@article{HaaseGrigorievMoehwaldetal.2010,
  author    = {Haase, Martin F. and Grigoriev, Dmitry and Moehwald, Helmuth and Tiersch, Brigitte and Shchukin, Dmitry G.},
  title     = {Encapsulation of amphoteric substances in a pH-sensitive pickering emulsion},
  issn      = {1932-7447},
  doi       = {10.1021/Jp104052s},
  year      = {2010},
  abstract  = {Oil-in-water (o/w) Pickering emulsions stabilized with silica nanoparticles were prepared. Droplets of diethyl phthalate (oil phase) act as reservoirs for 8-hydroxyquinoline (8-HQ), which is used as (a) the hydrophobizing agent for the silica particles and (b) an encapsulated corrosion inhibitor for application in active feedback coatings. The hydrophobization of silica nanoparticles with 8-HQ is determined by the amount of this agent adsorbed on the nanoparticle surface. The latter is governed by the 8-HQ concentration in the aqueous phase, which in turn depends on the degree of protonation and fir ally on the pH. We observe three ranges of 8-HQ adsorption value with respect to nanoparticle hydophobization: (I) insufficient, (2) sufficient, and (3) excessive adsorption by the formation of an 8-HQ bilayer, where only case 2 leads to the necessary nanoparticle hydrophobization. Hence emulsions stable in a narrow pH window between pH 5.5 and 4.4 follow. Here functional molecules are sufficiently charged to compensate for the charges on silica nanoparticles to make them interfacially active and thus able to stabilize an emulsion but they are still to a large extent uncharged and thereby remain in the oil phase. The emulsification is reversible upon changing the pH to a value beyond the stability region.},
  language  = {en}
}
@article{HaaseGrigorievMoehwaldetal.2011,
  author    = {Haase, Martin F. and Grigoriev, Dmitry and Moehwald, Helmuth and Tiersch, Brigitte and Shchukin, Dmitry G.},
  title     = {Nanoparticle modification by weak polyelectrolytes for pH-sensitive pickering emulsions},
  series = {Langmuir},
  volume    = {27},
  journal   = {Langmuir},
  number    = {1},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0743-7463},
  doi       = {10.1021/la1027724},
  pages     = {74 -- 82},
  year      = {2011},
  abstract  = {The affinity of weak polyelectrolyte coated oxide particles to the oil-water interface can be controlled by the degree of dissociation and the thickness of the weak polyelectrolyte layer. Thereby the oil in water (o/w) emulsification ability of the particles can be enabled. We selected the weak polyacid poly(methacrylic acid sodium salt) and the weak polybase poly(allylamine hydrochloride) for the surface modification of oppositely charged alumina and silica colloids, respectively. The isoelectric point and the pH range of colloidal stability of both particle-polyelectrolyte composites depend on the thickness of the weak polyelectrolyte layer. The pH-dependent wettability of a weak polyelectrolyte-coated oxide surface is characterized by contact angle measurements. The o/w emulsification properties of both particles for the nonpolar oil dodecane and the more polar oil diethylphthalate are investigated by measurements of the droplet size distributions. Highly stable emulsions can be obtained when the degree of dissociation of the weak polyelectrolyte is below 80\%. Here the average droplet size depends on the degree of dissociation, and a minimum can be found when 15 to 45\% of the monomer units are dissociated. The thickness of the adsorbed polyelectrolyte layer strongly influences the droplet size of dodecane/water emulsion droplets but has a less pronounced impact on the diethylphthalate/water droplets. We explain the dependency of the droplet size on the emulsion pH value and the polyelectrolyte coating thickness with arguments based on the particle-wetting properties, the particle aggregation state, and the oil phase polarity. Cryo-SEM visualization shows that the regularity of the densely packed particles on the oil-water interface correlates with the degree of dissociation of the corresponding polyelectrolyte.},
  language  = {en}
}