Rheological Control Of Microemulsions Is Possible By Admixture Of End–Capped Multi–Arm Polymers Of Different Functionality – A Study Of Structure And Dynamics

For many applications the interesting properties of microemulsion, which are thermodynamically stable mixture of oil and water facilitated by the presence of a surfactant, are highly interesting. However, for many of these potential applications a much higher viscosity or even gelation would be asked for. Accordingly, mixtures of telechelic polymers and microemulsions are interesting systems from a practical point of view as by the addition of the polymer one is able to exert rheological control over a rather wide range. Furthermore they are model systems of networks where concentration of nodes and connectivity can be tuned separately, which allows for a systematic understanding of the control of the rheological properties of these materials. In our investigation we employed end-capped multi-arm polymers for the bridging of the microemulsion droplets which leads to network formation. For that purpose we employed tailor-made bridging amphiphilic polymers with multiple linkers, which were synthesized by the RAFT procedure with poly(N,N-dimethylacrylamide) (PDMA) as hydrophilic central block. This synthesis allows to control the number of arms (functionality), the length of the hydrophilic group (maximum length for connection) and of the hydrophobic chain (stickiness). We employed various multiply bridging polymers with 2, 3, or 4 arms (see figure) and investigated their effect on structure and dynamics of nonionic O/W microemulsion droplets with radii in the range of 2.5-7 nm. Please click Additional Files below to see the full abstract

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3- and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol−1, narrow molar mass distribution (PDI ≤ 1.2) and high end group functionality (∼90%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.EC/FP7/226507/EU/Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy/NMI

Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 140, 034902 (2014) and may be found at https://doi.org/10.1063/1.4861894.The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers.BMBF, 05K10KT1, Verbundprojekt NanoSOFT: Teilprojekt 2: Neutronen Spin-Echo Experimente zur Untersuchung komplexer Soft-Matter Systeme mit extremer Präzissio

Towards an Intrinsic Doppler Correction for X-ray Spectroscopy of Stored Ions at CRYRING@ESR

We report on a new experimental approach for the Doppler correction of X-rays emitted by heavy ions, using novel metallic magnetic calorimeter detectors which uniquely combine a high spectral resolution with a broad bandwidth acceptance. The measurement was carried out at the electron cooler of CRYRING@ESR at GSI, Darmstadt, Germany. The X-ray emission associated with the radiative recombination of cooler electrons and stored hydrogen-like uranium ions was investigated using two novel microcalorimeter detectors positioned under 0∘ and 180∘ with respect to the ion beam axis. This new experimental setup allowed the investigation of the region of the N, M → L transitions in helium-like uranium with a spectral resolution unmatched by previous studies using conventional semiconductor X-ray detectors. When assuming that the rest-frame energy of at least a few of the recorded transitions is well-known from theory or experiments, a precise measurement of the Doppler shifted line positions in the laboratory system can be used to determine the ion beam velocity using only spectral information. The spectral resolution achievable with microcalorimeter detectors should, for the first time, allow intrinsic Doppler correction to be performed for the precision X-ray spectroscopy of stored heavy ions. A comparison with data from a previous experiment at the ESR electron cooler, as well as the conventional method of conducting Doppler correction using electron cooler parameters, will be discussed

The Gut Microbiota in Cardiovascular Disease and Arterial Thrombosis

The gut microbiota has emerged as a contributing factor in the development of atherosclerosis and arterial thrombosis. Metabolites from the gut microbiota, such as trimethylamine N-oxide and short chain fatty acids, were identified as messengers that induce cell type-specific signaling mechanisms and immune reactions in the host vasculature, impacting the development of cardiovascular diseases. In addition, microbial-associated molecular patterns drive atherogenesis and the microbiota was recently demonstrated to promote arterial thrombosis through Toll-like receptor signaling. Furthermore, by the use of germ-free mouse models, the presence of a gut microbiota was shown to influence the synthesis of endothelial adhesion molecules. Hence, the gut microbiota is increasingly being recognized as an influencing factor of arterial thrombosis and attempts of dietary pre- or probiotic modulation of the commensal microbiota, to reduce cardiovascular risk, are becoming increasingly significant

Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (Meth)acrylates

We report on the controlled free radical homopolymerization of 1-ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4-ferrocenylbutyl acrylate, 2-ferrocenylamido-2-methylpropyl acrylate, and 4-ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1-ferrocenylethyl acrylate did not exceed 10,000 g mol-1, while for 4-ferrocenylbutyl (meth)acrylate molar masses of 15,000 g mol-1 could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved. © 2011 Wiley Periodicals, Inc