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[en] We discuss how electrical current wires and micromagnetic elements can be used to trap or propagate paramagnetic beads, and consider their strengths and limitations. In particular, it is shown that the interactions can be effectively tuned by applying an external bias field. We demonstrate experimentally how to transport and structure a colloidal system using a domain wall, which could find use in microfluidic systems
[en] Langmuir monolayer isotherms and fluorescence microscopy (FM) techniques have been used to study the effect of two soluble surfactants on the methyl octadecanoate monolayer's compressibility at the air/water interface. The combination of these two techniques allows one to bridge the mechanical and morphological properties of the monolayer at different surfactant subphase concentrations. Our results show that the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) affects the monolayer elasticity differently. In addition, the outcome of this study emphasizes the role of the cationic and anionic surfactants on the monolayer compressibility. In fact, their effect was found to be primly depending on the monolayer thermodynamic situation. The isotherms of the monolayers at different surfactant concentrations underneath the monolayer preserve the characteristics behavior of the monolayer as imaged by FM. The calculated monolayer compressibility shows two different trends depending on the monolayer pressure and the surfactant type. A decreasing compressibility as a function of SDS concentration was found at pressure π = 5 mN/m, while no noticeable effect was found due to DTAB. At π = 10 mN/m both surfactants convert the monolayer from rigid to soft monolayer. Such characteristic behavior of the monolayer has been confirmed by FM. Highlights: → LM mechanical and morphological properties were bridged using isotherms and FM. → Monolayer compressibility shows two trends depending on the pressure and temperature. → Both surfactants drive the monolayer from rigid to soft at π = 10 mN/m, and T = 22 deg. C.