Optics: measuring and testing – For light transmission or absorption – By comparison
Reexamination Certificate
2002-02-06
2004-05-04
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
By comparison
C356S440000
Reexamination Certificate
active
06731387
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The rate of liquid droplet absorption by a capillary or porous substrate is measured by an optical electronic system.
2. Description of Related Art
Spontaneous penetration of viscous and viscoelastic fluids into pores is observed in various natural and physiological processes and has numerous application in medicine and biomedical engineering, cosmetics and personal care, oil recovery and agriculture, catalysis and separations paper and fiber industries etc. This process may be very fast. Fast absorption is commonly studied by high speed photography. The best commercial instrument known provides up to 350 drop images per second. This is known as the “Drop Shape Analysis System, DSA 10,” manufactured by Krüss of Charlotte, N.C.
The use of light beams for measuring and testing are common in the art. S. Hunt, U.S. Pat. No. 2,545,281, issued Mar. 13, 1951, tests liquid absorbency characteristics of materials during successive stages of absorption. The device uses a horizontal surface, a liquid dispenser, a timing device, a light beam and photo cell for determining liquid dispersal. The light beam and timer are used to measure the rate the liquid takes to pass through the dispenser to the material tested. B. Haley, U.S. Pat. No. 2,868,062, issued Jan. 13, 1959, tests absorption using optical means. A roller traverses a ramp and energizes a light source focused on the ramp. Photoelectric means receive light reflected from a liquid treated porous sheet on the ramp while the amount of reflect light with time is kept by a recording means. J. Banner, U.S. Pat. No. 4,720,636, issued Jan. 19, 1988, uses a light beam to detect liquid presence. Phototransistors respond to either the shadow or reflection from the liquid to furnish information to a comparator circuit and an integrator circuit. Thompson et al, U.S. Pat. No. 4,628,468, issued Dec. 9, 1986, teach light beam use for predicting pore-dependent physical properties of microporous solids. The apparatus includes a detector, recording units, a computer and memory. Fischer et al, U.S. Pat. No. 3,807,875, issued Apr. 30, 1974, teach a densitometry apparatus using a light beam passed through a sample to measure chemical concentrations, sedimentation rates, absorption, and light scattering phenomena.
STATE OF THE ART
To better understand the present invention, the art has recognized parameters and characteristics for absorption of materials and knowledge obtained by the expensive and time-consuming photographic procedures incorporated here. These are demonstrated by photographs and graphs. The concepts are inherently applicable to the present invention. To demonstrate these typical viscous and visco-elastic fluids, distilled water, water/glycerin mixture (50/50), aqueous solutions of polyethyleneoxide (PEO) with molecular mass of 4×10
6
, and polyacrylamide (PAM) with molecular mass of 11×10
6
, were used. Stainless steel capillaries of 0.46 mm and 0.65 mm diameters, glass capillaries of 0.65 mm inner diameter, and sugar cubes were used as absorbents.
The surface tension as measured by the drop weight method was 72 nN/m and 65 mN/m for water and for water-glycerin mixture, respectively. In the whole range of studied concentrations, the surface tension of PAM solutions was the same as that of water. The surface tension of PEO solutions depended on the concentration and decreased from 72 mN/m to 62 mN/m as the PEO concentration increased from zero to 100 ppm.
The rheological behavior of the fluids was analyzed by using a co-axial cylinder viscosimeter to measure the shear viscosity and the MicroRheotester developed for testing polymer solutions under stretching. Bazilevsky A. V., Entov V. M., Rozhkov A. N., “Liquid filament microrheometer and some of it's three applications”. The Golden Jubilee meeting of the British Society of Rheology and Third European Rheology Conference, 1990, Edinburgh, UK.
The dependencies of the shear viscosity versus the shear rate are presented in FIG.
4
. In the process of absorption, the high shear rates are typical. The shear rate can be estimated as &Ggr;−U/R where U is the velocity of fluid penetration and R is the capillary radius. Taking U~15 cm/s and R=0.3 mm we get the estimate of the shear rate as 500 s
−1
. At such large shear rates, &Ggr;
100 s
−1
, the shear viscosity of PEO solutions was practically the same as that of water, 1 mPa-s. At the same time, PAM solutions show a non-Newtonian behavior, especially in the range of shear rates between 100 s
−1
and 500 s
−1
. As the shear rate increases further, the viscosity of PAM solutions tends to a certain limiting value. For 200 ppm solution, this value is approximated by the viscosity of water, while for 500-1000 ppm solutions, the viscosity of water/glycerin mixture is a suitable estimate.
In MicroRheotester, the dynamics of thinning of liquid filaments is analyzed to characterize the Theological behavior of fluids in extensional flows. It is assumed that the fluid flow can be described by the upper convected Maxwell model. In addition to the shear viscosity inherent in simple liquids, this model involves another physical parameter, the relaxation time &lgr;. The latter is of the order of a time interval during which the polymer coil assumes its spheroidal shape after deformations. As shown in
FIGS. 4 and 5
, all polymer solutions showed well pronounced viscoelastic properties.
FIGS. 6-8
show video frames taken during droplet absorption The time intervals between the first, second and third images are about one second. The process takes about 10 ms between the third and fifth images. These images confirm that the droplet remains spherical until it touches the substrate. As soon as the contact is established and the absorption begins, we see the bridge formation preceding instant droplet detachment. Although the time intervals are very small, they are sufficient for stress relaxation. That is why the contact line is held pinned to the capillary brim, and, similarly to the traditional scheme of droplet formation, the detachment is caused by breakdown of the liquid bridge. While the process of bridge rupture is almost unaffected by the substrate properties, there is a striking difference between absorption of water and absorption of polymer solutions. The first four frames in
FIGS. 7 and 8
are almost identical and the time intervals between them are comparable. The time intervals between the first, second and third images of
FIG. 7
are about one second, between the last four—2-3 milliseconds. In
FIG. 8
the time intervals are: between the first, second and third images—2-3 secs, between the third, fourth and fifth—2-3 ms, between the fifth and sixth—14-16 ms, and 0.5 sec between the sixth and the eighth images. The polymer additives do not affect significantly the hydrodynamics of neck formation. They do affect the droplet snap off at the late stages when the neck transforms into a thin filament. Almost cylindrical filaments were detected for water droplets as well, but it disappears swiftly. The stability of the filament formed by a PEO solution reflects the effect inherent with macromolecular solutions: during the bridge thinning the coils are stretched thus forming a bundle of “pins” stabilizing the bridge. The filament lifetime is an order of magnitude longer than the time of neck formation. Thus, the fluid rheology influences the process of droplet detachment significantly. An analysis of the kinetics of filament thinning can be used for the determination of Theological parameters of the fluid.
The dynamics of droplet absorption is quantitatively characterized by
FIGS. 3
,
9
, and
10
. A typical record of the optical signals specifying the effect of fluid rheology is presented in FIG.
3
. As shown in
FIG. 9
, the initial droplet size does not influence the process of absorption. Thus the rate of absorption is controlled by pore level effects. The flow rates of water, water/glycerin and 200 ppm PAM solutions differ insignificantly.
Bazilevsky Alexander V.
Kornev Konstantin G.
Neimark Alexander V.
Rozhkov Aleksey N.
Coughenour Clyde I.
Geisel Kara
Smith Zandra V.
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