Studies of Critical Phenomena and Phase Transition with SANS and DKD in the Polymerblend PVME-PSD
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STUDIES OF CRITICAL PHENOMENA AND PHASE TRANSITION WITH SANS AND DKD IN THE POLYMERBLEND PVME-PSD
D. 1) 2) 3)
1 3
2 SCHWAHNO), K. MORTENSEN ) AND H. YEE-MADEIRA , ) Kernforschungsanlage Jilich, D-5170 JUlich, FRG Ris€ National Laboratory, DK-4000 Roskilde, Denmark DAAD - and also ESFM -IPN, Mexico
ABSTRACT Critical behaviour of PSD-PVME polymer blends are presented. Spinodal and binodal transition temperatures have been determined by the use of a SANS-camera, and non-meanfield characteristics have been observed close to the critical point. A dynamic decomposition study has been performed by the use of a neutron double crystal diffraction.
I.
INTRODUCTION
In this paper we give a short survey of neutron studies performed on PSD-PVME polymer blends. The spinodal and the binodal transition temperatures have been determined on the basis of the temperature dependence of the critical composition fluctuations, which were measured by use of a small angle neutron camera [i]. Studies have been performed on four systems (I-IV). The PVME component was the same, while different molecular weight PSD components (I-IV) were used. The polymer characteristics are given in table 1. By fitting the spinodal curve calculated by use of the FloryHuggins model to the experimental values, the interaction parameter, X, has been determined. For system III we used the obtained knowledge of the exact critical composition to study the change from meanfield to non-meanfield behaviour. This cross-over was found 1.8 K below the meanfield critical temperature [2]. Finally we give an example of a spinodal decomposition study of system IV using a neutron double crystal diffractormeter, DKD [3]. The SANS measurements have been performed at the cold source of Riso National Laboratory and the DKD measurements at the Jllich FRJ1 reactor.
. ..
. .
Me
codex
M.
PVME PSD 1
36 140 74 700
89 000 78 502
110890
155246
PSD 1
PSD 111 PSD IV
I
215 103 399461
231 990 472880
M, 163 480 81 872
219444
247 856 522 072
•
b ;.
,
1987 Materials Research Society
•M,
a -M-
2.5 1.05
1.84 1.04
1.08 1.18
1.07 1.1
1.4
Table 1. Molecular weight characteristics of the polymer components.
Mat. Res. Soc. Symp. Proc. Vol. 79.
.
1.41
124
II.
DETERMINATION OF SPINODAL AND BINODAL WITH SANS FROM MEANFIELD CRITICAL FLUCTUATIONS
The scatterin6 law of critical fluctuations are in approximation given in the form [4]
S(Q)I = S(Q)o -
+ So(Q)-
the random phase
- x(Q)
(1)
where So and So are the single chain scattering functions of PSD and PVME, respectively, and X is the Flory-Huggins interaction parameter. For a polydisperse component, the single chain scattering function should simply be replaced by the sum of those corresponding to specific molecular weight [1,9]:
S°(Q)
(2)
i
In the data evaluation we used the expansion of Eq. to Q, taking Eq. I into account 2
1 with respect
4
S(Q)-I = S(O)-i + AQ + BQ
(3)
Only very close to the spinodal temperature deviations from the Ornstein-Zernike form was observed, and the third term of Eq. 3 h
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