Ratiometric Flapping Force Probe That Works in Polymer Gels

A ratiometric flapping force probe that can evaluate the nanoscale stress concentration in the polymer chain network of common organogels has been developed. Stress-dependent dual-fluorescence properties of the chemically doped flapping force probe has been demonstrated even when the probe is solvated in the wet materials (Figure 1). The fluorescence ratiometric analysis is robust against the local concentration change induced by the macroscopic polymer deformation. While the force-responsive FRET dyads, widely used in mechanobiology, are sensitive to the distance and orientation of the two chromophores, the flapping fluorophore works as a single-component flexible force probe regardless of the FRET efficiency. Realtime and reversible spectral response to the mechanical stress is observed with a low threshold on the order of sub-MPa compression due to its conformational flexibility. The previously reported flapping probe only shows a negligible response in the solvated environments because the undesired spontaneous planarization occurs in the S1 excited state, even without mechanical force. The excited-state engineering by changing the flapping wings from the anthraceneimide units to the pyreneimide units endows this molecule with the force probe function in the wet conditions. The structurally modified force probe also has an advantage in terms of a wide dynamic range of the fluorescence response in solvent-free elastomers, which enabled the ratiometric fluorescence imaging of the molecular-level stress concentration during the crack growth in a stretched polyurethane film. The percentage of the stressed force probes has been experimentally estimated to be approximately 30–40% before the fracture of the elastomers. The flapping force probe is useful for elucidating the toughening mechanism of recently focused unique topological gels and elastomers at molecular level.

Investigation on mechanical properties and water stability of porous polyurethane concrete

Porous polyurethane concrete (PPUC) is a novel material for permeable pavements and is considered as an alternative to porous asphalt or porous cement concrete. However, studies of the mechanical properties of PPUC are still insufficient. In this study, the comprehensive mechanical properties and water stability of PPUC with different gradations and polyurethane dosages were investigated, and its water damage mechanism was preliminarily explored. The results show that the flexural strength and Marshall stability of PPUC can more easily reach the index in the standards of porous cement concrete or porous asphalt, while the compressive strength and abrasion resistance are the weak points of its mechanical properties and need to be further optimized. The mechanical properties and water stability of PPUC were effectively improved by increasing the polyurethane dosage and using continuously graded aggregates. PPUC is more susceptible to water damage because water reacts with the residual isocyanate groups within the polyurethane film to generate carbon dioxide gas, which reduces the cohesion and adhesion performance of polyurethane film. This study provides a comprehensive understanding of the mechanical properties of PPUC and an initial insight into the mechanism of water damage.

Development and Characteristics of Multipurpose Transparent Polyurethane Film

In industry, recent research developments include flexible films and foldable films. The next step is the development of stretchable films, and studies are being intensively carried out. Research on the development of stretchable and transparent materials is also increasing greatly. Currently, polydimethylsiloxane (PDMS) is the most commonly used film in the industry. However, PDMS surfaces are hydrophobic, so their use is limited to making materials and compounds with hydrophilic properties. In this study, we developed a transparent polyurethane film that can be used for multiple purposes. A transparency comparison between the transparent polyurethane film and the general polyurethane film was used to verify their future application. The conventional polyurethane films showed a transmittance rate of 2.2 percent, but the transparent polyurethane films achieved a high transmittance rate of 85 percent. To determine whether the film can be realized, we produced a conductive paste using resin for the transparent polyurethane film. In addition, a conductive paste was made based on the material used in the transparent polyurethane film to verify the hardness and reliability of the adhesion of electrodes, and we confirmed this with thermogravimetric analysis (TGA). The transparent polyurethane based paste was made with stretchable electrodes through a screen printing method. The manufactured stretchable electrodes were demonstrated by mechanical and adhesion tests. Finally, a permittivity test was conducted to determine the suitability of the film for application to printed electrodes for antennas in the future. The genetic rate of transparent polyurethane films was better than that of conventional polyurethane films. Moreover, the adhesion of the transparent polyurethane film and stretchable electrodes was as good as that of conventional polyurethane film and stretchable electrodes, and observation by optical microscopy confirmed that the printing performance was also excellent. In addition, the conductive paste made based on the transparent polyurethane film material was cured for 1 hour at 120 °C, and TGA analysis confirmed that both the binders and curing agent responded well in the test for curing the developed stretchable electrodes and transparent polyurethane.

Synthesis and Characterization of Epoxy Resins-Modified Waterborne Polyurethane Emulsion

Aqueous polyurethane emulsion was prepared with diphenylmethane diisocyanate (MDI), polybutylene adipate diol (PBA-1000) as main raw materials and 2, 2-dihydroxymethyl propionic acid (DMPA) as hydrophilic chain extender. On this basis, epoxy resin E-44 was introduced to modify the polyurethane prepolymer, and epoxy resin modified waterborne polyurethane emulsion was obtained. In order to obtain better performance waterborne polyurethane, the effect of DMPA content、the amount of epoxy resin added and modification method on the properties of polyurethane was discussed. The results show that when the DMPA content is 4wt%, the overall performance of the emulsion and the film is the best. And the addition of epoxy resin significantly improves the water resistance, solvent resistance and tensile strength of the waterborne polyurethane film, and its hardness and thermal stability are also improved to a certain extent. When the amount of epoxy resin added is 8wt%, the storage stability decreases significantly, the suitable amount of epoxy resin added is 6wt%. The overall performance of the film obtained by chemical modification is better than that of physical modification.