Liquid penetration time

The ADL is very important to provide a sense of dryness to the skin, providing additional separation between the wet pad and the skin. ADLs should be used whenever the mix of SAP in the absorbent core exceeds about 15% by weight or when the liquid penetration time requires a boost in order to avoid diaper leakage due to liquid accumulation inside the diaper. ADLs are made either of through air bond nonwovens, curly fibres such as in P G s pampers and some Ontex diapers, or some kind of highloft nonwoven. An aperture film, made of perforated plastic film, has also been used successfully in some markets. Lower priced diapers sometimes use resin-bonded nonwovens, but they do not work as well. 

Fig. 4 illustrates the time-dependence of the length of top s water column in conical capillary of the dimensions R = 15 pm and lo =310 pm at temperature T = 22°C. Experimental data for the top s column are approximated by the formula (11). The value of A is selected under the requirement to ensure optimum correlation between experimental and theoretical data. It gives Ae =3,810 J. One can see that there is satisfactory correlation between experimental and theoretical dependencies. Moreover, the value Ae has the same order of magnitude as Hamaker constant Ah. But just Ah describes one of the main components of disjoining pressure IT [13]. It confirms the rightness of our physical arguments, described above, to explain the mechanism of two-side liquid penetration into dead-end capillaries. 

A little thought will make it clear that the washing is much more effective if the liquid is removed as completely as possible each time before applying fresh wash liquid, and that a number of washings with a small amount of liquid each time is more effective than fewer washings with much greater quantities of wash liquid. It is, of course, evident that with each washing the liquid should penetrate to all parts of the solid material. 

This method consists of application of liquid to the surface of a sample, allowing the liquid to penetrate into the discontinuities in the sample. After some time the excess liquid on the surface is removed, leaving the liquid in the discontinuity intact. Then a developing agent is applied, which draws the liquid penetrant from the discontinuity to the surface of the sample, leaving a visible indication of the discontinuity on the sample. The liquid penetrant usually consists of a colored dye to enable ease of detection in either visible or ultraviolet light. 

The rate of liquid penetration has been investigated by Rideal and Washburn [7, 8]. For horizontal capillaries (gravity-neglected), the depth of penetration I in time t is given by the Rideal-Washbum equation [7, 8] ... 

Y = surface tension, 9 = contact angle, and ri = liquid viscosity. Alternatively for the purpose of these experiments it will be more convenient to employ the volume V, of liquid penetrating into the porous structure after time t. Thus from [l] it can be shown (4) that for capillaries so small that the external pressure is negligible in comparison to the capillary pressure... 

Hoyland (2) contends that aqueous liquids penetrate paper more by this process than by capillary action. Commencing with Fick s second law of diffusion which relates the diffusion coefficient D to a function of the concentration change of diffusing liquid in time t at any point x along the direction of diffusion ... 

Liquid water at room temperature can penetrate across the entire fiber in less than 15min and in less than 5min at 92°F [76], whereas more than 6h is required for single hbers to equilibrate in a humid atmosphere, and even longer for a hber assembly. Dyes like methylene blue (MW 320) and orange II (MW 350) generally require over an hour to penetrate through the cuticle layers to the cortex. Similar penetration times would be expected for typical anionic and cationic surfactants used in shampoos and hair conditioners. 

The mass transfer coefficient could be described with the penetration model supposing that the liquid residence time is very short compared to the diffusion... 

When liquid penetrates a single capillary of radius r, the length of flow /, in time t, for fluid of viscosity fi, is given by the Washburn [3, 4] equation... 

The drop penetration time can be estimated using a model, which considers the rate at which liquid flows into the pores in the powder surface under capillary action (6) ... 

Drop penetration time Is the liquid phase too viscous, or the particle size too small to achieve fast drop penetration ... 

When the rates of penetration are controlled by the viscosity of a liquid, the time dependence of the length I of the imbibed liquid column is described by... 

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