Micropatterning functional groups on polymer surfaces via masked vapor-phase photografting

Controlling cell behavior on biomaterial surface is the ultimate goal of cell and tissue engineering. Fabrication of biomaterials with alternatively hydrophilic/hydrophobic surface of parallel nanopatterned groves can provide biomaterial surfaces for the study of cell-surface interactions. In the present communication, masked vapor-phase photografting was used in patterning functional groups on flat polymeric substrates using poly (dimethylsiloxane) (PDMS) channels. Surface patterns were fabricated by UV-initiated photografting in the presence of a patterned PDMS mask. The approach is exemplified by patterning maleic anhydride (MAH) and acrylamide (AAm) onto poly (methyl methacrylate) (PMMA). The method offers another means to chemically functionalize and pattern polymer surface at the same time.     

离子交换纤维对绿原酸吸附特性的研究

研究了绿原酸在自制的强碱性阴离子交换纤维上的静态吸附行为，结果表明：该离子交换纤维对绿原酸的静态饱和吸附容量为252．2mg／g；等温吸附曲线服从Langmuir等温吸附式和Freundlich经验式；表观活化能Eα=15．498kJ／mol；表观速率常数随温度的升高而增大。用一定体积比的稀HCl-甲醇复合溶剂可将纤维上的绿原酸洗脱。     

Effects of chemical functional groups on elemental mercury adsorption on carbonaceous surfaces

A systematic theoretical study using density functional theory is performed to provide molecular-level understanding of the effects of chemical functional groups on mercury adsorption on carbonaceous surfaces. The zigzag and armchair edges were used in modeling the carbonaceous surfaces to simulate different adsorption sites. The edge atoms on the upper side of the models are unsaturated to simulate active sites. All calculations (optimizations, energies, and frequencies) were made at B3PW91 density functional theory level, using RCEP60VDZ basis set for mercury and 6-31G(d) pople basis set for other atoms. The results indicate that the embedding of halogen atom can increase the activity of its neighboring site which in turn increases the adsorption capacity of the carbonaceous surface for Hg(0). The adsorption belongs to chemisorptions, which is in good agreement with the experimental results. For the effects of oxygen functional groups, lactone, carbonyl and semiquinone favor Hg(0) adsorption because they increase the neighboring site's activity for mercury adsorption. On the contrary, phenol and carboxyl functional groups show a physisorption of Hg(0), and reduce Hg capture. This result can explain the seemingly conflicting experimental results reported in the literature concerning the influence of oxygen functional groups on mercury adsorption on carbonaceous surface.     

芘丁酸在玻璃基片表面的单层自组装

利用表面反应,在玻璃基片表面引入芘丁酸分子,制备成单分子层自组装荧光薄膜,测定了薄膜的润湿性和荧光光谱,考察了酰胺化温度对荧光传感薄膜荧光特性的影响,探究了薄膜在不同溶剂中的稳定性。结果表明,芘丁酸分子成功地固定在玻璃基片表面,降低温度对酰胺化反应有利,以及不同的介质对薄膜的稳定性有较大影响。     

Simulation and modeling of self-assembled monolayers of carboxylic acid thiols on flat and nanoparticle gold surfaces

Quantitative analysis of the 16-mercaptohexadecanoic acid self-assembled monolayer (C16 COOH-SAM) layer thickness on gold nanoparticles (AuNPs) was performed using simulation of electron spectra for surface analysis (SESSA) software and X-ray photoelectron spectroscopy (XPS) experimental measurements. XPS measurements of C16 COOH-SAMs on flat gold surfaces were made at nine different photoelectron emission angles (5-85° in 10° increments), corrected using geometric weighting factors and then summed together to approximate spherical AuNPs. The SAM thickness and relative surface roughness (RSA) in SESSA were optimized to determine the best agreement between simulated and experimental surface composition. On the basis of the glancing-angle results, it was found that inclusion of a hydrocarbon-contamination layer on top the C16 COOH-SAM was necessary to improve the agreement between the SESSA and XPS results. For the 16 COOH-SAMs on flat Au surfaces, using a SAM thickness of 1.1 ?/CH(2) group, an RSA of 1.05, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 21.5 ?) for the SESSA calculations provided the best agreement with the experimental XPS data. After applying the appropriate geometric corrections and summing the SESSA flat-surface compositions, the best fit results for the 16 COOH-SAM thickness and surface roughness on the AuNPs indicated a slightly thinner overlayer with parameters of 0.9 ?/CH(2) group in the SAM, an RSA of 1.06 RSA, and a 1.5 ? CH(2)-contamination overlayer (total film thickness = 18.5 ?). The 3 ? difference in SAM thickness between the flat Au and AuNP surfaces suggests that the alkyl chains of the SAM are slightly more tilted or disordered on the AuNP surfaces.     

Self-oriented glucose-modified infrared sensor for the detection of compounds bearing carboxylic acid groups

To explore the interactions of self-oriented glucose toward organic species, we prepared a glucose-modified infrared (IR) chemical sensor and examined its performance in the detection of compounds bearing carboxylic acid functional groups. Using a two-layer modification method, we chemically bonded glucose to the surface of an IR sensing element. The immobilized glucose moieties exhibited the ability to assemble into a chemical form similar to that of the cyclodextrins (CDs) such that they could trap targeted molecules. This modified sensing phase displayed an analysis capability similar to that of CDs, but without the problems encountered attempting to maintain the activity of the latter. From a systematic examination of three classes of structural analogs of acids, we found that the behavior of the glucose-modified sensing phase was similar to that of a CD-modified sensing phase. In terms of quantitative detection, we obtained an average regression coefficient of approximately 0.996 for the analytical signals of the examined compounds at concentrations less than 20 mg/L. The linearity of the standard curves was related to the detection time: the shorter the detection time, the greater the linearity. Defined as three times the noise level, we obtained detection limits of a few hundred parts per billion (microg/L) for the determination of high-polarity compounds using our glucose-modified sensing phase.     

Adsorption of hydrogen on porous Vycor glass

Hydrogen adsorption isotherms have been measured at temperatures between 15 K and 20 K for porous Vycor glass. The intermediate adsorption data were analyzed using a modified Brunauer-Emmett-Teller method, which is based on the assumption that two layers are coadsorbed, the first layer being very strongly attached. Our results indicate that, relative to the adsorption energy of the free surface of the bulk liquid, the adsorption energy of the second layer is approximately 60 K, much smaller than the adsorption energy of the first layer but still significant at the low temperature of the experiments. Our results are compared to those for adsorption of⁴He on Vycor.     

弱酸离子交换纤维对含镍废水的吸附性能研究

系统研究了自制羧基离子交换纤维对电镀废水中Ni 2＋的吸附性能。结果表明钠型羧酸纤维的平衡吸附容量远高于相应氢型纤维;静态条件下纤维对Ni 2＋的吸附容量可达220mg/g以上;溶液初始浓度、pH值以及温度越高,钠型羧酸纤维的平衡吸附量越大。100～300mg/L范围内的含镍电镀废水经柱吸附后可达国家规定排放浓度（≤0.5mg/L）,吸附Ni 2＋后的纤维可用2mol/L盐酸溶液解吸,纤维重复使用100次后吸附性能基本不变。     

Adsorption of3He on cesium surfaces

Vapor pressure isotherms of³He on Cs are reported which show that, in contrast to⁴He,³He weis Cs for 1.26K<T<2K. Although the isotherms are distinctly different from those taken on strong binding substrates, we have observed no evidence for a first order prewetting transition. The data suggest that the prewetting critical point is substantially below T=1.26K.     

Adsorption of calcitonin to glass

Surface adsorption of calcitonin on soda lime silica glass was investigated. An attempt was also made to examine the effect of additives on the inhibition of calcitonin adsorption. Results showed that the adsorption isotherms were of the Langmuir and Freundlich type, depending on pH. Less adsorption was found for calcitonin at pH 4.3. The addition of nonionic surfactants such as Pluronic F68 and Tween 80 to the calcitonin solutions demonstrated inhibition of adsorption and reduction of adsorption rate. The addition of chlorobutanol also showed the effect of minimizing adsorption.     

Morphological relaxation of glass surfaces

A model for calculating the morphological relaxation of two-dimensional glass profiles for arbitrary temperature-time schedules is described. The model is based on a Fourier expansion of the surface profile for which the decay with time can easily be calculated for each of the separate terms. The effect of the variable temperature with time was accounted for by discretization of the temperature-time profile. Necessary input data are the viscosity and surface tension of the glass. The sensitivity to various geometrical details is limited, but heating/cooling effects appeared to be important. The predictions of the model are verified by measurements on glass samples with various profiles and relaxed according to a certain temperature-time schedule. Using a surface tension value of 0.19 N m^–1, as determined with recent fibre-on-plate experiments, excellent agreement between theory and experiment was obtained. Possible options for extension to threedimensional profiles are indicated.     

Adsorption of benzene on noble metal surfaces studied by density functional theory with Van der Waals correction

We have studied the atomic geometries and the electronic properties of benzene/metal interfaces by using density functional theoretical (DFT) calculations with van der Waals corrections. Adsorption energies of benzene on Cu(111), Ag(111), and Au(111) surfaces calculated by van der Waals density functional proposed by Dion and co-workers agree reasonably well with experimentally reported values, while those calculated by a semi-empirical van der Waals correction proposed by Grimme are overestimated slightly. The work function change induced by benzene adsorption on the three surfaces are quite well reproduced by the semi-empirical correction, suggesting that weak adsorption geometries can be quite well reproduced by DFT with a semi-empirical dispersion correction scheme.     

Effect of the carboxylic acid groups on water sorption, thermal stability and dielectric properties of polyimide films

Films from copolyimides containing side carboxylic acid groups were prepared in -COOH and COO⁻Na⁺ forms to study the effect of the side groups content on some physical properties such as water absorption, thermal stability and electrical parameters. The thermal stability was evaluated by TGA and the results showed that degradation temperatures depended not only on the side groups content but also on the membrane ionic form. This dependence was also observed in the water sorption isotherms; the polyimides with the highest -COOH content showing the highest water sorption in the equilibrium. Dielectric impedance measurements revealed how the side groups and their ionic form affect the material electrical characteristics, in such a way that resistivity decreased and permittivity increased on introducing more -COOH groups in the polymer, which is also related to a higher water uptake of the films.     

Controlling binding site densities on glass surfaces

The density of surface-immobilized ligands or binding sites is an important issue for the development of sensors, array- or chip-based assays, and single-molecule detection methods. The goal of this research is to control the binding site density of reactive ligands on surfaces by diluting surface amine groups in self-assembled and cross-linked monolayers on glass prepared from solutions containing very low concentrations of (3-aminopropyl)triethoxysilane (APTES) and much higher concentrations of (2-cyanoethyl)triethoxysilane. The surface amine sites are suitable for attaching labels and ligands by reaction with succinimidyl ester reagents. Labeling the amine sites with fluorescent molecules and imaging the single molecules with fluorescence microscopy provides a means of determining the density of amine sites on the surface, which were incorporated into the self-assembled monolayer with micrometer spacings in proportion to the concentration of APTES in the synthesis. Biotin ligands were also bound to these surface amine sites using a succinimidyl ester linker, and the immobilized biotin was then reacted with either streptavidin-conjugated gold colloid particles or fluorescently labeled neutravidin. Imaging of these samples yields consistent amine and biotin site coverages, indicating that quantitative control and chemical conversion of binding sites can be achieved at very low (<10(-7)) fractions of a monolayer.     

Radiation effects on lead silicate glass surfaces

Radiation-induced changes in the microstructure of lead silicate glass were investigated in situ under Mg K irradiation in an ultra-high vacuum (UHV) environment by X-ray photoelectron spectroscopy (XPS). Lead-oxygen bond breaking resulting in the formation of pure lead was observed. The segregation, growth kinetics and the structural relaxation of the lead, with corresponding changes in the oxygen and silicon on the glass surfaces were studied by measuring the time-dependent changes in concentration, binding energy shifts, and the full width at half maximum. A bimodal distribution of the oxygen XPS signal, caused by bridging and non-bridging oxygens, was found during the relaxation process. All experimental data indicate a reduction of the oxygen concentration, a phase separation of the lead from the glass matrix, and the metallization of the lead occurred during and after the X-ray irradiation.     

Adsorption behavior of carbon nanotubes on polystyrene surfaces

Polystyrene (PS) was prepared using two different polymerization methods (dispersion polymerization and seed polymerization) to investigate the steric stabilizer effect during the adsorption process of carbon nanotubes (CNTs) on the surface of PS microspheres. Experiments with different microsphere diameters and difference types of CNTs were conducted to analyze the curvature effect of the spheres on the adsorption mechanism. The results showed that PS microspheres prepared through dispersion polymerization exhibited preferable adsorption behavior compared to PS spheres prepared through seed polymerization, suggesting that poly(N-vinylpyrrolidone) led to improved adsorption interactions between the CNTs and the PS microspheres in the CNTs dispersion. Additionally, the PS diameter and CNT curvature were examined with respect to the adsorption behavior between the PS microspheres and the CNTs. Multiwalled carbon nanotubes (MWCNTs) were found to be well adsorbed on the surface of PS microspheres measuring 2 microm. However, the MWCNTs were adsorbed much less on the surface of submicron-sized PS microspheres, compared with thinwalled carbon nanotubes (TWCNTs). On the other hand, TWCNTs were found to be suitable for adsorption on submicron-sized PS microspheres. These results also indicate that the curvature of the CNTs and the polymer microspheres are important to the CNT adsorption process.     

Impact of small steel spheres on glass surfaces

A high speed photographic study has been made as part of a detailed investigation of the impact of small steel spheres ( 800 and 1000 m diameter) on to Pyrex and soda-lime glasses. The velocity of the spheres was varied from 20 to 300 m sec^–1 and the fracturing process during the complete impact cycle was followed. Observations revealed substantial differences in the behaviour of the two glasses, particularly at higher velocities; Pyrex behaved as though indented by a sphere, whereas soda lime glass behaved as though indented with a pointed indenter. As with quasi-static pointed indentations, cracking was observed during the unloading cycle. It was also found that the angle of the Hertzian cone crack in Pyrex glass varied in a systematic manner with velocity. Rebound velocity, time of contact and extent of flattening of the steel spheres were also recorded. The relevance of these observations to impact erosion and strength degradation of brittle materials is pointed out.