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Understanding Hygroscopicity

Hygroscopicity is an important, but difficult to define attribute. The reason for this is that there is both a thermodynamic and a kinetic component in the term. We can simply describe this characteristics by the rate of moisture uptake of an object relative to the vapor pressure differential of the atmosphere Pa around the surrounding object having the vapor pressure Po of the saturated solution, assuming that the object does not have the ability to hydrate and Pa > Po. Based on the above, the rate of condensation shall be proportional to (Pa - Po) and the surface area A of the object. Accordingly we have,

Rate of moisture uptake = dW/dt = kA(Pa - Po),


dW = change in weight between initial state Wi and Wt at time t

Therefore, the weight of the object at time t is:

W = kA(Pa - Po)t + Wi

and the change of weight W in time t will have the slope of kA(Pa - Po),


k = intrinsic property of a material's moisture uptake rate relative to its "hygroscopicity"

The equilibrium moisture content (EMC) and the rate at which this level is achieved are referred to as hygroscopic properties of the substance. This characteristic is critical in the understanding of the product's stability.

Opulus provides various levels of solution products based on PyroButton Self-powered data-loggers, MACH1 (Multi Action Chamber for Humidity) system, communication controllers, and integrated software to meet the requirement for the measurement of hygroscopicity based on moisture penetration rate, EMC, %RH, and weight change.


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