Preparation And Characterization Of PDMS-magnetic Nanoparticle Composite Optical Films

Magnetorheological elastomers is a new branch of magnetorheological materials,which is the solid state of magnetorheological fluid. They consist of high polymer filled with micro-sized magnetic particles. Mechanical properties and electric properties of magnetorheological elastomers can be controlled by application of an external magnetic field. So far, numerous efforts have been devoted towards the characterization of larger-sized magnetorheological elastomers and their applications. However, the optical properties of magnetorheological elastomers on a micro scale are still very limited,especially about optical properties of the micro-scale magnetorheological elastomer films. In this paper, preparation and characterization of PDMS-magnetic nanoparticle composite optical films are studies.Firstly,based on the structure of magnetorheological elastomers, the dipole model and the coupling field model of magnetorheological elastomers are introduced. And the calculating formula of the shear modulus of magnetically induced magnetic field in the magnetorheological elastomers is deduced. Characterization of magnetorheological elastomers is introduced, such as modulus change, magnetostriction, electrical properties and so on.Secondly, in the micromachining platform anisotropic and isotropic films with Fe3O4 nanoparticle weight fractions ranging from 1 wt% to 13 wt% were fabricated in the presence and absence of an external magnetic field during the film fabrication process, respectively. UV–vis transmission spectra of the films indicate that the anisotropic films demonstrate higher transparency than the isotropic counterparts with the same weight fraction of Fe3O4 nanoparticles. Furthermore, it was observed that the transmittance of the films can be tuned by applying an external magnetic field, which might be due to changes in the Fe3O4 interparticle distance induced by magnetostrictive effect. We speculate that the contraction of the film along the magnetic field leads to smaller interparticle distance, stronger light scattering, and thus a decrease in transmittance.In the case of an anisotropic film with Fe3O4 nanoparticle weight fraction of 10 wt%, the transmittance decreases by 8.61% at the wavelength of 600 nm under a magnetic field of B=～800 Gs. The strain changes of an anisotropic film with Fe3O4 nanoparticle weight fraction of 5 wt% are quantitatively analyzed before and afterapplying a magnetic field by digital image correlation techniques. In the anisotropic and isotropic PDMS-Fe3O4 composite optical films, strain changes of Fe3O4 nanoparticale along the magnetic field direction are-0.0125% and-0.0192%, respectively.Then, anisotropic and isotropic films with Ni nanoparticle weight fractions ranging from 1 wt% to 20 wt% were fabricated by a spin coating method. Optical microscope images of isotropic and anisotropic PDMS-Ni composite optical films are observered by optical microscope. And film microtexture and magnetic field have an effect on the transmittance of PDMS-Ni composite optical films. Optical transmittance of PDMS-Ni composite optical film increases by an external magnetic field.Finally, the basic principles of the optical parameters of the films by spectroscopic ellipsometer is introduced. In ellipsometry measurements, we explain how to build an appropriate optical films model, and then build structure model and dispersion model of PDMS-magnetic nanoparticle composite optical films and introduce the measurement processes of elliptical polarization. The Cauchy model is proved to be effective in measuring and fitting the optical parameters of PDMS-magnetic nanoparticle composite optical films.