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1. Elastic broadband antireflection coatings for flexible optics using multi-layered polymer thin films

   https://doi.org/10.1039/D3TC00104K  

   Zhao, Yineng; Huo, Ni; Ye, Sheng; Tenhaeff, Wyatt E. (March 2023, Journal of Materials Chemistry C)

   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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2. Kirigami enhances film adhesion

   https://doi.org/10.1039/c7sm02338c  

   Zhao, Ruike; Lin, Shaoting; Yuk, Hyunwoo; Zhao, Xuanhe (January 2018, Soft Matter)

   Structures of thin films bonded on substrates have been used in technologies as diverse as flexible electronics, soft robotics, bio-inspired adhesives, thermal-barrier coatings, medical bandages, wearable devices and living devices. The current paradigm for maintaining adhesion of films on substrates is to make the films thinner, and more compliant and adhesive, but these requirements can compromise the function or fabrication of film–substrate structures. For example, there are limits on how thin, compliant and adhesive epidermal electronic devices can be fabricated and still function reliably. Here we report a new paradigm that enhances adhesion of films on substrates via designing rational kirigami cuts in the films without changing the thickness, rigidity or adhesiveness of the films. We find that the effective enhancement of adhesion by kirigami is due to (i) the shear-lag effect of the film segments; (ii) partial debonding at the film segments’ edges; and (iii) compatibility of kirigami films with inhomogeneous deformation of substrates. While kirigami has been widely used to program thin sheets with desirable shapes and mechanical properties, fabricate electronics with enhanced stretchability and design the assembly of three-dimensional microstructures, this paper gives the first systematic study on kirigami enhancing film adhesion. We further demonstrate novel applications including a kirigami bandage, a kirigami heat pad and printed kirigami electronics. 

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3. Microstructure Control of Polymer Films via Air-Assisted Electrospray for Binderless Electrodes

   https://doi.org/10.1021/acsapm.5c02254  

   Gordon, Kenneth; Ogbonna, Nduka; Usie, Griffin; Wei, Zhen; Owoso, Samuel Dayo; Zhang, Donghui; Lawrence, Jimmy; Wang, Yu; Fei, Ling (August 2025, ACS Applied Polymer Materials)

   With the growing number of applications for thin polymer films (e.g., corrosion-resistant coatings, photovoltaics, and optoelectronics), there is an urgent need to develop or advance cost-effective, versatile, and high-throughput manufacturing processes to produce thin polymer films and coatings with controllable properties (e.g., morphology, composition). In this work, we present a simple, cost-effective, and scalable approach: the air-assisted electrospray method for thin film coating. We systematically investigate its capabilities for producing coatings with a wide range of surface morphologies, its compatibility with three-dimensional substrates, and the fundamental understanding of the process. Through systematic control of concentration, needle configuration, and polymer selection, we demonstrate the ability to produce coating morphologies with diverse structural characteristics and excellent reproducibility. Notably, the introduction of air assistance through a coaxial needle greatly enlarges the range of achievable morphologies, particularly at lower concentrations. We also found that the position of the airflow relative to the solution is critical for determining the polymer film properties. Furthermore, we demonstrate its broad application potential in the fabrication of binderless electrodes for sodium-ion batteries. 

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4. Initiated Chemical Vapor Deposition Kinetics of Poly(4-aminostyrene)

   https://doi.org/10.3389/fbioe.2021.670541  

   Khlyustova, Alexandra; Yang, Rong (April 2021, Frontiers in Bioengineering and Biotechnology)

   Initiated Chemical Vapor Deposition (iCVD) is a free-radical polymerization technique used to synthesize functional polymer thin films. In the context of drug delivery, the conformality of iCVD coatings and the variety of functional chemical moieties make them excellent materials for encapsulating pharmaceutics. Poly(4-aminostyrene) (PAS) belongs to a class of functionalizable materials, whose primary amine allows decoration of the delivery vehicles with biomolecules that enable targeted delivery or biocompatibility. Understanding kinetics of PAS polymerization in iCVD is crucial for such deployments because drug release kinetics in thin-film encapsulation have been shown to be determined by the film thickness. Nevertheless, the effects of deposition conditions on PAS growth kinetics have not been studied systematically. To bridge that knowledge gap, we report the kinetics of iCVD polymerization as a function of fractional saturation pressure of the monomer (i.e., P m /P sat ) in a dual-regime fashion, with quadratic dependence under low P m /P sat and linear dependence under high P m /P sat . We uncovered the critical P m /P sat value of 0.2, around which the transition also occurs for many other iCVD monomers. Because existing theoretical models for the iCVD process cannot fully explain the dual-regime polymerization kinetics, we drew inspiration from solution-phase polymerization and proposed updated termination mechanisms that account for the transition between two regimes. The reported model builds upon existing iCVD theories and allows the synthesis of PAS thin films with precisely controlled growth rates, which has the potential to accelerate the deployment of iCVD PAS as a novel biomaterial in controlled and targeted drug delivery with designed pharmacokinetics. 

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5. Capillary transfer of soft films

   https://doi.org/10.1073/pnas.2000340117  

   Zhang, Yue; Yin, Mengtian; Baek, Yongmin; Lee, Kyusang; Zangari, Giovanni; Cai, Liheng; Xu, Baoxing (February 2020, Proceedings of the National Academy of Sciences)

   Existing transfer technologies in the construction of film-based electronics and devices are deeply established in the framework of native solid substrates. Here, we report a capillary approach that enables a fast, robust, and reliable transfer of soft films from liquid in a defect-free manner. This capillary transfer is underpinned by the transfer front of dynamic contact among receiver substrate, liquid, and film, and can be well controlled by a selectable motion direction of receiver substrates at a high speed. We demonstrate in extensive experiments, together with theoretical models and computational analysis, the robust capabilities of the capillary transfer using a versatile set of soft films with a broad material diversity of both film and liquid, surface-wetting properties, and complex geometric patterns of soft films onto various solid substrates in a deterministic manner. 

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