PHASE-BEHAVIOR OF MIXTURES OF RODS (TOBACCO MOSAIC-VIRUS) AND SPHERES(POLYETHYLENE OXIDE, BOVINE SERUM-ALBUMIN)

Aqueous suspensions of mixtures of the rodlike virus tobacco mosaic vi rus (TMV) with globular macromolecules such as polyethylene oxide (PEO ) or bovine serum albumin (BSA) phase separate and exhibit rich and st rikingly similar phase behavior. Isotropic, nematic, lamellar, and cry stalline phases are observed as a function of the concentration of the constituents and ionic strength. The observed phase behavior is consi dered to arise from attractions between the two particles induced by t he presence of BSA or PEG. For the TMV/BSA mixtures, the BSA adsorbs t o the TMV and bridging of the BSA between TMV produces the attractions . For TMV/PEO mixtures, attractions are entropically driven via exclud ed volume effects known alternatively as the ''depletion interaction'' or ''macromolecular crowding.''