MICROSTRUCTURING OF POLYMER SURFACES BY
DEPOSITION OF SOLVENT DROPS
G. Li, N. Höhn, E. Bonaccurso, H.-J. Butt, W. WiechertΔ, Th. HaschkeΔ, K. Graf
Δ
MPI for Polymer Research, Mainz, Germany
University of Siegen, Department of Simulation, Siegen, Germany
The deposition of micro-sized solvent droplets on soluble polymer substrates leads to
local dissolution of polymer into the liquid [1]. After evaporation of the droplet a
micro-topology is left in the polymer surface. The surface topology depends on
process parameters, as the velocity with which the droplet is deposited [2], and
intrinsic material parameters, as the polymer molar mass and the type of polymer [3].
As a model system the deposition of toluene drops on polystyrene is investigated. For
molar masses of ~ 200 kDa a concave surface topology is left [4]. This can be
described by assuming a flow to the outer rim of the pinned drop, where dissolved
polymer is accumulated [5]. This phenomenon is known from the formation of
coffeerims on a table. For molar masses as low as ~ 20 kDa, polymer is increasingly
dissolved, leading to gelation of the droplet: Thus a convex surface topology is
formed. For high molar masses (~ 1.4 MDa), in contrast, only local protrusions with a
size of ~ 50 μm are observed within the contact area of the droplet, which is a hint to
a low dissolution rate and instability-driven surface structuring. The concentration of
polymer inside the droplet can be tuned by controlling the initial deposition process.
This is demonstrated with a modified ink-jet “etching” technique, where a pendant
solvent drop is deposited on the polymer by moving the holder for the substrate up
and down. The slower the holder is retracted from the pendant droplet after contact
between liquid and solid, the more polymer is dissolved and the more pronounced is
the formation of a convex surface topology. This technique can be used to prepare
polymer surfaces acting e. g. as optical micro-lenses.
References
[1] T. Kawase, H. Sirringhaus, R. H. Friend, and T. Schimoda, Adv. Mater. 2001, 13,
1601-1605.
[2] G. Li, N. Höhn, K. Graf, APL 2006, 89, 241920.
[3] G. Li, H.-J. Butt, K. Graf, Langmuir 2006, 22, 11395-11399.
[4] E. Bonaccurso, B. Hankeln, B. Niesenhaus, H.-J. Butt, K. Graf, APL 2005, 86,
124101.
[5] R. D. Deegan, O. Bakajin, T. F. Dupont, G. Huber, S. R. Nagel, T. A. Witten, Nature 1997, 389,
827-829.
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