@article{vonKlitzingStehlPogrzebaetal.2017, author = {von Klitzing, Regine and Stehl, Dimitrij and Pogrzeba, Tobias and Schoma{\"a}cker, Reinhard and Minullina, Renata and Panchal, Abhishek and Konnova, Svetlana and Fakhrullin, Rawil and Koetz, Joachim and Moehwald, Helmuth and Lvov, Yuri}, title = {Halloysites Stabilized Emulsions for Hydroformylation of Long Chain Olefins}, series = {Advanced materials interfaces}, volume = {4}, journal = {Advanced materials interfaces}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {2196-7350}, doi = {10.1002/admi.201600435}, pages = {8}, year = {2017}, abstract = {Halloysites as tubular alumosilicates are introduced as inexpensive natural nanoparticles to form and stabilize oil-water emulsions. This stabilized emulsion is shown to enable efficient interfacial catalytic reactions. Yield, selectivity, and product separation can be tremendously enhanced, e.g., for the hydroformylation reaction of dodecene to tridecanal. In perspective, this type of formulation may be used for oil spill dispersions. The key elements of the described formulations are clay nanotubes (halloysites) which are highly anisometric, can be filled by helper molecules, and are abundantly available in thousands of tons, making this technology scalable for industrial applications.}, language = {en} } @article{VargasRuizSchulreichKostevicetal.2016, author = {Vargas-Ruiz, Salome and Schulreich, Christoph and Kostevic, Angelika and Tiersch, Brigitte and Koetz, Joachim and Kakorin, Sergej and von Klitzing, Regine and Jung, Martin and Hellweg, Thomas and Wellert, Stefan}, title = {Extraction of model contaminants from solid surfaces by environmentally compatible microemulsions}, series = {Journal of colloid and interface science}, volume = {471}, journal = {Journal of colloid and interface science}, publisher = {Elsevier}, address = {San Diego}, issn = {0021-9797}, doi = {10.1016/j.jcis.2016.03.006}, pages = {118 -- 126}, year = {2016}, abstract = {In the present contribution, we evaluate the efficiency of eco-friendly microemulsions to decontaminate solid surfaces by monitoring the extraction of non-toxic simulants of sulfur mustard out of model surfaces. The extraction process of the non-toxic simulants has been monitored by means of spectroscopic and chromatographic techniques. The kinetics of the removal process was analyzed by different empirical models. Based on the analysis of the kinetics, we can assess the influence of the amounts of oil and water and the microemulsion structure on the extraction process. (C) 2016 Elsevier Inc. All rights reserved.}, language = {en} } @article{DodooBalzerHugeletal.2013, author = {Dodoo, Samuel and Balzer, Bizan N. and Hugel, Thorsten and Laschewsky, Andr{\´e} and von Klitzing, Regine}, title = {Effect of ionic strength and layer number on swelling of polyelectrolyte multilayers in water vapour}, series = {Soft materials}, volume = {11}, journal = {Soft materials}, number = {2}, publisher = {Taylor \& Francis Group}, address = {Philadelphia}, issn = {1539-445X}, doi = {10.1080/1539445X.2011.607203}, pages = {157 -- 164}, year = {2013}, abstract = {The swelling behavior of polyelectrolyte multilayers (PEMs) of poly(sodium-4 styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared from aqueous solution of 0.1 M and 0.5 M NaCl are investigated by ellipsometry and Atomic Force Microscopy (AFM). From 1 double-layer up to 4 double-layers of 0.1 M NaCl, the amount of swelling water in the PEMs decreases with increasing number of adsorbed double layers due to an increase in polyelectrolyte density as a result of the attraction between the positively charged outermost PDADMAC layer and the Si substrate. From 6 double layers to 30 double layers, the attraction is reduced due to a much larger distance between substrate and outermost layer leading to a much lower polyelectrolyte density and higher swelling water. In PEMs prepared from aqueous solution of 0.5 M NaCl, the amount of water constantly increases which is related to a monotonically decreasing polyelectrolyte density with increasing number of polyelectrolyte layers. Studies of the surface topology also indicate a transition from a more substrate affected interphase behavior to a continuum properties of the polyelectrolyte multilayers. The threshold for the transition from interphase to continuum behavior depends on the preparation conditions of the PEM.}, language = {en} } @article{MicciullaDodooChevignyetal.2014, author = {Micciulla, Samantha and Dodoo, Samuel and Chevigny, Chloe and Laschewsky, Andr{\´e} and von Klitzing, Regine}, title = {Short versus long chain polyelectrolyte multilayers: a direct comparison of self-assembly and structural properties}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {16}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {40}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c4cp03439b}, pages = {21988 -- 21998}, year = {2014}, abstract = {Successful layer-by-layer (LbL) growth of short chain (similar to 30 repeat units per chain) poly(sodium styrene sulfonate) (PSS)-poly(diallyl dimethylammonium chloride) (PDADMAC) multilayers is presented for the first time and compared with the growth of equivalent long chain polyelectrolyte multilayers (PEMs). A detailed study performed by quartz crystal microbalance with dissipation (QCM-D) is carried out and three main processes are identified: (i) initial mass uptake, (ii) adsorption desorption during layer equilibration and (iii) desorption during rinsing. In contrast to the high stability and strong layer increment of high molecular weight (HMW) PEMs, layer degradation characterizes low molecular weight (LMW) multilayers. In particular, two different instability phenomena are observed: a constant decrease of sensed mass during equilibration after PDADMAC adsorption, and a strong mass toss by salt-free rinsing after PSS adsorption. Yet, an increase of salt concentration leads to much stronger layer growth. First, when the rinsing medium is changed from pure water to 0.1 M NaCl, the mass loss during rinsing is reduced, irrespective of molecular weight. Second, an increase in salt concentration in the LMW PE solutions causes a larger increment during the initial adsorption step, with no effect on the rinsing. Finally, the mechanical properties of the two systems are extracted from the measured frequency and dissipation shifts, as they offer a deeper insight into the multilayer structures depending on chain length and outermost layer. The paper enriches the field of PE assembly by presenting the use of very short PE chains to form multilayers and elucidates the role of preparation conditions to overcome the limitation of layer stability.}, language = {en} } @article{KristenHochreinLaschewskyMilleretal.2011, author = {Kristen-Hochrein, Nora and Laschewsky, Andr{\´e} and Miller, Reinhard and von Klitzing, Regine}, title = {Stability of foam Films of oppositely charged polyelectrolyte/surfactant mixtures - effect of isoelectric point}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {115}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {49}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp206964k}, pages = {14475 -- 14483}, year = {2011}, abstract = {In the present paper, the influence of the surfactant concentration and the degree of charge of a polymer on foam film properties of oppositely charged polyelectrolyte/surfactant mixtures has been investigated. To verify the assumption that the position of the isoelectric point (IEP) does not change the character of the foam film stabilities, the position of the IEP of the polyelectrolyte/surfactant mixtures has been shifted in two different ways. Within the first series of experiments, the foam. film properties were studied using a fixed surfactant concentration of 3 x 10(-5) M in the mixture. Due to the low surfactant concentration, this is a rather dilute system. In the second approach, a copolymer of nonionic and ionic monomer units was Used to lower the charge density of the polymer. This gave rise to additional interactions between the polyelectrolyte and the surfactant, which makes the description of the foam film behavior more complex. In both systems, the same characteristics of the foam film stabilities were found: The foam film stability is reduced toward the IEP of the system, followed by a destabilization around the IEP., At polyelectrolyte concentrations above the IEP, foam films are very stable. However, the concentration range where unstable films were formed was rather broad, and the mechanisms leading to the destabilization had different origins. The results were compared with former findings on PAMPS/C(14)TAB mixtures with an IEP of 10(-4)M.(1)}, language = {en} } @article{ZerballLaschewskyvonKlitzing2015, author = {Zerball, Maximilian and Laschewsky, Andr{\´e} and von Klitzing, Regine}, title = {Swelling of Polyelectrolyte Multilayers: The Relation Between, Surface and Bulk Characteristics}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {119}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.5b04350}, pages = {11879 -- 11886}, year = {2015}, abstract = {The odd even effect, i.e., the influence of the outermost layer of polyelectrolyte multilayers (PEMs) on their swelling behavior, is investigated. For that purpose poly(styrene sodium sulfonate) (PSS)/poly(diallyl-dimethylammonium chloride) (PDADMAC) polyelectrolyte multilayers are studied in air with 1\% relative humidity (RH), 30\% RH, 95\% RH, and in liquid water by ellipsometry, atomic force microscopy (AFM), and X-ray reflectometry (XRR). Since the total amount of water uptake in swollen PEMs is divided into two fractions, the void water and the swelling water, a correct evaluation of the odd even effect is only possible if both fractions are examined separately. In order to allow measuring samples over a larger thickness regime the investigation of a larger amount of samples is required. Therefore, the concept of separating void water from swelling water using neutron reflectometry is for the first time transferred to ellipsometry. The subsequent analysis of swelling water, void water, and roughness revealed the existence of two types of odd even effects: an odd even effect which addresses only the surface of the PEM (surface-odd even effect) and an odd even effect which addresses also the bulk of the PEM (bulk-odd even effect). The appearance of both effects is dependent on the environment; the surface-odd even effect is only detectable in humid air while the bulk-odd even effect is only detectable in liquid water. The bulk-odd even effect is related to the osmotic pressure between the PEM and the surrounding water. A correlation between the amount of void water and both odd even effects is not found. The amount of void water is independent of the terminated layer and the thickness of PEMs.}, language = {en} } @article{DodooSteitzLaschewskyetal.2011, author = {Dodoo, S. and Steitz, R. and Laschewsky, Andr{\´e} and von Klitzing, Regine}, title = {Effect of ionic strength and type of ions on the structure of water swollen polyelectrolyte multilayers}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {21}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp01357a}, pages = {10318 -- 10325}, year = {2011}, abstract = {This study addresses the effect of ionic strength and type of ions on the structure and water content of polyelectrolyte multilayers. Polyelectrolyte multilayers of poly(sodium-4-styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared at different NaF, NaCl and NaBr concentrations have been investigated by neutron reflectometry against vacuum, H2O and D2O. Both thickness and water content of the multilayers increase with increasing ionic strength and increasing ion size. Two types of water were identified, "void water" which fills the voids of the multilayers and does not contribute to swelling but to a change in scattering length density and "swelling water" which directly contributes to swelling of the multilayers. The amount of void water decreases with increasing salt concentration and anion radius while the amount of swelling water increases with salt concentration and anion radius. This is interpreted as a denser structure in the dry state and larger ability to swell in water (sponge) for multilayers prepared from high ionic strengths and/or salt solution of large anions. No exchange of hydration water or replacement of H by D was detected even after eight hours incubation time in water of opposing isotopic composition.}, language = {en} } @article{SchimkaGordievskayaLomadzeetal.2017, author = {Schimka, Selina and Gordievskaya, Yulia D. and Lomadze, Nino and Lehmann, Maren and von Klitzing, Regine and Rumyantsev, Artem M. and Kramarenko, Elena Yu. and Santer, Svetlana}, title = {Communication: Light driven remote control of microgels' size in the presence of photosensitive surfactant: Complete phase diagram}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {147}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4986143}, pages = {5}, year = {2017}, abstract = {Here we report on a light triggered remote control of microgel size in the presence of photosensitive surfactant. The hydrophobic tail of the cationic surfactant contains azobenzene group that undergoes a reversible photo-isomerization reaction from a trans-to a cis-state accompanied by a change in the hydrophobicity of the surfactant. We have investigated light assisted behaviour and the complex formation of the microgels with azobenzene containing surfactant over the broad concentrational range starting far below and exceeding several times of the critical micelle concentration (CMC). At small surfactant concentration in solution (far below CMC), the surfactant in the trans-state accommodates within the microgel causing its compaction, while the cis-isomer desorbs out of microgel resulting in its swelling. The process of the microgel size change can be described as swelling on UV irradiation (trans-cis isomerization) and shrinking on irradiation with blue light (cis-trans isomerization). However, at the surfactant concentrations larger than CMC, the opposite behaviour is observed: the microgel swells on blue irradiation and shrinks during exposure to UV light. We explain this behaviour theoretically taking into account isomer dependent micellization of surfactant within the microgels. Published by AIP Publishing.}, language = {en} } @article{ZakrevskyyRichterZakrevskaetal.2012, author = {Zakrevskyy, Yuriy and Richter, Marcel and Zakrevska, Svitlana and Lomadze, Nino and von Klitzing, Regine and Santer, Svetlana}, title = {Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant}, series = {Advanced functional materials}, volume = {22}, journal = {Advanced functional materials}, number = {23}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1616-301X}, doi = {10.1002/adfm.201200617}, pages = {5000 -- 5009}, year = {2012}, abstract = {The light-induced reversible switching of the swelling of microgel particles triggered by photo-isomerization and binding/unbinding of a photosensitive azobenzene-containing surfactant is reported. The interactions between the microgel (N-isopropylacrylamide, co-monomer: allyl acetic acid, crosslinker: N,N'-methylenebisacrylamide) and the surfactant are studied by UV-Vis spectroscopy, dynamic and electrophoretic light scattering measurements. Addition of the surfactant above a critical concentration leads to contraction/collapse of the microgel. UV light irradiation results in trans-cis isomerization of the azobenzene unit incorporated into the surfactant tail and causes an unbinding of the more hydrophilic cis isomer from the microgel and its reversible swelling. The reversible contraction can be realized by blue light irradiation that transfers the surfactant back to the more hydrophobic trans conformation, in which it binds to the microgel. The phase diagram of the surfactant-microgel interaction and transitions (aggregation, contraction, and precipitation) is constructed and allows prediction of changes in the system when the concentration of one or both components is varied. Remote and reversible switching between different states can be realized by either UV or visible light irradiation.}, language = {en} } @article{RichterZakrevskyyEiseleetal.2014, author = {Richter, Marcel and Zakrevskyy, Yuriy and Eisele, Michael and Lomadze, Nino and Santer, Svetlana and von Klitzing, Regine}, title = {Effect of pH, co-monomer content, and surfactant structure on the swelling behavior of microgel-azobenzene-containing surfactant complex}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {55}, journal = {Polymer : the international journal for the science and technology of polymers}, number = {25}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2014.10.027}, pages = {6513 -- 6518}, year = {2014}, abstract = {The contraction/swelling transition of anionic PNIPAM-co-AAA particles can be manipulated by light using interactions with cationic azobenzene-containing surfactant. In this study the influence of pH-buffers and their concentrations, the charge density (AAA content) in microgel particles as well as the spacer length of the surfactant on the complex formation between the microgel and surfactant is investigated. It is shown that the presence of pH buffer can lead to complete blocking of the interactions in such complexes and the resulting microgel contraction/swelling response. There is a clear competition between the buffer ions and the surfactant molecules interacting with microgel particles. When working in pure water solutions with fixed concentration (charge density) of microgel, the contraction/swelling of the particles is controlled only by relative concentration (charge ratio) of the surfactant and AAA groups of the microgel. Furthermore, the particle contraction is more efficient for shorter spacer length of the surfactant. The onset point of the contraction process is not affected by the surfactant hydrophobicity. This work provides new insight into the interaction between microgel particles and photo-sensitive surfactants, which offers high potential in new sensor systems. (C) 2014 Elsevier Ltd. All rights reserved.}, language = {en} }