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We report on a new class of magnetoactive elastomers (MAEs) based on bottlebrush polymer networks filled with carbonyl iron microparticles. By synergistically combining solvent-free, yet supersoft polymer matrices, with magnetic microparticles, we enable the design of composites that not only mimic the mechanical behavior of various biological tissues but also permit contactless regulation of this behavior by external magnetic fields. While the bottlebrush architecture allows to finely tune the matrix elastic modulus and strain-stiffening, the magnetically aligned microparticles generate a 3-order increase in shear modulus accompanied by a switch from a viscoelastic to elastic regime as evidenced by a ca. 10-fold drop of the damping factor. The developed method for MAE preparation through solvent-free coinjection of bottlebrush melts and magnetic particles provides additional advantages such as injection molding of various shapes and uniform particle distribution within MAE composites. The synergistic combination of bottlebrush network architecture and magnetically responsive microparticles empowers new opportunities in the design of actuators and active vibration insulation systems.

The nanostructures of polyelectrolyte complexes (PECs) fabricated from a series of rationally designed oppositely charged amphiphilic random copolymers with variable comonomer compositions were stu...

A series of copolymers with controlled monomer sequences are prepared via the reversible addition–fragmentation chain transfer polymerization of tert-butyl carbamate (Boc)-l-alanine (VBA) and Boc-l...

A possibility of microphase separation in a blend of oppositely charged polyelectrolytes, being immiscible when uncharged, is studied theoretically and by means of dissipative particle dynamics (DP...

International audience; The instability of a homogeneous complex coacervate phase induced by incompatibility of oppositely charged polyelectrolytes is studied by means of the random phase approximation (RPA) and the scaling approach. It is found that in a poor solvent for both polyions their short-range mutual repulsions may result in the formation of a microphase separated structure at low salt concentrations cs. At high cs, a decomposition of the homogeneous coacervate into two macroscopic globular phases enriched either with polyanions or with polycations takes place. Both the RPA and scaling estimations predict the period of the microphase separated structure on the order of a few nanometers in the vicinity of the spinodal. The binodal of macroscopic phase separation of the coacervate and the spinodal with respect to the microphase separation are calculated, and the phase diagram of the coacervate is constructed in terms of salt concentration and incompatibility of polyions. The possibility of experimental observation of a microsegregated coacervate is discussed.

A joint theoretical and experimental study is devoted to the swelling and electrical conductivity of highly charged polyelectrolyte (PE) gels in media of different polarity. Deprotected poly(tert-butyl carbamate l-alanine) gels provided with fluorine, bromine, chlorine, sulfate, and trifluoroacetic counteranions demonstrated different conductivity in aqueous medium as well as solvent uptake in water/methanol mixtures. Counterion specificity in PE gel properties was theoretically explained in the framework of the model which treats ion association within the network as a two-stage process. Manning-type condensation, being the first condensation stage not affected by counterion type, provides understanding of a gel maximal swelling at intermediate degrees of gel ionization f and a slight gel contraction at f tending to unity, which were earlier observed in experimental investigations. The second ion association stage is an ion pairing influenced by the kind of counterion. Since a considerable fraction of io...

We report a combined experimental and theoretical study on the swelling behavior of polyelectrolyte gels with various types of counterions. Experimental research was focused on poly(methacrylic acid) and poly(acrylic acid) gels in methanol neutralized with different bases providing sodium, cesium, tetramethyl-, tetraethyl- or tetrabutylammonium counterions. The novelty of the theoretical treatment is that the counterion size is explicitly taken into account as well as the dependence of the ion association constant on the volume fraction of polymer within the gel. We demonstrate that, depending on the counterion size, three different regimes of the gel behavior are realized. In case of bulky tetrabutylammonium counterions the gel swells upon ionization. For small counterions (Na+, Cs+) the gel swelling at low ionization degrees is succeeded by its collapse. New type of behavior was observed and theoretically described for the gels with counterions of intermediate sizes (tetramethyl- and tetraethylammonium)...

We develop a theory of microphase separation in a solution precipitate of flexible AB block copolymers consisting of charged (A) and neutral (B) blocks which are complexed with oppositely charged linear chains (C) via electrostatic interactions. We analyze regimes of selective solvents: the solvent is Θ for the A blocks and the C chains, whereas it is poor for the B blocks. Despite the selectivity, stoichiometric complexes precipitate because of fluctuations induced electrostatic attraction. Depending on composition of the diblock copolymer, selectivity of the solvent and fraction of charged groups, direct and inverse spherical, cylindrical and lamellar structures can be stable in the precipitant. Phase diagrams are constructed in the strong segregation approximation. Morphological transitions induced by changes of solvent quality and fraction of charged groups are predicted.

The simplest theory of the collapse transition of single polyelectrolyte chains in dilute solutions is reconsidered. A novel feature of the new treatment is that the counterions can either remain within the coil or float in the outer solution. It is shown that the latter possibility is realized in many cases; thus, for these situations, the electrostatic repulsion between the uncompensated charges plays an important role in the chain behavior. These uncompensated charges lead to a significant difference between the collapse behavior of single chains and macroscopic gels where electrostatic repulsion is normally negligible and the swelling is mainly due to the osmotic pressure of counterions kept inside the gel sample. In addition the intermediate case of microgel particles of different molecular masses is considered, and the role of counterion redistribution between polymer and solution is investigated.

Several experimental facts indicate that the collapse transition in weakly charged polyelectrolyte gels or single macromolecules can take place with an increase in the degree of ionization (e.g., during titration of a weak polyacid). This unusual behavior can be explained by the energy gain from the formation of ion pairs in the collapsed state of low polarity, which competes with the swollen state where most of the counterions are dissociated. An increasing degree of ionization increases the thermodynamic advantages of the collapsed state with an ionomeric multiplet structure over the swollen polyelectrolyte state. In some regimes, this effect can lead to reentrant phase transition behavior, i.e., to an initial decollapse of the gel upon charging with subsequent jumplike collapse at a higher fraction of charged monomer units.