Abstract
Gels of DNA nanostars, besides providing a compatible scaffold for biomedical applications, are ideal model systems for testing the physics of equilibrium colloidal gels. Here, using dynamic light scattering and photon correlation imaging (a recent technique that, by blending light scattering and imaging, provides space-resolved quantification of the dynamics), we follow the process of gel formation over 10 orders of magnitude in time in a model system of tetravalent DNA nanostars in solution, a realization of limited-valence colloids. Such a system, depending on the nanostar concentration, can form either equilibrium or phase separation gels. In stark contrast to the heterogeneity of concentration and dynamics displayed by the phase separation gel, the equilibrium gel shows absence of aging and a remarkable spatially uniform dynamics.
Highlights
Gels are low-packing disordered networks of interacting particles that are structurally arrested and able to support weak stresses
Upon further reducing the temperature, around Tb ≈ 40°C, the sticky ends belonging to different NSs start to hybridize forming bonds between the NSs, which become progressively longer lived on lowering the temperature
The dilute phase is composed of isolated NSs, while the dense phase consists in a network of NSs, the equilibrium gel phase
Summary
Gels are low-packing disordered networks of interacting particles that are structurally arrested and able to support weak stresses. Several gels, including the ones formed by arrested spinodal decomposition, are heterogeneous both in space and in time [14,15,16,17,18] and are characterized by aging and complex dynamics [16, 19] These materials often display intermittent microscopic dynamics, consisting of relatively long quiescent stages interspersed with rapid structural rearrangements involving the whole sample [16, 18, 20]. These events are caused by the relaxation of internal stresses generated during the sudden kinetic arrest [21] and affect the mechanical properties of the gels during their lifetime [18, 22]
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