Self-assembly of repulsive interfacial particles via collective sinking

Abstract

Charged colloidal particles trapped at an air-water interface are well known to form an ordered crystal, stabilized by a long ranged repulsion; the details of this repulsion remain something of a mystery, but all experiments performed to date have confirmed a dipolar-repulsion, at least at dilute concentrations. More complex arrangements are often observed, especially at higher concentration, and these seem to be incompatible with a purely repulsive potential. In addition to electrostatic repulsion, interfacial particles may also interact via deformation of the surface: so-called capillary effects. Pair-wise capillary interactions are well understood, and are known to be too small (for these colloidal particles) to overcome thermal effects. Here we show that collective effects may significantly modify the simple pair-wise interactions and become important at higher density, though we remain well below close packing throughout. In particular, we show that the interaction of many interfacial particles can cause much larger interfacial deformations than do isolated particles, and show that the energy of interaction per particle due to this "collective sinking" grows as the number of interacting particles grows. Though some of the parameters in our simple model are unknown, the scaling behaviour is entirely consistent with experimental data, strongly indicating that estimating interaction energy based solely on pair-wise potentials may be too simplistic for surface particle layers.

Adsorption and Crystallization of Particles at the Air–Water Interface Induced by Minute Amounts of Surfactant

“…3B). We believe that this is due to a 'collected sinking effect', leading to closer particle bounding at fluid interfaces when the number of interfacial particles increases (22). In the latter case, the local curvature of the interface decreases and particles move to the lower part of the meniscus1., which consequently leads to enhanced particle-particle attractions.…”

Capillary interactions between dynamically forced particles adsorbed at a planar interface and on a bubble

“…At equilibrium, buoyant (or heavy) particles trapped at an interface induce deformations that decay over distances of the order of the capillary length (Chan et al 1981). Such deformations give rise to long-range attractive forces between particles, which drive aggregation of the interfacial suspension (Vassileva et al 2005; Vella et al 2006; Bleibel et al 2011; Lee et al 2017). For micromicrometric particles, the weight of the particle is too small to appreciably deform the interface, but interface deformations can arise due to pinning of the three-phase contact line on surface roughness (Stamou et al 2000; Sharifi-Mood et al 2015; Zanini et al 2017), anisotropic shape of the particles leading to undulated contact line (Van Nierop et al 2005; Botto et al 2012), or external forces (Vella 2015) and torques (Davies et al 2014).…”

Perumusan Gaya Atraktif Bola Terapung dengan Metode Eksperimen dan Pengolahan Citra Digital

“…Pola pengelompokan objek-objek terapung (self assembly) [10] dianalisis dengan metode eksperimen menggunakan objek berbentuk bola berskala milimeter hingga nanometer [9] dan simulasi numerik [11]…”