Dynamics of suspensions of hydrodynamically structured particles: Analytic theory and experiment

We present an easy-to-use analytic toolbox for the calculation of short-time transport properties of concentrated suspensions of spherical colloidal particles with internal hydrodynamic structure, and direct interactions described by a hard-core or soft Hertz pair potential. The considered dynamic properties include self-diffusion and sedimentation coefficients, the wavenumber-dependent diffusion function determined in dynamic scattering experiments, and the high-frequency shear viscosity. The toolbox is based on the hydrodynamic radius model (HRM) wherein the internal particle structure is mapped on a hydrodynamic radius parameter for unchanged direct interactions, and on an existing simulation data base for solvent-permeable and spherical annulus particles. Useful scaling relations for the diffusion function and self-diffusion coefficient, known to be valid for hard-core interaction, are shown to apply also for soft pair potentials. We further discuss extensions of the toolbox to long-time transport properties including the low-shear zero-frequency viscosity and the long-time self-diffusion coefficient. The versatility of the toolbox is demonstrated by the analysis of a previous light scattering study of suspensions of non-ionic PNiPAM microgels [Eckert et al., J. Chem. Phys., 2008, 129, 124902] in which a detailed theoretical analysis of the dynamic data was left as an open task. By the comparison with Hertz potential based calculations, we show that the experimental data are consistently and accurately described using the Verlet-Weis corrected Percus-Yevick structure factor as input, and for a solvent penetration length equal to three percent of the excluded volume radius. This small solvent permeability of the microgel particles has a significant dynamic effect at larger concentrations.Comment: 25 pages, 24 figure

Об инвариантности кинематических базисных матриц планетарных рядов при анализе кинематики трансмиссий транспортных средств

Предложена универсальная матричная методика расчета кинематики планетарных механизмов. Показано, что кинематические матричные системы планетарных механизмов, несмотря на отличие в записи с различными значениями характерных параметров сателлитов, инвариантны по отношению к вектору неизвестных.The universal matrix design procedure of kinematics of planetary mechanisms is offered. It is shown, that kinematics matrix systems of planetary mechanisms, despite of distinction in record with different values of characteristic parameters of satellites, invariance in relation to a vector of unknown persons

Metallocene o-Phenylenebis(phenylphosphido) Chelates of Molybdenum and Tungsten

The reaction of the metallocene dichlorides Cp2MCl2 (Cp = η5-C5H5; M = Mo, W) with equimolar amounts of dilithium-o-phenylenebis(phenylphosphide) 1,2-(LiPPh)2C6H4 yields the five-membered chelate complexes Cp2M[1,2-(PPh)2C6H4] (M = Mo. 1; W, 2). Compounds 1 and 2 are characterized by IR, NMR and mass spectra

Gelation Of Bio–Polyelectrolytes: Interplay Between Backbone Hydrophobicity, Counterion Specificity And Counterion Valence

We study the rheological properties of carboxymethyl cellulose with counter-ions of different valences and binding constants. Increasing the counterion valence or its binding constant to the polymer backbone promotes inter-chain associations, which lead, above the entanglement concentration, to an increase in the solution viscosity and plateau modulus. At sufficiently high polymer concentrations, these interactions become sufficiently strong to cause the formation of weak gels. A different approach to promote inter-chain associations (and thereby gelation) is to increase the hydrophobicity of the polymer backbone. This is achieved by varying the average fraction of carboxymethyl groups substituted in each cellulose unit, also known as the degree of substitution. Combining these two approaches allows us to design the flow properties of carboxymethyl cellulose solutions and gels as well as to tune their response to changes in environmental conditions such as ionic strength, pH, or solvent composition

Adaptive microgels in complexes and at interfaces

Microgels are macromolecular networks swollen by the solvent they are dissolved in. They are unique systems that are distinctly different from common colloids, such as, e.g., rigid nanoparticles, flexible macromolecules, micelles or vesicles. When swollen, they are soft and have a fuzzy surface with dangling chains and the presence of cross-links provides structural integrity - in contrast to linear and (hyper-) branched polymers. Obviously, the cross-linker content will allow controlling whether microgels behave more ”colloidal” or ”macromolecular”. Finally, microgels reveal interfacial activity without being amphiphilic. The combination of being soft and porous while still having a stable structure through the cross-linked network allows for the possibility to introduce chemical functionality at different positions. The architectural diversity and compartmentalization of reactive groups enable thus short-range coexistence of otherwise unstable combinations of chemical reactivity. The capability of microgels to adjust both their shape and volume in response to external stimuli provides the opportunity to reversibly tune their physico-chemical properties. From a physics point of view, microgels are particularly intriguing and challenging, since their intra-particle properties are intimately linked to their inter-particle behavior. We will discuss the interaction of microgels of different architecture as, e.g., core-shell, hollow and multi-shell hollow microgels with polyelectrolytes and proteins. The formation of polyelectrolyte complexes was studied and especially amphoteric microgels enable controlled uptake and release. The solution structure was determined by means of neutron and light scattering as well as by (super-resolved) fluorescence microscopy. Furthermore, we investigate the influence of the structure of microgels on their behavior at interfaces. Here, the structure was probed by means of scanning force and electron microscopy. Compression isotherms of the microgel-laden oil-water interfaces reveal spreading of the microgels at the interface and counter-intuitive influences of charged groups and cross-link density on the compression modulus. The experimental results are fully supported by computer simulations and illustrate the special behavior of soft microgels at interfaces. Plamper, F. A.; Richtering, W. Functional Microgels and Microgel Systems. Accounts of Chemical Research 2017, 50, 131–140. Yaroslavov, A.; Panova, I.; Sybachin, A.; Spiridonov, V.; Zezin, A.; Mergel, O.; Gelissen, A.; Tiwari, R.; Plamper, F.; Richtering, W.; et al. Payload Release by Liposome Burst: Thermal Collapse of Microgels Induces Satellite Destruction. Nanomedicine: nanotechnology, biology, and medicine 2017, DOI:10.1016/j.nano.2017.02.001 Gelissen, A. P. H.; Oppermann, A.; Caumanns, T.; Hebbeker, P.; Turnhoff, S. K.; Tiwari, R.; Eisold, S.; Simon, U.; Lu, Y.; Mayer, J.; et al. 3D Structures of Responsive Nanocompartmentalized Microgels. Nano Lett. 2016, 16, 7295–7301. Schmid, A. J.; Dubbert, J.; Rudov, A. A.; Pedersen, J. S.; Lindner, P.; Karg, M.; Potemkin, I. I.; Richtering, W. Multi-Shell Hollow Nanogels with Responsive Shell Permeability. Scientific Reports 2016, 6, 22736. Sigolaeva, L. V.; Mergel, O.; Evtushenko, E. G.; Gladyr, S. Y.; Gelissen, A. P. H.; Pergushov, D. V.; Kurochkin, I. N.; Plamper, F. A.; Richtering, W. Engineering Systems with Spatially Separated Enzymes via Dual-Stimuli- Sensitive Properties of Microgels. Langmuir 2015, 31, 13029–13039. Geisel, K.; Isa, L.; Richtering, W. The Compressibility of pH-Sensitive Microgels at the Oil-Water Interface: Higher Charge Leads to Less Repulsion. Angew. Chem. Int. Ed. Engl. 2014, 53, 4905–4909

Temperature-sensitive Soft Microgels at Interfaces: Air-Water versus Oil-Water

The formation of smart emulsions or foams whose stability can be controlled on-demand by switching external parameters is of great interest for basic research and applications. An emerging group of smart stabilizers are microgels, which are nano- and micro-sized, three-dimensional polymer networks that are swollen by a good solvent. In the last decades, the influence of various external stimuli on the two-dimensional phase behavior of microgels at air- and oil-water interfaces has been studied. However, the impact of the top-phase itself has been barely considered. Here, we present data that directly address the influence of the top-phase on the microgel properties at interfaces. The dimensions of pNIPAM microgels are measured after deposition from two interfaces, i.e., air- and decane-water. While the total in-plane size of the microgel increases with increasing interfacial tension, the portions or fractions of the microgels situated in the aqueous phase are not affected. We correlate the area microgels occupy to the surface tensions of the interfaces, which allows to estimate an elastic modulus. In comparison to nanoindentation measurements, we observe a larger elastic modulus for the microgels. By combining compression, deposition, and visualization, we show that the two-dimensional phase behavior of the microgel monolayers is not altered, although the microgels have a larger total in-plane size at higher interfacial tension. A peer reviewed and extended version of this preprint and the electronic supplementary information can be found under S.~Bochenek, A.~Scotti, W.~Richtering, \textit{Soft Matter}, 2020, DOI: 10.1039/d0sm01774d

Aggregate real exchange rate persistence through the lens of sectoral data

15 páginas, 2 figuras, 3 tablas.-- El pdf es la versión pre-print del artículo.-- Trabajo presentado a la conferencia "Microeconomic Sources of Real Exchange Rates" (Vanderbilt University-USA, 2010).A novel approach to analyzing real exchange rate (RER) persistence and its sources is presented. Using highly disaggregated data for a group of EU-15 countries, it is shown that the distribution of sectoral persistence is highly heterogeneous and skewed to the right, so that a limited number of sectors are responsible for the high levels of persistence observed at the aggregate level. Quantile regression has been employed to investigate whether traditional theories, such as the lack of arbitrage due to nontradability or imperfect competition combined with price stickiness, are able to account for the slow reversion to parity of RERs.Financial support from the Spanish Government CICYT projects SEJ2006-00369 and ECO2008-03040Peer reviewe