Change in the Properties of a Magnetic Nanoparticle–Polymer Composite Langmuir Film at the Air–Water Interface via the Polymer Ratio and the Use of a Weak Magnetic Field

Abstract We aimed to create magnetic polymeric films with the desired physical properties by varying the ratio of a hydrophobic polymer (poly(isobutyl methacrylate), PIBM) to hydrophobic Fe3O4 nanoparticles (NPs) at an air–water interface and by applying a weak magnetic field. The effect of adding PIBM to the NPs was first determined by studying 100% NP, 100% PIBM and mixed PIBM-NP Langmuir films in the absence of a magnetic field. In the case of the 100% NP or PIBM films, the NPs and PIBM formed aggregates at the air–water interface. In the case mixed PIBM-NP films, the NPs aggregates were concluded to distributed between the PIBM aggregates. Increasing the ratio of PIBM in the mixed film (χpol) increased the NP aggregate sizes, but decreased the packing density of the NP aggregates. Applying a magnetic field to a 100% NP film increased the NP aggregation. A magnetic field did not change the PIBM film, a result explained by the nonmagnetic nature of PIBM. In the case of a mixed film, the magnetic field tended to homogenize the size of the NP aggregates. The change in the films by a magnetic field increased in the order of χpol = 1 (100% PIBM) < χpol = 0 (100% NP) ≈ χpol = 0.27 < χpol = 0.77 < χpol = 0.53. The magnetic field induced changes therefore increased with a decreased NP packing density, but decreased when the number of NPs in the film became too low. The low viscosity of PIBM was concluded to allow the magnetic field to move the NPs in the film. However, the magnetic field induced changes became less obvious when the number of NPs in the film is small. The properties of a Fe3O4 NPs film can therefore be varied via the ratio of polymer in the film and the application of a weak magnetic field.