基于分子间侧向氢键作用的电光材料制备及性能

通过重氮耦合和酯化等反应制备了一系列侧向含有酰胺基团的偶氮苯类非线性光学生色团, 并将其与聚合物进行掺杂或通过分子间的侧向氢键作用制备了主客体型及超分子型的电光薄膜材料. 生色团的结构通过核磁共振谱(¹H NMR, NMR)、 红外光谱(IR)、 质谱(MS)和元素分析(EA)等进行了表征, 结果表明, 生色团形成了分子间的氢键作用. 通过紫外-可见(UV-Vis) 光谱研究了材料的极化性能. 相比主客体型电光薄膜材料, 由分子间侧向氢键作用形成的超分子型电光薄膜材料无需与聚合物基体材料复合, 更有利于提高材料的生色团含量、 极化取向度及稳定性. 通过Teng-Man简单反射法研究了主客体型和超分子型电光材料的二阶非线性光学性质, 结果表明, 基于分子间侧向氢键作用形成的超分子体系具有更大的电光系数.     

ChargingE-perm for radon measurements

Recharging of commercial E-perm electret detectors used for radon measurement has been investigated. The E-perm was recharged using the poling charging method where a high voltage is applied on a metal nozzle to polarize the electret material. The optimum parameters to recharge the electrets were 5 kV charging voltage and 7 mm height of the nozzle from the electret surface and using an insulator while charging. Under these conditions, charging of E-perm carried out for 15 s attained required voltage and retained the charge for long durations. The response of recharged E-perm for radon activity measurements in a radon calibration chamber and in an open environment was compared with that of CR-39 detectors. Results showed close proximity in radon values.     

Bipolar cycling effects in BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BaTiO₃ (BF-BT) lead-free piezoelectric system has been paid much attention due to good piezoelectric properties and high Curie temperature. Poling is a process to align ferroelectric domains and increase the piezoelectric coefficients. During the poling process, unipolar direct current (dc) electric fields were applied conventionally, but recently bipolar alternating current (ac) cycling was reported to improve piezoelectric properties in rhombohedral structure piezoelectric materials. We investigated the effects of dc-poling and ac-cycling in BF-BT ceramics. The d₃₃ increased from 210 pC/N with dc-poling to 240 pC/N with ac-cycling in the morphotropic phase boundary region of BF-BT with domain engineering. This improvement of piezoelectric properties with ac-cycling was consistent with the structural evolution related to ferroelectric domains.     

Determination of the macroscopic optical properties for the NAEC/PEK-c guest–host polymer films

The polyetherketone (PEK-c) guest–host polymer films doped with (4′-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The films were poled by corona-onset poling at elevated temperature (COPET). The orientational order parameter of the chromophores NAEC in poled polymer film was determined by measuring the absorption spectra of the films before and after being poled. By using the two-level model, the measured dispersion of the refractive index of the polymer film, and the dispersion of the first hyperpolarizability of chromophore NAEC, the dispersion of the macroscopic second-order nonlinear optical (NLO) and linear electro-optic (EO) coefficients was evaluated for the NAEC/PEK-c guest–host polymer film.     

Measurement of the optical transmission modes and losses of the poled guest–host polymer NAEC/PEK-c planar waveguides

The polyetherketone (PEK-c) guest–host polymer planar waveguides doped with (4′-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The waveguide films were poled by corona-onset poling at elevated temperature (COPET), and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. By using the prism-in coupling method, the dark-line spectrum given by the reflected intensity versus the angle of incidence have been obtained, and the optical transmission losses of mth modes have been measured for the poled polymer waveguides at λ=632.8 nm. The measurement result showed that the optical loss of the fundamental mode is less than 0.7 dB cm⁻¹ for the TE polarization.     

Microscopic origin of the high-strain mechanical response of poled and non-poled poly(vinylidene fluoride) in the β-phase

Tensile mechanical tests have been applied to poled and non-poled poly (vinylidene fluoride) in its β-phase at several temperatures and strain rates, along the main directions of the material, in order to relate the mechanical response with the microscopic variations of the material, as well as to evaluate the performance of the material under use in different applications and environments. Poling increases mechanical strength along the preferential orientation of the microstructure but does not affect significantly the transversal mechanical properties. By increasing temperature, the effect of poling on the mechanical response is reduced due to increased molecular mobility and consequent de-poling of the system. The activation volume and enthalpy at yielding were calculated within the Eyring formalism. It is concluded that poling increases interaction among dipolar moments within the crystalline lamella and with the surrounding interphase and therefore increases cooperativity. This fact is also demonstrated by the decrease of the KWW β-exponent obtained from the stress-relaxation experiments.     

Second-order optical nonlinearity in bulk PbO/B2O3 glass

By investigating the second-harmonic generation (SHG) of the bulk PbO/B₂O₃ glass samples with different compositions after thermal poling, it was found that there was an optimal poling temperature for each sample with different compositions and there was also a relation between optimal poling temperature and glass transition temperature. At their own optimal poling temperatures, the samples had different frequency doubling efficiencies with the same applied voltage. We also found that the frequency doubling efficiency of PbO/B₂O₃ glass increased with the increase of poling voltage. An induced dipole model was proposed to explain the super-quadratic relation between the SHG intensity and the poling voltage.     

Investigation of the linear electro-optic effect for the guest–host polymer DR13/PEK-c thin films

The polyetherketone (PEK-c) guest–host polymer thin films doped with disperse red 13 were prepared by spin-coating method. The corona poling condition was optimized by the poling profiles. The polymer films were poled by corona-onset poling at elevated temperature, and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. The linear electro-optic coefficients of the poled polymer films have been determined at λ=632.8 nm by using a new simple interferometric technique, which is based on compensating the change of the optical length due to the electro-optic effect of the poled polymer film by the anti-piezoelectric effect of a quartz crystal.     

Self-assembled silver nanoparticles in glass microstructured by poling for SERS application

A simple technique to fabricate microchannels in glasses with self-assembled silver nanoparticles (NPs) in the channels is presented. It combines thermal-electric poling of silver-to-sodium ion-exchanged glass slides with a patterned anodic electrode, formation of the microchannels via selective etching off the unpoled slide regions, and hydrogen annealing. The annealing results in the growth of NPs only on the bottom of the channels. The studies performed allowed optimizing the channels’ depth and NPs surface density for Surface Enhanced Raman Scattering (SERS) based sensing and microfluidic applications. We have demonstrated that the formed NPs allow detection of 1/20 of BPE (1,2-Di(4-pyridyl)ethylene 97%) monolayer, the evaluated Raman enhancement factor being ~4·10⁷. The proposed approach based on the glass poling allowed us the fabrication of ~1 μm deep channels and easy multiplication of the structures because the anodic electrodes used for the poling are capable of multiple usage.