Both electron and phonon transport properties of single layer MoS₂ (SLMoS₂) are studied. Based on first-principles calculations, the electrical conductivity of SLMoS₂ is calculated by Boltzmann equations. The thermal conductivity of SLMoS₂ is calculated to be as high as 116.8 Wm⁻¹K⁻¹ by equilibrium molecular dynamics simulations. The predicted value of ZT is as high as 0.11 at 500 K. As the thermal conductivity could be reduced largely by phonon engineering, there should be a high possibility to enhance ZT in the SLMoS₂-based materials.

Inkjet technology is a commendable tool in many applications including graphics printing, bioengineering and micro-electromechanical systems (MEMS). Droplet stability is a key factor influencing inkjet performance. The stability can be analysed using dimensionless numbers that usually combine thermophysical properties and system dimensions. In this paper, a drop-on-demand (DOD) inkjet experimental system is established. A numerical model is developed to investigate the influence of the operating conditions on droplet stability, including nozzle dimensions, driving parameters (the pulse amplitude and width used to drive droplet formation) and fluid properties. The results indicate that the stability can be improved by decreasing the pulse amplitude and width, decreasing the fluid density and viscosity or increasing the nozzle diameter and fluid surface tension. Based on case analysis and modelling, a dimensionless number ( $Z$ ), the reciprocal of the Ohnesorge number, is numerically determined for a stable droplet to lie in a range between 4 and 8. To explicitly combine the driving parameters, a new stability criterion, $Pj$ , is further proposed. A general rule taking into account both $Pj$ and $Z$ is proposed for choosing appropriate driving parameters to eject stable droplets for a known nozzle and fluid, which is further validated by experiments.

In the drop-on-demand (DOD) inkjet system, deformation process and the direct relations between the droplet motions and the liquid properties have been seldom investigated, although they are very critical for the printing accuracy. In this study, experiments and computational simulations regarding deformation of a single droplet driven by a piezoelectric nozzle have been conducted to address the deformation characteristics of droplets. It is found that the droplet deformation is influenced by the pressure wave propagation in the ink channel related to the driven parameters and reflected in the subsequent droplet motions. The deformation extent oscillates with a certain period of $T$ and a decreasing amplitude as the droplet moves downwards. The deformation extent is found strongly dependent on the capillary number ( $Ca$ ), first ascending and then descending as the number increases. The maximum value of the deformation extent is surprisingly found to be within range of 0.068–0.082 of the $Ca$ number regardless of other factors. Furthermore, the Rayleigh’s linear relation of the oscillation frequency of the droplet to the parameter, $\sqrt{\unicode[STIX]{x1D70E}/\unicode[STIX]{x1D70C}r^{3}}$ (where $\unicode[STIX]{x1D70E}$ is the surface tension coefficient, $\unicode[STIX]{x1D70C}$ is the density and $r$ is the droplet’s radius), is updated with a smaller slope shown both by experiment and simulation.

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.

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.

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.