Spin casting has become an attractive method to fabricate polymer thin films found in organic electronic devices such as field-effect transistors, and light emitting diodes. Many studies have shown that altering spin casting parameters can improve device performance, which has been directly correlated to the degree of polymer alignment, crystallinity, and morphology of the thin film. To provide a thorough understanding of the balance of thermodynamic and kinetic factors that influence the stratification of polymer blend thin films, we monitor stratified polymer blend thin films developed from poly(3-hexylthiophene-2,5-diyl) and poly(methyl methacrylate) blends at controlled loading ratios, relative molecular weights, and casting speed. The structures of these thin films were characterized via neutron reflectivity, and the results show that at the fastest casting speed, polymer–polymer interactions and surface energy of the polymers in the blend dictate the final film structure, and at the slowest casting speed, there is less control over the film layering due to the polymer–polymer interactions, surface energy, and entropy simultaneously driving stratification. As well, the relative solubility limits of the polymers in the pre-deposition solution play a role in the stratification process at the slowest casting speed. These results broaden the current understanding of the relationship between spin casting conditions and vertical phase separation in polymer blend thin films and provide a foundation for improved rational design of polymer thin film fabrication processes to attain targeted stratification, and thus performance.
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Composition Gradient High-Throughput Polymer Libraries Enabled by Passive Mixing and Elevated Temperature Operability
The development of high-throughput experimentation (HTE) methods to efficiently screen multiparameter spaces is key to accelerating the discovery of high-performance multicomponent materials (e.g., polymer blends, colloids, etc.) for sensors, separations, energy, coatings, and other thin-film applications relevant to society. Although the generation and characterization of gradient thin-film library samples is a common approach to enable materials HTE, the ability to study many systems is impeded by the need to overcome unfavorable solubilities and viscosities among other processing challenges at ambient conditions. In this protocol, a solution coating system capable of operating temperatures over 110 °C is designed and demonstrated for the deposition of composition gradient polymer libraries. The system is equipped with a custom, solvent-resistant passive mixer module suitable for high-temperature mixing of polymer solutions at ambient pressure. Residence time distribution modeling was employed to predict the coating conditions necessary to generate composition gradient films using a poly(3-hexylthiophene) and poly(styrene) model system. Poly(propylene) and poly(styrene) blends were selected as a first demonstration of high temperature gradient film coating: the blend represents a polymer system where gradient films are traditionally difficult to generate via existing coating approaches due to solubility constraints at ambient conditions. The methodology developed here is expected to widen the range of solution processed materials that can be explored via high-throughput laboratory sampling and provides an avenue for efficiently screening multiparameter materials spaces and/or populating the large datasets required to enable data-driven materials science.
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- Award ID(s):
- 1922111
- NSF-PAR ID:
- 10340798
- Date Published:
- Journal Name:
- Chemistry of Materials
- ISSN:
- 0897-4756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT The thin film phase behavior of ternary blends consisting of symmetric poly(styrene) (PS)‐
b ‐poly(dimethylsiloxane)(PDMS), PS, and PDMS was investigated using X‐ray reflectivity (XRR) and atomic force microscopy (AFM). This system is strongly segregated, and the homopolymers are approximately the same length as the corresponding blocks of the copolymer. The XRR and AFM data are used to quantify changes in domain spacing (L ) and morphology evolution with increasing homopolymer content (ΦH ). In 100 nm thick films, from ΦH = 0 to 0.20, the system maintains a perfect parallel lamellar structure and domains swell as predicted based on theory; however, from ΦH = 0.30 to 0.50, a morphology transition to a “dot pattern” morphology (tentatively identified as perforated lamellae) and mixed morphologies were observed before macrophase separation. In thicker films, dot patterns were observed for a broad range of ΦH before macrophase separation. The absence of the bicontinuous microemulsion phase reported for bulk blends and thin films of perpendicular lamellae and the presence of dot patterns/perforated lamellae are attributed to preferential migration of the PDMS homopolymer to the wetting layers located at the substrate and free air interfaces, which leads to an asymmetric composition within the film and morphology transition. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2018 ,56 , 1443–1451 -
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ABSTRACT Coating biomaterials with thin, soft films can alter properties, such as the biocompatibility of the materials, whereas it remains a great challenge to probe the properties of such films. In this article, we show a method that allows for the determination of the viscoelastic moduli of thin, soft films deposited on the surface of a quartz crystal through the measurement of resonance frequency shifts and the broadening of the acoustic resonance of the crystal as a resonator. The method is based on transcendental equations, which describe the mechanical response of the quartz resonator with the deposited films. It differs from the currently widely used ones, which use a thin film approximation numerically through the solution of transcendental equations to determine the viscoelasticity of the films. We estimated the glass‐transition temperature of a thin poly(vinyl butyral) film by measuring the change in the viscoelastic moduli of the film with increasing temperature, and the results agree well with the temperature obtained from other techniques. The method was not constrained to the range of the elastic moduli of the film, except where the acoustic film resonance occurred, and thus, could be applied to the study of a wide variety of thin, soft layers under different conditions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci.
2017 ,134 , 44532. -
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.more » « less
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ABSTRACT The properties of thin supported polymer films can be dramatically impacted by the substrate upon which it resides. A simple way to alter the properties of the substrate (chemistry, rigidity, dynamics) is by coating it with an immiscible polymer. Here, we describe how ultrathin (ca. 2 nm) hydrophilic polymer layers of poly(acrylic acid) and poly(styrene sulfonate) (PSS) impact the aging behavior and the residual stress in thin films of poly(butylnorbornene‐
ran ‐hydroxyhexafluoroisopropyl norbornene) (BuNB‐r ‐HFANB). The aging rate decreases as the film thickness (h ) is decreased, but the extent of this change depends on the adjacent layer. Even for the thickest films (h > 500 nm), there is a decrease in the aging rate at 100 °C when BuNB‐r ‐HFANB is in contact with PSS. In an effort to understand the origins of these differences in the aging behavior, the elastic modulus and residual stress (σR) in the films were determined by wrinkling as a function of aging time. The change in the elastic modulus during aging does not appear to be directly correlated with the densification or expansion of the films, but the aging rates appear to roughly scale ash σR1/3. These results illustrate that the physical aging of thin polymer films can be altered by adjacent polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019 ,57 , 992–1000
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.chemmater.2c01500
