Soft Particles

Phase behavior of Dispersions of Thermosensitive Hydrogel Particles

Thermosensitive hydrogel particles enable us to study the phase behavior of weakly attractive colloids with an easy and accurate control over particle volume fraction and attractive potential. Due to their softness, these particles are deformable and their volume is not fixed; this allows us to dramatically increase the particle number concentration, as particles can shrink to accomodate more particles per volume. Surprisingly, even at such high concentrations the soft particle suspensions can still exhibit a liquid-like character, with the transition to a solid depending sensitively on the particle's elastic modulus.

We use rheology, and static & dynamic light scattering to study their phase behavior. We also develop new experimental approaches to study the bulk behavior of the microgel themselves; the goal here is to relate local mechanical properties to the macroscopic rheological response. We are particularly interested in nonequilibrium disordered states.

Diffraction pattern for a colloidal crystal consisting of PNIPAM-PAA hydrogel particles.


  • David Weitz (Harvard University)
  • Johan Mattsson (University of Leeds, UK)
  • Alberto Fernandez-Nieves (Georgia Institute of Technology)


  • "Temperature-controlled transitions between glass, liquid and gel states in dense p-NIPA suspensions"
    G. Romeo, A. Fernandez-Nieves, H.M. Wyss, D. Acierno, and D.A. Weitz
    Advanced Materials 22, 3441-3445 (2010)

  • "Capillary micromechanics: Measuring the elasticity of mescoscopic soft objects"
    H. M. Wyss, T. Franke, E. Mele, and D. A. Weitz
    Soft Matter 6 (18), 4550-4555 (2010)

  • "Soft Colloids make Strong Glasses"
    J. Mattsson, H. M. Wyss, A. Fernandez-Nieves, K. Miyazaki, Z. Hu, D. R. Reichman, and D. A. Weitz
    Nature 462 7269, 83 (2009)

  • "Strain-Rate Frequency Superposition: A rheological probe of structural relaxation in soft materials"
    H. M. Wyss, K. Miyazaki, J. Mattsson, Z. Hu, D. R. Reichman, D. A. Weitz
    Physical Review Letters 98 238303 (2007)