Gelation of particles with short-range attraction

• Published in: Nature 2008-05, Vol.453 (7194), p.499-503
• Main Authors: Lu, Peter J., Zaccarelli, Emanuela, Ciulla, Fabio, Schofield, Andrew B., Sciortino, Francesco, Weitz, David A.
• Format: Article
• Language: English
• Subjects: Analysis; Atoms & subatomic particles; Chemistry; Colloidal state and disperse state; Equilibrium; Exact sciences and technology; Gelation; General and physical chemistry; Humanities and Social Sciences; letter; multidisciplinary; Nanoparticles; Percolation; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Properties; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature06931

Gelation: Short-range attraction Nanoscale or colloidal particles change the properties of materials, imparting solid-like behaviour to a wide variety of complex fluids. This behaviour arises when particles aggregate to form mesoscopic clusters and networks. Numerous scenarios for gelation have been proposed, but no consensus has emerged. Lu et al . report experiments showing that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition; this thermodynamic instability triggers the formation of density fluctuations, leading to spanning clusters that dynamically arrest to create a gel. This simple picture of gelation should apply to any particle system with short-range attractions. Solid-like behaviour arises in a wide variety of complex fluids upon gelation — aggregation of particles to form mesoscopic clusters and networks. The authors show that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition. Nanoscale or colloidal particles are important in many realms of science and technology. They can dramatically change the properties of materials, imparting solid-like behaviour to a wide variety of complex fluids 1 , 2 . This behaviour arises when particles aggregate to form mesoscopic clusters and networks. The essential component leading to aggregation is an interparticle attraction, which can be generated by many physical and chemical mechanisms. In the limit of irreversible aggregation, infinitely strong interparticle bonds lead to diffusion-limited cluster aggregation 3 (DLCA). This is understood as a purely kinetic phenomenon that can form solid-like gels at arbitrarily low particle volume fraction 4 , 5 . Far more important technologically are systems with weaker attractions, where gel formation requires higher volume fractions. Numerous scenarios for gelation have been proposed, including DLCA 6 , kinetic or dynamic arrest 4 , 7 , 8 , 9 , 10 , phase separation 5 , 6 , 11 , 12 , 13 , 14 , 15 , 16 , percolation 4 , 12 , 17 , 18 and jamming 8 . No consensus has emerged and, despite its ubiquity and significance, gelation is far from understood—even the location of the gelation phase boundary is not agreed on 5 . Here we report experiments showing that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition; this thermodynamic instability triggers the formation of density fluctuations, leading