Polymer Langmuir-Blodgett Research Articles

PH-Responsive Ultrathin Nanoporous SiO2 Films for Selective Ion Permeation.

Ultrathin nanoporous (NP) films are an emerging field for selective and effective ion/molecular separation and electrochemical sensing applications. We describe selective ion permeation in surface-functionalized ultrathin NP SiO2 films (NP SiO2-NH2). The ultrathin NP SiO2 films with ca. 8 nm thickness were prepared from silsesquioxane-containing blend polymer Langmuir-Blodgett films (nanosheets) using the photo-oxidation method. The porous SiO2 surface was modified with a pH-responsive amine-containing silane coupling agent. Selective ion permeation was demonstrated under acidic pH conditions (pH ≤ 6) using two equally sized redox probes: negative (Fe(CN)63-/4-) and positive (Ru(NH3)62+/3+) ions. The current density for Fe(CN)63-/4- decreased as the pH value increased to pH = 6, whereas it increased for Ru(NH3)62+/3+. Control measurements revealed that the probes can penetrate the pores of nonfunctionalized SiO2 films irrespective of pH values, indicating that both the size and the surface charge response contributed to selective ion permeation. Results obtained from this study pave the way for new applications in molecular separation and sensing applications based on ultrathin nanoporous films (<10 nm) and tailored surfaces.

Improvement of sensing properties for polymer based gas sensors via host–guest principles

This study aimed at improving the sensing properties of polymer-based gas sensors by controlling the surface adsorption. For this purpose, a polymer was produced as a Langmuir–Blodgett (LB) thin film chemical gas sensor element. The polymer material used was characterized by FTIR, 1H and 13C NMR analyses. All LB thin film layers were characterized by UV–Vis spectroscopy, scanning electron microscopy (SEM), quartz crystal microbalance (QCM) and atomic force microscopy (AFM) techniques. The polymeric chemical sensor was exposed to four different harmful organic vapours using QCM. The diffusion coefficients were calculated for each organic vapour using the short time approximation of the Fick’s second diffusion law. The results showed that the response of the polymeric LB films to the harmful vapours was large, fast and reversible and the diffusion coefficients were found to increase in the order dichloromethane, chloroform, benzene and toluene at room temperature.

Chirality Transfer and Modulation in LB Films Derived From the Diacetylene/Melamine Hydrogen-Bonded Complex.

Introduction of hydrogen-bonding interaction into π-conjugated systems is a promising strategy, since the highly selective and directional hydrogen-bonding can increase the binding strength, provide enhanced stability to the assemblies, and position the π-conjugated molecules in a desired arrangement. The helical packing of the rigid melamine cores seems to play a dominating role in the subsequent formation of the peripheral helical PDA backbone. The polymerized Langmuir-Blodgett (LB) films exhibited reversible colorimetric and chiroptical changes during repeated heating-cooling cycles, which should be ascribed to the strong hydrogen-bonding interaction between the carboxylic acid and the melamine core. Further, the closely helical packing of the melamine cores could be destroyed upon exposure to HCl or NH(3) gas, whereas the peripheral helical polyaniline and polydiacetylene (PDA) backbone exhibited excellent stability. Although similar absorption changes could be observed for the films upon exposure to HCl or NH(3) gas, their distinct circular dichroism (CD) responses enabled us to distinguish the above two stimuli.

Fabrication of ultrathin films containing the metal organic framework Fe-MIL-88B-NH 2 by the Langmuir–Blodgett technique

Abstract In this work, the fabrication of ultrathin films containing the metal organic framework (MOF) Fe-MIL-88B-NH 2 by the Langmuir–Blodgett (LB) technique has been explored. MOF crystals of two different sizes (1.5 ± 0.3 and 0.07 ± 0.01 μm) have been synthesized and assembled at the air–liquid interface by the LB method. The effect of the subphase pH and particle size on the film formation process has been studied. Moreover, for the first time, mixed MOF + polymer (the commercial soluble polyimide Matrimid ® ) LB films containing different MOF loadings have been fabricated. These experiments show that it is possible to obtain ultrathin MOF + polymer films with a controlled MOF density. Furthermore, MOF particles are homogeneously distributed in the polymer matrix, even with very large amounts of MOF (up to 95 wt%). LB films have been incorporated into materials of different nature, including glass and mica substrates and also polymeric membranes based on polysulfone Udel ® and PIM-1 (polymer of intrinsic microporosity), and the modification of water contact angle after LB film deposition has been analyzed.

Flexible design of free-standing hybrid polymer nanosheets through bottom-up approach.

We describe the bottom-up design of highly ordered free-standing nanofilms consisting of polymer Langmuir-Blodgett films (polymer nanosheets). Polymer nanosheets enable the incorporation of a wide variety of functional groups such as reactive components and chromophores, which serve as building blocks of free-standing nanofilms. We demonstrated a free-standing fluorescent hybrid nanofilm in which the separation between gold nanoparticles and fluorophores was tuned at the nanometer scale. Moreover, we prepared a free-standing nanofilm consisting of a two-dimensional homogeneous nickel zinc iron oxide (NiZnFe22O4) nanoparticle monolayer assembled on polymer nanosheets.

Micro-Image with Photo-Acid Generator Polymer Nano Sheet

A new application of polymer Langmuir-Blodgett (LB) films which contain a photoacid generator introduced into polymer main chain as a co-monomer to draw photo patterns as a photolithographic is described here. The chemically positive-tone resist system terpolymers p (DDMA-DNMMA-AOPTs) s used here contains N-dodecylmeth acrylamide (DDMA), 1,4-dioxaspiro [4.4] nonane-2-methylmeth acrylate and 4-(allyloxy) phenyl-4-toluenesulfonate (AOPTs), which was prepared by free radical polymerization. In the terpolymers system, the acid generated by the PAG catalyzed the ketal moiety liberates cyclopentanone and regenerating derivative of glyceryl alcohol in an exposed region during the postexposure baking process. The rending moiety is dissolved into alkaline aqueous to form a positive tone in the expose region. The decompose mechanism of [p (DDMA-DNMMA-AOPTs) s] LB films irradiated by deep UV light was investigated. The photopatterning properties were also investigated. Results showed that the resolution of patterns with p (DDMA-DNMMA-AOPTs) s b LB films with 40 layers were 0.75μm which is the limit resolution of the photo-mask employed in the experiment. The effect of photogenerated acid from the photo-acid generator after irradiated by deep UV light on a typical chemically amplified resist system was studied by thermogravimetric analysis, which showed that the existence of the photoacid generator of AOPTs in terpolymer can improve the sensitivity of ketal-protected polymers without decreasing resolution.

Characterization of polymeric LB thin films for sensor applications

AbstractThe Quartz Crystal Microbalance (QCM) system is utilized to investigate the relationship between mass uptake and associated swelling for Langmuir‐Blodgett (LB) organic thin films obtained from pyrene end‐capped polystyrene (PS). The study was carried out using three different molecular weights of polymeric chains. The changes in resonance frequency associated with mass changes can be attributed to the swelling behavior of polymeric thin films during vapor absorption. This swelling is due to the capturing of organic vapor molecules in the sensor environment. To quantify real‐time QCM data for swelling, early‐time Fick's law of diffusion was adopted to fit the results, and a good linear relationship was observed between the mass uptake and square root of the swelling time. The diffusion coefficients for swelling were thus obtained from the slopes of the fitting curves and was found to be correlation with the amount of organic vapor content in the cell. It was also observed that diffusion of the organic vapor into higher molecular weight polystyrene thin films are much faster than low molecular weight ones in sensor applications. Diffusion coefficients were found to be 0.2–3.0 × 10−16, 5.0–13 × 10−16, and 1.0–1.6 × 10−15 cm2/s for PS1, PS2, and PS3 LB thin films, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Solid State Electrochemical Transistor Based on π-Conjugated Polymer Langmuir–Blodgett Film

A solid-state electrochemical transistor (ECT) was fabricated using a π-conjugated polymer Langmuir–Blodgett (LB) film, which was constructed from poly(N-dodecylacrylamide) (pDDA) and regioregular-poly(3-hexylthiophene) (RR-PHT) mixture. The π-conjugated polymer LB film was used as a channel layer and poly(ethylene oxide):LiClO4 was used as a solid electrolyte. The ECT showed an on/off ratio of 2.3 ×103 and a mobility of 7.7 ×10-2 cm2 V-1 s-1 at a low gate voltage (VG = -2.0 V) with a low charge consumption (1.8 ×10-9 mol of e-1 cm-2). Moreover, a clear saturation behavior was observed in the ECT. The saturation behavior was derived from the partial dedoping of RR-PHT located at the drain electrode because of the long channel length and low conductivity of the LB film. The low operation voltage with a clear saturation behavior is favorable for applying the ECT to the fabrication of a disposable sensor.

Polarization switching kinetics of ferroelectric nanostructures of vinylidene fluoride-trifluoroethylene copolymer

The polarization switching kinetics of ferroelectric polymer Langmuir-Blodgett films and copolymer nanocrystals (nanomesas) was investigated using piezoresponse force microscopy. The nanocrystals were prepared by self-organization from Langmuir-Blodgett films of a 70% vinylidene fluoride and 30% trifluoroethylene copolymer. The polarization switching time exhibits an exponential dependence on reciprocal voltage and decreases with temperature being consistent with the nucleation switching dynamics.

Flow behavior in surface-modified microchannels with polymer nanosheets

The paper describes water flow behavior in surface-modified microchannels. We prepared straight-type microchannels which had rectangular cross sections with four different combinations of microchannel surface wettability; cleaned glass substrates served as hydrophilic microchannel walls and the microchannel walls coated with polymer Langmuir–Blodgett (LB) films were used as hydrophobic surfaces. The polymer LB films were successfully transferred onto glass substrates by vertical dipping method. The flow rates and the water meniscus shape strongly depended on the microchannel surface wettability. The decrease in flow rate with the increasing number of hydrophobic (polymer LB film) surface was attributed to the higher adhesion energy of hydrophobic surface. The Reynolds number was also characterized to be in the order of 10 − 1 , implying a specific feature of microchannel; laminar flow.

Palladium-mediated construction of chiral coordination polymers of binaphthyl-bis(amidopyridyl) ligands at the air–water interface

Molecular assemblies and nanoparticles of chiral coordination polymers composed of connector of K 2PdCl 4 and linkers of bisdentate binaphthyl-bis(amidopyridyl) (BNBAPy) ligands have been constructed at the air–water interface. The chiral S- and R-BNBAPy ligands showed similar surface pressure–area isotherms on the K 2PdCl 4 subphase surface, with the limited molecular area of about 1.2 nm 2, which suggested that the ligands were nearly parallel to the subphase surface. The X-ray photoelectron spectra for the Langmuir–Blodgett (LB) films of the coordination polymers revealed that the films were composed of Cl, C, Pd and N elements. These Pd-(R-/S-)BNBAPy coordination polymers formed round nanoparticles at the interface with average diameters of 15–20 nm. It was found that the chirarity of ligands was almost remained in the LB films of Pd-(R-/S-)BNBAPy coordination polymers, indicating there was little influence on the orientation or arrangement of the ligand chiral center after the formation of their coordination polymer LB films. The present method could provide a facile way to construct chiral molecular and nanostructural materials.

Preparation of Ultrathin Silsesquioxane Nanofilms via Polymer Langmuir−Blodgett Films

This Article describes a unique approach to building silsesquioxane nanoassemblies based on the Langmuir−Blodgett (LB) technique. Poly(N-dodecylacrylamide-co-3-methacryloxypropyl-T8-heptatrifluoropropyl (or heptaphenylpropyl) POSS)s (p(DDA/SQ)s) were synthesized through free radical copolymerization using propyl methacrylate-substituted polyhedral oligomeric silsesquioxane (POSS) monomers containing seven nonreactive trifluoropropyl or phenyl groups (R7(Si8O12)(CH2CH2CH2OCOCH3C═CH2) (where R is either trifluoropropyl (SQF) or phenyl (SQPh)) and amphiphilic copolymers. The p(DDA/SQ)s formed stable monolayers at the air/water interface. The monolayers were transferred onto solid substrates as Y-type LB films using a vertical dipping method. The polymer LB films had a well-defined layer structure and a surface flatness (rms values < 1 nm in 1 μm2). The high heat-resistant properties of the p(DDA/SQ) LB films were demonstrated using UV−vis spectroscopic reflectometry and FT-IR. The refractive index and the th...

Photopatterning of heterostructured polymer Langmuir–Blodgett films

Heterostructured polymer Langmuir–Blodgett (LB) film prepared by using poly( N-dodecylacrylamide -co- t-butyl 4-vinylphenyl carbonate) ( p(DDA- tBVPC53)) and poly( N-neopentyl methacrylamide- co-9-anthrylmethyl methacrylate) ( p(nPMA-AMMA10)) polymer LB films which can act as photogenerator layers were investigated. Patterns with a resolution of 0.75 μm were obtained on heterostructured polymer LB films composed of 4 layers of p(nPMA-AMMA10) LB film (top layers) and 40 layers of p(DDA- tBVPC53) LB film (under layers) on a silicon wafer by deep UV irradiation followed by development with 1% tetramethylammonium hydroxide aqueous solution. The sensitivity of the heterostructured polymer LB films was improved without loss of the resolution compared with p(DDA- tBVPC53) LB film. The etch resistance of the heterostructured polymer LB films was sufficiently good to allow patterning of a copper film suitable for photomask fabrication.

Hybrid Polymer Nanoassemblies Consisting of Polymer Nanosheets and Metal Nanoparticle Arrays

The article describes hybrid polymer nanoassemblies consisting of polymer nanosheets and metal nanoparticle arrays. Ultrathin polymer Langmuir-Blodgett films were utilized to assemble metal nanoparticles, to make free-standing hybrid polymer nanosheets, to examine the possibility of hybrid polymer nanoassemblies as luminescence sensor application, and to orient nonlinear optical (NLO) active molecules. Assembling nanomaterials such as nanoparticle and organic functional molecules through bottom-up approach make it possible to strengthen free-standing nanofilm stability, enhance luminescence from luminescent molecules and second harmonic light from NLO molecules under the influence of localized surface plasmon.

Fabrication of Electrochemical Transistor Based on π−Conjugate Polymer Langmuir−Blodgett Film

We fabricated an efficient organic electrochemical transistor (OECT) composed of polymer Langmuir-Blodgett (LB) film. The pi-conjugated polymer LB film, which was constructed from a poly(N-dodecylacrylamide) (pDDA) and poly(3-hexylthiophene) (PHT) mixture, was used as a conduction channel layer to connect source and drain electrodes. The mixed-polymer LB film was characterized using UV-vis spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), and cyclic voltammetry. Subsequent UV spectra measurements, XRD measurements, and AFM measurements show that PHT forms a crystalline lamellar domain in the layered structure of pDDA. The OECT included 10 layers of the mixed-polymer LB film as the conduction channel layer. The OECT showed an on/off ratio of 1.1x10(4) and mobility of 7.5x10(-2) cm2 V(-1) s(-1) at low gate (VG=-1.2 V) and source-drain voltages (VDS=-0.5 V). Moreover, the necessary charge to operate the OECT was 1.1x10(-9) mol of e(-1) cm(-2), which was 2 orders smaller than the value reported using a similar device structure. The relatively high on/off ratio and low charge consumption suggest that this OECT, which is fabricated from pi-conjugated polymer LB films, is applicable to macroelectronic devices.

Hybrid Polymer Nanoassemblies: Polymer Nanosheets Organized with Metal Nanoparticle Arrays for Surface Plasmon Photonics

The paper describes fabrication of hybrid polymer nanoassemblies possessing polymer nanosheets and metal nanoparticle arrays. Based on a bottom-up approach with ultrathin polymer Langmuir-Blodgett films (polymer nanosheets) and metal nanoparticles, we constructed hybrid nanoassemblies for opto/electric nanodevice applications: nanoscale positioning of metal nanoparticles, free-standing hybrid polymer nanosheets, hybrid polymer nanoassemblies for luminescence sensor application, and enhancement of nonlinear optical (NLO) efficiency via surface plasmon coupling. Assembling nanomaterials such as nanoparticles and organic functional molecules through a bottom-up approach makes it possible to strengthen free-standing nanofilm stability, enhance luminescence of luminescent molecules, and enhance second harmonic light from NLO molecules under the influence of localized surface plasmons. The high potential of hybrid polymer nanoassemblies for precise nanoscale design is also demonstrated.

PEDOT multilayer LB films and their gas sensitivity based on quartz crystal microbalance

Multilayer ultrathin films of poly(3,4-ethylenedioxythiophene) (PEDOT)/stearic acid (SA) were fabricated using a modified Langmuir–Blodgett (LB) technique. The formation of LB ultrathin film was confirmed by UV–vis–NIR absorption spectrum and X-ray photoelectron spectroscopy (XPS) technique. The morphology of multilayer PEDOT/SA LB film was characterized by scanning electron microscopy (SEM). The results showed that small PEDOT grains were distributed in the polymeric LB film. The electrical conductivity of 40 layers as-prepared composite LB film was about 0.52 S cm −1, and conductivity varied from 10 to ca. 10 −4 S cm −1 after the films were treated by HCl and NH 3 gas alternately. The interaction or response of film coated QCM to NH 3 has been investigated, which indicates that the QCM coated with composite film has fast response and recovery time to 10 ppm NH 3 with good reversibility and recovery performance. At identical analyte concentration QCM sensitivity was enhanced with the increasing layer of LB film less than 80 layers, and the decrease of QCM sensitivity was observed in the case of layer number over 80 layers.

Nanoscale polarization manipulation and imaging of ferroelectric Langmuir-Blodgett polymer films

Piezoresponse force microscopy has been used to manipulate and image polarization of ferroelectric polymer Langmuir-Blodgett films at the nanoscale, achieving polarization control with a resolution below 50nm and imaging resolution below 5nm. Individual regions showed square polarization-voltage hysteresis loops, demonstrating bistability of the polarization state. Arbitrary polarization patterns could be repeatedly written and erased with a resolution of 25to50nm, limited by grain size, demonstrating the potential for high-density data storage and retrieval at densities exceeding 250Gbits∕in2.

Spectroscopic Characterization and Langmuir−Blodgett Films of a Novel Azopolymer Material

Spectroscopic characterization and fabrication of Langmuir and Langmuir-Blodgett (LB) films of an azopolymer-pyridine (PAzPy) are reported. UV-visible absorption and fluorescence spectra, Fourier transform infrared (FTIR) spectra, and Raman spectra were recorded. The vibrational assignment of the observed spectra is supported by a complete geometry optimization, followed by vibrational frequency and intensity computations of both the trans and cis forms of the monomer (AzPy) using density functional theory at the B3LYP 6-31G(d,p) level of theory. Langmuir monolayers of the polymer (PAzPy) were formed at the water-air interface, and LB films of high quality were formed onto solid substrates. The polymer LB films were investigated by surface-enhanced Raman scattering.

Functional Organized Molecular Assemblies Based on Polymer Nano-sheets

This review describes recent topics on functional organized molecular assemblies based on “polymer nano-sheet”. Polymer nano-sheets consisting of amphiphilic poly(alkylacrylamide)s are described as ultrathin polymer Langmuir-Blodgett films through two-dimensional hydrogen networks between polymer backbones, which have been developed to assemble various functional molecules and nanomaterials such as metal and magnetic nanoparticles. Surface modification and nanocoating using fluorinated polymer nano-sheets in confined area are given. Multicolored patterns based on structured color and photopatterning derived from nanostructures are demonstrated. The scope of polymer nano-sheets concerning the bottom-up soft nanodevice is also reviewed.