posted on 2024-02-28, 15:40authored byTyler
R. Heyl, Jeremy M. Beebe, Anthony J. Silvaroli, Arthur Perce, Dongchan Ahn, Shane Mangold, Victoria Mazure, Kenneth R. Shull, Muzhou Wang
Interpenetrating
polymer networks (IPNs) represent an effective
strategy for compatibilizing immiscible polymers to enhance the mechanical
properties of the final material. While it has been established that
the macroscopic properties are dependent on the microstructure, it
is unknown why various microstructures are formed in IPNs because
the microstructure is often trapped in a nonequilibrium state. To
explore this, we conducted a study to establish a relationship between
polymerization kinetics and microstructure formation in polydimethylsiloxane/poly(methyl
methacrylate) (PDMS/PMMA) IPNs. By manipulating the UV curing intensity,
we observed three distinct morphologies: isolated PMMA-rich spheres
within a PDMS matrix with a monomodal domain size distribution, spheres
with a bimodal size distribution, and a clustered domain microstructure.
To investigate the different phase separation mechanisms, we correlated in situ small-angle X-ray scattering (SAXS) to track microstructure
formation and Fourier transform infrared spectroscopy (FT-IR) to track
polymerization kinetics. Based on our findings, we propose that the
monomodal sphere microstructure formed via spinodal decomposition.
The positions of the domains are kinetically trapped in the PDMS network,
preventing macrophase separation. Similarly, the clustered domain
microstructure also arises from spinodal decomposition, but increased
mobility within the PDMS matrix enables domains to aggregate after
network percolation. In contrast, the bimodal spherical morphology
is attributed to a combination of nucleation and growth, and spinodal
decomposition. We postulate that these different mechanisms are dictated
by changes in the PMMA molecular weight during polymerization. Through
the examination of polymerization kinetics and microstructure formation,
we have proposed multiple mechanisms that explain the microstructure
formation in IPNs.