TY - JOUR A1 - Dolya, Natalya A1 - Rojas, Oscar A1 - Kosmella, Sabine A1 - Tiersch, Brigitte A1 - Koetz, Joachim A1 - Kudaibergenov, Sarkyt T1 - "One-Pot" in situ frmation of Gold Nanoparticles within Poly(acrylamide) Hydrogels JF - Macromolecular chemistry and physics N2 - 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. KW - gold nanoparticles KW - immobilization KW - ionic liquids KW - poly(acrylamide) hydrogels Y1 - 2013 U6 - https://doi.org/10.1002/macp.201200727 SN - 1022-1352 VL - 214 IS - 10 SP - 1114 EP - 1121 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Bertz, Andreas A1 - Wöhl-Bruhn, Stefanie A1 - Miethe, Sebastian A1 - Tiersch, Brigitte A1 - Koetz, Joachim A1 - Hust, Michael A1 - Bunjes, Heike A1 - Menzel, Henning T1 - Encapsulation of proteins in hydrogel carrier systems for controlled drug delivery influence of network structure and drug size on release rate JF - Journal of biotechnology N2 - 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. KW - Hydrogel KW - Hydrogel microspheres KW - Network structure KW - Release studies KW - Protein delivery KW - Mesh size Y1 - 2013 U6 - https://doi.org/10.1016/j.jbiotec.2012.06.036 SN - 0168-1656 VL - 163 IS - 2 SP - 243 EP - 249 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Friberg, Stig E. A1 - Kovach, Ildiko A1 - Koetz, Joachim T1 - Equilibrium topology and partial inversion of Janus Drops - a numerical analysis JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - The equilibrium topology of an aqueous Janus emulsion of two oils, O1 and O2, with water, W, [(O1+O2)/W], is numerically evaluated with the following realistic interfacial tensions (): (O2/W)=5 mNm(-1), (O1/O2)=1 mNm(-1), and (O1/W) varies within the range 4-5 mNm(-1), which is the limiting range for stable Janus drop topology. The relative significance of the two independently pivotal factors for the topology is evaluated, that is, the local equilibrium at the line of contact between the three liquids and the volume fraction of the two dispersed liquids within the drop. The results reveal a dominant effect of the local equilibrium on the fraction of the O2 drop surface that is covered by O1. In contrast, for a constant volume of O2, the impact of the interfacial tension balance on the limit of the coverage is modest for an infinite volume of O1. Interestingly, when the O1 volume exceeds this value, an emulsion inversion occurs, and the O1 portion of the (O1+O2)/W topology becomes a continuous phase, generating a (W+O2)/O1 Janus configuration. KW - emulsion inversion KW - interfaces KW - janus emulsions KW - liquids KW - semiempirical calculations Y1 - 2013 U6 - https://doi.org/10.1002/cphc.201300635 SN - 1439-4235 SN - 1439-7641 VL - 14 IS - 16 SP - 3772 EP - 3776 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Lemke, Karina A1 - Prietzel, Claudia Christina A1 - Koetz, Joachim T1 - Fluorescent gold clusters synthesized in a poly(ethyleneimine) modified reverse microemulsion JF - Journal of colloid and interface science N2 - This paper is focused on the formation of gold clusters in a tailor-made polyelectrolyte-modified reverse microemulsion using poly(ethyleneimine) (PEI) as a cationic polyelectrolyte. PEI incorporated into a ternary w/o microemulsion consisting of water/heptanol/zwitterionic surfactant 3-(N,N-dimethyl-dodecylammonio)-propanesulfonate (SB) acts as a reducing and stabilizing agent and shows an additional template effect. The nanoparticle synthesis is performed by a simple mixing of two microemulsions, one containing the PEI and the other one containing the gold chloride precursor. UV-vis measurements in the microemulsion show two pronounced absorption maxima, one at 360 nm and the other one at 520 nm, indicating two particle fractions. The absorption maximum at 360 nm in combination to the unique fluorescence properties indicate the formation of gold clusters. After a complete solvent evaporation the redispersed nanoparticles have been characterized by using UV-vis and fluorescence spectroscopy, in combination to dynamic light scattering and transmission electron microscopy (TEM). In addition to the gold nanoparticle fraction (>5 nm) the fluorescent gold cluster fraction (<2 nm) can be redispersed without particle aggregation. By means of asymmetric flow field flow fractionation (AF-FFF) two different cluster fractions with particle diameter (<2 nm) can be identified. KW - Microemulsion KW - Gold cluster KW - Field flow fractionation KW - Polymer capped gold nanoparticles Y1 - 2013 U6 - https://doi.org/10.1016/j.jcis.2012.11.057 SN - 0021-9797 VL - 394 SP - 141 EP - 146 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Thete, Aniket A1 - Rojas, Oscar A1 - Neumeyer, David A1 - Koetz, Joachim A1 - Dujardin, Erik T1 - Ionic liquid-assisted morphosynthesis of gold nanorods using polyethyleneimine-capped seeds JF - RSC Advances N2 - Seed-mediated gold nanorods with tunable lengths are prepared using new polyethyleneimine-capped gold nanoparticles synthesized in ionic liquid. The effect of polyethyleneimine and ionic liquid during nanorod growth is investigated and shows a marked effect on their final aspect ratio. Y1 - 2013 U6 - https://doi.org/10.1039/c3ra22112a SN - 2046-2069 VL - 3 IS - 34 SP - 14294 EP - 14298 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Thete, Aniket A1 - Rojas, Oscar A1 - Neumeyer, David A1 - Koetz, Joachim A1 - Dujardin, Erik T1 - Ionic liquid-assisted morphosynthesis of gold nanorods using polyethyleneimine-capped seeds N2 - Seed-mediated gold nanorods with tunable lengths are prepared using new polyethyleneimine-capped gold nanoparticles synthesized in ionic liquid. The effect of polyethyleneimine and ionic liquid during nanorod growth is investigated and shows a marked effect on their final aspect ratio. Y1 - 2013 UR - http://pubs.rsc.org/en/content/articlepdf/2013/ra/c3ra22112a U6 - https://doi.org/10.1039/C3RA22112A ER - TY - GEN A1 - Thete, Aniket A1 - Rojas, Oscar A1 - Neumeyer, David A1 - Koetz, Joachim A1 - Dujardin, Erik T1 - Ionic liquid-assisted morphosynthesis of gold nanorods using polyethyleneimine-capped seeds N2 - Seed-mediated gold nanorods with tunable lengths are prepared using new polyethyleneimine-capped gold nanoparticles synthesized in ionic liquid. The effect of polyethyleneimine and ionic liquid during nanorod growth is investigated and shows a marked effect on their final aspect ratio. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 245 KW - aqueous-solution KW - aspect-ratio KW - cationic surfactants KW - chemical-synthesis KW - delivery KW - metal nanoparticles KW - mixtures KW - shape KW - silver nanowires KW - surface-plasmon resonance Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-95196 SP - 14294 EP - 14298 ER - TY - JOUR A1 - Hasinovic, Hida A1 - Friberg, Stieg E. A1 - Kovach, Ildyko A1 - Koetz, Joachim T1 - Janus emulsion drops - equilibrium calculations JF - Journal of dispersion science and technology N2 - Experimental results indicated the contact angles in the drops of Janus emulsions formed in a one-step mixing process to be invariant within a significant range the oil volume ratios, similar to the results from microfluidics emulsification. Since this result points to a connection between the kinetically formed emulsions and the local equilibrium topology of emulsion drops, the effect of interfacial tensions on the morphology of Janus emulsions was estimated from the equilibrium interfacial tensions at the line of contact. Realistic values of the tensions revealed the limited range of these to obtain Janus drops and also offered correlation between the equilibrium entities and the curvature of the interface between the two oils. KW - Drop morphology KW - equilibrium topology KW - Janus emulsions KW - microfluidics KW - multiple emulsion preparation Y1 - 2013 U6 - https://doi.org/10.1080/01932691.2013.763728 SN - 0193-2691 SN - 1532-2351 VL - 34 IS - 12 SP - 1683 EP - 1689 PB - Taylor & Francis Group CY - Philadelphia ER - TY - JOUR A1 - Rojas, Oscar A1 - Tiersch, Brigitte A1 - Rabe, Christian A1 - Stehle, Ralf A1 - Hoell, Armin A1 - Arlt, Bastian A1 - Koetz, Joachim T1 - Nonaqueous Microemulsions Based on N,N '-Alkylimidazolium Alkylsulfate Ionic Liquids JF - Langmuir N2 - The ternary system composed of the ionic liquid surfactant (IL-S) 1-butyl-3-methylimidazolium dodecylsulfate ([Bmim][DodSO(4)]), 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. Y1 - 2013 U6 - https://doi.org/10.1021/la401080q SN - 0743-7463 VL - 29 IS - 23 SP - 6833 EP - 6839 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schulze, Nicole A1 - Tiersch, B. A1 - Zenke, I. A1 - Koetz, Joachim T1 - Polyampholyte-tuned lyotrop lamellar liquid crystalline systems JF - COLLOID AND POLYMER SCIENCE N2 - 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. KW - Polyampholytes KW - Lamellar liquid crystals KW - Vesicle formation KW - SAXS KW - Cryo-SEM KW - mu-DSC Y1 - 2013 U6 - https://doi.org/10.1007/s00396-013-2999-5 SN - 0303-402X SN - 1435-1536 VL - 291 IS - 11 SP - 2551 EP - 2559 PB - SPRINGER CY - NEW YORK ER -