Oscillating birefringence of the form and intrinsic anisotropy of polystyrene solutions

OSCILLATINGBIREFRINGENCEOFTHEFORMANDINTRINSIC ANISOTROPYOFPOLYSTYRENESOLUTIONS* S. N. PEN’KOVand V. P. BUDTOV A. A. Zhdanov State University, Leningrad (Received11 December1970)

IN EXPLAININO the “anomalous” angles of orientation [l] of dynamic birefringence (DB) in polymer solution flow it was suggested [2] that there is a difference between the orientation of intrinsic anisotropy of polarization properties and form. Possible mechanisms to account for this difference have been discussed in several papers [ 3-81. Oscillating dynamic birefringence (ODB) of polymethylmethacrylate (macroform effect) and polystyrene (PS) solutions (effect of intrinsic anisotropy in tetrabromethane) has been previously examined [9]. It was shown that the relaxation of intrinsic anisotropy and macroform effect in an oscillating mechanical field are similar (o=O-2000 see-l). For a more detailed study of the spectrum of relaxation times of the form and intrinsic anisotropy effects it is necessary to study the relaxation of these effects in the same solution of chain molecules. PS was therefore used which has negative optical aniso opy. Solvents were chosen to ensure the form effect ti’ in the solution which is always positive. If the relaxations of the macroform and intrinsic anisotropy effects differ, with the appropriate selection of molecular weight (M), concentration and solvent, changes can be expected in the sign of the overall ODB. EXPERIMENTAL DB in the field of constant shear stress was measured in an apparatus with a photoelectric attachment [lo, 111. ODB was measured in an apparatus previously described [12]. The frequency range was extended from 3 x lo4 c/s by using piezoceramicrods. The velocity gradient in the gap g < 400 see-1 (a more detailed description of the apparatus is given in another paper [ 131). A PS fraction with M= 6 x lo6 obtained by precipitation with methanol from solution in benzene was used. Decalin, dioxane, dimethylphthalateof different viscosities and properties (decalinis a poor solvent [la]) were used as solvents. The birefrmgenceobserved with low velocity gradients g and w=O was positive: the form effect,under these conditions is greater than the negative effect of intrinsic auisotropy. For comparison, ODB was measured in solutions of PS fraction in tetrabromethane, in which only intrinsic anisotropy was observed. * Vysokomol. soyed. A14: No. 8, 1869-1873, 1972.

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8. N.

fiN’KOV

and I’. P. BUDTOV

For PS solutione in decaliu experimental temperature was 26 and 46’; for PS in dioxaue and dimethyl phthalate -21°, in tetrabromethene experimental temperature was chosen to ensure a viscoeity equal to the viscosity of dimethyl phthalate (10”). The effect of solvent w8s taken into acoount in every case.

FIG. 1. Dependence of An (1) and 4, (2) on g for PS solutions iu de& g/ml, 46O.

when c=OM

x

IO-*

Figure 1 shows typical dependence curves of the extent and orientation of DB in a constant shear field, which had also been observed previously [2, 6, 6, 151. Figure 2 u-c shows the relstion of An value and the angle of lag Q,of ODB for the solution studied. A variation is clearly observed in the sign of ODB with an increase in frequency w, which proves a difference in the spectra of relaxation times of the macroform and intrinsic anisotropy effects. With small co values birefringence shows a phase lag (pO) and the Q,value decreases. For PS solutions in dimethyl phthalate (Fig. 2~) phase displacement becomes QI=O and then Q,irmreasesin absolute value (q
Oscillating birefringence of form and anisotropy of polystyrene solutions

2096

medium is due to varying orientations of form and intrinsic anisotropy effects [2-81. Ratios for an angle of orientation +Vand optical properties of the medium were derived (2,5) from the Sadron ratios [17] for polydispersed systems. Assuming

P

I

80 40

-20 -60

FIG.2.DependenceofAn/go (I-3, 7, 8, 11, 13,15)and p (4-6,9,10, 12, 14, 16) on w of PS solutions in decalin (a); dioxane (bj; dimethyl phthalata (c) asd tetrabromethane for &e&e of intrinsic aniaotropy (13, 14) and form (16, 16) (d) at 10, (13-16) 21 (7-B), 25 (2, 3, 6, 6) and 45’ (I, 4) and with concentrations of 0*86x lo-* (I, 2, 4, 5); 0.33 x 10-l (3, 6, II, 12); O-22x lo-’ (7, 9) and O-38x 10-a g/ml (8-10).

that vf-~t=6, where yf and v/c are angles of orientation of the form effect An, and intrinsic anisotropy effect An‘. Then [S] tan 2 (v--y/j+

sin 26 co8 26f An,/An(

(1)

S. N. PEN’KOV and V. P. BUDTOV

2096

W’hen v/--t+vf=45’ the value of An reaches its minimum and suddenly changes sign so that An#O in any region of g (Fig. 1). This was first observed [18] when measuring An in an apparatus equipped with photoelectric recording [lo]. The minimum value of Anmi,

An,,, = 1Ani 1sin 26

(2)

These ratios enable us to evaluate 6 for PS solutions in decalin. Its value is 5’ when g= 1500 set-l, the form effect being stronger than the effect of intrinsic anisotropy. Oscillating dynamic birefringence. The changes observed in the sign of ODB and the “anomalous” dependence of the phase on w can be described if we assume that the relaxations of intrinsic anisotropy Ani and macroform Anf are different. To simplify the ratios given we assume that relaxations Ant and A+ are only described by two times, zd and zf. Then An(w)=Ana(w)+Anf(w)=--ff--+f

1 +joq

1 +joz,

(3)

,

where at and af are parameters independent of frequency. After simple transformations we derive for the phase of overal ODB

tan q=o

(4)

and for the amplitude of ODB 1AnI = dAn2 Ana=

at

1 [

14!L+w2__ 2

1 + co”zT; 1 f 09r;

1+ot:+1+w2z; acre afrf

1 2

(5)

As for DB, the value of ODB is not zero when changing the sign An. The typical points of the dependence q=p(o) (p=O and 90”) enable us to derive simple ratios to evaluate zc and zf. Let q=O when o,#O and then

(6) and the value of o0 when q=O is determined from ratio (4): the numerator is zero. Let ~=90” when oBO# 0 and then this value of wg,,is given by ratio (4) in the event of the denominator being zero.

The relaxations of intrinsic anisotropy and form effects can be compred quantitatively for PS solutions in dimethyl phthalate and tetrabromethane

’Oscillating birefringenoe of form and anisotropy of polystyrene solutions

2097

a,s in fhese solution

solvent, viscosities and intrinsic viscosities of the solution are similar. Figure 2d shows experimental values of An (co) and Q(0) for PS in tetrabromethane and An (co) and q (0) values calculated for the macroform effect. It can be seen that when w<600 set-l IAnfIb=- IAnt\, when a>600 set-l IAnal> JA+(. The angle of lag for the form effect is larger than for the effect of intrinsic anisotropy, whereby when 0=600 set-l Pi-- CJQ~~‘,when o=104 see-1 o+-- pz % 7”. Thus, although results prove a difference in spectra of relaxation times, this difference is slight. It is interesting to compare measurements of DB and ODB for PS solutions in decalin. When measurements are carried out in constant shear field An, becomes minimum with gr1300 set-l, whereas in oscillating field An becomes minimum when 0=1600-2000 set-l. When the angular velocity of rotation is calculated in constant shear field &g/2 than the value observed

[19] then c&650

experimentally.

see-l, which is considerably

This difference is not unexpected

less as a

effects as regards g, whereas for ODB all effects are within the linear range of g. This proves a fundamental difference in the behaviour of macromolecules in variable and const,ant shear fields. change in the sign of DB is the consequence

of non-linear

CONCLUSIONS

Oscillating dynamic birefringence of polystyrene solutions was measured in different solvents in the frequency range o=O-2 x lo6 set-l. A change was observed in the sign of sirefringence and phase with an increase in frequency and it was found that phase depends on optical properties of the medium. Experimental data con&m the difference in the spectra of relaxation times of intrinsic anisotropy and form effects. Tram&ted

by E. SEMERE

REFERENCES 1. E. V. FBISMAN, Dokl. AN SSSR 118: 72, 1958 2. V. N. TSVETKOV and I. N. SHTENNIKOVA, Sb. Karbotsepnye vysokomolekulyarnye

soyedineniya (Carbon-Chain High Molecular Weight Compounds). Izd. AN SSSR, 1963 3. M. COPIC,J. Chem. Phys. 26: 1382, 1957 4. P. KOYAMA, J. Phys. Sot. Japan 16: 1366, 1961 5. V. N. TSVETKOV and I. N. SHTENNIKOVA, Vysokomol. soyed. 2: 640, 1960 (Not translated in Polymer Sci. U.S.S.R.) 6. E. V. FRISMAN and SYUI MAO, Vysokomol. soyed. 6: 34, 41, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 1, 37, 46, 1964) 7. Yu. Ys. GOTLIB and Yu. Ye. SVETLOV, Vysokomol. soyed. 6: 771, 1964; 7: 443, 1965 (Translated in Polymer Sci. U.S.S.R. 6: 5, 945, 1964; 7: 3, 492, 1965) 8. V. P. BUDTOV, Dissertation, 1965 9. S. N. PEN’KOV, Vestnik LGU, No. 16, 84, 1964 10. S. N. PEN’KOV and V. S. STEPANENKO, Opt&a i spektroskopiya 14: 156, 1963 11. E. V. FRISMAN and V. N. TSVETKOV, Zh. eksper. i teoret. fiziki 23: 690, 1952 12. S. N. PEN’KOV, Optika i spektroskopiya 10: 787, 1961

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L. Z. VILEN~HIE and B. G. BELEN’KII

13. S. N. PEN’KOV, V. P. BUDTOV and Yu. L. VAGIN, Symposium on Relaxation Effects in Liquid. Dyushambe, 1969 14. G. BERRY, J. Chem. Phys. 44: 4550, 1966 16. E. V. J?BISMAN and V. N. TSVETKOV, Dokl. AN SSSR 106: 42, 1956; Zh. tekhn. fiziki 29: 212, 1959 16. V. N. TSVETKOV, E. V. FBISMAN, 0. B. PTITSYN and 5. Ya. KOTLYAB, Zh. tekhn. fiziki 28: 1428, 1968 17. C. SADRON, J. Phisique 9: 384, 1938 18. S. N. PEN’KOV and Ye. I. RYUMTSEV, Vysokomol. soyed. 6: 964, 1964 19. B. ZIMM, J. Chem. Phys. 24: 269, 1956

MEiTHODSOFINVESTIGATION SPECIFICFEATURESOFTHECEROMATOGRAPHYOFPOLYMERS* L. Z. VILENCHIKand B. G. BELEN’KII Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences (Received 16 June

1970)

SPECIFIC features of polymer solutions are normally determined by the faot that their high molecular wqight components-the macromolecules-are complex independent systems, the properties axid behaviour of which determine the properties of the solution aa a whole. This results in several anomalies, compared with solutions of low moleoular weight substances. Two aspects can be distinguished in the chromatographio behaviour of polymer solutions: a general aspect oommon to solutions of low molecular weight substances and the aspect whioh is due to certain properties of macromolecules. The latter results in relationships, which are not observed in the ohromatography of low molecular weight substances, such as the dependenoe of retention volumes F’el on conformation changes taking place with maoromolecules on entering absorbent pores, the specific dependence of Vsl on the rate of elution, on solution concentration, temperature and the choice of solvent. Effect on the vCee8 of wnfwmation duwgea taking place with mac~omoleouleg on tranaitbn from the mobile i&o the Btationcrrypbe. Conformation changes taking place with macromolecules on transition from channels of the mobile phase into absorbent pores have a oonsiderable effect on results obtained in gel permeation chromatography. The probability of this transition being lmown it is easy to calculate the distribution coefficient k, and oonsequently, also v,,

[ll Vel= v,+kdvp,

(1)

where V, is the amount of solvent required for washing from the column the macromolecules, for whioh (because of large sizes) the area of absorbent pores is quite inaocessible, V, is the area of the entire space of absorbent pores [2]. * Vysokomol. soyed. A14: No. 8, 1874-1878. 1972