Customized Free-standing Thin Liquid Film Forming Based On Controllable Iris

Thin films and membranes are one of the important members of soft matter, they have played many essential roles in research fields such as chemistry, materials science, mathematics, etc. Although humankinds have figured out how to make films from soapy liquids hundreds of years ago, quantitative films forming is still an open challenge nowadays, especially for free-standing films. Conventional quantitative film preparation methods often use the interface between bubbles to quantitatively generate free-standing film. In addition, the edge injection method is also widely used to obtain free-standing films with smaller diameters (less than 10 mm). However, for the gravity-free environment, the above two conventional methods have certain drawbacks. In this paper, we propose a quantitative preparation strategy for free-standing thin liquid films. This is an experimental system that can complete quantitative thin film preparation even in a gravity-free environment. Digital holographic dynamic imaging has been used in this system to achieve closed-loop control of thin film fabrication process. It allows us to quantitatively characterize film formation and its final three-dimensional structure. The key concept of this system is an optical iris-based droplet opening device. For the preparation of thin films, a droplet is placed at the central aperture of the iris when it is closed; the diameter of this aperture is less than 1 mm, which also creates the possibility of using tiny droplets for film generation; then, by slowly opening the optical iris, a uniform pulling force distribution is created on the droplet. Therefore, a liquid film with known volume can be formed. Owing to the three-dimensional non-contact non-destructive measurement capability of digital holography for transparent liquid films, it has been used to monitor the forming process of thin film during opening. This allows us to quantitatively prepare thin liquid films with required thickness, and it is also possible to reach the common black film. Herein, we show the quantitative preparation of surfactant films and glycerol films, a series of experimental data were recorded and reconstructed by digital holography. The digitized thickness information also creates the possibility of dynamic modeling of the film forming process. By analyzing the spatiotemporal thickness model of the thin film preparation process, we reveal the liquid flow motion and thickness variation trends during film forming.