On the Nature of the Breath Figures Self-Assembly in Evaporated Polymer Solutions: Revisiting Physical Factors Governing the Patterning

In Search of a Green Process: Polymeric Films with Ordered Arrays via a Water Droplet Technique

As an efficient technique for the preparation of polymeric hexagonal orderly arrays, the breath figure (BF) process has opened a modern avenue for a bottom-up fabrication method for more than two decades. Through the use of the water vapor condensation on the solution surface, the water droplets will hexagonally pack into ordered arrays, acting as a template for controlling the regular micro patterns of polymeric films. Comparing to the top-down techniques, such as lithography or chemical etching, the use of water vapor as the template provides a simple fabrication process with sustainability. However, using highly hazardous solvents such as chloroform, carbon disulfide (CS2), benzene, dichloromethane, etc., to dissolve polymers might hinder the development toward green processes based on this technique. In this review, we will touch upon the contemporary techniques of the BF process, including its up-to-date applications first. More importantly, the search of greener processes along with less hazardous solvents for the possibility of a more sustainable BF process is the focal point of this review.

Breath-Figure Self-Assembly, a Versatile Method of Manufacturing Membranes and Porous Structures: Physical, Chemical and Technological Aspects

The review is devoted to the physical, chemical, and technological aspects of the breath-figure self-assembly process. The main stages of the process and impact of the polymer architecture and physical parameters of breath-figure self-assembly on the eventual pattern are covered. The review is focused on the hierarchy of spatial and temporal scales inherent to breath-figure self-assembly. Multi-scale patterns arising from the process are addressed. The characteristic spatial lateral scales of patterns vary from nanometers to dozens of micrometers. The temporal scale of the process spans from microseconds to seconds. The qualitative analysis performed in the paper demonstrates that the process is mainly governed by interfacial phenomena, whereas the impact of inertia and gravity are negligible. Characterization and applications of polymer films manufactured with breath-figure self-assembly are discussed.

Progress in low voltage reversible electrowetting with lubricated polymer honeycomb substrates

Electrowetting of silicone oil lubricated PC + EC substrates. (A)U= 0 V; (B)U= 55 V.

Revisiting the fine structure of the triple line

The fine structure of the triple line for water droplets deposited on porous polymer substrates was investigated. Substrates were obtained with the breath-figures self-assembly. Water droplets demonstrated the pronounced Cassie-Baxter wetting regime. The triple line was imaged with environmental scanning electron microscopy. The roughness of a triple line was characterized with its averaged root-mean-square (rms) width w(L), and its scaling experimental dependence upon the length L of the triple line w(L) is proportional to L(ζ) was analyzed. The values of exponents in the range of 0.60-063 were established. The deduced values of ζ evidence the local nature of the triple-line elasticity and support the idea that the elastic potential of the triple line includes only even powers of the displacement.

Electrically controlled membranes exploiting Cassie-Wenzel wetting transitions

We report electrically controlled membranes which become permeable when an electrical field is exerted on a droplet deposited on the membrane. Micro-porous polycarbonate membranes are obtained with the breath-figures assembly technique, using micro-scaled stainless steel gauzes as supports. The membranes demonstrate pronounced Cassie-Baxter wetting. Air cushions trapped by the droplet prevent water penetration through the membrane. We demonstrate two possibilities for controlling the permeability of the membrane, namely contact and non-contact scenarios. When an electrical field is exerted on a droplet deposited on the membrane, the triple-line is de-pinned and the wetting transition occurs in the non-contact scheme. Thus, the membrane becomes permeable. The contact scheme of the permeability control is based on the electrowetting phenomenon.