The ultrasoni c absorption coe ffici e nt (a) and velocity (v) of so lutions of polyvinyl chloride (PYC). in methy lethy lk etone. aceto phenone and cyclohexanone have been measured using ultrasonic pulse technique. at a frequency of 800 kHz and at a temperature of 303 K. Shear viscosity coefficient (Il s) and density (p) have bee n meas ured for these so luti ons. at thi s temperature. Relaxati on amplitudes (al /) exp and (al f \1 and relaxation times, 'exp and ' cJ (~ ' s)' Bulk viscosity

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... ffiecient (Ilb)' adiabatic bulk modu lus (K) , adiabatic compressibility (8) and spec ifi c acoustic impedance (2) ha ve been calcul ated from these measurem ents. The results show that p. Il s ' K and Z increase with concentration of PYC in the three so lv ents. while (al/) exp and (al/)cl> a and B decrease. ' exp and 'cJ show onl y negligible vari ati on. Their ratio ('exp It el) = (al /) exp I (al /)cl is alm ost independent of concentration. Ex perimental values of (al /) and , are found to be much larger th an classica l values. i.e. (al/)cJ ' s' The results are discussed in terms of Ilb and Il s ' It is fou nd that Ilb is far g reater than Il s' The variation of ultrasonic velocity (V) with frequency (f) is termed as dispersion , while reduction in the amplitude of the ultrasonic wave with di stance traversed by the wave in the medium is known as absorpt io n. Absorption and dispers ion exist together with defi n ite relati ons between them. There are various causes for absorption and dispersi on of the wave. Thermal conductivity o f the medium gives a small contribution to absorption, and is usually neglected. Shear viscosity (T] s) was found to be quite inadequate to explain the observed ultra so nic absorption in th e liquid. Various modem theories, proposed recently, ex plain the observed absorption adequately. T hey attribute ul-trasonic absorption mainly to intermolecular processes and intramol ec ular processes. T he former is due to vari-o us intermolecu lar (o r interato mic) forces, binding energies and re laxations due to structural changes, which lead to absorption and di spersion of the wave. T hese processes are associated main Iy with bulk v iscos ity (T]b), bulk modulu (K) and compress ibilit (8) o f the medium , which become complex and frequency-depende nt under the action of a high freque ncy ultrasonic wave, leading to absorption and dispersion of the wave. Intra-molecular processes are not di scussed here. Thi s paper di cusses experimental results t obtained by the authors) in term s ofll u and T] s of the medium , the ir vari ation and variation of B, K and Z of three different solutions, with concentration ofPVC(so]ute) in three different solvents. Experimental details-U ltrasonic pulse technique has been used to determ ine a and v in di fferent so lutions, obtained by disso lving PV C in methylethylketone, ace-tophenone and cyc lo hexanone in various concentrations. The solutions are homogeneous. Dens ity (p) has been measured for ellch concentration with a specific g ravity bottle-shear viscosity coefficient (T] s) has been determined for each concentration, with an Ostwald Viscometer, all at the same te mperature of 303 K. The frequency (f) of the acoustic pulse is 800 kHz. Table I gives a sample of the readings and calculations, for determination of the average values of a and v, for a concentrati on of 0.1 (=C%) of PVC in mehtyleth Ike-tone. 'C% = 0.1 ' indi cates a concentration of I kg of PVC in 1 m 3 of the so lvent. Equation s used-T he classical (cl) re laxation amplitude , due to shear viscosity (sv) is gi ven by: «(,(/t~)s" = (a/F)cI = (4 11 s13)(2 n 2 / p v 3) The classica l (shear) re laxation time ('s) is by: (s = (4 T] sl3) / P v 2 = ((,(If)cJ (vl2 n 2) = lei ... (I) given ... (2)