Self-similar chain conformations in polymer gels

We use molecular dynamics simulations to study the swelling of randomly end-cross-linked polymer networks in good solvent conditions. We find that the equilibrium degree of swelling saturates at Q_eq = N_e**(3/5) for mean strand lengths N_s exceeding the melt entanglement length N_e. The internal structure of the network strands in the swollen state is characterized by a new exponent nu=0.72. Our findings are in contradiction to de Gennes' c*-theorem, which predicts Q_eq proportional N_s**(4/5) and nu=0.588. We present a simple Flory argument for a self-similar structure of mutually interpenetrating network strands, which yields nu=7/10 and otherwise recovers the classical Flory-Rehner theory. In particular, Q_eq = N_e**(3/5), if N_e is used as effective strand length.Comment: 4 pages, RevTex, 3 Figure

PHF3 regulates neuronal gene expression through the Pol II CTD reader domain SPOC

The C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) is a regulatory hub for transcription and RNA processing. Here, we identify PHD-finger protein 3 (PHF3) as a regulator of transcription and mRNA stability that docks onto Pol II CTD through its SPOC domain. We characterize SPOC as a CTD reader domain that preferentially binds two phosphorylated Serine-2 marks in adjacent CTD repeats. PHF3 drives liquid-liquid phase separation of phosphorylated Pol II, colocalizes with Pol II clusters and tracks with Pol II across the length of genes. PHF3 knock-out or SPOC deletion in human cells results in increased Pol II stalling, reduced elongation rate and an increase in mRNA stability, with marked derepression of neuronal genes. Key neuronal genes are aberrantly expressed in Phf3 knock-out mouse embryonic stem cells, resulting in impaired neuronal differentiation. Our data suggest that PHF3 acts as a prominent effector of neuronal gene regulation by bridging transcription with mRNA decay

Segmental order in a uniaxially constrained polydimethylsiloxane network : a deuterium magnetic resonance study

The orientational order generated in a cross-linked rubber by a uniaxial stress is probed with deuterium NMR. Spectra of perdeuterated polymer chains of a polydimethylsiloxane model network exhibit quadrupolar doublets under both elongation and compression. Experiments for various orientations of the stress relative to the spectrometer magnetic field show that an uniaxial anisotropy is induced at the level of the chain segments. The doublet splitting has an explicit dependence on the extension ratio.L'ordre orientationnel induit dans un réseau élastique sous contrainte uniaxiale est étudié par RMN du deutérium. Les spectres de chaînes perdeutérées d'un réseau modèle de polydiméthylsiloxane sous tension ou compression présentent un doublet quadrupolaire. Des expériences pour différentes orientations de la contrainte par rapport au champ magnétique du spectromètre montrent qu'une anisotropie uniaxiale est mesurée au niveau des segments du polymère. De plus l'écartement du doublet a une dépendance explicite en fonction du taux d'élongation

Incorporation and distribution of noble metal atoms in polyacrylonitrile colloidal particles using different polymerization strategies

This work is focused on the incorporation of inorganic compounds into an organic framework. More precisely, noble metals are being incorporated in-situ in polyacrylonitrile colloidal particles (CPs) using, scalable and reproducible synthesis routes. For this purpose, oil-soluble platinum- and palladium-based precursors are used for physical entrapment based on mini-emulsion polymerization, while water soluble precursors of the same metals are used for the incorporation via chemical entrapment based on conventional emulsion polymerization. For the latter, it is shown that one can well alter the spatial distribution of the metal within the CPs by tuning the feeding strategy of the precursor. In addition, chemical entrapment requires the complexation of the metal with acrylonitrile, thus resulting in the incorporation of single atoms and dimers, as suggested by both X-ray absorption spectroscopy and indirectly by NMR-titration. The visualization of the extent of incorporation was performed by STEM-EDX on all synthesized CPs, while ICP-OES was applied for a quantitative evaluation

Polyacrylonitrile Nanoparticle-Derived Hierarchical Structure for CO2 Capture

The production of porous clusters by controlled aggregation of polyacrylonitrile nanoparticles and thermal treatment, and their application to CO2 capture are reported. The synthesis of the primary particles by emulsion polymerization exhibits good reproducibility and is easy to scale up. The subsequent gelation of the produced latexes (controlled destabilization by salt addition) results in the formation of macroporous monoliths of nanoparticles with a mean pore diameter of 100 nm. A carefully assessed thermal treatment is applied to the dried monolith after grinding. The produced porous clusters are processed with three high-temperature steps: oxidation, stabilization, and pyrolysis. The latter allows for the creation of micropores in the initially non-porous nanoparticles, thus enabling access to the remaining nitrogen-bearing species present in the pyrolyzed polymer. The relative contributions of the remaining nitrogen-bearing species and of the micropores are elucidated by applying different oxidation temperatures. In particular, the fraction of the pores with diameter smaller than 0.7 nm is decisive in determining the final capture ability. After a treatment including oxidation at 240 °C, stabilization at 350 °C, and pyrolysis at 900 °C, the best reported material shows an average CO2 adsorption capacity of 3.56±0.17 mol (CO2) kg−1 at 0 °C and 1 atm

Recent outbreak of chilblain‐like lesions is not directly related to SARS‐CoV‐2 infection

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Mechanical phase inversion of Pickering emulsions: Via metastable wetting of rough colloids

The possibility to invert emulsions from oil-in-water to water-in-oil (or vice versa) in a closed system, i.e. without any formulation change, remains an open fundamental challenge with many opportunities for industrial applications. Here, we propose a mechanism that exploits particle surface roughness to induce metastable wetting and obtain mechanically-responsive Pickering emulsions. We postulate that the phase inversion is driven by an in situ switch of the particle wettability from metastable positions at the interface following the input of controlled mechanical energy. Oil-in-water emulsions can be prepared at low energy using mildly hydrophobic rough colloids, which are dispersed in water and weakly pinned at the interface, and switched to water-in-oil emulsions by a second emulsification at higher energy, which triggers the relaxation of the particle contact angle. The same principle is demonstrated for the complementary emulsions using mildly hydrophilic colloids initially dispersed in oil. Our experiments and simulations support that the delicate interplay between particle surface design during synthesis and the energy of the emulsification process can encode a kinetic pathway for the phase inversion. Both organic and inorganic nanoparticles can be used, allowing for the future implementation of our strategy in a broad range of smart industrial formulations