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gas molecules only interact with adjacent layers; and; the Langmuir theory can be applied to each layer. the enthalpy of adsorption for the first layer is constant and greater than the second (and higher). the enthalpy of adsorption for the second (and higher) layers is the same as the enthalpy of liquefaction. The resulting BET equation is
Now, invoking the condition that the system is in equilibrium, that is, the chemical potential of the adsorbed molecules is equal to that of the molecules in gas phase, we have An example plot of the surface coverage θ A = P/(P + P 0) with respect to the partial pressure of the adsorbate. P 0 = 100 mTorr.
Since the momentum transfer is caused by free motion of gas molecules between collisions, increasing thermal agitation of the molecules results in a larger viscosity. Hence, gaseous viscosity increases with temperature. In liquids, viscous forces are caused by molecules exerting attractive forces on each other across layers of flow.
The dilute gas viscosity contribution to the total viscosity of a fluid will only be important when predicting the viscosity of vapors at low pressures or the viscosity of dense fluids at high temperatures. The viscosity model for dilute gas, that is shown above, is widely used throughout the industry and applied science communities.
The Knudsen layer, also known as evaporation layer, is the thin layer of vapor near a liquid or solid. It is named after Danish physicist Martin Knudsen (1871–1949). Definition
The molecules in the gas layer have a molecular kinetic energy which increases uniformly with distance above the lower plate. The non-equilibrium energy flow is superimposed on a Maxwell-Boltzmann equilibrium distribution of molecular motions.
Langmuir film consisting of complex phospholipids in liquid-condensed state floating on water subphase, imaged with a Brewster angle microscope.. A Langmuir–Blodgett (LB) film is an emerging kind of 2D materials to fabricate heterostructures for nanotechnology, formed when Langmuir films—or Langmuir monolayers (LM)—are transferred from the liquid-gas interface to solid supports during ...
If the liquid molecules are strongly attracted to the solid molecules then the liquid drop will completely spread out on the solid surface, corresponding to a contact angle of 0°. This is often the case for water on bare metallic or ceramic surfaces, [ 15 ] although the presence of an oxide layer or contaminants on the solid surface can ...