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  • 1
    Language: English
    In: Nano letters, 08 March 2017, Vol.17(3), pp.2010-2014
    Description: We report on a microscopic poly(N-isopropylacrylamide) hydrogel ribbon, coated by a thin gold layer, that shows helical coiling. Confined swelling and shrinkage of the hydrogel below and above its characteristic volume phase transition leads to a temperature actuated reversal of the sense of the helix. The extent and the shape of the winding are controlled by the dimensions and mechanical properties of the bilayer ribbon. We focus on a cylindrical helix geometry and monitor the morphing under equilibrium and nonequilibrium conditions, that is, when the temperature changes faster than the volume (millisecond range). For slow temperature variations, the water release and uptake follow the equilibrium transition trajectory determined by the time needed for the diffusion of water into and out of the microscopic gel. Much faster variations of the temperature are accomplished by internal heating of embedded gold nanorods by IR-light irradiation. This causes elastic stresses that strongly affect the motions. This method enables well-reproducible deviations from the equilibrium transition path and allows us to control rather precisely the spatiotemporal transformation in a cyclic repetitive process. Actuation and response are sensitive to small variations of temperature and composition of the aqueous sol in which the gel is immersed. The principle as described may be used to detect specific analytes that bind either to the surface of the gold layer or within the gel and can modify the interaction between the water and the gel. The reported nonequilibrium morphing implies that the system dissipates energy and may also be able to perform work as required for a microscopic motor.
    Keywords: Microgel ; Misfit-Strain ; Nonequilibrium Morphing ; Photothermal Actuation
    ISSN: 15306984
    E-ISSN: 1530-6992
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  • 2
    In: Chemical Communications, 2011, Vol.47(28), pp.8148-8150
    Description: In this communication we report on the base catalyzed Michael addition of the hydroxy methyl side groups in polyglycidol to diethyl vinyl phosphonate. Hydrolysis of the diethyl phosphonato ethyl side groups with bromotrimethylsilane leads to a new class of polyglycidols with pendant phosphonic acid groups.
    Keywords: Hydrolysis ; Phosphonates ; Phosphonic Acids ; Miscellaneous Sciences (So) ; Components and Materials (General) (Ea);
    ISSN: 1359-7345
    E-ISSN: 1364-548X
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  • 3
    Language: English
    In: Polymer, 2011, Vol.52(9), pp.1917-1924
    Description: In this work, the incorporation of reactive cyclodextrins (CDs) in aqueous nanogels based on poly(N-vinylcaprolactam) (VCL) is studied by surfactant-free precipitation polymerization process. α-, β-, γ-CDs were functionalized with acrylic groups and the average amount of vinyl bonds per CD molecule was adjusted to 2, 4, or 6. The increase of the CD concentration in the reaction mixture led to the reduction of the final hydrodynamic radius of nanogels from 227 nm to 62 nm. The increase of the vinyl groups number per CD molecule induced formation of smaller nanogels (Rₕ = 22.5 nm) and considerable increase of the crosslinking degree. Obtained cyclodextrin-modified nanogels show temperature sensitivity in aqueous medium with a volume transition point around 30 °C. The complexation properties of CDs incorporated in nanogel networks were proved by titration with phenolphthalein. ; p. 1917-1924.
    Keywords: Titration ; Cyclodextrins ; Crosslinking ; Hydrodynamics ; Polymerization ; Polymers ; Temperature
    ISSN: 0032-3861
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  • 4
    In: Physical Chemistry Chemical Physics, 2011, Vol.13(30), pp.13572-13578
    Description: The relevance of anion structure on the shape regulating effect of 3-ethyl-1-methylimidazolium-based ionic liquids during the seed-induced growth of gold nanocrystals is evaluated for the particular case of lactate, acetate, methylsulfate, ethylsulfate and tosylsulfonate anion systems. Carboxylate-based anions (lactate and acetate) are found to inhibit the reduction of the gold precursor salt presumably due to the deprotonation of the reducing agent ascorbic acid. The formation of non-uniform, ‘head-tail’-type anisotropic particle structures is observed in both methyl- and ethylsulfate anion systems whereas rapid precipitation is observed in the case of tosylsulfonate anions. The particular efficiency of the ethylsulfate solvent system in promoting shape anisotropic growth is interpreted to be a consequence of both reduced anion/cation interactions that act to support the coordination of imidazolium to the metal surface and the enhanced capacity of anions to participate in the particle stabilization process.
    Keywords: Anions -- Chemistry ; Gold -- Chemistry ; Imidazoles -- Chemistry ; Ionic Liquids -- Chemistry ; Metal Nanoparticles -- Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 5
    Language: English
    In: Macromolecules, 02/12/2013, Vol.46(3), pp.638-646
    ISSN: 0024-9297
    E-ISSN: 1520-5835
    Source: American Chemical Society (via CrossRef)
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  • 6
    Language: English
    In: Applied Physics Letters, 15 June 2015, Vol.106(24)
    Description: We discuss an evaporation-induced wetting transition on superhydrophobic stripes and show that depending on the elastic energy of the deformed contact line, which determines the value of an instantaneous apparent contact angle, two different scenarios occur. For relatively dilute stripes, the receding angle is above 90°, and the sudden impalement transition happens due to an increase of a curvature of an evaporating drop. For dense stripes, the slow impregnation transition commences when the apparent angle reaches 90° and represents the impregnation of the grooves from the triple contact line towards the drop center.
    Keywords: Surfaces And Interfaces
    ISSN: 0003-6951
    E-ISSN: 1077-3118
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  • 7
    Language: English
    In: Chemistry of Materials, 11/08/2011, Vol.23(21), pp.4748-4755
    ISSN: 0897-4756
    E-ISSN: 1520-5002
    Source: American Chemical Society (via CrossRef)
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  • 8
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 08 October 2013, Vol.29(40), pp.12331-6
    Description: It has been shown before that anisotropically microstructured surfaces exhibit anisotropic wetting phenomena. This study presents a possibility to control the anisotropy of wetting by tailoring the surface chemistry. PDMS microchannels were permanently hydrophilized and subsequently functionalized further. Thereby, systematic studies on the effect of the surface modification on the wetting properties of microstructures have been possible. Importantly, we found that the wetting parallel to the groove strongly depended on the chemical modification of the structure although the wetting perpendicular to the groove is almost unaffected. Through immobilization of a monolayer of Si nanoparticles (SiNPs) exclusively on the elevations of the hydrogel-coated microstructured PDMS substrate, the anisotropic wetting could be selectively altered unidirectionally along the pattern direction.
    Keywords: Mikrostruktur ; Immobilisation ; Nanopartikel ; Mikrokanal ; Monoschicht ; Hydrogel ; Anisotropie ; Oberflächenchemie ; Chemische Modifikation ; Polydimethylsiloxan ; Benetzbarkeit ; Chemistry;
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 9
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 10 July 2018, Vol.34(27), pp.8031-8041
    Description: Understanding the diffusion of gold nanorods (AuNRs) and their composites in dispersion is important at fundamental level and in fields as diverse as material science, nanobiotechnology to drug delivery. The translational and rotational diffusion of AuNRs decorated with thermoresponsive poly( N-isopropylacrylamide) brushes having hydrophilic and hydrophobic end groups was investigated in the dilute regime by dynamic light scattering. The same series of functionalized AuNRs were studied in the isotropic concentrated dispersions by high-resolution NMR diffusometry. The dependence of translational and rotational diffusivity upon molecular weight and polymer end group were measured as a function of temperature in the region of the brush phase transition. The effective hydrodynamic radius of AuNR composites proved to be the most sensitive quantity to the temperature-induced phase transition of brushes, allowing the evaluation of the brush thickness in the swollen and collapsed states.
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 10
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 22 April 2014, Vol.30(15), pp.4253-61
    Description: A facile approach for the microencapsulation of hydrophobic liquids in closed solid all-silica colloidosomes is reported. The method is based on the formation of oil-in-water emulsions stabilized by silica nanoparticles and subsequent gluing of the particles at the water/oil interface by a silica precursor polymer-hyperbranched polyethoxysiloxane. By this means different oils are successfully enclosed in hence formed all-silica colloidosomes with almost 100% efficiency. Via a systematical study it is demonstrated that this process is a delicate interplay between the emulsion stability, oil polarity, and sol-gel reaction kinetics. This approach allows fabricating microcapsules of hydrophobic liquid substances in a mechanically stable, chemically inert, and biocompatible matrix, silica, with high encapsulation capacity and a controlled release profile.
    Keywords: Colloids -- Chemistry ; Oils -- Chemistry ; Silicon Dioxide -- Chemistry
    ISSN: 07437463
    E-ISSN: 1520-5827
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