TY - JOUR
T1 - Dispersing nano- A nd micro-sized portlandite particulates
T2 - Via electrosteric exclusion at short screening lengths
AU - Timmons, Jason
AU - Mehdipour, Iman
AU - Gao, Shang
AU - Atahan, Hakan
AU - Neithalath, Narayanan
AU - Bauchy, Mathieu
AU - Garboczi, Edward
AU - Srivastava, Samanvaya
AU - Sant, Gaurav
N1 - Funding Information:
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.
Publisher Copyright:
This journal is © The Royal Society of Chemistry.
PY - 2020/4/14
Y1 - 2020/4/14
N2 - 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.
AB - 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.
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U2 - 10.1039/d0sm00045k
DO - 10.1039/d0sm00045k
M3 - Article
C2 - 32196056
AN - SCOPUS:85083085777
SN - 1744-683X
VL - 16
SP - 3425
EP - 3435
JO - Soft Matter
JF - Soft Matter
IS - 14
ER -