Polymerization induced by electron-beam irradiation of octadecyl methacrylate in the form of a multilayer or monolayer

In continuation of the previous series of studies, polymerization of octadecyl methacrylate (ODMA) induced by electron beams has been investigated in a form of its multilayer or monolayer in an attempt to prepare a stable thin polymer film having a regular layer structure. ODMA multilayers were prepared by the Langmuir-Blodgett technique and irradiated with electron beams from a Van de Graaff accelerator. Multiple reflection infrared spectroscopy and x-ray diffractometry revealed that the ODMA multilayer was polymerized to give a thin polymer film having a regular layered structure when irradiated in nitrogen atmosphere, but no indication of polymerization was observed when irradiated in air. A preliminary study on the ODMA monolayer at a nitrogen–water interface indicated that the monolayer was polymerized.     

Structure of solid monolayers and multilayers of n -hexane on graphite

We present all-atom molecular dynamics simulations ofn-hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules are observed to attain the perpendicular orientation at monolayer coverage. Dedicated to Professor C N R Rao on his 70th birthday     

Multilayer structure of an unsymmetrical monolayer lipid membrane with a 'head-to-tail' interface

A synthetic unsymmetrical 1-galactosamide bolaamphiphile self-assembles in methanol to form a multilayer structure comprising unsymmetrical monolayer lipid membranes linked via a sugar-carboxylic acid H-bonding interface.     

Surface-enhanced spectroscopic investigation of the adsorption properties of hydroxybenzoic acid isomers onto metallic surfaces

Surface-enhanced Raman Spectroscopy (SERS), surface-enhanced infrared absorption spectroscopy (SEIRA), temperature-programmed desorption (TPD), and density functional theory were used to characterize the adsorption properties of the hydroxybenzoic acid (HBA) isomers including ortho-hydroxybenzoic acid (OHA), meta-hydroxybenzoic acid (MHA), and para-hydroxybenzoic acid (PHA) using various deposition solvents with different polar properties. SERS typically enhances the Raman shifts of the monolayer, while SEIRA is a longer range effect, often providing vibrational enhancement to both the monolayer and multilayer. TPD analysis showed that OHA adsorption to silver is weaker than MHA/PHA, most likely as a result of the strong OHA intramolecular hydrogen-bonding. SERS and SEIRA demonstrated that OHA ionized efficiently in the monolayer and multilayer independent of the solvent polarity because of OHA's low pK_a (2.98). MHA/PHA ionized better than OHA in the multilayer in less polar deposition solvents, and a decrease in the polarity of the deposition solvent created additional ordering in the MHA monolayer while inducing stronger adsorption in the PHA monolayer. It is believed that a lower level of solvation with less polar deposition solvents allowed for more adsorbate/substrate interaction and more intermolecular attraction. The addition of more MHA to a multilayer resulted only in stronger SEIRA peaks. As a PHA multilayer thickened there was significant structural changes represented by new bands and spectral peak shifts with greater intermolecular attraction as the multilayer approached bulk properties. Due to the range of applications involving HBA isomers, these studies could find significant applications in biochemistry, medicine, nanotechnology and environmental science.     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（AFM）对有机分子HTDIOO单层和多层LB膜结构进行了观察·实验结果表明，针尖与LB膜表面分子间的相互作用力会对成像的膜结构有影响．当悬臂针尖与LB膜表面分子的相互作用力较大时，针尖会扰动HTDIOO分子在单层LB膜中的有序排列．HTDIOO单层LB膜具有有序结构；而在多层LB膜中，HTDIOO分子则聚集在一起形成了一定的畴结构．     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（ＡＦＭ）对有机分子ＨＴＤＩＯＯ单层和多层ＬＢ膜结构进行了观察。实验结果表明，针尖与ＬＢ膜表面分子间的相互作用力会对成像的膜结构有影响。当悬臂针尖与ＬＢ膜表面分子的相互作用力较大时，针尖会扰动ＨＴＤＩＯＯ分子在单层ＬＢ膜中的有序排列。ＨＴＤＩＯＯ单层ＬＢ膜具有有序结构；而在多层ＬＢ膜中，ＨＴＤＩＯＯ分子则聚集在一起形成了一定的畴结构。     

Fabrication of binary colloidal crystals and non-close-packed structures by a sequential self-assembly method

Binary colloidal films of polystyrene (PS) spheres and silica spheres were fabricated with a sequential growth method using differently sized colloidal particles. In particular, we demonstrate the structures formed by a silica monolayer growing on top of a PS monolayer and a silica multilayer growing on top of a PS monolayer. By removal of the bottom PS layers, non-close-packed hexagonal, pentagonal, and square silica arrays were obtained at the original silica/PS interface. The possible formation mechanism of the non-close-packed structure was discussed, which may be used to explain how 3D colloidal crystals grow on patterned substrates.     

Formation of langmuir-blodgett films containing two-dimensional monoatomic arrays of rare-earth cations

The work is focused on the preparation and characterisation of rare-earth containing stearic acid Langmuir-Blodgett (LB) films. Stearic acid monolayer behavior on the rare-earth containing aqueous subphase have been analyzed by thermodynamic measurements. The compression isotherm shape changed substantially under varying the anion type at the constant rare-earth cation content in aqueous subphase. The structure of formed multilayer rare-earth containing LB films was studied using small angle X-rays diffraction. The considerable structural defects in multilayer films were found when rare-earth chloride solution was exploited as aqueous subphase, caused presumably by electrostatic interactions at the monolayer surface under high binding of rare-earth cations. The use of monodentate complexones like acetic acid was proposed to form bulk phase quasi-neutral rare-earth complexes. The electroneutral ligand exchange reactions of such complexes with stearic acid monolayer allowed to neutralise monolayer surface under rare-earth cations binding and to form condenced monolayer below the triple-point temperature. The compression of such monolayer to the state of minimal compressibility and subsequent monolayer deposition resulted in the formation of high ordered LB films with high content of adsorbed multivalent rare-earth cations arranged in two-dimensional monoatomic arrays.     

X-ray investigations of Langmuir-Blodgett multilayer films of side-chain liquid crystal copolymers

X-ray reflectivity studies on Langmuir-Blodgett multilayer films of side-chain liquid crystal polymers are reported. The films have a high degree of lamellar order. The layer periodicity is independent of the type of monolayer deposition, implying a reorientation of the side group mesogens following the deposition process. X-ray reflectivity from thin films displays subsidiary maxima permitting a quantitative measure of the change in side-chain density between multilayer and monolayer. A unit cell density profile is calculated for thick films assuming a symmetric unit cell.     

SnO2纳米粒子-花生酸LB膜有序组合体的研究

采用胶体化学法制备了稳定的SnO2纳米粒子（nanoparticleNP）水溶胶，用膜天平和原位布儒斯特角显微镜（BAM）考察了经典成膜材料花生酸（AA）在此水溶胶气-液界面的成膜性，并用LB膜技术在不同基底上制得了单层和多层AA-Sno2NP复合LB膜，通过TEM、小角X-ray、IR和UV-VIS光谱，进一步考察了该有序组装体的结构和周期性，以及组装作中Sno2纳米粒子的形貌、粒度分布和表面聚集状态.结果表明，用这种方法能够制得粒度分布均匀、农致密的Sno2纳米粒子复合LB膜，并且多层复合膜具有良好的周期性.     

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di-minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indi-cates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.     

Langmuir-Blodgett films of a clay mineral and ruthenium(II) complexes with a noncentrosymmetric structure

Mono- and multilayers of amphiphilic [Ru(phen)(2)(dcC12bpy)](2+) (phen = 1,10-phenanthroline, dcC12bpy = 4,4'-caboxyl-2,2'-bipyridyl didodecyl ester) hybridized with a clay mineral have been prepared by a modified Langmuir-Blodgett method, and their structures and properties have been investigated. Formation of a hybrid monolayer of the Ru(II) complex cations and the clay platelets at an air-clay suspension interface was confirmed by surface pressure-molecular area (pi-A) isotherm measurement and atomic force microscopic (AFM) observation. Multilayers were fabricated by depositing the hybrid monolayers onto glass substrates. The absorbance at 492 nm due to the Ru(II) complex cation in the multilayer increased linearly with the increase in the layer number, indicating layer-by-layer deposition of the hybrid monolayers. Because no increase in the second-harmonic generation (SHG) signal from the multilayers against the layer number was observed, the orientation of the Ru(II) complex cations in the layer would be disturbed. The hydrophilic surface of the transferred hybrid monolayer can be converted to a hydrophobic surface by dipping it in an aqueous solution of octadecylammonium chloride (ODAH(+)Cl(-)). The multilayers modified with ODAH(+) showed a quadratic relation between the SHG intensity and the layer number. This means that the Ru(II) complex cations in the multilayer are successfully oriented in a noncentrosymmetric way by the conversion of the surface property. Both a racemic mixture and an enantiomer of the Ru(II) complex cations were employed to examine the chiral effect on the film properties. The chiral contribution to the SHG signal was enhanced in the multilayer modified with ODAH(+).     

A novel nanogold multilayer constructed by Langmuir-Blodgett and self-assembly techniques

A multilayer comprising nanogold particles and organic molecules was constructed by self-assembly of the small organic molecule 1-phenyl-5-mercaptotetrazole onto the octadecylamine-protected nanogold monolayer in the course of transferring the monolayer, layer by layer, from a Langmuir-Blodgett trough to solid substrates. The structure and properties of the constructed multilayer were characterized by TEM images and ATR-IR, XPS, and UV-vis spectra. It is evidenced for the first time that the combination of Langmuir-Blodgett and self-assembly techniques provides a new way to organize functional nanoparticles such as organic-nanogold complexes.     

Kinetics and mechanism of electrochemical reduction of multilayer oxides on a smooth platinum electrode surface in acidic electrolyte

The electrochemical reduction of multilayer oxides which were formed on a smooth Pt electrode surface under severe anodic conditions was investigated using a galvanostatic transient, a linear potential sweep and a potential step technique. Four regions of the surface oxide reduction were distinguished in the galvanostatic E?t curve and four corresponding cathodic current peaks were observed in the potentiodynamic i?E profile. These four regions or peaks are attributed to the reduction of four O-containing layers: an oxygen monolayer adsorbed on the oxide surface, two oxide layers in a first and a second lattice and a multilayer oxide in the deeper lattices having a phase property. The reduction rate of the first lattice oxide layer is determined by a second electron transfer. Under a rapid stripping condition, the reduction of the second oxide layer is considered to be controlled by the place exchange reaction. The extremely large reduction rate of the multilayer oxide compared with the formation rate is explained in terms of the proton-electron model.     

Elucidation of the mechanism of surface‐initiated atom transfer radical polymerization from a diazonium‐based initiator layer

This study elucidates the influence of the atom transfer radical polymerization initiator structure, monolayer versus disordered multilayer, on the growth kinetics and the structural transition of poly(methyl methacrylate) (PMMA) brush layers. The multilayer initiator film, prepared by acylation of the electrografted 2‐phenylethanol layer using 2‐bromoisobutyryl bromide, consists of ～4.6 times more tert‐butyl bromide groups compared to monolayer initiator prepared by self assembly technique. The results demonstrate the formation of precursor complex between Cu^I catalyst and the bromine initiator as a prerequisite step before the onset of polymerization. Furthermore, the PMMA brushes formed by the polymerization from the multilayered initiator layer at 50 °C are 20‐fold thicker compared to the polymerization at 25 °C due to the swelling of the multilayered initiator film. In contrast, the thickness of the PMMA layer on the monolayer initiator is less affected by the polymerization temperature. By varying the initiator density on the surface, the solvent content in the PMMA layer is shown to vary from 15% to 94%, resulting in the transition from concentrated over semidiluted to diluted brushes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Surface viscoelastic properties of floating polyelectrolyte multilayers films: a capillary wave study

A capillary wave technique was used to study the viscoelastic properties of floating polyelectrolyte multilayers of (PSS/PAH)(n) at the air-water interface. Oppositely charged polyelectrolyte layers were adsorbed onto two different Langmuir monolayers, either the lipid dimethyldioctadecylammonium bromide (DODAB) or the block copolymer poly(styrene-b-sodium acrylate) (PS-b-PAA). The results allow to propose a schematic representation of the multilayers in three zones: Zone I as a precursor, representing the adhesion between the Langmuir monolayer and the bulk polyelectrolyte multilayer. Zone II forms a bulk or core zone of the multilayer. Zone III as an outer zone in direct contact with the aqueous phase. The results show an increase of the elasticity after the formation of four polyelectrolyte layers accompanied by an apparent negative viscosity. This behaviour was interpreted as a translation of elasticity dominance from zone I to zone II. The Young modulus of seven layers was in the same order of magnitude as observed for planar polyelectrolyte multilayer films.     

Electron transfer studies on cholesterol LB films assembled on thiophenol and 2-naphthalenethiol self-assembled monolayers

We have formed the cholesterol monolayer and multilayer LB films on the self-assembled monolayers of 2-naphthalenethiol (2-NT) and thiophenol (TP) and studied the electrochemical barrier properties of these composite films using cyclic voltammetry and electrochemical impedance spectroscopy. We have also characterized the cholesterol monolayer film using grazing angle FTIR, scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Cholesterol has a long hydrophobic steroid chain, which makes it a suitable candidate to assemble on the hydrophobic surfaces. We find that the highly hydrophobic surface formed by the self-assembled monolayers (SAM) of 2-NT and TP act as effective platforms for the fabrication of cholesterol monolayer and multilayer films. The STM studies show that the cholesterol monolayer films on 2-NT form striped patterns with a separation of 1.0 nm between them. The area per cholesterol molecule is observed to be 0.64 nm2 with a tilt angle of about 28.96 degrees from the surface normal. The electrochemical studies show a large increase in charge transfer resistance and lowering of interfacial capacitance due to the formation of the LB film of cholesterol. We have compared the behavior of this system with that of cholesterol monolayer and multilayers formed on the self-assembled monolayer of thiophenol.     

Amperometric detection of superoxide dismutase at cytochrome c-immobilized electrodes: xanthine oxidase and ascorbate oxidase incorporated biopolymer membrane for in-vivo analysis.

Amperometric measurement of superoxide dismutase (SOD) was carried out at cytochrome c-immobilized monolayers and ascorbate oxidase (AOD)/xanthine oxidase (XOD)/cytochrome c- and (AOD, XOD)/cytochrome c-multilayers. Cytochrome c was covalently immobilized on mercaptopropionic acid-containing self-assembled monolayers on gold. A biopolymer membrane of poly-L-lysine confining XOD and AOD was cast on the monolayer of cytochrome c. While both the cytochrome c-immobilized monolayer and multilayer electrodes show anodic current responses to the generation of superoxide radical, the sensitivity of the multilayer system for the detection of superoxide radical was high relative to that of the monolayer system. In the case of the cytochrome c-multilayer electrodes, the generation of superoxide radical near the sensing element, cytochrome c, resulted in high sensitivity for the detection of superoxide. The use of a XOD and AOD-incorporated poly-L-lysine membrane enabled the detection of the generation of superoxide radical in the presence of L-ascorbic acid. Though L-ascorbic acid could scavenge superoxide radical, the biopolymer membrane confined with AOD will oxidize any L-ascorbic acid that permeated into the membrane. By using the multilayer electrodes, one could measure the activity of SOD in the presence of L-ascorbic acid.     

Kinetics of adsorption and proteolytic cleavage of a multilayer ovalbumin film by subtilisin Carlsberg

Adsorption and proteolytic activity of the enzyme subtilisin Carlsberg have been studied on an immobilized, multilayer ovalbumin film. The cross-linked multilayer substrate permits protease adsorption to be examined unencumbered by the surface inhomogeneity typically observed in monolayer studies of protease surface kinetics. Decline of the protein film was measured over time using ellipsometry. Resulting kinetic data as a function of aqueous enzyme concentration and temperature were well fit by a Langmuir-Michaelis-Menten model for surface proteolysis. We observed that both the protein degradation kinetics and the in situ adsorption data were well described by the proposed model. The temperature dependence of the kinetic rate parameter yielded an activation energy of 12 kcal/mol. Further, the apparent Langmuir adsorption equilibrium constant of the enzyme at the protein/aqueous interface was 0.11 L/mg at 22 degrees C, 0.034 L/mg at 36 degrees C, and 0.011 L/mg at 50 degrees C. Although enzyme adsorption at a given aqueous enzyme concentration decreased at higher temperature, the enzyme cleaved the substrate more rapidly, leading to a net increase in the ovalbumin film degradation rate. We observed that the maximum enzyme coverage on the immobilized protein surface was approximately 40% of a close-packed monolayer at ambient temperature (22 degrees C).     

碳纤维中的单层石墨物相及其对力学性能的影响

依据碳纤维中各种物相的X射线衍射特性, 确认PAN基碳纤维中除了乱层石墨微晶外, 还存在大量的单层六元环C原子层面物相, 建立起两种非完整结晶物相的定量分析方法. 实验结果表明, 随着退火温度由1350 ℃上升到2400 ℃, Tx-3高强型碳纤维中的单层石墨含量由59.6%下降到34.8%, 乱层石墨含量由40.4%上升为65.2%. 与此同时, 碳纤维的拉伸强度则由3.65 GPa下降到2.05 GPa, 而延伸率也由1.04%下降到0.58%. 并对PAN基碳纤维中单层石墨对其力学性能的影响也进行了初步的探讨.