Understanding deformation of polymer thin films at various
strains
is crucial for wide applications, especially the growing organic semiconductor
field. Thin films of immiscible polymer blends containing nanoparticles
are particularly interesting as the properties (thermal, mechanical,
optical) can be controlled by tuning the morphology. However, brittle
fracture of these blend thin films with or without nanoparticles can
hinder their fabrication, handling, and use. Herein, we fabricate
polymer blend thin films with a pseudo-bicontinuous morphology of
dispersed glassy polystyrene (PS) and continuous rubbery polyisoprene
(PI). Two-dimensional (2D) boron nitride (BN) nanoplatelets are incorporated
from 0 to 30 vol %. As-received BN was functionalized with polydopamine
and (3-aminopropyl)triethoxysilane (APTES) to enhance dispersion and
interfacial adhesion in the polymer matrix. Transmission electron
microscopic images show a majority of polydopamine-silane BN (ds-BN)
localized in the continuous rubbery PI and a small amount at the interface
of PS and PI. Without functionalization, processing defects occurred
at 15 vol % ds-BN, but this limit was increased to >25 vol % with
functionalization. We then present the deformation of these thin films
under uniaxial mechanical testing (tension, compression, and cyclic
tests) at 10, 20, and 30% strains by coupling a micromechanical stage
with an optical microscope. Most of the deformations observed were
recoverable when returning back to 0% strain from the maximum applied
strains. PI provides elastic recovery, PS maintains global stiffness,
and ds-BN provides a reinforcement effect in the thin films. We found
that polymer blend thin films loaded with notably high concentrations
of functionalized ds-BN (up to 25 vol %) localized primarily within
the continuous PI exhibited mostly recoverable mechanical performance.
These findings are valuable in selecting glassy and rubbery polymer
thin films loaded with nanoparticles to design resilient thin films
for mechanical, thermal, or electrical applications.