Droplet impact on solid surfaces is essential for natural and industrial processes. Particularly, controlling the instability after droplet impact, and avoiding the satellite drops generation, have ...aroused great interest for its significance in inkjet printing, pesticide spraying, and hydroelectric power collection. Herein, we found that breaking the symmetry of the droplet impact dynamics using patterned-wettability surfaces can suppress the Plateau-Rayleigh instability during the droplet rebounding and improve the energy collection efficiency. Systematic experimental investigation, together with mechanical modeling and numerical simulation, revealed that the asymmetric wettability patterns can regulate the internal liquid flow and reduce the vertical velocity gradient inside the droplet, thus suppressing the instability during droplet rebounding and eliminating the satellite drops. Accordingly, the droplet energy utilization was promoted, as demonstrated by the improved hydroelectric power generation efficiency by 36.5%. These findings deepen the understanding of the wettability-induced asymmetrical droplet dynamics during the liquid-solid interactions, and facilitate related applications such as hydroelectric power generation and materials transportation.
Mechanically driven light generation is an exciting and under‐exploited phenomenon with a variety of possible practical applications. However, the current driving mode of mechanoluminescence (ML) ...devices needs strong stimuli. Here, a flexible sensitive ML device via nanodopant elasticity modulus modification is introduced. Rigid ZnS:M2+(Mn/Cu)@Al2O3 microparticles are dispersed into soft poly(dimethylsiloxane) (PDMS) film and printed out to form flexible devices. For various flexible and sensitive scenes, SiO2 nanoparticles are adopted to adjust the elasticity modulus of the PDMS matrix. The doped nanoparticles can concentrate stress to ZnS:M2+(Mn/Cu)@Al2O3 microparticles and achieve intense ML under weak stimuli of the moving skin. The printed nano‐/microparticle‐doped matrix film can achieve skin‐driven ML, which can be adopted to present fetching augmented animations expressions. The printable ML film, amenable to large areas, low‐cost manufacturing, and mechanical softness will be versatile on stress visualization, luminescent sensors, and open definitely new functional skin with novel augmented animations expressions, the photonic skin.
A flexible, sensitive mechanoluminescence (ML) device is demonstrated via matrix elasticity modulus modification. Rigid ZnS:M2+(Mn/Cu)@Al2O3 microparticles are dispersed into soft poly(dimethylsiloxane) (PDMS) film and printed for preparing flexible devices. Via a SiO2‐nanoparticle dopant, the ML intensity for small strain is significantly increased. The ML devices achieve intense ML under the weak stimuli of moving skin, which will be significant for photonic‐skin devices.
Locusts have excellent jumping and kicking abilities to survive in nature, which are achieved through the energy storage and release processes occurring in cuticles, especially in the semi-lunar ...processes (SLP) at the femorotibial joints. As yet, however, the strain energy-storage mechanisms of the SLP cuticles remain unclear. To decode this mystery, we investigated the microstructure, material composition, and mechanical properties of the SLP cuticle and its remarkable strain energy-storage mechanisms for jumping and kicking. It is found that the SLP cuticle of adult Locusta migratoria manilensis consists of five main parts that exhibit different microstructural features, material compositions, mechanical properties, and biological functions in storing strain energy. The mechanical properties of these five components are all transversely isotropic and strongly depend on their water contents. Finite element simulations indicate that the two parts of the core region of the SLP cuticle likely make significant contributions to its outstanding strain energy-storage ability. This work deepens our understanding of the locomotion behaviors and superior energy-storage mechanisms of insects such as locusts and is helpful for the design and fabrication of strain energy-storage devices.
This review article summarizes the advances in the surface stress effect in mechanics of nanostructured elements, including nanoparticles, nanowires, nanobeams, and nanofilms, and heterogeneous ...materials containing nanoscale inhomogeneities. It begins with the fundamental formulations of surface mechanics of solids, including the definition of surface stress as a surface excess quantity, the surface constitutive relations, and the surface equilibrium equations. Then, it depicts some theoretical and experimental studies of the mechanical properties of nanostructured elements, as well as the static and dynamic behaviour of cantilever sensors caused by the surface stress which is influenced by adsorption. Afterwards, the article gives a summary of the analytical elasto-static and dynamic solutions of a single as well as multiple inhomogeneities embedded in a matrix with the interface stress prevailing. The effect of surface elasticity on the diffraction of elastic waves is elucidated. Due to the difficulties in the analytical solution of inhomogeneities of complex shapes and configurations, finite element approaches have been developed for heterogeneous materials with the surface stress. Surface stress and surface energy are inherently related to crack propagation and the stress field in the vicinity of crack tips. The solutions of crack problems taking into account surface stress effects are also included. Predicting the effective elastic and plastic responses of heterogeneous materials while taking into account surface and interface stresses has received much attention. The advances in this topic are inevitably delineated. Mechanics of rough surfaces appears to deserve special attention due to its theoretical and practical implications. Some most recent work is reviewed. Finally, some challenges are pointed out. They include the characterization of surfaces and interfaces of real nanomaterials, experimental measurements and verification of mechanical parameters of complex surfaces, and the effects of the physical and chemical processes on the surface properties, etc.
Solvent-free nanofluids hold promise for many technologically significant applications. The liquid-like behavior, a typical rheological property of solvent-free nanofluids, has aroused considerable ...interests. However, there has been still lack of efficient methods to predict and control the liquid-like behavior of solvent-free nanofluids. In this paper, we propose a semi-discrete dynamic system with stochastic excitation describing the temperature change effects on the rheological property of multiwall carbon nanotubes (MWCNTs) modified by grafting sulfonic acid terminated organosilanes as corona and tertiary amine as canopy, which is a typical covalent-type solvent-free nanofluid system. The vibration of the grafting branches is simulated by employing a structure-preserving approach, and the shear force of grafting branches at the fixed end is computed subsequently. By taking the shear forces as an excitation acting on the MWCNTs, the axial motion of the MWCNTs is solved with the 7-point Gauss-Kronrod quadrature rule. The critical temperature associated with the appearance of the liquid-like behavior as well as the upper bound of the moving speed of the modified MWCNTs is determined, which can be used to predict and control the liquid-like behavior of the modified MWCNTs in engineering applications.
Surface effects often play a significant role in the mechanical properties of soft materials such as hydrogels and biological tissues. In this paper, we investigate the plane-strain indentation of a ...soft elastic layer bonded to a rigid substrate. The surface effects on the indentation behavior of the elastic layer-substrate system are theoretically analyzed. Indentation tests using indenters with different elliptical shapes are compared. Analytical expressions are derived for the indentation force-displacement relation using the Kerr model with the effect of surface tension. The theoretical solution is verified by finite element simulations. The dependence of surface effects on the ratio of the indenter’s major and minor elliptical axes is also examined. This work helps understand the size effects on the indentation behaviors of soft materials and guides the design of corresponding measurement tests.
Precise separation and localization of microdroplets are fundamental for various fields, such as high‐throughput screening, combinatorial chemistry, and the recognition of complex analytes. We have ...developed a droplet self‐splitting strategy to divide an impacting droplet into predictable microdroplets and deposit them at preset spots for simultaneous multidetection. No matter exchange was observed between these microdroplets, so they could be manipulated independently. Droplet self‐splitting was attributed to anisotropic liquid recoiling on the patterned adhesive surface, as influenced by the droplet Weber number and the width of the low‐adhesive stripe. A quantitative criterion was also developed to judge the droplet self‐splitting capability. The precise separation and distribution of microdroplets enabled simultaneous arrayed reactions and multiple analyte detection using one droplet of sample.
Dropping into place: A droplet self‐splitting strategy was developed to divide a droplet into microdroplets and deposit them in a well‐defined array. Matter exchange between the generated microdroplets was fully prohibited in the self‐splitting process, thus enabling simultaneous arrayed reactions (see picture) and the detection of multiple analytes using only one droplet of sample.
In this paper, a phenomenological continuum theory of surface piezoelectricity accounting for the linear superficial interplay between electricity and elasticity is formulated primarily for elastic ...dielectric materials. This theory is inspired by the physical idea that once completely relaxed, an insulating free dielectric surface will sustain a nontrivial spontaneous surface polarization in the normal direction together with a tangential self-equilibrated residual surface stress field. Under external loadings, the surface Helmholtz free energy density is identified as the characteristic function of such surfaces, with the in-plane strain tensor of surface and the surface free charge density as the independent state variables. New boundary conditions governing the surface piezoelec- tricity are derived through the variational method. The resulting concepts of charge-dependent surface stress and deformation- dependent surface electric field reflect the linear electromechanical coupling behavior of nanodielectric surfaces. As an illustrative example, an infinite radially polarizable piezoelectric nanotube with both inner and outer surfaces grounded is investigated. The novel phenomenon of possible surface-induced polarity inversion is predicted for thin enough nanotubes.
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