Photon Factory Activity Report 2019 #37 (2020)

BL-6A/2017G172

Microphase-Separated Structure of a Diblock Copolymer Blended
with a Random Copolymer
Hajime HIRAI1 and Naoya TORIKAI1,2,*
Graduate School of Regional Innovation Studies, Mie University,
1577 Kurimamachiya, Tsu, Mie 514-8507, Japan
2
Graduate School of Engineering, Mie University,
1577 Kurimamachiya, Tsu, Mie 514-8507, Japan

1 Introduction
A block copolymer with incompatible components selfassembles into regularly-ordered microphase-separated
structure in bulk. So far, there have been many studies on
microphase-separated structure, and it has been clarified
that its morphology and size are dependent on thecomposition and molecular weight of block copolymer,respectively, that is, primary structure of the block
copolymer [1]. Also, the morphology of a block copolymer
can be controlled by blending the constituting
homopolymer in place of synthesizing a block copolymer
with specific composition. Unless molecular weight ofhomopolymer is higher than that of the block chain, it issoluble into the corresponding microdomain leading tomorphological transition. In this study, effects of blendinga random copolymer on the microdomain of a block
copolymer are investigated.
2 Experiment
The samples used in this study are a diblock and threerandom copolymers composed of styrene and methyl
methacrylate. The diblock copolymer has the molecularweight of 97´103, and the volume fraction of a polystyrene
block chain in a molecule of 0.54. The three random
copolymers have almost the same molecular weight ofabout 10´103, but different volume fractions, fs, of styrene
segments: 0.1, 0.5, and 0.8. The blend ratios, F, of therandom copolymers were 0.2 and 0.52.
The film specimens were prepared by solvent-castingfrom dilute solutions in chloroform, and then annealed at160˚C for 24 hours in a vacuum.
Small-angle X-ray scattering (SAXS) measurement wasconducted on BL-6A. The wavelength, l, of X-ray was
0.15 nm, and the camera length was about 2.5 m using
Pilatus as a two-dimensional position-sensitive detector.
SAXS was measured at both through and edge views, inwhich X-ray is irradiated along the direction perpendicularand parallel to the film surface, respectively.
3 Results and Discussion
The two-dimensional scattering patterns obtained for all
the samples at the through view were isotropic, and thenthe data were circularly averaged into scattering intensity
profiles as a function of scattering vector, q, defined as(4p/l)sinq, in which 2q is the scattering angle. The pure
diblock copolymer shows several Bragg peaks at theirrelative q positions of q1:q2:q3: ××× :qn=1:2:3: ××× :n, in which

qn is the position of n-th order peak, indicating formationof an alternating lamellar structure. The scattering intensityof the even-order peaks was weakened due to a form factor
of a lamella formed by a symmetric diblock copolymer.
The domain spacing, D, was estimated according to theBragg equation: D=2np/qn, its value, D0, of the pure
diblock copolymer was 48.8 nm.
All the blends with the random copolymers at F of 0.20
revealed several Bragg peaks attributed to a lamellar
structure in their SAXS profiles irrespective of fs. It was
found that the random copolymer is soluble into thelamellar microdomain resulting in D increment when F isrelatively low. At F of 0.52, the blends with the two
random copolymers having relatively higher fs experienced
macrophase-separation, and their D values were almost
unchanged from D0. On the other hand, the random
copolymer with fs=0.1 induced morphological change fromlamellar to cylindrical structure. Fig. 1 represents ratios ofD evaluated for the blends to D0 for the pure diblock
copolymer as a function of F. It was clarified that domain
spacing for the random copolymer with fs=0.1 was muchincreased with increasing F compared with the other two.
1.8

1.6

D/D 01fs
0.1
0.5
0.8

1.4

1.2

1.0
0.0

0.1

0.2

0.3

0.4

0.5

0.6

Φ

Fig. 1: The domain spacing ratio, D/D0, of the blend
with the random copolymer having different fs to thepure diblock copolymer as a function of F.
Reference[1] I. W. Hamley, “The Physics of Block Copolymers”
Oxford University Press (1998).
* ntorikai@chem.mie-u.ac.jp