云团中顺磁性粒子对三重态正电子素寿命的影响

Ferrell很早就提出了正电子素o-Ps的猝灭理论,指出介质中的顺磁性粒子是影响o-Ps寿命的重要因素.Lee等测出O_2猝灭o-Ps的速率常数为10~(10)～10~(11)mol·L~(-1)·s~(-1),得出了顺磁猝灭反应是扩散控制的结论.但前人没有对云团中瞬态活性粒子对o-Ps的影响加以探讨.本文通过o-Ps寿命与氧分压的关系来研究云团中瞬态活性粒子对o-Ps猝灭的影响.     

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱,得到了四个寿命组份,并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化,而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响,但随着质子酸浓度增加,o-Ps在沸石内表面湮没的几率大于笼内,故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系,以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

正电子湮没与沸石内静电场

本文测定了不同类型沸石的正电子寿命谱。发现o-Ps的湮没寿命, 与沸石静电场之间有良好的对应关系, 静电场愈强, 湮没寿命愈短。根据正电子寿命谱结果。含不同阳离子的Y沸石的静电场强弱次序为KY相似文献   

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱, 得到了四个寿命组份, 并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化, 而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响, 但随着质子酸浓度增加, o-Ps在沸石内表面湮没的几率大于笼内, 故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系, 以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

聚对苯二甲酸乙二酯的玻璃化转变和结晶化的正电子湮没研究

研究了聚对苯二甲酸乙二酯的玻璃化转变和结晶过程对正电子湮没寿命谱的影响.结果表明,结晶过程对正电子湮没的长寿命组份τ_3的寿命值不敏感,用这种方法测得的“T_g”不随结晶度而变化,而长寿命组份的相对强度则随结晶度的增加而减小.     

稀土离子掺杂铕三元配合物探针分子及其温敏漆的制备和性能研究

以氧化铕(Eu_2O_3)、氧化镝(Dy_2O_3)、氧化钇(Y_2O_3)、氧化钕(Nd_2O_3)、甲基丙烯酸(MAA)和邻菲罗啉(phen)为原料制备了Eu(MAA)_3phen,Eu_(0.5)Dy_(0.5)(MAA)_3phen,Eu_(0.5)Y_(0.5)(MAA)_3phen和Eu_(0.5)Nd_(0.5)(MAA)_3phen探针分子,并将不同探针分子分别加到甲基丙烯酸甲酯(MMA)中,在过氧化苯甲酰(BPO)引发下聚合,制得一系列温敏漆样品。采用红外光谱仪、能量色散谱仪、荧光光谱仪和扫描电子显微镜对探针分子的结构、发光性能、形貌和温敏漆的温度猝灭性能进行了表征,研究了掺杂不同稀土离子对探针分子发光性能和温敏漆温度猝灭性能的影响。结果表明,稀土离子(RE~(3+))与MAA配位,phen参与了配位,且掺杂离子未改变Eu(MAA)_3phen结构,Y~(3+)对Eu(MAA)_3phen发光具有敏化作用,Dy~(3+),Nd~(3+)对Eu(MAA)_3phen发光具有不同程度的猝灭作用,所制备的温敏漆在25~65℃范围内均具有良好的温度猝灭性能。综合分析得出,以Eu_(0.5)Y_(0.5)(MAA)_3phen为探针分子的温敏漆具有更好的应用前景。     

用正电子素探测叶绿素三线激发态浓度的变化

测量了在不同光强下叶绿素环已烷溶液(77 K)和酒精溶液(296 K)的正电子湮没寿命谱。提出正电子素光磁湮没模型以解释实验事实。在77 K固化的叶绿素环已烷溶液中, 正电子湮没寿命谱长寿命组分的湮没参数I_2和Λ_2随光强变化而呈现规律性变化, 表明可利用正电子素光磁猝灭效应来追踪光敏剂分子三线激发态浓度的变化。     

卤代荧光素荧光猝灭法测定肾上腺色腙

在pH=6.6 的缓冲介质中, 肾上腺色腙(CBZC)与二氯荧光素(DCF)、二溴荧光素(DBF) 和二碘荧光素(DIF)通过静电引力、芳基堆积作用和范德华力形成摩尔比为2: 1的复合物, 引起上述二卤代荧光素的荧光发生猝灭, 最大猝灭波长分别位于533, 536和560 nm. 其荧光猝灭值(ΔF)在一定范围内与肾上腺色腙浓度成正比, 荧光猝灭反应具有较高的灵敏度, 对CBZC的检出限分别为3.3 ng/mL(CBZC-DCF体系), 5.7 ng/mL(CBZC-DBF体系)和129.6 ng/mL(CBZC-DIF体系). 考察了共存物质的影响、荧光猝灭反应的适宜条件和影响因素, 结果表明, 该方法具有良好的选择性, 可用于CBZC的血药和尿药浓度的快速检测. 从温度的影响、荧光寿命以及Stern-Volmer图判断该反应为静态猝灭反应.     

茂铁基多核配合物猝灭*Cr(bpy)3+3发光过程研究

在过去的十年内,过渡金属联吡啶配合物的光物理和光化学过程得到了迅速发展,激发态的形成及其决定因素在几类经典的配合物中得以很好的研究,尤其是对d~3组态Cr(bpy)_3~(3+)和d~6电子组态Ru(bpy)_3~(2+)的研究尤为突出.二茂铁及其衍生物一直是有机金属化学研究的重要对象.其对Cr(bpy)_3~(3+),Ru(bpy)_3~(2+)等发光剂猝灭作用对分子器件的基础研究具有重要意义.为此,本文合成了一系列含茂铁基多核配合物,并研究了其对Cr(bpy)_3~(3+)发光过程的猝灭作用.     

不同配体的邻菲罗啉铽探针分子及其温敏漆的制备和性能研究

本文以氧化铽(Tb2O3)、甲基丙烯酸(MAA)、水杨酸(HSal)、肉桂酸(HCA)和邻菲罗啉(Phen)为原料,制备了Tb(MAA)_3Phen、Tb(Sal)_3Phen和Tb(CA)_3Phen探针分子,并将探针分子分别加入甲基丙烯酸甲酯(MMA)中,在过氧化苯甲酰(BPO)引发下聚合,制得3种温敏漆样品。采用红外光谱仪、荧光光谱仪和扫描电子显微镜,对探针分子的结构、发光性能、形貌和温敏漆的温度猝灭性能进行了表征,研究了不同配体对探针分子发光性能和温敏漆温度猝灭性能的影响。红外光谱表明成功合成了Tb(MAA)_3Phen、Tb(Sal)_3Phen和Tb(CA)_3Phen探针分子;扫描电镜照片显示Tb(MAA)_3Phen、Tb(Sal)_3Phen和Tb(CA)_3Phen的微观形貌分别为不同三斜棒状和不规则层状;荧光光谱表明Tb(MAA)_3Phen具有最佳的发光性能,相应的温敏漆在25~65℃范围内具有良好的温度猝灭性能和灵敏度。     

Free volume in imidazolium triflimide ([C3MIM][NTf2]) ionic liquid from positron lifetime: amorphous, crystalline, and liquid states

Positron annihilation lifetime spectroscopy (PALS) is used to study the ionic liquid 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [C(3)MIM][NTf(2)] in the temperature range between 150 and 320 K. The positron decay spectra are analyzed using the routine LifeTime-9.0 and the size distribution of local free volumes (subnanometer-size holes) is calculated. This distribution is in good agreement with Fürth's classical hole theory of liquids when taking into account Fürth's hole coalescence hypothesis. During cooling, the liquid sample remains in a supercooled, amorphous state and shows the glass transition in the ortho-positronium (o-Ps) lifetime at 187 K. The mean hole volume varies between 70 ?(3) at 150 K and 250 ?(3) at 265-300 K. From a comparison with the macroscopic volume, the hole density is estimated to be constant at 0.20×10(21) g(-1) corresponding to 0.30 nm(-3) at 265 K. The hole free volume fraction varies from 0.023 at 185 K to 0.073 at T(m)+12 K=265 K and can be estimated to be 0.17 at 430 K. It is shown that the viscosity follows perfectly the Cohen-Turnbull free volume theory when using the free volume determined here. The heating run clearly shows crystallization at 200 K by an abrupt decrease in the mean <τ(3)> and standard deviation σ(3) of the o-Ps lifetime distribution and an increase in the o-Ps intensity I(3). The parameters of the second lifetime component <τ(2)> and σ(2) behave parallel to the o-Ps parameters, which also shows the positron's (e(+)) response to structural changes. During melting at 253 K, all lifetime parameters recover to the initial values of the liquid. An abrupt decrease in I(3) is attributed to the solvation of e(-) and e(+) particles. Different possible interpretations of the o-Ps lifetime in the crystalline state are briefly discussed.     

Investigation of thermotropic phase transitions in a triple chain amphiphile forming hexagonal columnar and inverse micellar cubic mesophases: a positron annihilation lifetime study

Positron annihilation lifetime (PAL) measurements were performed between 25 and 100 C in order to study thermotropic phase transformations in an amphiphilic liquid crystal material with three hydrophobic alkyl chains. The lifetime spectra were separated into three exponential components, the long-lived of which is attributed to ortho-positronium (o-Ps) annihilation via pick-off processes. The lifetime of o-Ps, tau3, and its relative intensity, I, as well as the average positron lifetime, tau alpha I3tau3, respond to variations in the structural regularities of the environment. The phase transitions, which have the sequence and temperatures (C) Cr 59 Col(H II) 74 Cub(I II) 85 Iso, are well reflected in abrupt changes of, I3 and Tav. The o-Ps lifetime in the crystalline phase of tau3 = 2.35ns may be interpreted as a crystalline packing coefficient of 0.56 or, alternatively, as o-Ps confined in vacancy-type crystal imperfections with a volume of 0.132 nm3. During melting tau3 increases to 3.05 ns, and this is attributed to the preferential formation of Ps bubbles, with a size of 0.207 nm3, in mobile, liquid-like regions of hydrophobic alkyl chains. The bubble size remains at this value during the H-I transition and increases slightly to 0.216 nm3 during the transformation to the isotropic liquid phase. I3 shows variations during all of the phase transitions, which are attributed to changes in the Ps inhibition rate due to electron/positron mobility, and solvation effects varying as a consequence of different degrees of order of the molecular dipoles.     

Positronium as a probe of structure and stability of solid phases in binary n-alkane mixtures

Annihilation of triplet ortho-positronium (o-Ps) in binary mixture of odd numbered n-alkanes was investigated. Sensitivity of o-Ps lifetime to the size of free volumes in the sample structure allows to distinguish not only the phases of solid but also some details of their structure. It was found that in the rigid phase o-Ps locates in the interlamellar gap. In mixed systems the o-Ps lifetime in that phase is longer than in neat compounds due to the change of molecular arrangements around the gap. In the case of n-tricosane + n-nonadecane mixture a transient structure appears when the n-tricosane content is between 3% and 10%. Directly after the increase of temperature to the range of 285–292 K the sample transforms to the rotator phase, but returns (at least partially) to the previous rigid structure with recovery time constant of many hours. Above 292 K the structure is stable.     

Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes

The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition. Unexpectedly, the starch volume fraction (as probed through thermal gravimetry) decreases with T at a higher rate than the free volume fraction (as probed through PALS).     

嵌段共聚物溶液胶束温度行为的郑电子湮没研究

用正电子寿命技术研究了聚苯乙烯—二甲基硅氧烷／正庚烷二嵌段共聚物溶液胶束的温度行为．结果表明正电子湮没参数对溶液中出现的结构和微观环境的变化十分灵敏．在一定的温度范围o-Ps寿命和强度的陡然变化反映了溶液中共聚物分子聚集态随温度经历不同阶段的变化，超过临界胶束温度o-Ps寿命随温度增高而迅速地增大，这一行为反映了分子聚集体解离成自由共聚物分子的过程．     

Amorphous-amorphous transition in glassy polymers subjected to cold rolling studied by means of positron annihilation lifetime spectroscopy

In this study, polycarbonate (PC) and polystyrene (PS) are subjected to plastic deformation by means of cold rolling and the resulting variation of the free volume and its subsequent time evolution after rolling is investigated by means of positron annihilation lifetime spectroscopy (PALS). The value of the long lifetime component that is attributed to the decay of ortho-positronium (tau(o-Ps)) and its intensity (I(o-Ps)) are used to characterize, respectively, the size and the concentration of the free-volume holes. In addition to the PALS experiments, the effect of plastic deformation on the dynamic tensile modulus is investigated. The PALS results show that both for well-aged PC and PS an increase of tau(o-Ps) and a decrease of I(o-Ps) occur upon plastic deformation. During the subsequent aging, tau(o-Ps) tends to return to the value assumed before plastic deformation, while I(o-Ps) remains constant with time. These results corroborate the idea of an amorphous-amorphous transition, rather than that of a "mechanical rejuvenation" as proposed in the past to explain the ability of plastic deformation to reinitiate physical aging. Finally, a linear relation between the size of the free-volume holes and the dynamic tensile modulus is found, which suggests that the stiffness of amorphous glassy polymers is fully determined by their nanoscopic structure.     

含氢键吡啶合钴(Ⅱ)配合物的晶体结构和磁交换作用

合成了含水配合物［Co(py)₄Cl₂］·H₂O。分析了其单晶结构并与已知的无水配合物Co(py)₄Cl₂作了比较。发现结晶水的存在使含水配合物晶胞及分子对称性下降,由4方晶系I4₁/acd空间群变为单斜晶系P2₁/n空间群。并且水分子通过氢键作用把［Co(py)₄Cl₂］联接成一维长链。用Curie-Weiss定律,零场分裂磁化率公式加分子场校正磁化率公式拟合变温磁化率数据,发现分子间存在弱的反铁磁性交换作用。用Fisher一维线性链模型磁化率公式拟合,得出其氢键链内交换常数约为-1.03K。     

Free volumes in polystyrene probed by positron annihilation

Free volume characteristics in three samples of monodisperse polystyrene were investigated by positron annihilation technique over a temperature range from 300 to 380 K. The number-average molecular weight of the samples ranged from 5730 to 1,524,000. The observed lifetime spectra were resolved into three components, where the longest lifetime, τ₃ was associated with the pick-off annihilation of ortho-positronium (o-Ps) trapped by free volumes. The change of the temperature coefficient of τ₃ was observed at around 350 K, at which the value of τ₃ was a constant value of 2,3 ns for all specimens with different molecular weights. There was no discrete change of τ₃ in intensity, which is corresponding to the number of free volumes. The size of free volume at glass transition was evaluated to be 0.l nm³. © 1996 John Wiley & Sons, Inc.     

On the relationship between o-Ps lifetime in liquids and their surface tension

It is shown that the Nakanishi-Jean formulae for o-Ps lifetime vs. radius of spherical cavity gives the empirical relationship of Tao which links the o-Ps annihilation rate with macroscopic surface tension.     

High proton conduction in a chiral ferromagnetic metal-organic quartz-like framework

A complex-as-ligand strategy to get a multifunctional molecular material led to a metal-organic framework with the formula (NH(4))(4)[MnCr(2)(ox)(6)]·4H(2)O. Single-crystal X-ray diffraction revealed that the anionic bimetallic coordination network adopts a chiral three-dimensional quartz-like architecture. It hosts ammonium cations and water molecules in functionalized channels. In addition to ferromagnetic ordering below T(C) = 3.0 K related to the host network, the material exhibits a very high proton conductivity of 1.1 × 10(-3) S cm(-1) at room temperature due to the guest molecules.