Brigitte Tiersch

Universität Potsdam, Potsdam, Brandenburg, Germany

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Publications (43)106.91 Total impact

  • Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2014; 457:326–332. · 2.11 Impact Factor
  • N. Schulze, B. Tiersch, I. Zenke, J. Koetz
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    ABSTRACT: The influence of a polyampholyte, i.e., poly(N,N′-diallyl-N,N′-dimethyl-altmaleamic carboxylate) (PalH), on the lamellar liquid crystalline (LC) system sodium dodecyl sulfate (SDS)/decanol/water was investigated by means of microdifferential scanning calorimetry, small-angle X-ray diffraction (SAXS), and cryo-scanning electron microscopy. After incorporating PalH into the lamellar liquid crystalline system, SAXS measurements show that three different LC phases exist: i.e., a swelling, slightly swelling, and non-swelling one. At pH 4, the positively charged polymer with an extended conformation can directly adsorb at the anionic head groups of the surfactant and more compact vesicles are formed at room temperature. At pH 9, the electrostatic interactions between the polyampholyte (in a more coiled conformation) and the sulfate head groups of the SDS are leveled off and incompact vesicles are formed at room temperature. That means in presence of the polyampholyte the morphology of the LC phase, i.e., the supramolecular vesicle structure, can be tuned by varying the pH and/or the temperature. Figure pH-dependent tuning of the morphology of the lamellar phase
    Colloid and Polymer Science 11/2013; · 2.16 Impact Factor
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    ABSTRACT: The ternary system composed of the ionic liquid surfactant (IL-S) 1-butyl-3-methylimidazolium dodecylsulfate ([Bmim][DodSO4]), the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) and toluene has been investigated. Three major mechanisms guiding the structure of the isotropic phase were identified by means of conductometric experiments, which have been correlated to the presence of oil-in-IL, bicontinuous, and IL-in-oil microemulsions. IL-S forms micelles in toluene, which swell by adding RTIL as to be shown by Dynamic Light Scattering (DLS) and Small Angle X-ray Scattering (SAXS) experiments. Therefore, it is possible to form water-free IL-in-oil reverse microemulsions ≤ 10 nm in size as a new type of nanoreactor.
    Langmuir 05/2013; · 4.19 Impact Factor
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    ABSTRACT: This paper focuses on two different strategies to incorporate gold nanoparticles (AuNPs) into the matrix of polyacrylamide (PAAm) hydrogels. Poly(ethyleneimine) (PEI) is used as both reducing and stabilizing agent for the formation of AuNPs. In addition, the influence of an ionic liquid (IL) (i.e., 1-ethyl-3-methylimidazolium ethylsulfate) on the stability of the nanoparticles and their immobilization in the hydrogel is investigated The results show that AuNPs surrounded by a shell containing PEI and IL, synthesized according to the “one-pot” approach, are much better immobilized within the PAAm hydrogel. Hereby, the IL is responsible for structural changes in the hydrogel as well as the improved stabilization and embedding of the AuNPs into the polymer gel matrix.
    Macromolecular Chemistry and Physics 03/2013; 214(10):1114-1121. · 2.39 Impact Factor
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    ABSTRACT: Novel hydrogels based on hydroxyethyl starch modified with polyethylene glycol methacrylate (HES-P(EG)(6)MA) were developed as delivery system for the controlled release of proteins. Since the drug release behavior is supposed to be related to the pore structure of the hydrogel network the pore sizes were determined by cryo-SEM, which is a mild technique for imaging on a nanometer scale. The results showed a decreasing pore size and an increase in pore homogeneity with increasing polymer concentration. Furthermore, the mesh sizes of the hydrogels were calculated based on swelling data. Pore and mesh size were significantly different which indicates that both structures are present in the hydrogel. The resulting structural model was correlated with release data for bulk hydrogel cylinders loaded with FITC-dextran and hydrogel microspheres loaded with FITC-IgG and FITC-dextran of different molecular size. The initial release depended much on the relation between hydrodynamic diameter and pore size while the long term release of the incorporated substances was predominantly controlled by degradation of the network of the much smaller meshes.
    Journal of Biotechnology 07/2012; · 3.18 Impact Factor
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    ABSTRACT: Hydrogel systems based on hydroxyethyl starch-polyethylene glycol methacrylate (HES-P(EG)(6)MA) or hydroxyethyl starch methacrylate (HES-MA) were used to assess the protein release behavior. Here, we analyzed the in vitro release of FITC-anti-human antibodies incorporated in either HES-P(EG)(6)MA or HES-MA hydrogel delivery systems in PBS or human serum. In addition, hydrogel disks and microparticles prepared from the two polymers were subcutaneously implanted in BALB/c mice. The in vivo release of FITC-IgG was non-invasively monitored by an in vivo imaging system (IVIS 200) over a time period of up to 3 months. The imaging system allowed to asses individual animals over time, therefore only a small number of animals was required to obtain high quality data. The reduction in fluorescence intensity at the site of administration was compared to in vitro release profiles. These investigations demonstrated a sustained release from HES-MA hydrogel disks compared to rapidly degrading HES-P(EG)(6)MA disks and microparticles. The sustained release from HES-MA disks could be further optimized by using increased polymer concentrations. Human serum as in vitro release medium reflected better the in vivo release from HES-P(EG)(6)MA systems than PBS, suggesting that the presence of organic substances like proteins or lipids may play a significant role for the release kinetics.
    Journal of Controlled Release 06/2012; 162(1):127-33. · 7.63 Impact Factor
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    ABSTRACT: Mesoporous, highly structured silicon carbide (β-SiC) was synthesised from renewable plant materials (two Equisetaceae species) in a one-step carbothermal process at remarkably low temperatures down to 1200 °C. The SiC precursor is a silicon–carbon mixture with finely dispersed carbon prepared by pyrolysis of the organic plant matrix. Yields are 3 to 100% (ωSi/Si related to the silicon deposited in the plant material), depending on reaction temperature and time. IR spectroscopy, X-ray diffraction, and nitrogen sorption prove the formation of high-purity β-SiC with minor inorganic impurities after purification and a high specific surface area of up to 660 m2 g−1. Scanning electron microscopy shows that the plant morphology is maintained in the final SiC. Sedimentation analysis finds a mean particle size (diameters d50) of 20 μm.
    Journal of Materials Chemistry 04/2012; 22(18):9046-9051. · 5.97 Impact Factor
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    ABSTRACT: The present study reports a facile approach for sulfite biosensing, based on enhanced direct electron transfer of a human sulfite oxidase (hSO) immobilized on a gold nanoparticles modified electrode. The spherical core shell AuNPs were prepared via a new method by reduction of HAuCl(4) with branched poly(ethyleneimine) in an ionic liquids resulting particles with a diameter less than 10nm. These nanoparticles were covalently attached to a mercaptoundecanoic acid modified Au-electrode where then hSO was adsorbed and an enhanced interfacial electron transfer and electrocatalysis was achieved. UV/Vis and resonance Raman spectroscopy, in combination with direct protein voltammetry, are employed for the characterization of the system and reveal no perturbation of the structural integrity of the redox protein. The proposed biosensor exhibited a quick steady-state current response, within 2 s, a linear detection range between 0.5 and 5.4 μM with a high sensitivity (1.85 nA μM(-1)). The investigated system provides remarkable advantages in the possibility to work at low applied potential and at very high ionic strength. Therefore these properties could make the proposed system useful in the development of bioelectronic devices and its application in real samples.
    Bioelectrochemistry (Amsterdam, Netherlands) 12/2011; 87:33-41. · 2.65 Impact Factor
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    ABSTRACT: Phase behaviour and the mesoscopic structure of zwitanionic surfactant mixtures based on the zwitterionic tetradecyldimethylamine oxide (TDMAO) and anionic lithium perfluoroalkyl carboxylates have been investigated for various chain lengths of the perfluorosurfactant with an emphasis on spontaneously forming vesicles. These mixtures were studied at a constant total concentration of 50 mM and characterised by means of dynamic light scattering (DLS), electric conductivity, small-angle neutron scattering (SANS), viscosity, and cryo-scanning electron microscopy (Cryo-SEM). No vesicles are formed for relatively short perfluorosurfactants. The extension of the vesicle phase becomes substantially larger with increasing chain length of the perfluorosurfactant, while at the same time the size of these vesicles increases. Head group interactions in these systems play a central role in the ability to form vesicles, as already protonating 10 mol% of the TDMAO largely enhances the propensity for vesicle formation. The range of vesicle formation in the phase diagram is not only substantially enlarged but also extends to shorter perfluorosurfactants, where without protonation no vesicles would be formed. The size and polydispersity of the vesicles are related to the chain length of the perfluorosurfactant, the vesicles becoming smaller and more monodisperse with increasing perfluorosurfactant chain length. The ability of the mixed systems to form well-defined unilamellar vesicles accordingly can be controlled by the length of the alkyl chain of the perfluorinated surfactant and depends strongly on the charge conditions, which can be tuned easily by pH-variation.
    Soft Matter 11/2011; 7(23):11232-11242. · 3.91 Impact Factor
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    ABSTRACT: Using cationic polyelectrolytes with different molecular architectures, only hyperbranched poly(ethyleneimine) with maltose shell is suited to tailor the morphological transformation of anionic vesicles into tube-like networks. The interaction features of those materials partly mimic biological features of tubular proteins in nature.
    Soft Matter 11/2011; 7(22):10581-10584. · 3.91 Impact Factor
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    ABSTRACT: The synthesis of ultrafine gold nanoparticles in presence of maltose-modified hyperbranched poly(ethyleneimines) (PEI) is described. The polymer acted as both a reducing and stabilising agent in the particle formation process. The nanoparticles were characterised by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS). The mechanism of nanoparticle formation can be described in two steps. The reduction process of the Au ions located in the inner coil region of the hyperbranched PEI led to the formation of a compact gold core, and is accompanied by a collapse of the polymer coil. Therefore, in the subsequent reduction process a gold-polymer hybrid shell is formed. By using the PEI of higher molar mass, core-shell gold nanoparticles of about 3.6 nm size with a more narrow size distribution and special fluorescence behaviour could be synthesised.
    Journal of Dispersion Science and Technology - J DISPER SCI TECH. 01/2011;
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    ABSTRACT: A ternary system consisting of toluene, as oil phase, and two ionic liquids, i.e., 1-butyl-3-methylimidazolium octylsulfate (bmimOctOSO3) and 1-ethyl-3-methylimidazolium ethylsulfate (emimEtOSO3), has been investigated. The isotropic phase region was studied by means of conductometric, cyclic voltammetric and rheological measurements. The results show that microemulsions can be formed, where the bmimOctOSO3 take over the role of a surfactant in the spontaneous interfacial film formation process. Changes in the droplet–droplet exchange process can be assigned to transitions in the microstructure of the system from the IL-in-oil to oil-in-IL microemulsions, passing a bicontinuous phase. In the region between 5 wt.% and 21 wt.% of emimEtOSO3, reverse microemulsions with a droplet size of 2–10 nm were detected using Dynamic Light Scattering (DLS) and Cryo-Scanning Electron Microscopy (Cryo-SEM).
    Colloids and Surfaces A Physicochemical and Engineering Aspects 10/2010; 369(1-3):82-87. · 2.11 Impact Factor
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    ABSTRACT: The kinetics of the crystallization of thermoresponsive poly(2-isopropyl-2-oxazoline) in water and the time-dependent evolution of the morphology were examined using wide-angle X-ray scattering and conventional and cryogenic scanning electron microscopy. Results indicate that a temperature-induced phase separation produces a bicontinuous polymer network-like structure, which with the onset of crystallization collapses into individual particles (1–2 µm in diameter) composed of a porous fiber mesh. Nanofibers then preferentially form at the particle surface, thus wrapping the microspheres like a ball of wool. The particle morphology is severely affected by changes in temperature and less by the initial polymer concentration.
    Soft Matter 08/2010; · 3.91 Impact Factor
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    ABSTRACT: Amphiphilic alkyl-poly(ethyleneimine)s (alkyl-PEI) with different degrees of polymerization have been produced by alkaline hydrolysis of alkyl-poly(2-methyl-2-oxazoline). Potentiometric titration of the alkyl-PEI shows the influence of the alkyl chain and the degree of polymerization on the titration curves and hence on the polymer conformation. Karl Fischer titration has been used to determine the water content in the polymers. Subsequent X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) measurements prove the existence of different hydration states of the PEI even under dry storage conditions. Upon cooling from hot aqueous solutions, hydrogels form. The gelation concentration decreases with increasing degree of polymerization of the PEI segment. Scanning electron microscopy (SEM and cryo-SEM) of the hydrogels reveal an alkyl-PEI fibrous network composed of fan-like units. DSC shows that the percentages of bound and free water in the hydrogels depend on the concentration of polar amino groups.
    Langmuir 10/2009; 25(18):10558-66. · 4.19 Impact Factor
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    ABSTRACT: This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet-droplet interactions in the L(2) phase. (1)H nuclear magnetic resonance ((1)H NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), (1)H NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L(1) and L(2) phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.
    Journal of Colloid and Interface Science 06/2009; 333(2):782-90. · 3.17 Impact Factor
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    ABSTRACT: This article is focused on the characterization of the poly(ethylene glycol) (PEG)-induced bicontinuous microemulsion of the pseudo-ternary system sodium dodecylsulfate (SDS)/xylene-pentanol/water by means of differential scanning calorimetry, rheology, and conductometry. The influence of the polymer concentration (cp) and the molecular weight (Mw) on the microstructure of the microemulsion was investigated using Cryo scanning electron microscopy. It was found that an increase of cp influences the structure of the sponge-like phase significantly. These polymer-modified microemulsions can be used as a template phase for the formation of BaSO4 nanorods, where individual nanoparticles (5 nm in size) are ordered along the polymer backbone.
    Journal of Dispersion Science and Technology 06/2009; 30(6):745-752. · 0.60 Impact Factor
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    ABSTRACT: The epoxy system containing diglycidyl ether of bisphenol A and 4,4'-diaminodiphenyl sulfone is modified with poly(acrylonitrile-butadiene-styrene) (ABS) to explore the effects of the ABS content on the phase morphology, mechanism of phase separation, and viscoelastic properties. The amount of ABS in the blends was 5, 10, 15, and 20 parts per hundred of epoxy resin (phr). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate the final morphology of ABS-modified epoxy blends. Scanning electron microscopic studies of 15 phr ABS-modified epoxy blends reveal a bicontinuous structure in which both epoxy and ABS are continuous, with substructures of the ABS phase dispersed in the continuous epoxy phase and substructures of the epoxy phase dispersed in the continuous ABS phase. TEM micrographs of 15 phr ABS-modified epoxy blends confirm the results observed by SEM. TEM micrographs reveal the existence of nanosubstructures of ABS in 20 phr ABS-modified epoxy blends. To the best of our knowledge, to date, nanosubstructures have never been reported in any epoxy/thermoplastic blends. The influence of the concentration of the thermoplastic on the generated morphology as analyzed by SEM and TEM was explained in detail. The evolution and mechanism of phase separation was investigated in detail by optical microscopy (OM) and small-angle laser light scattering (SALLS). At concentrations lower than 10 phr the system phase separates through nucleation and growth (NG). However, at higher concentrations, 15 and 20 phr, the blends phase separate through both NG and spinodal decomposition mechanisms. On the basis of OM and SALLS, we conclude that the phenomenon of complex substructure formation in dynamic asymmetric blends is due to the combined effect of hydrodynamics and viscoelasticity. Additionally, dynamic mechanical analysis was carried out to evaluate the viscoelastic behavior of the cross-linked epoxy/ABS blends. Finally, apparent weight fractions of epoxy and ABS components in epoxy- and ABS-rich phases were evaluated from T(g) analysis.
    The Journal of Physical Chemistry B 04/2009; 113(16):5418-30. · 3.61 Impact Factor
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    ABSTRACT: Most toxic industrial chemicals and chemical warfare agents are hydrophobic and can only be solubilized in organic solvents. However, most reagents employed for the degradation of these toxic compounds can only be dissolved in water. Hence, microemulsions are auspicious media for the decontamination of a variety of chemical warfare agents and pesticides. They allow for the solubilization of both the lipophilic toxics and the hydrophilic reagent. Alkyl oligoglucosides and plant derived solvents like rapeseed methyl ester enable the formulation of environmentally compatible bicontinuous microemulsions. In the present article the phase behavior of such a microemulsion is studied and the bicontinuous phase is identified. Small angle neutron scattering (SANS) and freeze fracture electron microscopy (FFEM) measurements are used to characterize the structure of the bicontinuous phase and allow for an estimation of the total internal interface. Moreover, also the influence of the co-surfactant (1-pentanol) on the structural parameters of the bicontinuous phase is studied with SANS.
    Journal of Colloid and Interface Science 07/2008; 325(1):250-8. · 3.17 Impact Factor
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    ABSTRACT: The current paper shows that poly(ethylene imine) (PEI) is an efficient template for the fabrication of spherical calcium phosphate (CaP)/polymer hybrid particles at pH values above 8. The polymer forms spherical entities, which contain one or a few CaP particles with diameters of ca. 6 nm. The samples contain up to 20 wt % polymer, which appears to be wrapped around the small CaP particles. The particles form via a mineralization-trapping pathway, where at the beginning of the precipitation small CaP particles form. Further particle growth is then prevented by precipitation of the PEI onto these particles at pH values of ca. 8. Stabilization of the particles is provided by the re-protonation of the PEI, which is adsorbed on the CaP particles, during the remainder of the mineralization process. At low pH, much larger particles form. They most likely grow via heterogeneous nucleation and growth on existing, polymer-modified CaP surfaces.
    Langmuir 04/2008; 24(5):2102-9. · 4.19 Impact Factor
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    ABSTRACT: The influence of polystyrene (PS)-block–poly(1,4-butadiene) (PB)-block–poly(ethylene oxide) (PEO) and poly(1,4-butadiene)-block–polystyrene-block–poly(ethylene oxide) triblock terpolymers on the phase behaviour of the w/o microemulsion of the pseudo-ternary system made of water/sodium dodecylsulfate (SDS)/xylene–pentanol (1:1) was investigated by varying the sequence of the blocks. Independent on the terpolymer used an enlargement of L2 phase can be observed with increasing polymer concentration. Simultaneously, a decrease of the diameter of the mixed inverse terpolymer-surfactant micelles can be observed by dynamic light scattering. After cross-linking of the butadiene units, covalently closed nanocapsules with an average size between 20 and 30 nm can be observed.When the triblock terpolymer-modified microemulsion is used as a template for the nanoparticle formation, gold nanoparticles with diameters of about 10 nm are formed. After solvent evaporation, the terpolymer-modified, hydrophobic gold nanoparticles can be redispersed in a toluene–pentanol mixture, and eliminated from the non-soluble surfactant residue.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2008; 329(3):169-176. · 2.11 Impact Factor