Designing Better Absorbent Products

Think about what happens when the corner of a paper towel touches spilled water. The liquid seems to climb into the towel on its own, spreading through tiny spaces in the material. This process, known as wicking, is also at work in everyday products such as diapers and feminine hygiene pads. But these products present an additional challenge: many of the materials inside them swell and change shape as they absorb liquid. Understanding how liquid moves through a material that is changing at the same time is a surprisingly complex engineering problem.

Ryan Masoodi, PhD, a professor of mechanical engineering in the department of Construction Management and Engineering, is working to solve this. His research uses computer simulations to predict how liquids move through absorbent materials, with the goal of creating a virtual tool for exploring new designs before manufacturing physical prototypes — potentially helping companies develop better-performing products more quickly and efficiently.

In this conversation, Dr. Masoodi explains the science behind his work, what drew him to wicking research, and why solving this complex problem could have an impact far beyond the laboratory.

My research looks at how we can predict the behavior of absorbent materials using computer models. If we understand it better, we can help design absorbent products that take in liquid faster, distribute it more effectively, hold more of it, and remain comfortable for the user.

Many absorbent hygiene products are still developed through a process of trial and error. Engineers create a design, manufacture a prototype, test how it performs, make adjustments, and then repeat the process. That approach works, but it can take considerable time and resources.

My research focuses on developing computer simulations that can reproduce what is happening inside an absorbent product. The model predicts where the liquid will travel, how quickly it will move, and how the material will change as it absorbs fluid. Once we have a reliable model, engineers can test many different designs and conditions virtually instead of building and testing each one physically. 

Imagine trying to make a feminine hygiene pad thinner and lighter without reducing its ability to absorb liquid. A computer model could help engineers explore questions such as: What happens if we use less material? Where should the most absorbent material be placed? How quickly will liquid spread? Will the pad still hold enough fluid?

Answering questions like these could virtually reduce the amount of physical trial and error needed and help companies develop products that use materials more efficiently while maintaining performance and comfort.

As an engineer, I’m naturally drawn to problems that don’t have obvious solutions. Scientists have studied fluid movement through rigid porous materials, such as soil and sand, for a long time. But the problem becomes much more challenging when the material itself changes shape as it absorbs liquid. Now you are trying to predict two things at once: how the liquid changes the material and how the changing material affects the liquid.

This challenge caught my attention during my PhD studies when I worked on a project involving polymer wicks — small plastic rods designed to absorb and transport liquids — to dispense insecticides and fragrances.

As I continued working in this field, people from industry began reaching out to me for technical advice. That was exciting because it showed me that the questions I was studying were not only scientifically interesting; companies were encountering the same challenges while developing real products.

That connection between fundamental science and practical engineering motivated me to continue developing the field. 

One project I’m particularly proud of is editing the first research book devoted specifically to wicking in porous materials. The book brings together the fundamental physics of wicking, mathematical and computational methods for predicting it, and practical applications. The goal was to create a resource that researchers and engineers could use both to understand the science and to design systems involving liquid absorption and transport.

I am now editing a second book on the subject, 14 years after the first book. There is enough new research and technological development to warrant an entirely new volume. To me, that reflects how much the field has grown and how much interest there is in understanding and controlling these processes.

I always encourage young researchers to stay curious, be patient, and remember that meaningful progress often comes from tackling challenges that don’t have immediate answers. Being willing to stay with a difficult problem, learn from unsuccessful attempts, and keep asking new questions is an important part of becoming a researcher.

The best part of my job is being able to combine teaching and research.

Teaching makes me happy, especially when I see that “aha!” moment when a student suddenly understands a difficult concept in a challenging course such as thermodynamics or heat transfer. Helping students reach that moment is one of the most rewarding parts of being an educator.

Research is rewarding in a different way. Seeing my work published, cited and built upon by other researchers tells me that the ideas are contributing to a larger scientific conversation. I’ve also enjoyed opportunities to collaborate with leading companies such as Procter & Gamble, SC Johnson, and Kimberly-Clark.