The effect of amino acids on bubble coalescence in aqueous solution

Many salts reduce the size of bubbles and inhibit bubble coalescence. The phenomenon occurs above the same concentration for some ion pairs (0.17 M for 1:1 salts). For other ion pairs no such effect occurs. The phenomenon remains inexplicable by standard theories of colloid science. It occurs for a range of sugar isomers and not for others. Again, why this occurs is not known. The present work extends the effect to a wider range of solutes. Amino acids were found to inhibit bubble coalescence and reduce the size of bubbles. The effect is the same as that for inorganic salts but it is dramatically more efficient. A series of amino acids: DL-Alanine, L-Arginine, L-Leucine, DL-Methionine and L-Tyrosine was studied using a bubble column evaporator (BCE). The amino acid solutions were prepared at different concentrations and beyond their solubility limits. This remarkable effect also provides new hints into how bubble interactions affect crystallisation.