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Depositing on the patterned substrate in chemical vapor deposition is one of the most effective approaches to produce low‐dislocation‐density films. Existing experiments indicate that dislocation bending is the main cause of decreasing dislocation. However, what drives dislocation segments (DSs) to bend remains unclear, and existing numerical methods do not explain the mechanism fully. In this study, a multiscale scheme based on molecular dynamics (MD) and kinetic Monte Carlo (KMC) is proposed to unravel the multiscale mechanism of DSs bending. In this scheme, MD is employed to identify the off‐lattice structure and to calculate the diffusion activation energies. KMC is used to perform the temporal evolution of the deposition process. In a proof‐of‐concept, the growth rate and the film morphology in silane deposition are predicted in the cross‐scale comparable to the experimental measurements. With the proposed multiscale scheme, the calculated activation energies show that the repeated lateral deposition and the obliquely upward deposition of the dislocated atoms contribute to DSs bending. Moreover, the sharp decrease of dislocation density is quantitatively elucidated by the scheme. The study provides fundamental insight into dislocation bending reduction during crystal thin film growth. [ABSTRACT FROM AUTHOR]

To better understand the coalescence of droplets, which play critical roles in diverse natural processes and industrial applications, we give attention to the non-Newtonian rheology of liquid drops—in particular, studying the coalescence of two non-Newtonian droplets on a solid surface, with special attention to the effect of the shear thinning behavior. Based on a theoretical power-law model, we show that the height h 0 of the liquid bridge connecting two adjacent droplets grows with a power function of time as h 0 ∼ t n , where n indicates the power-law exponent. Through numerical simulations, we reveal a self-similar regime during the initial stage of coalescence and propose an accurate prediction for capturing the spatial structure of the flow. Our results also update the effect of the contact angle, which significantly alters the coalescence dynamics. [ABSTRACT FROM AUTHOR]

Line formation control plays a critical role in inkjet printing stability for its high relevance to industrial processes. The present study describes experiments for depositing droplets of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solutions using high-speed imaging technology. The line printing dynamics and ink drops coalescence were analyzed. Two stability criteria are proposed for the stability of the printed line at low substrate speeds, including the continuity criterion derived from the volume conservation and the bulging instability determined by the ratio of the transported flow rate and the applied flow rate. Stable printed lines are bound by the two stability criteria and equipment limitation, represented in a parameter space bound by the normalized drop spacing, p * , and the normalized substrate speed, U T * . We then discuss the changes of the normalized critical substrate speed between the stable and bulging regions U T 1 * and between the stable and discontinuous regions U T 2 * under a fixed injection frequency. Finally, the reasons for the formation of different printed line shapes are demonstrated by observing the coalescence processes of an impacting droplet and a sessile printed line. The relationship between the location of the liquid bridge and the drop spacing is discussed for determining the line shapes. [ABSTRACT FROM AUTHOR]

The breakup process of a charged, leaky-dielectric jet subjected to an axial perturbation is computationally analysed from the perspectives of linear and nonlinear dynamics using the arbitrary Lagrangian–Eulerian technique. The linear dynamics of the leaky-dielectric jet is quantitatively predicted by the dispersion relation from the linear stability analysis. Regarding the nonlinear dynamics, it is found that the charge relaxation is responsible for the radial compression of satellite droplets, which is validated by experiments. Two types of charge relaxations, namely, ohmic conduction and surface charge convection, define the pinching process into three breakup modes, i.e. ligament pinching, end pinching and transition pinching. In the ligament-pinching mode, the ohmic conduction dominates the jet breakup since the charge relaxes to the jet ligament instantaneously. In contrast, the surface charge convection takes effect in the end-pinching mode since the surface charge is convected to the jet end via fluid flow. When the ohmic conduction is comparable to the surface charge convection, the breakup occurs simultaneously at the end and the ligament. Finally, the influences of the perturbed wavenumber, the electric field intensity and the viscosity on the breakup mode and the local dynamics at pinch-off are comprehensively discussed. [ABSTRACT FROM AUTHOR]

Printable organic electronics are attractive owing to its high throughput and easy fabrication. Traditional coating methods (such as inkjet printing) are liquid‐solid contact‐based that deposit liquid solutions onto solid surfaces. Film quality is limited by surface energy of target surfaces and surface tension of the solvents. Furthermore, these printing methods are challenging to directly fabricate films on non‐flat or curved surfaces owing to the fluidity of liquid solution drops. In this work, a water transfer printing method that is solid‐solid contact‐based and assisted by Van der Waals force is reported. Nanometer‐thick films can be deposited on various surfaces: both high‐ and low‐surface energy, both flat and non‐flat surfaces. Water plays two roles: 1) as the transfer medium substrate and providing weak adhesion force between water and the transferred film; 2) high surface tension of water providing room to create surface tension gradient and producing Marangoni force to unfold the crumpled nanometer‐thick films. Electronic and optoelectronics on wrinkled skin and curved surfaces are demonstrated with this water transfer printing method. [ABSTRACT FROM AUTHOR]

Droplets wetting and impacting on porous substrates play a critical role in various printing processes and industrial applications. However, due to the lack of effective observation inside the pores, the dynamic behavior of the droplet is rather unclear. Here, we used a numerical method to investigate the dynamic behavior of droplets spreading on confined porous substrates with different surface fractions. The wetting process has been divided into two stages: the inertial stage and the viscous stage. The numerical results show a power-law evolution of the contact diameter with time, and the exponent has a linear relationship with the surface wettability. The scaling laws proved to have no dependence on the porosity. The presence of confined pores causes the spreading slower and makes the droplet reach an equilibrium state more easily. Then, the impacting process was reported by changing the initial velocities of the droplets. It was found that penetration is always observed after spreading. The wetting transition was captured, and the dimensionless maximum spreading was scaled. Finally, the coalescence-induced droplet jumping has been verified on confined porous substrates with a superhydrophobicity, suggesting the potential of porous structures in designing specific droplet behaviors. [ABSTRACT FROM AUTHOR]

Despite their remarkable effect on printing accuracy and uniformity, charge migrations that dominate the deformation of ink droplets during electrohydrodynamic jet printing have not been widely investigated. In this work, the large deformation mechanisms of a conductive nanodroplet under a strong electric field are examined from the point of view of charge migrations. It is found that the charge migrations include the charge relaxation in the bulk of the droplet and surface charge convection at the fluid interface. A conductive nanodroplet first evolves into an ellipsoid through charge relaxation. Then, the ellipsoid is deformed by the convection of the surface charges in four modes, namely, tip streaming (mode 1), lobe formation (mode 2), finger stretching (mode 3), and dumbbell stretching (mode 4). Finally, the stretched nanodroplet is broken into secondary droplets. Modes 1, 2, and 4 are in agreement with the experimental observations. Furthermore, it is found that over 20% of the charges are distributed inside the bulk nanodroplet and the other charges are distributed at the surface, causing the four deformation modes. Analysis based on the electric Reynolds number (the ratio of electric field force to viscous force) and the Coulombic capillary number (the ratio of surface tension to Coulombic force) shows that the nanodroplet is prolate if the electric field force is dominant. When the Coulombic force plays a crucial role, the nanodroplet deforms into an ellipsoid with wide cones. By contrast, the nanodroplet will generate hemispherical ends if the deformation is dominated by the effect of surface tension. [ABSTRACT FROM AUTHOR]

Breakup of a nanodroplet is a common phenomenon of great importance in the nanoprinting and the electrohydrodynamic jet printing, which affects the accuracy and efficiency of droplet delivery. When the diameter of a decaying jet reduces to nanometers, the breakup mechanism remains unclear because the traditional continuum theory fails. In this work, a mesoscale method, many-body dissipative particle dynamics, has been developed to investigate the breakup process of water, glycerol, and ethanol nanodroplets. Generally, a falling nanodroplet deforms and breaks up with the following stages, symmetrical deformation, thin-neck appearance, and drop-tip motion. The breakup time, the neck length, the minimum diameter of the neck before breakup, and the tip velocity of the formed tail after breakup have been examined. It is found that the neck length shows an exponential relationship with the time. Compared to the similarity solution near the separation point, the exponent relation between the minimum diameter of the neck and the reduced time has been verified. Moreover, the exponent (n) for different fluids can be roughly estimated by the Ohnesorge (Oh) number as n = 0.1015 log(Oh) + 0.6776. The tip velocity varies as the inverse square root of the reduced time when the tip shrinks slowly. When the tip shrinks rapidly, the exponential relationship between the tip velocity and the reduced time is predicted, which is also valid for shrinking a satellite droplet. This study provides a fundamental understanding of the nanodroplet breakup for improvement of their dynamical behaviors in a real application. [ABSTRACT FROM AUTHOR]

• The spread of nanodroplets on solid surfaces has been numerically studied. • The maximum spreading of nanodroplets is analyzed by changing the viscosities. • The combined effect of wettability, surface fraction and viscosity is considered. • The pillared structures approve to enhance the wettability of the substrates. To deposit droplets on substrates efficiently is critical for many technological and industrial applications, which requires a systematic understanding of the droplet spreading process. In the paper, mesoscopic modeling of viscous nanodroplets spreading on different solid surfaces has been conducted by many-body dissipative particle dynamics. The influence of fluid viscosity has been particularly analyzed by changing the interaction parameters and the maximum droplet spreading diameter has been obtained. The dimensionless maximum spreading diameter is correlated to the Reynolds numbers (Re) and Weber numbers (We) as β max = 0.7 Re 0.1445 We 0.066. With the droplets partially attached by polymer chains to exhibit a shear-thinning non-Newtonian property, we demonstrate that the maximum spreading diameters are extremely different under a small initial kinetic energy, and gradually become consistent at a larger Weber number. Investigation of the spreading process on the intricate surfaces decorated by regular pillared structures shows a special expansion effect to improve the intrinsic wetting characteristic of the substrates, which is strongly controlled by the surface fraction of the pillared structures. Moreover, it is found that the fluid viscosity can profoundly affect the rebounding behavior of the droplet. [ABSTRACT FROM AUTHOR]