Nonlinear Effects in the Shear Viscosity of Critical Mixtures

η(1) is found to increase as κ-9 near the critical point, where κ-1 is a parameter which measures the correlation range of concentration fluctuations assuming the Ornstein-Zernike type for the correlation, indicating the importance of the nonlinear effects near the critical point since η(0) increases as κ-1. This η(1) agrees with Botch and Fixman's except for a small correction to the numerical coefficient. On the other hand the k-integral contained in η(2) has been found to diverge as k-3 at small k even when κ ≠ 0, where k is a wave vector characterizing the local concentration fluctuation. Similar divergences appear in the two dimensional mixture already in η(1) which diverges as ln k, and in the linear bulk viscosity which again diverges as ln k. The nature and possible consequences of these divergences are discussed.