Title: Evolution of structure and dynamics of thermo-reversible nanoparticle gels—A combined XPCS and rheology study

Abstract

A combined X-ray photon correlation spectroscopy and rheology report is carried out to capture the evolution of structure, fast particle-scale dynamics, and moduli (elastic and loss) at early times of gel formation near the fluid-gel boundary of a suspension of nanoparticles. The system is made up of moderately concentrated suspensions of octadecyl silica in decalin (φ = 0.2) undergoing thermoreversible gelation. Near the gel boundary, the rate of gel formation is very sensitive to changes in attraction strength. Yet, we find that at different attraction strengths, the system goes through identical intermediate states of microscopic and macroscopic behavior, even though the absolute time needed to form a gel varies by orders of magnitude. We identify a single dimensionless time parameter, t _w/t _g, where t _w is the wait time following the quench and t _g is the rheologically determined gel time, that captures the similarity in gel formation at a range of attraction strengths. Following a temperature quench below the gel boundary, the system is initially fluidlike and forms diffusive clusters (similar to 8.5 times the particle diameter). After a lag-time, t _L, clusters aggregate to form a network like structure which is characterized by the onset of mechanicalmore » rigidity and a rapid growth in microscopic relaxation times. At t _g, the Baxter parameter obtained from adhesive hard sphere fits of the structure factor attains a constant value corresponding to the theoretical percolation boundary, thus demonstrating that gelation is percolation driven.« less

Authors:

Bahadur, Divya  ^[1];

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Zhang, Qingteng  ^[2];

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Dufresne, Eric M.  ^[2];

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Grybos, Pawel ^[3]; Kmon, Piotr ^[3]; Leheny, Robert L. ^[4]; Maj, Piotr ^[3]; Narayanan, Suresh ^[2]; Szczygiel, Robert ^[3]; Swan, James W. ^[5]; Sandy, Alec ^[2]; Ramakrishnan, Subramanian  ^[1]

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• Search DOE PAGES for ORCID "0000-0001-5108-2198"
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+ Show Author Affiliations

1. Florida A & M Univ.-Florida State Univ. (FAMU-FSU), Tallahassee, FL (United States). College of Engineering
2. Argonne National Lab. (ANL), Argonne, IL (United States)
3. AGH Univ. of Science and Technology, Krakow (Poland)
4. Johns Hopkins Univ., Baltimore, MD (United States)
5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Publication Date:

2019-09-09

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)

OSTI Identifier:

1574926

Alternate Identifier(s):

OSTI ID: 1560761

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 151; Journal Issue: 10; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY