Optics: measuring and testing – By particle light scattering – With photocell detection
Reexamination Certificate
2001-08-22
2004-12-14
Fuller, Rodney (Department: 2851)
Optics: measuring and testing
By particle light scattering
With photocell detection
C356S337000
Reexamination Certificate
active
06831741
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an arrangement for measuring the properties of multi-phase systems as well as the changes therein, such as changing interactions between particles in a solution. In particular, the invention relates to such an arrangement for use with multi-phase systems in which at least one of the phases is a liquid phase or fluid, such as gels, lattices, suspensions or emulsions.
The arrangement of the invention comprises a light source for producing a light beam. It is possible to use at least one source fibre having a first end arranged for receiving said laser beam and a second end arranged for emitting light in a multi-phase system, or to point the light directly into the multi-phase system. At least one detector fibre, arranged for detecting said light after being scattered by said multi-phase system, processing means arranged for receiving an output signal from said at least one detector fibre and for calculating predetermined parameters with respect to said multi-phase system.
Such an arrangement is known from D. S. Horne, Dynamic Light Scattering Studies of Concentrated Casein Micelle Suspensions, Chapter 15 in S. E. Hardings, e.a. Laser Light Scattering in Biochemistry, 1992.
The Diffusing Wave Spectroscopy (DWS) arrangement described by Horne, comprises a bifurcated optical fibre bundle as light guide. Half the fibres are connected to a randomly polarized He—Ne laser. The other half of the fibres is connected to a photomultiplier. The bundle of fibres is distributed randomly over the face of a common leg. In use, the non-connected ends of the fibres are dipped into a scattering multi-phase system, e.g. milk or a milk derived medium/solution. Those fibres which are connected to the laser emit laser light into the multi-phase system. Light backscattered by the multi-phase system is detected by the fibres connected to the photomultiplier. Masking by a slit and a pinhole may ensure that light from only a small area impinges on the detector.
With such an arrangement, intensity correlation functions can be measured. Examples of such functions are presented for 330 nm polystyrene latex and undiluted skim milk. Moreover, Horne shows that relaxation time as a function of casein micelle volume fraction in reconstituted milk can be measured, Horne also shows that the relaxation time changes due to curd formation. Thus, the transition from fluid to gel can be detected. One of Horne's conclusions is that: “It therefore appears that observation of DWS behaviour in these gelling systems, by virtue of its measurement of relaxation in the system, must eventually reflect changes in visco-elastic properties”. However, Horne does not indicate how visco-elastic properties may be quantitatively derived from DWS measurements.
Moreover, the measurements described by Horne can not easily be made quantitative because these measurements are made with a randomly distributed bundle of incoming and outgoing optical fibres.
A. C. M. van Hooydonk, e.a., Control and Determination of the Curd-setting during Cheesemaking, Bulletin of the International Dairy Federation (1988) (No. 255), pp. 2-10, observe that a lot of scientific research has been devoted to rennet-induced coagulation of milk. However, up to now no quantitative measurement of gel formation and the subsequent synersis of the curd is available. The optimum coagulum firmness must be determined on-line for cutting to obtain maximum cheese yield and cheese quality. Hooydonk e.a. note: “Up to now most cheesemakers judge the optimum cutting time by the “feel” of the curd and . . . with amazing accuracy”. Moreover, they note that although many instruments have been developed to carry out this task automatically, none of them have been widely accepted. The so-called “Gelograph” is considered as a standard instrument for measuring the gelation of cheesemilk at low gel strength. However, due to ongoing automation and increase of scale of cheesemaking plants there is a strong interest in automatic methods for monitoring the process of curd-setting.
In the U.S. Pat. No. 4,975,237 a dynamic light scattering apparatus is disclosed, comprising a laser as light source, optically coupled to a light scattering sample via a first optical fibre and a first lens. The lens produces a beam waist in a sample and scattered light is collected by a receive lens and a receive fibre. A photodetector detects light transmitted by the receive fibre and converts it in an electrical signal. The photodetector is connected to a correlator and computer. This correlater is not used for quantitative measurements of characteristics of the sample.
A primary object of the present invention is to provide an apparatus with which the properties of liquids, such as solutions, dispersions and emulsions can be measured and to relate physico-chemical properties to light scattering measurement in liquids.
SUMMARY OF THE INVENTION
For the purposes of the invention, the term “liquids” comprises both heterogeneous systems which contain two distinct phases, such as a liquid phase and a suspended solid phase, two immiscible liquid phases, or an emulsified (liquid) phase in a liquid phase, as well as more homogeneous systems which are subject to phase changes, phase transitions or phase formation, such as systems in which gel formation, coagulation, aggregation or changes in viscosity can occur.
These homogenous or heterogenous systems can comprise organic, inorganic as well as biological media or components, aqueous systems or solutions, or systems of a mixed organic/inorganic and/or biological nature. In a particular embodiment, the multi-phase system is milk or a milk derived medium/solution, for instance as used in cheese-making.
A further object of the present invention is to provide a method which can be carried out by an apparatus according to the invention and which is able to provide physico-chemical properties of such liquids by means of diffusing wave spectroscopy. Such a method may be related to monitoring the renneting of cheesemilk during cheese-making, but is not restricted thereto.
Thus, the arrangement according to a first aspect of the present invention as defined above is characterized in that a processing means is arranged to calculate a maximum value of the mean square displacement <&Dgr;r
m
2
> from the autocorrelation function g
(2)
as a function of time and the value of the physico-chemical property from said calculated maximum value of the mean square displacement <&Dgr;r
m
2
>.
In an embodiment the physico-chemical property is the gel-strength G′ which is calculated using the following equation:
G
′
≈
k
B
T
ξ
⟨
Δ
r
2
m
⟩
in which,
k
b
·T=thermal energy of particles in the gel;
&xgr;=size of a cluster in the gel.
The arrangement according to a second aspect of present invention is characterized in that a processing means is arranged to determine the half decay time as a function of time of the autocorrelation function and to determine the value of the physico-chemical property using a predetermined relation between the half decay time and the autocorrelation function. This value may be the gelstrength.
A further difference between the arrangement according to the invention and the Horne arrangement is the configuration of the optical fibres. Whereas the fibres in the Horne arrangement are distributed randomly and the mutual distances between the fibres is unknown, in the arrangement according to the invention the mutual distances between the detector fibres are predetermined. In order to facilitate the calculations the detector fibres are, preferably, single-mode fibres suitable for one specific monochromatic wavelength. The fibres are preferably set up in the so-called “back-scattering geometry”, which makes it possible to quantify the autocorrelation function that is measured. They may have the shape of a dipstick, so they can be easily stuck into any kind of liquid.
The advantage of DWS i
De Kruif Cornelis Gijsbertus
Nishimura Goro
Ten Grotenhuis Erik
Weitz David Allan
Yodh Arjun Gaurang
Bachman & LaPointe P.C.
Fuller Rodney
Stichting Nederlands Instituut voor Zuivelonderzoek (NIZO)
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