cm0c02095_si_001.pdf (574.07 kB)
Influence of Side Chain Hydrolysis on the Evolution of Nanoscale Roughness and Porosity in Amine-Reactive Polymer Multilayers
journal contribution
posted on 2020-08-06, 00:14 authored by Matthew
C. D. Carter, Matthew S. Wong, Fengrui Wang, David M. LynnWe
report the influence of side chain hydrolysis on the evolution
of nanoscale structure in thin films fabricated by the reactive layer-by-layer
(LbL) assembly of branched poly(ethylenimine) (PEI) and poly(2-vinyl-4,4-dimethylazlactone)
(PVDMA). LbL assembly of PEI and PVDMA generally leads to the linear
growth of thin, smooth films. However, assembly using PVDMA containing
controlled degrees of side chain hydrolysis leads to the growth of
thicker films that exhibit substantial nanoscale roughness, porosity,
and have resulting physicochemical behaviors (e.g., superhydrophobicity)
that are similar to those of some thicker PEI/PVDMA coatings reported
in past studies. Our results reveal that the degree of PVDMA partial
hydrolysis (or carboxylic acid group content) influences the extent
to which complex film features develop, suggesting that ion-pairing
interactions between hydrolyzed side chains and amines in PEI promote
the evolution of bulk and surface morphology. Additional experiments
demonstrate that these features likely arise from polymer/polymer
interactions at the surfaces of the films during assembly, and not
from the formation and deposition of solution-phase polymer aggregates.
When combined, our results suggest that nanoporous structures and
rough features observed in past studies likely arise, at least in
part, from some degree of adventitious side chain hydrolysis in the
PVDMA used for film fabrication. Our results provide useful insight
into molecular-level features that govern the growth and structures
of these reactive materials, and provide a framework to promote nanoscale
morphology reliably and reproducibly. The principles and tools reported
here should prove useful for further tuning the porosities and tailoring
the physicochemical behaviors of these reactive coatings in ways that
are important in applied contexts.