Eur. Phys. J. E 5, 207-219

Hydrodynamic-flow-driven phase evolution in a polymer blend film modified by diblock copolymers

J. Rysz¹, H. Ermer², A. Budkowski¹, A. Bernasik³, J. Lekki⁴, G. Juengst², R. Brenn², K. Kowalski³, J. Camra³, M. Lekka⁴ and J. Jedlinski<sup>3

1</sup>  Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, 30-059 Kraków, Poland
²  Fakultät für Physik, Universität Freiburg, H.-Herder-Str. 3, 79104 Freiburg i. Br., Germany
³  Surface Spectroscopy Laboratory, University of Mining and Metallurgy, Mickiewicza 39, 30-059 Kraków, Poland and Joint Centre for Chemical Analysis and Structural Research, Jagellonian University, Reymonta 23, 30-059 Kraków, Poland
⁴  Institute of Nuclear Physics, Radzikowskiego 152, 31-342 Kraków, Poland

ufbudkow@cyf-kr.edu.pl

(Received 15 March 2000 and Received in final form 9 February 2001)

Abstract
We have studied surface-directed phase separation in thin films of deuterated polystyrene and poly(bromostyrene) (with 22.7% of monomers brominated) using ³He nuclear reaction analysis, dynamic secondary ion mass spectroscopy and atomic force microscopy combined with preferential dissolution. The crossover from competing to neutral surfaces of the critical blend film (cast onto Au) was commenced: polyisoprene-polystyrene diblock copolymers were added and segregated to both surfaces reducing in a tuneable manner the effective interactions. Two main stages of phase evolution are characterised by i) the growth of two surface layers and by ii) the transition from the four-layer to the final bilayer morphology. For increasing copolymer content the kinetics of the first stage is hardly affected but the amplitude of composition oscillations is reduced indicating more fragmented inner layers. As a result, a faster mass flow to the surfaces and an earlier completion of the second stage were observed. The hydrodynamic flow mechanism, driving both stages, is evidenced by nearly linear growth of the surface layer and by mass flow channels extending from the surface layer into the bulk. The final bilayer structure, formed even for the surfaces covered by strongly overlapped copolymers, is indicative of long-range (antisymmetric) surface forces.

PACS
64.75.+g - Solubility, segregation, and mixing; phase separation.
68.55.-a - Thin film structure and morphology.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001