Scattering of Light by Gel Structures. I. Regenerated Cellulose

Abstract

A low‐angle light scattering photometer is described and applied to the study of regenerated cellulose gels. The scattering patterns were recorded over the angular range from 0.5° to ∼75° for the fresh gel in water (F film) and for the same sample solvent exchanged to an imbibition liquid of refractive index 1.543 (PF film). A sharp drop in over‐all turbidity was recorded in going from F to PF film, indicating an intimate penetration of the nonswelling imbibition liquid into the cellulose fine structure. The observed scattering for these samples was interpreted in terms of the Debye‐Bueche correlation function using the graphical integration method. The size of the regions of correlated variation in refractive index was 5800 Å for the F film and 6500 Å for the PF film; this corresponded to refractive index fluctuations of 0.005 and 0.001, respectively. It is calculated that these fluctuations in refractive index could arise from about a 3% variation in the degree of order over the respective correlation distances. Such structure heterogeneities would then be associated with a second level organization of the fine structure.