Interplay of Substrate Surface Energy and Nanoparticle
Concentration in Suppressing Polymer Thin Film Dewetting
Sudeshna Roy
Diya Bandyopadhyay
Alamgir Karim
Rabibrata Mukherjee
10.1021/ma501262x.s001
https://acs.figshare.com/articles/journal_contribution/Interplay_of_Substrate_Surface_Energy_and_Nanoparticle_Concentration_in_Suppressing_Polymer_Thin_Film_Dewetting/2212714
It
is known that dewetting of a polystyrene (PS) thin film on a
silicon substrate gets completely suppressed upon addition of small
amount of C<sub>60</sub> nanoparticles (NP). The NPs migrate to the film–substrate interface and forms
an enriched surface layer of the particles that eventually stabilizes
the film by apparent pinning. In this article we quantitatively highlight
the unexplored effect of substrate surface energy (γ<sub>S</sub>) on the migration of the NPs to the film–substrate interface
and their contribution on dewetting suppression. Depending on the
relative magnitudes of NP concentration (<i>C</i><sub>NP</sub>) and γ<sub>S</sub>, we identify three distinct stability regimes.
In regime 1 (<i>C</i><sub>NP</sub> < 0.2%) there is no
suppression of dewetting and the final polygonal arrangement of droplets
closely resemble dewetted structures in particle free films. However,
the size of the polygons becomes smaller in NP containing films when
γ<sub>S</sub> < γ<sub>C60</sub> (NP surface energy)
and larger as γ<sub>S</sub> exceeds γ<sub>C60</sub>. In
regime 2 (0.3% < <i>C</i><sub>NP</sub> < 0.75%) the
films dewet partially, and the extent of dewetting is seen to strongly
dependent on the relative magnitudes of γ<sub>C60</sub> and
γ<sub>S</sub>. While dewetting proceeds up to the stage of partial
hole growth and coalescence when γ<sub>S</sub> < γ<sub>C60</sub>, some random isolated holes are seen to form when γ<sub>S</sub> > γ<sub>C60</sub>. On the basis of direct AFM imaging,
we show that in both regimes 1 and 2 the NPs migrate to the substrate–film
interface only when γ<sub>S</sub> > γ<sub>C60</sub>. We
show complete suppression of dewetting in regime 3 (<i>C</i><sub>NP</sub> > 1.0%), where the particles are seen to migrate
to
the substrate for all values of γ<sub>S</sub>. The work highlights
that entropy driven migration of particles takes place on substrates
with any γ<sub>S</sub> only above a critical NP concentration
(<i>C</i><sub>NPC</sub>) and only on substrates with γ<sub>S</sub> > γ<sub>C60</sub> when <i>C</i><sub>NP</sub> < <i>C</i><sub>NPC</sub>. The findings, apart from
dewetting suppressing, can guide potential design criteria for applications
such as electron extracting layer in organic photovoltaic.
2015-01-27 00:00:00
Substrate Surface Energy
γ C 60
substrate
PS
AFM
CNPC
interface
C 60 nanoparticles
dewetting
γ C 60.
NP concentration
NP surface energy
film
regime
CNP
suppression
γ S