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Title: Microstructure and Rheology of Thermoreversible Nanoparticle Gels

;  [1]
  1. (UIUC)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Langmuir; Journal Volume: 22; Journal Issue: (18) ; 08, 2006
Country of Publication:
United States

Citation Formats

Ramakrishnan, S., and Zukoski, C.F.. Microstructure and Rheology of Thermoreversible Nanoparticle Gels. United States: N. p., 2015. Web. doi:10.1021/la060168j.
Ramakrishnan, S., & Zukoski, C.F.. Microstructure and Rheology of Thermoreversible Nanoparticle Gels. United States. doi:10.1021/la060168j.
Ramakrishnan, S., and Zukoski, C.F.. 2015. "Microstructure and Rheology of Thermoreversible Nanoparticle Gels". United States. doi:10.1021/la060168j.
title = {Microstructure and Rheology of Thermoreversible Nanoparticle Gels},
author = {Ramakrishnan, S. and Zukoski, C.F.},
abstractNote = {},
doi = {10.1021/la060168j},
journal = {Langmuir},
number = (18) ; 08, 2006,
volume = 22,
place = {United States},
year = 2015,
month = 2
  • The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and time-resolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropicmore » microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the “Delaware-Rutgers” rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response.« less
  • Graft copolymers consisting of a poly(DL-lactic acid–co–glycolic acid) backbone grafted with polyethyelene glycol (PLGA-g-PEG) side chains were synthesized and formed thermoreversible gels in aqueous solutions which exhibited solution behavior at low temperature and sol-gel transitions at higher temperature. The composition of the polymer and relative amounts of polylactic acid (LA), glycolic acid (GA), and ethylene glycol (EG) could be varied by controlling the precursor concentrations and reaction temperature. The gelation temperature could be systematically tailored from 15°C to 34°C by increasing the concentration of PEG in the graft copolymer. The gelation temperature decreased with increasing polymer molecular weight and decreasingmore » polymer concentration. This work has importance for the development of water soluble gels with tailored compositions and gelation temperatures for use in tissue engineering and as injectable depots for drug delivery.« less
  • Dynamic arrest transitions of colloidal suspensions containing non-spherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346–2349) and temperature-dependent attractions were introduced by coating themore » calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultra-small angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. We find the adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.« less