<p>Distinct pore morphologies are often observed in freeze-dried porous materials even under identical freezing conditions, which cannot be fully explained by classical ice-front–particle interaction models. In this work, the role of particle sedimentation during unidirectional freeze-drying is reexamined from a dynamic competition perspective. Based on a force balance analysis incorporating an effective viscous resistance, particle motion in concentrated suspensions is characterized by an effective terminal settling velocity. By comparing the characteristic time scales of particle sedimentation and ice-front propagation, a dimensionless sedimentation–freezing competition parameter, <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$K = V_{{\text{t}}} /V_{{\text{f}}}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mo>=</mo> <msub> <mi>V</mi> <mtext>t</mtext> </msub> <mo stretchy="false">/</mo> <msub> <mi>V</mi> <mtext>f</mtext> </msub> </mrow> </math></EquationSource> </InlineEquation> is proposed. When <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$K \gg 0.1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mo>≫</mo> <mn>0.1</mn> </mrow> </math></EquationSource> </InlineEquation>, particles are able to undergo sufficient rearrangement prior to solidification, favoring the formation of well-aligned lamellar structures. In contrast, when <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$K\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{ < } 0.1$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <munder> <mo><</mo> <mstyle displaystyle="false" scriptlevel="2"> <mo>∼</mo> </mstyle> </munder> <mn>0.1</mn> </mrow> </math></EquationSource> </InlineEquation>, particle motion is increasingly constrained by the advancing freezing front, leading to interface-dominated trapping, lamellar distortion, and interlamellar bridging. Experimental observations in SiO<sub>2</sub>, Mo, and W freeze-dried systems, spanning a wide range of particle densities, are consistent with the predicted trend of the proposed competition framework. The present approach provides a physically transparent and practical guideline for understanding and regulating microstructural evolution in freeze-dried porous materials.</p>

Sedimentation Behavior of Powder Particles and Formation Mechanism During Freeze-Drying

期刊论文
发表日期：

2026年7月2日

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Zijian Liu,
Wenge Chen,
Cechen Zhao,
Jiangjiang Ma,
Bowang Liu

摘要

Distinct pore morphologies are often observed in freeze-dried porous materials even under identical freezing conditions, which cannot be fully explained by classical ice-front–particle interaction models. In this work, the role of particle sedimentation during unidirectional freeze-drying is reexamined from a dynamic competition perspective. Based on a force balance analysis incorporating an effective viscous resistance, particle motion in concentrated suspensions is characterized by an effective terminal settling velocity. By comparing the characteristic time scales of particle sedimentation and ice-front propagation, a dimensionless sedimentation–freezing competition parameter, $K = V_{{\text{t}}} /V_{{\text{f}}}$ $K = V_{t} / V_{f}$ is proposed. When $K \gg 0.1$ $K ≫ 0.1$ , particles are able to undergo sufficient rearrangement prior to solidification, favoring the formation of well-aligned lamellar structures. In contrast, when $K\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}{ < } 0.1$ $K \underset{\sim}{<} 0.1$ , particle motion is increasingly constrained by the advancing freezing front, leading to interface-dominated trapping, lamellar distortion, and interlamellar bridging. Experimental observations in SiO₂, Mo, and W freeze-dried systems, spanning a wide range of particle densities, are consistent with the predicted trend of the proposed competition framework. The present approach provides a physically transparent and practical guideline for understanding and regulating microstructural evolution in freeze-dried porous materials.