Magnetic nanorod settlement through natural and centrifugal sedimentation
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Date
2019-06
Authors
Yew, Keat Yen
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Abstract
Iron oxide nanorod (IONRs) was selected as the subject of this study due to its shape anisotropy. The IONRs were surface functionalized with macromolecules of interest, Poly(diallyldimethylammonium chloride)(PDDA) as the surface coating to sterically stabilize the IONRs in deionized, DI water. The PDDA coating introduced electrosteric stabilization among the particles in the suspension with the formation of electro-physical barrier around the IONRs surface, which hinders the aggregation between the IONR particles due to van der Waals attraction and magnetic dipole-dipole interaction. Dynamic Light Scattering (DLS) has been used for characterization of naked and surface-functionalized IONRs by monitoring the hydrodynamic diameter and zeta potential measurement of the IONRs. This characterization is to verify the successful attachment of the macromolecules on the surface of IONRs. Two concentrations (20 and 25 ppm) of SF-IONRs samples were prepared for the study in natural and centrifugal sedimentation. The major focuses were the study of the effect of type of sedimentation and concentration on the cluster size formed as well as its suspension opacity with time. In addition, DLS was also used to probe the dynamic behavior of IONRs aggregation while UV-Vis spectrophotometer was used to monitor the kinetic of sedimentation of the IONRs. Natural sedimentation process of IONRs was probed as normalized absorbance curve made up of three regions, region 1 arose primarily due to aggregation; region 2 initiated by rapid sedimentation of IONRs particle cluster with achieved critical size and region 3 started as sedimentation of IONRs slowed down. The centrifugal sedimentation process made up of two region, region 1 with rapid sedimentation and region 2 with slowed down sedimentation. Time scale in between the natural and centrifugal sedimentation have been compared and analyzed by using sedimentation kinetic. The centrifugal sedimentation has a time scale where the value of time range is lower than the one in natural sedimentation of IONRs. For both the natural and centrifugal sedimentation process, settlement of IONRs clusters happened within this time range. Furthermore, the time range of natural sedimentation is larger than the one in the centrifugal sedimentation due to the greater broadening of hydrodynamic size distribution.