Phys*., 340,

Alkanes. Evidence for Short-Range Molecular Alignment J. Phys. Chem. *99, 17748-53* 

Vibrational Population Relaxation in 1-Methylperylene: Evidence for Short-Range

violet: rotational diffusion by a "sticking" boundary condition in the liquid phase

rotational reorientation of rhodamine B in mono- and polyalcohols. Picosecond

dipole moments of some exalite dyes from solvatochromic method using solvent

system, dimethyl sulphoxide (DMSO)+ water J. Chem. Soc., Trans. Faraday 67,

tetraethylene glycol dimethyl ether (tetraglyme) with chloroalkanes at 298.15K *J.* 

Tests of theory based on simulations of simple model solutions *J. Chem. Phys.* 102,

des uorescences. Translation et diffusion de moleculesellipsoidales, J. Phys.

86, 4244-56

*Phys.* 72, 2411-24

*Phys.* 52, 6353-63

*Mol. Liq.* 84, 327-37

976-81

1302-14

2888-2919

Radium 7, 1-11

*Chem. Phys. Lett.* 66, 435-40

149-57


**10** 

*Italy* 

**Flow Instabilities in Mechanically** 

*Industrial Chemistry and Materials Science, University of Pisa* 

A detailed knowledge of the hydrodynamics of stirred vessels may help improving the design of these devices, which is particularly important because stirred vessels are among

In the last two decades there was a change of perspective concerning stirred vessels. Previous studies were focused on the derivation of correlations able to provide global performance indicators (e.g. impeller flow number, power number and mixing time) depending on geometric and operational parameters. But recently the attention has been focused on the detailed characterization of the flow field and turbulence inside stirred vessels (Galletti et al., 2004a), as only such knowledge is thought to improve strongly the

The hydrodynamics of stirred vessels has resulted to be strongly three dimensional, and characterised by different temporal and spatial scales which are important for the mixing at

According to Tatterson (1991) the hydrodynamics of a mechanically agitated vessel can be

• *wall flows* including impinging jets generated from the impeller, boundary layers, shed

Trailing vortices originating behind the impeller blades have been extensively studied for a large variety of impellers. For instance for a Rushton turbine (RT) they appear as a pair, behind the lower and the upper sides of the impeller blade, and provide a source of turbulence that can improve mixing. Assirelli et al. (2005) have shown how micro-mixing efficiency can be enhanced when a feeding pipe stationary with the impeller is used to release the fed reactant in the region of maximum dissipation rate behind the trailing vortices. Such trailing vortices may also play a crucial role in determining gas accumulation behind impeller blades in gas-liquid applications, thus affecting pumping and power

But in the last decade lots of investigations have pointed out that there are other important vortices affecting the hydrodynamics of stirred vessels. In particular it was found that the flow inside stirred vessels is not steady but characterised by different flow instabilities,

• *impeller flows* including discharge flows, trailing vortices behind the blades, etc.;

the most widely used equipment in the process industry.

different levels, i.e. micro-mixing and macro-mixing.

vortices generated from the baffles, etc.; • *bulk tank flows* such as large recirculation zones.

optimization of stirred vessel design.

divided at least into three flow systems:

dissipation capacity of the impeller.

**1. Introduction** 

**Agitated Stirred Vessels** 

Chiara Galletti and Elisabetta Brunazzi

*Department of Chemical Engineering,* 

