Spectroscopic ellipsometry of superparamagnetic nanoparticles in thin films of poly(N-isopropylacrylamide)

Abstract

The versatility of spectroscopic Vis-ellipsometry (SE) to determine thin film properties was used to study Fe3O4-nanoparticles (NPs) embedded in thin films of poly(N-isopropylacrylamide). By using the optical constants of bulk Fe3O4 (magnetite) the volume fractions in different NP-polymer composites (0–3 vol. %) could be quantified with SE and verified with scanning electron microscopy (SEM) and atomic force microscopy. It was found that the best-fit results from SE matched well with data from SEM until 1 vol. %. The effect of the NP on the evolution of film thickness and surface morphology was analyzed. Over the whole concentration range the data obtained from SE measurements matched well with the suspended values and showed an expected linear behavior. Additionally, the optical constants (n and k) of the nanocomposites were extracted and compared to the pure polymer film. In the measured spectral range the data showed a physical meaningful behavior and the influence of the NP on the optical properties of the thin films could be observed.

Nanoparticle Distribution in Three‐Layer Polymer–Nanoparticle Composite Films: Comparison of Experiment and Theory

“…The diameter of the Fe 3 O 4 core determined from TEM images was 6.7 ± 1.0 nm. The hydrodynamic radius in n‐hexane that includes the thickness of the oleyl amine and oleic acid layer was 11.2 ± 3.5 nm as determined by dynamic light scattering …”

“…Phase separation of polymer blends or diblock copolymers with incorporated nanoparticles leads to ordered structures with nanoparticles either dispersed in one phase or enriched at the phase boundaries. Thin polymeric layers with self‐assembled nanoparticle structures have been created by spin‐coating nanoparticle–polymer– solvent dispersions on a flat substrate . Stable multilayer composites with individual film thicknesses have been prepared by several spin‐coating steps followed by thermal treatment and cross‐linking of the polymer …”

“…Distribution and self‐assembly of the particles are determined by interactions between the polymer molecules, between the particles and between particles and polymer, that is, by the miscibility of polymer and nanoparticles . Since inorganic particles and polymers are often immiscible, their compatibility can be improved by surface modification of the particles with surfactants, organic substances, or grafted polymers …”