Revisiting the Surface Energy Parameters of Standard Test Liquids with a Corrected Contact Angle Method over Rough Surfaces

Yirong Xu; Bingjun Han; Kang Xiao; Jinlan Yu; Jianzhong Zheng; Shuai Liang; Xiaomao Wang; Guoren Xu; Xia Huang

doi:10.1021/acs.langmuir.2c00726

Revisiting the Surface Energy Parameters of Standard Test Liquids with a Corrected Contact Angle Method over Rough Surfaces

Langmuir. 2022 Sep 6;38(35):10760-10767. doi: 10.1021/acs.langmuir.2c00726. Epub 2022 Aug 23.

Authors

Yirong Xu^{1

2}, Bingjun Han³, Kang Xiao^{1

2}, Jinlan Yu⁴, Jianzhong Zheng², Shuai Liang⁵, Xiaomao Wang⁴, Guoren Xu², Xia Huang^{4

6}

Affiliations

¹ Beijing Yanshan Earth Critical Zone National Research Station, University of Chinese Academy of Sciences, Beijing 101408, China.
² College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 101408, China.
³ College of Urban and Environmental Sciences, Peking University, Beijing 100084, China.
⁴ State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
⁵ College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China.
⁶ Research and Application Center for Membrane Technology, School of Environment, Tsinghua University, Beijing 100084, China.

PMID: 35998607
DOI: 10.1021/acs.langmuir.2c00726

Abstract

Interfacial free energy is a quantitative basis for explaining and predicting interfacial behavior that is ubiquitous in nature. The contact angle (CA) method can determine the surface free energy (γ) as well as Lifshitz-van der Waals (γ^LW) and Lewis acid/base (γ⁺/γ^-) components of a solid material from its CAs with a set of known test liquids according to the extended Young-Dupré equation. However, the reliability of the "known" parameters of the test liquids is questioned due to the long-neglected surface roughness effect during calibration of the liquids. This study proposed a simple and practicable two-step approach to correct the energy parameters of several test liquids by incorporating Wenzel's surface roughness relationship into CA measurement. Step 1: water and two apolar liquids (diiodomethane and α-bromonaphthalene) were used as benchmarks to calibrate the surface roughness and energy parameters of two reference solids [apolar poly(tetrafluoroethylene) and monopolar poly(methyl methacrylate)], and step 2: the reference solids were used to calibrate any other test liquids by solving the energy parameters from their CAs in the extended Young-Dupré-Wenzel model. Monte Carlo simulation was used to evaluate error transmission and robustness of the model solutions. The obtained energy parameters (γ^LW/γ⁺/γ^-) of four test liquids (dimethyl sulfoxide, formamide, ethylene glycol, and glycerol) are 28.01/13.68/4.67, 34.95/3.53/37.62, 26.26/7.51/15.74, and 32.99/9.24/26.02 mJ/m², respectively, and different from the literature values. The liquids were applied to characterize an example solid surface with true γ^LW/γ⁺/γ^- values of 28.00/1.00/8.00 mJ/m² and a roughness index (r) of 1.60. Without correction of the liquid parameters, the calculated surface energy, hydration energy, and hydrophobic attraction energy of the solid sample can deviate by 50, 13, and 27%, respectively. This proves the necessity of correcting parameters of the test liquids before they can be used in CA and interfacial energy studies in the presence of surface roughness.