Ultrablack Elastomers With A Dual-Gradient Design: Synthesis,Properities And Applications

Engineering flexible broadband light absorbers are crucial to various applications ranging from dark-level reduction to light harvesting.However,developing solvent free,ultrablack elastomers with high light-absorption performance and broad absorption band remains a challenge.Here,we reported a facile and simple method to prepare the highly flexible composite films with a dual-gradient design for the broad-spectrum and efficient light absorption.Then we further studied the formation mechanism of dual-gradient structure,influencing factors and application of the flexible composite films.We combined it with nano-imprint technology,conductive material,shape memory material and ice-templating method to further explore the application of composite film with dual-gradient structure in superhydrophobic materials,stress sensing,photoactuator and solar steam generation.The results can be summarized as follows:1.A class of composite elastomers are fabricated for ultrablack sheet materials.The fabrication process involves a fast photo-polymerization of acrylates in the presence of gradient deposited polypyrrole(PPy)nanoparticles.The resultant film shows a dual-gradient structure(i.e.lower side features lower polymer chain density while higher concentration of deposited PPy).Such structure design critically contributes to the formation of hierarchical surface microstructures for efficient light trapping.As a result,lower side of the films exhibits incident-light-angle independent,high light absorptivity of 98.43%at 250-2400 nm.Moreover,flexible and mechanically robust absorbers have been demonstrated to offer versatile solar energy related applications,such as sunlight heater,photoactuator,pattern display and anticounterfeiting.Rather than tedious processing ways generally used in carbon nanotube forests or plasmonic involved ultrablack materials,dual-gradient design principle is concise and compatible with polymer thin-film fabrication process,and applicable to various elastic substrates,thus will provide guidance for fabricating various flexible ultrablack sheet materials and devices in a cost-effective and large scalable way.2.Here,we reported flexible film producing superhydrophobic and antireflective surfaces with dual-gradient structure realized by ultraviolet-assisted nanoimprint lithography.We could change the macroscopic properties by adjusting the microstructure of the film.Light absorption and hydrophobicity were related to the surface morphology of the film,and the surface patterns could be well-tuned by controlling the deposition time before polymerization and the size of the template pattern.The concept of the combination of mold pattern and self-formed pattern offers a new insight into the design of robust superhydrophobic and antireflective surfaces aiming at various technological applications.3.We explored a concept based on the partially embedded of PPy on the lower side of the elastic matrices with dual-gradient structure to substantially maintain the stretchability of elastic,without affecting charge transport mobility.The partially embedded of PPy on the elastic matrices could reduce the influence of the elastic matrix on charge transport mobility and improve long-term performance of reliability and stability of strain sensor compared to the usual method.It is a facile,fast,low-cost and scalable route to prepare flexible sensors.Besides a good stretchability and sensitivity testified by human motion monitoring,the strain sensor produced average absorption of 98.48%at 250-2400 nm that may be use as light sensor and sunlight heater for thermal therapy.4.Benefiting from the excellent photothermal properties and the dual-gradientstructure,the composite film could offer reversible photo-responive actuation.Then,the shape memory polymer(SMP)was incorporated into actuator with the photothermal phase switch to enable a multi-SMP.when the film was placed directly under a xenon lamp,it could quickly bend as temperature rose and relax back to the initial state after the light was turned off.We could edit the shape of film when the film was under xenon to achieve shape memory.The film with photoeditable deformation has the advantages of simple preparation and quick response.It of great significance to expand the research on the photothermal properties of light-absorbing materials.5.Enlightened by conifer tracheid construction,the architecture with channels and pores for efficient water transport was realized by ice-template method and in situ copolymerization technique to prepare the ultrablack film with dual-gradient structure for solar steam generation.The lower side of the resultant film with high light absorption of 98.2%at 250-2400 nm could achieve efficient light trapping and porous structure could realize the efficient water transpiration.The composite film achieved a high evaporation rate under one sun(1 k W/m~2)at 1.9 kg/m~2h.