CdS空心微球的制备与表征

以不同粒径的苯乙烯-丙稀酸(酯)共聚物(PSA)乳胶粒为模板,制备出均匀的PSA/CdS核壳复合结构的微球,用有机溶剂溶去模板PSA后,分别制备了不同粒径的CdS空心微球.透射电镜分析结果表明,以直径250、340和600nm的PSA乳胶粒为模板,所得CdS空心球的粒径均匀,直径分别为340、450和800nm.紫外可见吸收光谱显示3个CdS空心球样品的最大吸收分别为480nm、410nm和485nm.     

苯乙烯-马来酸酐共聚物/氧化锌纳米粒子合成与表征

以N,N-二甲基甲酰胺为溶剂,乙酸锌为前驱物,苯乙烯-马来酸酐共聚物为大分子稳定剂,采用溶液化学法,制备了氧化锌纳米粒子。通过紫外-可见吸收光谱(UV-Vis)、荧光光谱(PL)、透射电子显微镜(TEM)等方法对合成的ZnO纳米粒子样品进行表征。结果表明,所合成样品具有量子尺寸效应,样品UV-Vis吸收光谱在350nm给出氧化锌纳米粒子的特征吸收峰,样品PL光谱显示在410nm处可产生明显的荧光发射。氧化锌纳米粒子的尺寸在50~100nm且粒径分布较窄,表明苯乙烯-马来酸酐共聚物对氧化锌纳米粒子的表面起到了良好稳定作用。     

普通乳液聚合法制备丙-苯纳米核壳乳液

文中通过预乳化-半连续的加料工艺制备出了以聚丙烯酸丁酯为核,聚苯乙烯-甲基丙烯酸甲酯为壳的丙-苯纳米核壳乳液,分析了这种乳液聚合的方法制备纳米乳液的机理。通过粒度分布仪测定的乳胶粒的粒径分布为93.4 nm～95.6 nm,分布很窄,乳胶粒的平均粒径为94.5 nm;通过透射电境(TEM)对乳液进行观察,所制的丙-苯纳米乳胶粒具有明显的正向核壳结构,实验证明这种核壳结构是稳定的。     

大粒径自消光核-壳丙烯酸树脂涂饰剂的合成与表征

以半连续投料法,通过种子乳液聚合-三次连续核长大-壳聚合的方式制备了具有核-壳结构、大粒径自消光丙烯酸树脂乳液。研究了不同投料方式对种子乳胶粒粒径的影响,探索了乳胶粒粒径连续长大的方法,同时还研究了乳胶粒粒径、乳胶粒的核-壳结构以及交联度等因素对丙烯酸树脂涂层消光性能的影响。结果表明,半连续法投料方式能够得到较大粒径的种子乳胶粒,控制乳化剂浓度和单体浓度使得种子乳液聚合遵循低聚物成核机理,并且反应中乳胶粒长大占据主导,从而得到大粒径的种子乳胶粒(200 nm左右)。种子乳胶粒经过3次长大后,粒径可达到700 nm左右,最后经过壳聚合反应,核-壳乳胶粒粒径进一步增大至800 nm左右。不同乳胶粒粒径、核-壳结构、交联度对涂层光泽产生重要影响,大的乳胶粒粒径使得涂层产生球形粒子状微粗糙表面,涂层光泽度降低;软核-硬壳结构导致成膜时乳胶粒变形困难,也可提高涂层表面粗糙度和消光度;壳层交联使得壳层结构致密度上升,自由度降低,乳胶粒难以变形和融合,涂层粗糙度进一步提高,光泽度进一步降低,最终所制备的皮革涂层光泽度可调控至1.2°。     

核壳型交联丙烯酸酯共聚物的合成及表征

采用种子乳液共聚方法合成了以BA、2-EHA为核层共聚单体。St、MMA为壳层共聚单体,1,4-丁二醇二丙烯酸酯为核壳层交联荆的共聚物(ACR)。借助动态光散射粒径分析仪、DSC、TEM分别考察了乳胶粒的粒径及其分布、共聚物玻璃化转变温度以及乳胶粒的微观形态结构。实验结果表明,共聚物具有明显的三个玻璃化转变温度(Tg),分别对应ACR的核层、接枝过渡层、壳层的Tg,且ACR乳胶粒呈现规整的核壳结构。当壳层苯乙烯含量大于70％时,所合成的乳胶粒结构表现明显的异常核壳形态(夹心形)。     

水性氟碳涂料的制备及其性能

核壳型氟代聚丙烯酸酯乳液、丙烯酸树脂、纳米粒子构成的氟碳涂料所得涂层具有优良的自清洁性能,过去对其研究不够。以过硫酸铵为引发剂,阴/非离子表面活性剂为复合乳化剂,采用半连续种子乳液共聚法,将丙烯酸丁酯(BA)、苯乙烯(ST)及γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MPMS)与甲基丙烯酸十二氟庚酯(DFMA)于水相中制备了一种核壳型含氟硅聚丙烯酸酯乳液,与丙烯酸树脂、纳米TiO2等制备了氟碳涂料。利用红外光谱(IR)和透射电镜(TEM)对乳液主组分结构、乳胶粒形貌及粒径大小进行了表征和分析,考察了固化温度、乳液用量对涂层性能的影响。结果表明:合成乳液的乳胶粒呈规则球状,具有核壳结构,平均粒径约为100 nm;当乳液用量为45 g、固化温度为160℃时,所得涂层性能最佳,与水的接触角达133°,具有较好的自清洁性。     

聚醋酸乙烯酯反向核壳结构乳胶粒制备及形成机制

以马来酸酐(MA)作为接枝共聚单体,亲水性的聚醋酸乙烯酯(PVAc)为核,疏水性的聚苯乙烯(PSt)为壳,成功构建出一种新颖的PVAc-MA/PSt反向异形核壳结构乳胶粒,从而解决了因竞聚率差异大而无法实现醋酸乙烯酯(VAc)与苯乙烯(St)复合的难题。同时,利用接枝共聚所形成的过渡层,能够很好地抑制核壳翻转,从而成功地解决了反向核壳结构乳胶粒容易发生核壳翻转的问题。所制备出的反向核壳结构乳胶粒子平均粒径为330 nm左右,粒径大小均一。通过热力学分析发现所制备的乳胶粒呈明显的相分离结构,且存在PVAc-MA-PSt过渡层结构;乳胶粒的形貌随着MA含量的变化发生明显的衍变趋势,且粒子形貌变化可控。提出了PVAc-MA/PSt反向核壳乳胶粒子的形成机制。     

聚苯乙烯-银胶体晶体的制备及自组装行为

利用冠醚可与银离子复合的特性,制备了聚苯乙烯-冠醚乳胶粒,采用原位还原的方法在乳胶粒表面引入银纳米颗粒,通过垂直沉降,乳胶粒子可自组装成紧密堆积具有面心立方的聚苯乙烯-银胶体晶体。结果表明:引入聚苯乙烯-银乳胶粒表面的银为胶粒总质量的6.7%,乳胶粒具有以银纳米颗粒为壳,聚苯乙烯为核的核壳结构,乳胶粒大小为260 nm,并具有很好的单分散性。由于Bragg散射,该胶体晶带隙位于580 nm,在可见光区域产生明显的光子带隙而呈现出亮丽的绿色。     

核壳结构PB-g-(SAN-co-Si)抗冲改性剂的合成与表征

采用种子乳液聚合法,在聚丁二烯(PB)乳液接枝苯乙烯-丙烯腈(SAN)的同时,加入γ-(甲基丙烯酰氧基)丙基三甲氧基硅烷(KH-570),制备了带有缩合反应活性基团的聚丁二烯接枝(苯乙烯-丙烯腈-有机硅)共聚物(PB-g-(SAN-co-Si)大分子改性剂。采用透射电镜(TEM)、傅立叶变换红外光谱(FT-IR)和SAN接枝率测定等方法对产物进行了表征。TEM显示乳胶粒具有典型的核壳结构,粒径为300nm,乳胶粒外分布有KH-570水解缩合形成的纳米硅粒子。FT-IR分析证实KH-570通过化学键接枝到PB链上。除通过自由基聚合外,SAN的接枝还可通过KH-570之间的水解缩合方式进行,KH-570的引入大幅度提高了接枝效率。     

细乳液法合成单核核壳结构氧化硅/聚苯乙烯复合微球

采用细乳液聚合法,以3-甲基丙烯酰氧基丙基三甲氧基硅烷(KH570)表面改性的直径50nm的氧化硅粒子为核,在乳化剂、助乳化剂、引发剂存在的情况下制备了小粒径、单核核壳结构氧化硅/聚苯乙烯纳米复合微球.研究表明,苯乙烯的浓度、超声细乳化时间,是制备这种小粒径、单分散、单核核壳结构的氧化硅/聚苯乙烯纳米复合微球的关键因素.透射电镜(TEM)的观察显示,在优化的实验条件下,可以制得平均粒径95nm,壳厚20nm,粒径均一、球形规整度较好、单核核壳结构的氧化硅/聚苯乙烯纳米复合微球.其平均粒径远低于用其它聚合方法制备的复合微球.     

Photoluminescence study of PVP capped CdS nanoparticles embedded in PVA matrix

Photoluminescence properties of polyvinyl pyrrolidone (PVP) capped cadmium sulphide (CdS) nanoparticles embedded in polyvinyl alcohol matrix (PVA) are reported. The PVP-CdS nanoparticles are prepared by non-aqueous method wherein cadmium nitrate is used as the cadmium source and hydrogen sulphide as the sulphur source. The synthesized nanoparticles are dispersed in polyvinyl alcohol (PVA) matrix and cast as self-standing flexible (PVP-CdS)-PVA films. The nanocomposites are characterized by optical absorption spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. XRD and TEM studies show the formation of cubic CdS particles with average size ∼3-5 nm. Thermal studies, carried out to observe the changes in PVA matrix due to the incorporation of PVP-CdS nanoparticles show strong interaction between the polymer matrix and nanoparticles. The photoluminescence emission spectra of the nanocomposites show two peaks, at 502 and 636 nm, which are attributed to the band edge and surface defects respectively, of CdS nanoparticles. Effective surface capping with optimum concentration of polyvinyl pyrrolidone leads to the quenching of surface defect-related emission.     

Synthesis, characterization and fluorescence property of CdS/P(N-iPAAm) nanocomposites

A novel nanocomposite in which CdS nanoparticles were embedded in poly(N-isopropylacrylamide) (P(N-iPAAm)) matrix have been fabricated. The particle size of CdS nanoparticles ranged from 10 nm to 40 nm could be adjusted with the varying of the inorganic contents. The nanocomposites have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermo-gravimetric analysis (TGA), high resolution transmission electron microscope (HRTEM), UV-vis absorption and fluorescence spectra (FLS) measurements. The cell volume of CdS nanoparticles embedded in polymer matrix was smaller than the standard value and the nanocomposites with 12.0% inorganic content showed a good fluorescence property.     

NiO包覆Ni纳米颗粒的制备及其氧化特性研究

通过对直流电弧等离子体制备的Ni纳米颗粒钝化处理得到NiO包覆Ni纳米颗粒。并对试样的组成成分、形貌、晶体结构、粒度和氧化特性采用高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、透射电子显微镜(TEM)和选区电子衍射(SAED)、热重和差示扫描量热分析仪(TGA/DSC)等手段进行分析。结果表明:经过表面钝化处理的NiO包覆Ni纳米颗粒具有明显的核-壳结构,内核为纳米Ni,外壳为NiO氧化物。颗粒呈球形,粒度均匀,分散性良好,粒径分布在20~70nm范围内,平均粒径为44nm,壳层氧化膜的厚度为5~8nm。壳核结构防止了纳米Ni颗粒的进一步氧化和团聚。     

Effect of Cr-doping on the structural and optical properties of CdS nanoparticles prepared by chemical precipitation method

Undoped and Cr doped CdS nanoparticles have been prepared by chemical precipitation method. X-ray diffraction analysis reveals that the undoped and Cr doped CdS nanoparticles exhibit hexagonal structure and the average particle size of the nanoparticles is in the range of 2.2–3.8 nm. The HRTEM studies show that the average particle size of undoped and Cr doped CdS nanoparticles is in the range of 2–3.7 nm. The compositional analysis results indicates that Cd, S and Cr are present in the samples. From the optical studies it is observed that the absorption edge of the prepared CdS and Cr doped CdS nanoparticles are shifted towards the shorter wavelength region (blue shift) when compared to that of bulk CdS and this shift is due to the quantum confinement effect present in the samples.     

过硫酸铵改性炭黑通过胶乳混合法补强天然橡胶胶乳

用过硫酸铵水溶液改性炭黑,制备亲水性的炭黑悬浮液。通过红外光谱仪和热失重表征改性后炭黑表面含氧基团的变化。利用激光粒度分析仪、紫外可见分光光度计观察炭黑水溶液的分散性和分散稳定性,改性前后粒径由155.7nm降到114.2 nm。采用胶乳共混法制备改性炭黑/天然橡胶胶乳复合材料的性能明显增强,拉伸强度提高14.5%,撕裂强度提高56.5%。通过扫描电镜(SEM)观察发现,改性后的炭黑在橡胶基体中粒径小且分散均匀,与基体的界面结合力增强,炭黑的补强效果得到提高。     

Temperature dependent luminescence of azobenzene capped CdS quantum dots

Cadmium sulfide (CdS) quantum dots (QDs) are prepared at room temperature by "form-fill-seal" method, while the azobenzene is used as surfactant to control the particle size and to prevent agglomeration. The typical size of CdS nanoparticles is estimated as 2 nm by X-ray diffraction. The absorption spectra of CdS QDs are measured at room temperature and a new absorption peak associated with the surface excited state is found. The luminescence property of the CdS QDs is studied at room temperature and low temperature. Two photoluminescence peaks exist in the temperature range of 8-300 K. One peak at 460 nm is attributed to CdS QDs, while the other one at 667 nm comes from the transition of surface excited state and its intensity decreases with temperature increasing.     

Two-photon absorption and degenerate four-wave mixing studies of sulfide semiconductor nanoparticles in polymeric solutions

The two-photon absorption coefficients (beta) and the third-order nonlinear susceptibilities (chi(3)) of several semiconductor nanoparticles (CdS, Cd(x)Ag(1-x)S, and core-shell CdS/Ag2S) that are confined and stabilized by random and block ionomers have been measured by nonlinear transmission and degenerate four-wave mixing techniques using 21 picosecond laser pulses at near-infrared spectral region. The imaginary part of the third-order nonlinear susceptibility that is related to the two-photon absorption coefficient was then calculated. The absorptive nonlinearity of the nanoparticles (2 approximately 9 nm) was found to be dependent on the particle size, composition and wavelength, i.e., larger CdS particles exhibit higher two-photon absorption coefficients and the presence of Ag improves two-photon absorption of CdS nanoparticles. The obtained two-photon absorption coefficients of nanoparticles corrected for their volume fraction in solution are significantly greater that those of corresponding bulk semiconductors.     

Synthesis and photocatalytic property of metal@SnO2 core-shell structure nanocomposites

A simple soft-chemical technique for processing of metal@SnO2 nanocomposites with core-shell morphology is reported. In the present technique metal nanoparticles are prepared by chemical reduction technique followed by deposition of tin dioxide. Thus a core-shell type structure is produced. The phase and morphology has been investigated by X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). As prepared Au@SnO2 and Ag@SnO2 core-shell nanocomposites have shown distinct surface Plasmon band in the UV-visible spectrum at 540 nm and 400 nm respectively. The core-shell morphology is confirmed from the TEM images. XRD patterns have suggested the presence of noble metal and tin dioxide in the Cassiterite form. These metal@SnO2 nanocomposites have been successfully used for the photocatalytic oxidation of acetaldehyde. Our investigations suggest that presence of noble metal core in contact with tin dioxide shell enhances the photocatalytic activity of the material.     

Structural and optical characterization of Ni-doped CdS quantum dots

Ni-doped CdS quantum dots have been prepared by chemical precipitation technique. The X-diffraction results indicated that the particle size of Ni-doped CdS nanoparticles is smaller than that of undoped CdS and no secondary phase was observed. The average grain size of the nanoparticles is found to lie in the range of 2.7–4 nm. The compositional analysis results show that Cd, Ni, and S are present in the samples. HRTEM studies reveal that the average particle size of undoped and Ni-doped CdS quantum dots is 2 and 3 nm, respectively. Raman spectra shows that 1LO, 2LO, and 3LO peaks of the Ni-doped CdS samples are slightly red shifted when compared to that of undoped CdS. The absorption edge of Ni-doped CdS nanoparticles is found to shift towards the higher-wavelength (red shift) side when compared to that of undoped CdS and the band gap is observed to lie in the range of 3.79–3.95 eV. This band gap is higher than that of the bulk CdS and is due to quantum confinement effect present in CdS nanoparticles.