Joris Sprakel: On fragility and strength; Soft colloids make strong glasses, or do they?
Plats: Kemicentrum, Lecture hall F
Dr. Joris Sprakel from Wageningen University, Netherlands, will give a seminar.
Suspensions of microgel particles have proven their value as a testing ground for the effects of softness on the phase behaviour and dynamics of soft materials. However, what is softness? Does this imply deformability, compressibility or both? In this talk, I will highlight some recent efforts from my group in understanding the effects of softness on the behaviour of dense suspensions of squishy colloids. I will try to answer the question how deformability and compressibility interplay when microgels become densely packed. In particular around the colloidal glass transition, the effects of softness become pronounced. Previous observations of the change in suspension viscosity upon densification have shown how the glass transition changes from a fragile vitrification for hard particles, to a strong, Arrhenius-like, transition for compressible particles, leading to the claim “Soft colloids make strong glasses”. I will discuss a simple model that explains these fragility changes as a consequence of osmotic equilibrium. Within this phenomenological approach, we find that the intrinsic particle compressibility acts as an order parameter for the colloidal glass transition. This leads to a simple universal picture of how fragility and strength emerge, and shows how soft colloids may make fragile glasses as well and vice-versa.