Extended-Chain Induced Bulk Morphologies Occur at Surfaces of Thin Co-Oligomer Films
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Schulze, Robert; Arras, Matthias M. L.; Destri, Giovanni Li; Gottschaldt, Michael; Bossert, Jörg; Schubert, Ulrich S.; Marletta, Giovanni; Jandt, Klaus D.; Keller, Thomas F.
- Abstract:
- One approach to create novel amphiphilic
surface nanostructures with typical lateral pattern dimensions
in the order of 10 nm is to employ double crystalline cooligomers
with domain sizes largely determined by the block
length of extended molecular chains. The aim of the study was
to test the hypothesis that the extended chain bulk
morphology of an asymmetric polyethylene-block-poly-
(ethylene oxide) (PE-b-PEO) co-oligomer can be induced at
its thin film surface. Furthermore, we explored the central role
of the extended oligomer orientation and the surface affinity to
achieve an amphiphilic surface nanostructure. The co-oligomer was drop-cast from dilute solution onto hydrophobic, neutral and
hydrophilic substrates. Atomic-force microscopy revealed that independent of the substrate chemistry, the film thickness was
quantized in integral multiples of the calculated extended chain length. At the same time, the terraces exhibited lateral domains
that coarsen with increasing substrate hydrophobicity. Although subsequent annealing tends to induce dewetting, on the neutral
substrate a residual polymer layer with perpendicular lamellar surface morphology remained. Grazing incidence X-ray diffraction
suggested the latter to be induced by crystallization. We propose that simultaneous formation of lateral domains and discrete
terraces during drop-casting are facilitated by surface-diffusion and due to a dense-packing and crystallization of vertically aligned,
extended oligomer chains. Annealing permits the polymer film on the neutral surface to overcome the energy barrier for chain
rotation from vertical to parallel to create amphiphilic surface nanostructures. To our best knowledge, we demonstrated for the
first time that double crystalline co-oligomers can be used to pattern surfaces laterally with asymmetric lamellae with dimensions
in the order of 10 nm.
- Year:
- 2012
- Type of Publication:
- Article
- Journal:
- Macromolecules
- Volume:
- 45
- Pages:
- 4740 - 4748