Stepwise Collapse of Monolayers of Cyclolinear Poly(organosiloxane)s at the Air/Water Interface:  A Brewster-Angle Microscopy and Scanning Force Microscopy Study

Abstract

We report studies of the collapse of monolayers of cyclolinear poly(organosiloxane)s that consist of six-membered rings joined by oxygen bridges and that contain two phenyl groups per monomer unit. Surface pressure−area isotherms show that these films undergo a stepwise collapse. The organization within the films has been examined at different stages of the collapse process by Brewster-angle microscopy. Films transferred to mica by the Langmuir−Blodgett technique have been imaged by scanning force microscopy. Five fractions of an atactic polymer with molecular weights (M W) ranging from 8900 to 85 000 and one trans-tactic polymer (M W = 8100) have been investigated. Bilayers of the fractions with the highest M W's appear in the form of islands but the bilayers in the other samples have the form of ribbons 50−250 nm wide.

Effects of Aggregate Charge and Subphase Ionic Strength on the Properties of Spread Polyelectrolyte/Surfactant Films at the Air/Water Interface under Static and Dynamic Conditions

“…Although absent in the film spread initially, linear white bands orthogonal to the direction of compression appear with increasing intensity as the film is compressed. Comparisons of these interfacial morphologies may be made to those observed in other systems under compression, e.g., silica nanoparticles modified by cationic surfactants that undergo a transition from a monolayer to multilayers above a critical surface pressure, 54 and extended structures of multilayers that are also formed upon compression in films of cyclolinear poly(organosiloxane)s. 55 As the stoichiometry of films spread from aggregates of different charge/structure studied under dynamic conditions are similar, and the total bulk concentrations are highly dilute, we infer that the activation of extended structures only in the films spread from compact, positively charged aggregates may be attributed to their presence embedded in the films. This inference is qualitatively consistent with the long ellipsometry data of sample H converging to a steady-state surface excess higher than that of a film at limiting monolayer coverage and the finite intensity in the steady state image from BAM.…”

“…Although absent in the film spread initially, linear white bands orthogonal to the direction of compression appear with increasing intensity as the film is compressed. Comparisons of these interfacial morphologies may be made to those observed in other systems under compression, e.g., silica nanoparticles modified by cationic surfactants that undergo a transition from a monolayer to multilayers above a critical surface pressure, and extended structures of multilayers that are also formed upon compression in films of cyclolinear poly­(organosiloxane)­s …”

Savinase proteolysis of insulin Langmuir monolayers studied by surface pressure and surface potential measurements accompanied by atomic force microscopy (AFM) imaging

“…Moreover, such phase domains have been observed in a wide variety of shapes, ranging from simple, circular disks to complex fractal patterns [24,25]. Buzin et al, experimentally demonstrated by Brewster angle microscopy and scanning force microscopy that monolayers of Cyclolinear Poly(organosiloxane)s undergo this kind of phase transitions [26]. The authors obtained BAM images that clearly showed the coexisting phases in the form of islands of a condensed phase separated by the regions of the other coexisting phase.…”

Distribution of Coexisting Solid and Fluid Phases Alters the Kinetics of Collapse from Phospholipid Monolayers

“…[4][5][6][7][8] This transition, commonly known as collapse, is physiologically important. In the lungs, specific cells secrete a mixture of constituents that together act as a surfactant, adsorbing to the air/ water interface of the thin liquid layer that lines the alveoli and lowering surface tension.…”