Gel formation and aging in weakly attractive nanocolloid suspensions at intermediate concentrations

Journal Article · Fri Dec 09 04:00:00 EST 2011 · J. Chem. Phys.

DOI:https://doi.org/10.1063/1.3653380· OSTI ID:1028019

Guo, Hongyu; Ramakrishnan, S; Harden, James L; Leheny, Robert L ^[1]

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1. Ottawa

We report x-ray photon correlation spectroscopy (XPCS) and rheometry experiments to study the temporal evolution of gel formation and aging in suspensions of silica nanocolloids possessing a tunable short-range attraction. The colloid volume fractions, {phi} = 0.20 and 0.43, are below the glass regime at high concentration and above the fractal regime at low concentration. Following a sudden initiation of the interparticle attraction, the suspensions display a protracted latency period in which they remain fluid before acquiring a measurable elastic shear modulus. The duration of the latency period and the subsequent rate of increase of the modulus vary strongly with the strength of the attraction. The XPCS results indicate dynamic heterogeneity among the colloids during this gel formation in which a growing fraction of the particles become localized. The temporal evolution of this localization correlates with that of the rheology. In particular, the time scale over which the fraction of localized particles increases tracks the duration of the latency period. Also, at {phi} = 0.20 the localization length characterizing the motion of the localized fraction scales onto the shear modulus with no free parameters as predicted by a self-consistent theory based on mode coupling [K. S. Schweizer and G. Yatsenko, J. Chem. Phys. 127, 164505 (2007)10.1063/1.2780861], while deviations from the predicted scaling at {phi} = 0.43 are observed near the gel point. The XPCS results also reveal slow, hyperdiffusive motion of the colloids in the newly formed gels that is attributed to strain from the relaxation of internal stress. While some features of this motion correlate with the evolving rheology, others appear decoupled from the macroscopic mechanical behavior.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: OTHER
• OSTI ID: 1028019
• Journal Information: J. Chem. Phys., Journal Name: J. Chem. Phys. Journal Issue: (15) ; 10, 2011 Vol. 135; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
AGING
COLLOIDS
FRACTALS
GLASS
LATENCY PERIOD
PHOTONS
RELAXATION
RHEOLOGY
SHEAR
SILICA
SPECTROSCOPY
STRAINS