Micron-scale restructuring of gelling silica subjected to shear

Liliana de Campo; Christopher J Garvey; Chris D Muzny; Christine Rehm; Howard J M Hanley

doi:10.1016/j.jcis.2018.08.024

Micron-scale restructuring of gelling silica subjected to shear

J Colloid Interface Sci. 2019 Jan 1:533:136-143. doi: 10.1016/j.jcis.2018.08.024. Epub 2018 Aug 10.

Authors

Liliana de Campo¹, Christopher J Garvey², Chris D Muzny³, Christine Rehm⁴, Howard J M Hanley⁵

Affiliations

¹ Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
² Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia. Electronic address: cjg@ansto.gov.au.
³ Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, CO 80305, USA.
⁴ Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia; Guangdong Technion Israel Institute of Technology, 241 Da Xue Road, Shantou, Guangdong Province 515063, People's Republic of China.
⁵ Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2600, Australia.

PMID: 30165295
DOI: 10.1016/j.jcis.2018.08.024

Abstract

Hypothesis/objective: We examine the time dependent viscometric behavior of a well-defined system of gelling colloidal silica and how this behavior may be understood from a simple theoretical model which incorporates the microstructure of the gel. The ultra-small angle neutron scattering (USANS) technique is used to interrogate structure during the gelation process.

Experiments: The investigations focused on a system where both particles and interactions are well-defined: 7 nm silica particle acid-treated aqueous solution subjected to a constant applied shear in Couette geometry. Ultra-small angle neutron scattering (USANS) time-dependent scattering intensities were measured at wave vectors, q, in the range, 1.0 × 10^-3 ≤ q/nm ≤ 7.3 × 10^-2 coupled with viscosity data recorded simultaneously. The interpretation of the USANS scattering data is reliant on an isotropic sample. This assumption has been investigated, over a limited range of scattering vectors, using more suitable small angle neutron scattering (SANS) instrumentation with a restricted q-range.

Findings: The first recorded direct kinetic measurements of the micron-scale structure in a gelling system. A critical micro-structural feature of the intensity-viscosity time behavior of a gelling colloid subjected to a shear is the cluster size. A viscosity/intensity coupling observed at the time of a viscosity maximum that corresponds to a time-dependent critical stress and speculated to be independent of the wave vector over a wide q-range.

Keywords: Anisotropy; Colloidal silica; Gelation; Kinetics; Micron length scale; Shear; USANS; Viscosity.