Holographic grating studies in pendant xanthene dyes containing poly(alkyloxymethacrylate)s

A series of xanthene dyes based poly(alkyloxymethacrylate)s were synthesized with even number of side-chain methylene spacers by free radical addition polymerization method for holographic grating studies. Chemical structure of monomers and polymers were confirmed by FTIR and ¹H-NMR spectroscopy. Thermal property was investigated by TGA and DSC. Lengthy spacers favor improved optical quality film formation than shorter spacer length containing polymers; however, thermal stability and Tm decreased. Absorption and emission spectra have been studied in different polar solvents. UV–vis absorption maxima were broad and red-shifted with increasing spacer length. Life-time decay analysis exhibited double exponential decay. Polymer films were tested for holographic grating formation and their diffraction efficiency compared. Photo bleaching mechanism of polymer films was disclosed by measuring electrochemical potential value.     

Polyarylates: thermal stability in air

Polyarylates were synthesized by the acidolysis of the diacetates of dihydric phenols with diacids using a melt-polymerization technique. These polymers were characterized by solution viscosity, number-average molecular weight and IR spectra. Thermal stability of these polyarylates were studied by dynamic TG in the presence of air. Relative thermal stabilities were compared at the 50% mass loss of a given polymer (T _h value). The data presented revealed that there is a definite relationship between the structure of a polymer chain and their thermo-oxidative stability. TheT _h values of some of these polyesters were found to be higher than those reported for highly stable fluoro-carbon polymers (e.g. PTFE). It was observed that the polymers with more cyclic structures in a chain tend to be stiffer and more resistant to deformation. A chain backbone consisting of large number of aromatic groups induced chain stiffening because of chain inflexibility, resonance effects and steric effects.     

Effect of the side chain length on the optical and electrical properties of soluble PPV derivatives

2-Alkoxy-5-methoxy poly(1,4-phenylenevinylene) derivatives with different lengths of the alkoxy side chain have been synthesized via a modified Gilch polymerization. Their number-average molecular weights are in the range of 10,000–14,000. ¹H NMR, ¹³C NMR, FT-IR spectroscopies have shown that the polymer structures are the expected ones and were free from defects. The polymers are amorphous and show good thermal stability up to 300 °C. The optical absorption band of MB-PPV, MH-PPV, MO-PPV and MDD-PPV thin films are at 496 nm, 496 nm, 494 nm and 507 nm, respectively. Photoluminescence emission maxima of the above polymers appear at 624 nm, 582 nm, 629 nm and 578 nm, respectively. A composite photoluminescence response is observed at the exception of MO-PPV showing a single PL maximum. Light-emitting diodes (LEDs) based on these polymers were fabricated and characterized by current–voltage measurements. The comparison of the optical and electrical properties of these different polymers showed a small influence of the length of the side alkoxy chain and/or to the length of the main polymeric chain.     

Stilbene-based liquid crystalline and photocrosslinkable polynaphthylphosphate esters

A series of liquid crystalline and photocrosslinkable polymers were synthesized from 4,4′-bis(m-hydroxyalkyloxy)stilbene (m = 2, 4, 6, 8, 10) with naphthylphosphorodichloridate. The synthesized polymers were characterized by spectroscopic techniques. Thermogravimetric analysis revealed that the polymers were stable between 283 and 341 °C, then underwent two-stage decomposition, and char yield increased with decreasing spacer length. DSC and HOPM analysis disclosed that the polymers III–V (m = 6, 8, 10) exhibited LC phases wherein flexible methylene spacer separates mesogenic alignment and reduces overall rigidity of polymers, while polymers I and II are unable to show LC phase. The photolysis was studied by UV–visible and fluorescence spectroscopy. The rate of photocrosslinking increases with increase in methylene chain. The fluorescence property decreased with successive UV irradiation in the polymers.     

Soft-type polyurethane foams derived from molasses

Molasses (ML)-based soft-type polyurethane (PU) foams were successfully prepared by controlling evolved heat during chemical reaction. Two kinds of isocyanate, poly(phenylene methylene) polyisocyanate (MDI) and tolylene diisocyanate (TDI), and polypropylene glycol with a long molecular chain length were utilized to control the chemical reaction. The hydroxyl group in ML was used as the reaction site and soft-type PU foams were synthesized at isocyanate (NCO)/hydroxyl group (OH) ratios of 1.05. Mechanical properties of the above foams were controlled by changing the mixing ratio of MDI and TDI. Pore size and distribution were measured by scanning electron microscopy. With increasing thickness of cell wall, compression strength and modulus increased. Thermal properties of PU foams were investigated by differential scanning calorimetry, thermogravimetry, and thermal conductivity measurements. Two-step glass transition temperatures were observed at around ca. ?55 and 80 °C, regardless of kind of isocyanate. The low temperature side glass transition is attributed to the molecular motion of long oxyethylene chains and the high temperature side transition is caused by rigid components including saccharide components. Thermal decomposition of PU foams started from ca. 270 °C. Thermal conductivity of soft-type PU was observed in a range from 0.034 to 0.035 J s^?1 m^?1 K^?1.     

Photo-switching and nonlinear optical behaviors of center linked bent-core azobenzene liquid crystalline polymers

A new class of two series (I and II) of center linked bent-core azobenzene liquid crystalline polymers were prepared. They were prepared from two different spacer lengths (2 and 10) between polymer backbone and bent-core mesogen. The bent-core mesogen possesses photoactive linking group with variable terminal chains (7, 8, and 9). The synthesized precursors, monomers, and polymers were characterized by FT-IR, ¹H NMR, and ¹³C NMR spectroscopy. Thermal stability of polymers was examined by thermogravimetric analysis. The mesophase transition of monomers and polymers were observed through polarized optical microscopy, and confirmed by differential scanning calorimetry. Among the two series of polymers, the second series of polymers possesses liquid crystalline properties. The photo-switching properties of bent-core azo polymers were investigated using UV–Vis spectroscopy, trans to cis isomerization occurs around 35 s in chloroform and 65 s in thin film, where as reverse processes take place almost 32 h in chloroform. The photo-switching processes of polymer IIa precedes faster and also longer time thermally stable when compared with recently reported similar polymers. Negative optical nonlinear refractive index and optical limiting properties of the polymers were measured using Nd-YAG laser.     

Effect of halogen substitution on azo-naphthol dye based poly(alkyloxymethacrylate)s and their Z-scan measurements

A series of photo addressable polymers bearing azo-naphthol moiety in the polymer side chain containing polymethacrylate backbone were synthesized for NLO applications. Various halogen atoms were substituted in the para position of the side chain azobenzene, and the effects of the substituents were investigated. The polymers were characterized by UV, FT-IR, ¹H-NMR and ¹³C-NMR spectroscopy. The photoisomerization property of all the polymers shows a clear dependence on the size of the halogen, indicating the rate of the switching time in the increasing order of F > Cl > Br > I. The glass transition temperature and thermal stability of the polymers were analyzed by DSC and TGA respectively. The third order nonlinear optical properties of the polymer film were measured by the Z-scan technique using Ar-ion laser and exhibited negative optical nonlinearity. The results revealed that these polymers possess potential applications in nonlinear optics and the value of nonlinear susceptibility for the iodine substituted polymer is higher than the other halogen substituted polymers chosen in the study.     

Fabrication of diffractive optical elements inside polymers by femtosecond laser irradiation

Bragg-type gratings were prepared by irradiation inside a series of optical polymers with femtosecond laser pulses and the preparation conditions of the grating were examined. Repeated scanning irradiation with femtosecond laser pulses formed gratings due to refractive index changes inside polymers. Among the polymers examined in the present study, polymethylpentene (PMP) showed the highest diffraction efficiency, which was an order of magnitude higher than those of other optical polymers. The density of PMP was the lowest among the polymers evaluated in the present study, and the large volume contraction based on its low density was responsible for the larger refractive index change of PMP. Furthermore, we fabricated large-area diffractive optical elements (DOEs) in PMP measuring 15 × 25 mm² by widening the scanning area.     

Proton induced modification in makrofol-DE

Irradiation effects of a 3 MeV proton beam on polycarbonate (makrofol-DE (MFD)) have been studied with respect to its electrical, thermal and structural behaviour by using an LCR meter, DSC/TGA and FTIR spectroscopy. The dielectric loss/constant was observed to change with the fluence. Thermal analysis revealed that chain scission is the dominant phenomena in irradiated samples based on the reduction of its thermal stability by about 19% at a fluence of 10¹⁵ ions/cm², which is also corroborated by FTIR spectra. No significant change in intensity of the absorbance bands of the irradiated sample was observed up to a fluence of 10¹⁴ ions/cm² while on increasing fluence (10¹⁵ ions/cm²) the polymer structure was modified. It appears from DSC thermograms thatT _g is observed to change with fluence.     

Systematic approach of blue-light-emitting copolymers by introducing various naphthalene linkages into fluorene containing PPV derivatives

We newly synthesized a series of naphthalene and fluorene containing alternating copolymers, poly[9,9-n-dihexyl-2,7-fluorenediylvinylene-alt-1,4-naphthalenevinylene] (1,4-PNFPV), poly[9,9-n-dihexyl-2,7-fluorenediylvinylene-alt-2,6-naphthalenevinylene] (2,6-PNFPV), and poly[9,9-n-dihexyl-2,7-fluorenediylvinylene-alt-2,3-naphthalene-vinylene] (2,3-PNFPV) through the well known Wittig polycondensation reaction. The conjugation lengths of the polymers were controlled by differently linked naphthalenes in the polymer main chain. The resulting polymers were completely soluble in common organic solvents and exhibited good thermal stability up to 400 °C. The synthesized polymers showed UV–visible absorbance and photoluminescence (PL) in the ranges 352–379 and 465–512 nm, respectively. The maximum emission peak of 1,4-PNFPV was found at 512 nm with green light. But, 2,6- and 2,3-PNFPV showed more blueshifted blue PL emission than that of 1,4-PNFPV at 477 and 465 nm, respectively. This result showed that 2,3- and 2,6-naphthalene linkage of the 2,3- and 2,6-PNFPV reduced π-conjugation length compared to 1,4-naphthalene linkage of the 1,4-PNFPV. The single-layer light-emitting device was fabricated which has a simple ITO (indium–tin oxide)/polymer/Al configuration. Electroluminescence (EL) maxima of 1,4-PNFPV and 2,6-PNFPV were shown at 523 and 484 nm, respectively. The measurement of current vs. electric field showed the threshold voltages of 1,4-PNFPV and 2,6-PNFPV to be about 1.7×10⁸ and 2.1×10⁸ V/m. The EL powers of 1,4-PNFPV and 2,6-PNFPV were reached 36 and 24 cd/m² at 2.3×10⁸ V/m (206 mA/cm²) and 2.8×10⁸ V/m (190 mA/cm²), respectively.     

Mechanical and thermal properties of physical vapour deposited alumina films Part I Thermal stability

Thermal stability of non-reactive physical vapour deposited alumina films of varying thickness on Al₂O₃-TiC and Si substrates, deposited at two different substrate biases, is examined. Substrate curvature measurements were used to determine the deposition stress and stress development during thermal cycling and annealing. Thermal cycling experiments revealed that the films deposited on Al₂O₃-TiC substrates become irreversibly more compressive on heating and annealing while films deposited on Si substrates become irreversibly more tensile. The deposition stress was found to be independent of film thickness, substrate material, and substrate bias during deposition. The thermal stability was independent of film thickness and substrate bias during deposition.     

Fast response photorefractive guest-host polymer composite

Abstract

A film of composite poly(N-vinylzarbazole): [[4-(dodecanecyl-methylamino) phenyl]methylene]-propanedinitrile: C₆₀ was proven to possess attractive photorefractive properties with fast response time. The diffraction efficiency was fitted to the square of a biexponential formula and the fast response time was deduced to be 12 ms at an erasing beam intensity of 1 W/cm². Meanwhile, the strong photorefractive effect was maintained. An amplitude of index grating as large as 3.1 × 10^?3 at an electric field of 78 V/μ and fitted a two-beam coupling gain coefficient of 43 cm^?1 at 57 V/μ were observed.     

Investigation of effect of protonic acid media on the optical and thermal properties of chemically synthesized poly(o-toluidine)

Conducting polymer, Poly(o-toluidine) was synthesized by chemical oxidative polymerization method using different inorganic acids such as HCl, H₂SO₄, HClO₄, HNO₃, H₃PO₄ and H₃BO₃ as protonic acid media. Synthesized polymers were characterized by UV-Visible and FT-IR spectroscopy. Conducting emeraldine salt phase of the polymer has been confirmed with the help of spectroscopic analysis. Thermal stability of these polymers were investigated by thermogravimetric (TG/SDTA) analysis. Increase in conductivity with increase in temperature was observed in all the samples.     

Novel metallomesogenic polyurethanes: Synthesis,characterization and properties

A series of tetradentate Schiff base metallomesogenic diols were synthesized from two simple dihydroxy benzenes. The metallomesogenic diol was constructed from three ring containing mesogen linked through ester and azomethine with terminal hydroxy group. This upon complexation with copper(II) formed metallomesogenic diol with varying terminal chain length. A series of metallomesogenic polyurethanes were synthesized using these metallomesogenic diols as chain extenders for the prepolymers based on polytetramethylene glycol (PTMG) of varying molecular weight (M_n = 650, 2000) and 2,4-toluene diisocyanate (TDI), or 4,4′-methylene bis(phenyl isocyanate) (MDI). The molar ratio of metallomesogenic diol and PTMG were varied in the polyurethane to find their role in liquid crystalline and mechanical properties. Extensive characterization of all metallomesogenic compounds and intermediates were carried out by FT-IR, ¹H and ¹³C NMR, EPR, VSM, Mass (EI and FAB) and UV–visible spectroscopy. Hot stage polarizing microscope and differential scanning calorimetry were used to ensure the phase characteristics such as nature of phase, melting and clearing temperatures and phase range. The appearance of enantiotropic smectic A phases indicated high molecular polarizability of the core due to the metal ion.     

Dichromated Gelatin Reflection Gratings

Abstract

Reflection gratings were recorded in dichromated gelatin by using a non-symmetrical recording geometry. In addition to the primary grating, secondary gratings were also formed, as is generally known. It is found that the secondary gratings assist the structure stability during development in the exposure energy range (50–100) mJ cm^?2. The structure containing these secondary gratings is more rigid than those without and the reflection grating period is more stable during the development process in this exposure energy range, which is most suitable for the transmission grating formation. Secondary gratings also cause unwanted noise, but the noise level is low and the improved stability outweighs the extra noise.     

Pd grating obtained by direct micromolding for use in high resolution optical diffraction based sensing

Pd grating patterns have been fabricated using the process of micromolding in capillary employing a Pd alkanethiolate precursor, which could be converted to metal in situ by thermolysis. Thus generated Pd grating were uniform in width (~950?nm) and spacing (~450?nm) over millimeter square areas on glass substrates. Importantly, the pattern when used as an optical grating produced a diffraction pattern with a high resolution (>2000); the intensities of widely separated (diffraction angle, ~26·8°) diffracted spots could be measured using a simple photodiode. By varying the concentration of Pd precursor (2?mM to 25?mM), thickness of the resulting gratings could be adjusted in the range of ~15?C115?nm. By adjusting the grating parameters optimally, a maximum diffraction efficiency of 36% has been achieved. Thus fabricated Pd grating was used as seed catalyst to deposit Cu by electroless plating. The Cu deposition process has also been monitored by employing AFM, SEM and EDS analysis. The diffraction efficiency values corroborate well with the changes in the grating thickness due to Cu deposition. The grating structures presented can be reproducibly fabricated for rapidly emerging optical diffraction based sensing applications. This has been demonstrated in the case of aqueous Cu^2?+? by depositing the latter electrolessly on Pd.     

Design and synthesis of chromophores used for the main-chain NLO materials

Second-order NLO chromophores used for main chain polymers have been designed, synthesized and characterized by ¹H NMR and FTIR. Their structures were optimized, and μ_g and β_o were calculated using the AM1/FF method. The doping film in PMMA was prepared and poled by the electric field. The poling efficiency is about 16.5%, and the macroscopic nonlinearity d₃₃ is estimated to be 19.8 pm/v. The temporal stability was measured and the result showed that 65% of the initial signal remained after 500 h at room temperature.     

Catalytic characterization of bi-functional catalysts derived from Pd-Mg-Al layered double hydroxides

Hydrotalcite like precursors containing Pd^II-Mg^II-Al^III with varying molar ratios, (Pd + Mg)/Al ≈ 3 and Mg/Pd ≈ 750 to 35, were prepared by coprecipitation of metal nitrates at constant pH. Characterization of samples as synthesized and their calcined products by elemental analyses, powder XRD, TG-DTA, FT-IR spectroscopy, TPR and N₂ physisorption indicated a well crystalline hydrotalcite like structure with incorporation of Pd²⁺ in the brucite layers. Thermal decomposition of hydrotalcite precursors at intermediate temperatures led to amorphous mixed oxides, Pd/MgAl(O), which on reduction yielded bi-functional catalyst, Pd°/MgAl(O). The resultant catalysts with acid, base and hydrogenating sites, were highly active and selective for one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen. The results showed an optimal balance between acid-base and metallic sites were required to increase the selectivity of MIBK and stability of the catalysts.     

Intercalation d'ions alkylammonium et d'alkylamines a longues chaines dans les gels de V2O5

C_nH_2n+1N⁺(CH₃)₃ ions and C_nH_2n+1NH₂ amines with n ranging from 1 to 18 have been intercalated into the lamellar structure of V₂O₅ gels. Alkyl chain orientation in the interfoliar space has been deduced from the basal d-spacing evolution with the chain length : the chains are parallel, then tilted and finally perpendicular to the host lamellae as the chain length increases. Their monolayer disposition is also demonstrated. The large adaptability of the host structure proceeding from its gel state, leads to fast reaction at room temperature, especially with small polar heads such as -NH₂ (less than an hour). Contrary to usual intercalates, due to the gel state, only a mean composition can be defined. It has been found to correspond to 0.3–0.4 intercalated species per V₂O₅ : this is in good agreement with the upper limit (0.5) deduced from sterical considerations based upon a full filling of the interfoliar space. Thermal decomposition of alkyl chains restricts the stability of these intercalates to 160°C. More likely of the cationic exchange type with trimethylammonium ions, intercalation mechanism appears more complex with amines, involving probably also a host-guest charge transfer.     

Demonstration of covalent sidewall functionalization of single wall carbon nanotubes by NMR spectroscopy: Side chain length dependence on the observation of the sidewall sp3 carbons

Carboxylic acid-functionalized single walled carbon nanotubes (SWNTs) prepared via the reaction of an amino acid, NH₂(CH₂) _n CO₂H where n = 1 (glycine, GLY), 5 (6-aminohexanoic acid, AHA), 10 (11-aminoundecanoic acid, AUDA), with fluorinated single walled carbon nanotubes (F-SWNTs) have been characterized by MAS ¹³C NMR spectroscopy. The ease of observing the aliphatic CH₂ groups and the resolution of the signal are dependent on the length of the amino acid’s aliphatic chain. We have proposed that where substituent chains are short (making NMR data collection difficult) chemical modification to extend the chain length should alleviate analysis problems. In this regard, we have investigated the esterification of the carboxylic acid termini. The amino acid-functionalized SWNTs were esterified with an appropriate alcohol to ensure parity of the overall substituent length, i.e., GLY-SWNT (C₁) + 1-dodecanol (C₁₂) = DOD-GLY-SWNT (1), AHA-SWNT (C₅) + 1-octanol (C₈) = OCT-AHA-SWNT (2), and AUDA-SWNT (C₁₀) + 1-propanol (C₃) = PRO-AUDA-SWNT (3). The ¹³C NMR shift for the sp³ nitrogen-substituted carbon atoms of the SWNT sidewall is observed at δ ≈ 75 ppm. Increasing the length of SWNT sidewall functional groups enhances the ability to observe the sidewall sp³ carbon. The methylene carbon signal intensity is less attenuated in the dipolar dephasing spectrum of the ester-functionalized SWNTs than their associated amino acid derivatives, suggesting more motional freedom of the side chain in the solid state. The confirmation of the dipolar dephasing spectral effects was assisted by the characterization of the ester of AUDA-SWNT with 1,3-propanediol: PPD-AUDA-SWNT (4). Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.