The fragile-to-strong dynamical crossover and the system viscoelasticity in attractive glass forming colloids

The dynamical arrest phenomena of an adhesive hard-sphere (AHS) colloid, L64-D2O system has been studied by using calorimetry and the complex shear modulus. This system is characterized by a rich temperature (T ) and volume fraction (φ) phase diagram with a percolation line (PT). According to the modecoupling theory (MCT), a cusp-like singularity and two glassy phases, one attractive (AG) and one repulsive (RG), are supposed to coexist in the phase diagram. *This paper is dedicated to Professor Heinz Hoffmann on the occasion of his 80 birthday in celebration of his long-time friendship with both of us (Professors Sow-Hsin Chen and Francesco Mallamace). For SHC, he has cherished the happy and productive memory during his stay at the University of Bayreuth as a Humboldt US Senior Scientist Awardee in 1988 and then the revisit again in 1995. During those two periods, he worked closely with Professors Heinz Hoffmann and Jürgen Kalus, and has established invaluable long-lasting friendship as well as constant scientific dialogue with them throughout the years in the last quarter century. FM thanks Heinz and Claudia for the sincere friendship born in the organization of a memorable meeting of the European Colloid and Interphase Science (ECIS) held in Copanello (Italy) on September 1990. We look forward to many more years of productive scientific discussions with Prof. Hoffmann! F. Mallamace · S.-H. Chen Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge MA 02139, USA E-mail: [email protected] E-mail: [email protected] F. Mallamace · C. Corsaro CNR-IPCF Messina, Viale F. Stagno D’Alcontres 37, 98166 Messina Dipartimento di Fisica e Scienze della Terra, University of Messina, Viale F. Stagno D’Alcontres 31, 98166 Messina D. Mallamace Dipartimento SASTAS, University of Messina, Viale F. Stagno D’Alcontres 31, 98166 Messina The MCT scaling laws used to study the shear viscosity with φ and T as control parameters propose the existence of fragile-to-strong dynamic crossover (FSDC) analogous to that observed in molecular supercooled liquid glass formers. The measured critical values of the control parameters, coincident with the PT line, where the clustering process generates the AG phase, define the FSDC locus. This is in agreement with the extended mode-coupling theory that takes into account both cage and inter-cluster hopping effects. In this work we demonstrate, by considering the frequency dependence of the complex moduli, that there is the onset of a system viscoelasticity as an effect of the clustering accompanying the FSDC. We will show as the measured frequency-dependent complex moduli satisfy the scaling relations predicted by the scalar elasticity percolation theory and well account for the system evolution toward the glass transition process.