@article{LiuBoeker2016, author = {Liu, Bing and B{\"o}ker, Alexander}, title = {Measuring rotational diffusion of colloidal spheres with confocal microscopy}, series = {Soft matter}, volume = {12}, journal = {Soft matter}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c6sm01082b}, pages = {6033 -- 6037}, year = {2016}, abstract = {We report an experimental method to measure the translational and rotational dynamics of colloidal spheres in three dimensions with confocal microscopy and show that the experimental values reasonably agree with the theoretical values. This method can be extended to study rotational dynamics in concentrated colloidal systems and complex bio-systems.}, language = {en} } @article{KathreinPesterRuppeletal.2016, author = {Kathrein, Christine C. and Pester, Christian and Ruppel, Markus and Jung, Maike and Zimmermann, Marc and B{\"o}ker, Alexander}, title = {Reorientation mechanisms of block copolymer/CdSe quantum dot composites under application of an electric field}, series = {Soft matter}, volume = {12}, journal = {Soft matter}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c6sm01073c}, pages = {8417 -- 8424}, year = {2016}, abstract = {Time- and temperature-resolved in situ birefringence measurements were applied to analyze the effect of nanoparticles on the electric field-induced alignment of a microphase separated solution of poly(styrene)-block-poly(isoprene) in toluene. Through the incorporation of isoprene-confined CdSe quantum dots the reorientation behavior is altered. Particle loading lowers the order-disorder transition temperature, and increases the defect density, favoring nucleation and growth as an alignment mechanism over rotation of grains. The temperature dependent alteration in the reorientation mechanism is analyzed via a combination of birefringence and synchrotron SAXS. The detailed understanding of the effect of nanoparticles on the reorientation mechanism is an important prerequisite for optimization of electricfield-induced alignment of block copolymer/nanoparticle composites where the block copolymer guides the nanoparticle self-assembly into anisotropic structures.}, language = {en} } @article{KathreinBaiNunnsetal.2016, author = {Kathrein, Christine C. and Bai, Wubin and Nunns, Adam and Gwyther, Jessica and Manners, Ian and B{\"o}ker, Alexander and Tsarkova, Larisa and Ross, Caroline A.}, title = {Electric field manipulated nanopatterns in thin films of metalorganic 3-miktoarm star terpolymers}, series = {Soft matter}, volume = {12}, journal = {Soft matter}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c6sm00451b}, pages = {4866 -- 4874}, year = {2016}, abstract = {We report the effect of electric field on the morphological transitions and ordering behavior of polyferrocenylethylmethylsilane block (PFEMS)-containing copolymers. By analyzing structures in solvent-annealed films of metalorganic sphere-and cylinder-forming diblock copolymers, as well as of 3-miktoarm polyisoprene-arm-polystyrene-arm-PFEMS (3 mu-ISF) terpolymers, we decouple two types of responses to the electric field: morphological transformations as a result of an increase in the volume fraction of the PFEMS block by oxidation of the ferrocenyl groups, and the orientation of the dielectric interfaces of microdomains parallel to the electric field vector. In the case of 3m-ISF, the former effect dominates at high electric field strengths which results in an unexpected cylinder-to-sphere transition, leading to a well-ordered hexagonal dot pattern. Our results demonstrate multiple tunability of ordered microdomain morphologies, suggesting future applications in nanofabrication and surface patterning.}, language = {en} } @article{HiltlBoeker2016, author = {Hiltl, Stephanie and B{\"o}ker, Alexander}, title = {Wetting Phenomena on (Gradient) Wrinkle Substrates}, series = {Langmuir}, volume = {32}, journal = {Langmuir}, publisher = {American Chemical Society}, address = {Washington}, issn = {0743-7463}, doi = {10.1021/acs.langmuir.6b02364}, pages = {8882 -- 8888}, year = {2016}, abstract = {We characterize the wetting behavior of nano structured wrinkle and gradient wrinkle substrates. Different contact angles on both sides of a water droplet after deposition on a gradient sample induce the self-propelled motion of the liquid toward smaller wrinkle dimensions. The droplet motion is self-limited by the contact angles balancing out. Because of the correlation between droplet motion and contact angles, we investigate the wetting behavior of wrinkle substrates with constant dimensions (wavelengths of 400-1200 nm). Contact angles of water droplets on those substrates increase with increasing dimensions of the underlying substrate. The results are independent of the two measurement directions, parallel and perpendicular to the longitudinal axis of the nanostructure. The presented findings may be considered for designing microfluidic or related devices and initiate ideas for the development of further wrinkle applications.}, language = {en} } @article{CharanKinzelGlebeetal.2016, author = {Charan, Himanshu and Kinzel, Julia and Glebe, Ulrich and Anand, Deepak and Garakani, Tayebeh Mirzaei and Zhu, Leilei and Bocola, Marco and Schwaneberg, Ulrich and B{\"o}ker, Alexander}, title = {Grafting PNIPAAm from beta-barrel shaped transmembrane nanopores}, series = {Biomaterials : biomaterials reviews online}, volume = {107}, journal = {Biomaterials : biomaterials reviews online}, publisher = {Elsevier}, address = {Oxford}, issn = {0142-9612}, doi = {10.1016/j.biomaterials.2016.08.033}, pages = {115 -- 123}, year = {2016}, abstract = {The research on protein-polymer conjugates by grafting from the surface of proteins has gained significant interest in the last decade. While there are many studies with globular proteins, membrane proteins have remained untouched to the best of our knowledge. In this study, we established the conjugate formation with a class of transmembrane proteins and grow polymer chains from the ferric hydroxamate uptake protein component A (FhuA; a beta-barrel transmembrane protein of Escherichia coli). As the lysine residues of naturally occurring FhuA are distributed over the whole protein, FhuA was reengineered to have up to 11 lysines, distributed symmetrically in a rim on the membrane exposed side (outside) of the protein channel and exclusively above the hydrophobic region. Reengineering of FhuA ensures a polymer growth only on the outside of the beta-barrel and prevents blockage of the channel as a result of the polymerization. A water-soluble initiator for controlled radical polymerization (CRP) was consecutively linked to the lysine residues of FhuA and N-isopropylacrylamide (NIPAAm) polymerized under copper mediated CRP conditions. The conjugate formation was analyzed by using MALDI-ToF mass spectrometry, SDS-PAGE, circular dichroism spectroscopy, analytical ultracentrifugation, dynamic light scattering, transmission electron microscopy and size exclusion chromatography. Such conjugates combine the specific functions of the transmembrane proteins, like maintaining membrane potential gradients or translocation of substrates with the unique properties of synthetic polymers such as temperature and pH stimuli handles. FhuA-PNIPAAm conjugates will serve as functional nanosized building blocks for applications in targeted drug delivery, self-assembly systems, functional membranes and transmembrane protein gated nanoreactors. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} }