@article{ZakrevskyyRichterZakrevskaetal.2012,
  author    = {Zakrevskyy, Yuriy and Richter, Marcel and Zakrevska, Svitlana and Lomadze, Nino and von Klitzing, Regine and Santer, Svetlana},
  title     = {Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant},
  series = {Advanced functional materials},
  volume    = {22},
  journal   = {Advanced functional materials},
  number    = {23},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1616-301X},
  doi       = {10.1002/adfm.201200617},
  pages     = {5000 -- 5009},
  year      = {2012},
  abstract  = {The light-induced reversible switching of the swelling of microgel particles triggered by photo-isomerization and binding/unbinding of a photosensitive azobenzene-containing surfactant is reported. The interactions between the microgel (N-isopropylacrylamide, co-monomer: allyl acetic acid, crosslinker: N,N'-methylenebisacrylamide) and the surfactant are studied by UV-Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans-cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant-microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.},
  language  = {en}
}
@article{RichterZakrevskyyEiseleetal.2014,
  author    = {Richter, Marcel and Zakrevskyy, Yuriy and Eisele, Michael and Lomadze, Nino and Santer, Svetlana and von Klitzing, Regine},
  title     = {Effect of pH, co-monomer content, and surfactant structure on the swelling behavior of microgel-azobenzene-containing surfactant complex},
  series = {Polymer : the international journal for the science and technology of polymers},
  volume    = {55},
  journal   = {Polymer : the international journal for the science and technology of polymers},
  number    = {25},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0032-3861},
  doi       = {10.1016/j.polymer.2014.10.027},
  pages     = {6513 -- 6518},
  year      = {2014},
  abstract  = {The contraction/swelling transition of anionic PNIPAM-co-AAA particles can be manipulated by light using interactions with cationic azobenzene-containing surfactant. In this study the influence of pH-buffers and their concentrations, the charge density (AAA content) in microgel particles as well as the spacer length of the surfactant on the complex formation between the microgel and surfactant is investigated. It is shown that the presence of pH buffer can lead to complete blocking of the interactions in such complexes and the resulting microgel contraction/swelling response. There is a clear competition between the buffer ions and the surfactant molecules interacting with microgel particles. When working in pure water solutions with fixed concentration (charge density) of microgel, the contraction/swelling of the particles is controlled only by relative concentration (charge ratio) of the surfactant and AAA groups of the microgel. Furthermore, the particle contraction is more efficient for shorter spacer length of the surfactant. The onset point of the contraction process is not affected by the surfactant hydrophobicity. This work provides new insight into the interaction between microgel particles and photo-sensitive surfactants, which offers high potential in new sensor systems. (C) 2014 Elsevier Ltd. All rights reserved.},
  language  = {en}
}