Dip coating in the presence of a substrate-liquid interaction potential

In this work we investigate theoretically the Landau-Levich problem of dip coating in the presence of a strong interaction potential normal to the substrate. This study is motivated by dip coating at very low capillary numbers when the deposited film thickness is less than 1 µm and such interaction forces become important. The objective of this work is to demonstrate that in the presence of an extra body force the solution procedure differs significantly from the classical one and leads to substantial deviations from the Landau-Levich law for the entrained film thickness. In particular, attractive potentials produce film thickening and the resulting film thickness is independent of speed to lowest order. Repulsive potentials bring about more complicated behavior and lead either to films whose thickness is also independent of speed, or to a modification of the leading order constant in the classical Ca^(2/3) law. Demonstration of these effects is given for a model potential. The analysis is generally applicable to many physical situations when there is an interaction between a coating liquid and a substrate, e.g., dip coating of ferromagnetic liquids on magnetic substrates, or dip coating of liquids carrying charges

Surfactant effects in the Landau–Levich problem

In this work we study the classical Landau–Levich problem of dip-coating. While in the clean interface case and in the limit of low capillary numbers it admits an asymptotic solution, its full study has not been conducted. With the help of an efficient numerical algorithm, based on a boundary-integral formulation and the appropriate set of interfacial and inflow boundary conditions, we first study the film thickness behaviour for a clean interface problem. Next, the same algorithm allows us to investigate the response of this system to the presence of soluble surface active matter, which leads to clarification of its role in the flow dynamics. The main conclusion is that pure hydrodynamical modelling of surfactant effects predicts film thinning and therefore is not sufficient to explain the film thickening observed in many experiments

Experimental study of substrate roughness and surfactant effects on the Landau-Levich law

In this work we present an experimental study of deviations from the classical Landau-Levich law in the problem of dip coating. Among the examined causes leading to deviations are the nature of the liquid-gas and liquid-solid interfaces. The thickness of the coating film created by withdrawal of a plate from a bath was measured gravimetrically over a wide range of capillary numbers for both smooth and well-characterized rough substrates, and for clean and surfactant interface cases. In view of the dependence of the lifetime of a film on the type of liquid and substrate, and liquid-gas and liquid-solid interfaces, we characterized the range of measurability of the film thickness in the parameter space defined by the withdrawal capillary number, the surfactant concentration, and substrate roughness size. We then study experimentally the effect of a film thickening due to the presence of surfactants. Our recent theory based on a purely hydrodynamic role of the surface active substance suggests that there is a sorption-controlled coating regime in which Marangoni effects should lead to film thinning. However, our experiments conducted in this regime demonstrate film thickening, calling into question the conventional wisdom, which is that Marangoni stresses (as accounted by the conventional interfacial boundary conditions) lead to film thickening. Next we examine the effect of well-characterized substrate roughness on the coated film thickness, which also reveals its influence on wetting-related processes and an effective boundary condition at the wall. In particular, it is found that roughness results in a significant thickening of the film relative to that on a smooth substrate and a different power of capillary number than the classical Landau-Levich law

Thermocapillary flows and their stability: Effects of surface layers and combination

The theoretical analysis of the fluid mechanics and heat transfer of motions driven by surface tension gradients (Marangoni convection) was researched. Convection accompanying the process of growing high quality single crystals from the melt in a micro-g environment was examined. The geometries considered include two dimensional liquid filled slots and axisymmetric float-zone configurations

Thermocapillary flows and their stability: Effects of surface layers and contamination

The fluid mechanics and heat transfer of motions driven by surface tension gradients (Marangoni convection) were analyzed theoretically to obtain an understanding of the convection accompanying the process of growing high quality single crystals from the melt in a mu-g environment. The geometries considered include two dimensional liquid filled slots and axisymmetric float zone configurations

Agency Law in the Arabian Peninsula and North Africa

This article examines the agency laws of Algeria, Egypt, Iraq, Jordan, Kuwait, Saudi Arabia, and the United Arab Emirates. These countries were chosen because they are representative of the different legal approaches to the regulation of agents in the Middle East. For example, Algeria and Iraq, which have state controlled economies, severely restrict the use of agents. Egypt has significantly relaxed state controls on its economy during the last decade and, in general permits the use of agents while retaining few restritions on their use in the sale of certain commodities. Saudi Arabi\u27s free enterprise economy is dominated by public sector procurements, and requires the use of local agents for all government purchases except armaments

Capacity, sustainability, and the community benefits of municipal utility ownership in the United States

Most literature on utility sustainability focuses on internal operations; this misses the role that utilities cold play within a community. This study measures the impact of municipal ownership of water and electric utilities on the sustainability policymaking of local governments. I find that municipalities with government-owned water utilities adopt more sustainability measures than those with investor-owned service. Similarly, municipally-owned electric utilities have higher levels of energy sustainability in the community, but not in government operations. The utilities provide fiscal and technical capacity to municipalities. This study brings potential community benefits to the discussion of private investment in public service delivery

Powering sustainability: municipal utilities and local government policymaking

Sustainability policymaking presents numerous challenges to local governments. Municipal leaders, especially in smaller cities and towns, report that they lack the fiscal capacity and/or technical expertise to adopt many environmental protection policies. This paper investigates whether the more than 2,000 municipally-owned utilities have the potential to mitigate those problems. Data from two surveys of local governments in the United States (n=861), modeled in a pair of negative binomial regressions, finds a positive correlation between those cities with municipal power companies and those with an increased number of community-wide sustainable energy policies. Follow-up interviews with officials reveal the potential mechanisms driving sustainability by local governments that own power companies. These mechanisms are the increased capacity that publicly-owned utilities provide by virtue of income generated and access to energy-specific grants as well as the local nature of their operations, which allows a better fit of sustainable energy measures to local circumstances