Interfacial properties of free-standing poly(3-hexylthiophene) films

Using full atomistic classical molecular dynamics simulations, the interfacial properties of free-standing poly(3-hexylthiophene) (P3HT) films have been investigated. The orientations of different parts of the P3HT chain and the surface tensions of the films were calculated in a temperature range of 540 K-600 K. At the liquid/vacuum interface, the P3HT chain shows ordering by exposing hexyl groups at the interface, while the chain backbone lays flat with the thiophene ring preferentially tilt toward the surface. At the interface, the terminal methyl groups of hexyl side chains are in excess compared to the methylene groups or thiophene rings. The surface tension of P3HT in its melt state shows similar temperature dependence to that of polymers that have long alkyl side chains. The surface tension values are comparable to those polymers that expose methyl or methylene groups on the surface. The surface tension values determined for the melt state are lower than the experimental reported values for crystalline P3HT films, as expected.     

Semicrystalline morphology in thin films of poly(3-hexylthiophene)

The thermodynamic phase behavior and the morphology in thin films of poly(3-hexylthiophene) (P3HT) has been studied using calorimetry, X-ray scattering, and scanning force microscopy (AFM). Around 225 °C a phase transition from the crystalline state to a layered, liquid crystalline structure occurs in regioregular P3HT, while the regiorandom counterpart material is disordered at all temperatures and displays a glass transition temperature T_g–3 °C. Regioregular P3HT is semicrystalline and forms needle or plate like crystallites which in solution cast thin films are oriented with respect to the substrate. Films produced by spin coating display a non-equilibrium structure with reduced order and orientation. Annealing of these films in the liquid crystalline state leads to the formation of a morphology similar to the one observed in solution cast films.

Surface-induced conformational changes in poly(3-hexylthiophene) monolayer films

With the aim of elucidating the surface-induced molecular ordering in regioregular poly(3-hexylthiophene) (P3HT) monolayer films, we have controlled the intermolecular interactions at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with two kinds of groups (-NH2 and -CH3). We have found that, depending on the surface properties of such modified insulator substrates, the P3HT chains in the monolayer films can adopt two different conformations (edge-on and face-on). This surprising variation in chain conformation arises because of the specific interactions of the P3HT chains with the modified insulator substrates, which can be explained in terms of the following factors: the unshared electron pairs of the SAM end groups (in the -NH2 system), the pi-H interactions between the thienyl backbone bearing pi systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs (in the -NH2 system).     

电场极化调控聚(3-己基噻吩)薄膜润湿性

本文首次采用电场极化技术精确控制共轭聚合物P₃HT薄膜表面的润湿性,通过调节极化条件,成功实现了对P₃HT薄膜表面润湿性的精确控制,薄膜表面水接触角可以实现从疏水性到亲水性的转变.通过光谱学、形貌学及接触角等表征手段,详细研究了电场极化作用下共轭聚合物分子取向聚集形态及作用机理.该工作不但扩展了共轭聚合物薄膜材料的应用范围,也为分子形态学的研究奠定了基础.     

Molecular ordering and 2D conductivity in ultrathin poly(3-hexylthiophene)/gold nanoparticle composite films

This paper reports the first comparison of the structure and electrical conductivity properties of spin cast (SC) and Langmuir-Schaeffer (LS) films of regioregular poly(3-hexylthiophene) (P3HT). In addition, the effect of incorporating highly monodisperse Au nanoparticles (NPs), with a core diameter of approximately 5 nm, into SC and LS P3HT films is described. A detailed picture of molecular organization in the films has been obtained using ultraviolet-visible absorption spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, X-ray diffraction, and X-ray reflectivity. Film morphology was correlated with pseudo-two-dimensional conductivity measured using scanning electrochemical microscopy, with P3HT in the semiconducting regime. It was found that SC films, which were slightly thicker than those formed with the LS technique, exhibited greater organization. This resulted in an order of magnitude higher lateral conductivity for the SC films. Inclusion of Au NPs (50 wt %) into both SC and LS films resulted in the formation of uniform and relatively flat (rms roughness approximately 1 nm) composite films. Surprisingly, the addition of NPs did not disrupt the characteristic crystal structure found for the native P3HT films. The effect of Au NPs on film lateral conductivity was found to be determined by the distribution of Au NPs within the polymer, which varied significantly between SC and LS films. Whereas Au NPs aggregated into hexagonally packed clusters in SC films, NPs in LS films were predominantly uniformly distributed between the lamella bilayer. It was found that, while the inclusion of Au NPs caused the lateral conductivity to decrease in SC films, in LS films, the lateral conductivity increased by a factor of 2.     

Structure of friction-transferred highly oriented poly(3-hexylthiophene) thin films

Oriented thin films of P3HT were obtained by a friction-transfer technique. The morphology and structure of the film were studied by means of optical microscopy, atomic force microscopy and transmission electron microscopy. Optical microscopy observation indicates that large size well-ordered P3HT thin films can be produced by a friction-transfer technique. Highly ordered lamellae were observed in P3HT friction-transferred films by electron microscopy. Electron diffraction results confirm the existence of high orientation with the a- and c-axes of P3HT crystals aligned in the film plane while the c-axis parallel to the friction-transfer direction. The atomic force microscopy observation of the as-prepared P3HT thin film shows, however, a featureless top surface morphology, indicating the structure inhomogeneity of the obtained film. To get highly oriented P3HT thin films with homogenous structure, high temperature annealing, solvent vapor annealing and self-seeding recrystallization of the friction-transferred film were performed. It is confirmed that solvent vapor annealing and self-seeding recrystallization methods are efficient in improving the surface morphology and structure of the frictiontransferred P3HT thin film. Highly oriented P3HT films with unique structure can be obtained through friction-transfer with subsequent solvent vapor annealing and self-seeding recrystallization.     

Time-temperature superposition for viscoelastic properties of regioregular poly(3-hexylthiophene) films

Shear moduli were determined for chemically polymerized and solvent cast regioregular poly(3-hexylthiophene) films, using thickness shear mode acoustic wave resonators. The results are strikingly different to those for electropolymerized regiorandom poly(3-hexylthiophene) films. The time scale of the measurement was varied directly by use of higher harmonics of the acoustic wave resonator and indirectly via temperature. The significant variations in shear modulus with effective time scale can be "normalized"onto a stress master relaxation curve by using the concept of time-temperature superposition; this is the first time this has been demonstrated for electroactive films. The shift factors required to effect this normalization do not follow the classical Williams-Landel-Ferry (WLF) equation developed for long-range backbone motions of bulk polymers. Instead, they follow an Arrhenius-like behavior, commonly used to describe secondary motions of polymer side-chains. The activation enthalpy associated with this is independent of applied potential, is the same as for as cast (undoped) films, and is similar to that for rotation about a carbon-carbon single bond. These all point to the hexyl side-chains as the origins of the observed phenomena, consistent with the "melting point" separating two temperature-dependent phases and with the different molecular packing arrangements that would necessarily apply to regioregular and regiorandom materials.     

Measurements of HOMO-LUMO levels of poly(3-hexylthiophene) thin films by a simple electrochemical method

Journal of Solid State Electrochemistry - Though poly(3-hexylthiophene) (P3HT) is one of the most commonly used polymers in organic solar cells, a broad range of values, derived from cyclic...     

Uniaxial alignment of poly(3-hexylthiophene) nanofibers by zone-casting approach

The preparation of large area coverage of films with uniaxially aligned poly(3-hexylthiophene)(P3HT) nanofibers by using zone-casting approach is reported.The length and the orientation of the nanofibers are defined by the solubility of the solvent,the P3HT molecular weight and the substrate temperature.The length of the oriented nanofibers could be increased from 1 μm to more than 10 μm by adding poor solvent into the P3HT solution.It is found that for P3HT of relatively low molecular weight,a solvent with relatively low solubility has to be chosen to get the oriented film.While for the high molecular weight P3HT,the solvent with a relatively high solubility has to be used.The well-aligned film could be obtained because of the solute concentration gradient in the region where the critical concentration is reached during the zone-casting process.Particularly,the solvent evaporation rate and crystallization rate must be chosen properly to satisfy the stationary conditions above,which were controlled by an appropriate choice of solvent and substrate temperature.The film prepared by zone-casting approach had microcrystalline P3HT domains with more inter-chain order than spin-coating film.Meanwhile,the P3HT π-π stacking direction was parallel to the alignment direction of the nanofibers.     

Enhanced visible light photocatalysis of TiO2 by Co-modification with Eu and Au nanoparticles

TiO₂ photocatalysis has been studied widely in environment protection and energy generation applications. But, the intrinsic absence of visible light response and the high recombination rate of photo-generated charge carriers significantly limited the efficiency of photocatalysis with TiO₂ materials. Herein, a facile approach was constructed to develop visible-light-induced TiO₂ photocatalysis by co-modification with Eu and Au nanoparticles. The synthesized Au/Eu-TiO₂ material was characterized by XRD, SEM, TEM, DRS, XPS, and N₂ adsorption measurements. Visible light catalytic performance of the Au/Eu-TiO₂ catalyst was evaluated by using the photodegradation of RhB as a model reaction. It was shown that this Au/Eu-TiO₂ exhibited a better photocatalytic activity than the single Au modified TiO₂ (Au/TiO₂) or the single Eu modified TiO₂ catalyst (Eu/TiO₂), and also exhibited a good reusability for the targeted reaction. This remarkably improved performance of Au/Eu-TiO₂ could be attributed to the synergetic effect of Eu and Au co-decoration, which not only enhanced visible light absorption but also promoted charge carriers transfers as evidenced by DRS, XPS and transient photocurrent spectra. Moreover, a possible reaction mechanism for the Au/Eu-TiO₂ photocatalysis was proposed.     

Surface characterization and liquid crystal alignment behavior of comb-like poly(oxyethylene)/poly(3-hexylthiophene) blend films

The blend surfaces of poly[oxy(n-decylsulfonylmethyl)ethylene] (CH(3)-10SE) and poly (3-hexylthiophene) (P3HT) with different weight ratios were prepared by spin coating the polymer solution mixtures. In this study, their surface properties such as surface morphology, chemical composition, molecular structure, and wettability were systematically studied and correlated with liquid crystal (LC) alignment behaviors on the blend films. Therefore, we found that CH(3)-10SE part with a well-ordered side chain structure predominantly affects the both of wettability and LC alignment behavior of the blend films while there was no clear association between the wettability and the LC alignment behavior.     

Structure and morphology optimization of poly(3-hexylthiophene) thin films onto silanized silicon oxide

The influence of the preparation conditions, including substrate functionalization with common silanizers, onto structure/morphology of the overlying poly(3-hexylthiophene) thin films has been investigated by using both grazing incidence X-ray diffraction and atomic force microscopy. The factors determining the formation of spin-coated films suitable for applications in field effect transistors, i.e. concentration, spin-speed, and thermal treatment are addressed. We have established, by a tuning of the preparation and post-deposition treatments, the optimal conditions to get films with the required structural/morphologic features. Moreover we have shown that the macromolecules orient and organize at the interface zone (?10 nm from the interface) better than in the upper layers, i.e. far away from the interface.     

Air-tolerant poly(3-hexylthiophene) synthesis via catalyst-transfer polymerization

The discovery of catalyst-transfer polymerization and its further developments have led to unprecedented control over the length and sequence of conjugated polymers. However, the methods themselves are technically challenging to perform due to the air- and moisture-sensitivities of the monomers and catalysts. Herein, we report a catalyst-transfer polymerization method that affords poly(3-hexylthiophene) in high yields without using an inert atmosphere. The synthesis capitalizes on a rapid Negishi cross-coupling using a moisture-tolerant organozinc monomer mediated by an air-stable Pd precatalyst. This simple method should make conjugated polymer synthesis more accessible to a broader range of researchers and may be generalizable to other monomer scaffolds.     

Nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine)

Peculiarities of the nucleation and growth of gold nanoparticles on adsorption layers and in ultrathin films of poly(2-vinylpyridine) (PVP) in the chemical reduction of sorbed Au(III) ions and the consequent thermal treatment of systems are studied by X-ray photoelectron spectroscopy and optical spectroscopy. It is shown that nitrogens of PVP pyridine groups coordinate gold atoms. It is revealed that, even at relatively short contact between PVP film saturated with chloroauric acid and the solution of strong reductant NaBH₄, Au(III) ions are reduced to metal. As a result, quasi-metal gold particles are formed. At the same time, when exposing a PVP-Au system to the solution of weak reductant NH₂OH, the process of reduction proceeds in several stages. First, Au(III) ions are reduced to Au(I) followed by the reduction to Au(0) as a result of disproportionation reaction. It is demonstrated for the first time that, upon using NH₂OH, the rate of reduction, as well as the structure of prepared PVP-Au nanocomposite films depends to substantial extent on solution pH. Prolonged annealing of ultrathin nanocomposites at 150 °C, i.e., above the glass transition temperature of polymer matrix, leads to an increase in the sizes of metal particles and the formation of systems characterized by intense absorption within the 500–600-nm range due to the localized plasmon resonance of gold nanoparticles.     

Modeling disorder in polymer aggregates: the optical spectroscopy of regioregular poly(3-hexylthiophene) thin films

Absorption and emission in polymer aggregates is studied theoretically, taking into account excitonic (intermolecular) coupling, exciton-phonon (EP) coupling, and disorder, all treated on equal footing within a generalized Holstein Hamiltonian with numerically generated eigenmodes and energies. The disorder is modeled as a Gaussian distribution of molecular transition frequency offsets of width sigma and spatial correlation length l(0). Both herringbone (HB) and lamellar aggregate morphologies are considered. The emission spectral line shape is shown to undergo marked changes in response to increasing disorder, with the intensity of the ac-polarized 0-0 emission peak generally increasing relative to the replica intensities (0-1,0-2,[ellipsis (horizontal)]) as sigma increases and/or as l(0) decreases. This is contrary to the behavior of the b-polarized component of the 0-0 intensity, which, in HB aggregates, decreases with increasing disorder. Comparisons are made to analogous trends in oligomer aggregates. Analytical results are obtained in the strong EP coupling regime appropriate for conjugated polymers while treating the disorder perturbatively. A method for uniquely determining sigma and l(0) from the emission and absorption spectra is presented. Applications are made to absorption and low-temperature emission in thin films of regioregular poly(3-hexylthiophene), with excellent agreement between theory and experiment obtained for a spatial correlation length of only 3-4 molecules.     

Fabrication of polymer Langmuir-Blodgett films containing regioregular poly(3-hexylthiophene) for application to field-effect transistor

Semiconducting thin films consisting of regioregular poly(3-hexylthiophene) (RR-PHT) and poly(N-dodecylacrylamide) (pDDA) were constructed by the Langmuir-Blodgett (LB) technique. A mixture of RR-PHT and pDDA spread from a chloroform solution on a water surface forms a stable monolayer, which can be transferred onto solid substrates by the LB method, yielding a well-defined polymer LB film. Surface morphology studies of the LB film indicate that the RR-PHT is dispersed uniformly throughout the surface. The polymer thin film was chemically doped by contacting with FeCl3 acetonitrile solution, and a conductivity of 5.6 S/cm was achieved. Further, the LB film was utilized as the semiconducting film in the field-effect transistor (FET), and mobilities of 2.2 x 10(-4) and 4.4 x 10(-4) cm2 V(-1) s(-1) were obtained by analyzing the saturated and linear regions of the current-voltage characteristic, respectively.     

Crystal growth rate in ultrathin films of poly(ethylene oxide)

Many dynamical properties of polymers, including segmental relaxation and chain diffusion, exhibit anomalies in thin‐film samples. We extend the studies of thin‐film dynamics to the case of semicrystalline polymers and present a study of the crystal growth rate for thin films of poly(ethylene oxide). We used optical microscopy and quartz crystal microbalance techniques to characterize the kinetics of crystallization for films with thicknesses from 40 to 1000 nm for a range of temperatures near the melting point. A remarkable slowing down of the crystal growth is observed at all temperatures studied for films with a thickness of less than ～100 nm. The results can be used to suggest reductions of the mobility of chains at the crystal/amorphous interface. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2615–2621, 2001     

Recombination luminescence of poly(arylene phthalide) films induced by visible light

Long-term afterglow emission (AG) of poly(arylene phthalide) films (PAP) irradiated with visible light has been discovered. Recombination nature of the AG was experimentally proven as in the case of UV irradiation. Features of the observed AG spectra were analyzed in comparison with the photo-, electro-, and thermoluminescence spectra of the PAP films in relation to the commonness of the AG generation mechanism, which is associated with the involvement of the two-photon reactions and triplet states in the photoprocesses in PAP.     

Photo-oxidation and ozonization of poly(3-hexylthiophene) thin films as studied by UV/VIS and photoelectron spectroscopy

The kinetics and the mechanisms of degradation of thin P3HT layers have been investigated quantitatively for ozonization and photo-oxidation. Both, decay kinetics and product evolution of the polymer degradation are monitored by in situ UV/VIS and X-ray photoelectron spectroscopy (XPS). The degradation pathways of ozonization and photo-oxidation of P3HT turn out to be significantly different. Ozone attacks the thiophene units mainly by direct addition to the double bonds, leading to the loss of UV/VIS absorption, while the aliphatic side chains [1] are hardly affected. During photo-oxidation, the polymer is primarily attacked at the alkyl side chain which leads to the formation of reactive peroxide species. These subsequently cause the oxidation of sulfur and concomitantly the destruction of the thiophene ring, resulting in the loss of absorption. From the kinetics of the blue shift of the optical absorption it is concluded that the polymer is mainly attacked at the terminal thiophene rings the case of photo-oxidation whereas ozone attacks positions more or less randomly distributed along the chain. The rate of photo-oxidation under AM 1.5 conditions is at least one order of magnitude faster than the decomposition of P3HT by ozone.