*2.1. Samples Preparation*

Three types of silicone-based MRE samples were prepared through a mixing process. The CIPs with 70 wt.% of CIP were mixed with 29 wt.% of silicon rubber (SR) (NS 625 A) with the curing agen<sup>t</sup> NS625B (Nippon Steel). A mechanical stirrer was used (multimix high speed dispersed (HSD), WiseStir HT-DX, PMI-Labortechnik GmbH, Lindau, Switzerland) for mixing, for approximately 10 min, until the mixture was visually seen to be homogenous. The conventional co-precipitation method was used to synthesize the nanosized Ni-Mg cobalt ferrites, namely Co0.5Ni0.2Mg0.3Fe2O4 (A1) and Co0.5Ni0.1Mg0.4Fe2O4 (A2). The procedures for the synthesized MRE samples, A1 and A2, were based on the previous method reported by Rosnan et al. [37]. The stoichiometric molar amounts of Ni(NO3)2·6H2O, Mg(NO3)2·6H2O, Co(CH3COO)2·4H2O and Fe(NO3)3·9H2O were introduced. The above-mentioned chemicals were purchased from Qrec (New Zealand) and used without further purification. The chemicals were weighted according to the required stoichiometric proportion. Then, as a filler, 1 wt.% of A1 and A2 nanosized Ni-Mg cobalt ferrites, with an average size of 35 to 80 nm, were sonicated using an ultrasonic bath (Clifton, SW6H, UK.) with a frequency of 20 kHz and power of 120 W for 20 min in 100 mL of liquid ethanol (Sigma Aldrich, Malaysia) to prevent agglomeration before mixing with the matrix and CIPs. The MRE and filler were then mixed thoroughly for another 10 min. Then, the curing agen<sup>t</sup> was added, during the mixing with the SR, to the curing agen<sup>t</sup> ratio, with a ratio of 95:5 and continuously stirred for another 1 min. Finally, the MRE samples were cured in the cylinder shape mold for 24 hours. The summary of the fabrication process flow is shown in Figure 1.

**Figure 1.** Fabrication flow chart of the proposed magnetorheological elastomer (MRE) samples.
