Monolayer and multilayer compact film formations on different substrates by physical deposition

Dissipative particle dynamics simulations are applied to investigate the monolayer and multilayer film formations on different solid substrates by physical deposition. The influences of the polymer concentration, the polymer chain length, the solvent quality, and the interactions between the polymer solution and the solid substrate surface on the film formation dynamics and the mechanism are studied in detail. The results are analyzed in terms of the thickness and the shape of the deposited film, the kinetics of phase separation in the polymer solution, and the contact angle formed between the polymer aggregations and the substrate surface. Moreover, we suggest two strategies, designing a deposition process analogous to “chemical titration” and physically blocking interlayer diffusion by a simple crosslinked network barrier, to deposit the compact monolayer and multilayer films with better quality, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 353–365, 2009     

银电极表面异亮氨酸单分子膜结构和表面性质的表面增强拉曼光谱研究

利用表面增强拉曼光谱(SERS)技术研究了在粗糙化银电极表面吸附的异亮氨酸自组装单层膜结构及其表面性质随溶液酸碱性和电极电位改变的特征.研究结果表明溶液pH值的变化并没有显著改变异亮氨酸分子在银电极表面以去质子化羧基吸附为主的特征.借助于高氯酸根离子这一SERS光谱探针,对异亮氨酸单分子膜的表面酸碱性质进行了表征和分析.而就电位改变对该单分子膜结构的影响而言,在所研究的电位范围内,单分子膜中的异亮氨酸分子是通过去质子化羧基与氨基两个位点而吸附的,且吸附作用随电位负移而呈现有规律的变化.     

层状二氧化锰和2,2'-联吡啶铁自组装膜的制备和光电性能研究

采用静电吸附层-层自组装方法制备了层状二氧化锰/2,2'-联吡啶铁自组装膜材料,借助扫描电镜(SEM),紫外可见光谱(UV-Vis)和电化学工作站等测试手段对自组装膜的结构与性能进行了表征.结果表明,该自组装膜具有均匀的表面和紧密的层状结构,在可见光照射条件下该自组装膜电极的氧化还原电流明显增加了.层状二氧化锰/2,2'-联吡啶铁自组装膜电极,在可见光照射条件下光电降解有机染料罗丹明B(1×10-5mol/L)反应80min降解率达到了57%.     

Determination of thiodicarb using a biosensor based on alfalfa sprout peroxidase immobilized in self-assembled monolayers

A biosensor based on alfalfa sprout (Medicago sativa) homogenate as a source of peroxidase is proposed for the determination of thiodicarb by square-wave voltammetry. This enzyme was immobilized in self-assembled monolayers of l-cysteine on a gold electrode. Several parameters were investigated to evaluate the optimum conditions for operation of the biosensor. The analytical curve was linear for thiodicarb concentrations of 2.27 × 10⁻⁶ to 4.40 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.75 × 10⁻⁷ mol L⁻¹. The lifetime of the Au-alfalfa sprout-SAMs was 20 days (at least 220 determinations). The average recovery of thiodicarb from samples of vegetable extracts ranged from 99.02 to 101.04%. The results obtained for thiodicarb in vegetable extracts using the proposed method are in close agreement with those using a high performance liquid chromatography procedure at the 95% confidence level.     

Self‐assembled Monolayers of Alkylphosphonic Acids on Aluminum Oxide Surfaces – A Theoretical Study

Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al₂O₃ (0001), bayerite β‐Al(OH)₃ (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting.