Axisymmetric drop shape analysis as penetration Langmuir balance

Abstract

A new Langmuir-type pendant-drop penetration film balance has been developed combining a Langmuir-type pendant-drop film balance with a new rapid-subphase-exchange technique. In addition to the determination of surface pressure—molecular area isotherms of insoluble monolayers deposited on the surface of a pendant drop, it allows the study of reactions with some surfactant added to the subphase. The monolayer is spread on the surface of a drop suspended from a capillary, which is the outer one of an arrangement of two coaxial capillaries connected to the different branches of a microinjector. Once the film is brought to the desired state of compression by varying the drop volume with the microinjector, the subphase liquid in the drop can be exchanged quantitatively by means of the coaxial capillaries. This exchange is complete for a through-flow of at least three times the drop volume, and the monolayers endure it at all tested film pressures. The determination of surface tension as a function of surface area is performed using axisymmetric drop shape analysis (ADSA). The complete set-up, i.e., the image capturing and microinjector system is fully computer controlled by a user-friendly and fully Windows integrated program, including the ADSA surface tension calculus algorithm. As a penetration film balance, pendant-drop methodologies offer a wide range of advantages such as a more stringent control of the environmental conditions and therefore, more uniform temperature, pressure and concentration along the interface, small amounts of material needed, and a 20 times greater interface/volume ratio than in conventional Langmuir toughs.

Development of a Constant Surface Pressure Penetration Langmuir Balance Based on Axisymmetric Drop Shape Analysis

“…1, a schematic representation of the setup is shown, which is essentially identical to the one used by CabrerizoVílchez et al, excepting the fuzzy control, and is described in detail elsewhere (18). It is completely computer controlled by a user-friendly, Windows-integrated program (Dinaten).…”

“…ADSA was originally developed for determining the interfacial tension, contact angle, drop surface area, and drop volume based on a drop profile (7), and among other uses has been applied successfully to the measurement of interfacial tensions between immiscible liquids (9), and to the determination of ultralow interfacial tensions (10). It also has been employed for relaxation kinetics studies of surfactant adsorption layers (11)(12)(13)(14) and as a film balance at the air-water interface (15)(16), at the oil-water interface (17), and recently as a penetration film balance at the air-water interface (18) and at the oil-water interface (19), offering a wide range of possibilities and advantages over conventional surface balances.…”

Drop profile analysis tensiometry with drop bulk exchange to study the sequential and simultaneous adsorption of a mixed β-casein /C12DMPO system

“…For the simultaneous adsorption, we mixed respective protein and surfactant solutions and allowed 30 min for protein-surfactant complex formation before starting the measurements. The surface tension measurements were performed with the drop profile analysis tensiometer PAT-1, equipped with a special Double Dosing System [7,8,12] (SINTERFACE Technologies, Berlin, Germany). The general setup and the details of the measuring principles are described in detail elsewhere [3].…”

“…The method was further developed then to allow also dilational rheological studies, including transient [5] and low frequency harmonic relaxations [6]. Another remarkable step was made by Wege et al [7,8] who managed for the first time to exchange the liquid within a single pendent drop during drop shape measurements. This idea is now practiced in a number of experimental protocols, such as for desorption studies [9], penetration experiments [10], wash off studies [11] or even for multilayer formation [12].…”

“…The used experimental technique is a special modification of drop profile analysis tensiometry equipped with a double coaxial capillary [7]. This arrangement allows to measure the simultaneous adsorption of both component from a mixed solution and also the subsequent adsorption of the protein first and then followed by the surfactant.…”