Modulating the Carbonization Degree of Carbon Dots for Multicolor Afterglow Emission.

Organic afterglow materials based on carbon dots (CDs) have aroused extensive attention for their potential applications in sensing, photoelectric devices, and anticounterfeiting. Effective methods to control the CD structure and modulate the energy levels are critical but still challenging. Here, we demonstrate a method to modulate the afterglow emission of CDs@SiO2 composites by controlling the carbonization degree of CDs with variable calcining temperatures. The CDs@SiO2-Raw prepared with a hydrothermal bottom-up synthesis method shows a more polymerized structure of CDs with low carbonization degree, which emits long-lived thermally activated delayed fluorescence (TADF) with the lifetime of 252 ms. After calcination at 550 °C, CDs@SiO2-550 exhibits a larger conjugated π-domain structure with higher carbonization degree, thus inducing room-temperature phosphorescence (RTP) emission with a lifetime of 451 ms. The transformation of the carbonization degree of CD structures leads to changes in energy levels and ΔEST, which affect their afterglow luminescence behaviors. This work proposes a new concept to modulate the afterglow emission of CDs@SiO2 composites and forecasts potential applications of CD-based afterglow materials.

Electrochemical Behavior and Interfacial Delamination of a Polymer-Coated Galvanized Steel System in Acid Media.

The degradation behavior of polymer coatings is essential for their protective performance under various corrosive environments. Herein, electrochemical impedance spectroscopy (EIS) is employed to study the corrosion behavior and interfacial delamination of a polymer-coated metal system exposed to 0.1, 0.5, and 1 mol/L H2SO4 solutions at 50 °C. The electrochemical impedance spectra are analyzed using different equivalent circuits to derive the time dependence of the parameters of the coating, delaminated area, and interfacial processes. The phase angle at 10 Hz (θ10 Hz) is not appropriate in the case of higher delamination area ratio α, while θ10 kHz provides a rapid approach to evaluate the degradation of polymer-coated metal systems. The frequency of the phase angle at -45° (f -45°) leads to a wrong evaluation for higher α and can be no longer viewed as the breakpoint frequency. The frequency f p obtained by the changing rate of phase angle (CRPA) method is proposed to monitor the coating degradation and determine the breakpoint frequency with the consideration of dispersive number n. The frequency f EIS derived from fitting EIS spectra shows a good agreement with f p, which can contribute to clarify the evolution in the process of degradation.

Water Absorption, Hydrothermal Expansion, and Thermomechanical Properties of a Vinylester Resin for Fiber-Reinforced Polymer Composites Subjected to Water or Alkaline Solution Immersion.

In the present paper, a vinyl ester (VE) resin, potentially used as a resin matrix for fiber-reinforced polymer (FRP) composite sucker rods in oil drilling, FRP bridge cables, or FRP marine structures, was investigated on its resistance to water and alkaline solution immersion in terms of water uptake, hydrothermal expansion, and mechanical properties. A two-stage diffusion model was applied to simulate the water uptake processes. Alkaline solution immersion led to a slightly higher mass loss (approx. 0.4%) compared to water immersion (approx. 0.23%) due to the hydrolysis and leaching of uncured small molecules (e.g., styrene). Water immersion caused the expansion of VE plates monitored with Fiber Bragg Grating (FBG). With the same water uptake, the expansion increased with immersion temperatures, which is attributed to the increased relaxation extent of the resin molecular networks. Although an obvious decrease of the glass transition temperatures (Tg) of VE due to water immersion (5.4 to 6.1 °C/1% water uptake), Tg can be recovered almost completely after drying. Tensile test results indicate that a short-term immersion (less than 6 months) enhances both the strength and elongation at break, while the extension of the immersion time degrades both the strength and elongation. The modulus of VE shows insensitive to the immersion even at elevated temperatures.