Preparation and characterization of AgSt/AgC1 composite grains

AgSt/AgC1 composite gains were prepared by adding chloride ions to a mixed solvent in which silver stearate （AgSt） grains were dispersed under the condition of controlled pH value and characterized by SEM, XRD, UV and DSC. The results showed that AgSt/AgC1 composite grains were composed of plateqike AgSt grains with small face-centered cubic AgC1 particles formed on the surface of AgSt. UV spectra displayed a red shift of absorption for AgSt/AgC1 relative to pure AgSt or AgC1. DSC showed a new thermal phase transition of AgSt/AgC1 grains.     

新型2-巯基苯并咪唑银/硬脂酸银(AgMBM/AgSt)的制备、表征及其在PTG材料中的成像性能研究

分别以硬脂酸银(AgSt)为本体、2-巯基苯并咪唑(MBM)为修饰剂,合成了一种新型的2-巯基苯并咪唑银/硬脂酸银(AgMBM/AgSt)复合结构颗粒.利用红外光谱仪(FTIR)、透射电子显微镜(TEM)、X射线衍射仪(XRD)以及热重-差示扫描量热仪(TG-DSC)对复合颗粒的微观结构、形貌、晶型以及热相变行为进行了表征,研究了AgMBM/AgSt作为光敏热成像(PTG)材料银源时的成像性能.结果表明,AgMBM/AgSt由本体AgSt以及其表面负载的AgMBM小颗粒构成.与本体AgSt相比,AgMBM/AgSt在80℃附近出现新的热相变峰,其热分解温度也有所降低.当AgMBM/AgSt为银源时,PTG材料的热显影密度显著增加,而灰雾仍然保持较低水平.     

Preparation and characterization of AgSt/AgCl composite grains

AgSt/AgCl composite grains were prepared by adding chloride ions to a mixed solvent in which silver stearate (AgSt) grains were dispersed under the condition of controlled pH value and characterized by SEM,XRD,UV and DSC.The results showed that AgSt/AgCl composite grains were composed of plate-like AgSt grains with small face-centered cubic AgCl particles formed on the surface of AgSt.UV spectra displayed a red shift of absorption for AgSt/AgCl relative to pure AgSt or AgCl.DSC showed a new thermal phase transition of AgSt/AgCl grains.     

AgSt/AgBr复合物的制备及其热行为研究

分别以溴化钠(NaBr)为溴源、硬脂酸银(AgSt)为底物,用原位法合成了复合物AgSt/AgBr.利用红外光谱(FTIR)、扫描电子显微镜(SEM)、X射线衍射(XRD)与热重-差示扫描量热(TG-DSC)技术对复合物的结构、尺寸、形貌、晶型以及热行为进行了表征.结果表明,1)复合物由底物AgSt与尺寸为30—50nm的外延立方体AgBr粒子构成;2)AgSt/AgBr复合物在较低的温度下出现两个新的吸热相变峰,分别对应于97.8℃和108.8℃;3)AgSt/AgBr复合物的起始分解温度较AgSt也有所降低.     

烟酸在热敏成像材料中的调色作用

本文将烟酸引入以硬脂酸银为银源的热敏成像材料中,可以明显提高显影密度,并使影像颜色由金黄色变成黑色;同时显影银粒子的尺寸变大、形貌也会发生改变,并且显影银粒子像链珠一样排成一条线,而线与线之间基本上是平行排列的.进一步实验结果表明,烟酸的引入会降低材料的pH、pAg值和银盐的相变温度,硬脂酸银与烟酸一起加热可能反应生成了新的化合物.     

苯并三氮唑在聚乙烯醇为粘合剂的光敏热成像材料中的化学增感

以水溶性聚乙烯醇(PVA)为粘合剂,硬脂酸银(AgSt)为银源,异位AgBr乳剂为光敏元,考察了苯并三氮唑(BZT)在光敏热成像(PTG)材料中的化学增感效应.实验结果表明:BZT首先增感AgBr乳剂,再与PTG材料的其它组分混合,可以明显提高PTG材料的感光度,而超过一定用量范围则导致影像和灰雾完全消失;在40℃增感温度下,增感70 min可取得最佳感光度;另外,BZT首先与AgSt作用一段时间后,再与PTG材料的其它组分混合,其与AgSt的摩尔比为15%左右,可使得PTG材料取得感光度最佳值.     

苯亚磺酸钠在聚乙烯醇为粘合剂的光敏热成像材料中的化学增感

以水溶性聚乙烯醇(PVA)为粘合剂,以异位法制备的颗粒尺寸为100nm的AgBr乳剂作光敏元,考察了苯亚磺酸钠(SBS)的用量、增感时间和增感温度对光敏热成像(PTG)材料照相性能的影响.实验结果表明:分别增感硬脂酸银(AgSt)、AgBr或者两者混合物,PTG材料均可取得明显的增感效果;灰雾随着苯亚磺酸钠用量增加而增加;增感温度以及增感时间不同,PTG材料的感光度不同.     

Crystallization of silver carboxylates from sodium carboxylate mixtures

Silver carboxylates can be made by the reaction of silver nitrate and the corresponding sodium carboxylates. The length of the alkyl chain has a significant impact on the product behavior. In this study, 18, 20, and 22 carbon chains (stearate, arachidate, and behenate, respectively) have been selected. All three sodium carboxylates are very insoluble in water at room temperature. Solutions are obtained above the Krafft temperature, which precipitates lamellar crystals if cooled at the proper cooling rate. Depending on the chain length, metastable morphologies, such as vesicles and tiny fibers, can be seen consecutively before hexagonal plates form. The carboxylate with the shorter chain length reaches equilibrium more quickly. All three silver carboxylates also take on a lamellar structure. Small-angle X-ray scattering (SAXS) shows that the d spacing of the crystals increases as the chain length increases. Cryo-TEM illustrates that the crystallites are the result of micelle nucleation and micelle aggregation. In addition, the crystallization process in the presence of silver bromide nanocrystals has been investigated. In the initial stage, an epitaxial interface is formed between the silver carboxylate crystallites and the cubic silver bromide grains. Budlike and strandlike structures grow because of it. The consequent strand enclosure restrains the crystal growth, which reduces the size and changes the morphology of the crystals.     

Acid soap and phase behavior of stearic acid and triethanolamine stearate

Crystals of partially neutralized stearic acid with triethanolamine (TEA) were prepared by mixing these two materials above 80 degrees C and then cooling. The crystalline composition and the structure and melting behavior of the resultant products were characterized with small-angle and wide-angle X-ray diffraction, thermal analysis, microscopy, and infrared spectroscopy. It was discovered that an acid-soap complex of 2:1 fixed stoichiometric ratio exists between stearic acid and TEA stearate. A binary phase diagram of stearic acid and TEA soap is built based on the experimental results; this is the first published record of a binary phase diagram for amine-based soap. Its behavior is significantly different from that of binary systems of fatty acid and alkali soap.     

Sodium stearate adsorption onto titania pigment

The interaction of sodium stearate with titania pigment particles from aqueous suspension has been investigated using thermal analysis and infrared spectroscopy combined with electrochemical studies. Thermogravimetric analysis (TGA) was used both to determine the adsorption isotherm and to investigate the interaction behavior. Monolayer coverage is determined to be 0.95 mg/m(2); however, unlike the case with organic solvents, multilayer adsorption occurs. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, combined with TGA, revealed that the surface monolayer is chemically bound. DRIFT spectroscopic data also indicated that the stearate bridged across two aluminum atoms. Subsequent stearate layers were physisorbed to the stearate monolayer and were readily removed with acetone washing.     

Preparation and the mechanisms of formation of silver particles of different morphologies in homogeneous solutions

Uniform, well-dispersed silver particles of various morphologies have been prepared by reducing highly acidic silver nitrate solutions with ascorbic acid in the presence of a sodium naphthalene sulfonate-formaldehyde copolymer as dispersing agent. By varying the temperature of the reaction, the free acid content, the addition rate of the reductant, and the aging time, both isometric and anisotropic silver particles could be obtained. It was found that the latter were formed by aggregation of nanosize subunits, which were identified by electron microscopy and X-ray diffractometry.     

Emulsion polymerization of vinyl stearate

The polymerization of vinyl stearate in aqueous emulsions with a non-ionic emulsifying agent and potassium peroxydisulfate as initiator has been investigated by use of a dilatometric method to follow the reaction. In general, the reaction kinetics do not follow the pattern established for styrene. Variation of initiator concentration produced latices containing approximately equal numbers of latex particles, even though the rate of reaction was almost directly proportional to the peroxydisulfate concentration. For a given initiator and monomer concentration polymerization occurs very slowly when the monomer is completely solubilized but as the number of micelles is reduced and the number of emulsion droplets increased, the rate increases to an optimum value, whereafter it decreases. A mechanism is proposed by which the sparsely soluble vinyl stearate reacts and redistributes itself into latex particles of a different size range from the micelles and emulsion droplets originally present.     

三苯基磷对PTG材料照相性能的影响

本文研究了三苯基磷(PPh₃)对以AgSt为银源的亲水型PTG材料照相性能的影响:PTG材料的感光度随PPh₃用量不同而变化,PPh₃用量相对较少时,感光度随PPh₃用量增加而提高;PPh₃用量增加到一定程度,感光度达到极大值;进一步增加PPh₃用量,感光度反而随PPh₃用量增加而下降.据分析结果推测,在PPh₃用量较少时,PPh₃的作用主要是打开AgSt二聚体的八元环而生成一种中间配合物,该中间体对热显影有促进作用;在PPh₃用量较多时,PPh₃的作用主要是与AgSt作用生成稳定的四元环配合物,该配合物对热显影有抑制作用.PPh₃的引入也会影响光敏元中潜影的形成效率,有利于提高感光度.     

Precipitation of different calcite crystal morphologies in the presence of sodium stearate

The influence of sodium stearate (NaSt) on the precipitation of calcium carbonate during the semicontinuous process of slaked lime carbonation was studied in the systems in which process parameters, like concentration of total dissolved calcium, temperature, CO(2) flow rate and initial addition rate of slaked lime, were controlled. It was found that calcite was the only calcium carbonate polymorph that appeared under the investigated experimental conditions, while FT-IR spectroscopy and thermogravimetric analysis of samples confirmed the presence of stearate on the surface of precipitated calcium carbonate (PCC). Specific surface area of PCC increased with increasing stearate content: the highest value, s = 52.8 m(2) g(-1), was obtained at t = 20 degrees C, c(tot) = 17.0 mmol dm(-3) and the stearate content of m(NaSt)/m(CaO) = 0.03. It was also found that hydrophobic calcite crystals in the form of rhombohedral and scalenohedral morphology can be produced at m(NaSt)/m(CaO) > 0.01. The exception is the case of nanosized PCC production, when much higher concentration of NaSt is needed, m(NaSt)/m(CaO) = 0.22. Minimal amount of stearate necessary to build up the monolayer and corresponding cross sectional area of one stearate molecule were estimated for the obtained calcite morphologies.     

Synthesis and electrochemical properties of composite films based on poly-3,4-ethylenedioxythiophene with inclusions of silver particles

The electrochemical behavior of PEDOT/Ag composite films obtained by chemical deposition of ultrafine Ag particles into the poly-3,4-ethylenedioxythiophene (PEDOT) matrix was studied. The film morphology was characterized by transmission electron microscopy (TEM). The changes in the mass of the films during the chemical deposition of silver into the polymer structure were evaluated microgravimetrically. The mass of the included metallic silver particles depends on the synthesis time and the initial concentration of silver ions in solution. The cyclic voltammograms (CVs) of PEDOT/Ag films in sodium nitrate solutions and sodium nitrate solutions with additions of chloride ions were studied. The cyclic voltammograms of PEDOT/Ag films in chloride-containing solutions showed the peaks of the oxidation of silver and reduction of the oxidation product, which were absent on the CVs of the starting PEDOT film.     

利用紫外-可见光谱研究水溶液中银纳米盘的生长过程及稳定性

Sliver nanoplates were prepared through a visible light induced reduction process by a reaction between sodium citrate and silver nitrate in an aqueous solvent at room temperature. UV-Vis spectra were employed to monitor the growth of the silver nanoplates. The resulting spectra indicated that, at an early stage,the products were spherical particles with planar nanoparticles appearing and growing subsequently. In the last stages of the process, some spherical particles were consumed by the growth of the nanoparticles,through an Ostwald ripening mechanism. Furthermore, it was found that the addition of either Poly(Vinyl Pyrrolidone) (PVP) or excessive citrate could stabilize the colloidal system effectively, and that rigorous stirring was necessary for the anticipant products. Introduction of a large quantities of sodium hydroxide can dramatically accelerate the reactive rate of the photoreduction process.     

A close look at silver oxide colloid for surface-enhanced Raman scattering

A silver oxide hydrosol has been prepared by reacting silver nitrate with sodium hydroxide in an aqueous solution. The colloidal particle composition and particle size have been characterized by X-ray diffractometry and transmittance electron microscopy. We have demonstrated that the sol is surface-enhanced Raman scattering active. One major advantage of this sol is the absence of the spectral interference arising from reaction products of the sol formation process. The mechanism of surface-enhanced Raman scattering activity is essentially contributed by the silver particles generated from the photochemical process during the laser excitation.     

Interaction of DNA bases with silver nanoparticles: assembly quantified through SPRS and SERS

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver-nucleobase interactions.     

Moderating effect of ammonia on particle growth and stability of quasi-monodisperse silver nanoparticles synthesized by the Turkevich method

A new method to stabilize silver nanoparticles by the addition of ammonia is proposed. Colloidal dispersions of silver nanoparticles were synthesized by the Turkevich method using sodium citrate to reduce silver nitrate at high pH and at 90 °C. After approximately 12 min, a diluted ammonia solution was added to the reaction flask to form soluble diamine silver (I) complexes that played an important growth moderating role, making it possible to stabilize metallic silver nanoparticles with sizes as small as 1.6 nm after 17 min of reaction. Colloidal dispersions were characterized by UV-visible absorption spectroscopy, X-ray diffraction, and transmission electronic microscopy.     

Destructive effect of solar light on morphology of colloidal silver nanocubes

Colloidal silver nanocubes (NCs) were successfully synthesized by reduction of silver nitrate with ethylene glycol and polyvinylpyrrolidon as capping agent. The effect of solar light irradiation on the formation and morphology of silver NCs was investigated. Moreover, altering the amount of sodium sulfide was used to control the morphology and shape of primary silver seeds. Scanning electron microscopy, transmitting electron microscopy, X-ray diffraction and UV-vis spectroscopy were used to characterize silver NCs. The samples prepared under the solar light irradiation do not possess cubic shape while highly monodispersed silver NCs were obtained in dark room conditions. For dark room synthesis, a decrease of the amount of Na₂S by only 10 μL resulted in formation of mixture of silver nanospheres and nanowires in addition to NCs instead of the monodispersed silver NCs. However, similar increase of the amount of sodium sulfide results in distortion of cubic geometry of particles. The results suggest that solar light has a negative effect on the shape evolution of the primary silver seeds.