İki dağılımlı magnetoreolojik akışkanlar

Superparamagnetic iron oxide nanoparticles (SPION) are exploited in many different fields from automotive to medicine. In every field, there is always a need for better performance that exhibits new challenges to scientists. In this thesis work magnetorheological fluids and magnetic hydrogels are studied to solve the problems and improve the properties of these materials. Magnetorheological Fluids (MRFs) are non-Brownian fluids that consist of micron-sized magnetic particles in carrier fluids, mostly different oils. The biggest challenge in MRFs is the prevention of sedimentation and enhancement of redispersibility to prolong shelf-life as well as life-in-use. This thesis work proposed and demonstrated a method to improve the stability and redisperability of MRFs with high particle loading while having good magnetorheological properties. Bidisperse MRFs composed of micron-sized magnetic particles and functional superparamagnetic nanoparticles which would interact with each other is proposed as the primary strategy. First, the idea was tested on a commercial MRF, 140-CG LORD® (with fatty-acid coated micron-sized particles in hydraulic oil). Poly(acrylic) acid and lauric-acid coated superparamagnetic iron oxide nanoparticles (SPION-PAA and SPION-LA) were synthesized and added in 5-20 weight percentages to 140-CG LORD® to understand the influence of surface coating and SPION content on the sedimentation and magnetorheological properties. Then, new bidisperse MRFs were prepared by adding commercial bare carbonyl iron (CI) and SPION-LA or SPION-PAA to different carrier fluids. Also, CI was coated with LA and bidisperse MRFs were prepared from CI-LA and SPION-LA or SPION-PAA in different carrier oils such as hydraulic oil, silicone oil, mineral oil and glycerol. Magnetorheological properties of prepared bidisperse MRFs were measured with Anton Paar 302 MCR rheometer in both rotational, and frequency modes and mechanical properties, as well as the sedimentation behavior of MRFs, were compared with 140-LORD MRF® as a benchmark. SPION-PAA particles provided the best MRFs in both formulations with enhanced stability for months, better redispersibility and rheological properties at least as good as the commercial one. Selected bidisperse MRFs were used in washing machine MR dampers by the group of Prof. İsmail Lazoglu. This research was funded by TUBITAK and Arçelik (ID: 5150060).