Abstract
In printed electronics, uniform and solute film formation by the inkjet method is very important. This study aims to clarify the relationship between Marangoni convection generated by adding surfactant and thinning of solute film. First, four types of surfactants were added one by one to the anisole-polystyrene solution with varying concentrations, and then a little amount of fluorescent polymer was added as tracer to each solution. Next, each solution was dropped on a hydrophilic substrate with a droplet diameter of 80 micrometers using an inkjet method, and the flow in the evaporation process and the shape of the solute film after drying were observed. As a result, Marangoni convection occurred when any surfactant was added at a certain concentration or more, and the solute film after drying of the droplets to which two kinds of surfactants were added became thin and approached a uniform shape. In addition, the measurement of surface tension showed that the visualized flow is the Marangoni convection.
Highlights
Printed electronics that uses inkjet technology for wiring of electronic devices and manufacturing of organic EL displays are attracting attention
An important issue has been the ‘‘coffee stain’’ problem, caused by outward flow that concentrates a solute near the edge of a liquid film. (Deegan et al, 1997) In our laboratory, we have investigated thinning of liquid film by addition of surfactant
The thinning of solute film was considered to be due to Marangoni convection towards the center of the droplet at the surface based on the difference in surface tension of the liquid film caused by the surfactant (Figure 1). the detailed mechanism of thinning by the addition of surfactant has not been clarified
Summary
Printed electronics that uses inkjet technology for wiring of electronic devices and manufacturing of organic EL displays are attracting attention. There is a problem that it is difficult to form a uniform and thin film by the inkjet method. An important issue has been the ‘‘coffee stain’’ problem, caused by outward flow that concentrates a solute near the edge of a liquid film. (Deegan et al, 1997) In our laboratory, we have investigated thinning of liquid film by addition of surfactant. The thinning of solute film was considered to be due to Marangoni convection towards the center of the droplet at the surface (inward convection) based on the difference in surface tension of the liquid film caused by the surfactant (Figure 1). The internal flow of the inkjet droplet added with surfactant was visualized, and influence of the surfactant on the internal flow and the film shape were examined
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