Publication Type
Journal
Journal Name
RSC Advances
Publication Date
Page Numbers
21336 to 21348
Volume
5
Issue
27
Abstract
Microphase separation in thin films of lamellar forming polydisperse di-block copolymers is
studied using self-consistent field theory (SCFT) and neutron reflectivity experiments. Diblock
copolymers containing a polydisperse block (poly(glycidylmethacrylate) (PGMA)) connected
to a near monodisperse block (poly(4,4-dimethyl-d6-2-vinylazlactone) (PVDMA-d6))
are considered in this work. Effects of chain length polydispersity, film thickness, substrate monomer
and monomer-monomer interactions on the microphase segregation are studied using
SCFT. The theoretical study reveals that an increase in polydispersity tends to decrease the
number of lamellar strata that can be packed in a film of given thickness, in comparison to a
film created with monodisperse di-block copolymers. This is a direct consequence of an increase
in lamellar domain spacing with an increase in polydispersity index. These predictions
are verified by comparison with neutron reflectity experiments done on thin films made from
moderately polydisperse PGMA-b-PVDMA-d6 di-block copolymer deposited on silicon substrates.
Furthermore, it is shown that polydispersity induces conformational asymmetry and
an increase in the polydispersity index makes the polydisperse blocks less flexible in comparison
with monodisperse blocks. It is shown that conformational asymmetry effects, which are
entropic in origin and of increasing importance as film thickness descreases, drive the polydisperse
blocks to the middle of the films despite favorable substrate interactions. Prediction
of neutron reflectivity profiles using the SCFT provides a facile and robust route for model
verification and leads to useful physical insights into behavior of di-block copolymers near
interfaces.
