Prüfung weicher Materialien mit Rheodialyse für das NETZSCH-Kinexus Rheometer

Soft materials rarely experience mechanical forces in isolation.

In real processes, shear and chemistry change at the same time.

Until now, commercial rotational rheometers could control mechanical stress and strain – but not the chemical environment dynamically during the test. This created a blind spot in understanding gels, biopolymers, pharmaceuticals, food systems and biological materials.

With the new Rheodialysis solution for the NETZSCH Kinexus rotational rheometer, this gap has been closed.

Consider an alginate hydrogel used to encapsulate an active pharmaceutical ingredient.

As soon as the material comes into contact with calcium ions, it begins to transform from a liquid into a gel. At the same time, diffusion processes occur, the structure changes, and its mechanical properties evolve continuously.

Until now, researchers could typically monitor either the chemical changes or the rheological response. Studying both simultaneously under realistic conditions remained extremely challenging.

Rheodialysis changes this. It enables researchers to observe how a material responds mechanically while its chemical environment evolves in real time – bringing laboratory measurements much closer to real-world conditions.

The term combines two concepts:

• Kriechen (Rheologie)Creep is one of the earliest “controlled stress” rheometer tests that quite literally “creeps” the material, i.e. we measure over a relatively prolonged period the small movement (the creep defined as creep compliance, J) of the sample by applying a small constant stress.Rheology – the study of how materials flow and deform
• Dialysis – the controlled transport of molecules through a membrane

Just as dialysis allows substances to pass through a membrane while keeping others separated, Rheodialysis enables controlled chemical exchange with a sample during a rheological measurement.

This makes it possible to mimic processes such as ion diffusion, solvent exchange, enzyme exposure, pH changes, or nutrient transport while continuously monitoring material behavior.

Many soft materials are designed to respond to their environment.

For example:

Alginate Hydrogels
Alginate, derived from seaweed, is widely used in drug delivery, tissue engineering and cell encapsulation. During exposure to calcium ions, the material gels through Ionic crosslinking. Rheodialysis allows researchers to monitor this gelation process in real time while measuring the evolving viscoelastic properties.

Food Digestion Studies
Food structures do not only experience mechanical deformation during consumption. They are simultaneously exposed to changing pH values, salts and digestive enzymes. Rheodialysis enables researchers to study how food texture and structure change under conditions that more closely resemble digestion.

Pharmaceutical Formulations
Drug delivery systems often rely on diffusion-controlled processes. With Rheodialysis, researchers can investigate how buffer solutions, ions or other reagents influence material structure and release behavior while mechanical forces are applied.

These examples demonstrate why controlling chemistry and shear simultaneously can provide insights that conventional rheological measurements cannot capture.

With Rheodialysis, researchers can:

✔ Control chemical diffusion rates via pump settings and concentration
✔ Identify precise gelation points during Ionic exchange
✔ Model real-world processing conditions more accurately

As shown in the new white paper, the convergence of oscillatory phase angles at different frequencies can pinpoint the exact gel point during in-situ Ionic exchange.

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