What is the capillary length of ethanol/water mixture ( ethanol 96%)?
The capillary length of a liquid (including homogeneous mixtures) is = square root[(surface tension/density.gravity acceleration g).
The surface tension of an (water/ethanol) mixture at ~96% EtOH (I precise in vol.!) is ~23.10^(-3) N/m at 20-25°C which is very close (quite identical) to that of pure EtOH at the same temperature (~22.7x10^(-3) N/m). In the same way, the density of the 96%EtOH/water mixture has quite the same density as “pure” EtOH (~800 kg/m^3). Putting the gravitational acceleration g=9.8 m/s^2 with the surface tension and density values of the mixture in the equation above gives you the sought value of the capillary length (keeping in mind that a N = kg.m/s^2). Overall, this should give you a capillary length of about 1.73 mm if correctely calculated.
One useful attribute of the capillary length scale is to make a judgement whether gravitational effects need to be considered in estimating/computing the shape of menisci. This is usually done in terms of the Bond number which is a ratio of the characteristic length scale for the physical system L and the capillary length scale L_c all squared; Bo=(L/L_c)^2, where L_c=gamma/(rho g), as noted by Hamido.
For example, if the characteristic length scale of a sessile drop is much less than L_c, (Bo
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