Neutron Scattering

For the intramolecular and intermolecular terms of interference one has PDD = PHH and
WT = WDD = WAH = W,, .
the total chain is given as
Because of z ZPT = 2 (z / 2)Z PDD + 2 (z / 2)Z PDH the form factor of
2PT = PDD +PDH (14 .37)
which wich nWT =-PT (Babinet principal) fmally leads to thé partial structure factor
z
[PDD - PT1
(14 .38)
and thé scattering cross section
dl(Q)=K 4
[PDD (Q)- PT (Q)1' (14 .39)
described as thé différence of thé intramolecular form factor of a single block ( PDD ; PDH )
and
thé total chain (PT ).
These form factors of a symmetrical diblock copolymer are plotted in
Figure14 .7. An interférence peak is observed whose position is according to Q * -R g =1 .9
related to thé radius of gyration and Q* therefore has to be observed at 1 .9 . 10 -Z A - ' . The
observation of an interférence peak in diblock copolymers becomes plausible from thé
consideration, that composition fluctuations of thé blocks A and B can only occur on thé
length scale of thé polymer . As an experimental example we show thé structure factor of a
melt .
0 .8
0 .4
Diblockcopolymer
0 .20
0 .15
-0 .4
xg100A
[/ 1
-0 .8
â 0 .10
â
0 .00
0 .00 0 .02 0 .04 0.06 0.08 0 .10 0.00 0 .02 0 .04 0 .06 0.08 0.10
Q[A
0 .05
Q[,A- ']
Figure 14.7 : Form factor ofa symmetrical diblock copolymer
1443