Weissenberg effect
Encyclopedia
The Weissenberg effect is a common phenomenon that occurs when a spinning rod is placed into a solution
of liquid
polymer
. Instead of being thrown outward, entanglements cause the polymer chains to be drawn towards the rod. It is named after Karl Weissenberg
.
Technically, it is due to a non-zero first normal stress difference. The strain tensor
of the motion of turning the rod produces a non-zero difference between the normal components of the resulting stress tensor, so there is a force up and down.
The polymer chains get wrapped around the rod and then as it keeps turning, the free ends in the bulk solution are trapped in the tangled bulk. As the rod is rotated, the end of the chain wrapped on the rod is under tension (a force on each end). To try to reduce the distance between the two ends it tries to move up or down the rod to a region where fewer chains are wrapped round and hence the effective diameter (the diameter of the rod plus wrapped-around chains) is less and hence the distance is shorter.
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
of liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
. Instead of being thrown outward, entanglements cause the polymer chains to be drawn towards the rod. It is named after Karl Weissenberg
Karl Weissenberg
Karl Weissenberg was an Austrian physicist, notable for his contributions to rheology and crystallography.The Weissenberg effect was named after him, as was the Weissenberg number...
.
Technically, it is due to a non-zero first normal stress difference. The strain tensor
Tensor
Tensors are geometric objects that describe linear relations between vectors, scalars, and other tensors. Elementary examples include the dot product, the cross product, and linear maps. Vectors and scalars themselves are also tensors. A tensor can be represented as a multi-dimensional array of...
of the motion of turning the rod produces a non-zero difference between the normal components of the resulting stress tensor, so there is a force up and down.
The polymer chains get wrapped around the rod and then as it keeps turning, the free ends in the bulk solution are trapped in the tangled bulk. As the rod is rotated, the end of the chain wrapped on the rod is under tension (a force on each end). To try to reduce the distance between the two ends it tries to move up or down the rod to a region where fewer chains are wrapped round and hence the effective diameter (the diameter of the rod plus wrapped-around chains) is less and hence the distance is shorter.