lab1 Molecular weight determination of polyvinyl chloride via dilute-solution viscometry.

MOLECULAR WEIGHT DETERMINATION OF POLYVINYL CHLORIDE VIA DILUTE-SOLUTION VISCOMETRY
OBJECTIVES
1. To determine the liquid viscosity using Oswald viscometer
2. To determine the molecular weight of polyvinyl alcohol (PVOH)
THEORY
Solutions of a high-molecular-weight polymer, even at low concentrations, can flow only slowly. Addition of a small amount of the polymer to the fluid can make it viscous, thereby preventing unwanted turbulence in the flow. Let consider a fluid filling a space between two parallel plates, as illustrated in Fig. 1.1. The bottom plate does not move, but the top plate slides in the z direction (perpendicular to x-axis) without changing the distance to the stationary plate. When the fluid adjacent to the plate sticks to the plate (nonslip boundary condition), the fluid moves in the same direction. Near the bottom plate, the fluid barely moves. However, with an increasing distance from the bottom plate, the fluid moves faster. As long as the flow is sufficiently slow, the fluid flows parallel to the plates. In other words, the velocity of the fluid has only an x component (vx). This flow mode is called a laminar flow. We can regard the fluid as a stack of sheets, each sliding against the sheet beneath it.