Study of dye diffusion in fibers by laser scanning confocal microscopy

Laser Scanning Confocal Microscopy (LSCM) is a fairly new type of optical microscopy. It has the advantages of non-invasive optical sectioning and reconstruction of three-dimensional image of a transparent object. In this work, LSCM was introduced in the study of dye diffusion in textile fibers for the first time. Two new approaches for studying dye diffusion in fibers were developed: the analysis of dye spatial distribution in fiber dyeing using LSCM and fluorescence recovery after photobleaching (FRAP) using LSCM. Both methods are simpler, quicker and provide microscopic information of the diffusion process than is possible by conventional methods used in the study of diffusion in fibers.; In the measurement of diffusion of fluorescein in nylon 66 fibers, the diffusion coefficients measured by these new approaches are in good agreement with the measurement by the conventional method.; In the second method spatial distributions of dye in fibers were quantified using optically sectioned fiber cross sections obtained by LSCM. The diffusion coefficient was calculated from Hill's solution of the diffusion equation. This method can be adapted to provide the dye spatial distribution in the fiber during the dyeing process.; In the FRAP experiment, a very small volume in the fiber dyed with a fluorescent dye is photobleached by an intense laser pulse. The fluorescent dye molecules in the surrounding area diffuse into the photobleached spot and cause a recovery of fluorescence. The time of the fluorescence recovery is a measure of the rate of diffusion. This method is able to measure the two-dimensional diffusion of dye molecules in the fiber at room temperature without the measurements of the fiber dyeing.; The major limitation for the accurate measurements by LSCM is the optical aberration in the image. In this work, the effect of optical aberration in the imaging of fibrous materials was investigated. Matching of refractive indices of the fiber, the mounting medium for the fiber and the immersion oil for the objective minimizes optical aberration effects. When the indices are matched, optical aberrations disappear.; Dye spatial distribution can affect the perceived color of fibers. A ring-dyed fiber has higher color yield than a uniformly dyed fiber even when they have the same dye concentration in the fiber. However, the measurements of refractive index of the fiber, the fluorescent spectrum of the fluorescent dye in the fiber and the orientation distribution of dye molecules in the fiber were not significantly different between ring-dyed and uniformly dyed fibers. The causes for the effect of dye spatial distribution on the color of fibers are not well understood.