Visualization of skin layer formation process on the aqueous colloidal solutions surface in the inkjet nozzle by using dynamic light scattering method

Abstract

The objective of this paper is to develop a method for visualizing the onset of skin layer formation at the gas-liquid interface during the evaporation of a water-based pigment ink filled in a narrow space such as the nozzle of an inkjet printhead. We developed two methods to visualize the surface and depth-wise distributions of the diffusion coefficient near the edge of a glass capillary filled with aqueous colloidal solution by using measurements based on the dynamic light scattering method. One method generates laser speckles at the gas-liquid interface of the ink, which are analyzed to determine the temporal changes in the surface distribution of particle diffusion coefficients. Another method uses an optical coherence tomography method to acquire cross-sectional images of the ink in the depth-wise direction, and analyzes the speckles that appear on the images to determine the temporal change in the depth distribution of the particle diffusion coefficient. It was observed that, depending on the type of hardly volatile solvent in ink, there are cases where the diffusion coefficient changes while remaining spatially uniform, and other cases where the diffusion coefficient differs remarkably near the gas-liquid interface. Since the motion of particles in the ink can be visualized in three dimensions, although pseudo-lightly, it has been possible to detect signs of skin layer formation.

Keywords

• visualization
• light scattering
• evaporation
• speckle imaging
• optical coherence tomography