Q2. What is the effect of the interface on the separation distance?
Note also that for the smallest values of D/R the influence of the interface becomes very weak, so that values given by Eqs. [9] and [10] are very close (straight lines are observed).
Q3. What is the effect of viscosity on the rupture distance of a bridge?
In the case of a viscous binder bridging moving particles (during powder granulation processes, for example) dynamic adhesion forces developed by the bridges can be several times higher than their static counterparts (12) and the rupture distance of the bridge can be significantly increased with the liquid viscosity (13).
Q4. What is the way to maintain the spheres at a different temperature?
A small thermostated chamber can be used to maintain locally the spheres at a temperature significantly different from the ambient temperature.
Q5. How many mm of separation gap was chosen?
The volume of liquid was chosen small enough (V = 0.5 µl) for the corresponding rupture distance to be smaller than the maximum separation gap (1 mm) for all separation velocities.
Q6. What can be suspected of a viscous bridge?
Squeezing of the liquid inside the gap and associated viscous (dynamic) effects arising from the measurement procedure can also be suspected (29).
Q7. What is the upper part of the apparatus?
The upper one is bolted under the platten of a counter-reaction scale (Sartorius MDRA200), which allows measurement of the vertical force applied to the sphere without displacement of it.
Q8. What is the order of magnitude of the Reynolds number?
Note that, in this experiment, whatever the separation distance and the spheres velocity, the order of magnitude of the Reynolds number is Re ≈ wb2v/ηD ¿ 1 where w is the volumic mass of the liquid.
Q9. How is the pressure of a liquid a function of height?
The mechanics of thin liquid films are described by the wellknown Reynolds equation, which relates the pressure P generated in the liquid to the relative displacement of the two solid surfaces (23):ddr[ r H 3(r ) dP(r )dr] = 12ηr dDdt . [8]
Q10. What is the simplest way to evaluate the attractive force of a liquid bridge?
This toroı̈dal approximation for the meniscus shape leads to an interface of nonconstant mean curvature, so that the resulting attractive force is not constant along the z axis and there are several ways of evaluating FCap.
Q11. How much is the rupture distance of the sphere?
The results clearly indicate that the rupture distance increases as the sphere velocity increases: for v = 10 µm/s, Ddrupt is 20% larger than the corresponding DSrupt.
Q12. How can the authors measure the volume of the spheres?
Images of the contact region before and after the formation of the meniscus and some image processing allow the determination of the bridge volume with a precision of about 5%.