Optical parameters of calix[4]arene films and their response to volatile organic vapors

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ContentslistsavailableatScienceDirect

Sensors

and

Actuators

B:

Chemical

j o u r n al hom e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / s n b

Optical

parameters

of

calix[4]arene

ﬁlms

and

their

response

to

volatile

organic

vapors

Z. Özbek

a

_,

_R.

_C¸

_apan

a,∗

_,

_H.

_Göktas¸

b

_,

_S.

_S¸

_en

b

_,

_{F.G. ˙Ince}

c

_,

_M.E.

_Özel

d

_,

_F.

_Davis

e

a_Balikesir_University,_Faculty_of_Arts_and_Science,_Physics_Department,₁₀₁₄₅_C¸_a˘gıs¸_,_Balikesir,_Turkey b_Onsekiz_Mart_University,_Faculty_of_Arts_and_Science,_Physics_Department,₁₇₁₀₀_C¸_anakkale,_Turkey

c_Tulane_University,_Department_of_Chemical_and_Biomolecular_Engineering,₆₈₂₃_St._Charles_Avenue,_New_Orleans,_LA_70118-5698,_United_States d_C¸_a˘g_University,_Faculty_of_Arts_and_Science,_Mathematics_and_Computer_Sciences_Department,₃₃₈₀₀_{Tarsus-Mersin,}_Turkey

e_Institute_of_Bioscience_and_Technology,_Cranfield_University_at_Silsoe,_Cranfield_Centre_for_Analytical_Science_Silsoe,_Cranfield_MK45_4DT,_UK

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received24March2011

Receivedinrevisedform30May2011 Accepted2June2011

Available online 12 June 2011 Keywords: Calixarene Vapors Gassensor Langmuir–Blodgettthinﬁlm

a

b

s

t

r

a

c

t

TheLangmuir–Blodgett(LB)techniquewasemployedtoproducethinLBfilmsusinganamphiphilic calix-4-resorcinareneontodifferentsubstratessuchasquartz,goldcoatedglassandquartzcrystals.The characteristicsofthecalixLBfilmsareassessedbyUV–visible,quartzcrystalmicrobalance(QCM)and surfaceplasmonresonance(SPR)measurements.UV–visandQCMmeasurementsindicatedthatthis materialdepositedverywellontothesolidsubstrateswithatransferratioof>0.95.UsingSPRdata, thethicknessandrefractiveindexofthisLBfilmaredeterminedtobe1.14nm/depositedlayerand 1.6respectively.ThesensingapplicationofcalixareneLBfilmstowardsvolatileorganicvaporssuchas chloroform,benzene,tolueneandethanolvaporsisstudiedbytheSPRtechnique.TheresponseofthisLB filmtosaturatedchloroformvaporismuchlargerthanfortheothervapors.Theresponseisfastandfully recoverable.Itcanbeproposedthatthissensingmaterialdepositedontogoldcoatedglasssubstrateshas agoodsensitivityandselectivityforchloroformvapor.Thismaterialmayalsofindpotentialapplications inthedevelopmentofroomtemperatureorganicvaporsensingdevices.

1. Introduction

Calix[n]arenematerialshavebeenextensivelystudiedfor sev-eral potentialapplications because of their syntheticflexibility andsuitabilityforhost–guestinteraction.Inthehost–guest inter-action, the conformational properties of these molecules allow theutilizationof calix[n]arenesas fundamental buildingblocks that can betailored to make calix[n]areneswith desired func-tionalitiesforquantitativeandqualitativeapplications[1].Most potentialapplicationsrequirethatthesematerialsshouldbe pre-paredasathinfilmformusingasuitabletechnique[2].Caliarenes and therelatedcalix[4]resorcinarenederivatives in theformof thin filmsare ofparticularinterest withinthesensing commu-nityduetotheirselectiverecognitionofdifferentmolecules.Films ofcontrolledthicknessof suitablecalix[4]resorcinarenescanbe easilyfabricatedusingtheLangmuir–Blodgett(LB)technique[3] onto varyingsubstrate which werethen usedas chemical sen-sors. Thecavity ofthe calix[4]resorcinareneprovides a site for thebindingoforganicguestmolecularspeciesandthe selectiv-ityofcalixarenesandcalix[4]resorcinarenestoparticularanalytes canbecontrolledsomehowbyalteringthesizeofthecavityas

∗ Correspondingauthor.Tel.:+902666121010;fax:+902666121215. E-mailaddress:[email protected](R.C¸apan).

wellas the peripheralsubstituted groups. Mostcommonly, for calixarenes thecavity sizecorrespondsto n=4, 6or 8and cal-ixresorcinarenesarenormallycyclic tetramers.Awide rangeof analytespecieshasbeenpreviouslystudiedincludingmetalions and amino acids.Variousanalytical techniqueshave beenused to follow thesensing response including UV–vis, surface plas-monresonanceandquartzcrystalresonance[4–7].Variousorganic polymers and co-polymers, as well as special architecture low molecularmassmoleculessuchascalixarenes,crown-ethersand phtalocyanines arecommonly used assensitivelayer materials ingassensors[8].Langmuir–Blodgett(LB)filmsofresorcinarene molecules absorb water ontheir surface while more lipophilic solvents such as benzene and toluene penetrate into the vol-ume of such films. Chemical gas sensor elements, which are basedondiscontinuousgoldfilmscoatedwithLBfilmof resor-cinarenes,wereshowntopossessgoodsensitivitytowardsalcohols [9–11].

Inthepresentwork,asuitablecalix[4]resorcinarenematerialis chosentoproduceathinLBfilmandtoinvestigatethequalityof LBfilmduringthedepositionprocessusingUV,QCMandSPR.The thicknessvalueandrefractiveindexofthis filmaredetermined andsensingpropertiesofthis filmagainstchloroform,benzene, tolueneandethanolvaporsarestudied.Ourresultsshowedthatthe sensitivityfortheSPRsignaltotheexposureofchloroformvapour isquitehigh,stableandreversible.

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Fig.1.ThechemicalformulaoftheCBTEAmolecule.

2. Filmpreparationandexperimentaldetails

Fig.1shows thechemical structure of thematerial (CBTEA) which is initially is synthesised as a resorcinol/benzaldehyde tetramerandthenfunctionalisedatthe2-positionbyaMannich reactionwithformaldehyde anddiethylamine andthen quater-nisedwith2-bromoethanoltogiveanorange-colouredpowder. Thesynthesisofthismoleculeandcharacterisationofits mono-layers on various subphases has already been reported in the literature[2].Theamphiphiliccharacterofthemolecules contain-inghydrophobicaromaticsidechains,andhydrophilicOHtogether withcationicammoniumgroupsmakesthemsuitablefortheLB deposition.A“NIMA622alternatelayerLBtrough”withanarea of 1200cm2 _was _employed _for _the _{investigation} _of _the _CBTEA

moleculeattheair–waterinterfaceandforthefabricationofLB thinﬁlms.Thetemperatureofthewatersubphasewascontrolled usinga“LaudaEcolineRE204”modeltemperaturecontrolunitand allexperimentaldataweretakenatroomtemperature.200␮l solu-tionofCBTEAinchloroformwithaconcentrationof∼0.2mgml−1 werespreadontoanultrapurewatersubphase.Atimeperiodof 20minwasallowedforthesolventtoevaporatebeforethearea enclosedbythebarrierswasreduced.Toinvestigatethebehaviour ofmonolayerattheair–waterinterface,–Aisothermgraphswere recordedusingabarriercompressionspeedof200cm2_min−1_._The

ﬂoatingmonolayerattheair–waterinterfacewasfoundtobe sta-bleatasurfacepressureof22.5mNm−1; therefore,this surface pressurevaluewasselectedforLBﬁlmdepositionprocedure.The depositionmodewasY-typewithaspeedof25mmmin−1forboth thedownandupstrokes.Severalsubstratessuchasaquartzslide forUV–visiblemeasurement,a50nmthickgoldcoatedglassslide forSPRmeasurementandaquartzcrystalforQCMmeasurement wereusedassubstratesforvariousmeasurementmethods.

UV measurements were recorded withan Ocean Optics UV lightsource(DH-2000-BALDeuteriumTungstenlightsource)anda spectrometer(USB4000)inabsorbancemodeintherangebetween 250and450nm.UVspectraforCBTEAsolutionweretakenina quartzcuvette.AfterthedepositionofLBﬁlmmultilayerontoa quartzsubstrate,UVspectrawererecordedasafunctionoflayer numbers.

ForQCMmeasurements,CBTEALBﬁlmlayersweredeposited ontoathinlycutwaferofraw quartzsandwichedbetweentwo goldelectrodesinanoverlappingkeyholedesign.Aftereach depo-sitioncycle,theLBﬁlmsamplewasdriedand themasschange

Fig.2.IsothermgraphoftheCBTEAmonolayer.

wasmonitoredusinganin-houseconstructedcomputercontrolled QCMmeasurementsystemwithsuitablesoftwarewhichallowsthe on-linerecordingofthechangesofthequartzresonancefrequency. Thequartzcrystalwasinsertedintotheelectroniccontrolunitand thefrequencyofoscillationwasmonitoredasafunctionoftime. Valuesoffrequencychanges,whichindicatethedegreeofresponse, aremeasuredwithanaccuracyof1Hzwhentheorganicvaporis present.AllQCMmeasurementsweretakenatroomtemperature usinganominalresonancefrequencyof9MHz.

Surfaceplasmonresonancespectrometer(BIOSUPLAR6Model) with a low power laser diode (630–670nm) light source was employed to monitor the SPR spectra with an angular resolu-tionabout0.003◦.A glassprism (n=1.62) wasmountedwithin a holder so as to be available for measurements in liquid or in air environments and glass slides with the dimensions 20mm×20mm×1mmwerecoatedontopbyaverythin homoge-neouslayerofgold.Acompatibletransparentplasticflowcellwith inletandoutletconnectedtosiliconetubeswasusedfororganic vapormeasurements.Severalmodessuchassinglemeasurements, trackingmodeorslopemodecouldbeutilizedandthesignalwas displayedasafunctionoftime.Biosuplar-Softwarewasusedto controltheSPRsystemsettings,measurementsanddata acqui-sitionas wellasdatapresentation.Thephotodetectorresponse wasrecordedasafunctionoftimeduringperiodicexposureofthe sampletotheorganicvaporforatleasttwominutes,whichwas thenallowedtorecoverafterinjectionoffreshair.WINSPALL soft-waredevelopedattheMax-Plank-InstituteforPolymerResearch, GermanywasutilizedforthefittingofSPRcurvestodetermine thicknessandrefractiveindexvaluesoftheLBfilms.

3. Resultsanddiscussion

3.1. Depositionproperties

The pressure–area (–A) behaviour or isothermgraph for a Langmuir monolayer is measured to understand how organic moleculescanbearrangedattheair–waterinterfaceandtoassess thecharacteristicsurfacebehaviourofanorganicmoleculeonthe watersurface.Fig.2givesthepressure-areabehaviourofCBTEA indicatingthesurfacepressureasafunctionofenclosedsurface area.Asexpected,thesurfacepressureincreaseswhenthesurface areadecreasedandthemonolayerbeginstocollapseatthe sur-facepressureofabout38mNm−1.Thisgraphwasrepeatedseveral timesandtheresultswerefoundtobereproducible.Isothermsof calixarenematerialswithdifferentsubstitutedgroupswere exten-sively studiedin the literature [5,6,12–14].Our result shows a similarisothermgraphattheair–waterinterface.AstableLB mono-layeris obtainedatapressure of22.5mNm−1 and thisvalueis

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Fig.3.TheUV–visiblespectraofaCBTEAsolution.

selectedfortheLBfilmdeposition.Thedepositionefficiencyofthe LBfilmisdenotedbythetransferratio(₎whichistheratioofthe areaofthemonolayerremovedfromtheair–waterinterface dur-ingdepositiontotheareaofsubstratetobedeposited.Itsvalueis givenasinEq.(1):

= A_AL

S (1)

whereAListhedecreaseintheareaoccupiedbythemonolayeron

thewatersurfaceandASisthecoatedareaofthesubstrate.Using

Eq.(1),aY-typecalixLBﬁlmisthenobtainedwithatransferratio closeto0.95.Thisvaluecanbeusedtoconcludethatsteady, repro-ducibleanduniformmonolayersofCBTEAweredepositedfromthe air–waterinterfaceontoaquartzcrystalsubstrate.

3.2. UV–visibleresults

Fig.3 shows theUV absorptionspectraof a CBTEAsolution inchloroform.Abroadabsorptionbandwasobservedat280nm. TheUVcharacterisationofcalix[4]arenes,carriedoutusing differ-entsolvents,showsthatthelinearaswellasthecyclicoligomers haveapairofabsorptionmaximanear280and288nm[15,16]. Whencomparedwithourresults,thesameUVabsorptionspectral structureswereobservedat285nmfortheCBTEAfilms[17–19]. AnumberofUV–visspectraofCBTEALBfilmstransferredontoa quartzsubstratewithseveraldifferentlayerthicknessesareshown inFig.4.Thisshowsthattheabsorptionintensityincreasedwhen thenumberoflayersincreased.TheUVspectraoftheLBfilmsare similartotheCBTEAspectrumofthesolutionform,exceptthat

Fig.4.UV–visabsorptionofCBTEALBﬁlms.Inset:linearrelationshipbetween absorbanceandthenumberofbilayers,correspondingtothethicknessoftheﬁlms.

Fig.5.Frequencychangesasafunctionoflayernumbers.

thebandsat280nmisbroadenedinthesolutionspectrumandis redshiftedbyabout90nm.Thismightbeexplainedbythe occur-renceofmolecularaggregationin theLBfilms. Theshiftin the absorptionbandoftheLBfilmmaybetheresult ofsomekind ofmolecularaggregationtakingplaceduringfilmformation,for whichthewavelengthincreaseswhileenergyisreducing.A sim-ilarredshiftisobservedattheabsorptionmaximaat350nmfor calix[4]resorcinarenesLBfilm[2].

TheinsetinFig.4showsvariationsofabsorptionintensityat 370nmasafunctionofnumberoflayers.Thislinearrelationship conﬁrmsafairlyconstanttransferratioduringsequentialdipping oftheslidethroughtheLBmonolayer.Thisdemonstratessuccessful adhesionofthemonolayerstothequartzsubstrate.

3.3. Quartzcrystalmicrobalance(QCM)measurements

QCMsensorsarebasedonthedetectionofthemasschangein thesensingoverlayerbythemeasurementoftheresonance fre-quencyofthedevice.Theprincipleofmeasurementisthechangeby finthefundamentaloscillationfrequencyf0uponmass

deposi-tiononthequartzcrystalsurface.Thus,uponexposure,theanalyte moleculesareadsorbedbythesensingoverlayerdepositedontothe quartzcrystal,causingachangeinitsmassand,inturn,achange inthefundamentaloscillationfrequencyf,inaccordancewiththe followingfrequency–massrelationshipcalledSauerbreyequation [20]:

f =−2f

2 0m

A√qq (2)

whereAthesurfaceareaofelectrodes(cm2₎_of_the_quartz_crystal,

q=2.947×1011g/cms2andq=2.648g/cm3aretheshear

modu-lusandthedensityofthequartzsubstrate,respectively.misthe amountofmasschange(g).

Fig.5givestheresonantfrequencychangeofthequartzcrystal asafunctionofthedepositedLBﬁlmlayersusinga9MHzquartz crystal.QCMmeasurementswerecarriedoutattheroom tempera-ture.Alinearrelationshipwasobservedbetweenthefrequencyand masschange.Thisshowsthatanequalmassisdepositedontothe quartzcrystalandauniformLBﬁlmisobtainedusingtheCBTEA material.UsingthegradientofFig.5andEq.(2),thetypical fre-quencyshiftisestimated∼66Hzperbilayerandthedepositedmass perbilayeriscalculatedtobe0.92_×10−6g.

3.4. Surfaceplasmonresonance(SPR)measurements

SPRcurvesindicatingthedependenceofreﬂectedlightintensity ontheinternalangleofincidencefortheCBTEALBﬁlmsareshown inFig.6.ThesecurvesfortheCBTEAlayersareshiftedwithrespect

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Fig.6.SPRcurvesofCBTEALBﬁlmswithincreaseinthickness.

tothecurveofabaregoldSPRcurveinproportionwiththenumber ofLBlayers.

The experimental SPR data were fitted using the Winspall software(writtenbyWolfgangKnoll,developedatthe Max-Plank-Institute for Polymer Research, Germany) [21–24] in order to evaluatethefilmthickness(d)anditsrefractiveindex(n).Itwas assumedthatk=0forourLBfilms,sincetheyaretransparentat =633nm[6].Fig.7aandbpresentstheexperimentallymeasured

Fig.7. (a)Completemeasured(dots)andfitted(lines)SPRcurvesforcleangold surface,(b)completemeasured(dots)andfitted(lines)SPRcurvesfor2CBTEALB film.

bytheWinspallcurveﬁttingprogramaregiveninTable1.The

ﬁt-tingcalculationsproduceameanvalueof1.14nmforthethickness permonolayer,andvaluesbetween1.64and1.82fortherefractive index.Fortherefractiveindicesofcalix[n]arene(n=4,8)thinﬁlms, similarresultswereobtainedby[4,6,25],1.46by[26,27],1.494 by[28],1.48by[29]andbetween1.54and1.43by[30] respec-tively.Katantsevaetal.studiedtherefractiveindexandthicknessof severalcalix[n]arenemoleculesanddeterminedrefractiveindices between1.47and1.70alongwiththicknessvaluesfrom0.80to 1.50[31].

4. Sensingproperties

TheSPRtechniquewasusedinordertoinvestigatethe adsorp-tionpropertiesofCBTEA LBfilms. Bothsteadystateandin situ adsorptionkineticcharacteristicswereobtained.Thisalloweda comparisonofthesensitivityofthedevicetofourvolatileorganic compounds(VOCs)andthedeterminationoftheselectivityofthe sensor.Fig.8showsthatadsorptionofthevolatileorganicvapour causesanincreaseinthethicknessandtherefractiveindexofthe LBfilm[4].Themechanismofadsorptionconsistsofincorporation andaccumulationofthevolatileorganicvapourfromthegasphase intothenanoporouscalixarenematrix,whichisaccompaniedby swellingofthefilm[23,26].Adsorptionanddesorptionprocesses areveryfastandafullrecoveryoftheLBfilmoccurs.The sen-sitivityfor theSPRsignaltotheexposureofchloroformvapour isquitehigh.Resultsobtainedalsoshowthepossibilitiesforthe developmentofopticalsensorsforaromaticcompoundsbasedon calix[4]areneLBfilms.

Sensitivityandselectivityoftheﬁlmtochloroform,benzene, tolueneandethanolvaporswerestudiedusingSPRmeasurements.

530 580 630 680 730 780 350 300 250 200 150 100 50 0 a.u Time, s chloroform benzene toluene ethanol 530 580 630 680 730 780 800 700 600 500 400 300 200 100 0 a.u Time, s chloroform

Fig.8. KineticresponseofsensorscoatedwithCBTEA(10layers)toinjectionof volatileorganicvaporsintoworkingcell.Inset:reproducibilityoftheﬁlmfor chlo-roform.

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The CBTEA sensing film was foundto be stable and exhibited nosignificantlossesinsensitivitywhenthemeasurementswere repeatedmanytimes.Fig.8displaysasetoftypicalcurves show-ingthereflectionintensityasafunctionoftimewhentheCBTEA LBfilmisexposedtosaturatedvolatileorganicvaporsfor2min followedbycleanairforafurther2minperiod.Thevalueofthe photodetectorresponseisproportionaltothechangesin reflectiv-itysincethemeasurementswerecarriedoutwithinthelinearpart oftheSPRcurves.Itcanbeseenthatitsresponsetoallvaporsare veryfastandreversible.Suchbehaviourofsensorscanbeexplained bytheinteractionbetweenthechemicalstructureofmaterialand theorganicvapour.Forexample,increasingthecalixarenecavity sizeleadstohighermagnitudesofresponsestoinjectionofvapors ofchlororganiccompounds[25,32,33].

ItcanbeconcludedthattheCBTEALBfilmstudiedhereshows someresponsetoallvaporsandismoresensitivetowards chlo-roformthanforothervapors.Thismightbeduetothestronger polarityof the chloroform molecules,allowing them toform a strongerinteractionwiththesensingmaterial;consequentlymore molecules are adsorbed.A similarresponse tochloroform was reportedforthesensorsbasedondifferentcalixarenematerials [32,34,35].The lowest response was given totoluene having a benzeneringandtoethanol.Itseemsthatthephysico-chemical propertiesofgasmoleculessuchastheirpolarityhaveaninfluence ontheadsorptionbehaviourwhenthegasmoleculesareadsorbed bythesensingfilms.Thedifferentabsorptionbehaviouroftoluene andbenzeneobservedinourstudiesmaybeattributedtothe differ-entsymmetryandpolarityoftheirmoleculesalongwiththelower saturatedvapourpressureoftoluene.Intoluenethispropertyis duetotheCH3groupinit.

5. Conclusions

In summary, we have studied the optical and gas sensing propertiesofcalix[4]arenesderivatives.CBTEAwasproducedand depositedasLBfilmsonquartz,gold-coatedglassandquartz crys-talsubstrates.Thefilmswerecharacterisedopticallybymeansof UV,QCMsystemandSPR.Isothermgraphresultsindicatedthat this molecule gives a stable monolayer at the air–water inter-faceandasurfacepressurevalueof22.5mNm−1 atsolid phase isselected fortheLBfilm deposition.Aplotof UVabsorbance, measured at 370nm as a function of number of layers gives a linear relationship. This proved that this material can be depositedontoaquartzsubstrate.Similarlinearrelationshipswere obtainedwithrespect tothedeposited mass onto quartz crys-talsubstrateswhichwasthenutilisedforQCMmeasurementsto determinetheresonantfrequenciesversuslayernumber[36,37]. A slope changeoccurred for small number of layers indicating a deposited mass value of 920ng permonolayer. Accordingto ourSPRresults,theLBfilmtransferontogold-coatedsubstrates was found to be successful and monolayers were transferred uniformly onto thegold-coated glasssubstrate. The film thick-ness t and refractive index n of CBTEA LB film was found to bet=1.14nm/depositedlayerandn=1.6,respectively.Monolayer thicknesses derived fromSPR reflectance curve fitting were in goodagreementwiththeabovefindings,andopticalparameters obtainedcompare very wellwiththose foundin theliterature [13].

Acknowledgement

ThisworkissupportedbyTurkishScientiﬁcandTechnological ResearchCouncil(TÜB˙ITAK).Projectno.:TBAG-107T343.

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Biographies

ZikriyeÖzbekreceivedherMScinphysicsfromtheUniversityofBalikesir,Turkey in2007.SheiscurrentlyworkingtowardsthePhDdegreeatUniversityofBalikesir, Turkey.

RifatÇapanreceivedMScdegreeatHacettepeUniversityPhysicsEngineering Departmentin1991,Ankara,TurkeyandhisPhDattheUniversityofSheffield (UK)in1998.HeestablishedfirstLangmuir–BlodgettThinFilmResearchGroupin Turkey.HehadaPhDscholarshipfromTurkishHighEducationCouncilbetween 1993and1998andhadOversea’sResearchStudentAward(UK)from1995to1998. Hismaininterestsarepyroelectricheatsensor,gassensorforenvironment appli-cations,theelectricalandopticalpropertiesoforganicthinfilmmaterials.Hewas appointedassistantprofessorbetween1999and2002andassociateprofessorfrom 2002to2007atUniversityofBalikesirinTurkey.Hebecameadeputyofheadof physicsdepartmentin2001andwastheheadofphysicsdepartmentbetween2003

professoratPhysicsDepartment,UniversityofC¸anakkaleOnsekizMartsince2009.

FatmaGül ˙IncereceivedherMScinphysicsfromtheUniversityofC¸anakkale OnsekizMart,Turkeyin2008.SheiscurrentlyworkingtowardsthePhDdegree atTulaneUniversityatNewOrleans,USA.

MehmetE.ÖzelhasreceivedhisMScandPhDdegreesatMiddleEastTechnical University(Ankara,Turkey)in1972and1978respectively.Hisresearchareahas beenhighenergyastrophysicsuntilhejoinedthestaffofÇanakkaleOnsekizMart Universityin2002.HeactedastheDirectorofGraduateSchoolforScienceand Engineeringinthesameuniversitybetween2002and2008.Duringthistime,hehas alsoparticipatedinthere-definitionofcurriculumofPhysicsMajorsinthePhysics Department.Heparticipatedindevelopingahealthphysicsandmaterialsciences optionsforphysicsgraduates.Hehelpedthedevelopmentofthesetopicsandrelated researchthroughTurkishNationalScienceFoundation(TUBITAK)projectsjointly withDr.RifatÇapanofBalıkesirUniversityandTurkishAtomicEnergyCommission (TAEK)programs.HeispresentlytheDeanofFacultyofArtsandSciencesatÇa˘g UniversityatTarsus,Mersin.

FrankDavisgraduatedfromLancasterUniversity(UK)in1987andobtainedhisPhD atthesameinstitutionin1991.FollowingpostdoctoralexperienceatManchester andSheffielduniversities,hethenspent4yearswithinthebatteryresearchgroup atGilletteUKRDL,Reading.HejoinedCranfieldHealth,CranfieldUniversity(UK)in August2002.Hehasawideexperienceofthesynthesisofcalixarenetypematerials andnovelamphiphilicandsurfactantmolecules.Muchofhisresearchisfocussed towardstheincorporationofnovelsensingmoietieswithinultra-thinfilmsandtheir usetodetectawidevarietyofspeciesincludingorganicsolventsandcarcinogens, aswellasbiologicalspeciessuchasascorbate.Heistheauthorofinexcessof80 publishedpapersand6patents.HeisamemberoftheRoyalSocietyofChemistry andaCharteredChemist.