Sound induced gelation

  Sound induced gelation is described in 2005 ^[1] in an organopalladium compound that in solution transforms from a transparent liquid to an opaque gel upon application of a short burst (seconds) of ultrasound. Heating to above the so-called gelation temperature T_gel takes the gel back to the solution. The compound is a dinuclear palladium complex made from palladium acetate and a N,N'-Bis-salicylidene diamine. Both compounds react to form an anti conformer (gelling) and a syn conformer (non-gelling) which are separated by column chromatography. In the solution phase the dimer molecules are bent and self-locked by aromatic stacking interactions whereas in the gel phase the conformation is planar with interlocked aggregates. The anti conformer has planar chirality and both enantiomers were separated by chiral column chromatography. The (-) anti conformer has a specific rotation of -375° but is unable to gelate by itself. In the gel phase the dimer molecules form stacks of alternating (+) and (-) components. This process starts at the onset of the sonication and proceeds even without further sonication.

References

• ^  Molecules That Assemble by Sound: An Application to the Instant Gelation of Stable Organic Fluids Takeshi Naota and Hiroshi Koori J. Am. Chem. Soc., 127 (26), 9324 -9325, 2005 Abstract Online details