Polydiacetylene Langmuir-Blodgett Films Research Articles

Photoluminescence of polydiacetylene membranes on porous silicon utilized for chemical sensors

Langmuir–Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavior, which is dependent on the type of the supporting substrate. While on polished silicon surfaces the photoluminescence (PL) of PDA is quenched, it is preserved on top of 2D patterned macro-porous silicon (2D-MPS). 2D-MPS, prepared by electrochemical etching of photo-lithographically pre-patterned silicon, is a 2D array of ca. 10 μm deep pores with lateral 2–4 μm repeating unit cells in orthogonal or hexagonal arrangements. LB films of PDA on such surfaces form membranes with continuous domains of the size sufficient to cover laterally many cell units. Apparently, the PL from this film results exclusively from the portion of the PDA membrane which is suspended over pore openings, while portions of the film which are attached to the silicon on top of the pores walls does not exhibit PL at all. We have used these membranes in different configurations and exposed them to different chemical and biological agents and followed the PL intensity change. This report demonstrates the effectiveness of the combined system: LB films of PDA on top of 2D-MPS as sensing probe for a variety of chemicals including, Cd ions and TNT explosives. In addition, the use of films of PDA, in which glycol-lipid were embedded, for binding and recognition of lectin protein, mimicking the cell membrane interaction with its environment, is also demonstrated.

Self-Alignment of Liquid Crystal Molecules on Polydiacetylene Langmuir-Blodgett Films

Alignment structure and optical properties of Langmuir-Blodgett (LB) films of urethane-substituted polydiacetylene (poly-4BCMU) was investigated. During compression, the coil to rod transition in molecular conformation of poly-4BCMU was induced and the polymer main chains were aligned perpendicular to the compressing direction. The dichroic ratio of absorption intensity of poly-4BCMU monolayer film was about 6. LC molecules were sandwiched with two glass plates covered with the poly-4BCMU monolayer films. LC molecules aligned spontaneously along the main chain direction of poly-4BCMU in the parallel cell. On the other hand, they formed a twisted structure of 90° in the crossed cell. The monolayer film of poly-4BCMU had a high potential as rubbing-free alignment layer of LC molecules.

Physical and chemical characterization of enolase immobilized polydiacetylene Langmuir–Blodgett film

Hexa histidine tagged recombinant Plasmodium falciparum enolase (His6-Pfen) was covalently immobilized on a Langmuir–Blodgett film of a self assembled mixture of 10,12-pentacosadiynoic acid and its N-succinimidyl ester derivative (PDA LB-film). The film was polymerized with a UV-lamp at 254nm to obtain a blue coloured, protein hooked polydiacetylene film. Atomic force microscopy (AFM) was used to characterize the surface morphology of the protein-immobilized film. The colorimetric response (CR) of the His6-Pfen hooked PDA LB-film to 2-phosphoglyceric acid (2-PGA), the substrate of enolase, in the presence of magnesium ions was studied spectrophotometrically. The CR of glutathione S-transferase-Pfen (GST-Pfen) immobilized film prepared by using similar procedure was also examined. The results suggest that binding of Mg (II) to the enzyme facilitates the interaction of the enzyme with 2-phosphoglycerate. This ligand-binding event could be detected by an observed increase in colorimetric response of the film by ∼10%. Thus the incorporation of enolase on a PDA film resulted in the formation of a novel material, which can serve as a biosensor.

Chromatic Transitions in Polydiacetylene Langmuir-Blodgett Films due to Molecular Recognition at the Film Surface Studied by Spectroscopic Methods and Surface Analysis

Langmuir-Blodgett films of polydiacetylene are used to create a biosensor on the basis of a surface hostguest recognition process. Functionalizing a 10 wt.% fraction of the diacetylene monomer with biotin leads to a visually observable color change in the resulting polymerized film when streptavidin in the molar ratio streptavidin: biotin = 1:2 is added. The chromatic transition, caused by a shortening of the conjugation length of the π-electron system in the polydiacetylene backbone, is investigated by monitoring the change of visible optical absorption and Raman spectroscopy. Chemical species and to some extent also the presence of surface-immobilized peptide are identified via time-of-flight secondary-ion mass spectrometry (TOF-SIMS) signal assignment and XPS studies.

Direct colorimetric study on the interaction of Escherichia coli with mannose in polydiacetylene Langmuir–Blodgett films

The membranes of polydiacetylene backbone decorated with mannose assembled by Langmuir–Blodgett technology can interact with Escherichia coli. The interactions lead to the color transition of the membranes which was readily visible to the naked eyes and could be quantified by visible absorption spectroscopy. To understand the mechanism of the chromatic transition, the affinochromism properties of polydiacetylene were examined by resonance Raman spectroscopy. The results demonstrated that the side chains of polymer backbone performed rearrangement, and the electronic structure in the polymer backbone changed from acetylene to butatriene form when the chromatic transformation from blue to red. The direct colorimetric detection by polydiacetylene membranes not only opens a new path for the use of these membranes in the area of biosensor development but also offers new possibilities for diagnostic applications and screening for binding ligand.

Monolayer Consisting of Two Diacetylene Analogues and Dioctadecyl Glyceryl Ether-β-glucosides

As potential materials for photosensitive biosensors, polydiacetylene Langmuir-Blodgett films are of great importance in disease diagnosis. The interactions between tricosa-2,4-diynoic acid (TCDA) and dioctadecyl glyceryl ether-β-glucosides (DGG) and between 10,12-pentacosadiynoic acid (PCDA) and DGG using surface pressure-area (π-A) isotherms have been studied in this paper. The analysis of the excess free energies of the isotherms showed that in monolayers TCDA and DGG molecules had good miscibility. In contrast, in PCDA/DGG monolayers molecules repulsed each other in most mixed ratios. The morphologies of pure TCDA, DGG, and PCDA and mixtures of TCDA/DGG and PCDA/DGG at the air/water interface were investigated using Brewster angle microscopy (BAM). BAM images confirmed the results obtained by π-A isotherms.

Chromatic Phase of Polydiacetylene Langmuir−Blodgett Film

The thermochromic phase-transition behavior of polydiacetylene (PDA) Langmuir−Blodgett (LB) films in the blue form and the bluish-green one was investigated from the viewpoint of the molecular lateral packings evaluated by the electron diffraction (ED) analysis. The PDA blue and bluish-green forms exhibit absorption peaks at the wavelengths 640 and 704 nm in the visible absorption spectrum, respectively. At an elevated temperature, the PDA LB films in both forms were converted into the red form with the absorption peak at the wavelength 540 nm. The chromatic phase transition of the PDA LB films was accompanied by the characteristic crystal phase transition in both cases. Further, the detailed structural analyses based on the ED measurement, the Fourier transform infrared external reflection spectrum, small-angle X-ray scattering, and X-ray photoelectron spectrum measurements revealed that the difference in the chromatic phase of the PDA LB film could be explained by the difference in the exciton energy le...

Langmuir-Blodgett Membranes of m-Alca-1,3-Diynylbenzoic Acids

Meta-alca-1,3-diynylbenzoic acids with different chain lengths were synthesized and the formation of Langmuir-Blodgett (LB) membranes was studied. Benzoic acids with alkyl chain length greater than 8 formed stable monolayers while those with 4 and 6 did not form good condensed phases. Multilayer films were irradiated with UV light and the diacetylenic groups polymerized to give polydiacetylene LB films having absorption maxima at around 640 nm.

Selective Generation of Defects in Polydiacetylene Langmuir-Blodgett Films on Si Substrates as Studied by X-Ray Photoelectron Spectroscopy

The defects in Langmuir-Blodgett films formed on Silicon substrates at the early stages of the accumulation process were studied by X-ray photoelectron spectroscopy for the first time. It was found that the defects are generated even in the first monolayer, especially on the thickly oxidized area and that the defects due to molecular elimination are generated selectively on the thickly oxidized area when the second layer is accumulated on the first layer. From this study, inelstic mean free paths of low-energy electrons in polymer material were also obtained, which are valuable for the analyses of their trajectories.

Cubic susceptibilities of polydiacetylene Langmuir-Blodgett films annealed before photopolymerization

The wave dispersion of cubic susceptibility χ (3) of green-form polydiacetylene, which can be obtained by annealing a diacetylene Langmuir-Blodgett film before photo-polymerization, was measured for the first time and compared with that of a blue form obtained from the same monomer without the anneal. The maximum ¦χ (3)¦ of the green form (0.97 × 10 −10esu) is smaller than that of the blue form (1.2 × 10 −10 esu). This result indicates that though the green form has a highly ordered structure by the anneal, π-electron delocalizability along its polymer main chain decreases.

Chromatic Phase and Molecular Packings of Polydiacetylene Langmuir-Blodgett Films

Abstract Molecular packings of polydiacetylene (PDA) Langmuir-Blodgett (LB) film in various chromatic phases such as blue, red and bluish-green forms have been clarified by the electron diffraction analysis for the first time. Spectroscopic properties - molecular packings relationships for the chromatic phases of PDA LB film indicate that the chromatic phase of PDA is strongly dependent on its molecular packing in the crystal phase.

Spin Magnetism of Polydiacetylene Langmuir-Blodgett Films.

In order to develop ultra-thin magnetic films, we investigated the structure and magnetism of Langmuir-Blodgett (LB) multilayers of polydiacetylene by X-ray diffraction and electron paramagnetic resonance (EPR). Using X-ray diffraction, we determined the orders of interlayer and of in-plane directions of the LB films. Upon ultraviolet irradiation, the LB film was found to tilt and to increase the ordering. In EPR measurements, angular variation of linewidth of monomer PDA LB films indicated a spin chain interaction of one-dimension. On the other hand, the polymeric PDA LB films exhibited a drastic extinction of EPR signal due to the onset of antiferromagnetic coupling by the decrease of distance between Mn ions. We concluded that the PDA LB films may permit the novel order structure with the low-dimensional spin magnetism.

A novel approach to the polydiacetylene Langmuir—Blodgett film by the surface-specific optical third harmonic generation based on the angular momentum conservation rule

A novel approach to the polydiacetylene Langmuir—Blodgett film by the surface-specific optical third harmonic generation based on the angular momentum conservation rule

Studies of generation of ultrafine semiconductor particles in polydiacetylene Langmuir-Blodgett films accompanied with colour transition

Ultrafine semiconductor particles of cadmium sulfide were generated through exposing poly-(pentacosa-10, 12-diynoic acid) (PDA) Langmuir-Blodgett (LB) films to hydrogen sulfide gas. With the generation of ultrafine particles, the blue form of PDA multilayers was converted to the red form. UV-visible absorption spectra and ellipsometric measurements were made to study the generation of ultrafine particles and the colour phase transition of PDA LB films.

Absorption properties and structure changes caused by pre-annealing in polydiacetylene Langmuir-Blodgett films

Absorption properties and structures are investigated as a function of pre-annealing temperature for PDA LB films. Absorption spectra of PDA LB films without pre-annealing have main peaks at 640 nm, while the pre-annealed 10-8 PDA LB films have new absorption peaks at 704 nm, i.e. a new blue phase. X-Ray diffraction measurements show that the pre-annealed films have extremely ordered layer structures. However, main peaks are observed at 640 nm for the pre-annealed 14-8 PDA LB films and the peaks only decrease with pre-annealing, because the layer spacing increases with pre-annealing and the polymerization is disturbed. Properties to the 10-8 PDA LB films depend upon the deposition temperature. The films, deposited at 20 °C and at 13 °C, have similar properties to the 10-8 PDA LB films and the 14-8 PDA LB films, respectively. The films having 704 nm peaks exhibit strong reversible color phase transitions between the new blue phase and the red phase. Pre-annealing is thought to be an important technique for controlling and improving characteristics of LB films.

Influence of Compression Process on Optical Properties of PDA Langmuir-Blodgett Films

ABSTRACTIn performing compression-expansion-recompression process during preparation of diacetylene (DA) monolayer, the change in colour of polydiacetylene (PDA) LB films was observed and more ordered structure of the films was achieved. The effect on optical properties could be ascribed to better arrangement of DA monomer which favoured the formation of PDA films in blue-form in polymerization.

Reversible colour phase transitions and annealing properties of Langmuir-Blodgett polydiacetylene films

The reversible colour phase transition between the blue phase and the red phase is investigated for pre-annealed Langmuir-Blodgett (LB) polydiacetylene (PDA) films. LB PDA films are pre-annealed before polymerization in order to improve the characteristics of the films. The main absorption peaks for the LB PDA films are observed at 640 nm without the pre-annealing, but the pre-annealed films under appropriate conditions have new main absorption peaks at 704 nm. The new peaks at 704 nm exhibit stronger reversibility of the colour phase transition than the peaks at 640 nm. Moreover, X-ray diffraction measurements show that the pre-annealed films have extremely ordered layer structures compared with the films that have not been pre-annealed.

Low energy electron transmission measurements on polydiacetylene Langmuir-Blodgett films

Results of low energy electron transmission (LEET) measurements are reported for polydiacetylene (PDA) Langmuir-Blodgett (LB) films deposited on copper substrates. The experiments were carried out with a low density electron beam in ultrahigh vacuum condition. The LEET spectra were mainly determined by the conduction band structure of the alkyl parts of the PDA LB film. The lower edge of the conduction band of the alkyl parts was found to be located at about 0.3 eV above the vacuum level at low temperature. With rising temperature, the spectra shifted to the lower energy side; a shift of 0.3 eV was observed for a temperature difference of 150 K. This indicates strong coupling between the band structure and thermal vibration of the alkyl chains. The transmission through the band gap was proportional to the reciprocal of the film thickness, showing that the gap conduction cannot be ascribed to electron tunnelling.

Electrical properties of metal-insulator-metal and metal-insulator-semiconductor structures containing Langmuir-Blodgett insulating multilayers

Electrical properties are investigated for metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures containing insulating Langmuir-Blodgett polydiacetylene (LBPDA) thin films. Schottky-type conduction currents are observed for MIM devices. Thermally stimulated currents (TSCs) of MIM diodes with LBPDA mono- and multilayers are measured. The TSC characteristics of the divices show dipolar polarization of the LBPDA mono-and multilayers below room temperature and charge injection from the electrodes above room temperature. From the TSC measurements, it is observed that an order-to-disorder structure change of the LBPDA films by annealing enhances the dipolar polarization. Capacitance-voltage ( C-V) characteristics are measured for A1/LBPDA/Si (MIS) structures. The C-V curves show hysteresis, and remarkable flat-band voltage shifts are observed after bias stressing is applied. These results show that both holes and electrons are easily injected from silicon into the LBPDA layers of the MIS devices.

Surface plasmon study of monolayer-bilayer transition in poly-4-BCMU and poly-3-BCMU polydiacetylene Langmuir-Blodgett films

Surface plasmon study of monolayer-bilayer transition in poly-4-BCMU and poly-3-BCMU polydiacetylene Langmuir-Blodgett films