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Stubenrauch, Cosima
Preferred name
Stubenrauch, Cosima
Official Name
Stubenrauch, Cosima
Research Output
Now showing 1 - 3 of 3
- PublicationGelled Polymerizable Microemulsions. Part 3 Rheology(RSC publications, 2009)
; ; ; ; This is the first report on the rheological properties of oil-gelled polymerizable bicontinuous microemulsions. The polymerizable base system consists of H2O / NIPAm / BisAm – n-dodecane – C13/15E5 (a technical grade n-alkyl polyglycol ether), where NIPAm denotes the monomer N-isopropylacrylamide and BisAm the cross-linker N,N′-methylene bisacrylamide. For the planned polymerization of the aqueous phase a scaffold is needed to preserve the structure of the templating microemulsion during the polymerization. This scaffold is supposed to be a gel, which was formed by adding the gelator 12-hydroxyoctadecanoic acid (12-HOA) to the oil phase of the microemulsion. The influence of the water-to-oil ratio α, of the gelator concentration β, and of the monomer concentration ψ on the rheological behavior of gelled microemulsions has been studied in detail. The most important result of the study at hand is the observation of a transition from a high viscous solution to a gel, i.e. from a transient to a permanent network, with increasing gelator concentration and increasing amount of the oil phase, respectively. In other words, it is only under well-defined conditions that an oil-gelled microemulsion is formed.479Scopus© Citations 16 - PublicationPhase diagrams of non-ionic microemulsions containing reducing agents and metal salts as bases for the synthesis of bimetallic nanoparticlesPhase diagrams of microemulsions containing metal salt(s) and reducing agent, respectively, were studied in detail. The microemulsions were based on non-ionic surfactants, namely pure tetraethyleneglycol monododecylether, C12E4, and technical grade Brij30. We studied the influence of the metal salts H2PtCl6, Pb(NO3)2, Bi(NO3)3, H2PtCl6 + Pb(NO3)2 (1:1 mixture), and H2PtCl6 + Bi(NO3)3 (1:1 mixture) as well as of the reducing agent NaBH4 on the location of the phase boundaries. The focus was on the water emulsification failure boundary (wefb) where the aqueous phase forms spherical droplets. The temperature shifts of the wefb, which were caused by the presence of the salt(s), are directly related with the shift of the clouding points of the corresponding oil-free systems. The location of the wefb is affected in a complex manner by the pH (the lower the pH the higher the temperature at which the wefb occurred), the ionic strength and by specific salting-in or salting-out effects of the electrolyte ions. The desired overlap of the wefb of the microemulsions containing the metal salt(s) and the reducing agent, respectively, could be achieved by adding NaOH to the C12E4-based microemulsions and by titrating 1-octanol to the Brij30-based microemulsions, respectively.
1066Scopus© Citations 18 - PublicationPhase diagrams of microemulsions containing reducing agents and metal salts as bases for the synthesis of metallic nanoparticlesWe studied the phase diagrams of microemulsions with a view to using these systems for the synthesis of metallic Pt, Pb, and Bi nanoparticles as well as of intermetallic Pt/Pb and Pt/Bi nanoparticles. The microemulsions consisted of H2O/salt – n-decane – SDS – 1-butanol. The salt was either one metal precursor (H2PtCl6·6H2O, Pb(NO3)2, or Bi(NO3)3·5H2O), a mixture of two metal precursors (H2PtCl6·6H2O + Pb(NO3)2 or H2PtCl6·6H2O + Bi(NO3)3·5H2O), or the reducing agent (NaBH4). In addition, other salts needed to be added in order to solubilize the metal precursors, to stabilize the reducing agent, and to adjust the ionic strength. Combining the microemulsion (μe1) that contains the metal precursor(s) with the microemulsion (μe2) that contains the reducing agent leads to metallic nanoparticles. To study systematically how the shape and size of the synthesized metallic nanoparticles depend on the size and shape of the respective microemulsion droplets, first of all one has to find those conditions under which μe1 and μe2 have the same structure. For that purpose we determined the water emulsification failure boundary (wefb) of each microemulsion as it is at the wefb where the water droplets are known to be spherical. We found that the ionic strength (I) of the aqueous phase as well as the hard acid and hard base properties of the ions are the key tuning parameters for the location of the wefb.
932Scopus© Citations 23