Mikroemulsionen als smarte Reaktionsmedien (English shop)

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Abstract

Recently, the application of microemulsions as smart media for organic and inorganic syntheses has received considerable attention.
Water swollen micelles can be regarded as nano-sized reaction vessels for the synthesis of metal nanoparticles. However, the effect of the micelles’ exchange kinetics on the shape and size of the particles has not yet been clarified.
Therefore, I investigated the micelles’ exchange kinetics for the non-ionic surfactant based system H2O – n-alkane – CiEj (n-alkyl polyoxyethylene). The rate constant of the exchange does not depend on the size of the micelles and weakly on their concentration.
In efficient microemulsion systems, the exchange kinetics are slowed down considerably.
Microemulsion systems are not yet optimized as potential reaction media for highly reactive reagents.
Thus, the most reactive component, namely water, was replaced by the inert tetrahydrothiophen-1,1-dioxide (sulfolane).
By chosing the long chained surfactants C18E6 and C18E8 as amphiphiles, I was the first to formulate a water-free microemulsion system containing sulfolane – n-octane – C18E6/C18E8.
At first, inorganic synthesis of platinum, bismuth and lead nanoparticles was conducted in inexpensive ionic surfactant based microemulsion systems of the type H2O/salts – oil – ionic surfactant – cosurfactant. Moreover, bicontineous microemulsions comprising H2O – oil – nonionic surfactant – cosurfactant were effectively used to overcome reagent incompatibilities for the epoxidation of D,E-unsaturated enones.
The reaction in the microemulsion systems was up to 35 times faster than in heterogeneous two-phase systems.

Short summary

In recent years, the use of microemulsions as smart reaction media for organic and inorganic synthesis has attracted increasing attention.
Thus, nano-scaled water swollen micelles are used as templates for the synthesis of nanoparticles.
The influence of the temporary coalescence of these swollen micelles on the shape and size of the nanoparticles has not yet been clarified. This work first investigates the coalescence kinetics of water swollen micelles of the type H2O – n-alkane – n-alkyl polyglycol ether (CiEj). The exchange kinetics do not depend on the size of the droplets and hardly on their concentration. More efficient microemulsion systems considerably slow down the exchange kinetics.
In order to formulate inert microemulsions, the most reactive component, water, was replaced by the inert tetrahydrothiophen-1,1-dioxide (sulfolane).
By using very long chained surfactants, a microemulsion consisting of sulfolane – n-octane – C18E6/C18E8 could be formulated for the first time.
Initially, however, platinum, lead and bismuth nanoparticles were synthesised from inexpensive water-in-oil microemulsions of the type H2O – n-alkane – ionic surfactant – cosurfactant.
In addition to these rather inorganic reactions, bicontinuous microemulsions of the type H2O – oil – nonionic surfactant – cosurfactant were used as reaction media for the epoxidation of D,E-unsaturated enones.
Thereby, reactant incompatibilities were successfully overcome and reaction accelerations of up to a factor of 35 were achieved.