Abstract
Coated paper is an example of a multi-layer porous medium, involving a coating layer along the two surfaces of the paper and a fibrous layer in the interior of the paper. The interface between these two media needs to be characterized in order to develop relevant modeling tools. After careful cutting of the paper, a cross section was imaged using focused ion beam scanning electron microscopy. The resulting image was analyzed to characterize the coating layer and its transition to the fibrous layer. Such image analysis showed that the coating layer thickness is highly variable, with a significant fraction of it being thinner than a minimum thickness required to keep ink from invading into the fibrous layer. The overall structure of the coating and fibrous layers observed in this analysis provide insights into how the system should be modeled, with the resulting conclusion pointing to a specific kind of multi-scale modeling approach.
Highlights
Cellulose-based papers are the main substrate for the printing industry as well as the main component of a new generation of “biodegradable” medical diagnostic devices
We focus on understanding the characteristics of the interface between the coating layer and the fibrous layer in a coated paper system and its effect on ink absorption into the coated paper
As seen in the figure, the coated paper has a base layer made of cellulose fibers covered with coating layer consisting of a pre-coat and a topcoat, these are clearly delineated by particle size
Summary
Cellulose-based papers are the main substrate for the printing industry as well as the main component of a new generation of “biodegradable” medical diagnostic devices. Similar considerations apply to microfluidic kits for diagnostic devices (cf López-Marzo and Merkoçi 2016), where movement of water into and between cellulose fibers is largely controlled by the hydrophilic property of the fibers. A cartridge delivers tiny droplets of ink (Pico-liter in size) on the paper surface. As soon as a pico-liter size droplet of ink reaches the paper, it starts penetrating into the porous substrate. Uncoated paper is an anisotropic porous medium, which consists of bundles of fibers crossing over each other in a planar orientation.
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