Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Langmuir. 2013 Mar 5;29(9):2897-905. doi: 10.1021/la304571u. Epub 2013 Feb 25.
Poly(dimethylsiloxane) (PDMS) materials have been extensively shown to function as excellent fouling-release (FR) coatings in the marine environment. The incorporation of biocide moieties, such as quaternary ammonium salts (QAS), can impart additional antibiofouling properties to PDMS-based FR coating systems. In this study, the molecular surface structures of two different types of QAS-incorporated PDMS systems were investigated in different chemical environments using sum frequency generation vibrational spectroscopy (SFG). Specifically, a series of PDMS coatings containing either a QAS with a single ammonium salt group per molecule or a quaternary ammonium-functionalized polyhedral oligomeric silsesquioxane (Q-POSS) were measured with SFG in air, water, and artificial seawater (ASW) to investigate the relationships between the interfacial surface structures of these materials and their antifouling properties. Although previous studies have shown that the above-mentioned materials are promising contact-active antifouling coatings, slight variations of the QAS structure can lead to substantial differences in the antifouling performance. Indeed, the SFG results presented here indicated that the surface structures of these materials depend on several factors, such as the extent of quaternization, the molecular weight of the PDMS component, and the functional groups of the QAS used for incorporation into the PDMS matrix. It was concluded that in aqueous environments a lower extent of Q-POSS quaternization and the use of ethoxy (instead of methoxy) functional groups for QAS incorporation facilitated the extension of the alkyl chains away from the nitrogen atom of the QAS on the surface. The SFG results correlated well with the antifouling activity studies that indicated that the coatings exhibiting a lower concentration of longer alkyl chains protruding out of the surface can neutralize microorganisms more effectively, ultimately leading to better antifouling performance. Furthermore, the results of this study provide additional evidence that incorporated QAS exert their antimicrobial activity through a two-step interaction. The first step is the adsorption of the bacteria on the surface as a result of the electrostatic attraction between the negatively charged microorganisms and the positively charged QAS nitrogen atoms on the surface. The second step is the disruption of the cell membranes by the penetration of the QAS long, extended alkyl chains.
聚二甲基硅氧烷（PDMS）材料已被广泛证明是海洋环境中优异的防污（FR）涂料。引入季铵盐（QAS）等杀生剂基团可以赋予 PDMS 基 FR 涂层系统额外的抗生物污染性能。在这项研究中，使用和频发生振动光谱（SFG）研究了两种不同类型的 QAS 掺入 PDMS 系统在不同化学环境下的分子表面结构。具体来说，一系列含有单铵盐基团的 PDMS 涂层或季铵官能化的多面体低聚倍半硅氧烷（Q-POSS）的 PDMS 涂层用 SFG 在空气、水和人工海水中进行了测量，以研究这些材料的界面表面结构与其防污性能之间的关系。尽管先前的研究表明，上述材料是有前途的接触活性防污涂料，但 QAS 结构的微小变化会导致防污性能的显著差异。事实上，这里呈现的 SFG 结果表明，这些材料的表面结构取决于几个因素，例如季铵化程度、PDMS 成分的分子量以及用于掺入 PDMS 基质的 QAS 的官能团。得出的结论是，在水相环境中，较低程度的 Q-POSS 季铵化以及使用乙氧基（而不是甲氧基）官能团用于 QAS 掺入，有利于烷基链从 QAS 表面的氮原子上延伸出来。SFG 结果与抗污活性研究很好地相关，该研究表明，从表面突出的较长烷基链的浓度较低的涂层可以更有效地中和微生物，最终导致更好的抗污性能。此外，这项研究的结果提供了更多证据表明，掺入的 QAS 通过两步相互作用发挥其抗菌活性。第一步是由于带负电荷的微生物和表面上带正电荷的 QAS 氮原子之间的静电吸引，细菌在表面上的吸附。第二步是 QAS 长而延伸的烷基链的穿透导致细胞膜的破坏。
