Phase separation control of nanoscopic structure
Universität Bayreuth
Copolymers made of incompatible
blocks are known to form ordered networks with a nanoscopic
structure resulting from local phase separation. Using
appropriate sample preparation, one can achieve a thermodynamic
equilibrium where the network presents a long-range crystalline
order. This is particularly important since this network can be
used as a template for nanotechnologies. The characteristic
wavelength is controlled by the polymer chain length. In the case
of very thin films of the order of this length, the equilibrium
morphology becomes highly sensitive to the film thickness and the
interface film/substrate.
We have developed in Bayreuth an
extensive knowledge about block copolymer film morphologies, both
in solution and in bulk or thin films. We can study the kinetics
of the approach to equilibrium of simple systems using real time
AFM imaging by annealing films under controlled solvent vapour
exposure, In addition, electric fields have successfully been
applied to bulk systems to control the orientation of the
nano-domains.
Above: AFM phase image of a
PE-b-PEP-b-PEO film.
We intend through the PolyFilm
network to focus on more complex systems where phase separation
is not the only mechanism controlling nano-morphology. The most
typical example is block copolymers with a semi-crystalline
block. In this case, the crystallization of one block can
completely change the morphology if occurring faster than the
phase separation. Indeed, complex patterns have been reported in
the literature that cannot be predicted at the moment. Regarding
the competition between different mechanisms, sample preparation
appears to be a critical parameter. By carefully controlling the
sample history, we expect to vary the relative kinetics of the
different mechanisms and change the resulting morphology of the
system because it does not necessarily reach thermodynamic
equilibrium.
To achieve this goal, we benefit
from close interaction with the macromolecular chemistry groups
in Bayreuth, lead by Professors Axel Müller and Hans-Werner
Schmidt, who can custom synthesise polymers with various
chemistries and molecular geometries.
