Thestudyofdielectricrelaxationin propyleneglycol±polypropyleneglycol)mixtures R.J.Sengwa a, * ,R.Chaudhary a ,S.C.Mehrotra b a Microwave Research Laboratory, Department of Physics, J.N.V. University, Jodhpur 342 005, India b Department of Electronics and Computer Science, Dr B.A.M. University, Aurangabad 431 004, India Received23April2001;receivedinrevisedform2July2001;accepted20August2001 Abstract DielectriccomplexpermittivityofpropyleneglycolPG),polypropyleneglycol)PPG-2000)andtheirmixtureswithconcentrationof25, 50and75vol%ofPGweremeasuredinthefrequencyrange10MHz±4GHzat258Cusingtimedomainre¯ectometryTDR).Forthese molecules and their mixtures, only one frequency independent dielectric loss peak was observed. The relaxation for these systems is describedbyasinglerelaxationtimeusingDebyemodel.ThelargevalueofobservedrelaxationtimeforPGmoleculesshowstheformation ofmolecularclusters.ItisfoundthattherelaxationtimeforPG±PPGmixturesissmallerincomparisontotherelaxationtimesofPGand PPG molecules, and it linearly increases with the concentration of the PG in the mixtures. The values of relaxation times of PG±PPG mixturesarediscussedparticularlywithrespecttothesolventPG)behaviour,whichcanbeassignedtounaffected,looselyaffectedand tightlyboundsolventandalsowithrespecttothePPGchaincoiling.Asapeculiarfeaturetheobservedrelaxationtimeisdirectevidenceof theinterchangeofsolvent±solventtosolvent±polymerinteraction. q 2001PublishedbyElsevierScienceLtd. Keywords:Propyleneglycol±polypropyleneglycol)mixtures;Dielectricrelaxationbehaviour;Molecularconformations 1. Introduction Recently [1±10], dielectric relaxation behaviour of mixtures of polar molecules small and macromolecules) under varying conditions of composition have evoked considerable interest, because, it helps in formulating adequatemodelsofliquidrelaxationandalsoinobtaining informationabouttherelaxationprocessesinmixtures.For ordinarymixturesthereexisttheoreticaltoolsthatallowone todealwithspeci®cinteractionsinarathersatisfactoryway. Whenthemixturecontainscomponentsthatcanassociate, e.g. through hydrogen bonding) the situation becomes complicated. In case of associating polymer systems [3±10], the situation is further complicated because the chain character of the components linked by hydrogen bondsleadstoassociationcomplexesthatarethree-dimen- sional in character, and the degree of theoretical develop- mentislesssatisfactory. Inrecentyearsglass-formingH-bondedpropyleneglycol PG) [HO±CHCH 3 ) CH 2 ±OH] and polypropylene glycol)s [H{O±CHCH 3 )CH 2 } n ±OH] PPG) liquids have received considerable attention. The four sites available for H-bonding in a PG molecule it can be viewed as a dihydric anisotropic alcohol molecule) promote a set of transient crosslinks between neighbouring molecules. Similarly PPG can form both inter- and intramolecular hydrogen bonds. Recently [11,12], broad-band dielectric spectroscopy 10 22 ±10 9 Hz) is employed to study the molecular dynamics of PG molecules con®ned to porous sol±gelglasses.Carinietal.[13]investigatedthereorienta- tionaldynamicsofneatliquidPGmoleculesandcompared withthatofcon®nedmoleculesin2.5and7.5nmporesofa sol±gelporousglassbymeansofdepolarisedlight-scatter- ing spectroscopy, and con®rmed that the neat PG, charac- terised by intermolecular crosslink effects imposed by H bonding,andbyintramolecularlinksbetweenthetwoOH endgroups.MorerecentlyLeonetal.[14]studiedthelow frequencydielectricrelaxationonPGandoligomershaving differentnumberofrepeatunitsn  2; 3and69)andestab- lished the relationship between the primary and secondary dielectricrelaxationprocesses.Theysuggestedthatthereis anincreaseinintermolecularcooperativitywithincreasing numberofrepeatunitsintheseoligomermolecules. The measurements of dielectric relaxation time of the associating macromolecules are interesting in understand- ing the molecular ¯exibility and coiling in the molecular chain, the mobility of polymer segments, internal group Polymer432002)1467±1471 0032-3861/02/$-seefrontmatter q 2001PublishedbyElsevierScienceLtd. PII:S0032-386101)00662-0 www.elsevier.com/locate/polymer * Correspondingauthor. E-mail address: rjsengwa@rediffmail.comR.J.Sengwa).