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1.
Proc Natl Acad Sci U S A ; 119(2)2022 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-34992136

RESUMO

Various physical tweezers for manipulating liquid droplets based on optical, electrical, magnetic, acoustic, or other external fields have emerged and revolutionized research and application in medical, biological, and environmental fields. Despite notable progress, the existing modalities for droplet control and manipulation are still limited by the extra responsive additives and relatively poor controllability in terms of droplet motion behaviors, such as distance, velocity, and direction. Herein, we report a versatile droplet electrostatic tweezer (DEST) for remotely and programmatically trapping or guiding the liquid droplets under diverse conditions, such as in open and closed spaces and on flat and tilted surfaces as well as in oil medium. DEST, leveraging on the coulomb attraction force resulting from its electrostatic induction to a droplet, could manipulate droplets of various compositions, volumes, and arrays on various substrates, offering a potential platform for a series of applications, such as high-throughput surface-enhanced Raman spectroscopy detection with single measuring time less than 20 s.

2.
Adv Sci (Weinh) ; : e2103834, 2022 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-35032105

RESUMO

Rapid droplet shedding from surfaces is fundamentally interesting and important in numerous applications such as anti-icing, anti-fouling, dropwise condensation, and electricity generation. Recent efforts have demonstrated the complete rebound or pancake bouncing of impinging droplets by tuning the physicochemical properties of surfaces and applying external control, however, enabling sessile droplets to jump off surfaces in a bottom-to-up manner is challenging. Here, the rapid jumping of sessile droplets, even cold droplets, in a pancake shape is reported by engineering superhydrophobic magnetically responsive blades arrays. This largely unexplored droplet behavior, termed as pancake jumping, exhibits many advantages such as short interaction time and high energy conversion efficiency. The critical conditions for the occurrence of this new phenomenon are also identified. This work provides a new toolkit for the attainment of well-controlled and active steering of both sessile and impacting droplets for a wide range of applications.

3.
Adv Mater ; : e2108567, 2021 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-34865264

RESUMO

High-performance droplet transport is crucial for diverse applications such as biomedical detection, chemical micro-reaction, and droplet microfluidics. Despite extensive progresses, traditional passive strategies and active strategies are restricted to limited liquid types, small droplet volume ranges, and poor biocompatibilities. Moreover, more challenges occur for the biological fluids due to the large viscosity and low surface tension. Here we report a vibration-actuated omni-droplets rectifier (VAODR) consisting of slippery ratchets arrays fabricated by femtosecond laser and vibration platforms. Through the relative competition between the asymmetric adhesive resistance originating from the lubricant meniscus on VAODR and the periodic inertial driving force originating from isotropic vibration, the fast (up to ∼60 mm/s), programmable and robust transport of droplets are achieved for a large volume range (0.05-2,000 µL, Vmax /Vmin ∼40,000) and in various transport modes including liquid slugs transport in the VAODR-based tube, programmable and sequential transport, and "cable-car"-like bidirectional transport. Our VAODR is also general to a high diversity of biological and medical fluids, and thus can be used for the biomedical detection such as ABO blood group test and anti-cancer drugs screening. Our strategies provide a complementary and promising platform for maneuvering omni-droplets that are fundamental to biomedical applications as well as other high-throughput omni-droplet operation fields. This article is protected by copyright. All rights reserved.

4.
Adv Mater ; : e2105996, 2021 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-34734449

RESUMO

Shaping soft and conductive materials into preferential architectures via 3D printing is highly attractive for numerous applications ranging from tactile devices to bioelectronics. A landmark type of soft and conductive materials is hydrogels/ionogels. However, 3D-printed hydrogels/ionogels still suffer from a fundamental bottleneck: limited stability in their electrical-mechanical properties caused by the evaporation and leakage of liquid within hydrogels/ionogels. Although photocurable liquid-free ion-conducting elastomers can circumvent these limitations, the associated photocurable process is cumbersome and hence the printing quality is relatively poor. Herein, a fast photocurable, solid-state conductive ionoelastomer (SCIE) is developed that enables high-resolution 3D printing of arbitrary architectures. The printed building blocks possess many promising features over the conventional ion-conducting materials, including high resolution architectures (even ≈50 µm overhanging lattices), good Young's modulus (up to ≈6.2 MPa), and stretchability (fracture strain of ≈292%), excellent conductivity tolerance in a wide range of temperatures (from -30 to 80 °C), as well as fine elasticity and antifatigue ability even after 10 000 loading-unloading cycles. It is further demonstrated that the printed building blocks can be programmed into 3D flexible tactile sensors such as gyroid-based piezoresistive sensor and gap-based capacitive sensor, both of which exhibit several times higher in sensitivity than their bulky counterparts.

5.
Artigo em Inglês | MEDLINE | ID: mdl-34753623

RESUMO

HYPOTHESIS: Droplet spreading on surfaces is a ubiquitous phenomenon in nature and is relevant with a wide range of applications. In practical scenarios, surfaces are usually associated with certain levels of vibration. Although vertical or horizontal modes of vibration have been used to promote droplet dewetting, bouncing from immiscible medium, directional transport, etc., a quantitative understanding of how external vibration mediates the droplet behaviors remains to be revealed. METHODS: We studied droplets impacting on stationary and vibratory surfaces, respectively. In analogy to the Weber number We=ρUi2D0/γWe = ρUi2D0/γ, we define the vibration Weber number We*=ρUv2D0/γ to quantitively analyze the vibration-induced dynamic pressure on droplet behaviors on vibratory surfaces, where ρ,γ,D0,UiandUv are liquid density, surface tension, initial droplet diameter, impact velocity of the droplet, and velocity amplitude of vibration, respectively. FINDINGS: We demonstrate that the effect of vibration on promoting droplet spreading can be captured by a new scaling number expressed as We*/[We1\2sin(θ/2)], leading to (Dm - Dm0)/Dm0 âˆ We*/[We1\2sin(θ/2)], where θ is the contact angle, and Dm0 and Dm are the maximum diameter of the droplet on stationary and vibratory surfaces, respectively. The scaling number illustrates the relative importance of vibration-induced dynamic pressure compared to inertial force and surface tension. Together with other well-established non-dimensional numbers, this scaling number provides a new dimension and framework for understanding and controlling droplet dynamics. Our findings can also find applications such as improving the power generation efficiency, intensifying the deposition of paint, and enhancing the heat transfer of droplets.

6.
Natl Sci Rev ; 8(5): nwaa153, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-34691630

RESUMO

Superhydrophobic surfaces are widely used in many industrial settings, and mainly consist of rough solid protrusions that entrap air to minimize the liquid/solid area. The stability of the superhydrophobic state favors relatively small spacing between protrusions. However, this in turn increases the lateral adhesion force that retards the mobility of drops. Here we propose a novel approach that optimizes both properties simultaneously. Inspired by the hydrophobic leaves of Salvinia molesta and the slippery Nepenthes pitcher plants, we designed a Salvinia-like slippery surface (SSS) consisting of protrusions with slippery heads. We demonstrate that compared to a control surface, the SSS exhibits increased stability against pressure and impact, and enhanced lateral mobility of water drops as well as reduced hydrodynamic drag. We also systematically investigate the wetting dynamics on the SSS. With its easy fabrication and enhanced performance, we envision that SSS will be useful in a variety of fields in industry.

7.
Mater Horiz ; 8(12): 3409-3416, 2021 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-34697619

RESUMO

Hydrogels have emerged as a landmark soft material for a wide range of applications such as in biomedical devices, soft robotics, artificial electronic skins, and the Internet of Things (IoT). To date, engineering hydrogels that simultaneously possess high stretchability (>3000%) and strong on-skin adhesion (>30 kPa) has not been an easy task. Generally, good stretchability is mainly dominated by the bulk interactions of hydrogels, whereas robust adhesion relies on the interfacial interactions of hydrogels with their surroundings. Here, we report a facile strategy to engineer an ultra-stretchable, highly adhesive and self-healable hydrogel, by virtue of tannic-acid-enabled dynamic interactions (TEDI) to fully substitute conventional covalent crosslinking. The TEDI strategy allows us to synchronously regulate both bulk and interfacial interactions to obtain exciting properties that outperform conventional hydrogels, including an extraordinary stretchability of over 7300%, remarkable self-healing abilities, and a robust on-skin adhesion of 50 kPa. With these intriguing merits, TEDI hydrogels are demonstrated to be a wearable strain sensor that accurately detect the motion of the human body. Moreover, our TEDI strategy unlocks new opportunities to design next-generation ionic hydrogels that may be valuable for applications in wearable electronic devices and healthcare monitoring.

8.
ACS Appl Mater Interfaces ; 13(42): 50451-50460, 2021 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-34652895

RESUMO

Pressure-sensitive adhesives (PSAs) are extensively used in diverse applications such as semiconductor manufacturing, labeling, and healthcare because of their quick and viscoelasticity-driven physical adhesion to dry surfaces. However, most of the existing PSAs normally fail to maintain or even establish adhesion under harsh conditions, particularly underwater, due to the lack of robust chemical functionalities for chemistry-based adhesion. Meanwhile, these PSAs are incapable of altering the adhesion in response to external stimuli, limiting their employment in applications requiring dynamic adhesion. Here, we develop a chemically functionalized PSA (f-PSA) with enhanced and phototunable underwater adhesion by incorporating an underwater adhesion enhancer (i.e., mussel-inspired catechol) and a photoresponsive functionality (i.e., anthracene) into a standard acrylic PSA matrix. The synergistic coupling of viscoelasticity-driven physical adhesion originating from the matrix with catechol-enabled chemical adhesion secures sufficient interfacial molecular interactions and leads to enhanced underwater adhesion. The efficient dimerization of anthracene via light-triggered cycloaddition facilely mediates the viscoelastic property of f-PSA, rendering the phototunable adhesion. We envision that this f-PSA can open up more opportunities for applications such as underwater manipulation, transfer printing, and medical adhesives.

9.
Adv Mater ; 33(44): e2104290, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34510586

RESUMO

Laser-induced graphene (LIG) has emerged as a promising and versatile method for high-throughput graphene patterning; however, its full potential in creating complex structures and devices for practical applications is yet to be explored. In this study, an in-situ growing LIG process that enables to pattern superhydrophobic fluorine-doped graphene on fluorinated ethylene propylene (FEP)-coated polyimide (PI) is demonstrated. This method leverages on distinct spectral responses of FEP and PI during laser excitation to generate the environment preferentially for LIG formation, eliminating the need for multistep processes and specific atmospheres. The structured and water-repellant structures rendered by the spectral-tuned interfacial LIG process are suitable as the electrode for the construction of a flexible droplet-based electricity generator (DEG), which exhibits high power conversion efficiency, generating a peak power density of 47.5 W m-2 from the impact of a water droplet 105 µL from a height of 25 cm. Importantly, the device exhibits superior cyclability and operational stability under high humidity and various pH conditions. The facile process developed can be extended to realize various functional devices.

10.
Microsyst Nanoeng ; 7: 49, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34567762

RESUMO

Electric energy generation from falling droplets has seen a hundred-fold rise in efficiency over the past few years. However, even these newest devices can only extract a small portion of the droplet energy. In this paper, we theoretically investigate the contributions of hydrodynamic and electric losses in limiting the efficiency of droplet electricity generators (DEG). We restrict our analysis to cases where the droplet contacts the electrode at maximum spread, which was observed to maximize the DEG efficiency. Herein, the electro-mechanical energy conversion occurs during the recoil that immediately follows droplet impact. We then identify three limits on existing droplet electric generators: (i) the impingement velocity is limited in order to maintain the droplet integrity; (ii) much of droplet mechanical energy is squandered in overcoming viscous shear force with the substrate; (iii) insufficient electrical charge of the substrate. Of all these effects, we found that up to 83% of the total energy available was lost by viscous dissipation during spreading. Minimizing this loss by using cascaded DEG devices to reduce the droplet kinetic energy may increase future devices efficiency beyond 10%.

11.
Langmuir ; 37(40): 11931-11938, 2021 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-34570495

RESUMO

Frost accretion occurs ubiquitously in various industrial applications and causes tremendous energy and economic loss, as manifested by the Texas power crisis that impacted millions of people over a vast area in 2021. To date, extensive efforts have been made on frost removal by micro-engineering surfaces with superhydrophobicity or lubricity. On such surfaces, air or oil cushions are introduced to suspend the frost layer and promote the rapid frost sliding off, which, although promising, faces the instability of the cushions under extreme frosting conditions. Most existing hydrophilic surfaces, characterized by large interfacial adhesion, have long been deemed unfavorable for frost shedding. Here, we demonstrated that a hydrophilic and slippery surface can achieve efficient defrosting. On such a surface, the hydrophilicity gave rise to a highly interconnected basal frost layer that boosted the substrate-to-frost heat transfer; then, the resulting melted frost readily slid off the surface due to the superb slipperiness. Notably, on our surface, the retained meltwater coverage after frost sliding off was only 2%. In comparison to two control surfaces, for example, surfaces lacking either hydrophilicity or slipperiness, the defrosting efficiency was 13 and 19 times higher and the energy consumption was 2.3 and 6.2 times lower, respectively. Our study highlights the use of a hydrophilic surface for the pronounced defrosting in a broad range of industrial applications.

12.
Nat Commun ; 12(1): 5470, 2021 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-34526498

RESUMO

Converting various types of ambient mechanical energy into electricity, triboelectric nanogenerator (TENG) has attracted worldwide attention. Despite its ability to reach high open-circuit voltage up to thousands of volts, the power output of TENG is usually meager due to the high output impedance and low charge transfer. Here, leveraging the opposite-charge-enhancement effect and the transistor-like device design, we circumvent these limitations and develop a TENG that is capable of delivering instantaneous power density over 10 MW/m2 at a low frequency of ~ 1 Hz, far beyond that of the previous reports. With such high-power output, 180 W commercial lamps can be lighted by a TENG device. A vehicle bulb containing LEDs rated 30 W is also wirelessly powered and able to illuminate objects further than 0.9 meters away. Our results not only set a record of the high-power output of TENG but also pave the avenues for using TENG to power the broad practical electrical appliances.

13.
Science ; 373(6561): 1344-1348, 2021 09 17.
Artigo em Inglês | MEDLINE | ID: mdl-34529472

RESUMO

[Figure: see text].

14.
iScience ; 24(7): 102789, 2021 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-34278275

RESUMO

The properties of mechanical metamaterials such as strength and energy absorption are often "locked" upon being manufactured. While there have been attempts to achieve tunable mechanical properties, state-of-the-art approaches still cannot achieve high strength/energy absorption with versatile tunability simultaneously. Herein, we fabricate for the first time, 3D architected organohydrogels with specific energy absorption that is readily tunable in an unprecedented range up to 5 × 103 (from 0.0035 to 18.5 J g-1) by leveraging on the energy dissipation induced by the synergistic combination of hydrogen bonding and metal coordination. The 3D architected organohydrogels also possess anti-freezing and non-drying properties facilitated by the hydrogen bonding between ethylene glycol and water. In a broader perspective, this work demonstrates a new type of architected metamaterials with the ability to produce a large range of mechanical properties using only a single material system, pushing forward the applications of mechanical metamaterials to broader possibilities.

15.
Nano Lett ; 21(17): 7411-7418, 2021 09 08.
Artigo em Inglês | MEDLINE | ID: mdl-34176267

RESUMO

Water collection by dew condensation emerges as a sustainable solution to water scarcity. However, the transient condensation process that involves droplet nucleation, growth, and transport imposes conflicting requirements on surface properties. It is challenging to satisfy all benefits for different condensation stages simultaneously. By mimicking the structures and functions of moss Rhacocarpus, here, we report the attainment of dropwise condensation for efficient water collection even on a hydrophilic surface gated by a liquid suction mechanism. The Rhacocarpus-inspired porous surface (RIPS), which possesses a three-level wettability gradient, facilitates a rapid, directional, and persistent droplet suction. Such suction condensation enables a low nucleation barrier, frequent surface refreshing, and well-defined maximum droplet shedding radius simultaneously. Thus, a maximum ∼160% enhancement in water collection performance compared to the hydrophobic surface is achieved. Our work provides new insights and a design route for developing engineered materials for a wide range of water-harvesting and phase-change heat-transfer applications.


Assuntos
Água , Interações Hidrofóbicas e Hidrofílicas , Sucção , Propriedades de Superfície , Molhabilidade
16.
Phys Rev Lett ; 126(23): 234503, 2021 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-34170170

RESUMO

While the drop impact dynamics on stationary surfaces has been widely studied, the way a drop impacts a moving solid is by far less known. Here, we report the physical mechanisms of water drops impacting on superhydrophobic surfaces with horizontal motions. We find that a viscous force is created due to the entrainment of a thin air layer between the liquid and solid interfaces, which competes with the capillary and inertia forces, leading to an asymmetric elongation of the drop and an unexpected contact time reduction. Our experimental and theoretical results uncover consolidated scaling relations: the maximum spreading diameter is controlled by both the Weber and capillary numbers D_{max}/D_{0}∼We^{1/4}Ca^{1/6}, while the dimensionless contact time depends on the capillary number τ/τ_{0}∼Ca^{-1/6}. These findings strengthen our fundamental understandings of interactions between drops and moving solids and open up new opportunities for controlling the preferred water repellency through largely unexplored active approaches.

17.
Micromachines (Basel) ; 12(6)2021 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-34074051

RESUMO

Millions of years' evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems.

18.
ACS Appl Mater Interfaces ; 13(20): 24321-24328, 2021 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-33998790

RESUMO

The rapid detachment of liquid droplets from engineered surfaces in the form of complete rebound, pancake bouncing, or trampolining has been extensively studied over the past decade and is of practical importance in many industrial processes such as self-cleaning, anti-icing, energy conversion, and so on. The spontaneous trampolining of droplets needs an additional low-pressure environment and the manifestation of pancake bouncing on superhydrophobic surfaces requires meticulous control of macrotextures and impacting velocity. In this work, we report that the rapid pancake-like levitation of impinging droplets can be achieved on superhydrophilic surfaces through the application of heating. In particular, we discovered explosive pancake bouncing on hot superhydrophilic surfaces made of hierarchically non-interconnected honeycombs, which is in striking contrast to the partial levitation of droplets on the surface consisting of interconnected microposts. This enhanced droplet bouncing phenomenon, characterized by a significant reduction in contact time and increase in the bouncing height, is ascribed to the production and spatial confinement of pressurized vapor in non-interconnected structures. The manifestation of pancake bouncing on the superhydrophilic surface rendered by a bottom-to-up boiling process may find promising applications such as the removal of trapped solid particles.

19.
Chem Sci ; 12(17): 6136-6142, 2021 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-33996010

RESUMO

There has been great interest in the fabrication of solid surfaces with desirable under-liquid wettability, and especially under-liquid dual-lyophobicity, because of their potential for widespread use. However, there remains the lack of a general principle to modulate the under-liquid wettability in terms of surface energy (SE). Herein, we found that the relative proportion between the polar and dispersive components in SE that reflects the competition between hydrophilicity and lipophilicity governs the under-liquid wettability of the solid surface. For the first time, we introduced hydrophilic-lipophilic balance (HLB) calculated solely based on the amount and type of hydrophilic and lipophilic fragments in surface molecules to rapidly predict the under-liquid wettability of a solid surface, thereby guiding the fabrication of solid surfaces with desirable under-liquid wettability. Accordingly, the under-liquid dual superlyophobic surfaces in a nonpolar oil-water-solid system were fabricated by grafting molecules with appropriate HLB values (e.g., 6.341-7.673 in a cyclohexane-water-solid system) onto porous nanofibrous membranes, which were able to achieve continuous separation of oil-water mixtures. This work provides reasonable guidance for the fabrication of solid surfaces with targeted under-liquid wettability, which may lead to advanced applications in oil-water-solid systems.

20.
ACS Nano ; 15(6): 10076-10083, 2021 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-34014070

RESUMO

Daytime passive radiative cooling is a promising electricity-free pathway for cooling terrestrial buildings. Current research interest in this cooling strategy mainly lies in tailoring the optical spectra of materials for strong thermal emission and high solar reflection. However, environmental heat gain poses a crucial challenge to building cooling at subambient temperatures. Herein, we devise a scalable thermal insulating cooler (TIC) consisting of hierarchically hollow microfibers as the building envelope that simultaneously achieves passive daytime radiative cooling and thermal insulation to reduce environmental heat gain. The TIC demonstrates efficient solar reflection (94%) and long-wave infrared emission (94%), yielding a temperature drop of about 9 °C under sunlight of 900 W/m2. Notably, the thermal conductivity of the TIC is lower than that of air, thus preventing heat flow from external environments to indoor space in the summer, an additional benefit that does not sacrifice the radiative cooling performance. A building energy simulation shows that 48.5% of cooling energy could be saved if the TIC is widely deployed in China.

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