纳米材料对阔叶纤维素包装膜性能影响的研究

采用NMMO法,以阔叶纤维素为原料制备纤维素膜,通过向铸膜液中添加经硅烷偶联剂KH-550改性的纳米SiO2,钛酸酯偶联剂改性的CaCO3以及载银TiO2材料制备纳米／纤维素复合膜。对制备纳米／纤维素复合膜微观结构采用原子力显微镜（AFM）和扫描电子显微镜（SEM）进行了表征,并结合力学性能和透氧性能测试分析了纳米材料结构和含量对膜综合性能的影响。结果表明：纳米材料的加入可以改善NMMO法纤维素膜的透氧性能,当改性纳米SiO2、改性纳米CaCO3和载银TiO2添加质量分数分别为2％、1％和1．5％时制备的纤维素纳米复合薄膜的综合性能达到最优。     

不同原料NCC对NCC/PVA复合膜性能的影响

分别以微晶纤维素、脱脂棉和漂白芦苇浆为原料,硫酸水解法制备纳米纤维素(NCC),与聚乙烯醇(PVA)简单共混流延成膜法制备NCC/PVA复合膜.m(NCC)/m总为7％时制备NCC/PVA复合膜,红外光谱分析结果表明复合膜中PVA分子链和NCC分子链间存在能提高两者相容性的氢键缔合作用力;热重分析结果表明复合膜的热稳定性与NCC热稳定性基本一致.扫描电子显微镜分析结果表明m(NCC)/m总为0.5％时制备NCC/PVA复合膜的表面和断面较为规整.3种原料中漂白芦苇浆NCC长径比最高(约为25),且m(NCC)/m总为0.5％时制备NCC/PVA复合膜拉伸强度最大,较PVA膜拉伸强度提高40.8％.3种原料NCC分别制备的3种NCC/PVA复合膜断裂伸长率,均较PVA膜断裂伸长率降低.随着m(NCC)/m总的增加,NCC/PVA复合膜透光率较PVA膜透光率降低;3种原料中微晶纤维素NCC/PVA复合膜透光率较PVA膜透光率降低最小.     

新型纳米纤维素聚砜复合膜的制备及表征

采用L-S浸没沉淀相转化法制备纳米纤维素（NCC）／聚砜（PSF）复合膜材料。考察了NCC添加量及异丙醇凝胶浴浓度（10％、30％、50％,体积分数,下同）对膜结构和性能的影响。通过扫描电子显微镜（SEM）观察了复合膜材料断面和皮层的孔结构,发现随着异丙醇浓度的增加,复合膜中的指状孔由细长贯通、连接紧密逐渐变得短粗、疏...     

热塑性淀粉/NCC纳米复合薄膜的制备及性能

先用硫酸水解微晶纤维素制得纳米纤维素晶体(NCC),再用溶液浇铸成膜法制得甘油塑化热塑性淀粉/NCC纳米复合薄膜,并考查NCC含量对纳米复合薄膜性能的影响.结果表明:当NCC含量小于9%时,拉伸强度和断裂伸长率均随NCC含量增加而增大,热稳定性也增强;当NCC含量增加到12%时,力学性能和热稳定性反而变差.添加不同含量NCC后,纳米复合薄膜的吸水率没有明显改变,透光率有所降低.     

NCC改性海藻酸钠可降解复合膜的制备及性能研究

通过硫酸水解微晶纤维素制备纳米尺寸的纤维素晶体-纳米纤维素(NCC),以NCC为增强体,通过流延法制备了纳米纤维素/海藻酸钠复合膜,采用红外光谱(FT-IR),X射线衍射(XRD)对复合膜的结构进行了表征,研究了复合膜的吸湿性能,阻隔性能,透光率及拉伸性能。结果表明:纳米纤维素可以显著提高膜的力学性能,与纯海藻酸钠膜相比,含量15%NCC使拉伸强度提高了近45%,同时NCC的引入降低了材料的吸湿率。水蒸汽透过性下降了24.9%,有效提高了材料的阻隔性能,红外光谱与XRD分析表明NCC与基体之间存在分子间氢键相互作用,具有较好的相容性。     

不同改性剂对纳米SiO2／NR复合材料结构与力学性能的影响

采用硅烷偶联剂（Si-69、KH-590和KH-550）、钛酸酯偶联剂（NGT-201）和十二烷基硫酸钠作为纳米SiO2的表面改性剂，研究了不同改性剂对纳米SiO2／NR复合材料结构与力学性能的影响。结果表明，所采用的改性剂对纳米SiO2／NR复合材料具有较好的改性效果，其增强了纳米SiO2与天然橡胶的界面作用，改善了...     

乳酸原位聚合改性纳米纤维素的制备及应用

乳酸原位聚合改性纳米纤维,并和聚乳酸制备复合材料。先由64%硫酸水解微晶纤维素(MCC)制备纳米纤维素(NCC),再乳酸原位聚合接枝纳米纤维素得到改性后纳米纤维素(g-NCC),最后将g-NCC按0%~5%质量比与聚乳酸(PLA)共混,制成复合材料g-NCC/PLA。透射电子显微镜观察得到棒状纳米纤维素长度为100~200nm,直径为10~25nm,傅里叶变换红外光谱和核磁共振谱证明乳酸均聚物已接枝到纳米纤维素,复合材料性能分析表明g-NCC与PLA相容性比未改性NCC与PLA相容性好,g-NCC含量为2%时,复合材料拉伸强度可达到45 MPa,比纯PLA提高85%,结晶度提高10%。     

纳米纤维素接枝环氧基的制备与表征EI北大核心CSCD

以微晶纤维素(MCC)为原料,采用酸水解法制备纳米纤维素(NCC),再以N,N-羰基二咪唑(CDI)活化纳米纤维素表面的羟基,最后将其与环氧氯丙烷进行接枝反应,得到接枝环氧基的纳米纤维素(NCC-g-ECH)。采用透射电镜、红外光谱、溶解性、接枝率、X射线衍射对所制得的样品NCC和NCC-g-ECH的结构和性能进行表征。结果表明,实验制得的NCC符合纳米尺寸; NCC-g-ECH的红外图中出现明显的环氧基峰; NCC-g-ECH的接枝率最大达到8. 47%;与NCC相比,样品NCC-g-ECH在丙酮中能均匀、稳定地分散; NCC和NCC-g-ECH均为纤维素Ⅰ晶型,NCC-g-ECH的结晶度比NCC减小8. 59%。     

水热还原法制备Ag@C壳核纳米结构及其表征

以棉花纤维制备的纤维素微晶为碳源,采用水热还原法制备了Ag@C壳核结构纳米颗粒,并用扫描电子显微镜、投射电子显微镜、X射线能谱仪、X射线衍射仪对产品进行表征,结果表明,所得产品为Ag@C核／壳结构纳米颗粒,外壳是碳层,内核为纳米银颗粒。最佳的制备条件是,180％反应15h,pH=1-2,纤维素微晶的浓度为0．083g／L。讨论了碳包银核／壳结构的生长机理,     

纳米纤维素/CdS纳米复合光电材料的制备和性能

以NaClO2为主要氧化剂,使用氧化漂白桉木浆制备C-6位羧基含量为0.8mmol/g的TEMPO氧化纤维素,然后将其剪切为纳米纤维素(NCC)。再以NCC为基材,以无水氯化镉及硫化钠为前驱体,用声化学法制备了NCC/CdS纳米复合光电材料。用X射线衍射(XRD)、场发射扫描电镜(SEM)、傅里叶红外光谱仪(FT-IR)以及光电化学实验对复合材料的结构及性能进行表征。结果表明,大量CdS纳米粒子复合在NCC基材上形成NCC/CdS纳米复合材料,CdS晶粒为立方型晶体,大小为7.3nm。用NCC/CdS纳米复合材料形成的薄膜器件在可见光区域的透光率高达60%。这种复合材料可产生1.35μA的光电流,其光电转换效率为微晶纤维素/CdS复合材料的6倍。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.     

Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.