Hanna, Faika F

Saad, Azima L G

Shafik, Adel H

IACS Institutional Repository

Indian J. Phys. 72B (5), 495-504 (1998)IJ P  Ban international journalDielectric relaxation of some diol / alcohol mixtures in different solventsAzima L G Saad, Adel H Shafik and Faika F Hanna*National Research Centre. Microwave Physics Department. El-Tahnr St , Dokki, Cairo, EgyptReceived 12 FebruaryI99M, accepted 20 May 199HA bstract : The static permittivity and dielectric loss in the frequency range 0 1-18 GHz at 20"C for four ternary mixtures of diol / diol / alcohol in three nonpolar solvents namely heptane, cyclohexane and mesitylenc have been studied The systems used are 1,6 hexanediol + 1 ,2  ethanediol + n-hcxanol (HEH), I, 6 hexanediol + 1 , 2  ethanediol + cyclohexanol (HEC), I, 12 dodecanediol + 1 , 2  ethanediol + /i-hcxanol (DEH) and I, 12 dodecanediol + 1 , 2  ethanediol + cyclohexanol (DEC) The relaxation spectra have been analysed in three Debye terms The lower frequency term characterized by t( is predominating and is related to the association process The dielectric behaviour in the different solvents is discussed.Keywords . Dielectric spectroscopy, hydrogen bonding, ternary mixtures PACS Nos. . 77.22 gm. 82.30 Nr1. IntroductionThe structure and dynamics of hydrogen-bonded liquids can be studied by dielectric relaxation spectroscopy. Alcohols as a large class of associating liquids have been extensively studied by dielectric spectroscopy regarding only pure liquids as well as their mixtures with nonpolar solvents! 1-5]. Recently, association in mixtures like water or diol / mono-alcohol have been reported!6-7]. Further informations on the association in diol / alcohol mixtures could be gained by the study of dielectric behaviour of binary mixtures of diol / n-alcohol on dilution with a nonpolar solvent. From our laboratory the first results on the dielectric properties of a diol or a mixture of two diols in a monohydric alcohol diluted with a non-polar solvent (heptane) have becnreported[8-l()].The aim of this work is to study the effect of two non-polar solvents, ol structure deferent from that of heptane (namely mesitylenc and cyclohexane), on the dielectric properties of some quaternary systems . diol / diol //i-hexanol / solvent. The effect of using cyclohexanol instead of n-hexanol on the dielectric behaviour of these systems will also be studied.* For correspondence.© 1998 IACS496 Azima L G Saaci, Adel H Shafik and Faika F Hanna2. ExperimentalThe dielectric loss f" for the investigated solutions at frequencies between 0.2-18 GHz was measured using a microwave swept frequency transmission spcctrometerf 11J. The description and calibration of a similar spectrometer have been given bcfore[ 12]. The £*" values are uncertain to about ±4%.The static permittivity es was measured at 2MHz using a WTW dipolcmcler with an uncertainly of better than ± 2%. The refractive index nf) was measured by an Abbe rcfractomctcr to an uncertainty of ± I AO'4. Chemicals from Fluka, Merck, B.D.H and Aldrich (purity > 98 -  99%) were used as obtained.Measurements of es and e" were carried out at 20°C. Using a four letter abbreviation. DEAS where D denotes the first diol, E the second diol ‘ethancdiol' which is common in all mixtures, A the monohydric alcohol and S the non polar solvent, the following systems arc investigated :1. 1,6 Hcxancdiol +1,2 Ethancdiol + //-Hcxanol in Cyclohexane (HEHC)1 .6  H exa ncd io l  + 1 ,2  E thancd io l  + / /-H cxanol in M e s i iy lc n e j (H E H M )1. 6  Hexancdiol +1,2 Ethancdiol + //-Hcxanol in Heptane (HEHH)*2. 1 . 6  Hexancdiol +1,2 Ethancdiol + Cyclohcxanol in Cyclohexane (HECC)1. 6  Hexancdiol +1,2 Ethancdiol + Cyclohcxanol in Mesitylcnc (HECM)1. 6  Hcxancdiol + 1,2 Ethancdiol + Cyclohcxanol in Heptane (HECH)3. 1,12 Dodccancdiol +1,2 Ethancdiol + //-Hcxanol in Cyclohexane (DEHC)1.12 Dodccancdiol +1,2 Ethancdiol + //-Hcxanol in Mesitylcnc (DEHM)1.12 Dodccancdiol +1,2 Ethancdiol + //-Hcxanol in Heptane (DEHH)*4. 1,12 Dodecancdiol + 1,2 Ethancdiol + Cyclohcxanol in Cyclohexane (DECC)1.12 Dodccanediol +1,2 Ethancdiol + //-Hcxanol in Mesitylcnc (DECM)1.12 Dodccancdiol +1,2 Ethancdiol +//-Hcxanol in Heptane (DECH)In the mentioned systems, the diols and alcohols are the solutes, while heptane, cyclohexane and mesitylcnc arc the non-polar solvents used. Heptane and cyclohexane are aliphatic solvents. They are of different shapes. Heptane is a straight chain compound ol formula : CH3 (CH0)S CH V Cyclohexane is a ring or closed chain compound composed of six saturated carbon atoms of formula : CH2(CH9)4CH2 On the other hand, the third solvent, mesitylcnc, or 1 ,3, 5-trimcthylbcnzcnc, is an aromatic hydrocarbon of formula : (CH<)3C6H^  ofert-i / j\ i  c - c  * *structure n -c  c -c ii,x c  - C  7 / \CH, "The molar ratio 1 :4 for the first diol to ethanediol is kept the same for all systems. Also.data for HEHH and DEHH were taken from reference f 13JDielectric relaxation of some diol/alcohol mixtures etc 497the molar ratio of the diols in the aliphatic alcohols 1 :9 is kept the same. Concentrations of the alcoholic mixtures in the non-polar solvents ranging lrom 0.08 to 0.3 mole fraction only were used as higher concentrations could not be measured by the available apparatus.3. Results and DiscussionStatic permittivity :The static permittivity cs and refractive index nt) lor the investigated systems were measured al 20°C. The values of the normalized dispersion step S /  x = (Ac s- — An'p ) / x were calculated and are given in Table 1. Ae s and An~D arc the diftercnces in the static permittivities and refractive indices square o( the solution and solvent and x is the total alcoholic concentration in mole fraction in the different non-polar solvents.Tabic 1. Normalized dispersion step \/\  for ihc investigated quaternary diol/diol/alcohol/ solvent systems at 20‘C x is the total alcoholic concentration in mnl%n-Hexanol systems (xEHx)X[mol%]s/x X[mol%ls/x X|mol%]s/xI1EHH HEHM HEHC8 1 53 12 2 60 12 2 4514 1 75 15 2 66 15 2 6320 2.15 20 2 89 20 2 9525 2 41 25 3 15 25 3 3830 * 2 75 30 3 44 30 3 88DEH If DEHM DEHC12 1 72 10 2 46 10 2 2415 1 83 15 2 62 15 2 4920 2 08 20 2 80 20 2 8125 2 38 25 3 05 25 3 2230 2 66 30 3 34 30 3 68Cyclohexanol systems (xECx)X s/x X s/x X s/x[mol%l [molc/H |mol%]H ECII HELM H ECC8 1 95 8 2 65 10 2 5714 2 37 14 2 84 15 2.8920 2 77 20 3 12 20 3 2925 3 1 1 25 3 35 25 3 8530 3 43 30 3 67 30 4 52DECH DECM DECC12 2.16 12 2 60 10 2.8315 2 32 15 2 79 15 3.1120 2.63 20 3 13 20 3 5325 2 78 25 3 37 25 3.9930 3 13 30 3 76 30 4.50498 Azima L G Saad, Adel H Shafik and Faika F HannaThe measured values of S/x for the investigated systems at 20°C are illustrated versus x in Figure 1. It is clear that the mixtures diluted with heptane have the lowest values of S/x while those using cyclohexane are higher than them. In the case of mesitylene solutions, S/x values are higher than those for heptane solutions for all concentrations. For cyclohexane solutions, only for high concentrations (x > 15 mol %) S/x is higher than that for mesitylene solutions, with the exception of the DECC system where S/x values are higher than the DECM values for all concentrations.a432HV 14321Figure I. Normalized dispersion step S/\ versus concentration x, 2(),,C x (mole fraction) is the concentration of the total alcoholic mixture in (he different solvents................1 ■ 1.......................................... 1 1 r*.B  HEHH 4  HEH1Ie  HEHC ,  o  *. •  ■ ;  •■aBHexuftol systems (HEHi). ................. ...................... ..................... ..B  HECH •: 4  HEClf: © HECC mAs  a  ■ ;4  BBB: Cyclohsxanol systems (HtCi) ■□ DEHH □ DECK V4  DEHM : 4  DECM \o DEHC - O DECC o \o *rs \_ A\J  \AOA O A  □■ □<1OA D A 8  □A  □ □o□ : □  :□ °Hexsnol systems (DEHx) : Cyclohexsool systems (DECz)0 10 20 30 0 10 20 30Relaxation spectra :The specific dielectric loss At'lx was measured for the same systems at frequencies if) between0.2 and 16 GHz and at 20°C. A here means the difference in dielectric loss between the investigated solutions and solvents used. The data obtained are illustrated graphically in Figure 2. All spectra arc broader than a Debye curve, as commonly found with alcoholic systems which suggests a distribution of relaxation times. So, we tried to fit the experimental data by the sum of two Debye terms using the equation :4 £"/(Aes -An1D)=YdG 2 ■>"  l + a r r , -where is the relaxation strength of each term and Z C  = 1 . The fit quality is improved by employing an additional Debye-type spectral component on the high frequency side. Anyhow, due to the restricted experimental frequency range (0.2-16 GHz), we could not fit the data by more than three Debye components (characterized by r,, r2 and r3). Results for systems HEHCDielectric relaxation of some diol/alcohol mixtures etc 499and HECC, chosen as a representative selection, are illustrated in Figure 3. This figure shows that T, and could be accurately determined from the experimental data, is less accurate asH E H H• *. □  X -  Bx *  □  A X - U x  A n  o  X -2 0 Xo  X -2B X  1 D •  X -3 0 X  :H EH M□ X -1 2 X  A X -1 5 X  © X -20X  o  X -2 5 X  ' •  X -3 0 X----- -—............. ........ .—............. I ■ » 'H E H C□ □  x » 1 2 xA X - l f t*  o  X -2 0 X  o  X -2 3 X  : •  X -3 0 Z  :D E H H D E H if D E H C0 °- rP□  X -1 2 Z a □ X -1 0 X n °  □  X -1 0 X  '4  D L X -I5 X a X -1 5 X °  A X -1 5 X□ o  X "20X o X -2 0 X □ o  X -2 0 Xo  X -2B X  : o  X -2 5 X  ^ o  X -2 3 Z  -•  X -3 0 X  : •  x - a o x  : •  x - 3 o x  :0.1 1 10 0.1 1 10 0.1 1 10f / G H zFigure 2(a). Specific dielectric loss (Ae"/x) versus frequency (/) lor /i-hcxunol systems for different concentrations \ and 20TFigure 2(b). Same as in Figure 2(a) Cyclohexanol is used instead of n-hexanol500 Azima L G Saad, Adel H Shafik and Faika F Hannathe maximum of this absorption term lies outside the experimental data and it is found to be around lOps. Such a value was found before! 11-13] and so it is kept constant throughout theo . i  1 to  0.1 1 10f/GHzFigure 3. Absorption curves for (he systems HEHC and HECC, 20'’C Fitting the experi­mental (Ae“/x) values using 3 Debye terms (solid line)analyses. The values of r,, r2, r3 and the normalized relaxation strengths (Gj = SVS) for r, and r2 are given in Table 2. In this table, the values of G3 arc not given as the accuracy in them is less than that in G, and G7 and we contented ourselves with the values of TI ~ I C  ] and us variation with concentration as it gives an insight about the dipolar absorption in the millimeter and FIR regions. Fitting of the data was done by a computer program. The results arc uncertain to about 5%. \We arc mainly interested in the principal absorption term for the investigated systems in the different solvents. r i values arc illustrated in Figure 4 versus concentration in mol %. ItFigure 4. Principal relaxation lime r, ps versus total alcoholic concenlration x for theinvestigated systems in the different solvents.Dielectric relaxation o f some diol/alcohol mixtures etc 501T ab ic  2. R elaxation lim es r  (/ = 1-3) and norm alized relaxation  strengths G for the investigated quaternary d lo l/d io l/a lcoho l/so lvcn t system s. 20“C ji is the total alcoholic concentration in mol9t and rj the viscosity.n-H exanol systems (xE H x )X[m ol% ]r ,[psjZ2[psl fps]G ll ~ ± G ,H E H H8 130 40 10 0 15 0 12 0 7414 206 48 10 0 21 0 16 0 6320 27 5 63 10 0 29 0 19 0 522 5 336 69 10 0 18 0 2 1 0 4 130 37 7 7 5 10 0 43 0 2 1 0 36H K H M1 2 1 1 3 37 10 0 2 1 0 2 1 0 581 5 1 34 39 1 0 0 27 0 21 0 5220 1 84 42 10 0 33 0 22 0 4525 225 46 10 0 38 0 2 1 0 4030 267 62 10 0 43 0 23 0 34H E H C1 2 213 40 1 0 0 23 0 17 0 601 5 268 4 8 1 0 0 27 0 1 8 0 .5  520 * 335 63 1 0 0.32 0 19 0 4 92 5 410 7 1 1 0 0 37 0 18 0 4530 460 83 10 0 40 0. 16 0 .44D E H H1 2 1 89 40 10 0 19 0 16 0 641 5 225 4 1 1 0 0 22 0 19 0 6020 275 49 10 0 26 0 2 1 0 5325 336 62 10 0 30 0 .22 0 4830 377 7 1 10 0 .37 0 .23 0 4 1p E IIM10 120 40 10 0 18 0 17 0 651 5 126 40 1 0 0 .25 0.21 0 5420 179 40 10 0 33 0 22 0 4525 212 40 10 0 38 0 .2 4 0 3830 26 0 40 10 0 44 0 .27 0 28D E H C1 0 177 4 0 10 0 17 0 IK 0 .6415 225 43 10 0 26 0 19 0 5520 284 50 10 0 30 0 18 0 5225 348 60 10 0 33 0. 19 0 .4830 390 69 10 0 37 0 .18 0 45502T able 2. {Cont'd.)Cyclohexanol systems (xECx)Azima L G Saad, Adel H Shafik and Faika F HannaX[mol%]T ![PS]T ,IpsJhLpslG, C2 ' - i c ,i = iHECII8 184 40 10 0.22 0.12 0 6614 245 50 10 0 29 0.15 0 5520 300 62 10 0 34 0 19 0.4725 146 69 10 0 38 0 22 0 4030 400 80 10 0 48 0.24 0 27HECM8 126 39 10 0 10 0.22 0.6914 159 40 10 0 22 0 24 0.5520 195 44 10 0 31 0.24 0 4525 245 49 10 0.38 If).25 0.3730 275 55 10 0 44 0 31H ECC \10 224 43 10 0.23 0 \l 2 0.6515 2R0 54 10 0 30 0 14 0 5620 353 62 10 0 36 0 13 0 5125 450 71 10 0 40 0 13 0 4730 555 82 10 0 43 0 13 0 44DECH12 123 33 10 0.J3 0 1.2 0 6515 150 36 10 0 25 0 15 0 5920 225 44 10 0.35 0 17 0.4825 29 1 56 10 0 39 0 23 0 3730 356 63 10 0.46 0 25 0 28DECM12 1 13 42 10 0 22 0.18 0 6015 126 42 10 0 27 0 19 0 5520 179 42 10 0.33 0 23 0.4525 212 42 10 0 37 0 24 0.3930 267 42 10 0 44 0.28 0 28DECC10 136 33 10 0.23 0 1 1 0.6715 189 36 10 0.28 0.14 0 5820 248 46 10 0.32 0.14 0.5325 321 56 10 0.34 0.17 0 4930 368 66 10 0 38 0.16 0.46Dielectric relaxation o f some diol/alcohol mixtures etc 503is clear from (his figure thal t ] increases with increasing concentration. values are different in the different solvents used. The lowest values or r] arc found in the systems using the aromatic solvent mesitylene although the viscosity of mcsilylene (Tj = 0.85 mPa. s) is much higher than that of heptane (77 = 0.41 mPa. s). This could be due to the solute-solvent interactions which are influenced by the nature of the solvent. In mesitylene, the solute-solvent interactions arc much higher than thal in heptane due to interaction between H-atom of an OH-group and /relectrons in the aromatic ring ol mesitylene molecule. This interacting environment around solute molecules leads to shorter life time t, of the formed complexes. This behaviour was noticed before in benzene by Swain and Roy[ 14]. He stated also that “the interacting environment around solute species gives favourable alignment of dipoles of solute species resulting in high dipole moments i.e. highS/v” . Figure 1 shows lhaiS/r for systems using mesitylene arc higher than those using heptane where the interaction of solute molecules in /i-heptane environment is least. This is in favour of our interpretation for the behaviour of mcsilylene systems. For cyclohexane solutions, T, is higher than that for heptane solutions (Figure 4), this behaviour could be due to the cyclic shape of the cyclohexane molecule which will make the interaction of the solute molecules in cyclohexane environment lower than in mesitylene and heptane leading to longer life time r, of complexes.For the assignment of relaxation processes to the different terms obtained from the analysis, the first lenn characterized by T, is surely related to the association process, we cannot exclude the existence of long-lived, well defined clustered objects, r, reflects the life lime of these clusters. The relaxation strength G, is dependent on concentration and increases with increase in concentration as expected. The second absorption region characterized by is related to orientation of fragmental parts of these large clusters in the case of the solvent heptane as the relaxation strength G^ in this case increases with increase in concentration. While in the case of the solvents mcsilylene and cyclohexane G2 is found to be the same in each solvent for all systems. In this case T-, could describe the switch over process from one hydrogen bond to another within the cluster. The term with short relaxation time may be related to segmental motion in single molecules. Its relaxation strength is included in the term 1 - I C ( and the rest of this term may be related to polar group rotation or libcrational motion.To sum up, the change of solvent alters the dielectric behaviour of the different systems. The solute-solvent interaction in mesitylene is found to be much higher than in heptane and cyclohexane. The change from /i-hcxanol to cyclohexanol causes some disturbances in the medium due to its cyclic shape.R eferences[1 | B Gcsiblom and J Sjoblom Acta Cheat Stand A38 575 (1984)12] S C  Mchrotia, B Gesiblom and J Sjobloin Finn Cheat Lett, 34 (1985)[3] V I Zhuravlev, V A Durov and Y D Feldman Zh. Ft: Khin 1 60 1513 (1986)[4] F F Hanna, I K Hakim. A L G Saad, F Hufnagel and F Drcxler J Mai Ltq 49 49 (1991)|5 | A Lux and M Stockhausen Phys Cheat Ltq. 26 67 (1993)16] B Gcsiblom and J Sjoblom Acta Cheat Stand A38 47 (1984). J Phys. Cheat. 90 4175 (1986)[7] B Gcsiblom, A El-Samahy and J Sjoblom J Solution Cheat 14 375 (1985)[8] F Hufnagel, F F Hanna, A M Ghoneim, A L Saad and G Turky J Chem. Soc. Faraday Trans. 88 1819(1992)[9J G Turky, F F Hanna, G Klagcs, A M Ghoncim and M Stockhausen ZNaturforsch 49a 503 (1994) (101 F F Hanna, A H Shafik and M Stockhausen Z Naiurjorsch. 50a 785 (1995)[11) A L G  Saad Ph. D . Thesis (Cairo University) (1988)(12) F F Hanna and H Hammel Z Phys Cheime (Leipzig) 263 323 (1982)113] A H  Shafik M.Sr Thesis (Cairo University) (1995)114] B B Swain and G S Roy J Mol Ijq  34 257 (1987)504 Azima L G Saad, Adel H Shafik and Faika F Hanna

Dielectric Relaxation of Some Diol / Alcohol Mixtures in Different Solvents

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Dielectric Relaxation of Some Diol / Alcohol Mixtures in Different Solvents

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