Molecular dynamics simulations on synergistic underwater oleophobicity mechanism of dual-biomimic surfaces

doi:10.11949/0438-1157.20250313

Abstract

Abstract:

Through molecular dynamics simulations, the underwater oleophobicity of dopamine-grafted zwitterionic trimethylamine N-oxide (DOPA-TMAO) was investigated and compared with that of dopamine-grafted sulfobetaine methacrylate (DOPA-SBMA) zwitterionic compound. The underwater oleophobicity of the DOPA-TMAO system was also explored under different salt concentrations. Simulation results show that, in terms of underwater oleophobic performance, the oil droplet contact angle of the DOPA-TMAO system is 20° higher than that of the DOPA-SBMA system, along with more hydrogen bonds. Compared with the DOPA-SBMA system, the DOPA-TMAO system exhibits superior salt-resistance, demonstrates stronger oleophobic performance under various NaCl concentrations. This could be attributed to the unique direct connection between the positive and negative groups in the TMAO molecule (without carbon chain spacing), which leads to significantly concentrated charge density at one end and stronger hydration capability compared with that of the SBMA molecule. Additionally, after grafting dopamine with zwitterions, the surface adhesion is significantly enhanced, with the surface adhesion performance improved by nearly 50% compared with that of the surface without DOPA grafting. Further investigation demonstrated that the catechol groups in DOPA significantly enhance surface adhesion performance through van der Waals forces and electrostatic interactions. This character combines with the hydration barrier function of TMAO to form an “anchoring-shielding” synergistic effect, ensuring stable oleophobic performance in the DOPA-TMAO system. Notably, the cooperative interplay between TMAO's superior hydration capability and salt-resistance mechanism guarantees consistent anti-oil properties even in high-salinity environments. Based on the mussel biomimetic strategy, this study successfully improved the stability of the zwitterionic surface in the underwater oleophobic process; and revealed the significant advantages of the new zwitterionic TMAO in oleophobic and salt resistance, providing a theoretical basis for its application in complex environments.

Key words: underwater oleophobicity, interface contact angle, zwitterionic material, molecular simulation, biomimetic material

摘要：

通过分子动力学(MD)模拟方法，考察了多巴胺接枝的三甲胺N-氧化物(DOPA-TMAO)新型两性离子化合物的水下疏油性能，并将其与多巴胺接枝的甲基丙烯酸磺基甜菜碱(DOPA-SBMA)两性离子化合物的水下疏油性能进行了对比，还考察了不同盐浓度环境下DOPA-TMAO体系的水下疏油性能变化。结果表明，与DOPA-SBMA体系相比，纯水环境中DOPA-TMAO体系的水下疏油接触角更大，且有着厚度更大的水化层，其疏油能力更强。DOPA-TMAO体系在含盐水溶液中展现出良好的抗盐特性，这与TMAO分子中正负基团的极短间距有关，这进一步拓宽了其应用潜力。进一步研究发现，DOPA的邻苯二酚基团通过范德华力与静电相互作用显著增强表面黏附性能，与TMAO的水合屏障功能形成“锚固-屏蔽”协同效应，从而使DOPA-TMAO体系保持稳定的疏油性能；同时，TMAO优异的水合作用与抗盐机制的协同作用保障了高盐环境下的稳定疏油性能。基于贻贝仿生策略，本研究成功提升了两性离子表面在水下疏油过程中的稳定性，并揭示了新型两性离子TMAO在疏油和抗盐性能方面的显著优势，为其在复杂环境中的应用提供了理论依据。

关键词: 水下疏油性, 界面接触角, 两性离子材料, 分子模拟, 仿生材料

CLC Number:

O 647.11

Xianghai LI, Delin LAI, Gang KONG, Jian ZHOU. Molecular dynamics simulations on synergistic underwater oleophobicity mechanism of dual-biomimic surfaces[J]. CIESC Journal, 2025, 76(9): 4551-4562.

李相海, 赖德林, 孔纲, 周健. 双仿生表面水下疏油协同机制的分子动力学模拟研究[J]. 化工学报, 2025, 76(9): 4551-4562.

Figures/Tables 13

Fig.1 Molecular structures

Fig.2 Initial configuration of the water-oil-surface three-phase system

Fig.3 Contact angle determination via arc fitting[50]

Fig.4 OCA snapshots of DCE on different surfaces in a pure water environment

Fig.5 Number density distribution of key functional groups and DCE molecules

Fig.6 Snapshots of water and DCE molecule distributions around key functional groups in different systems

Fig.7 Hydration capability analysis of DOPA-SBMA and DOPA-TMAO systems

Table 1 Residence time of water molecules and hydrogen bond counts in different systems under pure aqueous environment

体系	水分子配位数	停留时间τ/ps	氢键总数	平均氢键数
DOPA-SBMA	7.19	56.9±3.4	155	1.6
DOPA-TMAO	10.14	69.7±4.8	305	3.2

Fig.8 Snapshots of OCA in pure water and different saline solutions

Fig.9 Radial distribution functions of water molecules and ON- in TMAO molecules

Fig.10 Radial distribution functions of N+- ON- interactions in TMAO molecules

Fig.11 Radial distribution functions of ON--Na+ and N+-Cl⁻ in the DOPA-TMAO system within a saline solution environment

Fig.12 Variation of pulling forces during steered molecular dynamics simulations

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