An experimental study on the effect of fatty acid chain length on the magnetorheological fluid stabilization and rheological properties

• Improving MRF stability and MR effect by using stearic acid additive.
• Fatty acids with longer carbon chain as additive creates stronger gel structure.
• Stronger gel structure improves stability and yield stress, consequently more efficient MRF.

An experimental study was conducted on the effect of acid additives on the stability and rheological properties of a suspension of carbonyl iron (CI) microparticles dispersed in silicone oil. A series of acids with the same carboxyl group but different carbon chain lengths (C12, C14, C16 and C18) were added to magnetorheological fluids (MRFs) to investigate their effect on the stability and rheological behavior. MR effect was measured with the aid of a magnetorheometer and stability measurements were made by simple determining the height of the transparent layer in the MRF over a 6-month period. Experimental results showed that by increasing carbon chain length of acids, yield stress and stability increased up to 22 times (at H = 362 kA/m) and 7 times, respectively, in comparison to the additive-free MRF. Model fitting confirmed that all of the acid-based MRFs showed a yield stress with shear thinning behavior and followed Herschel–Bulkley model. Further investigations suggested that 3 wt% stearic acid was the most promising additive in increasing MR effect and stability. The results of stability and rheological tests showed that further increase in stearic acid fraction improved stability slightly and, at the same time, increased the off-state viscosity to a huge extent undesirably.

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