SMALL-ANGLE NEUTRON-SCATTERING STUDIES ON BINARY-MIXTURES OF CHARGED-PARTICLES

Small-angle neutron scattering (SANS) studies have been carried out on a binary mixture of polystyrene-h(8) particles (A, radius 168 Angstro m) and polystyrene-d(8) particles (B, radius 510 Angstrom). Two disper sions were prepared at a total volume fraction of ca. 0.03 and with nu mber ratios N-A/N-B of 9 and 15. The electrolyte content of these disp ersions was 6 x 10(-5) mol dm(-3) sodium chloride. Experiments were ca rried out at 3 contrasts using H2O, 75% D2O, and D2O so that the data obtained enabled evaluation of the three partial structure factors, S( Q)(AA), S(Q)(BB), and S(Q)(AB). Prior to examining the mixtures, separ ate SANS experiments were carried out to characterize the particles an d to obtain the structure factors for the individual latices, S(Q)(A) and S(Q)(B). This enabled a comparison to be made of the single-compon ent dispersions and the binary mixtures. The results indicate that the larger particles retain their structure in the mixture but that the s tructure of the smaller particles is distorted with evidence of long-r ange correlations resulting in ''weak'' cluster formation. The variati on in the partial structure factors is consistent with the calculation that the strongest electrostatic interaction is between the larger B particles and the weakest between the smaller A particles.