Langmuir and Langmuir-Blodgett (LB) films of poly[(2-methoxy,5-n-octadecyl)-p-phenylenevinylene] (OC1OC18-PPV)

A PPV derivative, poly(2-methoxy,5-(n-octadecyl)-p-phenylenevinylene) (OC₁OC₁₈-PPV), has been synthesized via the Gilch route and used to fabricate Langmuir and Langmuir-Blodgett (LB) films. True monomolecular films were formed at the air/water interface, which were successfully transferred onto different types of substrate. Using UV-visible absorption, FTIR, fluorescence and Raman scattering spectroscopies we observed that the polymer molecules were randomly distributed in the LB film, with no detectable anisotropy. This is in contrast to the anisotropic LB films of a previously reported PPV derivative, poly(2-methoxy-5-n-hexyloxy)-p-phenylenevinylene (OC₁OC₆-PPV), which is surprising because the longer chain of OC₁OC₁₈-PPV investigated here was expected to lead to more ordered films. As a consequence of the lack of order, LB films of OC₁OC₁₈-PPV exhibit lower photoconductivity and require higher operating voltage in a polymer light-emitting diode (PLED) in comparison with LB films of OC₁OC₆-PPV. This result confirms the importance of molecular organization in the LB film to obtain efficient PLEDs.     

X-ray diffraction study of the structure of thin polyfluorene films

The molecular arrangement in thin films of poly(9,9-dioctylfluorene) and poly(9,9-dihexylfluorene) deposited on silicon substrates has been investigated with grazing incidence X-ray diffraction. In particular, the effect of the interface on the molecular orientation is highlighted. Both materials display a periodicity normal to the surface arising from stacked sheets of fluorene chains in both the crystalline and liquid crystalline phases. For the crystalline phase, a periodicity in the plane of the surface of 4.15 Å is observed corresponding to half the fluorene ring repeat distance along the backbone, consistent with interdigitating side-chains. For crystalline films deposited onto rubbed polyimide films, strong orientation effects are observed. In the liquid-crystalline phase, this strong in-plane ordering of backbones is lost. Poly(9,9-dihexylfluorene) exhibits an additional degree of ordering in the plane of the interface, which is likely to arise from hexagonal ordering of the backbone chains.     

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.     

Strategy for self-assembly of the poly(9,9-dihexylfluorene) to microspheres: optimizing the self-assembling conditions

Self-assembly of π-conjugated polymers upon slow precipitation was comprehensively studied by suffusion of a vapor of non-solvents into polymer solutions. However, it was reported that only copolymers with steric hindrance in their backbone tended to form ordered spheres, while homopolymers having a single monomer component were hard to form ordered microstructure. This article presented here a strategy for the self-assembly of microspheres of a π-conjugated polymer having a single monomer component, e.g., poly(9,9-dihexylfluorene) (PDHF). The microspheres of PDHF were fabricated in the methanol vapor by the non-solvent vapor method. To obtain the optimized assembling parameters, the effect of self-assembling conditions including polymer concentration, the injection volume, the types of the non-solvent vapor, and solvent on the microstructural formation of PDHF were well investigated. The experimental results indicated that the increase of polymer concentration and injection volume led to the increase of partial aggregate of the spheres. Besides, the relatively uniform microsphere could be easily obtained with the concentration ranged from 2.5 to 5.0 mg/mL, and the injection volume of 5.0 μL in the methanol vapor. Furthermore, the polar solvent was advantageous to form well-ordered microspheres in the methanol vapor.     

Reaction and characterization of crosslinking hyperbranched poly(amine-ester) with succine anhydride

Basing on hydroxyl terminated hyperbranched poly(amine-ester)s (HPAEs), the cross-linking reactions and preparation of ester-crosslinked HPAE films were investigated using succine anhydride (SA) as crosslink reagent. It was proved that the cross-linking reaction between HPAE and SA followed a two-step mechanism. This mechanism provides an efficient route to prepare HPAE/SA cross-linked films, in which, the precursor films were prepared by casting HPAE/SA solution at a lower temperature, and then curing the films at a higher temperature. By varying SA content, the solid HPAE/SA films with different cross-linking degrees were prepared successfully. The highest tensile strength of the cross-linked film could reach 59.60 MPa. With all water contact angle smaller than 74.3°, the crosslinked films demonstrated good hydrophilic properties. __________ Translated from Journal of East University of Science and Technology (Natural Science Edition), 2006, 32(10): 1,164–1,168 [译自: 华东理工大学学报 (自然科学版)]     

Preparation and electrical conductivity of Langmuir–Blodgett films of poly(3-alkylthiophene)s

Five poly(3-alkylthiophene)s (P3ATs) with different alkyl side chains were synthesized. Pure P3ATs alone are not well suited for manipulation by the Langmuir–Blodgett (LB) technique, but their mixed systems with arachidic acid can be used to prepare high-quality Y-type films with the vertical dipping method, which was proved by UV-visible spectra and small-angle X-ray diffraction patterns. Conductivities of the LB films were measured using a two-probe method at room temperature. The conductivities exhibited obvious anisotropy and could increase by 2–4 orders of magnitude after iodine vapor doping. The influence of alkyl chain length on the conductivity in the LB films was revealed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1–6, 1998     

Surface,interface and electronic properties of F8:F8BT polymeric thin films used for organic light‐emitting diode applications

Ultrathin polymeric films consisting of poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (F8) blended with poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) grown onto PEDOT:PSS/ITO/PET were investigated by X‐ray photoelectron spectroscopy (XPS), depth‐profiling XPS, reflection electron energy loss spectroscopy (REELS) and angle‐dependent X‐ray absorption spectroscopy (XAS) to gain information on the films' electronic, order and interface properties. AFM studies provide valuable information on the films' nanotopographical properties and homogeneity. Spectroscopic ellipsometry and photoluminescence spectroscopy were used also to obtain information on the optoelectronic properties. Well‐ordered films were observed from the XAS analysis, measured at the sulfur K absorption edge. XPS measurements demonstrated that the surface composition of the polymer thin films prepared by a spin‐coating wet‐chemical deposition method matches the expected F8:F8BT blend stoichiometry. The interfacial properties were studied through an argon ion sputtering process coupled to the XPS acquisition, showing an enhancement of oxygen components at the interface. The films' inhomogeneity was verified by AFM images and analysis. We obtained a value of 3.1 eV as the electronic bandgap of the F8:F8BT film from REELS data, whereas analysis of the spectroscopic ellipsometry spectra revealed that the optical bandgap of F8:F8BT has a value of 2.4 eV. A strong green emission was obtained for the produced films, which is in agreement with the expected emission due to the 1:19 ratio of the F8 and F8BT blended polymers. © 2018 Society of Chemical Industry     

Molecular structure modulated properties of azobenzene-substituted polydiacetylene LB films: Chirality formation and thermal stability

Langmuir-Blodgett (LB) films of three novel azobenzene-substituted diacetylene monomers (DA1, DA2 and DA3) were fabricated and their optical and chiroptical properties were investigated in detail by ultraviolet-visible (UV-vis) spectra and circular dichroism (CD) spectra. Achiral DA1 molecules could form chiral LB films through overcrowded packing of the azobenzene moiety, while achiral DA2 and DA3 molecules not. When exposed to left-or right-handed circular polarized UV light (CPUL), striking left- or right-handed (opposite) CD signals for azobenzene chromophores and polydiacetylene chains were observed for the polymerized DA1 (PDA1) and DA2 (PDA2) LB films. However, DA3 LB films could hardly be polymerized in this case, and only striking opposite CD signals for azobenzene chromophores could be observed. It was demonstrated that the intermolecular steric hindrance and irregular arrangement of azobenzene chromophores were not favorable for the topo-polymerization and chirality formation of polydiacetylenes backbone. Further, the effects of thermal treatment on the supramolecular chirality of above three LB films were studied. Strong collective noncovalent interactions (π-π stacking) were believed to be responsible for the thermal stability of chiral supramolecular assemblies.     

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).     

Effect of spreading solvents on Langmuir monolayers and Langmuir–Blodgett films of PS-b-P2VP

Langmuir monolayers of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers (with the same PS block length and different P2VP block lengths) formed at the air/water interface were characterized with the Langmuir film balance technique. Nonselective and selective solvents were used to spread the samples on the water surface and the spreading solvents showed large effect on the surface pressure–molecular area isotherms. The corresponding Langmuir–Blodgett (LB) films of the samples were characterized with atomic force microscopy. The LB films transferred from the Langmuir monolayers spread with a nonselective solvent only exhibited isolated circular micelles, while those with a selective solvent exhibited quite different morphologies including planar structure, rodlike structure, circular micelles, and labyrinth pattern. As far as we know, the labyrinth pattern appears in the LB films for the first time.     

Effects of subphase pH and temperature on the interfacial behavior of double hydrophilic diblock copolymer PDEGMA-b-PDIPAEMA

The aggregation behavior of two pH- and temperature-responsive diblock copolymers of poly[di-(ethylene glycol) methyl ether methacrylate]-block-poly[2-(diisopropylamino) ethyl methacrylate] (PDEGMA-b-PDIPAEMA) at the air/water interface and the structures of their Langmuir–Blodgett (LB) films were studied by the Langmuir monolayer technique and atomic force microscopy, respectively. At the air/water interface, PDEGMA-b-PDIPAEMA tends to form the core-shell-corona micellar structure composed of a PDIPAEMA main chain core, an amino ethyl ester shell, and a PDEGMA corona. Under acidic, neutral, and alkaline conditions, PDIPAEMA blocks are completely protonated, partially protonated, and completely non-protonated, respectively, and the protonated amino ethyl ester groups are immersed in water before monolayer compression, whereas PDEGMA coronas are adsorbed at the interface. At pH 3, 7, and 10, the limiting areas (A₀) for PDEGMA42%-PDIPAEMA58% (weight percents) and PDEGMA55%-PDIPAEMA45% are 8.2/10.2/14.0 and 6.7/8.3/8.4 nm², respectively. The A₀ values of the former copolymer are larger than those of the latter. This is because the shells in the former copolymer are denser due to the higher polymerization degree of PDIPAEMA blocks, providing greater steric hindrance for PDEGMA coronas and making the latter more extended at the interface. In contrast to other copolymer systems, the effect of temperature on the isotherms of PDEGMA-b-PDIPAEMA is less obvious.     

Dual-Emissive Langmuir–Blodgett Films of a 9,9-Bis(4-ethynylphenyl)fluorene Derivative of Gold(I) and Some Europium-Substituted Polyoxometalates: Preparation, Characterization and Photoelectric Properties

A new family of organometallic/inorganic composite Langmuir–Blodgett (LB) films consisting of the rigid-rod dinuclear gold(I) complex coordinated with 9,9-bis(4-ethynylphenyl)fluorene (denoted as Au-DPF) as the π-conjugated organometallic molecule coupled with some europium-substituted polyoxometalates (POM; POM = Na₉EuW₁₀O₃₆, K₁₃[Eu(SiW₁₁O₃₉)₂] and K₅[Eu(SiW₁₁O₃₉)(H₂O)₂]) as the inorganic component were prepared and characterized by π–A isotherms, UV–vis absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and surface photo-voltage spectroscopy. Luminescence spectra of the prepared hybrid LB films show that the near-white emission spectra can be obtained due to the dual-emissive nature of the mixed Au-DPF/POM blends, and POM can facilitate broad aggregate emission bands. These Au-diyne-based LB films displayed interesting electric conductivity behavior. Among them, Au-DPF/K₁₃[Eu(SiW₁₁O₃₉)₂] 13-layer film showed a good electrical response, with the tunneling current up to ±100 nA when the voltage was monitored between −1.3 and 1.8 V. The photovoltage response of Au-DPF/EuW₂₂ amounts to 1.5 μV.     

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.     

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma‐polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O₂ mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx‐deposited OPP film was decreased from 2230 to 37–52 cm³/m²/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm³/m²/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000     

Photo-reversible Reaction in Polymer Langmuir-Blodgett Films

Preparation of photoreactive Langmuir-Blodgett (LB) films was carried out using polymers/oligomers prepared from long-chain dialkyl esters of di-and tetra-olefins and having cyclobutane rings in the main chain. These polymers/oligomers formed stable monolayers on a water surface when mixed with arachidic acid. These monolayers could be deposited onto a substrate successfully forming Y-type films. The oligomer LB films were polymerized on irradiation. The polymer LB films showed a photo-reversible process between polymers and oligomers, depending on wavelength of the irradiating light. On the basis of spectral data and molecular weight change, this behaviour was found to be caused by cleavage and formation of cyclobutane rings.     

Synthesis of azopolymers with controlled structure and photoinduced birefringence in their LB films

The molecular architecture of azopolymers may be controlled via chemical synthesis and with selection of a suitable film-forming method, which is important for improving their properties for practical uses. Here we address the main challenge of combining the photoinduced birefringence features of azopolymers with the higher thermal and mechanical stabilities of poly(methyl methacrylate) (PMMA) using Atom Transfer Radical Polymerization (ATRP) to synthesize diblock- and triblock-copolymers of an azomonomer and the monomer methyl methacrylate. Langmuir-Blodgett (LB) films made with the copolymers mixed with cadmium stearate displayed essentially the same optically induced birefringence characteristics, in terms of maximum and residual birefringence and time for writing, as the mixed LB films with the homopolymer poly[4-(N-ethyl-N-(2-methacryloxyethyl))amino-2′-chloro-4′-nitroazobenzene] (HPDR13), also synthesized via ATRP. In fact, the controlled architecture of HPDR13 chains led to Langmuir films that could be more closely packed and reach higher collapse pressures than the corresponding films obtained with HPDR13-conv synthesized via conventional radicalar polymerization. This allowed LB films to be fabricated from neat HPDR13, which was not possible with HPDR13-conv. The enhanced organization in the LB films produced with controlled azopolymer chains, however, led to a smaller free volume available for isomerization of the azochromophores, thus yielding a lower photoinduced birefringence than in the HPDR13-conv films. The combination of ATRP synthesis and LB technology is then promising to obtain optical storage in films with improved thermal and mechanical processabilities, though a further degree of control must be sought to exploit film organization while maintaining the necessary free volume in the films.     

Surface modification of linear low‐density polyethylene film by amphiphilic graft copolymers based on poly(higher α‐olefin)‐graft‐poly(ethylene glycol)

In this article, a series of amphiphilic graft copolymers, namely poly(higher α‐olefin‐co‐para‐methylstyrene)‐graft‐poly(ethylene glycol), and poly(higher α‐olefin‐co‐acrylic acid)‐graft‐poly(ethylene glycol) was used as modifying agent to increase the wettability of the surface of linear low‐density polyethylene (LLDPE) film. The wettability of the surface of LLDPE film could be increased effectively by spin coating of the amphiphilic graft copolymers onto the surface of LLDPE film. The higher the content of poly(ethylene glycol) (PEG) segments, the lower the water contact angle was. The water contact angle of modified LLDPE films was reduced as low as 25°. However, the adhesion between the amphiphilic graft copolymer and LLDPE film was poor. To solve this problem, the modified LLDPE films coated by the amphiphilic graft copolymers were annealed at 110° for 12 h. During the period of annealing, heating made polymer chain move and rearrange quickly. When the film was cooled down, the alkyl group of higher α‐olefin units and LLDPE began to entangle and crystallize. Driven by crystallization, the PEG segments rearranged and enriched in the interface between the amphiphilic graft copolymer and air. By this surface modification method, the amphiphilic graft copolymer was fixed on the surface of LLDPE film. And the water contact angle was further reduced as low as 14.8°. The experimental results of this article demonstrate the potential pathway to provide an effective and durable anti‐fog LLDPE film. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Orientation of merocyanine dye in Langmuir-Blodgett films of mixtures of poly(γ-benzyl l-glutamate)/poly(ethylene oxide)/ poly(γ-benzyl l-glutamate) block copolymer and dye

Summary Merocyanine dye(MD) can be spread with poly(γ-benzyl L-glutamate)/poly(ethylene oxide)/poly(γ-benzyl L-glutamate)(PBLG/PEO/PBLG) onto the air-water interface from a solvent in which the copolymer assumes a helical conformation. The expanded isotherm of the copolymer changed into compressed one with mixing of MD in the copolymer monolayer. Langmuir-Blodgett(LB) assemblies can be built up from copolymer/MD mixture layer when the helical axes of the polypeptide chains are oriented in the compression direction. The dichroic absorption of the copolymer/MD mixtures indicates that dyes are located with a preferential orientation of their molecular axes with regard to the director axis of the polypeptide.     

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.