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The ordering phenomena of various ionic species in solutions or dispersions, such as synthetic and biological polyelectrolytes and spherical colloidal particles, have been intensively studied. 1 In an effort to expand the study to rodlike polyion systems, we became interested in cellulose derivatives first and initiated a systematic study of cellulose hydrolysates by using an ultra-smallangle X-ray scattering (USAXS) technique. During the course of our study, our attention was drawn to papers by Marchessault and Gray et al.,2,3 which reported that the dispersions were found to separate into anisotropic and isotropic phases above a critical concentration and the concentrations of the hydrolysates in these two phases did not much differ from each other. The second finding was highly unexpected to us, since similar phase separation is known to occur with a much greater concentration difference as clearly shown by the vaporliquid condensation equilibrium for ionic polymer latex particle dispersions. 4 Thus we examined this problem by using the USAXS technique and report here briefly the relevant results.Cotton linter (15 g) was treated with 65 wt % sulfuric acid (150 mL) at 70°C for 30 min. The hydrolysate was washed with ion-exchanged water by successive dilution and centrifugation to remove excess acid. Further purification was carried out by dialysis against Milli-Q water (Millipore, Bedford, MA). The dispersion was concentrated to 5.9 wt % by ultrafiltration, dispersed by subsequent ultrasonic treatment, and kept as a stock dispersion. The stock dispersion was diluted with Milli-Q water for measurements at 1.0, 2.0, and 4.0 wt %. The size and shape of the hydrolysate particles were determined using a transmission electron microscope on the dilute dispersions. Though the micrographs are not shown here, the particles were rodlike (as seen from Figure 1 of ref 3), and the average length and width were 1500 and 100 Å, respectively. The analytical charge density was determined by a conductometric titration to be 0.8 µC/cm 2 .The USAXS apparatus was described in previous papers. 5,6 Single crystals of Ge were used in the Bonse-Hart camera system. Desmeared scattering intensities from salt-free dispersions at various concentrations are given as a function of the magnitude of the scattering vector q ()(4π/ λ) sin θ, where 2θ is the scattering angle and λ the wavelength of an X-ray, 1.54 Å) in Figure 1. Clearly there exists a distinct single broad peak for all the concentrations except for 1.0 wt %, at which the peak became barely detectable. The peak position shifted toward smaller q and the intensity became lower with decreasing hydrolysate concentration.As has often been pointed out (see, for example, ref 1), a single broad peak has been observed for various ionic polymer solutions and ionic colloidal particle dispersions by small-angle X-ray scattering and smallangle neutron scattering measurements. 1a The "poly-electrolyte" peak is known to be sensitive toward added salt; The peak position for synthetic and biologica...

A two‐dimensional ultra‐small‐angle X‐ray scattering (USAXS) apparatus was constructed using a rotating‐anode X‐ray generator and a Bonse–Hart camera. In this camera, two sets of two channel‐cut single crystals were used to collimate the X‐ray beam in both the horizontal and the vertical planes. The measured intensity profile of the direct beam showed a high small‐angle resolution in all directions on the detector plane. The full width at half‐maximum was 17′′, indicating that the apparatus can be applied to structural analysis in the range up to 2 μm, even for directionally oriented samples. One‐ and two‐dimensional USAXS profiles from colloidal silica powder agreed well with each other, showing that the desmearing procedure adopted in the previous one‐dimensional USAXS experiments were justified.

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