Effect of contact angle hysteresis on moving liquid film integrity

A study was made of the formation and breakdown of a water film moving over solid surfaces (teflon, lucite, stainless steel, and copper). The flow rate associated with film formation was found to be higher than the flow rate at which film breakdown occurred. The difference in the flow rates for film formation and film breakdown was attributed to contact angle hysteresis. Analysis and experiment, which are in good agreement, indicated that film formation and film breakdown are functions of the advancing and receding angles, respectively

Film models for transport phenomena with fog formation: The fog film model

In a preceding paper (Brouwers and Chesters, Int. J. Heat Mass Transfer35, 1–11 (1992)) possible supersaturation in a film and in the bulk of a binary mixture has been discussed. In the present analysis the exact conditions for fog formation and the magnitude of the fogging and superheated regions in the film are first determined. Next, the governing equation of diffusion and energy (coupled with the saturation condition) of the fog layer is solved numerically. An evaluation of various mixtures of water vapour and air illustrates the substantial effect of fog formation on heat and mass transfer rates. Subsequently, a thorough asymptotic analysis of the fog layer's governing equation yields an excellently matching approximation solution. Furthermore, this solution leads to analytical film model correction factors for the combined effects of fog formation and injection/suction on transfer rates. Finally, the fog film model is applied to channel flow of a binary mixture. This approach provides new procedures for the computation of condensers and evaporators, allowing both fog formation in the film (affecting transfer rates) and/or in the bulk (affecting the incremental balances of mass and energy)

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. The type of surface finish (topography) as related to scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film, and various complex surface overgrowths on the film. These nodular growth features have progressively more undesirable effects on the film behavior as the film thickness increases

Theoretical description of mixed film formation at the air/water interface : carboxylic acids–fatty amines

Thermodynamic parameters of mixed monolayer formation of aliphatic amines CnH2n+1NH2 and carboxylic acids CnH2n+1COOH (n = 6–16) are calculated using the quantum chemical semiempirical PM3 method. Four types of mixed dimers and tetramers amine–acid are considered. The total contribution of interactions between the hydrophilic parts of amine and acid into clusterization Gibbs energy is slightly lower than the corresponding interactions for individual surfactants. It suggests a synergetic interaction between the regarded amphiphilic compounds as proved by experimental data in the literature. Two types of competitive film formation are possible: mixed 2D film 1, where the molecules of the minor component are single distributed among the molecules of the prevailing second component (mixture of components on molecular level), and 2D film 2 with a domain structure comprised of pure component “islands” linked together. The dependence of the Gibbs energy of clusterization per monomer for 2D film 1 on the component mole fraction shows that the maximum synergetic effect is typical for the case that both surfactants have the same even number of carbon atoms in the hydrocarbon chain and form an equimolar mixture. Formation of 2D film 1 is more preferable than that of 2D film 2, if the difference of the hydrocarbon chain lengths is not larger than 5 methylene units. The limiting mole fraction of carboxylic acids in such mixed monolayers is 66.7%

Estimation of vortex density after superconducting film quench

This paper addresses the problem of vortex formation during a rapid quench in a superconducting film. It builds on previous work showing that in a local gauge theory there are two distinct mechanisms of defect formation, based on fluctuations of the scalar and gauge fields, respectively. We show how vortex formation in a thin film differs from the fully two-dimensional case, on which most theoretical studies have focused. We discuss ways of testing theoretical predictions in superconductor experiments and analyse the results of recent experiments in this light.Comment: 7 pages, no figure

MWNT Surface Self-Assembling in Fire Retardant Polyethylene-Carbon nanotubes nanocomposites

Multiwall carbon nanotubes (MWNT) were melt blended at different concentration with linear low density polyethylene (LLDPE). The nanotubes impart the fire-retardant characteristics to the polymer by formation of a thin protective film of MWNT/carbon char generated on the surface of the nanocomposites. The film formation mechanism is discusse

A film model for heat and mass transfer with fog formation

An analysis is presented of a binary film with fog formation and a negligible induced velocity (traditionally referred to as “Stefan—Nusselt flow”). The governing equations of energy diffusion, coupled with the saturation condition, are solved and analytical correction factors are derived. Subsequently, the “negligible induced velocity” (NIV) fog film model is applied to channel flow, yielding analytical expressions for the variation of bulk vapour mass fraction, bulk temperature, and the possible creation of bulk fog. Multiplying the NIV correction factor for fog only by the classical film model correction factors for induced velocity, reveals that the product corresponds to the film model correction factors for the combined effects of fog and induced velocity. Furthermore, a thorough comparison with theoretical and experimental results of foregoing two-dimensional studies, concerning fog formation in the presence of free and forced convection, confirms the accuracy of the present fog film model

Preparation of aqueous dispersion of thermoplastic sizing agent for carbon fiber by emulsion/solvent evaporation

In this work, different sizing agent aqueous dispersions based on polyetherimide (PEI) were elaborated in order to improve the interface between carbon fibers and a thermoplastic matrix (PEEK). The dispersions were obtained by the emulsion/solvent evaporation technique. To optimize the stability and the film formation on the fibers, two surfactants were tested at different concentrations, with different concentrations of PEI. The dispersions obtained were characterized by dynamic light scattering (DLS) and the stability evaluated by analytical centrifugation (LUMiFuge). The selected dispersions were tested for film formation ability by scanning electron microscopy (SEM), and the sizing performance was assessed by observation of the fiber/matrix interface by SEM. The results revealed that an aqueous dispersion of PEI,stabilized by sodium dodecyl sulfate as the surfactant, led to very stable sizing agent aqueous dispersion with ideal film formation and better interface adhesion