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Stirring Polymers in Solution Can Influence the Paint Applications, Find Researchers

Published on 2014-10-14. Author : SpecialChem

Researchers from FOM Institute AMOLF and the German Forschungzentrum Jülich have discovered why polymers in a solution become fluid if the solution is stirred. They discovered that the polymer structure changes from an entanglement of spaghetti into aligned layers of hairpin-shaped filaments that can slide past each other. The discovery can help to provide a better understanding of biological processes such as flows in the cells of embryos.

Polymers become fluid in a solution that is stirred or smeared and this property is used in a wide range of everyday materials, including toothpaste and paint. If the material remains unused in the pot, the polymers become entangled with each other and form a solid network that thickens the fluid by smearing the solution or spreading it out the polymers become fluid again. At high flow rates in particular, the viscosity of the solution strongly decreases: the faster you stir the thinner it becomes.

This behavior also occurs in natural polymers, for example in the actin fibers that provide stiffness to biological cells. Solutions of actin fibers not only become fluid if you stir them from the outside but can also make themselves fluid by the action of molecular motor proteins that slide the fibers past one another.

As polymers are very small and consequently difficult to observe, researchers did not yet fully understand why polymers exhibit this behavior. The research groups of professor Gijsje Koenderink (Amsterdam) and professor Pavlik Lettinga (Julich) have changed this.

Spaghetti and hairpins

The researchers rendered the three-dimensional form of individual polymer threads within an entangled solution visible at the moment the substance started to flow. They did this using actin fibers purified from biological cells. The physicists marked the fibers with a fluorescent dye. Then they induced the solution to flow while observing the polymer threads through a microscope. They could precisely follow the changes in shape and direction of individual polymer threads.

The scientists saw that in the absence of a flow, the filaments were strongly entangled with each other. If the system became fluid, the filaments assumed a hairpin-like shape and disentangled from each other. At high flow rates the filaments freely glided over each other.

Applications

Now the researchers have a better understanding of how the flow behavior of a polymer solution arises, they can also influence this. That can be done by varying the properties of the polymers such as fiber length and stiffness. A change in the flow behavior can, for example, influence the 'mouth feeling' of foods or the application of paint to a wall.

Furthermore the results will help to understand biological processes such as cytoplasmic flow. This flow occurs in the cells of some animal embryos and in large plant cells where protein filaments together with molecular motor proteins ensure a flow that transports cell components and nutrients.

The new microscopy method also opens up possibilities for studying more complex systems. For example, the researchers intend to study the basic mechanism of blood coagulation, by observing the interaction between the network formation of fibrin biopolymers, blood platelets and red blood cells.

About FOM Institute AMOLF

FOM Institute AMOLF is one of the research laboratories of the Foundation for Fundamental Research on Matter (FOM), part of the Netherlands Organization for Scientific Research (NWO). AMOLF employs about 130 fte research staff and 70 fte support staff. AMOLF's yearly budget is 14 million euro. The institute is located in Science Park Amsterdam.

Source: FOM Institute AMOLF


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