Structure, Wettability, and Thermal Stability of Organic Thin-Films on Gold Generated from the Molecular Self-Assembly of Unsymmetrical Oligo(ethylene glycol) Spiroalkanedithiols
Structure, Wettability, and Thermal Stability of Organic Thin-Films on Gold Generated from the Molecular Self-Assembly of Unsymmetrical Oligo(ethylene glycol) Spiroalkanedithiols
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DOI：
10.1021/acs.langmuir.6b03803
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发表时间：
2017-02-28
期刊：
影响因子：
3.9
通讯作者：
Lee, T. Randall
中科院分区：
文献类型：
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作者：
Chinwangso, Pawilai;Lee, Han Ju;Lee, T. Randall
金上的有机薄膜制备从一组新的，定制设计的双齿烷硫醇具有正构烷烃和甲氧基封端的三（乙二醇）链的混合物。新的不对称螺烷二硫醇吸附物的形式为[CH_3 O（CH_2CH_2 O）（3）（CH_2）（5）]-[CH_3（CH_2）（n+1）]C[CH_2SH]（2），其中n = 3和14;分别命名为EG_3C_7-C_7和EG_3C_7-C_（18）。表征了它们相应的在金上的自组装单分子膜（SAM），并与衍生自类似的正链烷硫醇（C18 SH）和用低聚（乙二醇）（OEG）部分封端的链烷硫醇（即，EG3C7SH）。椭圆偏振数据显示，减少膜厚度的双链二硫醇盐自组装膜，这可能是由相不相容的合并的烃链与OEG部分，有助于在膜中的无序和/或链倾斜的增加。使用水作为接触液体，衍生自EG 3C 7 SH和EG 3C 7-C7的SAM的可比较的润湿性与OEG部分在两个界面处的暴露一致，而衍生自EG 3C 7-C18的SAM的较低润湿性与烃链在界面处的暴露一致。通过X-射线光电子能谱收集的数据证实了新的OEG封端的二硫醇盐自组装膜的形成，并且还揭示了它们作为不太致密的单层，部分原因是OEG部分的大分子横截面和它们具有双表面键的双链结构。混合自组装膜形成的对单硫醇具有类似的链组成的新的二硫醇的链表明，一个EG 3C 7 SH/庚硫醇混合SAM和EG 3C 7-C7 SAM产生几乎相同的表征数据，揭示了有利的膜形成动力学的吸附物结构的烷基链可以组装下的相不相容的OEG终端。对于由EG 3C 7SH/CI 8 SH形成的混合SAM，数据表明EG 3C 7SH组分未能掺入膜中，表明当两种链存在于单一吸附物结构上时，有时最好地实现相不相容链的共混。此外，溶液相热脱附测试的结果表明，从双齿EG 3C 7-C7和EG 3C 7-C18吸附物产生的OEG封端的膜表现出增强的热稳定性时，相比于从单齿EG 3C 7SH产生的膜。在蛋白质吸附的简要研究中，多组分自组装膜显示出更大的能力，以抵抗纤维蛋白原在其表面上的吸附相比，SAM衍生自C18 SH，但不优于单层衍生自EG 3C 7 SH。
Organic thin-films on gold were prepared from a set of new, custom-designed bidentate alkanethiols possessing a mixture of normal alkane and methoxy-terminated tri(ethylene glycol) chains. The new unsymmetrical spiroalkanedithiol adsorbates were of the form [CH3O(CH2CH2O)(3)(CH2)(5)]-[CH3(CH2)(n+1)]C[CH2SH](2) where n = 3 and 14; designated EG3C7-C7 and EG3C7-C18, respectively. Their corresponding self-assembled monolayers (SAMs) on gold were characterized and compared with monothiol SAMs derived from an analogous normal alkanethiol (C18SH) and an alkanethiol terminated with an oligo(ethylene glycol) (OEG) moiety (i.e., EG3C7SH). Ellipsometric data revealed reduced film thicknesses for the double chained dithiolate SAMs, which perhaps arose from the phase-incompatible merger of a hydrocarbon chain with an OEG moiety, contributing to disorder in the films and/or an increase in chain tilt. The comparable wettabilities of the SAMs derived from EG3C7SH and EG3C7-C7, using water as the contacting liquid, are consistent with exposure of the OEG moieties at both interfaces, whereas the lower wettability of the SAMs derived from EG3C7-C18 is consistent with exposure of hydrocarbon chains at the interface. The data collected by X-ray photoelectron spectroscopy confirmed the formation of the new OEGterminated dithiolate SAMs, and also revealed them as less densely packed monolayers due in part to the large molecular cross section of the OEG moieties and to their double-chained structure with dual surface bonds. Mixed SAMs formed from pairs of monothiols having chain compositions analogous to those of the chains of the new dithiols showed that an EG3C7SH/ heptanethiol-mixed SAM and the EG3C7-C7 SAM produced almost identical characterization data, revealing the favorable film formation dynamics for adsorbate structures where the alkyl chains can assemble beneath the phase-incompatible OEG termini. For the mixed SAM formed from EG3C7SH/CI8SH, the data indicate that the EG3C7SH component failed to incorporate in the film, demonstrating that the blending of phase-incompatible chains is sometimes best accomplished when both chains exist on a single adsorbate structure. Furthermore, the results of solution-phase thermal desorption tests revealed that the OEGterminated films generated from the bidentate EG3C7-C7 and EG3C7-C18 adsorbates exhibit enhanced thermal stability when compared to the film generated from monodentate EG3C7SH. In a brief study of protein adsorption, the multicomponent SAMs showed a greater ability to resist the adsorption of fibrinogen on their surfaces when compared to the SAM derived from C18SH, but not better than the monolayer derived from EG3C7SH.