Polymer domains, gelation models and sickle cell crises.

The multistranded fibers formed by deoxygenated sickle hemoglobin form well ordered spherulitic arrays called domains. Employing laser photolysis of the carboxy derivative to initiate polymerization and domain formation, we have monitored the evolution of the spatial character of domains by light scattering and birefringence. Spatial growth is analyzed by observing a 62.5 microns square area of the sample and storing the image as 2500 discrete elements. Domain formation appears to consist of two phases. In the early phase even symmetric domains are not radially isotropic. Although the domain expands during this period, the internal polymer density as inferred by the light scattering intensity also increases. In the second phase, the domain becomes structurally symmetric and spatially homogeneous, and changes in the scattered intensity including pronounced overshoots occur uniformly across the monitored region. In this phase, the birefringence increases as the scattering decreases, with the same apparent rate.