A portable microfluidic device for thermally controlled granular sample manipulation.

Effective granular sample manipulation with a portable and visualizable microfluidic device is significant for lots of applications, such as point-of-care testing and cargo delivery. Herein, we report a portable microfluidic device for controlled particle focusing, migration and double-emulsion droplet release via thermal fields. The device mainly contains a microfluidic chip, a microcontroller with a DC voltage control unit, a built-in microscope with a video transmission unit and a smartphone. Five microheaters located at the bottom of the microfluidic chip are used to unevenly heat fluids and then induce thermal buoyancy flow and a thermocapillary effect, and the experiments can be conveniently visualized through a smartphone, which provides convenient sample detection in outdoor environments. To demonstrate the feasibility and multifunctionality of this device, the focusing manipulation of multiple particles is first analyzed by using silica particles and yeast cells as experimental samples. We can directly observe the particle focusing states on the screen of a smartphone, and the particle focusing efficiency can be flexibly tuned by changing the control voltage of the microheater. Then the study focus is transferred to single-particle migration. By changing the voltage combinations applied on four strip microheaters, the single particle can migrate at predetermined trajectory and speed, showing attractiveness for those applications needing sample transportation. Finally, we manipulate the special three-phase flow system of double-emulsion drops in thermal fields. Under the combined effect of the thermocapillary effect and increased instability, the shell of double-emulsion droplets gradually thins and finally breaks, resulting in the release of samples in inner cores. The core release speed can also be flexibly adjusted by changing the control voltage of the microheater. These three experiments successfully demonstrate the effectiveness and multifunctionality of this thermally actuated microfluidic device on granular manipulation. Therefore, this portable microfluidic device will be promising for lots of applications, such as analytical detection, microrobot actuation and cargo release.

Influence of Particle Size on the Mechanical Performance and Sintering Quality of Peanut Husk Powder/PES Composites Fabricated through Selective Laser Sintering.

This study intends to enhance the mechanical strength of wood-plastic composite selective laser sintering (SLS) parts by using a sustainable composite, peanut husk powder (PHP)/poly ether sulfone (PES) (PHPC). The study aims to address agricultural waste pollution by encouraging the eco-friendly utilization of such waste in SLS technology. To ensure the sintering quality and mechanical properties and prevent deformation and warping during sintering, the thermo-physical properties of PHP and PES powders were analyzed to determine a suitable preheating temperature for PHPC. Single-layer sintering tests were conducted to assess the formability of PHPC specimens with varying PHP particle sizes. The study showed the effects of different PHP particle sizes on the mechanical performance of PHPC parts. The evaluation covered various aspects of PHPC SLS parts, including mechanical strength, density, residual ash content, dimensional accuracy (DA), and surface roughness, with different PHP particle sizes. The mechanical analysis showed that PHPC parts made from PHP particles of ≤0.125 mm were the strongest. Specifically, the density bending strength, residual ash content, tensile, and impact strength were measured as 1.1825 g/cm3, 14.1 MPa, 1.2%, 6.076 MPa, and 2.12 kJ/cm2, respectively. Notably, these parameters showed significant improvement after the wax infiltration treatment. SEM was used to examine the PHP and PES powder particles, PHPC specimen microstructure, and PHPC SLS parts before and after the mechanical tests and waxing. Consequently, SEM analysis wholly confirmed the mechanical test results.

Flexible droplet transportation and coalescence via controllable thermal fields.

Flexible droplet transportation and coalescence are significant for lots of applications such as material synthesis and analytical detection. Herein, we present an effective method for controllable droplet transportation and coalescence via thermal fields. The device used for droplet manipulation is composed of a glass substrate with indium tin oxide-made microheaers and a microchannel with two transport branches and a central chamber, and it's manipulated by sequentially powering the microheaters located at the bottom of microchannel. The fluid will be unevenly heated when the microheater is actuated, leading to the formation of thermal buoyancy convection and the decrease of interfacial tension of fluids. Subsequently, the microdroplets can be transported from the inlets of microchannel to the target position by the buoyancy flow-induced Stokes drag. And the droplet migration velocity can be flexibly adjusted by changing the voltage applied on the microheater. After being transported to the center of central chamber, the coalescence behaviors of microdroplets can be triggered if the microheater located at the bottom of central chamber is continuously actuated. The droplet coalescence is the combined effect of decreased fluid interfacial tension, the shortened droplet distance by buoyancy flow and the increased instability of droplet under the elevated temperature. The droplet coalescence efficiency is also related to the voltage of microheater, by increasing the voltage from 3.5 V to 7 V, the needed time for droplet coalescence dramatically decrease from 220s to 1.4 s. Finally, by the droplet coalescence-triggered calcium hydroxide precipitation reaction, we demonstrate the applicability of the droplet manipulation method on specific sample detection. Therefore, this approach used for droplet transportation and coalescence can be attractive for many droplet-based applications such as analytical detection.

Programmable, Changeable, Origami Cellulose Films for Magnetically Controllable Soft Robots.

Magnetic soft robots composed of stimuli-responsive materials are promising for biomedical engineering applications; however, typical responsive materials are fabricated with nondegradable polymeric substrates. In this study, we report a flexible, biodegradable, and magnetically sensitive cellulose film (M-film) that can be utilized for magnetically controllable soft robots (M-robots) with programmable locomotion, cargo delivery, and remote wireless operation functions. The M-film with good foldability, origami, and magnetic properties is synthesized by a simple paper-making process using cellulose nanofibers, additive sodium alginate, and BaFe12O19 particles. Through the following origami-magnetization process, the M-robot with multimodal movements is designed: climbing over the obstacles in the walking environment; additionally, this process can complete various cargo transport tasks by clawing, rolling, and flipping. This approach expands the precise controllability and manipulability of environmentally friendly cellulose nanomaterials beyond the known applications and opens the prospects of their implementation in stimuli-responsive robots, wireless control electronics, and intelligent devices.

Dual-Mode Coupled Triboelectric Nanogenerator for Harvesting Random Vibration Energy.

As a new energy harvesting technology, triboelectric nanogenerators are widely used for vibration mechanical energy harvesting. However, the current schemes ignore the composite characteristics of vibration, with problems such as utilization and low collection efficiency. In this paper, a random resonance cantilever beam triboelectric nanogenerator (RCB-TENG) with dual-mode coupled is presented, the working mode is a coupling form of in-plane sliding and vertical contact-separation that can effectively collect complex vibration energy in transverse and longitudinal directions. The influences of the structural parameters of the RCB-TENG and different dielectric materials on the output performance are systematically investigated. The single vibration module achieved a power density of 463.56 mW/m2 and a transfer charge of 10.7 µC at a vibration frequency of 46 Hz, an increase in power density, and a transfer charge of 4.94 and 3.82 times, respectively, compared to the conventional contact-separation mode. Finally, the RCB-TENG was tested in practice, and it was observed that nine 1 W commercial LED bulbs and 500 5 mm diameter LED lamps were successfully lit. This work offers new ideas for distributed energy harvesting technologies and holds broad promise in the field of energy harvesting from wind, water, wave, and random vibrations caused by mechanical energy.

Flexible on-chip droplet generation, switching and splitting via controllable hydrodynamics.

Flexible droplet preparation and manipulation are significant for lots applications such as immunoreaction and monocellular culture. Herein, we present a novel method for effective on-chip droplet generation, splitting and switching via controllable hydrodynamics. The microchannel of the designed chip has 6 inlets and 3 three outlets. The water solution is injected from a specific inlet (inlet d), and the other 5 inlets are used to inject oil fluids. Under the shearing effect of immiscible oils, the water phase breaks into dispersed droplets first, and the generated droplets can be further split into daughter drops or switched into side outlets from the middle outlet. To investigate the hydrodynamic droplet manipulation behaviors, a two-dimensional simulation model based on phase-field method is established. Utilizing the computational model, we systematically analyze the influences of the flow rates of continuous and dispersed fluids and the manipulation modes on droplet generation, splitting and switching. The numerical results indicate that the droplets can be generated with controlled sizes. For instance, at Qd = 5 µL/min and Qc1,2 = 5 µL/min, the droplet diameter decreases from 89.2 µm to 49.2 µm as Qs1,2 gradually rises from 15 µL/min to 40 µL/min. Moreover, the prepared droplets can realize on-demand splitting and switching. When Qd, Qc1,2, and Qs1,2 are fixed at 5 µL/min, 5 µL/min and 25 µL/min, respectively, the generated droplet is split into different proportional daughter drops with the rising of Qs3 (or Qs4) at first, and finally it is switched into the side-outlets when Qs3 (or Qs4) is higher than 80 µL/min. Therefore, this proposed droplet manipulation approach will be promising for various applications, and the numerical simulations can provide useful guidelines on the design and operation of droplet-based microfluidic systems.

Online moisture measurement of dead fine fuel on the forest floor using near-infrared reflectometry.

A method for online measurement of the levels of moisture in dead fine fuels on the forest floor is proposed based on near-infrared reflectometry. A linear relationship is found between the moisture content of dead fine fuels and the intensity of light absorption at a wavelength of 1450 nm, and this forms the basic principle of measurement for different forest species. An online moisture-monitoring device is designed and developed based on this principle. This uses long-distance wireless data-transmission to adapt to the lack of telecoms service in remote forests. Moisture-measurement experiments were conducted continuously for 24 h in rainless weather during the summer of 2019 in the Harbin Urban Forestry Demonstration Base of Northeast Forestry University using leaves from four different forest species, specifically, larch, dryland willow, silver birch, and walnut. These measurements were verified using simultaneous measurements employing a weighing method. The results from the field experiments agreed well with the weighing results. The uncertainty in the moisture-content measurements using the proposed system was ∼3.4% when the true moisture content was 20.0% or less. This proposed system has the advantages of online measurement and high accuracy. This method for monitoring moisture levels in dead fine fuels is an important advance in terms of improving the accuracy and simultaneity of measurements for prediction of forest-fire-risk ratings and fire behavior.

Design and Experimentation of a Self-Sensing Actuator for Active Vibration Isolation System with Adjustable Anti-Resonance Frequency Controller.

The vibration isolation system is now indispensable to high-precision instruments and equipment, which can provide a low vibration environment to ensure performance. However, the disturbance with variable frequency poses a challenge to the vibration isolation system, resulting in precision reduction of dynamic modeling. This paper presents a velocity self-sensing method and experimental verification of a vibration isolation system. A self-sensing actuator is designed to isolate the vibration with varying frequencies according to the dynamic vibration absorber structure. The mechanical structure of the actuator is illustrated, and the dynamic model is derived. Then a self-sensing method is proposed to adjust the anti-resonance frequency of the system without velocity sensors, which can also reduce the complexity of the system and prevent the disturbance transmitting along the cables. The self-sensing controller is constructed to track the variable frequency of the disturbance. A prototype of the isolation system equipped with velocity sensors is developed for the experiment. The experiment results show that the closed-loop transmissibility is less than -5 dB in the whole frequency rand and is less than -40 dB around, adding anti-resonance frequency which can be adjusted from 0 Hz to initial anti-resonance frequency. The disturbance amplitude of the payload can be suppressed to 10%.

Magnetically Driven 3D Cellulose Film for Improved Energy Efficiency in Solar Evaporation.

The architecture of cellulose nanomaterials is definitized by random deposition and cannot change in response to shifting application requirements. Herein, we present a magnetic field-controlled cellulose film derived from wood that exhibits great magnetic properties and reliable tunability enabled by incorporated Fe3O4 nanoparticles and cellulose nanofibers (CNF) with a large length-diameter ratio. Fe3O4 nanoparticles are dispersed in suspensions of CNF so as to enhance the magnetic response. The plane magnetic CNF can be processed to form a three-dimensional (3D) flower-like structure along the magnetic induction line after applying an external magnet. Inspired by the fluidic transport in natural flowers, a bilayer structure was created using the 3D flower-like film as the solar energy receiver and natural wood as the water pathway in a solar-derived evaporation system. Compared with a planar cellulose film decorated with Fe3O4, the 3D structure design can greatly improve the evaporation rate from 1.19 to 1.39 kg m-2 h-1 and the efficiency from 76.9 to 90.6% under 1 sun. Finite element molding further reveals that the 3D structural top layer is beneficial for the formation of a gradient temperature profile and the improvement of the energy efficiency through the reduction of thermal radiation. The magnetically controlled fabrication represents a promising strategy for designing cellulose nanomaterials with a complicated structure and controllable topography, which has a wide spectrum of applications in energy storage devices and water treatment.

Mesoporous carbon prepared by etching halloysite nanotubes (HNTs) with pyrrole as a precursor for a sulfur carrier of superior lithium-sulfur batteries.

Using pyrrole as a carbon precursor and halloysite nanotubes (HNT) as a templating agent, mesoporous carbon (MC) was prepared by template etching and combined with sulfur as a composite cathode for lithium-sulfur batteries. The mesoporous carbon/sulfur (MC/S) composite cathode exhibits a first cycle discharge specific capacity of 1355 mA h g-1 at 0.2C, and the utilization rate of active sulfur can reach 80.9%. Even after 500 cycles, the discharge specific capacity still remains at 496.9 mA h g-1 when tested at 0.5C. Furthermore, the hollow groove structure present in the MC/S electrode provides a large number of active sites for electrochemical reactions. The prepared MC/S composite cathode not only has a high discharge specific capacity and good cycle stability, but also increases the energy density of the lithium-sulfur battery. Therefore, this preparation process of MC is more conducive to practical application.