Moisture diffusivity

The cure rate of a sihcone sealant is dependent on the reactivity of the cross-linker, catalyst type, catalyst level, the diffusion of moisture into the sealant, and the diffusion of the leaving group out of the sealant. For one-part sealants, moisture diffusion is the controlling step and causes a cured skin to form on the exposed sealant surface and progress inward. The diffusion of moisture is highly dependent on the temperature and relative humidity conditions. 

The objective of the immersion test is to determine the moisture content (percent weight gain) of a material as a function of its immersion time. To interpret immersion test data, moisture diffusion through the thickness of a test specimen can be described using a one-dimensional Fickian equation... 

The diffusivity Dq and equilibrium moisture content Wg are parameters which describe a specimen s moisture diffusion properties. 

This measurement methodology and data analysis is general and can be extended to other porous media. The results from MRI moisture profiles can also be used to measure moisture diffusivity that enable moisture transport models to be developed for a wide range of materials. 

Permeability of an FML is evaluated using the Water Vapor Transmission test.28 A sample of the membrane is placed on top of a small aluminum cup containing a small amount of water. The cup is then placed in a controlled humidity and temperature chamber. The humidity in the chamber is typically 20% relative humidity, while the humidity in the cup is 100%. Thus, a concentration gradient is set up across the membrane. Moisture diffuses through the membrane, and with time the liquid level in the cup is reduced. The rate at which moisture is moving through the membrane is measured. From that rate, the permeability of the membrane is calculated with the simple diffusion equation (Fick s first law). It is important to remember that even if a liner is installed correctly with no holes, penetrations, punctures, or defects, liquid will still diffuse through the membrane. 

The extent of hydration or solvation of a molecule also has a profound effect on the transport of the substance. The apparent solubility of the drug in both aqueous and nonaqueous media may be influenced by the absence or presence of moisture. Diffusion of drugs in polymeric systems may also be influenced by the hydration of the polymers and hydration of the membrane through which transport is occurring for example, skin hydration may enhance the diffusion of drug molecules significantly. 

The larger the solute molecular size, the higher the water loss and the lower the sugar uptake under fixed process conditions. Using the right size of osmotic solute, satisfactory moisture diffusivities, with nearly zero net solute uptake, can be obtained. 

Although effective moisture diffusivity decreased normally in osmotically treated fruits, there are some quality characteristics that are always better in osmodehydrated-dried than in fresh-dried ones. 

Information on the fatigue, moisture diffusion and damage accumulation in polymer composites is understood to be available in the Delaware Composites Design Encyclopedia [21]. 

Dust control is a major problem in corrosion control by silicone polymers. Dust particles which may bridge, or meerly lay upon conductors will absorb moisture diffusing through the silicone and result in a localized site of corrosion. We found this to be the case in a number of our early saunples. Following the results of this study, all of our encapsulated assemblies will be cleaned and encapsulated in a clean room which is serviced by HEPA filters. 

Interaction of the adhesive at the hydrophilic sections of the tissue, when it displaces moisture from these sections, creates a strong adhesion joint, whereupon moisture diffusion at the interface will be less probable than in the case of hydro-phobic interactions. Consequently, the edges of the wound will be held under these conditions for a long period of time. 

Measurement of the moisture diffusion coefficient as a function of position in wheat grain was performed [47] the moisture diffusion rate normal to the transverse 1.3 mm section of wheat grain was measured in structural features at a 150 pm resolution. The motion of water was most severely hindered in the endosperm, and water appeared less hindered in the vascular bundles. 

The empirical model for calculating moisture diffusivity as a function of moisture and temperature ... 

It should be pointed out that the amount of moisture that enters or leaves a building by diffusion is usually negligible compared to the amount that enters with infiltrating air or leaves with exfiltrating air. The primary cause of interest in the moisture diffusion is its impact on the performance and longevity of building materials. 

Another factor augmectting the heat conductivuty of plastic foams under conditions is the absorbed moisture. For example, for CCljF-foamed polyurethane at 25 °C and a relative humidity of 65%, the ambient moisture diffusion rate is 10-20 g/m for 24 h. Especially strong is the effect of moisture on heat conductivity if the temperature differential across the sample is considerable. For example, in plastic foams used in cryogenic technology, the inner layers are exposed to low temperatures the water vapor first condenses and is then convected into ice. Since the thermoconductivity of water and ice are 0.5 and 1.5 kcal/m x h °C, respectively, even minor tunounts have a considerable detrimental effect of the heat insulating capacity of a foam material... 

Gas and moisture diffusion may be prevented by the application onto the material surface of a tin, foil or synthetic coating however, this is not always feasible technically or economically. For example, coating of a plastic foam with a 3 mm thick ABS-plastic film stabilizes the gas composition inside the foam for several... 

The colorants of choice for these applications are lakes and inorganic pigments. In addition to providing color, pigments have been reported to reduce moisture diffusion through the film and improve light stability as compared with dye. ° ... 

The Moisture Diffusion Coefficient. The one-dimensional moisture flux (/) (g/cm s) of water through wood customarily is given as the product of the moisture diffusion coefficient D (cm /s) and the gradient dcjdx of moisture concentration (g/cm ) in the direction of flow, or... 

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