Comment on “Discussion on a mechanical equilibrium condition of a sessile drop on a smooth solid surface” [J. Chem. Phys. 130, 144106 (2009)]

2011 ◽  
Vol 134 (24) ◽  
pp. 247101
Author(s):  
H. Ghasemi ◽  
C. A. Ward
Keyword(s):  
Solid Surface ◽  
Equilibrium Condition ◽  
Sessile Drop ◽  
Chem Phys ◽  
Mechanical Equilibrium

Non-isolated drop impact on surfaces

2017 ◽  
Vol 835 ◽  
pp. 24-44 ◽  
Author(s):  
Y. Wang ◽  
L. Bourouiba
Keyword(s):  
Momentum Transfer ◽  
Impact Velocity ◽  
Solid Surface ◽  
Weber Number ◽  
Sessile Drop ◽  
Impact Force ◽  
New Paradigm ◽  
Existence Conditions ◽  
Secondary Droplets ◽  
Sessile Drops

Upon impact on a solid surface, a drop expands into a sheet, a corona, which can rebound, stick or splash and fragment into secondary droplets. Previously, focus has been placed on impacts of single drops on surfaces to understand their splash, rebound or spreading. This is important for spraying, printing, and environmental and health processes such as contamination by pathogen-bearing droplets. However, sessile drops are ubiquitous on most surfaces and their interaction with the impacting drop is largely unknown. We report on the regimes of interactions between an impacting drop and a sessile drop. Combining experiments and theory, we derive the existence conditions for the four regimes of drop–drop interaction identified, and report that a subtle combination of geometry and momentum transfer determines a critical impact force governing their physics. Crescent-moon fragmentation is most efficient at producing and projecting secondary droplets, even when the impacting drop Weber number would not allow for splash to occur on the surface considered if the drop were isolated. We introduce a critical horizontal impact Weber number $We_{c}$ that governs the formation of a sheet from the sessile drop upon collision with the expanding corona of the impacting drop. We also predict and validate important properties of the crescent-moon fragmentation: the extension of its sheet base and the ligaments surrounding its base. Finally, our results suggest a new paradigm: impacts on most surfaces can make a splash of a new kind – a crescent-moon – for any impact velocity when neighbouring sessile drops are present.

scholarly journals A new equation for period vectors of crystals under external stress and temperature in statistical physics: mechanical equilibrium condition and equation of state

2021 ◽  
Vol 136 (1) ◽  
Author(s):  
Gang Liu
Keyword(s):  
Equation Of State ◽  
Equilibrium Condition ◽  
Statistical Physics ◽  
Structural Phase ◽  
External Pressure ◽  
External Stress ◽  
Mechanical Equilibrium ◽  
Dependent Form ◽  
New Equation ◽  
External Forces

AbstractStarting with the rigorous derivation of the work done on the center cell by external forces, a new equation is derived for the period vectors (cell edge vectors) in crystals under external stress and temperature. Since the equation is based on the principles of statistical physics, it applies to both classical and quantum systems. The existing theory for crystals under external pressure is covered as a special case. The new equation turns out to be the mechanical equilibrium condition and the equation of state for crystals under external stress and temperature. It may be used to predict crystal structures and to study structural phase transitions and crystal expansions. For linear elastic crystals, it takes the microscopic and temperature-dependent form of the generalized Hooke’s law, and may therefore be used to calculate the corresponding elastic constants. It should be helpful in studying piezoelectric and piezomagnetic materials, as the period vectors change with external stress. It is also consistent and can be combined with the previously derived corresponding one for Newtonian dynamics.

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