A study of the heat transfer properties of CIP doped magnetorheological elastomers

This work investigates the enhancement of thermal transport in polydimethylsiloxane (PDMS) thin films with aligned carbonyl iron particles (CIP) embedded, also known as magnetorheological elastomers (MREs). The flash method is used to measure the effective thermal conductivity of PDMS/CIP thin films in the direction parallel to the magnetic field. Under an external magnetic field, the CIPs form chain-like structures, which become effective thermal paths inside the composites. Hence, a significant increase in the thermal conductivity of aligned MREs has been achieved compared with the composites prepared without a magnetic field. The effects of the volume fraction of CIP and pre-structured magnetic flux density have also been studied. The increase in the CIP volume fraction from 5% to 20% brings about a twofold improvement in the thermal conductivity of the aligned MREs. For 2.5 mu m CIP doped MREs with a volume fraction of 10%, when the pre-structured magnetic flux density changes from 0 mT to 100 mT, the thermal conductivity k increases by approximately 50%. However, a further increase in the magnetic field intensity only leads to a slight increase in k. Scanning electron microscopy (SEM) inspections demonstrate that the chain length keeps growing with the strength of the pre-structured magnetic field while the structure transition turns into lateral congregation as the strength of the pre-structured magnetic field reaches 100 mT. A finite element method (FEM) model is proposed to investigate in detail the relationship between the MREs' thermal conductivity and inner chains. This work provides an effective way to improve thermal conductivity of MREs used for electromagnetic radio-absorbers and builds a connection between the thermal properties of MREs and their inner microstructures.