Session: 01-04 Multifunctional Composites/Nanocomposites

Paper Number: 164704

164704 - Mechanical and Thermal Properties of Liquid Metal Elastomer Composites With Hybrid Fillers: Modeling and Experiment 

Soft multifunctional composites, such as liquid metal elastomer composites (LMECs), are advancing technologies like flexible electronics and wearable devices by combining high mechanical compliance with enabling thermal and electrical properties. The effective property of LMEC is constrained by the polymer matrix and the liquid metal volume fraction. Embedding a secondary filler phase into LMECs leads to the formation of hybrid filler composites (HFCs), a promising strategy to enhance their effective properties and introduce additional functionalities. However, predicting the effective properties become a challenging problem for composites with both liquid-phase and solid-phase due to biphasic fillers and naturally high filler volume fraction introduced by the secondary solid phase. There is a pressing need for a modeling tool that can determine the effective structural and functional properties of polymer composites with multiphase inclusions and high filler content. Analytical micromechanics models stand out for their accuracy and efficiency to accelerate the design of these composites with tailored properties. However, the main challenge in the micromechanics model for these composites lies in two areas: improving reliability at high LM fractions and addressing the existing research gap for hybrid filler composites (HFCs) with liquid and solid inclusions.

In this presentation, we will showcase the development and capabilities of our multi-step Mori-Tanaka (MMT) model, which provides accurate predictions for both the thermal conductivity and elastic modulus of LMEC and HFC. By integrating an iterative scheme into the Mori-Tanaka based framework, the MMT model achieves enhanced accuracy in predicting thermal and mechanical properties, particularly for composites with high filler volume fractions. We first validate this accuracy for LMEC with filler volume fractions exceeding 50% and then extend to hybrid composites with liquid and solid inclusions. The validated MMT model demonstrates better accuracy over finite element analysis and alternative physics-based models. We will then present experimental studies that investigate how liquid and solid filler phases, the ratio between solid and liquid fillers, and the elastomer matrix influence the composite properties. Using liquid metal (LM) droplets and ZnO particles as the liquid and solid inclusions, we synthesized three types of composites: LM-ZnO-PDMS, LM-PDMS, and ZnO-PDMS. Sylgard 184 and Ecoflex 00-30 were used as elastomer matrices to synthesize these composites. We will show how both ZnO and LM enhance thermal conductivity as their volume fractions increase, with ZnO offering a cost-effective alternative to LM. Moreover, we will demonstrate the emergence of a “Mechanical Cloaking” phenomenon in composites where ZnO is fixed at 10% and LM is varied, resulting in a nearly constant Young’s modulus despite improved thermal conductivity. Finally, failure strain analysis of the three composite types shows that strain at failure decreases from around 100% in LM-PDMS and LM-ZnO-PDMS to around 45% in ZnO-PDMS, demonstrating that ZnO tends to cause premature failure in composites. This work demonstrates the capabilities of the MMT model to provide insights into novel multifunctional composites design and discovery.

Presenting Author: Lijun Zhou University of Washington

Presenting Author Biography: Lijun Zhou is a PhD student in Mechanical Engineering at the University of Washington, advised by Professor Mohammad Malakooti.