Exploring the science behind everyday material behavior through the lens of the 1st International Conference on Rheology and Modeling of Materials
Have you ever wondered why honey drips slowly while water pours quickly? Or why ketchup sometimes refuses to leave the bottle, then suddenly gushes out? These everyday phenomena are governed by a fascinating scientific discipline called rheology—the study of how materials deform and flow under force. Despite being a relatively unknown field outside scientific circles, rheology touches nearly every aspect of our lives, from the foods we eat and the medicines we take to the cars we drive and the buildings we inhabit.
In 2013, a landmark event occurred in the picturesque Hungarian town of Miskolc-Lillafüred: the 1st International Conference on Rheology and Modeling of Materials (ic-rmm1). This gathering represented a significant step toward bridging the gap between theoretical models and practical applications in rheology.
Scientists from Australia, Brazil, China, France, Germany, Japan, Korea, Portugal, Russia, and the United States converged to discuss recent achievements in measuring, modeling, and applying rheology to everything from nanomaterials and biomaterials to ceramics and food products 5 7 .
From toothpaste to Silly Putty, many common materials exhibit complex flow behaviors that challenge simple solid/liquid classifications.
The ic-rmm1 conference brought together researchers from over 10 countries to advance rheological science.
The term "rheology" comes from the Greek words "rheo" (meaning flow) and "logos" (meaning study). Simply put, rheology examines how materials respond to applied forces. While we often think of materials as either solids or liquids, the reality is far more complex and interesting. Many common substances don't fit neatly into either category—they exhibit properties of both.
Material Behavior Spectrum
Consider toothpaste: It maintains its shape like a solid in the tube but flows like a liquid when squeezed out. Similarly, silicone putty (often called "Silly Putty") can be rolled into a ball that bounces like a solid but will slowly flow and spread like a liquid if left undisturbed. These dual-character materials are called viscoelastic substances, and understanding their behavior is at the heart of rheology.
The applications of rheology extend far beyond trivial examples. In the medical field, rheological principles help researchers understand how blood flows through vessels, how mucus clears pathogens from our lungs, and how tissues respond to surgical procedures. In the food industry, rheology determines whether ice cream feels creamy, whether bread has the right texture, and whether ketchup pours properly.
Medical Diagnostics
Food Science
Manufacturing
Coatings
To visualize and mathematically describe viscoelastic behavior, rheologists often use mechanical analogs consisting of springs (representing elastic behavior) and dashpots (representing viscous behavior). These components can be arranged in various configurations to model different material responses.
| Model Name | Components | Behavior | Common Applications |
|---|---|---|---|
| Kelvin-Voigt | Spring and dashpot in parallel | Solid-like with gradual recovery after deformation | Soft tissues, gels |
| Maxwell | Spring and dashpot in series | Fluid-like with gradual flow under constant stress | Polymers, simple liquids |
| Standard Linear Solid | Spring in series with Kelvin-Voigt unit | Combined solid and fluid characteristics | Biological tissues, complex materials |
| Burgers | Maxwell and Kelvin-Voigt in series | Multiple relaxation times | Complex polymers, foods |
Different materials require different models to accurately capture their behavior. A primary goal of rheological research is to identify which models work best for specific materials and applications. As researchers noted in a 2022 study, "Any model that can accurately describe a variety of important experimental results, and can do so with only a few parameters, is objectively a strong candidate for consensus adoption" 1 .
The ic-rmm1 conference specifically addressed this challenge by creating a platform for discussing recent achievements in rheological modeling and its applications across material classes 7 . Such discussions are crucial for advancing the field and developing more accurate predictive models.
To understand how rheologists evaluate different models, let's examine a comprehensive study that compared the performance of three established models for characterizing soft tissues. Published in Acta Biomaterialia in 2022, this research addressed a fundamental question: which rheological model best describes the behavior of biological tissues like liver tissue 1 ?
Determine which rheological model could most accurately predict both time-domain and frequency-domain behaviors of biological tissues.
The research team employed a sophisticated experimental design to thoroughly test each model's capabilities:
The findings revealed striking differences in model performance:
| Model | Parameters | Time Domain Accuracy | Frequency Domain Accuracy | Mutual Consistency |
|---|---|---|---|---|
| Kelvin-Voigt | 2 | Poor | Limited | No |
| Standard Linear Solid | 3 | Moderate | Moderate | Partial |
| Kelvin-Voigt Fractional Derivative | 3 | >98% | >96% | Yes |
The Kelvin-Voigt Fractional Derivative (KVFD) model demonstrated superior performance, providing "the only mutually consistent rendering of time and frequency domains data for liver" 1 .
Rheological research requires specialized tools and approaches to probe material behavior. The following table highlights key methodologies and their applications, drawn from the tissue characterization experiment and broader rheological practice.
| Tool/Method | Function | Application Example |
|---|---|---|
| Stress Relaxation Testing | Measures how internal stress decreases over time under constant strain | Characterizing time-dependent behavior of soft tissues |
| Shear Wave Speed Dispersion | Tracks how shear wave velocity changes with frequency | Assessing tissue stiffness and viscosity across frequencies |
| Rheometer | Applies controlled stresses/strains and measures material response | Harmonic testing of soft materials at various frequencies |
| Ultrasound Elastography | Uses ultrasound to track shear wave propagation | Medical imaging of tissue mechanical properties |
| Optical Coherence Elastography | Employs light to visualize wave propagation | High-resolution imaging of superficial tissues |
| Fractional Derivative Models | Mathematical framework for complex material behavior | Accurate prediction of both time and frequency domain responses |
Advanced methods for measuring material properties
Frameworks for predicting material behavior
Tools for visualizing material responses
The 1st International Conference on Rheology and Modeling of Materials in 2013 represented a significant milestone in bringing together diverse perspectives to advance our understanding of material behavior 5 7 . The gathering highlighted rheology's essential role in bridging scientific disciplines and translating theoretical models into practical applications.
From helping doctors diagnose diseases earlier to understanding tissue responses, rheology continues to advance healthcare.
Rheology enables food scientists to create better textures and materials engineers to develop improved products.
The next time you struggle with a stubborn ketchup bottle or enjoy the perfect texture of ice cream, take a moment to appreciate the complex rheological principles at work. The science of flow, though often unseen, touches nearly everything we encounter in daily life, making it a field worthy of both scientific study and public appreciation.
As rheology continues to evolve through conferences, collaborations, and ongoing research, we can expect even more exciting developments in understanding and harnessing the fascinating ways that materials deform, flow, and respond to the forces around us.