Water Vapor Permeability
Water Vapor Permeability - Related Videos
01:18
Vaporization
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2019
The physical form of a substance changes by changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize (convert into vapor). The process is called vaporization—a surface phenomenon. For vaporization to occur, kinetic energy must be greater than the intermolecular forces that keep molecules bonded. The amount of energy needed to vaporize a quantity of liquid at a given pressure and a constant temperature is called the heat of vaporization. When...
02:34
Vapor Pressure
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2020
When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally collide with the surface of the condensed phase, and in some cases, these collisions will result in the molecules re-entering the condensed phase. The change from the gas phase to the liquid is called condensation. When the rate of condensation becomes equal to the rate of vaporization, neither the amount of the liquid nor the amount of the vapor...
14:20
Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example
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Cited by 20 •
2014
Measuring the osmotic water permeability coefficient (Pf) of cells can help understand the regulatory mechanisms of aquaporins (AQPs). Pf determination in spherical plant cell protoplasts presented here involves protoplasts isolation and numerical analysis of their initial rate of volume change as a result of an osmotic challenge during constant bath perfusion.
11:32
Vapor-liquid Equilibrium
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2023
Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA Vapor-liquid equilibrium is paramount in engineering applications such as distillation, environmental modeling, and general process design. Understanding the interactions of components in a mixture is very important in designing, operating and analyzing such separators. The activity coefficient is an excellent tool for relating molecular interactions to mixture...
03:28
Vapor Pressure Lowering
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2020
The equilibrium vapor pressure of a liquid is the pressure exerted by its gaseous phase when vaporization and condensation are occurring at equal rates: Dissolving a nonvolatile substance in volatile liquid results in a lowering of the liquid’s vapor pressure. This phenomenon can be explained by considering the effect of added solute molecules on the liquid's vaporization and condensation processes. To vaporize, solvent molecules must be present at the surface of the solution. The presence of...
FAQs
A water vapor pressure gradient supplies the driving force for transport, while the material’s structure determines how readily molecules move through it. Water vapor first dissolves at the exposed surface, diffuses through the material, and then desorbs at the opposite surface. This sequence explains why two materials with similar thicknesses can show different barrier performance.
Affinity for water affects how readily vapor enters the material. If the material interacts strongly with water, more vapor can dissolve at the surface before diffusion begins; its internal structure then influences movement through the material. Considering both effects prevents researchers from attributing permeability differences only to diffusion and supports informed comparisons among polymers, coatings, films, and membranes.
Thickness and temperature are essential variables when comparing results. A thicker material presents a longer path for diffusion, while temperature can alter the observed permeability. Measurements therefore have meaning only alongside the material dimensions and test temperature. Reporting these conditions helps distinguish an intrinsic material difference from a difference created by how or under what conditions the sample was evaluated.
Water vapor permeability measurements let researchers rank candidate materials by barrier performance rather than relying on composition alone. Comparing values across samples can reveal which films, coatings, or polymers better limit moisture transport. The resulting comparisons support selection of materials for moisture control, especially when stability depends on restricting vapor movement.
The property is relevant across polymers, coatings, films, membranes, and packaging materials, but the reason for evaluating it can differ. For a film or package, the focus is moisture barrier performance; for a membrane, controlled transport may be desirable. Coatings can be assessed for protective value, while pharmaceutical containers are considered in relation to stability.
In chemistry, the dissolution-diffusion-desorption sequence provides a way to connect molecular behavior with a measurable material property. Surface affinity influences entry into the material, internal structure influences passage, and the opposite surface controls release. This framework helps chemists relate composition and architecture to moisture control in coatings, packaging, containers, and membranes.