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Accurate measurement and estimation on the trends and spatial distributions of VOCs emissions in China are critical to establishing efficient local or regional pollution control measures, while less is known about the discrepancies on VOCs emissions estimated by previous studies. In this study, two of the estimation approaches including the bottom-up and top-down methods have been reviewed with the data collected from many studies. The approaches demonstrated that the total anthropogenic VOCs emissions in China have been increasing since 1949. The contributions of industrial and solvent use to total VOCs emissions have been increasing since 2000, whereas the contributions of transportation sector have shown a decreasing trend since 2000. The contributions of fuel combustion have also been decreasing since 1950. The gaps of emission estimates for the industry and solvent use were 99.3 ± 22.7% and 81.5 ± 41.8%, respectively, which distributed in much wider ranges than other sources (e.g. 28.9 ± 16.7% for fuel combustion). In comparison to the top-down method, larger variations on the annual VOCs emission estimates were seen using the bottom-up method that comprised different data sources. For the view of spatial pattern, most hot emission estimate spots were concentrated in the eastern China, consistent to their relatively stronger strengths in the industrialization and urbanization. Although the total VOCs emission in China has been continuously increasing during 2008–2016, the VOCs emissions per gross domestic production (GDP) showed a decreasing trend. As for individual compounds, large discrepancy was seen on formaldehyde, with the coefficient of variation (CV) ranged from 37% to 128% over the years. In overall of view, the importance of industrial process and solvent use is increasing. More focuses must be made to these two sources. Emissions of individual compound, particularly those of oxygenated VOCs, were not completely determined and should be better quantified.

Herein, cationic latex particles (CL) of different particle sizes were introduced as a cross-linking center to enhance the mechanical properties of the hydrophobically-associated hydrogels (P(AAm-co-HMA)-CL). Firstly, cationic polymethylmethacrylate (PMMA) latex particles were synthesized via soap-free emulsion polymerization. Subsequently, P(AAm-co-HMA)-CL hydrogels with outstanding mechanical properties were prepared using acrylamide as the monomer, hexadecyl methacrylate as the hydrophobic molecule, and CL as the cross-linking center. The size of CL had a significant effect on the mechanical properties and self-recovery properties of the P(AAm-co-HMA)-CL hydrogels. The hydrogel with larger CL size exhibited low mechanical properties due to weak hydrophobic interactions. In contrast, the hydrogel with small CL size displayed excellent mechanical properties due to an effective entanglement of the hydrophobic chains with the smaller size CL, which significantly affects the mechanical properties of the hydrogel. As a result, the maximum fracture stress and fracture strain of the hydrogel were up to 1.47 MPa and 2847%, respectively. This study can have a profound impact on the development of the technology of toughening hydrogels with latex particles.

Hydrogels have been applied in flexible strain sensors due to good conductivity, stretchability and sensitivity to strain. However, gaining rapid and effective self-healing hydrogels for the durability of flexible strain sensors is still a challenging. Herein, we report a tough, conductive hydrogel that can rapidly self-healing at room temperature. The hydrogel is fabricated by incorporating polystyrene-co-poly (N,N-dimethylacrylamide) (P (St-co-DMAA)) microspheres prepared by emulsion polymerization into hydrophobic association hydrogels networks composed of polyacrylamide-co-poly (hexadecyl methacrylate) (PAAm-co-PHMA), sodium dodecyl sulfate (SDS) and sodium chloride (NaCl). The hydrogel possesses a dual dynamic crosslinking comprising of multiple hydrogen bonds and hydrophobic association. The multiple hydrogen bonds formed between the outer regions of microspheres and PAAm chains provide rapid self-healing of hydrogels and contribute to re-association of hydrophobic chains and further improve self-healing efficiency. (99% Self-healing efficiency at room temperature for 2 h). At the same time, the dual crosslinking also gives the hydrogel good mechanical properties and fatigue resistance. In addition, the existence of sodium ions and chloride ions also endowed the hydrogel high sensitive deformation-dependent conductivity, make the hydrogel able to sensitive sensing of large and small strain signals (e.g. finger bending and breathing). And the sensing ability of hydrogel can be also recovered quickly after self-healing. Therefore, this strategy will expand the application range of a new generation of hydrogels such as self-healing conductors, robotic electronic skin and strain sensors, etc.