Shear influence on colloidal cluster growth: a SANS and USANS study

Chris Muzny; Liliana de Campo; Anna Sokolova; Christopher J Garvey; Christine Rehm; Howard Hanley

doi:10.1107/S1600576723006726

Shear influence on colloidal cluster growth: a SANS and USANS study

J Appl Crystallogr. 2023 Aug 25;56(Pt 5):1371-1380. doi: 10.1107/S1600576723006726. eCollection 2023 Oct 1.

Authors

Chris Muzny¹, Liliana de Campo², Anna Sokolova², Christopher J Garvey³, Christine Rehm², Howard Hanley⁴

Affiliations

¹ Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, CO 80305, USA.
² Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
³ Forschungs-Neutronenquelle, Heinz Maier-Leibnitz (FRM II), Technische Universität München, Lichtenbergstraße 1, Garching, 85748, Germany.
⁴ Applied Mathematics, Research School of Physics, Australian National University (ANU), Canberra, ACT 2600, Australia.

Abstract

This study examines the time evolution of silica/water clusters where the formation of a gel network from unitary silica particles is interrupted by a simple Couette shear field. The aim is to enable the general understanding of this simple system by examining the microscopic basis for the changes in viscosity by providing structural inputs from small-angle scattering for a simple theoretical model. The experimental system is an 8.3 nm particle silica solution (Ludox) where the gelation has been initiated by lowering the pH in a Couette cell providing a constant shear rate of 250 s^-1. A unified small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) procedure is described to measure the scattered intensity in a wavevector range of 3 × 10^-4 ≤ q (nm^-1) ≤ 3.1 × 10^-1, probing structural changes over a broad range of length scales from the nanometre to the micrometre. Scattering data provide a new means of better understanding the behaviour of colloidal clusters when subjected to an external applied shear over a continuous time sequence after gel initiation; a fit of the time-dependent scattered intensity leads to an estimation of the cluster's effective volume fraction and size as a function of time. A reductionist theoretical basis is described to predict the time-dependent viscosity behaviour of the sheared colloidal suspension gel-initiated cluster growth from the volume fraction of the clusters.

Keywords: SANS; USANS; applied shear; colloidal silica; micrometre scale; retarded gelation; small-angle neutron scattering; structure factor derivation; time-dependent phenomena; ultra-small-angle neutron scattering; viscosity; volume fraction.

Grants and funding

This work benefited from the use of the SASView application, originally developed under NSF award DMR-0520547. SASView also contains code developed with funding from the EU Horizon 2020 Programme under the SINE2020 project (grant No. 654000).