气相生长纳米碳纤维与聚合物复合材料的性能研究

气相生长纳米碳纤维/聚合物复合材料是一种性能优良的复合材料。与传统的聚合物导电复合材料相比这种材料表现出优良的电学性能,屏蔽效能与热性能。本文首先对气相生长纳米碳纤维的生产、性能做了总体的介绍,然后对影响气相生长纳米碳纤维/聚合物导电复合材料的电学性能、屏蔽效能以及热学性能的因素做了详细的阐述,特别强调了纳米纤维的分散分布程度、填充浓度和纵横比等方面的影响。本文还对熔融聚合、原位聚合和溶液聚合等加工方法对气相生长纳米碳纤维(VGCNF)/聚合物复合材料最终性能的影响进行了综述,着重介绍了影响气相生长纳米碳纤维/聚合物复合材料电学性能的因素,其中最重要的影响因素是加工方法和加工条件。     

气相生长碳纤维的表面改性及表征

用浓硝酸(65%~68%)对气相生长碳纤维(VGCF)进行了不同时间的表面化学改性。X射线衍射(XRD)分析表明：改性使得VGCF的石墨晶型结构改变，其改变的程度随改性时间的延长而加深；BET比表面积(S_BET)测试表明：改性后的VGCF的S_BET有一定的变化，经120 min长时间的改性处理后，S_BET明显降低；傅立叶变换红外光谱(FTIR)测定得出：改性后VGCF表面上生长了不同类型的含氧基团，其总含量随改性时间的增大而增加；程序升温还原(TPR)得出：改性后VGCF表面上生成有2类以上的热稳定性不同的含氧基团，计算求得含氧基团的氧总含量为2 mmol·g^-1以上；NH₃吸附微量量热测定得出：表面酸性基团的强度和含量随改性时间增加而增大；透射电子显微镜(TEM)结果表明：改性没有明显破坏VGCF的外观结构；吸油值(AOV)实验给出：改性后VGCF的AOV显著降低而亲水性增强；双液法接触角测试给出：改性后VGCF的表面能(SE)明显增大；偶联剂与VGCF作用的FTIR研究表明：改性后VGCF表面含氧基团和偶联剂发生反应，增强了偶联剂在VGCF表面上的结合强度。     

Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

Photodiode properties of molecular beam epitaxial InSb on a heavily doped substrate

Photodiodes of InSb were fabricated on an epitaxial layer grown using molecular beam epitaxy (MBE). Thermal cleaning of the InSb (0 0 1) substrate surface, 2° towards the (1 1 1) B plane, was performed to remove the oxide. Photodiode properties of МВЕ-formed epitaxial InSb were demonstrated. Zero-bias resistance area product (R₀A) measurements were taken at 80 K under room temperature background for a pixel size of 100 μm × 100 μm. Values were as high as 4.36 × 10⁴ Ω/cm², and the average value of R₀A was 1.66 × 10⁴ Ω/cm². The peak response was 2.44 (A/W). The epitaxial InSb photodiodes were fabricated using the same process as bulk crystal InSb diodes with the exception of the junction formation method. These values are comparable to the properties of bulk crystal InSb photodiodes.     

加工工艺对气相生长碳纤维填充聚苯乙烯复合体系导电逾渗与动态流变特性的影响

研究了加工工艺对气相生长碳纤维(VGCF)填充聚苯乙烯(PS)复合体系导电逾渗与动态流变特性的影响.结果表明,低转速、短时间混合有利于VGCF形成较为完善的逾渗网络结构,其复合体系逾渗阈值低、导电性能好.使用作者提出的两相模型描述VGCF/PS复合体系的流变特性,发现低转速、短时间(30 r/min、5 min)混合条...     

Polycarbonate Crystallization by Vapor‐Grown Carbon Fiber with and without Magnetic Field

Polycarbonate (PC)/vapor‐grown carbon fiber (VGCF™) composite was prepared through melt compounding. It was unexpectedly found from differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) that the crystallization of PC was substantially accelerated in the presence of the ordered graphite surface of VGCF™. To make an aligned structure of PC crystallization together with the orientation of VGCF™, a magnetic field of 2.4 T was applied to the composite under several temperature profiles. The WAXD pattern revealed that not only dispersed VGCF™ but also matrix PC crystallization was magnetically aligned through the optimization of processes. The evidence for PC crystallization by VGCF™ with and without magnetic force is described.

Optical micrograph (a) and WAXD pattern (b) of PC/VGCF™ (95:5 wt. ratio) composite which was treated under a magnetic field (vertical direction) of 2.4 T under an optimized heating profile.