Photothermal Nanoconfinement Reactor: Boosting Chemical Reactivity with Locally High Temperature in a Confined Space.

A photothermal nanoconfinement reactor (PNCR) system is proposed and demonstrated by using hollow carbon nanospheres (HCNs) to enhance the performance of the chemical reaction. Under light irradiation, the local temperature of the HCN inner void space was much higher than the bulk solution temperature because the confined space concentrates heat and inhibits heat loss. Using the temperature-sensitive model reaction, peroxydisulfate (PDS) activation to oxidize micropollutant, it is shown that the degradation rate of sulfamethoxazole in the PNCR system is 7.1 times of that without nanoconfinement. It is further discovered that the high-quality local heat inside the nanoconfined space shifted the model reaction from an otherwise non-radical pathway to a radical-based pathway. This work provides an interesting strategy to produce a locally high temperature, which has a wide range of applications to energy and environmental fields.

Development of wearable air-conditioned mask for personal thermal management.

A mask that creates a physical barrier to protect the wearer from breathing in airborne bacteria or viruses, reducing the risk of infection in polluted air and potentially contaminated environments, has become a daily necessity for the public especially as COVID-19 has exploded around the world. However, the use of masks often causes soaring temperatures and thick humid air, leading to thermal and wear discomfort and breathing difficulties for a number of people, and further increasing the elevated risk of heat illnesses including heat stroke and heat exhaustion. When wearers become highly active or work under high tension, the excess sweat generated negatively affects the functionality of masks. Here, we report on an innovative design of an air-conditioned mask (AC Mask) system, facilitating thermoregulation in the mask microclimate, ease of breathing, and wear comfort. The AC Mask system is developed by integrating a cost-effective and lightweight thermoelectric (TE) and ventilation unit in a wearable 3D printed mask device, compatible with existing disposable masks, to protect end users safely against toxic particles such as viruses. A wind-guided tunnel has been developed for quick and efficient ventilation of cooling air. Based on a human trial, reductions in the apparent microclimate temperature and the humidity by 3.5 °C and 50%, respectively, have been achieved under a low voltage. With the excellent thermal management properties, the AC Mask will find also wide application among professional end-users such as construction workers, firefighters, and medical personnel.

Self-Assembly of TiO2 Nanofiber-Based Microcapsules by Spontaneously Evolved Multiple Emulsions.

We demonstrate hierarchical nest/crust-like colloidosomes composed of interlocked titanium dioxide (TiO2) nanofibers using spontaneously evolved n-butanol/water/ n-butanol (B/W/B) emulsions. We find two mechanisms to produce colloidosomes from B/W/B droplets due to their mutual solubility and dewetting discrepancy. Porous TiO2 colloidal capsules with loosely intertwined nanofibers were obtained after the dewetting of nanofiber-coated B/W/B droplets, while crustlike TiO2 colloidosomes with a thin shell and large hollow interior are developed from amphiphilic polymer-stabilized B/W/B droplets. We further investigate the effect of experimental parameters, including the initial droplet size, the nanofiber concentration, and the water/butanol ratios in butanol phases, on the droplet-to-colloidosome evolution and resultant morphology of colloidosomes. Our simple and versatile approach for fabricating TiO2 colloidosomes can be extended to a range of irregular colloidal particles, and the products have great potential to act as host systems in electrochemical catalysis, photothermal therapy, or filtration materials.

3D Cellular Solar Crystallizer for Stable and Ultra-Efficient High-Salinity Wastewater Treatment.

Recent developed interfacial solar brine crystallizers, which employ solar-driven water evaporation for salts crystallization from the near-saturation brine to achieve zero liquid discharge (ZLD) brine treatment, are promising due to their excellent energy efficiency and sustainability. However, most existing interfacial solar crystallizers are only tested using NaCl solution and failed to maintain high evaporation capability when treating real seawater due to the scaling problem caused by the crystallization of high-valent cations. Herein, an artificial tree solar crystallizer (ATSC) with a multi-branched and interconnected open-cell cellular structure that significantly increased evaporation surface is rationally designed, achieving an ultra-high evaporation rate (2.30 kg m-2  h-1 during 2 h exposure) and high energy efficiency (128%) in concentrated real seawater. The unit cell design of ATSC promoted salt crystallization on the outer frame rather than the inner voids, ensuring that salt crystallization does not affect the continuous transport of brine through the pores inside the unit cell, thus ATSC can maintain a stable evaporation rate of 1.94 kg m-2  h-1 on average in concentrated seawater for 80 h continuous exposure. The design concept of ATSC represents a major step forward toward ZLD treatment of high-salinity brine in many industrial processes is believed.

2D and 3D Electrospinning of Nanofibrous Structures by Far-Field Jet Writing.

Electrospinning offers remarkable versatility in producing superfine fibrous materials and is hence widely used in many applications such as tissue scaffolds, filters, electrolyte fuel cells, biosensors, battery electrodes, and separators. Nevertheless, it is a challenge to print pre-designed 2D/3D nanofibrous structures using electrospinning due to its inherent jet instability. Here, we report on a novel far-field jet writing technique for precisely controlling the polymer jet in nanofiber deposition, which was achieved through a combination of reducing the nozzle voltage, adjusting the electric field, and applying a set of passively focusing electrostatic lenses. By optimizing the applied voltage, the circular aperture of lenses, and the distance between the adjacent lenses, the best precision achieved using this technique was approximately 200 µm, similar to that of a conventional polymer-based 3D printer. This development makes it possible for printing 2D/3D nanofibrous structures by far-field jet writing for different applications with enhanced performance.

Temperature-adaptive rooftop covering with synergetic modulation of solar and thermal radiation for maximal energy saving.

The energy consumption for maintaining desired indoor temperature accounts for 20% of primary energy use worldwide. Passive rooftop modulation of solar/thermal radiation without external energy input has a great potential in building energy saving. However, existing passive rooftop modulation techniques failed to simultaneously modulate solar/thermal radiation in response to rooftop surface temperature which is closely related to the building thermal loads, leading to limited or even counter-productive overall energy saving. Here, we report the development of a surface temperature-adaptive rooftop covering with synergetic solar and thermal modulations. The covering, made of a scalable metalized polyethylene film, demonstrated excellent solar absorptance modulation (72.5%) and thermal emissivity modulation (79%) in response to its temperature change from 22°C (indoor heating setpoint) to 25°C (indoor cooling setpoint), and vice versa. Building energy simulations demonstrate that the proposed rooftop covering can achieve all-season energy savings across all climate regions.

A Numerical Analysis of the Cooling Performance of a Hybrid Personal Cooling System (HPCS): Effects of Ambient Temperature and Relative Humidity.

Hybrid personal cooling systems (HPCS) incorporated with ventilation fans and phase change materials (PCMs) have shown its superior capability for mitigating workers' heat strain while performing heavy labor work in hot environments. In a previous study, the effects of thermal resistance of insulation pads, and latent heat and melting temperature of PCMs on the HPCS's thermal performance have been investigated. In addition to the aforementioned factors, environmental conditions, i.e., ambient temperature and relative humidity, also significantly affect the thermal performance of the HPCS. In this paper, a numerical parametric study was performed to investigate the effects of the environmental temperature and relative humidity (RH) on the thermal management of the HPCS. Five levels of air temperature under RH = 50% (i.e., 32, 34, 36, 38 and 40 °C) and four levels of environmental RH at two ambient temperatures of 36 and 40 °C were selected (i.e., RH = 30, 50, 70 and 90%) for the numerical analysis. Results show that high environmental temperatures could accelerate the PCM melting process and thereby weaken the cooling performance of HPCS. In the moderately hot environment (36 °C), HPCS presented good cooling performance with the maximum core temperature at around 37.5 °C during excise when the ambient RH ≤ 70%, whereas good cooling performance could be only seen under RH ≤ 50% in the extremely hot environment (40 °C). Thus, it may be concluded that the maximum environmental RH under which the HPCS exhibiting good cooling performance decreases with an increase in the environmental temperature.

Spreading-induced dewetting for monolayer colloidosomes with responsive permeability.

Herein, we present a spreading-induced dewetting approach of Pickering emulsion droplets for fabricating monolayer colloidosomes. The dewetting of the water-in-oil-in-water (W/O/W) double emulsion droplets is triggered by the quick spreading and wetting of the fluorinated oil phase on the water/air surface. By combining this colloidosome formation mechanism with thermo-responsive copolymer that adsorbs or desorbs at the surface of the colloidosome shell, we fabricated smart monolayer colloidosomes using a microfluidic-templated approach. These colloidosomes are highly monodisperse and possess a well-defined shell microstructure, tunable permeability, biocompatibility, mechanical stability, and high encapsulation efficiency. These attributes will pave the way for effective encapsulation, transport, and release of a range of active ingredients, especially the biologically active materials.

A Dewetting Model for Double-Emulsion Droplets.

The evolution of double-emulsion droplets is of great importance for the application of microdroplets and microparticles. We study the driving force of the dewetting process, the equilibrium configuration and the dewetting time of double-emulsion droplets. Through energy analysis, we find that the equilibrium configuration of a partial engulfed droplet depends on a dimensionless interfacial tension determined by the three relevant interfacial tensions, and the engulfing part of the inner phase becomes larger as the volume of the outer phase increases. By introducing a dewetting boundary, the dewetting time can be calculated by balancing the driving force, caused by interfacial tensions, and the viscous force. Without considering the momentum change of the continuous phase, the dewetting time is an increasing function against the viscosity of the outer phase and the volume ratio between the outer phase and inner phase.

Droplet Breakup in Expansion-contraction Microchannels.

We investigate the influences of expansion-contraction microchannels on droplet breakup in capillary microfluidic devices. With variations in channel dimension, local shear stresses at the injection nozzle and focusing orifice vary, significantly impacting flow behavior including droplet breakup locations and breakup modes. We observe transition of droplet breakup location from focusing orifice to injection nozzle, and three distinct types of recently-reported tip-multi-breaking modes. By balancing local shear stresses and interfacial tension effects, we determine the critical condition for breakup location transition, and characterize the tip-multi-breaking mode quantitatively. In addition, we identify the mechanism responsible for the periodic oscillation of inner fluid tip in tip-multi-breaking mode. Our results offer fundamental understanding of two-phase flow behaviors in expansion-contraction microstructures, and would benefit droplet generation, manipulation and design of microfluidic devices.

Tip-multi-breaking in Capillary Microfluidic Devices.

We report tip-multi-breaking (TMB) mode of droplet breakup in capillary microfluidic devices. This new mode appears in a region embraced by Cai = 0 and lg(Cai) = -8.371(Ca0) -7.36 with Ca0 varying from 0.35 to 0.63 on the Cai - Ca0 phase diagram, Cai and Ca0 being the capillary numbers of inner and outer fluids, respectively. The mode is featured with a periodic, constant-speed thinning of the inner liquid tip and periodic formation of a sequence of droplets. The droplet number n in a sequence is determined by and increases with outer phase capillary number, and varies from two to over ten. The distribution of both pinch-off time and size of the droplets in a sequence is a geometric progression of common ratio that depends exclusively on and increases monotonically with the droplet number from its minimum value of 0.5 at n = 2 to its maximum value of 1 as n tends to infinity. These features can help identify the unique geometric morphology of droplet clusters and make them promising candidates for encryption and anti-fake identification.