Gold Chloride

After conducting several experiments with palladium chloride, we found that it was not very water-soluble. This posed as a major setback since an aqueous solution is required for the experiment. Gold chloride was found to be very soluble and there was an abundance of literature on gold nanoparticle formation via sonochemistry. For these reasons, it was decided that we would use gold chloride solution instead of palladium chloride solution.

Coolant System

Experiments were conducted to determine the temperature change due to sonocation with and without temperature control. Although temperature control was preferred, it was found that the temperature increase without control was tolerable. Since a heat exchanger requires large amounts of extra equipment (including a water reservoir) and chemical cooling packs do not cool the system effectively, the importance of temperature control was investigated. Several pieces of literature stated that temperature seemed to have little effect on yield and size distribution of nanoparticles formed by sonocation. Therefor, temperature control was excluded from the final experimental setup.

PEG

Preliminary experiments showed that the gold nanoparticles formed during sonication aggregated over the course of several hours and came out of solution. We also noted that the absorbency of the nanoparticles actually increased over time. Since the particles were coming out of solution, we expected that the absorbency of the particles would decrease. This phenomenon can be explained by chemical reactions that take place after the experiment. Gold nanoparticles that are larger than a critical size will act as a nucleus for gold crystals to form. As crystals form around these nuclei, their size increases, thus increasing the absorbency of the particles. In order to prevent crystallization and aggregation, a water-soluble polymer called PEG was added to the solution. These polymers have a hydrophobic and a hydrophilic end, which causes the PEG to surround the particles creating a charged shell, which repels the particles from one another. This keeps the system colloidal and prevents crystals from forming on existing particles.