LB膜技术的应用研究进展

LB膜技术是在分子水平上制备有序分子超薄膜的先进技术。对LB膜技术的研究和应用进行了综述，介绍了目前LB技术在实现超微细粒子的二维有序组装，在光学，电化学器件和气体传感器中的应用以及通过LB膜技术组装生物仿生膜等方面的最新研究成果。     

Studies on Langmuir-Blodgett multilayer formation from preformed poly(N-alkylacrylamides)

The spreading behaviour of preformed poly(N-alkylacrylamides) having hexyl (PHA), octyl (POA), decyl (PDA), dodecyl (PDDA), tetradecyl (PTDA), hexadecyl (PHDA), and octadecyl (PODA) substituents on a water surface, and the properties of the Langmuir-Blodgett (LB) films deposited from these polymer monolayers were investigated. The surface pressure (F)-area (A) isotherms of the polymer monolayers were changed by the chain length of the substituents and the subphase temperature. The optimum conditions for the formation of a stable condensed monolayer from the polymer series of similar molecular weight (c. 4 × 10³) were found when the alkyl substituent was the dodecyl group (i.e. PDDA) and the subphase temperature was 19°C. The condensed monolayers of PDA, PDDA, and PTDA could be transferred successively on to solid supports such as quartz slides, giving the Y-type uniform polymer LB films. The successive uniform depositions of PDDA monolayer up to 320 layers were confirmed by a relationship between the absorbance at around 200 nm due to carbonyl group and the number of layers deposited. The thickness of PDDA monolayer in the LB film was 1.72nm which agrees with the length of the dodecylamide substituent. F-A isotherms, FTIR, and X-ray diffraction measurements support that the polymer main chains are laid horizontally on the water surface and the alkyl substituents are oriented perpendicular to the chain in the condensed monolayer (see Scheme 1).     

Preparation, characterization and taste sensing properties of Langmuir-Blodgett Films from mixtures of polyaniline and a ruthenium complex

Langmuir-Blodgett (LB) films from a ruthenium complex, mer-[RuCl₃(dppb)(py)] (dppb=PPh₂(CH₂)₄PPh₂; py=pyridine) (Rupy), and from mixtures with varied amounts of polyaniline (PANi) were fabricated. Molecular-level interactions between the two components are investigated by surface potential, dc conductivity and Raman spectroscopy measurements, particularly for the mixed film with 10% of Rupy. For the latter, the better miscibility led to an interaction with Rupy inducing a decrease in the conducting state of PANi, as observed in the Raman spectra and conductivity measurement. The interaction causes the final film properties to depend on the concentration of Rupy, and this was exploited to produce a sensor array made up of sensing units consisting of 11-layer LB films from pure PANi, pure Rupy and mixtures with 10 and 30% of Rupy. It is shown that the combination of only four non-specific sensing units allows one to distinguish the basic tastes detected by biological systems, viz. saltiness, sweetness, sourness and bitterness, at the μM level.     

8-氨基喹啉两亲配体的光谱性质、Langmuir-Blodgett膜及其对铜离子的传感作用

研究了两亲配体2-十二烷基丙二酸二(8-氨基喹啉)酰胺(H2A)的UV-Vis光谱和荧光光谱。铜离子对配体的荧光有明显的猝灭作用。研究了H2A及其与铜的两类配合物的单分子成膜性能和LB膜的俄歇电子能谱。CuA的成膜性能明显比H2A好,俄歇电子能谱表明H2A单分子膜在膜/水界面与亚相Cu2+生成了1∶1的配合物。H2A的LB膜可以用作为Cu2+离子的传感材料,线性范围为0.1～1.0μmol/L。     

Studies on the release of polymeric Langmuir-Blodgett multilayers from the solid supports on which they were prepared

It has been shown that polymeric Langmuir-Blodgett (LB) multilayers may be released from the supports on which they were prepared by first thermally evaporating thin films of stearic acid onto the support. The acid can subsequently be washed away, so undercutting the film and releasing it to float to the water surface. The films were redeposited onto fresh silicon wafers or onto glass microscope slides. Under the optical microscope, the films on the glass microscope slides were clear and featureless. By XRD the transferred films had the same or fewer orders of Bragg peaks and the corresponding bilayer spacings were the same or slightly larger than those of the original films. Thus, it appears that most films lose a small amount of their order in the transfer process. By second harmonic generation (SHG) the transferred alternating LB films formed from a poly(4-vinylpyridine) partially quaternised by reaction with n-docosyl bromide and from the poly(4-vinylpyridinium bromide) formed by the zwitterionic polymerisation of 4-vinylpyridine with 4(12-bromododecyloxy)-4′-trifluoromethylazobenzene displayed essentially the same SHG properties as the original films. Moreover, the SHG films could be stacked successfully to give thicker films. Several of the transferred films, but not all, contained traces of stearic acid, which appears to be present as small domains of Y-type layers. In one typical case, where the LB film consisted of 100 layers of a poly(4-vinylpyridine), it was shown that the amount of stearic acid present corresponded to an average of one monolayer.     

Langmuir and Langmuir-Blodgett Films of Polyfluorenes and Their Use in Polymer Light-Emitting Diodes

The Langmuir and Langmuir-Blodgett (LB) film properties of two polyfluorene derivatives, namely poly(2,7-9,9′-dihexylfluorene-dyil) (PDHF) and poly(9,9 dihexylfluorene-dyil-vynilene-alt-1,4-phenylene-vyninele) (PDHF-PV), are reported. Surface pressure (П-A) and surface potential (ΔV-A) isotherms indicated that PDHF-PV forms true monolayers at the air/water interface, but PDHF does not. LB films could be transferred onto various types of substrate for both PDHF and PDHF-PV. Only the LB films from PDHF-PV could withstand deposition of a layer of evaporated metal to form a light-emitting diode (PLED), which had typical rectifying characteristics and emitted blue light. It is inferred that the ability of the polymer to form true monomolecular layers at the air/water interface seems to be associated with the viability of the LB films in PLEDs.     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Interfacial Chemistry of Langmuir-Blodgett Deposited Polyimide Films on Si (100)

Using the Langmuir-Blodgett (LB) technique, ultrathin films of the octadecylammonium salt of polyamic acid (PACS) on (100) oriented silicon wafers with one, three and five monolayers were prepared. The imidization of the films was investigated with x-ray photoelectron spectroscopy (XPS) during a stepwise heating procedure in vacuum. Significant differences in the XPS spectra indicate an incomplete polymerization of the films as a function of film thickness. It is believed that the chemical interaction at the interface between Si substrate and PACS is responsible for the incomplete polymerization of the LB film in direct contact with the substrate. From ellipsometric measurements the absolute thickness of a PACS and a polyimide layer has been determined to be 1.7 nm and 0.6nm, respectively. These measurements allow us to determine the electron mean free path for the Si2p electrons (E_k=1153 eV) of λ = 4.2±0.1 nm through these films.     

Temperature dependence of photoinduced birefringence in mixed Langmuir-Blodgett (LB) films of azobenzene-containing polymers

The temperature dependence of photoinduced birefringence was investigated for mixed Langmuir-Blodgett (LB) films from the homopolymer poly[4′-[[2-(methacryloyloxy)ethyl]ethyl-amino]-2-chloro-4-nitroazobenzene] (HPDR13) and cadmium stearate (CdSt) and from the copolymer 4-[N-ethyl-N-(2-hydroxyethyl)]amino-2′-chloro-4′-nitroazobenzene (MMA-DR13) and CdSt. Birefringence was achieved by impinging a linearly polarized light on the LB films. The maximum birefringence achieved decreased with temperature as thermal relaxation of the chromophores was facilitated. The buildup curves for birefringence were fitted with biexponential functions representing distinctly different mechanisms with time constants. The first, fast process is thermally activated and may be represented by an Arrhenius process. The decay of birefringence after switching off the laser source was described by a Kohlraush-Williams-Watts (KWW) function, consistent with a distribution of relaxation times for the polymer system. Activation energies were obtained from Arrhenius plots of the rate constant of the exponential functions and KWW function, which showed that the buildup of birefringence was very similar for the two polymer systems. The decay, however, was slower for the LB film from MMA-DR13/CdSt.     

Electrochemical properties of carbon nanotubes-hydrogenase conjugates Langmuir-Blodgett films

We report the preparation of Langmuir-Blodgett (LB) films composed of oxidized carbon nanotubes (CNTs) and hydrogenase (H₂ase) conjugates and their electrochemical properties. Both single-walled (SWNTs) and multi-walled CNTs (MWNTs) were used to form mixed monolayers with H₂ase on the Tris-HCl subphase surfaces. By using the LB method, the CNTs-H₂ase monolayers were transferred onto CaF₂ and indium tin oxide (ITO) electrode surfaces. The LB film modified electrodes showed a couple of waves centered at around −500 mV (versus Ag/AgCl), which corresponding to the redox reaction of [4Fe-4S]^2+/1+ clusters in the H₂ase. The current intensity was enhanced after co-assembly with CNTs. Because of the different diameters of CNTs, this current intensity was proportional to the scan rate (υ) for the electrodes modified with the LB films of pure H₂ase and SWNTs-H₂ase, but to the root of scan rate (υ^1/2) for those modified with the MWNTs-H₂ase LB film. The products of diffusion coefficient and concentration (D^1/2C) increased in the order of pure H₂ase, SWNTs-H₂ase, and MWNTs-H₂ase LB films.     

Electronic transfer through Langmuir-Blodgett layers of capped platinum nanoparticles: An electrochemical approach

Amine functionalized platinum nanoparticles have been modified by over-grafting two different molecules, 2-thiophenecarbonyl chloride (Pt-1) and 1-hexyl-4-(4-isothiocyanatophenyl)-bicyclo (2, 2, 2) octane (Pt-2). Cyclic voltammetry was performed at gold electrodes coated with Langmuir-Blodgett (LB) mixed films of Pt-1 and Pt-2 nanoparticles, and behenic acid. From five layers the electrochemical response was essentially provided by the last LB component. The electrochemical responses towards the [Fe(CN)₆]^3−/4− couple were strongly influenced by the nature of the over-grafted molecules: films of Pt-2 presented an almost complete blocking effect, while films of Pt-1 allowed the redox reaction to occur on Pt nanoparticles. In order to understand the reasons for such different behaviors we built up hetero-nanostructures by superposing Pt-1 and Pt-2 LB layers in different ways, yielding different kinds of “sandwich” structures. The electrochemical response depended on the electrode ending. When Pt-1 nanoparticles were in the outer layer, in contact with the electrolyte solution, the electrode was electroactive toward the redox probe, while when Pt-2 layers were in the outer layer no electroactivity was detected. For sandwiches made of Pt-1, with a variable thickness of an intercalated film of Pt-2, the electrode response to [Fe(CN)₆]^3−/4− was modulated by the thickness of the inter-layer: the thicker the layer, the lower the response.     

热塑性聚合物的反应挤出与双螺杆挤出机

介绍了热塑性聚合物的反应挤出的基本原理、反应类型及应用和相关的反应挤出设备。     

DNA Langmuir-Blodgett modified glassy carbon electrode as voltammetric sensor for determinate of methotrexate

A highly sensitive electrochemical biosensor for the detection of trace amounts of methotrexate has been designed. Double stranded (ds)DNA molecules are immobilized onto a pretreated glassy carbon electrode (GCE(ox)) surface with Langmuir-Blodgett (LB) technique. The adsorptive voltammetric behaviors of methotrexate on DNA-modified electrode were explored by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The oxidation mechanism was proposed and discussed in this work. In addition, the optimum experimental conditions for the detection of methotrexate were explored, and the currents measured by SWV presented a good linear property as a function of the concentrations of methotrexate in the range of 2.0 × 10⁻⁸ to 4.0 × 10⁻⁶ mol L⁻¹, with an LOD of 5.0 × 10⁻⁹ mol L⁻¹. The method proposed was applied for the determination of methotrexate in pharmaceutical dosage and diluted human urine with wonderful satisfactory successfully.     

Optical Properties of Highly Birefringent Polymer Films Using Simple Techniques

ABSTRACT

Two optical systems are used for characterizing free-standing highly birefringent polymer films. The first system is the Michelson interferometer and is utilized, in the presence of a polarizer, to determine the refractive indices in the two principal vibration directions along and across the axis of the sample, and the birefringence. The second system directly determines the birefringence. It is based on measurements of the optical path difference and the light intensity before and after striking the sample. The results show that the obtained values of birefringence, by the two methods, are in good agreement with each other. Certain optical parameters related to the measured values of refractive indices and birefringence are also calculated. The used methods are recommended for investigating thick and highly birefringent materials, where the conventional methods face certain problems such as the large number of interference fringe order and the highly refractive indices of the used immersion liquids.     

Evolution of Rim Instabilities in the Dewetting of Slipping Thin Polymer Films

Using optical microscopy, we investigated the amplification of instabilities of the moving rim which formed during dewetting of slipping polymer films. At the onset, the wavelength of the rim instability grew in time and proportional to the width of the rim. At later stages, these instabilities led to finger and subsequent droplet formation. Droplet size was found to be proportional to the width of the rim at break-off of droplets, which, in turn, was proportional to the initial film thickness. Our experiments suggest that the decrease of the dewetting velocity with increasing width of the rim is the key mechanism responsible for this instability. Droplet formation provided a possibility for self adjustment of the dewetting front resulting in a constant mean self-regulated dewetting velocity. This mean velocity was significantly higher than the velocity for the corresponding stable rim.     

Silicon-containing polymer nanosheets for oxygen plasma resist application

In this paper, we prepared a silicon-containing polymer nanosheet, poly(neo-pentylmethacrylamide-co-4-(trimethylsilyl)phenyl)methacrylamide (p(nPMA/SiPhMA)), for positive-tone photoresist application. p(nPMA/SiPhMA) forms a stable monolayer at the air-water interface and the polymer monolayer can be transferred onto a solid substrate using the Langmuir-Blodgett technique, when the SiPhMA molar contents are below 38%. Sixty layers of p(nPMA/SiPhMA) nanosheet were deposited onto a silicon substrate and deep UV was irradiated through a photomask to the deposited film. After development of the irradiated film with alkaline solution, a positive-tone fine pattern with a 0.75 μm resolution, which is the highest resolution of the photomask, was clearly drawn. UV-vis and FT-IR spectroscopy indicates the formation of alkaline soluble groups, such as CO and Si-O-Si after photodecomposition. Moreover, p(nPMA/PhSiMA) polymer nanosheet shows three times higher oxygen etching resistance compared to poly(methylmethacrylate) (PMMA). The high plasma resistance of the polymer nanosheet film is caused by not only the presence of Si atom in the film but also a closely packed and high molecular orientated structure of the polymer nanosheets.     

Evolution of Rim Instabilities in the Dewetting of Slipping Thin Polymer Films

Using optical microscopy, we investigated the amplification of instabilities of the moving rim which formed during dewetting of slipping polymer films. At the onset, the wavelength of the rim instability grew in time and proportional to the width of the rim. At later stages, these instabilities led to finger and subsequent droplet formation. Droplet size was found to be proportional to the width of the rim at break-off of droplets, which, in turn, was proportional to the initial film thickness. Our experiments suggest that the decrease of the dewetting velocity with increasing width of the rim is the key mechanism responsible for this instability. Droplet formation provided a possibility for self adjustment of the dewetting front resulting in a constant mean self-regulated dewetting velocity. This mean velocity was significantly higher than the velocity for the corresponding stable rim.     

Langmuir-Blodgett film based biosensor for estimation of galactose in milk

A mono-enzyme amperometric biosensor has been developed for the estimation of galactose in milk and milk products. Galactose oxidase was immobilized with poly(3-hexyl thiophene)/stearic acid (P3HT/SA) on to indium tin-oxide (ITO) coated glass plates using Langmuir-Blodgett (LB) film deposition technique. The immobilized galactose oxidase in P3HT/SA LB films was characterized using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy. This P3HT/SA/GaO LB film on ITO-coated glass plate was used as working electrode with platinum as reference electrode for development of galactose biosensor. The biosensor shows the linearity 1-4 g/dl galactose. The effect of galactose concentration, pH, temperature, detection limit, response time and stability of the immobilized galactose oxidase in LB films were also studied. The electrode was found stable upto 45 °C and has a shelf life of more than 90 days.     

The synthesis of novel perylene-like dyes and their aggregation properties in Langmuir and Langmuir-Blodgett films

The synthesis of novel perylene-like dyes with different length and molecular structure of terminal chains substituted to the main perylene core is described. The dyes are able to form compressible and stable monolayers at the air-water interface (Langmuir films), which can be easily transferred onto solid substrates (Langmuir-Blodgett films). In the Langmuir and Langmuir-Blodgett films, the dye molecules show tendency to creation of self-aggregates, both in the ground and excited electronic states. The influence of the molecular structure of the substituents on the aggregation properties is observed and discussed.