Apparent Diffusion Coefficients for Reactive Dyes in Swollen Cellulosic Micro Capillaries
Apparent diffusion coefficients dictate internal fiber dye transport rate, governing shade levelness and fixation efficiency in swollen cellulosic processing.
Hydrodynamic Radius
Effective Size
Apparent size of a solvated polymer coil or dye molecule moving through a liquid medium determines its physical diffusion rate. The hydrodynamic radius includes not only the molecule itself but also the surrounding layer of tightly bound solvent molecules. This value dictates how easily a dye molecule can penetrate the narrow pores of swollen cellulose fibers.
It is a critical parameter for predicting the behavior of finishing agents.
Sizing Technique
Dynamic light scattering measures this value by tracking the Brownian motion of particles in solution. Small molecules move rapidly, while larger molecules with a larger hydrodynamic radius move more slowly. The instrument translates these motion rates into a size distribution profile.
This profile helps chemists select dyes that match the pore size of specific fibers.
Diffusion Behavior
Large solvated molecules struggle to enter the internal pore network of the fiber, leading to surface-only dyeing. This poor penetration results in fabrics with low rub fastness and poor wash fastness. Selecting dyes with a smaller radius ensures deep penetration and better color durability.
Temperature Effect
Increasing dye bath temperature reduces the solvated layer around the dye molecules. This reduction decreases the hydrodynamic radius and accelerates fiber penetration. The process allows for shorter dyeing cycles.