Towards Complex Microarchitectural Composites Using Multi-Field Processing

摘要

In this study, we investigate the hierarchical microarchitecture formation of magnetic bariumhexaferrite (BF) platelets in polydimethylsiloxane (PDMS) using electric and magnetic field assemblytechnique. First, external fields are applied to the colloidal solution to form the microstructure beforecuring the composites. After microstructure formation, the composites are thermally cured to freeze themicrostructure. We investigate two different cases in this study-(1) magnetic field processed compositesand (2) multi-field processed composites, which were processed under both magnetic and electric fields.We observe that macro-chains formed due to simultaneous application of electric and magnetic fields hada much higher length compared to the macro-chains formed due to just magnetic field. For both casesindividual BHFs are found to be oriented in the direction of the external field. The analysis of SEMmicrostructures using ImageJ and MATLAB showed that at least two different levels of hierarchies arepresent in the microstructure for both cases, which are referred to as BHF stacks and micro-chains. Fromthe experimental quantitative microstructure analysis, BHFs are found to be slightly better oriented(magnetic easy-axis direction in relation to the external field) at all scales for the electric and magneticfield processed composites compared to just the magnetic field processed composites. Magneto-electrohydrodynamicsmodeling of the polymer-particulate mixture predicts a similar behavior. Computationalsimulations are performed wherein particulates, subjected to both DEP forces resulting from an appliedelectric field, and magnetic dipole interactions in response to applied magnetic field, are allowed to formquasi-equilibrium structures before locking in a final structure to represent curing. Results fromsimulation confirms the finding on longer macro-chain formation similar to the experiment for the case ofmagnetic and electric fields compared to just magnetic field. Analysis of the microstructures fromsimulation also confirms that multiple levels of hierarchies are present in the composites’ microstructurefor both cases. In future, quantifying the corresponding metrics at each level of hierarchy will help tobetter understand the microstructure and can be served as input to the model and also used to validate themodel.