Stress relaxation in quasi-two-dimensional self-assembled nanoparticle monolayers

Journal Article · Fri May 11 00:00:00 EDT 2018 · Physical Review E

DOI:https://doi.org/10.1103/PhysRevE.97.052803· OSTI ID:1464757

Boucheron, Leandra S. ^[1]; Stanley, Jacob T. ^[1]; Dai, Yeling ^[1]; You, Siheng Sean ^[2]; Parzyck, Christopher T. ^[1]; Narayanan, Suresh ^[3]; Sandy, Alec R. ^[3]; Jiang, Zhang ^[3]; Meron, Mati ^[2]; Lin, Binhua ^[2]; Shpyrko, Oleg G. ^[1]

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1. Univ. of California San Diego, La Jolla, CA (United States)
2. Univ. of Chicago, Chicago, IL (United States)
3. Argonne National Lab. (ANL), Argonne, IL (United States)

Here, we experimentally probed the stress relaxation of a monolayer of iron oxide nanoparticles at the water-air interface. Upon drop-casting onto a water surface, the nanoparticles self-assembled into islands of two-dimensional hexagonally close packed crystalline domains surrounded by large voids. When compressed laterally, the voids gradually disappeared as the surface pressure increased. After the compression was stopped, the surface pressure (as measured by a Wilhelmy plate) evolved as a function of the film aging time with three distinct timescales. These aging dynamics were intrinsic to the stressed state built up during the non-equilibrium compression of the film. Utilizing x-ray photon correlation spectroscopy, we measured the characteristic relaxation time (tau) of in-plane nanoparticle motion as a function of the aging time through both second-order and two-time autocorrelation analysis. Compressed and stretched exponential fitting of the intermediate scattering function yielded exponents (beta) indicating different relaxation mechanisms of the films under different compression stresses. For a monolayer compressed to a lower surface pressure (between 20 mN/m and 30 mN/m), the relaxation time (tau) decreased continuously as a function of the aging time, as did the fitted exponent, which transitioned from being compressed (>1) to stretched (<1), indicating that the monolayer underwent a stress release through crystalline domain reorganization. However, for a monolayer compressed to a higher surface pressure (around 40 mN/m), the relaxation time increased continuously and the compressed exponent varied very little from a value of 1.6, suggesting that the system may have been highly stressed and jammed Despite the interesting stress relaxation signatures seen in these samples, the structural ordering of the monolayer remained the same over the sample lifetime, as revealed by grazing incidence x-ray diffraction.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1464757
• Alternate ID(s): OSTI ID: 1436901
• Journal Information: Physical Review E, Vol. 97, Issue 5; ISSN 2470-0045
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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