It is now possible to create angstrom-scale channels that can be viewed as if one or a few atomic planes are pulled out of a bulk crystal leaving behind a two-dimensional space. I shall overview our recent work on this subject, which covers the properties of gases, liquids and ions under the extreme confinement.

In recent years, experiments from different groups have reported that evaporation under sunlight from hydrogels and other porous materials can exceed the thermal evaporation limit by several times, i.e., super-thermal. We hypothesize that photons can directly cleave off water clusters at the liquid-vapor interface in a way similar to the photoelectric effect, which we call the photomolecular effect. We carried out over 20 different experiments on both hydrogel and a water-air interface to demonstrate this effect. Some key experiments include: (1) partially wet hydrogels become absorbing despite their constituent materials are transparent; (2) super-thermal evaporation; (3) polarization, angle-of-incidence, and wavelength dependences of optical responses at a single air-water interface to visible-light where bulk water does not absorb; (4) cooling of air under visible light irradiation; and (5) Raman and IR signatures of water clusters in the air. We also demonstrate that visible light heats up a thin layer of fog, with temperature rise peaking at the green wavelength where water is least absorbing. Our work could resolve an 80-year puzzle in atmospheric science: experiments reported more cloud absorption than theory could predicts. Progress in theoretical description of the photomolecular effect will also be summarized. Our study suggests that the photomolecular effect should happen widely in nature, from clouds to fogs, ocean to soil surfaces, and plant transpiration, and can also lead to new applications in energy and clear water.

A fundamental challenge of modern physical science is to form structure that is not frozen in place but instead reconfigures internally driven by energy throughput and adapts to its environment robustly. With catalytic enzymes, we find problems of mechanobiology. With chemical reactions, we find problems of active matter. Exploring the potential of liquid-phase TEM to image individual molecules and their mutual interactions, we analyze failed and successful encounters of polymers and proteins, and visualize enzyme conformational changes in real time. A picture emerges in which simple experiments, performed at single-particle and single-molecule resolution, can dissect macroscopic phenomena in ways that surprise.

Since the beginning of this century, the development trend of information technology to intelligent technology is increasing, the sustainable development problems, such as climate, green energy and how to understand human brain, become increasingly urgent. This trend makes scientists face the challenge of multi-phase media, multi-scale strong nonlinear coupling, especially the force-electric-magnetic-light-thermal coupling at the solid-liquid interface. We will review the recent advances in hydrovoltaics for harvesting environmental energy, serving as a potential Negative thermal emission energy technology, and briefly discuss the role of confined water in our brain and envision the hydrovoltaic intelligence.

Life system presents an ultralow energy consumption in high-efficiency energy conversion, information transmission and bio-synthesis. The total energy intake of human body is about 2000 kcal/day to maintain all our activities, which is comparable to a power of ~ 100 W. The energy required for brain to work is equivalent to ~ 20 W, while the rest energy (~ 80 W) is used for other activities. All in vivo bio-syntheses take place only at body temperature, which is much lower than that of in vitro reactions. To achieve these ultralow energy-consumption processes, there should be a kind of ultralow-resistivity matter transport in nanochannels (e.g., ionic, molecular channels), in which the directional collective motion of ions or molecules is a necessary condition, rather than the traditional Newton diffusion. Directional collective motion of ions and molecules are considered as ionic/molecular superfluid. The research of ionic/molecular superfluid will promote the development of neuroscience and brain science, develop quantum ionic technology, construct future chemical reactors with high flux, high selectivity and low energy consumption, and produce a series of disruptive technologies.

The fluid-solid interface contains a complex process characterized with momentum transfer, heat transfer and mass transfer, where the fluid behavior is closely related to heat transfer and cooling capacity. Based on the basic physical process of the droplet impacting on the smooth hot surface, the technology of 2c-PLIF and micro-PIV is employed to achieve high-resolution simultaneous measurement of the internal velocity field and temperature field of the droplet, and the overall morphology and microscopic flow and heat transfer patterns in the complete boiling regimes of the droplet are quantitatively measured. The heat transfer of droplet at the solid-liquid interface is observed to spread outward from a local hot spot. The mechanisms of contact boiling slowing down the contact time of transitional boiling droplet and the scaling correlation of droplet heat absorption as a function of time are proposed. On this basis, we can also observe the dynamic Leidenfrost phenomenon of droplet impacting on the smooth hot surface and the microscopic flow and heat transfer process inside the droplet. Further on, the influence of surface micro/nanoengineering on fluid behavior at the fluid-solid interface is studied. In view of the boiling morphology and flow heat transfer process of droplet impacting the surface of aluminum-lithium alloy modified by thermal oxidation, it proves that the modified aluminum-lithium alloy is endowed with micro/nano-scale structures, and the nucleate boiling heat transfer of droplet per unit time on the modified surface is enhanced by 260% compared with that of the original surface, followed with advanced film boiling. The spray cooling performance of the modified aluminum-lithium alloy is also improved, and the critical heat flux is increased by 130%. At the same time, the capillary flow phenomenon at the fluid-solid interface also provides the basis for spontaneous transport of liquid. Due to the attraction of the liquid phase to the solid phase, a curved liquid surface is formed at the phase interfaces of solid, liquid and gas. After the surface liquid evaporates, the following liquid will move and replenish to maintain the stability of the liquid level by capillary force. Based on MEMS manufacturing technology of micro-model and micro-PIV velocity measurement method, the mechanism of capillary flow driven by evaporation inside porous structures is deeply studied, and a self-pumping and self-adaptive capillary cooling scheme based on capillary force under heating is proposed. Micro/nanoengineering design is used to improve the surface wettability of porous media and enhance the capillary suction capacity. According to the actual cooling requirements, combined with 3D printing, particle sintering, fiber weaving and other processing and manufacturing methods, the variable-pore porous structures based on different material systems such as ceramics, metals and composites are designed to achieve evaporation-driven phase change cooling without mechanical pumps under extreme and complex thermal environments, and the critical heat flux reaches 3.1 MW/m2. Further, the micro/nanoengineered capillary cooling technology can provide long-term thermal protection under test conditions of supersonic wind tunnel, providing a lightweight and reliable thermal protection scheme for key components of aerospace vehicles.