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1、International Standard ,NTERNAT,ONAL ORGANlZATlON FOR STANDARDIZATION*MEI(AYHAPOHAR OPrAHHSAl the interfacial tension of such systems can only be determined by the drop volume method (which will form the subject of IS0 9101). NOTES 1 Various methods have been established to determine interfacial ten
2、sion, such as : a) methods by drawing up liquid films by a plate, stirrup or ring; b) drop volume method; c) drop sessile method; d) suspended drop method; e) rotated drop method. 2 References IS0 862, Surface active agents - Vocabulary. IS0 2466, Surface active agents - Water used as a solvent for
3、tests.* 3 Definitions 3.1 interfacial tension : See IS0 862. NOTE - The SI unit of interfacial tension is the newton per metre (N/m). In practice, the sub-multiple millinewton per metre (mN/m) is used. 3.2 age of the liquid - liquid interface : The time which has elapsed between the formation of the
4、 interface in the measuring cup and drawing up of the interfacial liquid film. 4 Principle Measurement of the maximum force which can be exerted before the film breaks, the force being exerted vertically on a stirrup or ring, in contact with the inter-facial liquid film between two immiscible liquid
5、 phases placed in a measuring cup, in order to draw up the interfacial film. The force must pass through a maximum, otherwise the measurement is not valid. . * 1 mN/m = 1 dyn/cm * At present at the stage of draft. 1 Copyright International Organization for Standardization Provided by IHS under licen
6、se with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:42:38 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6889-1986 (E) 5 Apparatus Ordinary laboratory apparatus and 6.1.2 The temperature of the solutions shall be maintained to withi
7、n 0,5 OC. 5.1 Tensiometer, which can be fitted with stirrups and rings, and which shall comprise the following items : a) A horizontal platform, which can be moved vertically in both directions by means of a micrometer screw. It shall be fitted with a millimetric scale allowing estimation of ver- ti
8、cal movements of 0.1 mm. b) A dynamometer, for continuous measurement of the force applied to the measuring unit with an accuracy of a least 0,l mN/m. c) A junction piece between the lower end of the dynamometer and the upper end of measuring unit. This piece shall have an indicator for the “zero po
9、sition” for the measuring unit, and also a device for wedging it. d) A device for indicating or recording the values measured by the dynamometer. The assembly shall be shielded from vibrations and draughts. 5.2 Measuring unit, which shall comprise at least one of the items a) and b), and also item c
10、). a) A stirrup, of platinum - iridium wire of diameter not exceeding 0,l mm; the length of the horizontal arms is 20 to 40 mm, and the length of the two vertical branches is 10 mm. The ends of these branches terminate in two small platinum balls which act as counterweights (see figure I). b) A ring
11、, of platinum - iridium wire 0,3 mm in diameter. The circumference of the ring is generally between 40 and 60 mm. It is fixed to a suspending rod by means of a platinum wire stirrup (see figure 2). c) A measuring cup, to hold the test portion of the two- phase system to be examined, consisting of a
12、small cylin- drical glass tank of diameter at least 8 cm and height at least 4 cm. In the case of a ring, when a smaller measuring cup is used, the ring shall be guided, since a wall effect may attract the ring to the wall of the measuring cup, and the forces measured will not then be perpendicular
13、to the horizontal surface. 6 Procedure 6.1 Preparation of solutions of surface active agents 6.1.1 The solutions of surface active agents for the deter- minations shall be prepared with all necessary care. The water used for their preparation shall be double-distilled water (see sub-clause 5.2 of IS
14、0 2456), checked by measuring its surface tension. Cork stoppers and, more particularly, rubber stoppers, shall on no account be used, either in the construction of the distillation apparatus or for sealing containers in which the water is kept. NOTE - Determinations carried out close to temperature
15、s of critical solubility, such as the Krafft temperature or cloud point temperature of non-ionic surface active agents, are seriously affected by errors. It is preferable to carry out the test at a temperature higher than such temperatures or at a temperature lower than the cloud point temperature o
16、f non-ionic surface active agents. 6.1.3 As the interfacial tension of solutions varies with time, due to the mutual saturation of the liquid phases, and as the adsorption of surface active agents onto the interface are not instantaneous phenomena, it is difficult to recommend a standard age for the
17、 interface. It is, therefore, desirable to make several measurements over a period of time in order to obtain a curve for the interfacial tension as a function of time, and from this to determine the position of the plateau, which gives the age at which the interface reached its stationary state. 6.
18、1.4 The surface of liquids is extremely sensitive to con- tamination by atmospheric dust or by vapours from solvents handled in the vicinity. Therefore no volatile products shall be handled in the room where the determinations are carried out, and all the apparatus shall be protected by a bell of th
19、e kind used for balances. These precautions also reduce variation in temperature. 6.1.5 The recommended method of taking the test portion of the liquid phases to be examined is to suck it, with a pipette, from the centre of the mass of these phases, as the surface may be liable to soiling by insolub
20、le particles and dust. 6.2 Cleaning the measuring unit 6.2.1 Cleaning the measuring cup In the presence of impurities such as silicones, which are not removed by sulfo-chromic acid mixture, phosphoric acid or a solution of potassium persulfate in sulfuric acid, wash the measuring cup using special p
21、roducts (for example toluene, perchloroethylene or methanolic potassium hydroxide solution). If these impurities are absent, or after cleaning with these pro- ducts, wash the measuring cup carefully with hot sulfo- chromic acid mixture, and then with concentrated phosphoric acid 83 to 98 % (mlm)l. F
22、inally, rinse in double-distilled water until the rinsings are neutral. The double-distilled water shall be freshly prepared in accordance with sub-clause 5.2 of IS0 2456. Before the determination, the measuring cup shall be com- pletely dried. 6.2.2 Cleaning the stirrup or ring If necessary, clean
23、the stirrup or ring (5.2) with the special products as specified in 6.2.1. In the absence of impurities requiring cleaning with these products, or after cleaning with these products, wash the platinum measuring unit with hot concentrated sulfuric acid (20 = 1,839 g/ml), and then rinse with double-di
24、stilled water until the rinsings are neutral. 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:42:38 MDTNo reproduction or networking permitted without license from IHS -,-,-
25、 IS0 6889-1986 (El Dry the rings by passing them through a methanol flame for a few seconds. Do not touch the measuring units or the inner surface of the measuring cup with the fingers. Check that the arm of the stirrup, or the circumference of the ring, is horizontal, as described in 6.321. Raise t
26、he platform with the measuring cup and immerse the 6.3 Determination (see also annex B) measuring unit in the aqueous phase until the horizontal arm of the stirrup or the ring just touches the liquid - liquid interface. 6.3.1 Levelling the tensiometer Place a liquid level on the platform 5.1 a) and
27、adjust the screws fixed in the base of the tensiometer until the platform is horizontal. 6.3.3 Determination of force before drawing up the film Unwedge the junction piece. By simultaneously adjusting the force applied by the dynamometer and the height of the platform, bring the horizontal arm of th
28、e stirrup or the circumference of the ring to the height of the liquid - liquid interface, and the indicator of the junction piece to the “zero position”. Wedge the junction piece. 6.3.2 Preparation for the measurement Attach the junction piece f5.1 cl1 to the dynamometer f5.1 b)l. Connect the measu
29、ring unit f5.2) to the junction piece. By means of the dynamometer, apply the force necessary to bring the indicator to the “zero position”. Wedge the junction piece. 6.3.2.1 Case where the aqueous phase has the higher density Place the measuring cup on the platform. Introduce, into the measuring cu
30、p, a sufficient volume, measured to the nearest 0,05 ml, of the aqueous phase to obtain a liquid height of about 15 mm. Strictly avoid foaming, by placing the end of the pipette against the lateral internal wall of the measuring cup. Check that the arm of the stirrup, or the circumference of the rin
31、g, is horizontal, by using the surface of the aqueous phase as a mirror and observing the image of the measuring unit almost in contact with the surface of this phase. NOTE - If the surface of the aqueous phase does not give a sufficient- ly clear image, remove the measuring cup. Place a mirror on t
32、he plat- form, checking that it is horizontal by means of a liquid level. Check that the arm of the stirrup, or the circumference of the ring, is horizon- tal as previously described. Gently raise the platform with the measuring cup until the arm of the stirrup or the ring just touches the aqueous p
33、hase. Then introduce the non-aqueous phase in sufficient volume, measured to the nearest 0,05 ml, to obtain a liquid height of about 15 mm. Strictly avoid the formation of droplets or bubbles at the inter- face. 6.3.2.2 Case where the aqueous phase has the lower density Place the measuring cup on th
34、e platform. Introduce, into the measuring cup, a sufficient volume, measured to the nearest 0,05 ml, of the non-aqueous phase to obtain a liquid height of about 15 mm. Then introduce, with all necessary care, a sufficient volume, measured to the nearest 0,05 ml, of the aqueous phase to ob- tain a li
35、quid height of about 15 mm. Strictly avoid the formation of droplets or bubbles at the interface, and foaming at the surface of the aqueous phase, by placing the end of the pipette against the lateral internal wall of the measuring cup, above the surface of the non-aqueous phase. Wait until the time
36、 corresponding to the desired age for the liquid - liquid interface (see 3.3) has elapsed, then unwedge the junction piece. If the indicator is displaced from the “zero position”, bring it back to the initial position by adjusting the force applied by the dynamometer. Carefully note the force which
37、maintains the “zero position” (see figure 4). The value of this force, F, is the “force before drawing up the film”. 6.3.4 Determination of the force after drawing up the film 6.3.4.1 Case where the aqueous phase has the higher density Gently lower the platform through 0,l mm by means of the microme
38、ter screw. Bring back the indicator to the “zero pos- ition”, without passing it, by suitably increasing the force applied by the dynamometer to the measuring unit. Carefully note the value of this force. Repeat the operations described in the last paragraph until the interfacial liquid film breaks.
39、 The value of the force noted just before the film breaks, F2, is the “force after drawing up the film”. 6.3.4.2 Case where the aqueous phase has the lower density Gently raise the platform through 0,l mm by means of the micrometer screw. Bring back the indicator to the “zero pos- ition” without pas
40、sing it, by suitably decreasing the force applied by the dynamometer to the measuring unit. Carefully note the value of this force. Repeat the operations described in the last paragraph until the inter-facial liquid film breaks. The value of the force noted just before the film breaks, F3, is the “f
41、orce after drawing up the film”. 6.3.5 Repetition of determinations Carry out the determinations specified in 6.3.2 to 6.3.4 several times, using new test portions for the two liquid phases each time. The volumes of these phases shall always be the same, to the nearest 0,05 ml, as those used for the
42、 first determination. 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/23/2007 22:42:38 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6889-1986 (El 6.3.6
43、 Force for drawing up the film 6.3.6.1 Case where the aqueous phase has the higher density The “force for drawing up the film”, designated AF, is the mean value of the differences F2 - F, between the forces ap- plied by the dynamometer to the measuring unit after and before drawing up the inter-faci
44、al liquid film. 6.3.6.2 Case where the aqueous phase has the lower density The “force for drawing up the film”, designated AF, is the mean value of the differences F1 - F3 between the forces applied by the dynamometer to the measuring unit before and after drawing up the interfacial liquid film. 6.4
45、 Calibrating the tensiometer NOTE - Generally, except in case of a stirrup, the application of theoretical formulae giving the value of the interfacial tension as a function of the force exerted by the dynamometer on the measuring unit and of its geometry, does not always allow determination of exac
46、t values of the interfacial tension. Sometimes, with systems having two mutually saturated pure liquid phases, the values obtained differ widely from those given in the literature. It is necessary, therefore, to calibrate each measuring unit. For determinations not requiring very great precision, th
47、e tensiometer fitted with the stirrup or ring may be calibrated by using two-phase systems comprising two mutually saturated, superficially pure liquids having a known interfacial tension and densities similar to those of the two-phase system to be ex- amined. In these conditions, a direct relations
48、hip may be assumed between the values of inter-facial tension and the forces applied by the dynamometer to the measuring unit to draw up the inter-facial liquid film so that it does not break. Carry out the calibration using the procedure specified in 6.3 using a standard two-phase system comprising
49、 two mutually saturated superficially pure liquids, having a known interfacial tension and densities similar to those of the system to be ex- amined. Ensure that the volumes of the phases of the standard system are the same, to the nearest 0,05 ml, as those of the system to be examined. Values of the inter-facial tension between water and some organic liquids are given in annex A. where yet is the interfacial tension, in millinewtons per metre, of the standard two-phase syste
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