A STUDY OF CAPTIVE BUBBLES WITH AXISYMMETRICAL DROP SHAPE-ANALYSIS

Of the many methodologies used in surface thermodynamic experimentatio n, Axisymmetric Drop Shape Analysis (ADSA) has proven to be one of the most accurate and versatile. Until recently, however, ADSA has had tw o main limitations: (1) the inability to analyse drops with near-zero curvature at the apex; and (2) problems with drop edge detection when the contrast between the drop and the background is not adequately sha rp. In this paper, 'second-generation' ADSA algorithms and new image a nalysis schemes are introduced as solutions to these shortcomings. To illustrate these improvements, an inverted sessile air bubble in a pul monary surfactant suspension is used. This 'captive bubble' geometry w as chosen to overcome the problems of film leakage at low surface tens ions. The modified experimental apparatus, called ADSA-captive bubble (CB), in conjunction with the new software, proves to be a powerful te chnique to investigate these types of systems. ADSA-CB is fully automa ted, requiring less user intervention, enabling the collection of larg e amounts of data, and thereby providing intricate details of surface behaviour. The so-called 'squeeze-out' and him collapse phenomena are examined closely. To demonstrate the problems of film leakage, pendant (hanging) drop experimental results are also presented. (C) 1998 Else vier Science B.V.