2006 APS March Meeting
Monday–Friday, March 13–17, 2006;
Baltimore, MD
Session N4: Polymer Crystallization
8:00 AM–11:00 AM,
Wednesday, March 15, 2006
Baltimore Convention Center
Room: 308
Sponsoring
Units:
DPOLY DMP
Chair: Freddy Khoury, National Institute of Standards and Technology
Abstract ID: BAPS.2006.MAR.N4.1
Abstract: N4.00001 : A new approach to study of the onsets of tethered chain overcrowding and highly stretched brush regime utilizing crystalline-amorphous diblock copolymers
8:00 AM–8:36 AM
Preview Abstract
Abstract
Author:
Stephen Cheng
(Maurice Morton Institute and Department of Polymer Science, University of Akron, Akron, Ohio 44325-3909 USA)
Two series of diblock copolymers, PEO-$b$-PS and PLLA-$b$-PS,
were used as
templates to generate tethered PS blocks on the single crystal
surfaces.
Controlled and tunable reduced tethering density, $\tilde {\sigma
}$,
defined by \textit{$\sigma \quad \pi $} $R_{g}^{2}$ (where
\textit{$\sigma $ }is the tethered chain density), could be
achieved in a broad range (up to 24) by changing the molecular
weights
(MW's) of the crystalline and amorphous blocks and by varying the
crystallization temperature ($T_{x})$ of different PEO-$b$-PS and
PLLA-$b$-PS
solutions. The $\tilde {\sigma }$ of the tethered PS chains on
the crystal
surface increased with increasing $T_{x}$ because at a fixed MW
of the PEO or
PLLA block, an increase in the lamellar thickness ($d_{CRYST})$
was evidence
of a decrease in the number of folds. When we plotted the
relationships
between 1/$d_{CRYST}$ and $T_{x}$ for these two series of diblock
copolymers,
sudden and discontinuous changes of the slopes in some of these were
observed at $\tilde {\sigma }$ = 3.7 ($\tilde {\sigma }$*). This
was as a
result of the drastic interaction change of the neighboring PS
tethered
chains. An average reduced surface free energy of the tethered PS
chains
(\textit{$\Gamma $}$^{PS})$ was used as a parameter to
characterize the PS tethered chain
interactions. The relationship between \textit{$\Gamma $}$^{PS}$
and $\tilde {\sigma }$ showed
a discontinuous transition at $\tilde {\sigma }$*. This could be
identified
as the onset of the tethered PS chain overcrowding in solution. This
transition indicates that the extra entropic surface free energy
created by
the repulsion of tethered PS chains started to affect the
nucleation barrier
of the PEO or PLLA block crystallization. Based on the scaling
laws, the
onset of highly stretched brush regime could be identified at
$\tilde
{\sigma }$ = 14.3 ($\tilde {\sigma }$**). In the \textit{$\Gamma
$}$^{PS}$ versus $\tilde
{\sigma }$ plot, the transition appears to be continuous. Thus, a
crossover
regime in the tethered PS chains exists between $\tilde {\sigma
}*$ = 3.7 and
$\tilde {\sigma }$*$*$ = 14.3. It is defined as the regime where the
interaction of the tethered PS chains undergo changes from being
non-interacting towards penetration to, finally, chain stretching
normal to
the surface.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2006.MAR.N4.1