应用于聚合物中的正电子湮没寿命谱技术

正电子湮没寿命谱技术是一种新型聚合物结构探测与表征技术,针对此技术在聚合物自由体积研究中的应用,首先介绍了该技术的基本原理和应用理论,接着针对寿命谱数据的处理手段和计算方法,对国内外的研究进展进行了概述和总结,最后展示了该技术在聚合物材料研究中用于基本理论,实际运用和结构理论等三个方面的情况。     

正电子湮没谱研究聚烯烃聚氨酯的自由体积、微观结构和溶剂的扩散行为

用正电子湮没技术(PAS)结合示差扫描量热法(DSC)研究了聚烯烃聚氨酯的自由体积特征和微相分离结构的关系.结果表明,硬段含量增加,自由体积孔洞平均半径和自由体积分数减小;丁腈聚氨酯相分离程度小,相应自由体积孔洞平均半径和自由体积分数小,而丁羟聚氨酯的情况正好相反.石英弹簧法对苯和乙醇蒸气的溶解和扩散行为的研究表明,聚烯烃聚氨酯的自由体积孔洞平均半径和自由体积分数与苯和乙醇溶剂蒸气的无限稀释扩散系数呈正相关,但它们的无限稀释扩散系数和自由体积分数关系无法用Fujita的自由体积模型描述,可能归因于它们对聚烯烃聚氨酯复杂的溶胀行为.     

Positron annihilation and electrical studies on the influence of loading magnesia nanoribbons on PVA-PVP blend

This work aims to study the effect of loading magnesia (0.5–2.0 wt%) on the positron annihilation parameters and electrical properties of the PVA-PVP blend. The films were synthesized by solution casting and checked by different techniques. XRD and HR-TEM of sol-gel prepared magnesia revealed that the average crystallite size was 14.29 nm with ribbon-like morphology with varying widths and lengths up to a few micrometers. SEM showed that the blend surface appeared smooth and homogenous and this confirmed the compatibility between PVA and PVP. However, loading magnesia increased surface roughness. TGA confirmed the thermal stability enhancement of blend film with magnesia incorporation. Ortho–positronium lifetime τ₃ and the free volume $V_f$ decrease with loading magnesia while the intensity I₃ is nearly constant. These features were interpreted in view of the hole-filling mechanism, the interaction between magnesia & blend and magnesia morphology. The equilibrium swelling ratio ESR was found for the studied films and a positive correlation between ESR and $V_f$ was reported. The current density-electric field, J-E, characteristics were of non-ohmic type. J increased with increasing magnesia levels and heating. The Richardson-Schottky effect was the dominant dc conduction mechanism at low temperature and low magnesia loading levels while it changed to Poole–Frenkel emission at higher values. Finally, a correlation between Log J and the intensity I₂ was reported.     

尼龙6/碳纳米管纳米复合材料自由体积特性的正电子湮没研究

采用正电子湮没寿命谱技术研究了尼龙6/碳纳米管纳米复合材料的自由体积特性。实验结果发现碳纳米管对纳米复合材料的自由体积孔洞尺寸影响甚微,而自由体积孔洞数目和相对自由体积分数均随碳纳米管含量的增加而明显减小。导致这种减小的原因可能来自两方面,其一是由于碳纳米管和基质聚合物间的相互作用限制了高分子链段运动;其二是碳纳米管填充增强了尼龙6基体结晶性能。此外,力学性能研究表明,碳纳米管在复合材料中较均匀的分散和较好的界面接触可以提高材料的力学强度,而自由体积分数的减小则使材料的韧性变差。     

正电子湮没技术（PAT）在高分子材料中的应用（下）

正电子湮没技术（ＰＡＴ）在高分子材料中的应用（下）李桂芝，施良和，叶美玲（中国科学院化学研究所高分子物理开放实验室，北京，１０００８０）３．４高分子导体高分子导体有两种：（１）靠共轭分子链导电的高分子；（２）因掺入小分子而具有导电作用的高分子。现在已...     

Epoxy/Rectorite自由体积分布温度特性的正电子谱学研究

采用正电子寿命谱(PLA)技术,通过探测聚酰胺固化环氧树脂(Epoxy)及环氧树脂/累托土(Epoxy/Rectorite)复合材料分别在不同温度点自由体积分布特性的变化,结果表明:在低温T=30K时,分子链段被冻结,自由体积分布变窄;温度在T_g及以上时,聚酰胺固化DGEBA环氧树脂中出现微相分离情况,观测到两种大小不同的自由体积孔洞的存在;纳米复合材料中累托土片层与高分子链段相互作用,同时片层促进了环氧树脂的交联,阻碍了复合材料的微相分离.     

侧链型丙烯酸酯共聚物相变的正电子湮没谱研究

利用正电子湮没技术对侧链型热致高分子液晶丙烯酸酯共聚物进行了变温相变研究．除实验标识出样品的相变温度点外，根据试样中自由体积随温度的变化关系，对高分子液晶材料内部立链、侧链以及介晶基元的相变行为特点进行了探讨，并就与小分子液晶变化特点的一些不同做了解释．     

明胶大分子中的正电子湮没行为

The microstructural properties of gelatin samples derived from the bovine bone as well as skin of fish which inhabit in the cold sea were examined at molecular scale by using the positron annihilation lifetime spectroscopy（PALS）. The longest-lived component of PALS provides information about the free-volume holes in gelatin macromolecules. The results show that both average size and number of free-volume holes in the fish gelatin macromolecules are lower than those in the bovine gelatin macromolecules. Silver halide emulsions were also precipitated by using the balanced double-jet technique,for which two types of media containing fish gelatin and bone gelatin were used in the stage of nucleus formation,respectively. The monodispersibility of silver halide crystallites can be improved and the growth and coalescence of nucleus grains can be restricted when the fish gelatino-peptizer was used as dispersion medium at the nucleus formation. It thus suggested that the function of gelatino-peptizers as protective colloid is correlated with the microstructure character of gelatin macromolecules established by PALS. The gelatino-peptizer derived from the fish skin possesses stronger power governing nucleation and growth of silver halide grains compared with that made from the bovine bone.     

Free Volume of Montmorillonite/Styrene‐Butadiene Rubber Nanocomposites Estimated by Positron Annihilation Lifetime Spectroscopy

Summary: The size and concentration of free‐volume holes of two kinds of montmorillonite (MMT)/styrene‐butadiene rubber (SBR) nanocomposites were investigated by positron annihilation lifetime spectroscopy (PALS). Strong interfacial interaction caused an apparent reduction of the free‐volume fraction of rubber probably by depressing the formation of free‐volume holes in the interfacial region. Interfacial interaction in MMT/SBR nanocomposites was weaker than that in SBR filled with carbon black.

Dependence of normalized o‐Ps intensity of four kinds of composites on filler volume fraction.     

用正电子湮没谱学研究氯化稀土在NaY沸石上的分散

用正电子湮没谱学研究氯化富铈稀土与NaY沸石机械混合形成的稀土NaY沸石(RE-NaY)中,氯化稀土在NaY中的分散．分别测量不同质量比的RE-NaY(1％-20％)经500℃烘烤1h,RE-NaY(5％)经过不同温度烘烤1h,以及RE-NaY(5％)经500℃烘烤不同时间后的正电子寿命谱．所有寿命谱都出现了5个寿命分量,其中第3,4,5寿命分别与β笼、超笼及沸石微粒界面空洞的大小和数量相关．实验表明了正电子湮没谱学能敏感地表征氯化稀土在NaY中的分散．     

Effects of oxygen in gamma irradiated aromatic polyesters in film

The effect of gamma irradiation in air is investigated on four thermoplastic polyesters (PET, PBT, PEN, PCT-co-ET) in films containing aromatic rings, in order to evaluate the influence of aromatic density and the role of oxygen on radiation resistance. Physical-chemical-nuclear analyses were used to this purpose. EPR measurements were carried out to detect radical stability against oxygen permeation. Viscometric investigations reported a very similar trend for all the investigated polyesters: a chain break effect that decreases at the highest doses. FT-IR analyses focused on the formation of oxidized species. Positron annihilation spectra pointed out a decrease of the intensity of ortho-positronium formation, while its lifetime remains unchanged with radiation dose.     

Studies on the free volume and the volume expansion behavior of amorphous polymers

In order to estimate the free volume contribution on the volume change, we investigated the relationship between the volume expansion behavior by Pressure–Volume–Temperature measurement apparatus and the free volume behavior by Positron Annihilation Lifetime Spectroscopy for some amorphous polymers. From these results, the free volume fraction of the amorphous polymers was calculated by assuming that the core volume increases at a constant rate with temperature. It was found that the amount of free volume was not constant even in the glassy state and it played a very important role in the volume expansion.     

用正电子谱学研究USY沸石中二次孔的脱水

超稳Ｙ型沸石（ＵＳＹ）分子筛是石油催化裂化中的优异催化剂,它是由ＨＹ型沸石经高温水热处理制备的,它的特点之一是具有良好的热稳定性．因而,对ＵＳＹ的改性研究一直受到关注［１-５］,尤其是在制备ＵＳＹ过程中由于水热处理所产生大量二次孔,它与ＵＳＹ的结构与?..     

照相明胶层中金催化的无电沉积的正电子湮没研究

采用正电子湮没技术(PAT)研究了照相明胶中的自由体积空穴在无电沉积过程中的作用机理。研究结果表明,活化饱和后,照相明胶的自由体积空穴的平均尺寸约减小0.011nm³,相当于一个Au原子的体积的大小,即照相明胶大分子中的每个自由体积空穴平均被填充了一个Au原子,该Au原子作为催化活性核催化铜的沉积,使物理显影生成的影像为紧密铜粒子的堆积形貌,而不是丝状形貌。铜经无电沉积饱和后,照相明胶的自由体积空穴的平均大小约减小了0.020nm³,即照相明胶的自由体积空穴对铜物理显影过程中铜的沉积没有阻碍作用,铜无电沉积近似为各向同性的球状堆积。     

聚酯聚氨酯透气性的正电子研究

用正电子湮没寿命谱(PALS)研究了温度和PEG含量对以聚己二酸丁二醇酯(PBA)为软段的聚酯聚氨酯的自由体积特性和透气性的影响.实验结果表明,自由体积空洞的体积随着温度的升高而增加,分布变宽,导致透气性增大.不同PEG含量的聚酯聚氨酯PBA-10,PBA-15和PBA-20的水汽渗透系数(WVP)基本相同.结果表明,在这类聚氨酯中,影响透气性的主要因素不仅是自由体积,而且与材料的亲水性有关.     

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．     

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

Epoxy/clay nanocomposites are synthesized using clay modified with the organic modifier N,N‐dimethyl benzyl hydrogenated tallow quaternary ammonium salt (Cloisite 10A). The purpose is to investigate the influence of the clay concentration on the nanostructure, mainly on the free‐volume properties and the interfacial interactions, of the epoxy/clay nanocomposite. Nanocomposites having 1, 3, 5 and 7.5 wt. % clay concentrations are prepared using the solvent‐casting method. The dispersion of clay silicate layers and the morphologies of the fractured surfaces in the nanocomposites are studied using X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The observed XRD patterns reveal an exfoliated clay structure in the nanocomposite with the lowest clay concentration (≤1 wt. %). The ortho‐positronium lifetime (τ₃), a measure of the free‐volume size, as well as the fractional free volume (f_v) are seen to decrease in the nanocomposites as compared to pristine epoxy. The intensity of free positron annihilation (I₂), an index of the epoxy–clay interaction, decreases with the addition of clay (1 wt. %) but increases linearly at higher clay concentrations. Positron age‐momentum correlation measurements are also carried out to elucidate the positron/positronium states in pristine epoxy and in the nanocomposites. The results suggest that in the case of the nanocomposite with the studied lowest clay concentration (1 wt. %), free positrons are primarily localized in the epoxy–clay interfaces, whereas at higher clay concentrations, annihilation takes place from the intercalated clay layers.     

Study of the size and numerical concentration of the free volume of carbon filled HDPE composites by the positron annihilation method

In this paper, the size and numerical concentration of free volume of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with changing the temperature of HDPE/CB composite containing 25 phr CB. It was found that the important parameters of PALS show their fluctuation around the percolation threshold. The conductivity of HDPE/CB is controlled by CB contribution, and that can be reflected in o-Ps lifetime. The temperature dependence of positron lifetimes reveals that the existence of glass transition temperatures and the size of free volume holes increases when temperature increases above glass transition. The results observed from the second set of samples suggest that positive temperature coefficient is in some way related with free volume expansion. The experiment facts implied that the conductivity of HDPE/CB was related with not only the size of free volume holes but also the number of free volume holes. The Doppler-broadening of HDPE/CB was also investigated.     

LaFe1-xCuxO3的光催化性及正电子湮没研究

研究LaFeO3及微量掺铜LaFeO3的光催化活性,利用正电子湮没谱分析掺杂的影响,发现随着掺杂百分比的增加,正电子寿命逐渐下降达到一最小值,然后又上升;而光催化活性随掺杂百分比的增加逐渐上升达到最大值,然后下降。结果表明：LaFeO3掺杂后光催化活性得以提高;正电子湮没技术是研究点阵缺陷结构的有效方法之一。     

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone-added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free-volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free-volume holes from the addition of PVP to the casting solution. However, the percentage of o-Ps pick-off annihilation intensity, I₃, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 589–598