Freezing Transition and Interaction Potential in Monolayers of Microparticles at Fluid Interfaces

Abstract

The structure and the interaction potential of monolayers of charged polystyrene microparticles at fluid interfaces have been studied by optical microscopy. Microparticles of different sizes have been studied over a broad range of surface particle densities. The structural characterization is based on the analysis of images obtained by digital optical microscopy. From the experimental images, radial distribution functions, hexagonal bond order correlation functions, and temporal orientational correlation functions have been calculated for different monolayer states at both the air/water and oil/water interfaces. The interaction potential has been calculated from the structure factor using integral equations within the hypernetted chain closure relationship. For particles trapped at the oil-water interface, it was found that, upon increasing the surface coverage, a freezing transition occurs, that leads to the formation of a 2D crystalline structure. We have studied the freezing densities of particle monolayers at the oil/water interface and compared them with Monte Carlo simulation results reported by H. Löwen. In contrast, at the air-water interface, freezing is inhibited due to the formation of particle aggregates.

Thermodynamics and dynamics of two-dimensional systems with dipolelike repulsive interactions

“…It is straightforward to verify that with this definition of R, the low-q series expansion of Eqs. (19) and (20) will reproduce the acoustic velocities given by (17). Note also that in the strong coupling regime the excess energy is mainly associated with the static contribution, u ex M Γ.…”

“…(14) and (15). The black dashed curves correspond to the "simplified" QCA given by analytical expressions (19) and (20). The agreement between the two versions of QCA and MD dispersions is satisfactory at sufficiently long wavelengths (q 2 for the longitudinal and q 3 for the transverse mode).…”

Numerical calculation of interaction forces between paramagnetic colloids in two-dimensional systems

“…Here we utilize a smoothed profile method to develop a numerical solution to the threedimensional (3D) Laplace's equation describing the magnetic field of a system that consists of superparamagnetic particles trapped in a 2D plane in an external magnetic field. 2D colloidal systems are widely used experimentally to study various thermodynamic phenomena such as melting [13] and phase behavior [21,22] since individual colloidal particles can be easily visualized using optical microscopy [23]. Therefore we focus on the 2D system, but this method can also be used for 3D systems.…”

Surface dilational moduli of latex-particle monolayers spread at air–water interface

“…Cicuta et al [21] have performed shear rheological measurements on dense insoluble monolayers of micron sized PS latex particles at the oil-water interface. Moreover, Bonales et al [22] have studied the freezing transition of PS latex particle monolayers at the oil-water interface as a function of surface coverage using four particle diameters.…”