Orientational phenomena in magnetic liquid-crystal hybrid materials

• Applicants: Dr. Joachim Landers; Professorin Dr. Annette M. Schmidt
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 492620405

Magnetoactive complex systems composed of structured matrices doped with magnetic nanoparticles (MNP) encompass versatile potential for applications in actuators, sensors, and field-controlled switches and valves. We envisage new, otherwise unprecedented functional material properties, in particular by combining well-defined MNP with thermotropic liquid crystalline (LC) molecular and polymer components, based on the active control of their behavior by external stimuli like temperature or magnetic and electric fields.In the scope of this project, we study the internal interactions and dynamic processes in ferronematic fluids and elastomers on the molecular, particulate and macroscopic scale, and plan to analyze and optimize the influence of the local architecture and the interfacial coupling between MNP and matrix to achieve an efficient magneto-mechanical and magneto-nematic coupling in magnetically doped liquid crystalline fluids and polymers, with the ultimate goal to develop ferronematic elastomers with field-dependent properties.Such new phases based on liquid crystalline siloxane-based polymer molecules with mesogenic side groups offer a large variety of synthetically accessible material architectures, opening a wide parameter space by tailored selection of the components and enabling a detailed analysis of underlying physical mechanisms with respect to particle-matrix interaction.To understand the magneto-nematic coupling behavior on a fundamental level, and in order to achieve a systematic variation of the coupling mechanism and strength, we employ superparamagnetic nanoparticles as well as magnetically blocked particles of varying size and shape as dopants in liquid-crystalline fluids, polymers and elastomers of increasingly complex structure. As a general strategy, the embedded magnetic nanoparticles serve as field-controllable actoric components and likewise as nanoscopic probes for the analysis of local structure and dynamics.To understand field-dependent optical and mechanical properties of the new hybrid materials, the ability to analyze the local reciprocal orientation processes of the MNP (magnetic and/or geometric reorientation) and the mesogens relative to the macroscopic directors such us external fields or shear is essential. For that purpose, Mössbauer spectroscopy provides the ability to access information on the translational diffusive particle motion and the magnetic alignment simultaneously under variation of temperature and/or external fields. In combination with AC-susceptometry, the impact of local architecture of the particles’ environment on their orientational dynamics will be studied. In direct correlation to complementary global techniques such as (macro)rheology, thermomagnetometry and small and wide-angle X-ray scattering, we anticipate deep insights into structuring and relaxation phenomena in newly developed functional materials, enabling their future optimization and development.

• DFG Programme: Research Grants