聚酰亚胺/SiO_2纳米复合抗原子氧气凝胶的合成与性能

以3,3′,4,4′-联苯四酸二酐(sBPDA)和2,2′-二甲基-4,4′-二氨基联苯胺(DMBZ)为聚合单体,八(氨基苯基)聚倍半硅氧烷(OAPS)为交联剂,SiO2纳米粒子为填料,采用超临界二氧化碳干燥工艺制备了一系列聚酰亚胺(PI)/SiO2纳米复合气凝胶(CPIA-SiO2-0~CPIA-SiO2-7)。研究表明:SiO2纳米粒子的引入对PI气凝胶的耐热性能未产生显著的影响。然而,随着SiO2纳米粒子含量的增加,PI气凝胶的孔隙率从89.6%逐渐降低至79.4%,BET表面积也随之从425.5m2/g降低至380.2m2/g,纳米泡孔孔径分布呈现出变宽的趋势。SiO2的引入显著提高了PI气凝胶的抗原子氧侵蚀能力,含量为7%(质量分数,下同)的PI/SiO2复合气凝胶CPIA-SiO2-7的原子氧侵蚀率(2.6%)仅为不含SiO2气凝胶CPIA-SiO2-0的原子氧侵蚀率(12.3%)的1/5左右。     

Mechanically strong, flexible polyimide aerogels cross-linked with aromatic triamine

Polyimide gels are produced by cross-linking anhydride capped polyamic acid oligomers with aromatic triamine in solution and chemically imidizing. The gels are then supercritically dried to form nanoporous polyimide aerogels with densities as low as 0.14 g/cm(3) and surface areas as high as 512 m(2)/g. To understand the effect of the polyimide backbone on properties, aerogels from several combinations of diamine and dianhydride, and formulated oligomer chain length are examined. Formulations made from 2,2'-dimethylbenzidine as the diamine shrink the least but have among the highest compressive modulus. Formulations made using 4,4'-oxydianiline or 2,2'dimethylbenzidine can be fabricated into continuous thin films using a roll to roll casting process. The films are flexible enough to be rolled or folded back on themselves and recover completely without cracking or flaking, and have tensile strengths of 4-9 MPa. Finally, the highest onset of decomposition (above 600 °C) of the polyimide aerogels was obtained using p-phenylene diamine as the backbone diamine with either dianhydride studied. All of the aerogels are suitable candidates for high-temperature insulation with glass transition temperatures ranging from 270-340 °C and onsets of decomposition from 460-610 °C.     

碳纳米纤维增强聚酰亚胺复合气凝胶的合成与性能EI北大核心CSCD

以4,4′-二氨基二苯醚(ODA)、均苯四甲酸二酐(PMDA)为单体,酸化碳纳米纤维(a-CNF)为增强材料,采用溶胶-凝胶方式成型,运用冷冻干燥技术制备PI复合气凝胶。对复合气凝胶的形貌、隔热、吸波以及压缩性能等进行表征分析。研究结果表明:随着a-CNF含量的增加,PI复合气凝胶的收缩率从45.52%降至35.32%,密度也随之从0.084 g/cm^(3)降至0.069 g/cm^(3),气凝胶孔洞分布呈增大增宽趋势。a-CNF的引入有效抑制了PI复合气凝胶的收缩率,热导率降低;整个体系的导电损耗增加,同时由于气凝胶的多孔结构提供了较好的阻抗匹配,使得PI复合气凝胶的反射损耗(RL)在8.3 GHz达到-9.7 dB。加入质量分数为15%的CNF/PI复合气凝胶压缩强度和压缩模量分别是纯PI气凝胶的近1.5倍和2倍。     

Thin polymer films from polyimide vacuum thermal degradation with and without a glow discharge

Polyimide-like thin films were deposited by thermal degradation of polyimide with and without simultaneous activation by a glow discharge excited using an r.f. planar magnetron. The films deposited without discharge are similar in composition to conventional polyimide, whereas the deposition with plasma results in cross-linked coatings with composition typical for plasma polymers e.g. prepared by r.f. sputtering of polyimide. AFM reveals rough surface topography for the films evaporated without plasma. The application of plasma leads to very smooth plasma polymer films.     

交联透明质酸凝胶薄膜的制备及性能研究

用三偏磷酸钠(STMP)对透明质酸(HA)进行交联,制备出HA-STMP凝胶薄膜,研究了不同交联程度HA-STMP薄膜的吸水保水性能和体外降解性能。研究结果表明,实验中控制STMP与HA的结构单元比在1/5以上都可以得到成膜性能良好的交联薄膜;HA-STMP交联薄膜可以吸附自身质量7～10倍的水分,且随着交联程度的提高,薄膜的吸水能力下降,保水性能提高;交联改性能改善HA的耐降解性能,使高聚物在体内的存留时间延长,且耐降解性能随交联程度的增加而提高。     

Synthesis and characterization of functional ladder-like polysilsesquioxane and their hybrid films with polyimide

Ladder-like polyphenylsilsesquioxane has been synthesized by a convenient two-step approach and then modified to ladder-like poly(nitrophenyl)silsesquioxane (LPNPSQ) and poly(aminophenyl)silsesquioxane (LPAPSQ) by nitration and reduction reaction. These ladder-like polysilsesquioxanes (LPSQs) were characterized by Fourier transform infrared, nuclear magnetic resonance and X-ray diffraction (XRD). The results confirm the ladder-like structures of LPSQs and suggest the decrease of regularity after the chemical modification. Then high performance polyimide/ladder-like polysilsesquioxane (PI/LPSQ) hybrid films have been prepared by incorporating synthetic LPSQs with different functional groups into PI matrix, respectively, using conventional techniques. The interfacial interactions between PI matrix and LPSQ were investigated with XRD and scanning electron microscopy. Then the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that different functional groups in LPSQs have great effects on the interfacial interactions and the properties of the hybrids. Both LPNPSQ and LPAPSQ can be dispersed uniformly in PI matrix because of the physical or chemical interaction between functional groups and PI. With these strong interfacial interactions, PI/LPNPSQ and PI/LPAPSQ hybrid films show higher glass transition temperatures and better mechanical properties.     

聚(3-羟基丁酸酯-co-4-羟基丁酸酯)/POSS共混体系的性能

采用熔融模压法分别制备了聚(3-羟基丁酸酯-co-4-羟基丁酸酯)[P(3HB-co-4HB)]和两种多面体笼型硅氧烷(POSS)[八异丁基倍半硅氧烷(OIBS)和八氨基苯基倍半硅氧烷(OAPS)]的共混物,考察了不同含量的OIBS,OAPS对共混体系性能的影响。结果表明,两种POSS都起到成核剂的作用。OIBS,OAPS的质量分数小于1%时,可以提高体系结晶温度,力学性能;随着OIBS,OAPS质量分数的提高,成核性有所增加,但因分散性变差,体系热稳定性和力学性能变差。由于OAPS的活泼氨基可与P(3HB-co-4HB)发生化学反应,改性效果较OIBS优。     

海藻酸盐基纳米复合气凝胶的制备与性能研究

以海藻酸铵(ALG)、纳米氢氧化铝(ATH)和纳米蒙脱土(MMT)为原料,采用溶液共混法和真空冷冻干燥法制备了海藻酸盐基纳米复合气凝胶。采用扫描电子显微镜、傅里叶红外光谱仪、电子万能实验机、X射线衍射仪、热重分析仪对气凝胶进行了形貌、结构表征,并分析了其力学性能和热稳定性能。结果表明:采用ALG和MMT制备的气凝胶具有典型的三维骨架网络结构,交联反应不影响气凝胶的形貌;气凝胶具有较低的密度和较好的力学性能,密度低至0.12 g/cm³,压缩模量最高可达9.48 MPa;Ca²⁺交联和MMT的加入显著提高了气凝胶的热稳定性,A5MMT5Ca气凝胶的耐热温度高达205℃。     

聚合物气凝胶研究进展

气凝胶是经溶胶-凝胶过程结合一定的干燥方法制备得到的多孔纳米材料。聚合物气凝胶不仅具有聚合物材料的低介电常数、良好力学性能和灵活的分子设计性等特性,同时还具有无机气凝胶材料低密度、高孔隙率和低热导率等特点,被广泛应用于隔热、吸附和储能等领域。从合成、结构、性能和应用等方面介绍了聚氨酯(PU)、聚脲(PUA)、聚酰亚胺(PI)、聚苯并噁嗪(PBZ)和间规聚苯乙烯(sPS)类等常见聚合物气凝胶的研究进展,并对其未来的发展方向做出了展望。     

High transparent polyimide/titania multi-layer anti-reflective hybrid films

In this study, polyimide-titania hybrid thin films (6FDA-6FpDA-4ABA/TiO₂, PIT) were prepared from soluble fluorine-containing polyimide and titanium butoxide. The soluble polyimide with carboxylic acid terminal groups (6FDA-6FpDA-4ABA-COOH) was synthesized from the precursor s 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA), and 4-aminobenzoic acid (4ABA). Such end groups undergo a condensation reaction with titanium butoxide to provide organic-inorganic bonding and thus prevent macrophase separation. The titania content in the hybrid films was varied from 0 to 90 wt.% (PIT0-PIT90). The effects of TiO₂ content on the hybrid film properties and the optimum operating conditions were also investigated. TGA and DSC analysis showed that the decomposition temperature of polyimide was about 468 °C. T_d increased as the titania content in hybrid thin films increased. HRTEMM and XRD results indicated the formation of nanocrystalline-titania domains of around 4-11 nm in the hybrid films. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. FTIR spectra indicated that the amidization was complete and that a cross-linked Ti-O-Ti network had formed. UV-vis and n&k analysis showed that the prepared hybrid films had high refractive index (1.931) and good optical properties. Moreover, the prepared polyimide/titania hybrid thin films were further applied to develop a three layer antireflective (AR) coating on glass and PMMA substrates. The results showed that the average reflectance of the AR coating on the glass and PMMA substrates was 0.5% and 0.8%, respectively. The transparency at 550 nm was greater than 90% for both AR coatings.     

Synthesis and characterization of porous silsesquioxane dielectric films

The silsesquioxane (SSQ) films with low dielectric constant have been successfully synthesized by covalently binding a thermally decomposable porogen [poly(amidoamine), PAMAM] to a host polymer (hydrogen methyl silsesquioxane, HMSQ) via a coupling agent. The decomposition behavior of the porogen as well as the thermal and dielectric properties of the host polymer heat-treated in different atmospheres have been studied and compared. The dielectric properties of the HMSQ-PAMAM porous films have been investigated as a function of porogen concentration. An average dielectric constant about 2.06 could be obtained with leakage current density on the order of 10^-7 A/cm² for a film with 20-wt.% loading of the PAMAM polymer.     

粒子型块状TiO_2气凝胶的制备与表征

以钛酸丁酯为原料,采用溶胶-凝胶法和超临界干燥,成功制备了酸催化的粒子型块状TiO2气凝胶,并用BET、TEM、SEM、IR等仪器对其结构性能进行了表征。结果表明,该气凝胶具有较高的比表面积(713.9m2/g)和较低的密度(最低为35mg/cm3),网络分布不均匀,孔径较小,孔径分布主要集中在10～25nm。红外光谱表明,该气凝胶是由钛的羟基氧化物组成,不存在碳氧键。     

Effect of the drying conditions on the microstructure of silica based xerogels and aerogels

Nanostructured silica based xerogels and aerogels are prepared by sol-gel technology, using methyltrimethoxysilane as precursor. The influence of the drying method and conditions on the microstructure of the obtained materials is investigated, since the drying stage has a critical influence on their porosity. Two types of drying methods were used: atmospheric pressure drying (evaporative), to produce xerogels, and supercritical fluids drying, to obtain aerogels. Although the supercritical fluids drying technique is more expensive and hazardous than the atmospheric pressure drying, it is well known that aerogels are less dense than the xerogels due to less pore shrinkage. However, the ideal situation would be to use atmospheric pressure drying in conditions that minimize the pore collapse. Therefore, in this work, different temperature cycles for atmospheric pressure drying and two heating rates for the supercritical fluids drying are tested to study the gels' shrinkage by analyzing the density and porosity properties of the final materials. The best materials obtained are aerogels dried with the lower heating rate (approximately 80 degrees C/h), since they exhibit very low bulk density (approximately 50 kg/m3), high porosity (95%)-mainly micro and mesopores, high surface area (approximately 500 m2/g), moderate flexibility and a remarkable hydrophobic character (>140 degrees). It was proved that the temperature cycles of atmospheric pressure drying can be tuned to obtain xerogels with properties comparable to those of aerogels, having a bulk density only approximately15 kg/m3 higher. All the synthesized materials fulfill the requirements for application as insulators in Space environments.     

Synthesis and characterization of cross-linked silicone thin films by pulsed laser ablation deposition (PLAD)

Stable, uniform and cross-linked silicone films have been synthesized by pulsed laser ablation deposition (PLAD) for the first time. A KrF excimer (248 nm) laser was used in the synthesis. The effect of incident energy density on the deposited film chemistry was examined in depth. The surface analysis showed that at low energy densities (100–150 mJ/cm²), smooth, hydrophobic films similar in structure to the starting cross-linked silicone elastomer were obtained. Beyond 200 mJ/cm², hydrophilic films with oxygen contents much higher than the starting polymer were obtained. These films also exhibited a more particulate texture suggesting ablation of particles and/or polymeric clusters from the silicone target. The results demonstrate that the PLAD process may prove valuable for the preparation of cross-linked silicone thin films with tailored properties. Received: 27 June 2001 / Accepted: 17 July 2001     

(3-Glycidoxypropyl)-terminated silsesquioxane impact on nanomechanical properties of polyimide coatings exposed to atomic oxygen

Based on (3-glycidoxypropyl)silsesquioxane (GSSO) derived from the hydrolytic condensation of (3-glycidoxypropyl)trimethoxysilane (GPMS), GSSO-containing polyimide hybrid films were prepared using the sol-gel process and spin coating. Nanoindentation tests were carried out to study the influence of GPMS in the hybrid films on nanomechanical properties before and after exposure to atomic oxygen (AO) environments. The results show that hybrid films are three to four times harder than the usual plastic substrates. Compared with the unexposed AO samples, the elastic modulus (E) and the hardness (H) of the pristine Kapton AO-exposed samples significantly decreased, whereas the hardness of AO-exposed hybrid films increased slightly. This difference in nanomechanical properties is attributed to the chemical and the microstructural sample changes.     

Influence of various processing parameters on water-glass-based atmospheric pressure dried aerogels for liquid marble purpose

Experimental results on the influence of various processing parameters on water-glass-based atmospheric pressure dried aerogels for liquid marble purpose are reported. Silica aerogels were prepared by varying the parameters namely washing temperature of the gels with water, washing period of the gels, protic solvents, and drying method. The physical properties of silica aerogels were studied by measuring granular bulk density, contact angle with water, thermal conductivity, and thermal stability in the furnace. The elemental analyses were carried out using Atomic Absorption Spectroscopy (AAS) and FT-Raman spectroscopy. The structural studies were carried out using Transmission Electron Microscopy (TEM). Also, the effect of humidity on the silica aerogels was studied in humidity chamber. Opaque silica aerogels with hydrophobicity (150°), low density (0.053 g/cm³), and low thermal conductivity (0.068 W/mK) have been obtained for the molar ratio of Na₂SiO₃: H₂O: citric acid: TMCS at 1:146.67:0.72:9.46. The hydrophobic powder of silica aerogels can form the liquid marbles.     

Characterization of ZnO：Al Films Deposited on Organic Substrate by r.f. Magnetron Sputtering

Transparent conducting Al-doped zinc oxide (ZnO:AI) films with good adhesion have been deposited on polyimide thin film substrates by r.f. magnetron sputtering technique at low substrate temperature (25-180℃). The structural, optical and electrical properties of the deposited films were investigated. High quality films with electrical resistivity as low as 8.5×10-4 Ω·cm and the average transmittance over 74% in the wavelength range of the visible spectrum have been obtained. The electron carrier concentrations are in the range from 2.9×1020 to 7.1×1020 cm-3 with mobilities from 4 to 8.8 cm2 V-1s-1. The densities of the films are in the range from 4.58 to 5.16 g/cm-3.     

Poly(dimethylsiloxane)-polyimide blends in the formation of thick polyimide films

Thick polyimide layers can be formed by using some unique properties of poly(dimethylsiloxane)-polyimide (PDMS/PMDA–ODA) blends followed by surface modification and deposition of a second layer of polyimide precursor chemicals. The method is based on the micro-phase separation characteristics of these blends to yield surfaces that have PDMS-like character. Upon modification with UV/ozone treatment, a surface that is essentially SiO _x and hydrophilic in nature is produced. This surface is amenable to reaction and deposition of a second polyimide layer from polyimide precursors. The thicker polyimide layer has enhanced adhesion between the original layer of the blend and the new polyimide layer and this approach finds extensive applications for products that require thick polymer layers. Changes in surface energy for various blend compositions were monitored by measurement of advancing contact angle with de-ionized water. Contact angle for unmodified polyimide films was on the order of 70° and it increased to about 104° after blending with PDMS and curing. UV/ozone treatment reduced the contact angle of the doped polyimide to less than 5°. X-ray photoelectron spectroscopy (XPS) and angle resolved XPS (ARXPS) measurements were used to monitor the chemical compositions of the various surfaces. High-resolution XPS spectra in the Si2p region confirm the transformation of O–Si–C bonds in PDMS to SiO _x , where x is about 2. Scanning electron microscopy (SEM) of some selected samples shows that the blends contain phase separation of the polymers at the surfaces of the samples. Atomic force microscopy (AFM) of siloxane-free polyimide, and PDMS/PMDA–ODA blends both prior to and after UV/ozone exposure, show that the films are essentially flat at short treatment times (less than 60 min). AFM also reveals the separation of PDMS into micro-domains at the cured film surface and throughout the layer below the surface of the blended films. Adhesion of a subsequently deposited polyimide layer to the modified polyimide surface was found to be greatly improved when compared to the adhesion obtained for deposition onto a pristine polyimide surface.     

A characterization of Kapton polyimide by X-ray photoelectron spectroscopy and energy dispersive spectroscopy

Kapton polyimide films were characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). The samples characterized include Kapton-H and Kapton-HN. The XPS data suggest that the Kapton films are mainly poly(4,4-oxydiphenylene pyromellitimide). The Kapton-HN films were found to have imbedded particles which were identified by EDS to contain calcium and phosphorus. These films also give solid residues of approximately 0.4 wt% after the films were heated to 800° C in air.Mound is operated by Monsanto Research Corporation for the US Department of Energy under Contract Number DE-AC04-76DP00053.     

常压制备低孔径高比表面积疏水SiO2气凝胶

以正硅酸乙酯为先驱体,丙三醇为干燥控制化学添加剂(DCCA),通过酸碱两步溶胶-凝胶法制备了二氧化硅气凝胶,同时利用六甲基二硅氮烷(HMDZ)和正己烷的混合液对湿凝胶进行表面疏水改性。测试分析了所制备气凝胶的密度、疏水性、比表面积和形貌。结果表明,经过表面改性的SiO2气凝胶具有良好疏水性,与水的接触角约为139.4°,比表面积为952m2/g,平均孔径为5～10nm,孔隙率达94.2%,且其密度仅为0.127g/cm3。