Silver and mercury ions are reduced in a common solution by sodium borohydride in the presence of poly(ethyleneimine). Colloidal alloy particles are formed, whose plasmon absorption band is blue-shifted with increasing mercury-to-silver ratio. The reduction mechanism is rather complex: large mercury "drops" are first formed, although silver ions are reduced simultaneously. This effect is explained by an interaction of the two metal redox systems, as silver clusters are reoxidized by mercury ions. The final particles are formed in a reaction of the mercury drops with reduced silver clusters, yielding amalgam particles smaller than the mercury drops. These processes are followed by spectrophotometric and light-scattering measurements. The alloy colloids are stable up to a mercury to silver molar ratio of 2. Upon exposure to air, part of the mercury in the alloy particles is oxidized.

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Freeze fracture-electron microscopy (FF-EM) was used to study the structure of the colloidal components present in Definity w and to determine changes that occur when the pharmaceutical is "activated" by shaking -a process by which the hydrophobic gas present in the headspace of the vial is incorporated into micro-bubbles.Photomicrographs of the initial pharmaceutical show the presence of small colloidal structures which are also present after the formulation is shaken. While the product initially contains mainly small and some large gas bubbles, they mostly disappear upon shaking to be replaced by larger, more regular micro-bubbles. This more regular distribution of larger micro-bubbles is responsible for the functioning of the product as an ultrasonic contrast enhancement agent.The structure of the gas-liquid interface is found to consist of a mixed phospholipid monolayer and not the previously hypothesized ordered interfacial liposome assembly.