Highly Efficient Fabrication of Polymer Nanofiber Assembly by Centrifugal Jet Spinning: Process and Characterization

Centrifugal jet spinning (CJS) is a highly efficient, low-cost, and versatile method for fabricating polymer nanofiber assemblies, especially in comparison to electrospinning. The process uses centrifugal forces coupled with the viscoelastic properties and the mass transfer characteristics of spinning solutions to promote the controlled thinning of a polymer solution filament into nanofibers. In this study, three different spinning stages (jet initiation, jet extension, and fiber formation) were analyzed in terms of the roles of fluid viscoelasticity, centrifugal forces, and solvent mass transfer. Four different polymer solution systems were used, which enables a wide range of fluid viscoelasticity properties and solvent mass transfer properties, and polymer fibers were fabricated under different rotational speeds for these polymer solutions. The key dimensionless groups that determine the product morphology (beads, beads-on-fiber, and continuous fiber) and the radius of the fiber (when fibers are formed) were identified. The obtained morphology state diagram and fiber radius model were tested using a fifth polymer solution system. Results indicate that Weissenberg number and capillary number are important during the fiber extension stage to enable fiber formation while the elastic processability number is the determinative dimensionless number for fiber diameter prediction

Effect of Surface Modification on Magnetization of Iron Oxide Nanoparticle Colloids

Magnetic iron oxide nanoparticles have numerous applications in the biomedical field, some more mature, such as contrast agents in magnetic resonance imaging (MRI), and some emerging, such as heating agents in hyperthermia for cancer therapy. In all of these applications, the magnetic particles are coated with surfactants and polymers to enhance biocompatibility, prevent agglomeration, and add functionality. However, the coatings may interact with the surface atoms of the magnetic core and form a magnetically disordered layer, reducing the total amount of the magnetic phase, which is the key parameter in many applications. In the current study, amine and carboxyl functionalized and bare iron oxide nanoparticles, all suspended in water, were purchased and characterized. The presence of the coatings in commercial samples was verified with X-ray photoelectron spectroscopy (XPS). The class of iron oxide (magnetite) was verified via Raman spectroscopy and X-ray diffraction. In addition to these, in-house prepared iron oxide nanoparticles coated with oleic acid and suspended in heptane and hexane were also investigated. The saturation magnetization obtained from vibrating sample magnetometry (VSM) measurements was used to determine the effective concentration of magnetic phase in all samples. The Tiron chelation test was then utilized to check the real concentration of the iron oxide in the suspension. The difference between the concentration results from VSM and the Tiron test confirmed the reduction of magnetic phase of magnetic core in the presence of coatings and different suspension media. For the biocompatible coatings, the largest reduction was experienced by amine particles, where the ratio of the effective weight of magnetic phase reported to the real weight was 0.5. Carboxyl-coated samples experienced smaller reduction with a ratio of 0.64. Uncoated sample also exhibits a reduction with a ratio of 0.6. Oleic acid covered samples show a solvent-depended reduction with a ratio of 0.5 in heptane and 0.4 in hexane. The corresponding effective thickness of the nonmagnetic layer between magnetic core and surface coating was calculated by fitting experimentally measured magnetization to the modified Langevin equation