Understanding the way liquid spreads through paper

November 29, 2016

WASHINGTON, D.C., November 29, 2016 - Molecules move randomly, colliding with each other in continual motion. You can even smell this process at times; it's how perfume spreads across a room when the air is still. The process is termed diffusion and the theory of diffusion can be applied to liquid spreading through paper, too - a process at work in a range of everyday products, from ink pens to paper sampling patches for medical tests.

Now, a team of researchers in India have developed a model that deepens their conceptual grasp of how liquids spread through paper.

"Liquid spreading in a paper is essentially random liquid motion through a randomly distributed network of fibers," said Suman Chakraborty, lead researcher of the investigation at the Indian Institute of Technology Kharagpur, and the Advancement Technology Development Centre, both located in Kharagpur, India. Results are published this week in Applied Physics Letters, from AIP Publishing.

Diffusion is a well-known process. But the team's elaboration of diffusion theory in the context of paper-liquid interactions, which pose tortuous fiber networks to transport dynamics, is novel and reveals new theoretical detail. In their experiment, the researchers observed ink spreading on filter paper using a scanning electron microscope.

The team mapped liquid spreading dynamics from a single fiber capillary to a larger network of the fibers. They then computed the resulting transport characteristics, with results confirming a generalized unified perspective of diffusion at work in the process of liquid moving through a paper matrix. Scanning micrographic images show paper fiber distributions, along with the micro-particle-image-velocimetry measure of random liquid movement through the network.

"Our study reveals that, despite such diversified uses of paper interacting with liquids, there is a fundamental uniqueness of liquid spreading through paper leading toward a general and unified theory about it," Chakraborty said.

The theory holds that molecules of a liquid move through the fiber network of paper following the principles of universal diffusive dynamics. "Paper is constituted of a network of fibers distributed randomly," said Chakraborty. "As a consequence, random motion of the liquid in all possible directions occurs. We know molecules move randomly and collide with each other, and this is the premise of diffusion."

Despite wide use of liquid-infused paper technologies, there are gaps in the understanding of the basic science behind its behavior. Chakraborty and his students, Kaustav Chaudhury and Shantimoy Kar, help fill that gap.

By understanding liquid spread in the paradigm of diffusion, scientists can control it more precisely to create and refine new products that involve liquid spreading through paper. For example, current markets have validated an important potential property of paper: acting as the essential building block of a rapid diagnostic kit in an ultra-low-cost paradigm.

Examples of this application include pregnancy test strips; alkalinity or acidity tests of beauty and baby soaps using a paper strip; paper-strips for checking water quality; and medical diagnosis aided by paper-strip tests of urine, saliva and blood. The author's diffusion model of liquid spreading in paper can also improve papers and inks used for writing, drawing and painting.

Next, the investigators plan to develop smart and compact technologies for diagnostic purposes, advancing the existing paper based platforms.

"The key objectives are to obtain rapid results at the expense of low costs. To this end, the paper shows a promising prospect of being a tool to serve both the objectives. The present work, as we believe, will pave the way for the design and development of the paper-based technologies to serve a wider public," Chakraborty said.
-end-
The article, "Diffusive dynamics on paper matrix," is authored by Kaustav Chaudhury, Shantimoy Kar and Suman Chakraborty. The article will appear in the journal Applied Physics Letters on November 29, 2016 (DOI: 10.1063/1.4966992). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/109/20/10.1063/1.4966992

About the journal:

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology.

American Institute of Physics

Related Paper Articles from Brightsurf:

Paper recycling must be powered by renewables to save climate
The study, published in Nature Sustainability, found that greenhouse gas emissions would increase by 2050 if we recycled more paper, as current methods rely on fossil fuels and electricity from the grid.

Your paper notebook could become your next tablet
Purdue engineers developed a simple printing process that renders any paper or cardboard packaging into a keyboard, keypad or other easy-to-use human-machine interfaces.

'A litmus paper for CO2:' Scientists develop paper-based sensors for carbon dioxide
A new sensor for detecting carbon dioxide can be manufactured on a simple piece of paper, according to a new study by University of Alberta physicists.

Researchers grow cells in 'paper organs'
Long before scientists test new medicines in animals or people, they study the effects of the substances on cells growing in Petri dishes.

Moneyball advantage peters out once everyone's doing it: Rotman paper
Sixteen years after author Michael Lewis wrote the book Moneyball, every Major League Baseball (MLB) team uses the technique.

New paper on the phylogeny of the Brassicaceae
A recent study from the Max Planck Institute for Plant Breeding Research in Cologne, published in the New Phytologist, helps resolve these issues by reporting new insights into the relationships among Brassicaceae species

Write with heat, cool and then repeat with rewritable paper
Even in this digital age, paper is still everywhere. Often, printed materials get used once and are then discarded, creating waste and potentially pollution.

A paper battery powered by bacteria
In remote areas of the world, everyday items like electrical outlets and batteries are luxuries.

Scientists create biodegradable, paper-based biobatteries
The batteries of the future may be made out of paper.

Paper: Surprise can be an agent of social change
Surprising someone -- whether it's by a joke or via a gasp-inducing plot twist -- can be a memorable experience, but a less heralded effect is that it can provide an avenue to influence people, said Jeffrey Loewenstein, a professor of business administration at the Gies College of Business at Illinois.

Read More: Paper News and Paper Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.