Dispersing nano- A nd micro-sized portlandite particulates: Via electrosteric exclusion at short screening lengths

Jason Timmons, Iman Mehdipour, Shang Gao, Hakan Atahan, Narayanan Neithalath, Mathieu Bauchy, Edward Garboczi, Samanvaya Srivastava*, Gaurav Sant

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Özet

In spite of their high surface charge (zeta potential ζ = +34 mV), aqueous suspensions of portlandite (calcium hydroxide: Ca(OH)2) exhibit a strong tendency to aggregate, and thereby present unstable suspensions. While a variety of commercial dispersants seek to modify the suspension stability and rheology (e.g., yield stress, viscosity), it remains unclear how the performance of electrostatically and/or electrosterically based additives is affected in aqueous environments having either a high ionic strength and/or a pH close to the particle's isoelectric point (IEP). We show that the high native ionic strength (pH ≈ 12.6, IEP: PH ≈ 13) of saturated portlandite suspensions strongly screens electrostatic forces (Debye length: κ-1 = 1.2 nm). As a result, coulombic repulsion alone is insufficient to mitigate particle aggregation and affect rheology. However, a longer-range geometrical particle-particle exclusion that arises from electrosteric hindrance caused by the introduction of comb polyelectrolyte dispersants is very effective at altering the rheological properties and fractal structuring of suspensions. As a result, comb-like dispersants that stretch into the solvent reduce the suspension's yield stress by 5× at similar levels of adsorption as compared to linear dispersants, thus enhancing the critical solid loading (i.e., at which jamming occurs) by 1.4×. Significantly, the behavior of diverse dispersants is found to be inherently related to the thickness of the adsorbed polymer layer on particle surfaces. These outcomes inform the design of dispersants for concentrated suspensions that present strong charge screening behavior.

Orijinal dilİngilizce
Sayfa (başlangıç-bitiş)3425-3435
Sayfa sayısı11
DergiSoft Matter
Hacim16
Basın numarası14
DOI'lar
Yayın durumuYayınlandı - 14 Nis 2020

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Publisher Copyright:
This journal is © The Royal Society of Chemistry.

Finansman

The authors acknowledge financial support for this research from the National Science Foundation (DMREF: 1922167, CMMI: 1562066, CAREER: 1253269), Department of Energy: Office of Fossil Energy via the National Energy Technology Laboratory (NETL; DE-FE0029825 and DE-FE0031718), and TRANSCEND: a joint UCLA-NIST Consortium that is funded by its industry and agency partners. This research was conducted in the Laboratory for the Chemistry of Construction Materials (LC2) and the Electron Microscopy Core Facility at UCLA. The authors gratefully acknowledge the support provided by these laboratories. The authors thank BASF Corporation: Construction Chemicals (Beachwood, Ohio) for their assistance in polymer characterization. The contents of this paper reflect the views and opinions of the authors, who are responsible for the accuracy of the datasets presented herein, and do not reflect the views and/or policies of the funding agencies, nor do the contents constitute a specification, standard or regulation.

FinansörlerFinansör numarası
DMREF1253269, 1562066
National Science Foundation1922167
U.S. Department of Energy
Office of Fossil Energy
National Energy Technology LaboratoryDE-FE0031718, DE-FE0029825

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