Abstract This study investigates the long-term sedimentation stability of high-viscosity linear polysiloxane-based magnetorheological fluids (HVLP MRFs) using an automated vertical-axis inductance monitoring system (AVAIMS). While the inverse relationship between carrier fluid viscosity and sedimentation rate is theoretically established through Stokes’ law, experimental validation over multi-year timescales remains unreported, and no systematic framework exists for quantifying the relative contributions of formulation parameters to multi-boundary sedimentation stability. This work addresses this gap by tracking the sedimentation behavior of three HVLP MRF samples over an unprecedented 1095 days. Variables include particle loading (35 vol% and 45 vol%) and carrier fluid viscosity (5,000 cSt and 10,000 cSt), with a commercial MRF (LORD Corp., MRF-140CG) serving as a benchmark. The AVAIMS enables detailed characterization of three sedimentation boundaries—the mud-line, gel-line, and cake-line—extending beyond conventional mud-line tracking. The HVLP MRF with 45 vol% particle loading and 10,000 cSt carrier fluid maintained 78.0% of its original concentration zone after 1095 days, whereas the LORD MRF-140CG underwent complete stratification by day 267. Building upon this qualitative characterization, a quantitative framework was developed comprising normalized sensitivity coefficients and a novel Comprehensive Stability Index (CSI) that integrates all boundary measurements into a single metric. This analysis reveals that particle loading is approximately four times more effective than carrier fluid viscosity in achieving multi-boundary sedimentation stability, providing actionable guidelines for formulation optimization.
Choi et al. (Mon,) studied this question.