GB2071841A - Measurement of dispersion particle size - Google Patents
Measurement of dispersion particle size Download PDFInfo
- Publication number
- GB2071841A GB2071841A GB8008662A GB8008662A GB2071841A GB 2071841 A GB2071841 A GB 2071841A GB 8008662 A GB8008662 A GB 8008662A GB 8008662 A GB8008662 A GB 8008662A GB 2071841 A GB2071841 A GB 2071841A
- Authority
- GB
- United Kingdom
- Prior art keywords
- radiation
- dispersion
- particle size
- wavelength
- measured
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000002245 particle Substances 0.000 title claims abstract description 34
- 239000006185 dispersion Substances 0.000 title claims abstract description 24
- 238000005259 measurement Methods 0.000 title claims description 15
- 230000005855 radiation Effects 0.000 claims abstract description 25
- 238000000034 method Methods 0.000 claims abstract description 22
- 239000000839 emulsion Substances 0.000 claims abstract description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 8
- -1 silver halide Chemical class 0.000 claims abstract description 7
- 229910052709 silver Inorganic materials 0.000 claims abstract description 6
- 239000004332 silver Substances 0.000 claims abstract description 6
- 238000010521 absorption reaction Methods 0.000 claims abstract description 4
- 238000012544 monitoring process Methods 0.000 claims abstract description 4
- 230000005540 biological transmission Effects 0.000 abstract description 3
- 238000001739 density measurement Methods 0.000 description 5
- 230000005070 ripening Effects 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- 239000007788 liquid Substances 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- ADZWSOLPGZMUMY-UHFFFAOYSA-M silver bromide Chemical compound [Ag]Br ADZWSOLPGZMUMY-UHFFFAOYSA-M 0.000 description 3
- 238000004879 turbidimetry Methods 0.000 description 3
- 108010010803 Gelatin Proteins 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 2
- 229910001634 calcium fluoride Inorganic materials 0.000 description 2
- 229920000159 gelatin Polymers 0.000 description 2
- 239000008273 gelatin Substances 0.000 description 2
- 235000019322 gelatine Nutrition 0.000 description 2
- 235000011852 gelatine desserts Nutrition 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 239000002609 medium Substances 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000004677 Nylon Substances 0.000 description 1
- 238000005119 centrifugation Methods 0.000 description 1
- 238000005112 continuous flow technique Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000000386 microscopy Methods 0.000 description 1
- 229920001778 nylon Polymers 0.000 description 1
- 238000000424 optical density measurement Methods 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000000790 scattering method Methods 0.000 description 1
- 238000004062 sedimentation Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000005029 sieve analysis Methods 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
Landscapes
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
It is practicable to measure the average particle size of an aqueous dispersion using near infra-red radiation of a wavelength in the range 1.35 to 6 <0>m despite the strong absorption by water of such radiation. In the preferred method, the specular density of the dispersion in an unusually thin (less than 1 mm) cell is measured using radiation corresponding to a transmission maximum of water within the specified wavelength range. The method is useful for monitoring processes, such as photographic silver halide emulsion grain growth, in which particles of a predetermined average size are produced.
Description
SPECIFICATION
Measurement of dispersion particle size
This invention relates to a radiation scattering method of measuring the average particle size of an aqueous dispersion.
Dispersions of solid or liquid substances in water are of importance in a number of industries, and the usefulness of a particular dispersion may depend critically on the size of the dispersed particles. This is especially the case in the photographic industry where the size of the lightsensitive silver halide crystals forming the 'grains' of the photographic 'emulsion' has a considerable effect on the sensitivity and other properties of that emulsion. Another industry in which dispersions are important is that of paint manufacture where the size of resin-pigment particles in emulsion paints, affects the properties of the product.
A variety of experimental methods are available which give information about the size of dispersed particles. These methods include both light- and eiectron-microscopy, optical scattering techniques, disc centrifugation, Coulter Counter analysis and sieve analysis. Of the scattering techniques turbidimetry is particularly convenient, because it can allow size to be assessed from a single optical density measurement, but because of problems associated with data interpretation it has not found wide application in the photographic industry.
If a beam of monochromatic radiation of intensity lo is passed through a cell of thickness L containing a dispersion of particles of diameter d comparable with the wavelength Ao of the radiation in air, then some of the radiation is scattered by the particles, reducing the intensity of the beam to I, and the turbidity T of the dispersion is defined as:
1 lo 1 lo T = - In - = - . 2.303 log - L I L
The specular optical density D is given by:
lo
D = log
I and so:
2.303 D
T =
L
Thus the specular optical density is directly proportional to the turbidity and so provides a convenient measure of it.
A plot of turbidity against particle size is a curve having three portions, the first being an upwardly curving portion, the second a portion in which the density is roughly proportional to the particle diameter, and the third a portion in which the density oscillates irregularly. If the turbidity is measured for a dispersion in which (as is normally the case) the particles are not all of the same size, the reading obtained will be a measure of an average particle size provided that the largest particles are not of a diameter falling within the third portion of the turbiditydiameter curve. It is possible, in principle, to study particle size distributions having means diameters falling within the third, undulating, portion of the curve, but it is necessary to make specular density measurements for a number of wavelengths and to subject the results to complex analysis.
For homogeneous spheres of equal diameter dispersed at a concentration not great enough to cause multiple scattering of radiation, it is possible to calculate the turbidity. The calculation for the first portion of the curve is comparatively simple, being effected using an equation published by Rayleigh in 1871. For the remainder of the curve, the calculation is by means of expressions published by Mie in 1 908 which are sufficiently complex to require computer evaluation.
The scattering process depends upon the relative values of the particle diameter and the wavelength of the measuring radiation, and it is convenient in calculating scattering to use, instead of the particle diameter d, a particle size parameter a defined by: Hod no (Y = --- A0 where nO is the refractive index of the dispersing medium.Since a is directly proportional to the diameter, a specular density-a curve has the same form as the specular density-particle diameter curve described above. Accordingly, it is possible to determine an average particle size from a single specular density measurement provided that a for the largest particles present, does not exceed the value, aax, at which the third portion of the curve commences.This limiting value depends upon a quantity m, the relative refractive index, defined by:
refractive index of particles n " " II medium nO np and nO being values for radiation of wavelength Ao Figure 1 of the accompanying drawings gives a necessarily approximate indication of how amax depends upon m, the values having been taken from W. Heller, Proceedings of the Interdisciplinary Conference on Electromagnetic Scattering, New York, edited M. Kerker (1963).
In deciding upon the suitability of a turbidimetric method of the present invention for measuring any particular dispersion, it is helpful to calculate the turbidity using the Rayleigh equation, which is:
wherein T, m, nO, Ao and d are as already defined, c is the concentration in weight/unit volume of the dispersed particles and p is the density of the dispersed particles. When, as may be the case, an exact value for m is not avaiiable, a value obtained by extrapolating refractive indices measured using visible light may allow useful approximate calculations. The value of a up to which the Rayleigh equation predicts the turbidity depends upon the value of m.A rough guide is included in Fig. 1 where the broken line shows the value of a for which the Rayleigh equation gives a 5 per cent error plotted against the relative refractive index. This plot is based on Heller (op cit), the portion of m greater than 1.35 having been obtained by extrapolating the straight line plot of Fig. 2 (page 105) of that reference.
For a dispersion of silver bromide particles in water or a dilute aqueous gelatin solution, the relative refractive index for red light of wavelength of 650 nm is estimated to be 1.68 and so it is evident from Fig. 1 that the maximum value of a which can be measured unambiguously from a single density measurement is about 1.7 which corresponds to an average particle diameter of about 0.3 pm. Silver bromide grains of this diameter have in fact been measured with red light (e.g. Mailliet and Pouradier, J. Chim. phys. 58711(1961)).
Some commercially important photographic emulsions have silver bromide grains of appreciably greater average diameter than 0.3 pm and so their size cannot be assessed by simple turbidimetry with visible light. From the value of a max = 1.68 quoted above it is evident that for grains of 1 pm diameter, near infra-red radiation of about 2 pm is necessary.
Few turbidimetric studies of aqueous dispersions of any kind have been made using near infra-red radiation and these have been limited to wavelengths up to 1.35 pm (see, for instance,
Chemical Abstracts 91 404 (abstract 91: 18159w)). Water strongly absorbs radiation of longer wavelengths and this fact has evidently deterred workers from making turbidimetric measurements in this region.
Instead of measuring the reduction in intensity of a beam on passing through a dispersion, it is useful to study the intensity and/or polarisation of radiation scattered out of the incident beam in chosen directions. For instance Napper and Othewill have pointed out (J. Photo. Sci. II 84 (1963)) that the polarisation ratio of scattered light is a useful measure of particle size over a certain range.
According to the present invention there is provided a method of measuring the average particle size of an aqueous dispersion which comprises measuring the scattering by that dispersion of near infra-red radiation of a wavelength in the range 1.35 to 6 pm.
Preferably the specular density, i.e. turbidity, of the dispersion is measured in a cell considerably thinner than the smallest ( mm) conventionally used so as to reduce the amount of radiation absorbed by the aqueous dispersion medium. This absorption can also be reduced by selecting radiation of a wavelength within a transmission window of water. By both these means it is possible to increase the amount of radiation transmitted to such an extent that accurate specular density measurements are readily made.
Involving only a single density measurement per size determination, the preferred. turbidimetric. method is very convenient, and lends itself to the monitoring of a process in which it is desired to form dispersed particles having a given average size. For example it is very suitable for monitoring the growth of photographic silver halide emulsion grains, during either precipita tion or ripening. Silver halides are not, unless specially sensitized, sensitive to near infra-red radiation and so the method does not fog the measured grains. The use of a cell unusually thin for turbidimetry has the advantage in the case of certain photographic emulsions, of allowing measurement of the undiluted emulsion.
In carrying out turbidimetric measurements in accordance with the invention, a cell of thickness less than 1 mm, and especially less than 0. 1 mm is preferably employed. The cell can conveniently consist of a pair of windows separated by a spacer of an inert plastics material such as polytetrafluoroethylene or nylon. The cell has such a small volume that the loss of dispersion caused by a series of measurements can in many cases be ignored. When it is desired to follow a fairly rapid change in particle size, dispersion can be withdrawn continuously from the main volume, passed through the cell and either returned to that volume or run to waste.
The preferred wavelengths for the measuring radiation are 1.7, 2.2, 3.8 and 5.4 pm because these correspond to maxima of the near infra-red transmission curve for water. A glass cell is suitable for measurements at 2.2 ym whereas a cell having infra-red transmitting windows, for instance of calcium fluoride, is required for longer wavelengths. The path length selected for the cell is preferably such that the maximum density to be measured is 2. It can either be directly measured or calculated from the density increase on substituting a liquid of known absorption coefficient for a liquid transparent at a given wavelength.
The invention is illustrated by the following Examples.
Example 1
The increase in size of the grains of a photographic gelation-silver bromoiodide dispersion during ripening was measured both turbidimetrically, by the method of the invention, and by the disc centrifuge and electron microscope techniques. The dispersion contained 0.5 mole of silver halide and 10 grams of gelatin per kilogram.
The turbidimetric measurements were made using a quartz cell of 57.5 pm path length and infra-red radiation of 2.22 pm wavelength in a Cary 1 7 Spectrophotometer. Small samples of the emulsion were periodically withdrawn for the several measurements.
The results obtained from the turbidity and disc centrifuge measurements are presented graphically in Figs. 2 to 4. Fig. 2 shows the specular density readings plotted as a function of the ripening time, a second ordinate scale giving the equivalent turbidity values. The rapid fall off in density after about two hours is believed to be associated with grain sedimentation and clumping. Fig. 3 shows the average grains size from the disc centrifuge measurements plotted against the ripening time, the vertical lines showing the probable error of each measurement.
Fig. 4 combines the data of Figs. 2 and 3, showing the specular density (and turbidity) as a function of average grain size, the ripening times being indicated against the horizontal lines showing the probable error in the size measurements. The drawn curve is not the curve best fitting the experimental results but is the curve calculated from turbidity theory. The curve is that for the Raleigh equation (quoted above) for a grain size up to about 0.6 ym (a = 1. 1). For larger grain sizes, the Mie theory has been used for the calculation.
It will be noted from Fig. 4 that for grains of diameter up to about 0.7 pm the disc centrifuge grain size results were some 10 per cent greater than values calculated from the measured turbidity. The electron microscopic results were some 10 per cent smaller than the calculated values.
Example 2
The growth of grains similar to those ripened in Example 1 was followed turbidimetrically using infra-red radiation of 3.8 pm wavelength and a calcium fluoride flow cell of thickness 100 pm. Emulsion withdrawn from the main volume was circulated through this cell and the specular density was measured with a Perkin Elmer 580 spectrophotometer and continuously recorded.
Samples were withdrawn periodically for disc centrifuge measurement. Fig. 5 shows the densityripening time curve obtained.
Example 3
Application of the continuous flow and measurement technique described in Example 2 using a glass cell and radiation of wavelength 2.22 pm produced results closely similar to those of
Example 1 shown in Fig. 2.
Claims (6)
1. A method of measuring the average particle size of an aqueous dispersion which comprises measuring the scattering by that dispersion of near infra-red radiation of a wavelength in the range 1.35 to 6 pm.
2. A method according to Claim 1 wherein the wavelength of the radiation chosen for the scattering measurement lies within one of the infra-red absorption minima or water at 1.7, 2.2, 3.8 and 5.4 micrometres.
3. A method according to Claim 1 or 2 wherein the specular density is employed as a measure of the scattering.
4. A method according to Claim 3 wherein the specular density is measured using a cell of thickness less than 1 mm.
5. A method of monitoring a process in which dispersed particles of a preselected average size are produced, wherein the average size of the particles is measured by a method according to any of the preceding claims.
6. A method according to Claim 5 wherein the monitored process is the growth of photographic silver halide emulsion grains.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8008662A GB2071841B (en) | 1980-03-14 | 1980-03-14 | Measurement of dispersion particle size |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8008662A GB2071841B (en) | 1980-03-14 | 1980-03-14 | Measurement of dispersion particle size |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2071841A true GB2071841A (en) | 1981-09-23 |
| GB2071841B GB2071841B (en) | 1984-01-25 |
Family
ID=10512089
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8008662A Expired GB2071841B (en) | 1980-03-14 | 1980-03-14 | Measurement of dispersion particle size |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2071841B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5236473A (en) * | 1992-11-10 | 1993-08-17 | Eastman Kodak Company | Sipper tube with ultrasonic debubbling |
| GB2280749A (en) * | 1993-08-07 | 1995-02-08 | Kodak Ltd | Measurement of droplet size of a photographic dispersion |
| WO1996024830A1 (en) * | 1995-02-10 | 1996-08-15 | Wolfking Danmark A/S | Method for determining the particle size of a material |
| US5557405A (en) * | 1994-08-02 | 1996-09-17 | Eastman Kodak Company | Measurement of droplet size in a photographic dispersion |
-
1980
- 1980-03-14 GB GB8008662A patent/GB2071841B/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5236473A (en) * | 1992-11-10 | 1993-08-17 | Eastman Kodak Company | Sipper tube with ultrasonic debubbling |
| GB2280749A (en) * | 1993-08-07 | 1995-02-08 | Kodak Ltd | Measurement of droplet size of a photographic dispersion |
| GB2280749B (en) * | 1993-08-07 | 1997-05-14 | Kodak Ltd | Measurement of droplet size in a photographic dispersion |
| US5557405A (en) * | 1994-08-02 | 1996-09-17 | Eastman Kodak Company | Measurement of droplet size in a photographic dispersion |
| WO1996024830A1 (en) * | 1995-02-10 | 1996-08-15 | Wolfking Danmark A/S | Method for determining the particle size of a material |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2071841B (en) | 1984-01-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19960314 |