Surface hydrophilicity-mediated migration of nano/microparticles under temperature gradient in a confined space

Haolan Xu; Xu Zheng; Xinghua Shi

doi:10.1016/j.jcis.2023.01.112

Surface hydrophilicity-mediated migration of nano/microparticles under temperature gradient in a confined space

J Colloid Interface Sci. 2023 May:637:489-499. doi: 10.1016/j.jcis.2023.01.112. Epub 2023 Jan 26.

Authors

Haolan Xu¹, Xu Zheng², Xinghua Shi³

Affiliations

¹ Laboratory of Theoretical and Computational Nanoscience, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing 100049, China.
² State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. Electronic address: zhengxu@lnm.imech.ac.cn.
³ Laboratory of Theoretical and Computational Nanoscience, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Chinese Academy of Sciences, Beijing 100190, China; University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing 100049, China. Electronic address: shixh@nanoctr.cn.

PMID: 36724663
DOI: 10.1016/j.jcis.2023.01.112

Abstract

Hypothesis: Particle transport by a temperature gradient is prospective in many biomedical applications. However, the prevalence of boundary confinement in practical use introduces synergistic effects of thermophoresis and thermo-osmosis, causing controversial phenomena and great difficulty in understanding the mechanisms.

Experiments: We developed a microfluidic chip with a uniform temperature gradient and switchable substrate hydrophilicity to measure the migrations of various particles (d = 200 nm - 2 μm), through which the effects of particle thermophoresis and thermo-osmotic flow from the substrate surface were decoupled. The contribution of substrate hydrophilicity on thermo-osmosis was examined. Thermophoresis was measured to clarify its dependence on particle size and hydrophilicity.

Findings: This paper reports the first experimental evidence of a large enthalpy-dependent thermo-osmotic mobility χ ∼ ΔH on a hydrophobic polymer surface, which is 1-2 orders of magnitude larger than that on hydrophilic surfaces. The normalized Soret coefficient for polystyrene particles, S_T/d = 18.0 K^-1µm^-1, is confirmed to be constant, which helps clarify the controversy of the size dependence. Besides, the Soret coefficient of hydrophobic proteins is approximately-four times larger than that of hydrophilic extracellular vesicles. These findings suggest that the intrinsic slip on the hydrophobic surface could enhance both surface thermo-osmosis and particle thermophoresis.

Keywords: Hydrophobicity; Nanoparticle; Soret coefficient; Thermo-osmosis; Thermophoresis.