Abstract
The behavior of deformable threadlike particles in suspensions subjected to velocity gradients has been studied. For a given value of (shear rate) × (viscosity of suspending medium), there exists a critical length at which threadlike particles in suspension will bend during rotation under the stresses imposed by the shear field. Over a limited range of particle lengths above the critical length, the deformation increased as the length was increased. However, the particles straightened twice during each rotation, during that part of the orbit in which they lay parallel to the planes of shear. When the particle length was increased further, the particles formed rotating helices or coils. As the shear rate was increased, the change in shape of the projection of the coils on the plane parallel to the velocity gradient resembled the change in shape of deformed fluid drops. The periods of rotation of permanently bent particles were shown to be appreciably lower than those of straight particles. Whereas the product (period of rotation) × (velocity gradient) was constant for rigid spheres, ellipsoids, and rods, it increased with deformable particles at a rate which was related to the amount of deformation resulting from shear. The work is of interest in connection with the viscosity and other flow properties of suspensions and the streaming birefringence of solutions of macromolecules. It also forms the basis of a method of measuring the flexibility of wood-pulp fibers.
Published Version
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