Micro- Magnetic-Manipulation of Multiblock Copolymers – MANIOC

Since the emergence of the nanotechnologies era in the 80s, block copolymers are frequently used to design host patterns allowing to control the structure of inorganic nanoparticles assemblies. The pivotal idea of MANIOC is at the opposite, it consists of manipulating the microstructure of triblock copolymers by adsorbing selectively their extremities onto the surface of "stimulable" and "guidable" nanoparticles. The experimental process, enabling the production of out-of-equilibrium microstructures on-demand, can be summarized in the following three steps :
1. Homogenization of the polymer matrix through magnetic hyperthermia. This step consists of irradiating magnetic nanoparticles embedded into the block copolymer with a high frequency oscillatory magnetic feld (ca. 1 MHz). The heat dissipation induced by the magnetic hysteresis then allows to heat quickly the material above its order-disorder transition temperature to make it liquid-like.
2. Reorganization of the nanoparticles into dipolar chains oriented according tot he magnetic filed lines. This step, which relies on the migration of magnetic nanoparticles, starts as soon as the host polymer has reached its disordered state.
3. Selective reassociation of the block copolymers at the interface with the nanoparticles upon cooling. This last step allows to pilot the microstructure of the polymer hard domains, based on the nanoparticles organization. Magnetic field lines can be adapted from the inductor geometry. The resulting material is a highly anisotropic thermoplastic elastomer.

The system we target is based on a P2VP-b-PnBuA-b-P2VP triblock copolymer, or its P4VP counterpart, loaded with colloids of magnetite (Fe3O4). While the P2VP (Tg=100°C) is well-known to interact favorably with the surface of polar inorganic particles through hydrogen bonds, the PnBuA (Tg=-55°C) barely interact with them, ensuring a pronounced phase separation at the interface with the particles.

One of the most challenging aspects of MANIOC resides in the simultaneous detection of the three constituants of the material: (i) the soft organic phase that occupies the largest part of the volume, (ii) the hard organic phase located at the interface with the nanoparticles, and (iii) the magnetic nanoparticles. To do so, we propose an advanced structural characterization that combines state-of-the art microscopy techniques such as Peak-Force AFM, chemical staining and electronic tomography.

Beyond structural aspects, we expect the magnetic manipulation to impact significantly the macroscopic properties of the nanocomposites. In particular, we propose a series of rheological tests, performed both under moderate and large amplitudes, to investigate the structure-properties relationships in-depth. For the first time to our knowledge, we will also run rheological tests under high frequency magnetic stimulus, requiring the design of ceramic-based accessories. Beyond the mechanical effect, the manipulation of the organic phase is expected to enhance ions and gas permeability properties, notably through the formation of interfacial "tunnels", accelerating the diffusion of small molecules in the material. This part of MANIOC will possibly be oriented towards applications, notably in the fields of (i) solid-state battery polyelectrolyes, and (ii) gaz filtration membranes.