表面张力测试方法 Standard Test Method for Interfacial Tension of Oil Against Water by the Ring Method

Introduction： The method described in the Standard clearly states that the interfacial tension between a mineral oil and water is obtained under strict non-equilibrium conditions whereby the measurement is completed within 60 seconds after the formation of the oil/water interface. The force used to calculate the non-equilibrium tension is the force required to ‘break’ the liquid from the ring. A correction factor by Zuidema & Waters1 based on Harkins & Jordan’s2 work is applied. It should be noted that the work of the latter is the basis for measuring the absolute or theoretically correct value of interfacial tension. The force used must be the maximum pull on the ring where the contact angle of the liquid attached to the ring is zero and not the break point as the liquid detaches itself from the ring which is a lower value, see Section 2 and Fig.1. The apparatus described in the standard and shown schematically is a manual device which relies on the dexterity of the operator to lower the platform on which the sample vessel sits and turn a dial with the other hand to maintain the torsion arm in the zero position. However a variety of means to measure force can be used (torsion wire, load cell or other means to linearly determine tension) and raise or lower the platform (mechanical screw, electronic drive or other means to precisely change vertical position). In the diagram there is no means to control temperature although the standard requires the water to be at 25º C. The following paragraphs describe the work of 1 & 2, the method developed using a fully automatic software controlled system, Camtel CIT-100 Interfacial Tensiometer to conform with D971-99a and the questions posed as a result of this work.