Dear Sir,

there exist some chemicals known as water-structure-breaking and water-structure-forming compounds. So, I think here the glycerine is breaking the structure of water by making new hydrogen bonds and more free volume. Regards

Blair - surface tension of glycerin is about 60 versus water about 70mNm-1 - are you sure that effect is huge :-)?

Light emission during SL does not have a straight answer. Rather, it is determined by a combination of physical and chemical factors: ultimately, the final temperature during the collapse is the most important factor (higher temp -> more light), and this is determined by both physical and chemical processes. The type of molecules emitting the light is also a factor because this determines the spectrum. Therefore, when we speak of light emission we have to specify the spectral range: is it visual (400-700nm) or does it include UV down to the limit of most liquids ~180nm. In the case of water, light intensity increases toward the UV down to 180 nm.

The factors determining the maximum temperature are mainly the ratio of Cp/Cv and the thermal conductivity of the bubble contents.  Furthermore, the bubble contents are determined by both the dissolved gas (in the liquid) and the liquid being used (both liquid vapor diffuses and nanodroplets of liquid are thrown into the bubble due to surface instabilities during the collapse), as well as the products of the gas and liquid molecules resulting from their breakup due to high temperatures in the bubble (e.g, H and OH in the case of water, H2O and SO3 in the case of H2SO4, and H2, C2H2, CH4, C2H4, etc. in the case of alkanes, H2O, CH2O, CH3OH in the case of glycerine)

How much of the products remain in the bubble interior depends on the solubility of the products, so this is also an important factor.

In the case of dissolved gases (H2, and noble gases), the heavier the better for light emission because of the low thermal conductivity leading to high temp during collapse.  H2 is particularly bad because of high thermal conductivity and its dissociation is endothermic. Argon is a good compromise between cost and utility, but Xe is best.

Viscosity also seems to help due to its role in suppressing surface instabilities, therefore allowing bubble to be driven harder (higher amplitude sound fields).

In the case of glycerin, which is only a little better than water (and a low emitter compared to H2SO4 and other low-vapor-pressure liquids), the low vapor pressure helps keep glycerine out of the interior and the reaction products are less of a problem because they’ll be less H2 (due to the oxygens in glycerine) and more H2O, CH2O, CH3OH, etc., which are very soluble in glycerine.

I agree with Alan that surface tension is a minor factor, unless we are talking about liquid metals where surface tension could be as high as 3x-5x vs water. But, unfortunately, liquid metals are not transparent.

I hope this helps.