3.2. Interferometry and microscopy observation
Typical interferograms of lubricating films generated by the BSA aqueous solution are shown in Fig. 4 and Fig. 5. The slider-on-disc contact was run with load w=4 N, inclination α=5.92×10−4 rad and speed ud=21.27 mm/s. At the beginning of the experiment, interference fringes were straight and smooth as shown in Fig. 5 (time instant: 0), indicating a perfect wedge gap. However, at about 20 min the horizontal fringes were bent at the side edge of the slider (Fig. 5 shows only the left part of the slider images). With increase in running time, fringe pattern within the contact changed locally. Two distinct Regions I and II could be classified, as shown in Fig. 4. Region I, which is near the outlet, has undistorted fringes. One interesting finding in the present study is the occurrence of Region II, which started from the inlet and grew towards the outlet region. Region II appeared darker with slightly blurred fringes, which indicates a quite different nature from Region I. During further running of the test, the blurred fringes near the inlet edge in Region II became slightly distinct again and formed a relatively brighter strip as shown in the top edge of the images under 40 and 80 min in Fig. 5. Furthermore, the boundary between Regions I and II is not straight.