Chandok, R S

Khare, P K

IACS Institutional Repository

Indian J. Phys. 69A (5), 545-551 (1995)I JP— an international journalDielectric behaviour of solution grown poly(vinyl) pyrrolidone filmsP K Khare and R S Chandok*Deportment of Post Graduate Studies & Research in Physics, Rani Durgavati Vishwavidyalaya, Jabalpur, Madhya Pradesh-482 001, IndiaReceived 21 December 1994, accepted 2 June 1995Abstract : Measurements on dielectric relaxation in poly(vinyl) pyrrolidone (PVP) films, of approximately>20 microns in thickness, were made for similar (AI-AI) and dissimilar (Al- Sn/Cu/Ag) electrode combinations in the frequency range (500 Hz-20 kHz) and temperature range (40-200°C). PVP films exhibit two dielectric loss maxima, one around 100 ± 5°C and the other around 170 ± 5°C, respectively With increasing frequency, the magnitudes of capacity and of both the loss peaks decrease and also the loss peak positions shift towards higher temperature side Pronounced effect of electrode material on the capacity and loss peaks has also been observed. The results of the experiments and the mechanisms involved have been discussed.Keywords : Poly(vinyl) pyrrolidone, capacity and losses; dipole-dipole interactions PACS Nos. : 77.55.+f, 77.22.GmDielectric studies are o f  special interest in relation to polymers since they provide vital information on the molecular configuration o f a system. The evaluation o f the dielectric properties o f  insulator films is carried out by measuring simultaneously the capacitance and dissipation factor over a wide range o f  frequencies and temperatures. A knowledge o f  the dielectric loss behaviour o f thin polymer films is very important because o f their possible technical application for insulation, isolation and passivation in microelectronic circuits. The capacity and the dissipation factor are the crucial quantities required in the design of  devices and furthermore, as a function o f temperature or frequency they reveal much information on the chemical or physical state o f  the polymer.Dielectric behaviour of a number of polar and nonpolar polymers have been investigated in the last decade [1-5]. Poly(vinyl) pyrrolidone (PVP) is known to be of a growing pharmaceutical importance [5-7]. A systematic study of dielectric behaviour over* Shri Guru Teg Bahadur Khalau College. label pur-482 001, Indie© 1995IACS546 P  K K hare an d  R S  Chandoka range o f  freq u en c ies  and tem peratures w as undertaken to understand the nature o f  the  relaxation s in PV P.P o ly (v in y l)  p yrro lidon e (P V P ), m o lecu lar  w e ig h t 4 0 ,0 0 0  w a s ob ta ined  from  M /s  L oba C h em ica l, B om b ay . P V P  is know n as a polar polym er, due to its carbonyl group o f  dou ble  bond in pyrrolidone ring [8]. T he netw ork structure o f  P V P  has d ifferent length  o f  n  and a  bon ds in b etw een , n itrogen , o x y g e n , carbon  and h y d rogen  a to m s [9 ,1 0 ] , T he  asym m etric  distribution o f  e lectron ic  charges near d ifferent atom s (N , O , C and H ) m ay be  p o ss ib le  in P V P , h en ce  it is know n as a d isordered  m aterial. In P V P , the asym m etric  m onom ers are present in the structure and it p o sse sse s  a side group (as pyrrolidone ring). Its structure is as fo llo w s  [11].C H 2 ---C H 2 1 !I IC H 2 ---------C  =  0\  /NIC H  — C H ZT h e so lu tio n  w as prepared in a g la ss  beaker by d isso lv in g  2.1 g P V P  in 3 0  cm 3 o f  chloroform  at room  tem perature. T he so lu tion  w as continuou sly  stirred for about 30  min by  m eans o f  a te flo n -co a led  m agnetic stirrer. Thereafter, the so lution  w as stirred and heated to 5 0 °C  to en su re  a h o m o g en eo u s m ix in g  o f  the so lv en t. T he g la ss  beaker con ta in in g  the so lu tion  w as then im m ersed  in a constant tem perature oil bath. U ltrason ica lly  c lean ed  g lass  s lid e  w ere  im m ersed  vertica lly  into  the so lu tio n  for a period o f  30  m in. A fter  the film  d ep o sitio n , the g la ss  s lid e  w as taken out and ou tgassed  in air at 5 0 °C  for 2 4  hrs. fo llo w ed  by room  tem perature o u tgassin g  at 10“* torr for a further period o f  24  hrs. V acuum  coated  e lectro d es w ere used throughout the work. T he th ickness o f  the sam ple w as approxim ately  2 0  m icrons. T he geom etry  o f  the sandw ich  configuration  o f  the e lectrod es, and th ickness o f  the sam p le w as sam e as reported earlier [12,134-T h e  a ssem b ly  w as held  in a therm ostat and the tem perature w as m easured  using  calibrated copper-constantan  therm ocoup le. T he capacitance and lo sse s  w ere m easured with  a S y stron ics L C R  bridge T yp e 921 using a P h ilip s A F  generator m odel G M  2 3 0 8 /9 0 .F igu re  1 sh o w s the capacity  o f  P V P  film s as a function o f  tem perature at d ifferent freq u en c ies  (5 0 0  H z, 1 kH z, 5 kH z, 10 kH z and 2 0  kH z). T he capacity  va lu es have been  found to d ecrease  w ith  increasing frequency. F igure 2  sh o w s the capacity  va lue o f  P V P  as a fun ction  o f  freq uency  (lo g  f) at constant tem peratures. F igure 3 sh o w s the lo sse s  at d ifferent freq u en c ies  as a fun ction  o f  tem perature for sim ilar  e lectrod e  (A 1 -P V P -A 1 ) sy s tem . T he  lo s s  c u r v es  h a v e  b een  fo u n d  w ith  tw o  m a x im a  aroud 10 0  ±  5 °C  and 1 7 0  ±  5 °C , r esp ectiv e ly . F igu re 4  sh o w s the variation o f  lo ss  o f  P V P  film s w ith  sim ilar  ( A l - A l )  andd iss im ila r  (A l-S n /C u /A g )  e lectrod e  sy stem s. B oth  the lo ss  peaks sh ift tow ards h igher  tem perature. It is observed  that the m agnitude o f  capacity and lo ss  peaks are h igher in the case o f  the d issim ilar  electrode system  than in the case  o f  A l—Al e lectrode system .Dielectric behaviour o f solution grown poly(vinyl) pyrrolidone films 547Figure 1 . Vanaiion of capacity with temperature at different frequencies for AI-PVP-AI samplesFigure 2. Capacity versus log f  for AI-PVP-AI samples at different temperatures.T he carbonyl group o f  P V P may p o ssess orientation w ith respect to  the active groups [ 14). T he d ifferent types o f  rotational m otions o f  polar groups o f  P V P  structure attribute to higher lo sse s . T he m axim um  value o f  lo sse s  ( lo ss  peak) in certain tem perature reg ion s are p ossib le , due to phase transition behaviour o f  PVP. At a certain temperature, the side chains are im m o b ile . T h e se  cha in s are tightly bound at d ifferen t p o in ts d u e to d ip o le -d ip o le  in teractions o f  pyrrolidone groups. A s the tem perature is  increased, m ore and m ore polar  groups are re leased  from  their bound state. T he h igher d ip o le  m om en t o f  pyrro lidon e548 P K Khare and R S Chandokadjacent group and their strong d ip o le  interactions w ith  the m ain chain m ight be responsib le  for the h igher d ie lectric  lo sse s  in PV P.FREQUENCYFigure 3. Variation of loss tacior with temperature at different frequencies for AI-PVP-AI samples.TEMPERATURE l ’ C )Figure 4. Variation of loss factor with temperature at constant frequency for dissimilar electrode (Al-PVP-Sn. AI-PVP-Cu and Al-PVP-Ag) combinat ons.T he increase in capacity  va lu es ab o v e  the room  tem perature m ay be due to increase  in m o lecu la r  m o b ility  and a lso  m ay b e  partly d u e to  the ex p an sion  o f  the la ttice  [15 ] and partly d u e  to  the e x c ita tio n  o f  charge carriers w h ich  are lik e ly  to be presen t in sid e  the sp ec im en  at the im p erfectio n  s ite s . A t lo w er  tem perature, m o lec u le s  are im m o b ile  and th erefo re, the nurfiber o f  d ip o le s  w h ich  fa c ilita te  to o r ien t w ith  the f ie ld  w ill be less. In crease  in tem perature in creases the m olecu lar  m o b ility  and therefore, m ore num ber o f  d ip o le s  or ien t th e m se lv es  in the fie ld  d irection . T he am orphou s-crysta l 1 rmr in terphases in P V P  b eh ave  as trapping cen tre  for carriers [5]. S in ce  the arrangem ent o f  m o lec u le s  in theD ielec tric  behaviour o f  solution grow n p o ly ( vinyl) pyrro lidon e film s  5 4 9am orphous state  is not regular, the van der W all's fo rces betw een  the m o lec u le s  vary from  p la c e  to  p la ce . It is  th erefore, e a sy  to  c o n fo rm , or m o v e  the m o lecu la r  ch a in s in the  am orphou s state. T he m olecu lar  packing in the am orphous reg io n s is  lo o se  and so  the  den sity  is sm aller  than that o f  crystalline regions. T hus, the chains in the am orphous phase  are m o re  f le x ib le  and are cap ab le  o f  o r ien tin g  th e m se lv es , r e la tiv e ly  m ore  e a s ily  and  rapidly. In cry sta llin e  reg ions, the forces w h ich  hold the structural un its togeth er are o f  a h om op olar  ch em ica l binding nature and are m uch stronger than the van der W all's forces. T herefore, the m o v em en t o f  a segm en t o f  chains in the higher density  crysta lline  reg ions is hindered  by o ther neigh b ou rin g  structural un its. T he m olecu la r  ch a in s w ith  d iffe re n t  m o b ilitie s  for the am orphous-crystalline regions try to adjust th em selves in such a w ay as to add to the polarization  o f  the system  [161. T his m olecu lar a lign m en t o f  chains m ay ca u se  the ob served  increase in the capacity values.T h e  variation  in capacity  and lo ss  va lues, su g g ests  the net e ffe c t  o f  so m e internal f ie ld  w ith in  the p o ly m er  a lo n g w ith  the external a c  field . T h e d ip o le -d ip o le  in teractions  betw een  the d ifferent groups or m any body interactions su ggest the low er lo sse s  w ith higher  freq uency  range. T he depen d en ce  o f  the capacity on frequency can be  determ ined from  the fo llo w in g  equation [17]C =  C  +S r+  r  2W 20 )w here C K is the geom etrica l capacitance, S  the conductance corresponding to the absorption  current, r  the d ip o le  relaxation  tim e and W the angular frequency. T he above equation sh ow  that C  sh ou ld  d im in ish  w ith increasing frequency.T h e  in crea se  in lo s se s  (F igu re  3) at lo w  frequency c o u ld  be asso c ia ted  w ith  the  p o la r iza tion  o f  the trapped charge carriers. W ith the in crease in freq uency , po larization  d ecrea ses and b eco m es van ish in g ly  sm all at h igh frequencies. T he decrease  in lo sse s  w ith  frequency a lso  seem s to sh o w  the d ecrease in the num ber o f  charges and delay in settling  o f  d ip o le s  d u e to ava ilab ility  o f  very short tim e in one h a lf  c y c le  o f  alternating vo ltage. T he  general ex p ression  for d ie lectric  lo ss  is g iven  by the equation [17]tan <5 =y y V (G in + 5) + c in w{5t + c <(W2r2 + i ) } ’(2)w here Cjn is the condu ctan ce  for the residual current. From  cq. (2 )lim  tan 5  s  CO,W  -» 0lim  tan5  =  0. w «D ifferen tia tin g  eq . (2 )  w ith  respect to W  and then equating  the d er iv a tiv e  to zero , it is  p o ss ib le  to obtain  the value o f  W* o f  the frequency corresponding to  m axim um  loss.550 P K Khare and R S ChandokT he lo ss  peak at 170 ±  5°C  m ay be attributed to  segm en ta l m o b ility  o f  glass transition type and a lso  to release o f  all types o f  ions/carriers at g la ss  transition range ( Tg) o f  P V P  (around 170°C ). The side group (C = 0 )  is attached w ith nitrogen atom  o f  P V P . This group is com bined  with other active groups (> N -C = 0 ) ,  hence there m ay be a larger number o f  d ip o le s  apart from  the m olecu lar  m otion  and a h igher am ount o f  en erg y  m ust be associated  with the rotation o f  adjacent side o f  the polym er structure. T he rotational energy  a longw ith  m any body interaction at or near Tg (secon d  lo ss  peak) m ust be associated  with different atom s o f  m ain chain such as C -C  or C -N  atom s. T h ese  bonds o f  nitrogen and o xygen  are different in nature and they posses different types o f  binding tendencies between  C, O and N atom s. A t T R o f  the polym er, the bonds are loosened  to som e exten t and results a higher lo ss peak in higher temperature range, whereas, the lopal m otion o f  adjacent group is associated  in com paratively  low er region o f  temperature. P y P  form s a com plex  network o f  conjugated  ch em ical reactions in the presence o f  m oisture\ The ch em ica l reactions in com plete  phase transition m ay be g iven  byH O H ^ H + + O H '> N - C = 0  + OH ->  N -C O O H  + H+ + c~.T he d isso c ia ted  water m ay produced the H+ and O H -  pair. T he ion ic/c lectro n ic  charge  carriers released at rubber g lass transition temperature and the com p lete  phase transition is observed  w ith a sterio-change in its long  chain structure. T he losp peak has been found at 100 ±  5°C  is related to the unfreezing o f  side group iflotion in less ordered dom ain and the second  loss peak (at about 170 ±  5°C ) is associated  to the unfreezing o f  segm ental m obility  w ithin the non-crystalline  clusters and possib ly  to the appearance o f  a certain m obility  o f  different results o f  loss peaks can be understood with the help o f  different considerations o f  the P V P  structure.F igure 4 exh ib its the variation o f  lo sse s  versus  tem perature for e lectrode m etals, alum in ium , copper, s ilv er  and tin having work function  3 .3 8 , 4 .4 6 , 4 .31  and 4 .0 9  eV , resp ectiv e ly . It is clear from  the figures that the lo sse s  (at d ifferent tem peratures) differ  w hen the upper electrode alum inium  is replaced by copper, silver  or tin. T he m agnitude o f  lo ss  peaks w ere found to be higher in dissim ilar e lectrode (A l-C u  and A l-A g )  than sim ilar e lectro d e  (A l- A l)  com binations. T his sh o w s the e ffec t o f  the m aterials o f  e lectrod es on lo sse s  o f  the sam p le sandw iched  betw een  [hem . V a lu es o f  lo sse s  seem  to be controlled  by the e ffe c tiv e  work function o f  m etal-insulator-m etal interfaces i.e.  the d ifference in energy  betw een  the Ferm i leve l in m etal and the bottom  o f  the conduction  band in the insulator. T h erefo re , d ie lec tr ic  param eters are changed  w hen  the e lectro d e  form in g  m aterial is changed . T he d ifference betw een  the work function o f  m etal (1 ) and m etal (2 ) w ill control the m agn itud e o f  lo ss  but for A l-A l e lectrode  system , the characteristics o f  the polym er  m ay prevail as the net contribution o f  charges injected  from the e lectrodes w ou ld  then be zero [ 18 ,19 ]. T he various therm ogram s represent the distributed relaxations in term s o f  loss peaks. T he reason for distributed relaxations m ay be due to the com b in ed  e ffe c t o f  space  charge injected from  electrod es and dipolar relaxations in the polym er. T he appearance o f551the peaks at distributed position is perhaps due to uniform polarization. In these results, it is also suggestive that the internal field of polymer may gel modified by the difference in the work function of various electrode metals [20],References[ I ] G K Narula, Kashmi and P K C Pillai Acta Polymerica 40 46 (1989)[2] P C Mohendru, Ramadhar Singh, Naresh Kumar and N P Gupta Indian J. Pure Appl. Phys. 23 64 (1985) [31 Y K Kulshrcstha and A P Srivastava Thin Solid Films 71 41 (1980)[4) I M Tulwar, H C Sinha and A P Snvastava J. Mater Scl L*tt. 4 448 (1985)151 P K Khare, M S Gaur and Ranject Singh Indian J. Phys 68A 545 (1994)[6 ] F J Prescatl Druf> and Cosmetic Indus 97 497 621 (1965)[7] P K Khare, H L Vishwakarma and A P Srivastava Indian J. Phys. 68A 571 (1994)[8J Y Y Tan and G Challa Polymer 17 739 (1976)[91 Horizon in Biochemistry (Albert S^ent Gyooryi Debicatory Vol) eds. M Kasha ahd B P PulIcnan (New York Academic) p 364 (1962)[10] J Banadup and Inimorgut /-// Polymer Hand Book 2nd edn (New York : Wiley) p i l l  (1975)[111 Encyclopedia o f Chemical Technology, Vol 21 ed. E J Palaski (New Voik : John Wiley) p 427 . Hasmaextenders in Kirk Othmev. Encyclopedia o f Chemical Technology, Vol 10 (1st edn) eds. A Standen j)ndJ Scoot (New York : Inierscience) p 421 (1970)112] P K Khare and A P Snvastava Indian J. Pure Appl. Phys. 30 102 (1992)113] P K Khare, M S Gaur and A P Srivastava Indian J. Pure Appl. Phys. 32 14 (1994)114] S K Chatleriee and K R Sethi J Polvm. Chem. 21 1050(1983)[15] W R Beam Eleuronks of Solids (New York : McGraw Hill) p 385 (1965)[16] PC Mahendru, J P Agarwal and K Jain Indian J. Pure Appl. Phys 19 2 17 (1981)117] B Tareev Physics of Dielectric Materials (Moscow Mir Pub) (1975)118] P K Khare and A P Srivastava Indian J. Pure Appl. Phys, 30 131 (1992)[19] P K Khare, P Surmder and A P Snvastava Indian J. Pure Appl Phys. 30 165 (1992)[20] P K Khare and A P Srivastava Indian J Phys. 68A 291 (1994)D ielec tr ic  behaviour o f  solution grow n po ly(v in yl) pyrro lidone film s

Dielectric Behaviour of Solution Grown Poly(Vinyl) Pyrrolidone Films

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Dielectric Behaviour of Solution Grown Poly(Vinyl) Pyrrolidone Films

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