TY - JOUR A1 - Raju, Rajarshi Roy A1 - Kosmella, Sabine A1 - Friberg, Stig E. A1 - Koetz, Joachim T1 - Pickering Janus emulsions and polyelectrolyte complex-stabilized Janus gels JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - Janus emulsions, containing olive oil (OO) and silicone oil (SiO), were formed in presence of polyelectrolyte complex particles, i.e., gelatin-sodium polyacrylate (NaPAA) complexes. The diameter of completely engulfed Janus droplets can be tuned between 50 and 200 mu m by varying the gelatin/NaPAA complex particle size between 200 and 400 nm. The gelatin/NaPAA complex particles adsorbed at the olive oil interface decrease the interfacial tension and stabilize the resulting completely engulfed Pickering Janus emulsions. Long-term stable Janus gels can be synthesized in presence of gelatin/sodium carboxymethylcellulose (NaCMC) mixtures. In that case Coulombic forces are of relevance with regard to the stabilization of the Janus droplets embedded in a gelatin/NaCMC gel matrix. Janus gels show elastic reological behavior and thixotropic properties. KW - Pickering Janus emulsions KW - Janus gels KW - Interfacial tension KW - Ring tensiometry KW - Gelatin-NaCMC KW - Gelatin-NaPAA composites Y1 - 2017 U6 - https://doi.org/10.1016/j.colsurfa.2017.08.022 SN - 0927-7757 SN - 1873-4359 VL - 533 SP - 241 EP - 248 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kovach, Ildiko A1 - Won, Jooyoung A1 - Friberg, Stig E. A1 - Koetz, Joachim T1 - Completely engulfed olive/silicone oil Janus emulsions with gelatin and chitosan JF - Colloid and polymer science : official journal of the Kolloid-Gesellschaft N2 - Janus emulsions, formed by mixing two oil components (i.e., olive oil (OO) and silicone oil (SiO)) with water in the presence of two surface active biopolymers, i.e., gelatin and chitosan, are investigated in more detail. The stability of Janus droplets formed strongly depends on the polymer components used. The mixture of both biopolymers represents an extraordinary effect which can be related to the complex formation of gelatin and chitosan. Taken into account that under the given pH conditions, in the acidic pH range between 4 and 6, below the isoelectric point of gelatin, both polymers are polycations, one can conclude that non-Coulombic interactions are of relevance for the enhanced surface activity of the complexes. Dynamic interfacial tension (gamma) measurements by using the drop profile analysis tensiometry (PAT) indicate a strong adsorption of the polymer complexes at the olive oil/water interface in contrast to the silicone/water interface. In a first step, the polymer complexes are adsorbed at the interface, and in a second step, a more rigid skin-like polymer layer is formed. This first example of a polymer-stabilized Janus emulsion opens new perspectives for the application, e.g., in food emulsions or for making scaffold materials. KW - Janus emulsions KW - Interfacial tension KW - Ring method KW - Drop profile analysis tensiometry KW - Gelatin-chitosan composites Y1 - 2016 U6 - https://doi.org/10.1007/s00396-016-3828-4 SN - 0303-402X SN - 1435-1536 VL - 294 SP - 705 EP - 713 PB - Springer CY - New York ER - TY - JOUR A1 - Kovach, Ildiko A1 - Rumschöttel, Jens A1 - Friberg, Stig E. A1 - Koetz, Joachim T1 - Janus emulsion mediated porous scaffold bio-fabrication JF - Colloids and surfaces : an international journal devoted to fundamental and applied research on colloid and interfacial phenomena in relation to systems of biological origin ; B, Biointerfaces N2 - A three dimensional biopolymer network structure with incorporated nano-porous calcium phosphate (CaP) balls was fabricated by using gelatin-chitosan (GC) polymer blend and GC stabilized olive/silicone oil Janus emulsions, respectively. The emulsions were freeze-dried, and the oil droplets were washed out in order to prepare porous scaffolds with larger surface area. The morphology, pore size, chemical composition, thermal and swelling behavior was studied by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and micro-Differential Scanning Calorimetry (micro-DSC). Microscopic analysis confirmed that the pore size of the GC based sponges after freeze-drying may be drastically reduced by using Janus emulsions. Besides, the incorporation of nanoporous calcium phosphate balls is also lowering the pore size and enhancing thermal stability. (C) 2016 Elsevier B.V. All rights reserved. KW - Janus emulsions KW - Calcium phosphates KW - Gelatin-chitosan scaffolds Y1 - 2016 U6 - https://doi.org/10.1016/j.colsurfb.2016.05.018 SN - 0927-7765 SN - 1873-4367 VL - 145 SP - 347 EP - 352 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kovach, Ildyko A1 - Koetz, Joachim A1 - Friberg, Stig E. T1 - Janus emulsions stabilized by phospholipids JF - Colloids and surfaces : an international journal devoted to the principles and applications of colloid and interface science ; A, Physicochemical and engineering aspects N2 - Janus emulsions were formed by mixing three immiscible liquids; this implies two oil components (i.e. olive oil (00) and silicone oil (SiO)) with water in presence of interfacial active components. The morphology and size of Janus droplets formed strongly depended on the type of surfactant used. In presence of a non-ionic surfactant, i.e. Tween 80, large engulfed Janus droplets were formed. By adding phospholipids to the system the droplet size was decreased and more stable Janus droplets formed. Interfacial tension measurements carried out using a spinning drop apparatus and a ring tensiometer demonstrate that interfacial tension is the most important factor controlling the size, morphology and stability of Janus droplets. When the interfacial tension between oil and water becomes <= 1 mN/m, smaller Janus droplets are formed. Such conditions are fulfilled when phospholipids are used in combination with non-ionic surfactant Tween 80. The morphology of the double droplets is predominantly controlled by the viscosity and interfacial tension between the two oil phases. By using different types of phospholipids, i.e. asolectin and lecithin instead of a more concentrated phosphatidylcholine (phospholipon), the interfacial tension is decreased and different morphologies of engulfing can be observed. KW - Janus emulsions KW - Spinning drop KW - Interfacial tension KW - Phospholipids Y1 - 2014 U6 - https://doi.org/10.1016/j.colsurfa.2013.08.065 SN - 0927-7757 SN - 1873-4359 VL - 441 SP - 66 EP - 71 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hasinovic, Hida A1 - Boggs, Cami A1 - Friberg, Stig E. A1 - Kovach, Ildiko A1 - Koetz, Joachim T1 - Janus emulsions from a one-step process; optical microscopy images JF - Journal of dispersion science and technology N2 - The optical microscopy images of an emulsion are commonly distorted when viewed between a cover glass and a planar microscopy slide. An alternative method is to place the sample on a slide with a cavity, which in turn suffers from incomplete information for high internal phase ratio (HIPR) emulsions, due to the inevitable crowding of the drops. This problem is particularly acute for more complex emulsions, such as those with Janus drops, for which a detailed image of the drop is essential. A number of publications have recently described Janus emulsions prepared by a one-step high energy emulsification process with microscopy images obtained by the sample between a planar slide and a cover glass. The correlation to the morphology of emulsions in bulk of these images is critical, but, so far, a potential equivalence has not been established. Since the images are central in order to understand why Janus emulsions should form under such conditions, the need to ascertain any such association is urgent. With this contribution, we compare images from different microscopy methods to those of gently diluted HIPR emulsions. The results reveal that the images of the emulsion samples between a cover glass and a planar microscope slide actually present a realistic representation of the drop topology in bulk emulsions. KW - Janus drops KW - Emulsification KW - microemulsions KW - emulsion microscopy Y1 - 2014 U6 - https://doi.org/10.1080/01932691.2013.801019 SN - 0193-2691 SN - 1532-2351 VL - 35 IS - 5 SP - 613 EP - 618 PB - Taylor & Francis Group CY - Philadelphia 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 - Kosmella, Sabine A1 - Koetz, Joachim A1 - Friberg, Stig E. A1 - Mackay, R. A. T1 - Interactions of polyelectrolytes with the lyotropic liquid crystalline system - hexadecyltrimethylammonium bromide / decanol / water Y1 - 1996 SN - 0927-7757 ER - TY - JOUR A1 - Kosmella, Sabine A1 - Koetz, Joachim A1 - Friberg, Stig E. A1 - Mackay, R. A T1 - Interactions of polyelectrolytes with the lyotropic liquid crystalline system Na-dodecylsulfate / decanol / water Y1 - 1996 ER - TY - JOUR A1 - Ruppelt, Dirk A1 - Koetz, Joachim A1 - Jaeger, Werner A1 - Friberg, Stig E. A1 - Mackay, R. A. T1 - The influence of cationic polyelectrolytes on structure formation in lamellar liquid crystalline systems Y1 - 1997 ER - TY - JOUR A1 - Beyermann, Jochen A1 - Koetz, Joachim A1 - Jäger, Werner A1 - Friberg, Stig E. T1 - Influence of charge density of anionic polyelectrolytes on structure formation in liquid crystalline systems Y1 - 1999 ER - TY - JOUR A1 - Beitz, Toralf A1 - Koetz, Joachim A1 - Friberg, Stig E. T1 - Polymer-modified ionic microemulsion formed in the system SDS/Water/Xylene/Pentanol Y1 - 1999 ER - TY - JOUR A1 - Bechthold, Nina A1 - Tiersch, Brigitte A1 - Koetz, Joachim A1 - Friberg, Stig E. T1 - Structure Formation in polymer-modified liquid crystals Y1 - 1999 ER - TY - JOUR A1 - Beitz, Toralf A1 - Koetz, Joachim A1 - Wolf, Gunter A1 - Kleinpeter, Erich A1 - Friberg, Stig E. T1 - Poly(N-vinyl-2-pyrrolidone) and 1-octyl-2-pyrrolidinone modified ionic microemulsions Y1 - 2001 ER -