Time-of-flight concept applied for determination of ion mobility

Summary form only given. In recent years there has been an increasing interest in using dielectric techniques for in situ monitoring of resin curing processes. These techniques consist in monitoring of changes of ionic conductivity. Although many investigations have been made, difficulties in direct measurements of physical quantities related to ionic conductivity and the complexity of the investigated polymer materials make the interpretation and understanding of the results difficult. Because the key parameter is the ion mobility which is related to the medium viscosity, a direct ion mobility measurements would be of great importance. In the present paper we show, that the time-of-flight (TOF) concept can be used for determination of the changes of the ion mobility in a course of resin curing. The TOF method applied to ions consists of two steps: i) accumulation of mobile ions close to one electrode of the capacitor-type sensor filled with the investigated resin by means of constant electric field applied to the sample; and ii) recording of the transient current caused by a step-like change of the field polarity. In an ideal case the current should be initially constant and then it should decrease rapidly when the ions reach the opposite electrode. Multiple repetition of the above two-step sequence allows one to follow the changes of the transient times during the resin curing. The measurements were carried for the well known DGEBA/3DCM epoxy/amine system cured isothermally at different temperatures. It was found, that the ionic mobility decreases linearly with the conductivity up to the gelation point. Then the conductivity starts to decay faster. Parallel TOF measurements show that this decrease is only partially caused by the decay of ionic mobility; it means that simultaneously the concentration of the mobile ions decreases also. The obtained results prove usefulness of the TOF method for studies of ionic conductivity.