Investigation on the nonlinear optical properties of the DCNP/PEK-c guest–host polymer films

The polyetherketone (PEK-c) guest-host polymer thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. The polymer films were investigated with in situ second-harmonic generation (SHG) measurement. The corona poling temperature was optimized by the temperature dependence of the in situ SHG signal intensity under the poling electric field applying. The temporal and temperature stability of the second-order properties of the poled polymer film were measured by the in situ SHG signal intensity probing. The second-order NLO coefficient L₃₃⁽²⁾=32.65 pm/V at 5=1064 nm was determined by using the Maker fringe method after poling under the optimal poling condition. The dispersion of the NLO coefficient of the guest-host polymer system was determined by the measured value of L₃₃⁽²⁾ at 1064 nm and the two-level model.     

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.     

Investigations of the E-O behavior in the poled polymer waveguide

The electro-optic (E-O) properties of the slab polymer waveguide induced by electric poling have been studied experimentally. The thin film waveguide was prepared by a synthesized polymer polypelargonamide and poled by applying voltage between the electrodes. I–V curves and E-O characteristics of the polymer films were in-situ measured during poling. In order to evaluate the molecular dipole orientation under the poling field, the absorption spectra of this film was observed by FTIR. The E-O performance of the polymer slab film was also estimated by the Mach–Zehnder interferometer.     

Second-order non-linear optical studies on CdS microcrystallite-doped alkali borosilicate glasses

CdS microcrystal-doped alkali borosilicate glasses were prepared by conventional fusion and heat-treatment method. Utilizing Maker fringe method, second-harmonic generation (SHG) was both observed from CdS-doped glasses before and after certain thermal/electrical poling. While because the direction of polarization axes of CdS crystals formed in the samples is random or insufficient interferences of generated SH waves occur, the fringe patterns obtained in samples without poling treatments showed no fine structures. For the poled samples, larger SH intensity has been obtained than that of the samples without any poling treatments. It was considered that the increase of an amount of hexagonal CdS in the anode surface layer caused by the applied dc field increased the SH intensity. The second-order non-linearity χ⁽²⁾ was estimated to be 1.23 pm/V for the sample poled with 2.5 kV at 360 °C for 30 min.     

Enhancement of second harmonic intensity in thermally poled ferroelectric nanocrystallized glasses in the BaO-TiO2-SiO2 system

The transparent nanocrystallized (heat-treatment: 750 ^°C, 1 h) glasses consisting of ferroelectric Ba₂TiSi₂O₈ nanocrystals (size: 100-200 nm) have been prepared in 40BaO-20TiO₂-40SiO₂ glass, and the effect of a thermal poling (DC electric voltage: 8.8 kV/cm, temperature: 110-300 ^°C, time: 1 h) on the second harmonic (SH) intensity has been examined. It is found that the formation behavior of nanocrystals at the surface differs from that in the interior of glass, giving a new insight into the well-known concept for nanocrystallization or homogeneous nucleation in glass. The Maker fringe patterns with fine structures are observed, indicating a high orientation of the polarization axes of Ba₂TiSi₂O₈ crystals formed at the surface. The prominent enhancement in the SH intensity is observed due to thermal poling, demonstrating that thermal poling is an effective method in enhancing anisotropic polarization of ferroelectric Ba₂TiSi₂O₈ nanocrystals in crystallized glasses. The present study proposes that the Maker fringe pattern for SH intensity of nanocrystallized glasses is very sensitive to the anisotropic polarization of nanocrystals at the surface, indicating the importance of the Maker fringe technique for the characterization of nanocrystals in materials.     

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.     

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: Novel fluorescence measurements

Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine the effects of decreasing film thickness on glass transition temperature, T _g, the relative strength of the glass transition, and the relative rate of physical aging below T _g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at T _g. Positive deviations from bulk T _g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T _g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of physical aging in films as thin as 10 nm. Received 21 August 2001     

Investigation of the polyetherketone guest–host DR1/PEK-c polymer films by real-time monitoring of the second-harmonic generation

The real-time monitoring of the second-harmonic generation (SHG) was used to optimize the poling condition and to study the nonlinear optical (NLO) properties of the polyetherketone (PEK-c) guest–host polymer films. The high second-order NLO coefficient χ₃₃⁽²⁾=11.02 pm/v measured at 1.064 μm was achieved when the weight percent of DR1 guest in the polymer system is 20%. The NLO activity of the poled DR1/PEK-c polymer film can maintain more than 80% of its initial value when temperature is under 100°C, and the normalized second-order NLO coefficient can maintain more than 85% after 2400 s at 80°C.     

In Situ Synthesis of Oil-Based Polymer/Silver Nanocomposites by Photoinduced Electron Transfer and Free Radical Polymerization Processes

In this study, in situ synthesis of oil-based polymer–silver nanocomposites was achieved by using photoinduced free radical polymerization processes in which silver nanoparticles were formed by electron transfer reaction. An oil-based macromonomer was prepared and then copolymerized with styrene in the presence of AgNO₃. Copolymerization was started with free radicals formed by photolysis of 2,2-dimethoxy-2-phenyl acetophenone and simultaneously silver nitrate was reduced to metallic silver in nanosize by electron transfer reaction. The amount of photoinitiator influenced the size of silver nanoparticles formed within the polymer films. Nanocomposite films were characterized by TEM and TGA analysis. The obtained polymer nanocomposite film was also examined in respect of surface coating material that would have an antibacterial effect against Gram-positive, Gram-negative and spore-forming bacteria. It was demonstrated that suitably coated nanocomposite samples exhibited an antibacterial effect against these bacteria.     

用光强衰减方法测量交联型聚氨基甲酸酯的交联温度

提出了用导波光学方法测量交联型聚合物材料的交联温度。即在对聚合物薄膜处理时,利用光波导的衰减全反射光谱中导模峰对聚合物材料的折射率敏感的特性,来测量聚合物材料参量。研究了交联型聚氨基甲酸酯材料在升温过程中薄膜折射率的变化。实验结果发现,温度相关的折射率dn/dT会发生不连续变化。整个dn/dT曲线有两个交叉点,这两个交叉点之间的温度范围就是聚合物材料的交联温度范围。第一个和第二个交叉点的温度分别被称之为材料的开始交联温度和完全交联温度。测得的交联型聚氨基甲酸酯材料的交联温度即最佳极化温度范围为85～122℃。通过对不同极化条件(是指开始极化的温度在测得的交联温度范围中变化)下聚氨基甲酸酯材料电光系数的测量验证了交联温度测量结果的准确性。     

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.     

聚四氟乙烯多孔膜的压电活性及其稳定性

研究了经单向机械拉伸形成的非极性空间电荷型薄膜驻极体聚四氟乙烯(PTFE)多孔膜的压电性.讨论了由PTFE多孔膜和非多孔的聚合物薄膜（PTFE，聚酰亚胺PI，氟化乙丙烯共聚物FEP 和聚三氟氯乙烯PCTFE）组成的双层膜的突出压电活性.初步研究结果指出：在优化的极化条 件下形成的上述双层压电膜以外电极测量的准静态压电d₃₃常数可达186 pC/N， 这个数值与压电陶瓷锆钛酸铅PZT的相应常数接近，而比铁电聚合物聚偏氟乙烯(PVDF)的相 应常数约高出一个数量级.还研究了这类柔性多孔膜 关键词： 聚四氟乙烯多孔膜 压电性 空间电荷驻极体 充电参数 压电活性的热稳定性     

掺杂型聚合物的电晕极化特性及其机理研究

实验研究了聚甲基丙烯酸甲脂(PMMA)掺杂生色团分散红DR19的电光聚合物的电晕极化特性.结合吸收光谱法和显微镜形貌分析了极化电压、极化温度以及极化时间对极化效果的影响.理论和实验分析得出极化电压增大可以增大聚合物内部极化电场,但电压过大会引起薄膜击穿而降低极化效果;而极化温度升高可以增大分子取向力,但在聚合物玻璃化温度以上会导致相分离;极化时生色团分子的取向随时间增大并逐渐达到动态平衡.实验结果表明:表征极化效果的序参数随极化电压的增大而先增大后减小,随极化温度的升高而先增大后减小,随极化时间的增长先增大后趋于稳定.     

Determination of the absorption for incident light propagating parallel through the guest–host polymer film waveguide

Guest–host polymer thin films of polymethyl methacrylate (PMMA) incorporated with (4′-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were fabricated by spin coating and then poled by the method of corona-onset poling at elevated temperature. The absorption mechanism of the polymeric film, which is very important for the optical transmission losses and directly relates to the orientation of chromophore NAEC in polymer PMMA, was investigated in detail. From the UV–visible absorption spectra for NAEC/PMMA film before and after being poled, we determined the change of absorption coefficient κ with the wavelength and approximately calculated the maximum absorption A_max as 3.46 for incident light propagating parallel through the film, i.e. the ordinary polarized light, which cannot be directly measured in the spectrophotometer.     

椭圆偏振光谱实时在线监测与离线分析微晶硅薄膜的生长

采用甚高频等离子体增强化学气相沉积技术高速沉积了有无籽晶层两个系列微晶硅薄膜,通过椭圆偏振光谱、拉曼光谱和XRD对薄膜进行了分析,发现采用籽晶层后,在薄膜沉积初期有促进晶化的作用;由于籽晶层减少了薄膜的诱导成核时间,提高了薄膜的沉积速率,对比了实时在线和离线椭圆偏振光谱两种测量状态对分析微晶硅薄膜的影响,研究发现,当薄膜较薄时,实时在线测量得到的薄膜厚度小于离线下的数值;当薄膜较厚时,两种测量条件下得到的薄膜厚度差异较小;实时在线条件下得到的表面粗糙度要大于离线条件下得到的数值,这是由于薄膜暴露在大气中后表面有硅氧化物生成,对表面有平滑作用.     

Second-order optical nonlinearities from χ gratings induced by holographic all-optical poling

The paper presents the second-order optical nonlinearities from χ⁽²⁾ gratings induced by holographic all-optical poling for azobenzene polymer. Second harmonic (SH) signal along the directions with two different vectors was measured. One is strong SH signal diffracted in the same direction as 2ω writing beam with wave vector k_2ω and the other is weak SH signal diffracted in the direction of wave vector of 4k_ω - k_2ω + Δk where k_ω is wave vector of ω beam and Δk is the wave vector mismatch whose vector is parallel to k_ω. The latter signal was used as a tool to monitor the formation of holographic χ⁽²⁾ gratings in real-time because it has off-axis wave vector different from both k_ω and k_2ω. The increase of 2ω intensity on poling process led to the large increase of second-order optical nonlinearity. The real-time monitoring showed that it also gave the large relaxation of second-order optical nonlinearity on poling process. The increase of 2ω (532 nm) energy enhanced the increase of local heating, which led to easier alignment of azobenzene chromophore and also larger relaxation of aligned chromophore.     

直流电场诱导LB膜中分子重新取向研究

用旋转二次谐波产生方法研究了半花菁/花生酸Y型交替LB多层膜中由外加法向直流电场诱导的分子的重新取向.外加法向直流电场能够有效地改变LB膜中光学活性半花菁分子的取向,迫使其长轴转向电场的方向.随着极化电场的增大,分子在基板平面内的各向异性逐渐减小,而二次谐波强度的增量则随外加电场的增大而呈现平方增长的规律.在室温下,用1.3×10⁶V/m的电场极化10min,可以使半花菁LB多层膜的二次谐波强度增大一个量级.     

The properties of free polymer surfaces and their influence on the glass transition temperature of thin polystyrene films

We present a detailed study of free polymer surfaces and their effects on the measured glass transition temperature (T_g) of thin polystyrene (PS) films. Direct measurements of the near-surface properties of PS films are made by monitoring the embedding of 10 and 20 nm diameter gold spheres into the surface of spin-cast PS films. At a temperature T = 378K( > T_g), the embedding of the spheres is driven by geometrical considerations arising from the wetting of the gold spheres by the PS. At temperatures below T_g ( 363K < T < 370K), both sets of spheres embed 3-4 nm into the PS films and stop. These studies suggest that a liquid-like surface layer exists in glassy PS films and also provide an estimate for the lower bound of the thickness of this layer of 3-4 nm. This qualitative idea is supported by a series of calculations based upon a previously developed theoretical model for the indentation of nanoscale spheres into linear viscoelastic materials. Comparing data with simulations shows that this surface layer has properties similar to those of a bulk sample of PS having a temperature of 374 K. Ellipsometric measurements of the T_g are also performed on thin spin-cast PS films with thicknesses in the range 8nm < h < 290nm. Measurements are performed on thin PS films that have been capped by thermally evaporating 5 nm thick metal (Au and Al) capping layers on top of the polymer. The measured T_g values (as well as polymer metal interface structure) in such samples depend on the metal used as the capping layer, and cast doubt on the general validity of using evaporative deposition to cover the free surface. We also prepared films that were capped by a new non-evaporative procedure. These films were shown to have a T_g that is the same as that of bulk PS (370±1 K) for all film thicknesses measured (> 7 nm). The subsequent removal of the metal layer from these films was shown to restore a thickness-dependent T_g in these samples that was essentially the same as that observed for uncapped PS films. An estimate of the thickness of the liquid-like surface layer was also extracted from the ellipsometry measurements and was found to be 5±1 nm. The combined ellipsometry and embedding studies provide strong evidence for the existence of a liquid-like surface layer in thin glassy PS films. They show that the presence of the free surface is an important parameter in determining the existence of T_g reductions in thin PS films.     

Assembly of Gold Nanoparticles on Gold Nanorods Using Functionalized Poly(N‐isopropylacrylamide) as Polymeric “Glue”

A telechelic thermoresponsive polymer, α‐amino‐ω‐thiol‐poly(N‐isopropylacrylamide) (H₂N‐PNiPAM‐SH), is used as the polymeric glue to assemble gold nanoparticles (AuNPs) around gold nanorods (AuNRs) into a satellite structure. Prepared by reversible addition‐fragmentation chain transfer polymerization followed by hydrazinolysis, H₂N‐PNiPAM‐SH is able to interlink the two types of the gold building blocks with the thiol‐end grafting on AuNRs and the amine‐end coordinating on the AuNP surface. The density of the grafted AuNPs on AuNRs can be tuned by adjusting the molar ratio between AuNPs and AuNRs in the feed. The resulted satellite‐like assembly exhibits unique optical property that was responsive to temperature change.