Engineering Surface Chemistry to Enhance Ferroelectric Phase Formation in Ultrathin PVDF-TrFE Films

TL;DR

This paper shows how changing the surface chemistry of substrates can improve the formation of ferroelectric phases in ultrathin PVDF-TrFE polymer films.

Contribution

A new strategy for enhancing ferroelectric phase formation in ultrathin films by modifying substrate surface chemistry.

Findings

Hydrophobic surfaces promote higher electroactive β-phase content and better crystalline texture in PVDF-TrFE films.

Film coverage and crystalline domain size are significantly improved on hydrophobic substrates.

Brush chemistry and copolymer composition both strongly influence phase behavior and morphology.

Abstract

The development of
flexible, lightweight electronic devices
has
driven growing interest in ferroelectric polymers, with a focus on
poly­(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymers.
These materials offer solution processability, mechanical flexibility,
and high remanent polarization, making them well-suited for applications
in sensors, nonvolatile memories, and energy harvesters. However,
as film thickness is reduced below 50 nm, crystallization becomes
increasingly sensitive to interfacial interactions, leading to variations
in phase composition and surface morphology. This work investigates
how controlled modifications to substrate surface chemistry influence
the crystallization behavior of ultrathin PVDF-TrFE films. To this
end, polymer brushes of varying polarity were grafted onto silicon
oxide substrates to create a systematic gradient in surface energy,
spanning from hydrophilic to hydrophobic regimes. PVDF-TrFE copolymers
with VDF:TrFE ratios of 80:20, 75:25, and 70:30 were spin-coated onto
these surfaces to produce uniform films with thicknesses below 50
nm. Ellipsometry and contact-angle measurements were used to confirm
brush coverage and film thickness. Crystalline phase composition was
quantified using attenuated total reflectance Fourier-transform infrared
spectroscopy (ATR-FTIR) and grazing-incidence wide-angle X-ray scattering
(GIWAXS), while atomic force microscopy (AFM) was employed to characterize
nanoscale surface topography. Results demonstrate that both brush
chemistry and copolymer composition significantly affect β-phase
content and crystalline texture. Hydrophobic surfaces consistently
promoted superior film coverage, larger crystalline domains, and higher
electroactive β-phase content compared to hydrophilic counterparts.
These findings provide a detailed framework for controlling phase
behavior and morphology in nanoconfined PVDF-TrFE films. By controlling
the interface rather than the material itself, this study offers a
simple and effective strategy for improving ultrathin ferroelectric
films, providing useful design guidelines for flexible electronics
and opening new directions for research in nanoscale polymer engineering.

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