@misc{Santer2018,
  author    = {Santer, Svetlana},
  title     = {Remote control of soft nano-objects by light using azobenzene containing surfactants},
  series = {Journal of physics ; D, Applied physics},
  volume    = {51},
  journal   = {Journal of physics ; D, Applied physics},
  number    = {1},
  publisher = {IOP Publ.},
  address   = {Bristol},
  issn      = {0022-3727},
  doi       = {10.1088/1361-6463/aa95ca},
  pages     = {17},
  year      = {2018},
  abstract  = {We review recent progress in the field of light responsive soft nano-objects. These are systems the shape, size, surface area and surface energy of which can be easily changed by low-intensity external irradiation. Here we shall specifically focus on microgels, DNA molecules, polymer brushes and colloidal particles. One convenient way to render these objects photosensitive is to couple them via ionic and/or hydrophobic interactions with azobenzene containing surfactants in a non-covalent way. The advantage of this strategy is that these surfactants can make any type of charged object light responsive without the need for possibly complicated (and irreversible) chemical conjugation. In the following, we will exclusively discuss only photosensitive surfactant systems. These contain a charged head and a hydrophobic tail into which an azobenzene group is incorporated, which can undergo reversible photo-isomerization from a trans-to a cis-configuration under UV illumination. These kinds of photo-isomerizations occur on a picosecond timescale and are fully reversible. The two isomers in general possess different polarity, i.e. the trans-state is less polar with a dipole moment of usually close to 0 Debye, while the cis-isomer has a dipole moment up to 3 Debye or more, depending on additional phenyl ring substituents. As part of the hydrophobic tail of a surfactant molecule, the photo-isomerization also changes the hydrophobicity of the molecule as a whole and hence its solubility, surface energy, and strength of interaction with other substances. Being a molecular actuator, which converts optical energy in to mechanical work, the azobenzene group in the shape of surfactant molecule can be utilized in order to actuate matter on larger time and length scale. In this paper we show several interesting examples, where azobenzene containing surfactants play the role of a transducer mediating between different states of size, shape, surface energy and spatial arrangement of various nanoscale soft-material systems.},
  language  = {en}
}
@article{YadavalliKoenigSanter2015,
  author    = {Yadavalli, Nataraja Sekhar and K{\"o}nig, Tobias and Santer, Svetlana},
  title     = {Selective mass transport of azobenzene-containing photosensitive films towards or away from the light intensity},
  series = {Journal of the Society for Information Display},
  volume    = {23},
  journal   = {Journal of the Society for Information Display},
  number    = {4},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {1071-0922},
  doi       = {10.1002/jsid.306},
  pages     = {154 -- 162},
  year      = {2015},
  abstract  = {Here, we report on two photosensitive amorphous polymers showing opposite behavior upon exposure to illumination. The first polymer (PAZO) consists of linear backbone to which azobenzene-containing side chains are covalently attached, while in the second polymer (azo-PEI), the azobenzene side chains are attached ionically to a polyelectrolyte backbone. When irradiated through a mask, the PAZO goes away from the intensity maxima, leaving behind topography trenches, while the direction of the mass transport of the azo-PEI polymer points towards the intensity maxima. This kind of behavior has been reported only for certain liquid crystalline polymers that exhibit in-phase reaction on illumination, that is, topography maxima coincides with the intensity maxima. Furthermore, flat nanocrystals placed on top of azo-PEI film was found to be moved together with the mass transport of the underlying polymer film as visualized using in situ atomic force microscopy (AFM) measurements. It was also demonstrated that the two polymer films respond differently on irradiation with the polarization and intensity interference patterns (IPs). To record the kinetic of the surface relief grating formation within two polymers during irradiation with different IPs, we utilized a homemade setup combining the optical part for the generation of IP and AFM. A possible mechanism explaining different responses on the irradiation of amorphous polymers is discussed in the frame of a theoretical model proposed by Saphiannikova et al. (J. Phys. Chem. B 113, 5032-5045 (2009)).},
  language  = {en}
}
@article{YadavalliLindeKopyshevetal.2013,
  author    = {Yadavalli, Nataraja Sekhar and Linde, Felix and Kopyshev, Alexey and Santer, Svetlana},
  title     = {Soft matter beats hard matter - rupturing of thin metallic films induced by mass transport in photosensitive polymer films},
  series = {ACS applied materials \& interfaces},
  volume    = {5},
  journal   = {ACS applied materials \& interfaces},
  number    = {16},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/am4006132w},
  pages     = {7743 -- 7747},
  year      = {2013},
  abstract  = {The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa. Usually, the deformation process involves strains varying over large lateral dimensions because of excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at submicrometer length scales. Recently, we have created a metal polymer interface system with strains varying over periods of several hundred nanometers. This was achieved by exploiting the formation of surface relief grating (SRG) within the azobenzene containing photosensitive polymer film upon irradiation with light interference pattern. Up to a thickness of 60 nm, the adsorbed metal film adapts neatly to the forming relief, until it ultimately ruptures into an array of stripes by formation of highly regular and uniform cracks along the maxima and minima of the polymer topography. This surprising phenomenon has far-reaching implications. This is the first time a direct probe is available to estimate the forces emerging in SRG formation in glassy polymers. Furthermore, crack formation in thin metal films can be studied literally in slow motion, which could lead to substantial improvements in the design process of flexible electronics. Finally, cracks are produced uniformly and at high density, contrary to common sense. This could offer new strategies for precise nanofabrication procedures mechanical in character.},
  language  = {en}
}