Polymer Langmuir-Blodgett Films 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.

Titania Nanofilms from Titanium Complex-Containing Polymer Langmuir-Blodgett Films.

This paper proposes a method of fabricating low-dimensional TiO2 nanofilms at room temperature under ambient pressure conditions. The titanium-containing polymer complex Ti-p(DDA/acac) was synthesized by reacting an amphiphilic copolymer (p(DDA/acac)) with a titanium complex. Its ultrathin films were prepared using the Langmuir-Blodgett (LB) technique. The monolayer was found to be free from hydrolysis and cross-linking side reactions, even at the air-water interface. The transferred LB films (nanosheets) were oxidized by ultraviolet irradiation at room temperature. The photo-oxidized material has an amorphous and porous structure with subnanometer-scale controllability (0.18 nm per layer). Photocatalytic performance was demonstrated by converting multilayered LB films of Ti-(DDA/acac) and the silicon-containing polymer p(DDA/SQ) into ultrathin hetero-multilayers of TiO2 and SiO2 under UV-O3 treatment. The scalability affords a uniform photopattern formation of photo-oxidized TiO2 films over several hundreds of micrometers.

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.

Electro-Optic Hysteresis in Ferroelectric Polymer Langmuir–Blodgett Films

The hysteresis and kinetics of the electro-optic response of multilayer ferroelectric polymer Langmuir–Blodgett films have been investigated.

Langmuir and Langmuir–Blodgett films of low‐bandgap polymers

AbstractLow‐bandgap conjugated polymers have provided a considerable increase in organic photovoltaic efficiencies, however, an understanding of class‐specific nanostructures, necessary to further improve device qualities, remains scarce. Their self‐assembly and associated electronic behaviors in Langmuir−Blodgett (LB) films are used here to provide relationships specific to each polymer, clarifying their structure−property characteristics. The behavior of two low‐bandgap polymers based on cyclopentadithiophene (PCPDTBT) and dithienosilole (Si‐PCPDTBT) units in the Langmuir trough were investigated and it is shown that it is possible to fabricate nanostructured films of low‐bandgap polymers on solid substrates with the LB deposition technique. The polymers were mixed with amphiphilic molecules at well‐defined concentrations to improve the formation of the LB films. The polymers were also deposited by drop‐casting and LB techniques onto interdigitated electrodes to evaluate their electrical properties, and the LB films were characterized for their optical and morphological properties. It was found that both LB and drop‐cast films of PCPDTBT showed higher electrical conductivities than those of Si‐PCPDTBT. Importantly, LB films resulted in higher electrical conductivities – by an order of magnitude − compared to their equivalent mixtures with stearic acid in drop‐cast films, although drop‐cast films without stearic acid gave higher conductivities. This fine‐tuning of the molecular architectures of the films is thus demonstrated to directly affect the physical properties and may lead to an improvement in device efficiencies in future applications. © 2018 Society of Chemical Industry

Controlled Growth of Gold Nanoparticles Preorganized in Langmuir-Blodgett Monolayers.

A method is described for the in situ growth of substrate-supported organized gold nanoparticles. Upon exposure to an aqueous solution of a gold salt and a mild reducing agent, the particle size can be significantly increased without any loss of superstructure organization. Furthermore, no secondary nucleation is observed. The surface-supported regrowth procedure can be combined with the Langmuir-Blodgett technique to produce a rich library of plasmonic nanoparticle assemblies. Controlled particle regrowth plays a crucial role in this assembly method because only relatively small metallic nanoparticles can be directly dispersed in polymeric Langmuir-Blodgett films. The versatility of the method is demonstrated through the fabrication of several specific nanoparticle structures, including contiguous plasmonic rings, core-satellite structures, and necklace assemblies. Plasmon extinction spectra are presented for the various nanoparticle superstructures and illustrate the importance of controlling both particle size and assembly architecture in achieving targeted optical properties. The reported approach constitutes a viable bottom-up assembly route for the fabrication of surface-supported nanoparticle superstructures for plasmonic applications.

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.

Self-polarization in ultrathin Langmuir–Blodgett polymer films

Ultrathin copolymer films of vinylidene fluoride and trifluoroethylene were deposited on Al-coated polyimide substrates, by the Langmuir–Blodgett method. A top Al electrode was evaporated onto the polymer film, to form an Al/polymer/Al structured infrared detector. The pyroelectric voltage response of the detector under various polarizing processes was characterized. The detector with only one transferred polymer layer exhibited a preferential polarization direction. This was considered to result from the self-polarization of the ultrathin polymer film. It was due to the preferred alignment of the dipoles on the Al substrates. This process can be applied for designing stable fast-response infrared detectors.

Polarization switching kinetics in ultrathin ferroelectric barium titanate film

The investigation of polarization switching kinetics in an ultrathin barium titanate film reveals true threshold switching at a large coercive electric field, evidence that switching is of intrinsic thermodynamic nature, rather than of extrinsic nature initiated by thermal nucleation, which has no true threshold field. The switching speed of a 7nm thick epitaxial film exhibits a critical slowing as the threshold is approached from above, a key characteristic of intrinsic switching. In contrast, a bulk crystal exhibits nucleation-initiated switching, which has no threshold, and proceeds even at fields well below the nominal coercive field, which was determined independently from the polarization-electric field hysteresis loop. Previously, this phenomenon was only reported for ultrathin ferroelectric polymer Langmuir–Blodgett films. Since both the thermodynamic coercive field and the intrinsic switching kinetics are derived from the mean field theory of ferroelectricity, we expect that these phenomena will be found in other ferroelectric films at the nanoscale.

QDs Supported on Langmuir-Blodgett Films of Polymers and Gemini Surfactant

Different LB films of poly(octadecene-co-maleic anhydride), PMAO, poly(styrene-co-maleic anhydride) partial 2 butoxy ethyl ester cumene terminated, PS-MA-BEE, and Gemini surfactant ethyl-bis(dimethyl octadecylammonium bromide), 18-2-18, have been used to study the effect of the substrate coating on the surface self-assembly of CdSe quantum dots (QDs). Results show that all the “coating molecules” avoid the 3D aggregation of QDs observed when these nanoparticles are directly deposited on mica. Different morphologies were observed depending on the molecules used as coatings, and this was related to the surface properties, such as wetting ability, and the morphology of the coating LB films.

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.

Ferroelectricity of ultrathin ferroelectric Langmuir–Blodgett polymer films on conductive LaNiO3 electrodes

LaNiO3 (LNO) films with a surface roughness rms of 0.384nm and a sheet resistance of about 200Ω were prepared on SrTiO3 and Si/SiO2 substrates respectively by rf magnetron sputtering technique. The surface of LNO on Si/SiO2 substrate is smoother than that on SrTiO3 substrate. A nominal 2-monolayer (ML) poly(vinylidenefluoride-trifluoroethylene) film with a thickness of about 3nm was deposited on LNO coated Si/SiO2 substrate by Langmuir–Blodgett (LB) technology. Piezoresponse force microscopy (PFM) measurements show that the LB films demonstrate an obvious feature of polarization switching and good voltage durability. The results suggest that the ultrathin polymer films may be utilized to explore ferroelectric tunnel junctions.

Self-organized dendritic patterns in the polymer Langmuir–Blodgett film

We report the formation of a self-organized dendritic pattern of nanometer thickness in polymer Langmuir–Blodgett (LB) films. Poly(N-dodecylacrylamide) (pDDA)/chloroform solution was spread on a water surface to form a stable polymer monolayer. A pDDA monolayer was deposited onto a hydrophilic silicon substrate by upward deposition from a water subphase, and a second layer was then deposited by downward deposition. The substrate with the two layers was withdrawn from a clean water surface at a high speed to form the dendritic pattern, which was imaged by atomic force microscopy. The height of the pattern, 3.5nm, corresponds to the height of a bilayer pDDA LB film, suggesting that the pattern forms when the deposited outermost layer overturns by meniscus oscillation. A similar dendritic structure of narrower width and lower height was fabricated on a hydrophobic silicon substrate.

Ferroelectric field effect transistors using very thin ferroelectric polyvinylidene fluoride copolymer films as gate dielectrics

We report electrical characterization of memory elements consisting of a p-type silicon field-effect transistor incorporating a ferroelectric polymer Langmuir–Blodgett film into the gate insulator to produce bistability through polarization hysteresis. The thin gate insulator, consisting of a 10 nm thick silicon oxide layer and a 35 nm thick ferroelectric polymer film, enabled bistable operation at 4 V. Device hysteresis as a function of gate voltage was evident both in the device capacitance, which was measured between the gate and drain, and in the source-drain conductance. The ferroelectric film polarization was not saturated, even up to operating voltages of 10 V. This is likely the reason for the short state retention of less than 10 s at room temperature. The hysteresis vanished as the sample was heated toward the ferroelectric-paraelectric phase transition temperature, showing that the bistability was due to ferroelectric polarization reversal.

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.

Glass transition of Langmuir-Blodgett polymer films

The dielectric dispersion of vinylidene fluoride-trifluoroethylene copolymer P(VDF/TrFE) (70/30) films obtained by the Langmuir-Blodgett technique was investigated in the low-temperature range from 20 to −100°C. The thickness of the explored films was 40 nm. A glass-transition range from −25 to −40°C was detected; this indicates the presence of an amorphous phase in the LB films.

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.