No abstract

Monolayers from electrically charged micrometer-sized silica particles, spread on the air/water interface, are investigated. Because of the electrostatic repulsion, the distances between the particles are considerably greater than their diameters, i.e., we are dealing with nondensely packed interfacial layers. The electrostatic repulsion between the particles occurs through the air phase. Surface pressure vs area isotherms were measured by Langmuir trough, and the monolayers' morphology was monitored by microscope. The mean area per particle is determined by Delaunay triangulation and Voronoi diagrams. In terms of mean area, the surface pressure for monolayers from polydisperse and monodisperse particles obeys the same law. The experiments show that Π ∝ L(-3) at large L, where Π is the surface pressure and L is the mean interparticle distance. A theoretical cell model is developed, which predicts not only the aforementioned asymptotic law but also the whole Π(L) dependence. The model presumes a periodic distribution of the surface charge density, which induces a corresponding electric field in the air phase. Then, the Maxwell pressure tensor of the electric field in the air phase is calculated and integrated according to the Bakker's formula to determine the surface pressure. Thus, all collective effects from the electrostatic interparticle interactions are taken into account as well as the effects from the particle finite size. By evaporation of water, the particle monolayers are deposited on a solid substrate placed on the bottom of the trough. The electrostatic interparticle repulsion is strong enough to withstand the attractive lateral capillary immersion forces that are operative during the drying of the monolayer on the substrate. The obtained experimental results and the developed theoretical model can be useful for prediction and control of the properties of nondensely packed interfacial monolayers from charged particles that find applications for producing micropatterned surfaces.

Non-densely packed interfacial monolayers from charged micrometre-sized colloid particles find applications for producing micropatterned surfaces. The soft electrostatic repulsion between the particles in a monolayer on an air/water (or oil/water) interface is mediated by the non-polar fluid, where Debye screening is absent and the distances between the particles are considerably greater than their diameters. Surface pressure versus area isotherms were measured at the air/water interface. The experiments show that asymptotically the surface pressure is inversely proportional to the third power of the interparticle distance. A theoretical model is developed that predicts not only the aforementioned asymptotic law but also the whole surface pressure versus area dependence. An increase in the surface pressure upon aggregation of charged particles in the interfacial monolayers is experimentally established. This effect is explained by the developed theoretical model, which predicts that the surface pressure should linearly increase with the square root of the particle mean aggregation number. The effect of added electrolyte on the aggregation is also investigated. The data lead to the conclusion that 'limited aggregation' exists in the monolayers of charged particles. In brief, the stronger electrostatic repulsion between the bigger aggregates leads to a higher barrier to their coalescence that, in turn, prevents any further aggregation, i.e. negative feedback is present.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

The present theoretical and experimental investigations concern static and dynamic properties of capillary bridges (CB) without gravity deformations. Central to their theoretical treatment is the capillary bridge definition domain, i.e. the determination of the permitted limits of the bridge parameters. Concave and convex bridges exhibit significant differences in these limits. The numerical calculations, presented as isogones (lines connecting points, characterizing constant contact angle) reveal some unexpected features in the behaviour of the bridges. The experimental observations on static bridges confirm certain numerical results, while raising new problems of interest related to the stability of the equilibrium forms. The dynamic aspects of the investigation comprise the capillary attraction (thinning) of concave bridge. The thinning velocities at the onset of the process were determined. The capillary attraction, weight of the plates and viscous forces were shown to be the governing factors, while the inertia forces turned to be negligible.

The STAR-LM 300 to 400 MWt class modular, factory fabricated, fully transportable, proliferation resistant, autonomous, reactor system achieves passive safety by taking advantage of the intrinsic benefits of inert lead-bismuth eutectic heavy liquid metal coolant, 100+% natural circulation heat transport, a fast neutron spectrum core utilizing high thermal conductivity transuranic nitride fuel, redundant passive air cooling of the outside of the guard/containment vessel driven by natural circulation, and seismic isolation where required by site conditions. Postulated loss-of-heat sink without scram, overcooling without scram, and unprotected transient overpower accidents are analyzed for the 300 MWt STAR-LM design using a coupled thermal hydraulics-neutron kinetics plant dynamics analysis computer code. In all cases, STAR-LM is calculated to exhibit passive safety with peak cladding and coolant temperatures remaining within the existing database for lead-bismuth eutectic coolant and ferritic steel core materials.