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Title: Particle Restabilization in Silica/PEG/Ethanol Suspensions: How Strongly do Polymers Need To Adsorb To Stabilize Against Aggregation?

We study the effects of increasing the concentration of a low molecular weight polyethylene glycol on the stability of 44 nm diameter silica nanoparticles suspended in ethanol. Polymer concentration, c{sub p}, is increased from zero to that characterizing the polymer melt. Particle stability is accessed through measurement of the particle second-virial coefficient, B{sub -2}, performed by light scattering and ultrasmall angle X-ray scattering (USAXS). The results show that at low polymer concentration, c{sub p} < 3 wt %, B{sub -2} values are positive, indicating repulsive interactions between particles. B{sub -2} decreases at intermediate concentrations (3 wt % < c{sub p} < 50 wt %), and particles aggregates are formed. At high concentrations (50 wt % < c{sub p}) B{sub -2} increases and stabilizes at a value expected for hard spheres with a diameter near 44 nm, indicating the particles are thermodynamically stable. At intermediate polymer concentrations, rates of aggregation are determined by measuring time-dependent changes in the suspension turbidity, revealing that aggregation is slowed by the necessity of the particles diffusing over a repulsive barrier in the pair potential. The magnitude of the barrier passes through a minimum at c{sub p} {approx} 12 wt % where it has a valuemore » of {approx}12kT. These results are understood in terms of a reduction of electrostatic repulsion and van der Waals attractions with increasing c{sub p}. Depletion attractions are found to play a minor role in particle stability. A model is presented suggesting displacement of weakly adsorbed polymer leads to slow aggregation at intermediate concentration, and we conclude that a general model of depletion restabilization may involve increased strength of polymer adsorption with increasing polymer concentration.« less
Authors:
;  [1]
  1. (UIUC)
Publication Date:
OSTI Identifier:
1021798
Resource Type:
Journal Article
Resource Relation:
Journal Name: Langmuir; Journal Volume: 27; Journal Issue: (9) ; 05, 2011
Research Org:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
Sponsoring Org:
NSF
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ADSORPTION; ELECTROSTATICS; ETHANOL; LIGHT SCATTERING; MOLECULAR WEIGHT; POLYETHYLENE GLYCOLS; POLYMERS; SCATTERING; SILICA; STABILITY; TURBIDITY