Covalent Hybrid Elastomers Based on Anisotropic Magnetic Nanoparticles and Elastic Polymers

Abstract

Particle-filled elastomers are ubiquitous composite materials with applications ranging from durable materials, such as tires, to smart actuators and sensor materials. By employing magnetic nanoparticles as multifunctional, inorganic cross-linkers, PDMS-based hybrid elastomers with a novel unique architecture and a defined type of particle-matrix interaction are obtaineda direct covalent coupling between magnetic and elastic properties. The resulting particle-cross-linked elastomers possess application potential due to their defined magnetomechanical coupling and their large extensibility. As the filler phase, spindle-shaped hematite nanoparticles with a silica shell are used, and the swelling, thermal, magnetic, and mechanical properties of the resulting particle-cross-linked elastomers are systematically evaluated and compared to the properties of analogous yet conventionally cross-linked particle-filled elastomers of a similar composition. Some unique features are found for the hybrid elastomers, such as a large strain at break of up to εB ≈ 1700%, that are attributed to the exceptional architecture, combining a well-integrated network of long polymer chains that are interconnected by network nodes with a high cross-linker functionality formed by the anisotropic magnetic nanoparticles.

Strain- and field-induced anisotropy in hybrid elastomers with elongated filler nanoparticles

“…For this purpose, we analyze the internal structure in well-defined hybrid elastomers of different architecture by means of a combination of methods under the influence of strain or magnetic fields. We compare the behavior of elastomers exclusively crosslinked via covalent polymer-particle linkage, 16 to that of conventionally crosslinked networks of similar composition with initially either isotropic or anisotropic distribution of the nanoparticles within the matrix. Comparing the materials with different architecture, we correlate the differences in material behavior and architecture to the strain-induced orientation behavior of the embedded filler particles.…”

“…For the novel particlecrosslinked elastomers, this will only lead to very small torques on the particle, as the mesh size is essentially the particle distance and the particles are connected by very long polymer chains. 16 Thus, we interpret the torque on the particles as additionally originating from a friction component of the disentangling polymer chains on the particle surface, in analogy to the orientation of elongated particles dispersed in a viscous matrix in shearing experiments.…”

“…Particle-crosslinked elastomers, 16 contrary to other elastomer networks, contain no specific crosslinker except for the multifunctional, inorganic nanoparticles, which leads to networks having highly functional nodes based on inorganic nanoparticles connected by long polymer chains. The resulting material properties of these particle-crosslinked elastomers are strongly dependent on the particle content.…”

“…The latter materials are recently introduced by us as a novel architecture of elastomers, that are crosslinked exclusively via surface-attachment of the polymer chains to magnetic nanoparticles. [16][17][18][19][20] These novel hybrid materials show strongly particle content dependent properties. In the case of poly(dimethylsiloxane)-based elastomers crosslinked via elongated hematite fillers, the mechanical properties are characterized by an enormous strain at break of up to 1700% and a pronounced strain-hardening regime.…”

“…In the case of poly(dimethylsiloxane)-based elastomers crosslinked via elongated hematite fillers, the mechanical properties are characterized by an enormous strain at break of up to 1700% and a pronounced strain-hardening regime. 16 Due to their unique properties, they are excellent candidates for an indepth analysis of the influence of network architecture on the strain-induced order in particle filled elastomers, and their properties will be compared to conventionally crosslinked elastomers throughout this paper. In addition, we investigate the influence of intrinsic particle preorientation in conventionally crosslinked elastomers by immobilization of a preoriented particle structure during the crosslinking process.…”