Evaporation Kinetics and Breaking of a Thin Water Liquid Bridge between Two Plates of Silicon Wafer

Abstract

In ceramic processing, the study of the different phases of the drying stage considers the material at a macroscopic scale. Very often, the various parameters (among which the temperature and the relative humidity) are chosen in an empirical way, mostly through visual observations. This stage is governed by capillary phenomena which take place within the material, responsible for both the shrinkage and the risk of cracks which can damage the final piece. As part of a better understanding of the local mechanisms during drying, liquids contained in the pores have been reproduced in an ideal case. Drying kinetics and parameter measurements from 303 to 343 K of deionized water liquid bridges between two plates of silicon wafers are presented. Experimental work was carried out using specific device to create liquid bridges, coupled with image analysis and within an adapted instrumented climatic chamber. While the volume and the exchange surface of liquid bridges decrease regularly throughout the drying process, contact angles only diminish at the end. One of the four contact angles may have a different variation, which results in a pinned contact line in its area and reveals a local change of the surface state. From these measurements and observations, the liquid bridge break is proposed as a cracking criterion of porous materials during drying. Indeed, the challenge is to limit the risk of cracking and damaging pieces during this crucial step in material processing.

Study of the Contact and the Evaporation Kinetics of a Thin Water Liquid Bridge between Two Hydrophobic Plates

“…We encourage the interested reader to find more details about the specific device used in this study in our previous work [11].…”

“…These measurements consist in a three steps procedure. First, liquid bridges with an initial volume of 4.0 μL ± 0.1 μL were produced and observed during drying (varying the initial volume is investigated in our previous work in the case of hydrophilic contacts [11]). The dimensions are given in Figure 5…”

“…The initial inserted volume to create the liquid bridge was 4 μL. From these conditions, liquid bridges were evaporated, at temperatures from 303 K to 343 K and at a fixed relative humidity of 55 % (variations of relative humidity were previously discussed in a recent study [11]). The results are given in Figure 9.…”

Extending Lifetime of Water Droplets Using Mirror‐Nanoporous Surfaces

“…The linear m versus t relationship, meaning a constant evaporation rate, has also been observed in previous experiments carried out under conditions similar to the setup reported here, though addressed to investigate liquid bridge instabilities and the capillary force between surfaces. [24][25][26] Of course, our straightforward model is expected to depart from experimental data when the thinned liquid bridge finally breaks up, and hence Equation 4should not be extrapolated to the final period of drop evaporation. Still, the slope of the curve on the first stages of evaporation appropriately represents the kinetics, and it will be the object of analysis hereafter.…”

“…This argument is also supported by a previous experimental investigation that measured the evaporation rate of droplets squeezed between parallel plates under different RH conditions. [25] These authors found that, for a 4 mL droplet placed between (noncoated) silicon wafers with a gap of 0.5 mm, the evaporation time was duplicated, whereas RH ambient condition was increased from 35% to 75%. It is worth to remember that, in our experiments with N-W surfaces, the RH increase is not externally controlled but self-generated around the peripheries of the squeezed drop.…”