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14 pages, 4321 KiB

Open AccessArticle

BaSO₄/TiO₂ Microparticle Embedded in Polyvinylidene Fluoride-Co-Hexafluoropropylene/Polytetrafluoroethylene Polymer Film for Daytime Radiative Cooling

by Mohamed Mahfoodh Saleh Altamimi, Usman Saeed and Hamad Al-Turaif

Polymers 2023, 15(19), 3876; https://doi.org/10.3390/polym15193876 - 25 Sep 2023

Cited by 3 | Viewed by 1060

Abstract

Radiative cooling is a new large-scale cooling technology with the promise of lowering costs and decreasing global warning. Currently, daytime radiative cooling is achieved via the application of reflective metal layers and complicated multilayer structures, limiting its application on a massive scale. In our research, we explored and tested the daytime subambient cooling effect with the help of single-layer films consisting of BaSO₄, TiO₂, and BaSO₄/TiO₂ microparticles embedded in PVDF/PTFE polymers. The film, consisting of BaSO₄/TiO₂ microparticles, offers a low solar absorbance and high atmospheric window emissivity. The solar reflectance is enhanced by micropores in the PVDF/PTFE polymers, without any significant influence on the thermal emissivity. The BaSO₄/TiO₂/PVDF/PTFE microparticle film attains 0.97 solar reflectance and 0.95 high sky-window emissivity when the broadly distributed pore size reaches 180 nm. Our field test demonstrated that the single-layer BaSO₄/TiO₂/PVDF/PTFE microparticle film achieved a temperature 5.2 °C below the ambient temperature and accomplished a cooling power of 74 W/m². Also, the results show that, when the humidity rises from 33% to 38% at 12:30 pm, it hinders the cooling of the body surface and lowers the cooling effect to 8%. Full article

(This article belongs to the Special Issue Multifunctional Advanced Polymeric Films)

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15 pages, 3488 KiB

Open AccessArticle

Enhancement of Stability in n-Channel OFETs by Modulating Polymeric Dielectric

by Po-Hsiang Fang, Peng-Lin Kuo, Yu-Wu Wang, Horng-Long Cheng and Wei-Yang Chou

Polymers 2023, 15(11), 2421; https://doi.org/10.3390/polym15112421 - 23 May 2023

Cited by 2 | Viewed by 1096

Abstract

In this study, a high-K material, aluminum oxide (AlO_x), as the dielectric of organic field-effect transistors (OFETs) was used to reduce the threshold and operating voltages, while focusing on achieving high-electrical-stability OFETs and retention in OFET-based memory devices. To achieve this, we modified the gate dielectric of OFETs using polyimide (PI) with different solid contents to tune the properties and reduce the trap state density of the gate dielectric, leading to controllable stability in the N, N’-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃)-based OFETs. Thus, gate field-induced stress can be compensated for by the carriers accumulated due to the dipole field created by electric dipoles within the PI layer, thereby improving the OFET’s performance and stability. Moreover, if the OFET is modified by PI with different solid contents, it can operate more stably under fixed gate bias stress over time than the device with AlO_x as the dielectric layer only can. Furthermore, the OFET-based memory devices with PI film showed good memory retention and durability. In summary, we successfully fabricated a low-voltage operating and stable OFET and an organic memory device in which the memory window has potential for industrial production. Full article

(This article belongs to the Special Issue Multifunctional Advanced Polymeric Films)

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17 pages, 5136 KiB

Open AccessFeature PaperArticle

Polyimide-Derived Supramolecular Systems Containing Various Amounts of Azochromophore for Optical Storage Uses

by Andreea Irina Barzic, Ion Sava, Raluca Marinica Albu, Cristian Ursu, Gabriela Lisa and Iuliana Stoica

Polymers 2023, 15(4), 1056; https://doi.org/10.3390/polym15041056 - 20 Feb 2023

Cited by 4 | Viewed by 1277

Abstract

The progress of digital technologies demands more speed and larger storage capacity. Optical storage systems have the advantage of being cheap, fast and capacious. This article explores the potential use of polyimide-based films as a recording medium for optical storage devices. The materials were designed through a host–guest approach that involves a cyano-containing polyimide precursor and an azochromophore combined in the following ratios: 1:0.25, 1:0.5, 1:0.75 and 1:1. After thermal treatment up to 200 °C, polyimide systems were formed with supramolecular structures constructed via hydrogen bonding as shown by molecular modeling and FTIR at around 3350 cm⁻¹. The aspects arising from the variation of the azo-dye content in the polyimide samples and their impact on the vitrification temperature, colorimetric features, refractive index, band gap, non-linear optical susceptibility and birefringence were investigated for the first time. The thermal analysis indicated a slight decrease in the vitrification temperature from 190.84 °C for the sample without azo dye to 163.91 °C for the film containing the highest leading of azo dye. The morphology images revealed the occurrence of periodic structures in azo-derived materials exposed to a UV laser, which is accentuated by the addition of more azo dye molecules. Optical tests allowed observation of the increase in the dominant wavelength, refractivity and optical conductivity of the samples, produced by the incorporation of azochromophore and laser irradiation. The photo-generated birefringence increased from 0.014 (sample with 1:0.25) to 0.036 (sample with 1:1), which in combination with the created regular topography pattern, is essential for the use of these materials as recording media in optical storage applications. Full article

(This article belongs to the Special Issue Multifunctional Advanced Polymeric Films)

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