Reentrant equilibrium disordering in nanoparticle–polymer mixtures

Journal Article · 31 January 2017 · npj Computational Materials

DOI: https://doi.org/10.1038/s41524-016-0005-8 · OSTI ID:1341748

Meng, Dong ^[1]; Kumar, Sanat K. ^[2]; Grest, Gary S. ^[3]; Mahynski, Nathan A. ^[4]; Panagiotopoulos, Athanassios Z. ^[5]

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1. Columbia Univ., New York, NY (United States); Mississippi State Univ., Starkville, MS (United States)
2. Columbia Univ., New York, NY (United States)
3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
4. Princeton Univ., Princeton, NJ (United States); National Institutes of Standards and Technology, Gaithersburg, MD (United States)
5. Princeton Univ., Princeton, NJ (United States)

A large body of experimental work has established that athermal colloid/polymer mixtures undergo a sequence of transitions from a disordered fluid state to a colloidal crystal to a second disordered phase with increasing polymer concentration. These transitions are driven by polymer-mediated interparticle attraction, which is a function of both the polymer density and size. It has been posited that the disordered state at high polymer density is a consequence of strong interparticle attractions that kinetically inhibit the formation of the colloidal crystal, i.e., the formation of a non-equilibrium gel phase interferes with crystallization. Here we use molecular dynamics simulations and density functional theory on polymers and nanoparticles (NPs) of comparable size and show that the crystal-disordered phase coexistence at high polymer density for sufficiently long chains corresponds to an equilibrium thermodynamic phase transition. While the crystal is, indeed, stabilized at intermediate polymer density by polymer-induced intercolloid attractions, it is destabilized at higher densities because long chains lose significant configurational entropy when they are forced to occupy all of the crystal voids. Finally, our results are in quantitative agreement with existing experimental data and show that, at least in the nanoparticle limit of sufficiently small colloidal particles, the crystal phase only has a modest range of thermodynamic stability.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1341748
• Report Number(s): SAND--2017-0129J; PII: 5
• Journal Information: npj Computational Materials, Journal Name: npj Computational Materials Journal Issue: 1 Vol. 3; ISSN 2057-3960
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United States
• Language: English