The development of new structural materials for passive daytime radiative cooling (PDRC) of buildings will significantly reduce global building energy consumption. Cellulose aerogels are potential PDRC materials for building cooling, but the cooling performance and mechanical strength of cellulose aerogels are considered as challenges for their practical applications. Herein, a bio-inspired hierarchically structured cellulose aerogel (HSCA) was fabricated through an assembly strategy assisted by a high-voltage electrostatic field. The HSCA possesses outstanding PDRC performance and moderate mechanical strength owing to aligned hierarchical porous network microstructures reinforced with in situ-assembled crystalline cellulose nanofibers. Promisingly, the HSCA achieves a max cooling temperature of 7.2 °C and exhibits 1.9 MPa axial compressive strength. There was no significant cooling performance degradation after the hydrophobically modified HSCA was placed outdoors for 3 months. A simulation of potential cooling energy savings shows that by using HSCA as the building envelopes (side wall and roof), it can save 52.7% of cooling energy compared to the building baseline consumption. This new strategy opens up the possibility of developing advanced functionally regenerated cellulose aerogel, which is expected to provide a revolutionary improvement in aerogel materials for building cooling.
Molecular-scale compositional heterogeneities
can slash
the nonspecific
interaction between proteins and surfaces, resisting surface contamination.
In this work, an amphiphilic copolymer containing a soft fluorosilicone
macromonomer with controllable chain length as low-surface-energy
hydrophobic component and a zwitterionic monomer as hydrophilic component
was prepared to establish molecular-scale compositional heterogeneities.
The length of the fluorosiloxane side chains can significantly impact
the surface compositional heterogeneities, thus influencing the antifouling
performance of the copolymer coatings. Even under water, the coating
still retains a large number of low-surface-energy fluorosilicone
segments on the surface. The balance between hydrophilic and hydrophobic
segments on the surface provides a better synergistic effect, which
endows the copolymer coatings with excellent resistance to various
proteins.
Conventional reversible addition−fragmentation chain transfer (RAFT) emulsion polymers contain sulfur residues and low-molar-mass surfactants that contribute to undesired odor and deleterious effects of final materials. Herein, we show how living polymer chains obtained by catalytic chain transfer polymerization of surface-active monomers allyloxy polyoxyethylene(10)nonyl ammonium sulfate and methyl methacrylate can be used as an efficient stabilizer in sulfur-free RAFT (SF-RAFT) emulsion polymerization, resulting in soap-free latexes. The reactive surfactant concentration could decrease to 0.8 wt % in the final emulsion; meanwhile, the resultant latexes show good colloidal stability with an average particle size ranging from 110 to 135 nm. Furthermore, semibatch SF-RAFT emulsion polymerization results in a well-controlled polymerization process, as evidenced by the smooth increase in molecular weight of polymer chains as the polymerization progressed. It is also apparent from the chain extension experiments that the SF-RAFT emulsion polymerization of methacrylic monomers exhibits a living characteristic.
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