Recycled polydopamine particles used for special wetting
Graphical abstract
Introduction
The polydopamine (PDA) modification method has become a state-of-the art surface modification method. This attracting area is derived from the bio-imitation of the adhesive proteins of marine organisms. Messersmith’s group discovered that dopamine (3,4-dihydroxyphenethylamine) could act as a structural mimic of the mussel adhesive protein [1]. This discovery opens a new route to surface modification because dopamine could polymerize and deposit on all kinds of organic and inorganic surfaces. The as-formed PDA is of chemical versatility, which enables it to perform as a platform for secondary reactions. Up till now, PDA has found a broad spectrum of applications such as biological, energy, optics uses [2], [3], [4], [5], [6], [7], [8]. And the research around the PDA is still bursting. Although a lot of work has been done, from the PDA structure to its applications, seldom attention has been paid to the use of the wasted PDA particles. Normally, when a dopamine solution is used to modifying solid objects, such as glass substrates, the PDA does not only polymerize on the solid surface, but also in the solution, leading to an amount of PDA particulates which usually is disposed as wastes. In this report, these PDA particulates were collected to prepare particles with special wetting behaviour, in which shows one way to make use of the recycled particles.
Special wetting behaviors of solid surfaces have gained much attention in both basic research and industry field due to the unique properties. Especially superhydrophobic surfaces, which defined as surfaces with water contact angles (CA) exceeding 150°, have aroused long lasting interests in the related field [9], [10]. Surface wettability is known to be controlled by both surface morphology and surface chemical component. To achieve high water repellence, low surface energy materials and surface roughness are required. Lotus leaf, the nature occurring prototype of superhydrophobic surfaces, has provided a clever way to fulfil the demands. The micro-papillae on the surfaces of lotus leaf are covered with nano protrusions of waxy crystal, which gives hierarchical structure and low surface energy at the same time, ensuring the superior water repellent ability. Inspired by the lotus leaf, an amount of effort has been devoted to preparing superhydrophobic surfaces or particles with hierarchical structures. The superhydrophobic surfaces could find wide applications in self-cleaning [11], [12], [13], drag reduction [14], oil/water separation [15], [16], [17], anti-freezing [18], microfluidic devices [19], and biological field [20]. Although various methods and techniques have been employed to fabricating superhydrophobic surfaces, there is still an urgent need for low demanding methods with mild preparing conditions, simple steps and large scalability. Moreover, superhydrophobic surfaces with smart behaviors, such as pH sensibility, could offer additional values in practical application.
Herein, the recycled PDA microparticles and Ag nanoparticles (AgNPs) were combined together to prepare hierarchical-structured particles to mimic the micro protrusions of the lotus leaf. The particles achieved superhydrophobicity after modified by thiol fluoroalkanes, which could withstand water under different pHs. A mixture of thiols with fluorinated alkyl and carboxylic acid groups was also used to modify the PDA/Ag particles and the resultant particles revealed pH sensibility.
Section snippets
Chemicals and materials
1H,1H,2H,2H-Perfluorodecanethiol (97%, ρ = 1.678) and dopamine hydrochloride (98%) were purchased from Sigma-Aldrich. 11-Mercaptoundecanoic acid (95%) were purchased from J&K. Silver nitrate (99.8%) were purchased from Aladdin. Tris (hydroxymethyl) aminomethane (Beijing Chemical Company, AP), silver nitrate, sodium hydroxide, hydrochloride, ethanol (Beijing Chemical Works, CP) and deionized water were used as received.
Preparation of PDA/Ag particles
The recycled polydopamine particles were collected from a used dopamine
Results and discussion
The PDA particles were collected from a used dopamine solution by filtration. The collection rate of PDA particles was about 69 wt% of total dopamine. The polymerization mechanism of dopamine is not clearly known yet. It is hypothesized that dopamine forms indole skeleton by oxidative ring closure and then the 5,6-dihydroxyindole monomers are covalently cross-linked via aryl–aryl linkages on different possible reaction sites on the indole ring (Fig. S1a) [1], [21], [22], [23]. The PDA is likely
Conclusion
In summary, hierarchical-structured particles with special wetting behaviours were prepared by using the recycled PDA particulates. Fluorinated PDA/Ag microparticles did not only achieve superhydrophobicity and superoelophility, but also could withstand acidic and basic solutions. The PDA/Ag microparticles modified by mixed thiols containing carboxylic acid and fluorinated alkyl groups was sensitive to pH variations, which showed superhydrophobic ability at the pH range from 1 to 12 and turned
Acknowledgements
This work was supported by NSFC (No. 51303010), Specialized Research Fund for the Doctoral Program of Higher Education (20130006120019), and the Fundamental Research Funds for the Central Universities (No. FRF-TP-14-014A2).
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