Applications in soft, flexible optical, and optoelectronic applications demand polymer thin film coatings that can accommodate substantial physical deformations. The preparation of high refractive index polymers (HRIPs) through the quaternization of poly(4‐vinylpyridine) (P4VP) thin films with (di)halomethanes is presented. P4VP thin films are prepared by initiated chemical vapor deposition (iCVD) and then quaternized through exposure to saturated vapors of iodomethane (CH3I), dibromomethane (CH2Br2), and diiodomethane (CH2I2), resulting in refractive indices (RI) as high as 1.67, 1.71, and 2.07, respectively (at 632.8 nm). Fourier‐transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) confirmed the quaternization of pyridine pendant groups on the polymer chain to n‐methylpyridinium with primarily an iodide or bromide counterion, though a minor fraction of polyiodides are also detected. Additionally, these films demonstrate superior thermal stability, retaining their refractive index and thickness after thermal excursions to 200 °C. The halogenated P4VP films exhibit superior mechanical flexibility relative to conventional inorganic coatings (Al2O3and Ta2O5) and do not fracture at uniaxial tensile strains as high as 10%. This new material chemistry and fabrication approach method may enable advanced optical designs and functionality in a wide range of substrates and device architectures.
Elastic broadband antireflection coatings for flexible optics using multi-layered polymer thin films
Flexible optics and optoelectronic devices require stretchable and compliant antireflection coatings (ARC). Conventional optical coatings, typically inorganic thin films, are brittle and crack under strain, while porous or patterned surfaces often lack environmental endurance and/or involve complex processing. Polymeric optical thin films prepared by initiated chemical vapor deposition (iCVD) comprise a promising alternative class of materials. With iCVD, multilayered, uniform thin film coatings can be synthesized conformally on the surface of a temperature-sensitive substrate near room temperature with precise compositional and thickness control. In this study, a model two-layer coating design consisting of poly(1 H ,1 H ,6 H ,6 H -perfluorohexyl diacrylate) (pPFHDA) with a refractive index at 633 nm of n 633 = 1.426 was deposited atop poly(4-vinylpyridine) (p4VP, n 633 = 1.587). Broadband antireflection over the visible wavelength range (400–750 nm) was conferred to a transparent, flexible thermoplastic polyurethane (TPU) substrate ( n 633 ∼ 1.51), reducing the front-surface reflectance from ∼4% to ∼2%. The superior mechanical compliance of polymer ARCs over conventional inorganic coatings (MgF 2 , SiO 2 , and Al 2 O 3 ) on the TPU substrate was thoroughly investigated by monitoring the evolution of film morphology and tensile fracture with applied equibiaxial strain. The polymer ARC withstood at least ε = 1.64% equibiaxial strain without fracture, while all inorganic coatings cracked. Through a repeated application of strain over hundreds of cycles, the antireflection by the polymer film was shown to possess excellent stability and fatigue resilience. Finally, simulations of established iCVD polymer chemistries possessing larger index contrast revealed that reflectance can be further reduced to <1% or better.
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- NSF-PAR ID:
- 10403704
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 11
- Issue:
- 12
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 4005 to 4016
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3TC00104K
