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Dispersing nano- and micro-sized portlandite particulates via electrosteric exclusion at short screening lengths
Soft Matter ( IF 2.9 ) Pub Date : 2020-03-16 , DOI: 10.1039/d0sm00045k Jason Timmons 1, 2, 3, 4, 5 , Iman Mehdipour 2, 3, 4, 5, 6 , Shang Gao 2, 3, 4, 7 , Hakan Atahan 2, 3, 4, 5, 6 , Narayanan Neithalath 4, 8, 9, 10 , Mathieu Bauchy 2, 3, 4, 6, 11 , Edward Garboczi 4, 12, 13, 14, 15 , Samanvaya Srivastava 2, 3, 4, 7, 16 , Gaurav Sant 1, 2, 3, 4, 5
Soft Matter ( IF 2.9 ) Pub Date : 2020-03-16 , DOI: 10.1039/d0sm00045k Jason Timmons 1, 2, 3, 4, 5 , Iman Mehdipour 2, 3, 4, 5, 6 , Shang Gao 2, 3, 4, 7 , Hakan Atahan 2, 3, 4, 5, 6 , Narayanan Neithalath 4, 8, 9, 10 , Mathieu Bauchy 2, 3, 4, 6, 11 , Edward Garboczi 4, 12, 13, 14, 15 , Samanvaya Srivastava 2, 3, 4, 7, 16 , Gaurav Sant 1, 2, 3, 4, 5
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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.
中文翻译：
通过短距离屏蔽通过电立体排除法分散纳米级和微米级的硅酸盐颗粒
尽管其表面电荷较高（ζ电位ζ = +34 mV），但硅酸盐的水悬浮液（氢氧化钙：Ca（OH）2）表现出强烈的聚集趋势，因此存在不稳定的悬浮液。尽管各种商业分散剂试图改变悬浮液的稳定性和流变性（例如，屈服应力，粘度），但仍不清楚在具有高离子强度和/或水离子的水性环境中，静电和/或静电位添加剂的性能如何受到影响。或接近粒子等电点（IEP）的pH。我们表明，饱和的波特兰悬浮液具有很高的天然离子强度（pH≈12.6，IEP：pH≈13）可以强烈屏蔽静电力（德拜长度：κ -1= 1.2 nm）。结果，仅库仑斥力不足以减轻颗粒聚集并影响流变性。但是，由于引入梳形聚电解质分散剂而引起的电空间位阻，导致了更长距离的几何颗粒间排斥，对改变悬浮液的流变性质和分形结构非常有效。结果，伸入溶剂中的梳状分散剂与线性分散剂相比，在相似的吸附水平下，悬浮液的屈服应力降低了5倍，从而提高了临界固体负载量（即，即发生卡纸的位置）1.4倍。重要地，发现各种分散剂的行为与颗粒表面上吸附的聚合物层的厚度固有地相关。这些结果说明了呈现强电荷筛选行为的浓缩悬浮液分散剂的设计。
更新日期：2020-04-24
中文翻译：
通过短距离屏蔽通过电立体排除法分散纳米级和微米级的硅酸盐颗粒
尽管其表面电荷较高（ζ电位ζ = +34 mV），但硅酸盐的水悬浮液（氢氧化钙：Ca（OH）2）表现出强烈的聚集趋势，因此存在不稳定的悬浮液。尽管各种商业分散剂试图改变悬浮液的稳定性和流变性（例如，屈服应力，粘度），但仍不清楚在具有高离子强度和/或水离子的水性环境中，静电和/或静电位添加剂的性能如何受到影响。或接近粒子等电点（IEP）的pH。我们表明，饱和的波特兰悬浮液具有很高的天然离子强度（pH≈12.6，IEP：pH≈13）可以强烈屏蔽静电力（德拜长度：κ -1= 1.2 nm）。结果，仅库仑斥力不足以减轻颗粒聚集并影响流变性。但是，由于引入梳形聚电解质分散剂而引起的电空间位阻，导致了更长距离的几何颗粒间排斥，对改变悬浮液的流变性质和分形结构非常有效。结果，伸入溶剂中的梳状分散剂与线性分散剂相比，在相似的吸附水平下，悬浮液的屈服应力降低了5倍，从而提高了临界固体负载量（即，即发生卡纸的位置）1.4倍。重要地，发现各种分散剂的行为与颗粒表面上吸附的聚合物层的厚度固有地相关。这些结果说明了呈现强电荷筛选行为的浓缩悬浮液分散剂的设计。
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