Radio and microwave dielectric properties of PMA and. ·PiBMA in solution

Aashees Awasthi, Madhu Rastog, Ma Nisha Gupta, J Shukla
2000 Indian Journal of Pure & Appli ed Ph ysics   unpublished
Th e di electric ah sorption of dilute so luti ons of poly (methy l acry late) (PMA) and poly (isohu ty l methacry late) (PiBMA) in henze ne ha ve heen slU di ed in the radio and Illicrowave freq uency reg ion of 10 to SOO k Hz and 10 GHz res pecti ve ly and at fi ve dill rellt temperatures 303. 3 13. 323. 32K and 333 K. Us ing frequency va ri ation techniqu e enthal pi es of aet ivati on for PM A and Pi BM A h:lVe been found to be I 1.4 and 26.1 kJ / lllol res pecti ve ly. For hoth the
more » ... or hoth the systems. data eva luated usi ng frequency variati(ln Illeth od we re also supported hy th e measurements carri ed out using concentrati on variation method at th e mi crowa ve frequency. • Th e ellthalpies or acti vat ion !:J. I-/£ ohserved here were expected to be arising due to the intern al rotation in vo lv in g th e es ter o II !!roup-C \ ' OR I Introductio n Po lyacrylates ha ve fo und nume rous appl icat ions as industrial plast ic s du e to th e i I' stre ngth. tra nsparenc y and low spec ific g ra vit y in co mparison [(l g lasses. The pol y-me rs ha vc bee n ex te ns ive ly st udi ed for th e ir mec hani ca l and e lec lri cal prope rti es us in g u ltraso ni c;, mec hani cal, NMR, lig ht-scattering and di e lectric tec hniqu es l. 7 T he dielectric in vest igat io ns prov id e a fundam e nta l method fo r stud y in g th e rotational process in vo lved in th e po ly-me rs. Th e measureme nt o f di e lectric parameters as a funct ion of frequ e ncy and te mpe rature is among the we ll establi shed me th ods fo r de tec tin g th e dipo le reo ri e nta-tion by mo lec ul ar and g ro up rota tio n K. Many di electri c. ')· 11 relaxa ti on m eas ure m e nt ~ o n alk yl poly mers ha vc heen made with a view to study the relaxation processe~ occ urri ng in the " idc gro up and the main c hain. T he dielectric re laxations ca n be gro uped into two categu-ri es, pri mary (a) and seco ndary (B , y, 0 .. .). C all eja e l {/1. 1~ have studi ed a. a nd B-relaxari o ns of pol y (d ime th yl-phen y l m e th a~ ry late). Th e a-rclaxation involves long-range. generalizf'd and highly coo perative motions of th e mai n chain hut B-relaxation confines only to the local moti ons o f the "ide g roup. T he activa tion parameters associat ed with the ~-relaxa ti o n or poly (cyclohexy-lac rylate) have been reported by Ca ll eja e l 01.1 ' 1 Schartel and Wendorff·l.J have studied the :econdary relaxati o n (y-reiaxation) beha vio ur or a set of polyac rylates. The y-re laxation has to be co nnected both with inte r and intra mo lec ular mo tions , the corre lation le ng th o f which cannot be mu c h larger than th e sca le set by a-; in g le repea t unit. The dielectric re laxati o ns de pe nd stro ng l) 1-upon te mpe rature a nd pressure. Pu gh e l al. ' ha ve re-po n ed the di e lectri c pro pe r! ies us in g press ure a~ ~I pa-ram e te r in additi o n to tempe rature and frequ e nc y. Pressu re exerts larger e ffects on the a-process than on the B-process. Pel issou el 01 .16 ha ve re po rted .di e lectri c and v iscoe la sti c re laxati o n of pol y (2-c hl oro e th yl methacry late) and pol y (3-chloro propyl me thac ry late) between-140 °C a nd glass tran s iti o n temperatures. Ca ll eja el 01. I? have studied the electri c rel a xation III acry late pol y me rs with ri g id side g roups. Recent ly. die lectri c absorpti on studi es o n ' >o me polymers in P U I\' fo rm were reported hy o ur g rou pl K usin g mat rix technique . S ince very limited d ata are availab le on polymer sol ution s in literature and als the dil ute so lution m ea~­ ure me nts on pol y me rs seem to facilitate the rotation of the substi tue nt gro up s exhibiting th e relaxation process, it wa s cons idered important to stud y th e di electri c ab-sorpt ion of dilute solutions of PMA and PiBMA In be nzene at radi o and mi crowave frequen cies and ~I t vary ing temperatures. 2 Expcl'imental Dctails The HP im pedance/gain phase anal yse r (HP-l-l lJ4 A) wi th spec iall y des ig ned coax ial , cy lindri ca l sa mpiL:
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