Viscoelasticity and density correlation function at the onset of the glass transition in a colloidal system with both repulsive and attractive interactions

We report quantitative comparison of dynamics and rheological properties of suspensions of micellar particles near the fluid/glass transition. The interaction between the particles is varied so as to explore the repulsive and attractive interaction side of the state diagram. We give an extended characterization of the viscoelastic properties of these suspensions in conjunction with their dynamics properties. For this purpose, Fourier transform analysis of the density correlation function is performed and the results are compared to those from conventional rheology, i.e., to the viscoelastic modulus in the frequency domain. The data show that the relaxation mechanisms in the repulsive system, probed at length scales of the order of the neighbor cage, are responsible for both transient decay of the correlation function and frequency variation of the viscoelastic modulus. The data on the attractive system show qualitative similarities of both relaxation functions, namely stretched relaxation behavior resulting from the involvement of both caging and bonding effects. However, quantitative differences are present in the two sets of data probably due to major contributions of short range relaxation mechanisms, reminiscent of the short length scale bonding effect, which are assessable only at large range of scattering vectors.