Study of polyaniline polyacrylamide composites by positron annihilation technique

Polyaniline doped with nonoxidizing Bronsted acids is recognized as a conducting material, as its electrical conductivity changes with percentage of doping. In the present work, different percentages of doped polyaniline were blended with polyacrylamide and their electrical conductivities as well as the positron annihilation lifetimes were measured. Analysis of data yielded three lifetime components. It was observed that the value of the short lifetime component remained constant for doping concentration, whereas that of the intermediate component τ₂ decreased. The relative intensity pertaining to τ₂, however, increased with the increase in doped PANI concentration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 930–933, 2003     

Surface acidity by positron annihilation lineshapes

An alternative new method to measure the specific acidity of catalytic materials with large internal surface areas by using positron annihilation spectroscopy was introduced. Results of lineshape parameter evaluations from two-dimensional angular correlation and Doppler broadened annihilation radiation measurements for a zeolite ZSM-5 were presented.     

The influence of acrylic acid groups on the microstructure of HDPE/BT system studied by positron annihilation

Two types of composites, high‐density polyethylene (HDPE)/Bentonite (BT) and high‐density polyethylene grafted with acrylic acid (HDPE‐g‐AA)/(BT), are prepared by melt compounding. The microstructure of the composite has been studied by the means of positron annihilation lifetime spectroscopy (PALS). It has been found that the mean free volume size is nearly the same in composites and HDPE matrices with different BT concentration. While the ortho‐positronium (o‐Ps) intensity decreased for HDPE‐g‐AA and its lifetime distribution is narrower than that for pure HDPE. With the increasing of BT content, the o‐Ps intensity increases for HDPE‐g‐AA/BT composites and the o‐Ps intensity decreases for HDPE/BT composites. It is found that the carboxyl group of Acrylic acid plays a significant chemical inhibition on positronium formation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The use of positron annihilation lifetime technique to study the effect of doping metal salts on polyhydroxamic acid polymers

Polyhydroxamic acid (PHA) from polymethacrylamide (PMAA) was prepared. Chromium chloride (CrCl₃) and ferric chloride (FeCl₃) salts were added to the polymer in order to increase its electrical conductivity, i.e., the dopants help produce semiconducting properties. The positron annihilation lifetime technique spectroscopy (PALS) was used to study the changes in the free volume as a function of FeCl₃ and CrCl₃ concentrations. ortho-Positronium lifetime components were used to estimate the free volume parameters. It was found that the hole size and the total free volume fraction decreased with FeCl₃ concentration. On the other hand, the hole size increased slightly with CrCl₃ concentration and then decreased, while the total free volume fraction increased continuously. The free volume distributions were determined from ortho-positronium distributions. The electric conductivity as a function of FeCl₃ and CrCl₃ concentrations showed fluctuation behavior and showed a continuous increase with the increase in temperature. The correlation between positron annihilation parameters and electric conductivity were discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2095–2101, 2001     

Positron annihilation studies of ageing in polystyrene

Structural relaxation processes are reported in polystyrene as a function of ageing time using positron annihilation lifetime and Doppler broadening spectroscopy. Changes in the intensity, lifetimes and line shapes with increasing temperature for ortho positronium annihilation show an internal consistency between the two experiments and may be described in terms of a simple logarithmic decay process. The isochronous and isothermal ageing data show internal consistency and are best described by either a Narayanaswamy distribution or a double exponential fit of the data. The possible effects of charging during the isothermal decay measurements are explored and found to influence the short term decay behaviour. Measurements of the liquid phase are extrapolated to lower temperatures to allow estimation of the equilibrium lifetimes in the glassy phase. Changes in the lifetimes and the long time component of the intensity are interpreted as being indicative of the structural relaxation process; they are not influenced by the effects of charging and exhibit a good correlation with physical ageing behaviour as determined by other techniques. © 1998 SCI.     

Study of Brønsted acidity of NaHY zeolite by positron spectroscopy

Angular correlations of positron annihilation gammas were applied to study NaHY zeolite catalysts whose acidity was altered by an ion-exchange process. The Brønsted acidity was found to vary linearly with the lineshape parameter of the angular correlation spectrum of the sample.     

Effect of adding feldspar on free volume properties of crosslinked polyester studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PAL) was applied to study the feldspar effect on the free volume properties of crosslinked polyester based on neopentyl glycol, succinic acid, phthalic anhydride, and maleic anhydride. The measurements have been carried on the polyester resin samples cured with three crosslinking agents namely styrene (SS) or styrene/methyl methacrylate (SM) or styrene/acrylonitrile (SA) comonomers mixtures in the ratios of 2 : 1 and loaded with different concentrations of feldspar in the range from 0 to 80 wt %. The free volume parameters (size and fractions of holes) depend on type of the crosslinking agent as well as the feldspar content added to the polyester. The results are supported by a significant variation in the nanoscale free volume hole size distributions. Moreover, the correlation between positron annihilation parameters and electrical parameters was discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

BiVO4的光催化活性及其正电子湮没谱

以2,4-二硝基苯酚光催化降解为探针反应,考察了BiVO4的光催化降解活性。利用正电子湮没谱分析了焙烧温度对BiVO4光催化活性的影响。结果表明,焙烧温度能引起特定的缺陷数目变化,改变了光催化剂的微观结构。经900 ℃焙烧的BiVO4催化剂比在其它温度下焙烧的催化剂有较多的表面缺陷数目,可产生表面光生电子-空穴的数目较多,不均匀性、缺陷位的电子密度大,使得其光催化氧化活性增强,即2,4-二硝基苯酚的降解率较高。     

Positron annihilation spectroscopic investigation of Al-pillared montmorillonites

We report, for the first time, our result on characterisation of Al-pillared clay using positron annihilation spectroscopy (PAS) along with XRD and BET techniques. Positron life-time spectra for Al-pillared montmorillonite, as received and calcined at different temperature (100–500°C), along with the parent natural clay are measured. The annihilation rate of ortho-positronium (o-Ps) increases monotonically with calcination temperature up to 300°C and falls subsequently. Similar behaviour is seen for the fraction of o-Ps formed. We interpret the initial rise in annihilation rate of o-Ps to be due to the increase in Brønsted acidity with dehydroxylation of pillars. The reduction in annihilation rate on calcination at higher temperatures could be due to loss of acidity and/or due to mesopore formation following delamination of clay structure.     

Application of positron annihilation: Study of pervaporation dense membranes

Separation of liquid mixtures, particularly azeotropic mixtures, is being tried out by pervaporation process, which utilizes dense membranes. Such membranes, although are of non-porous type, still requires determination of free volume sizes which is crucial to the understanding of the process. Positron annihilation technique has been developed into a powerful characterization tool for the study of free volume and free volume fraction in polymers. In the present work, an attempt has been made to estimate the free volume sizes of commercial and laboratory made pervaporation membranes with the application of positron annihilation lifetime spectroscopy. The positron lifetime spectra were analyzed, assuming 3 or 4 exponential components. Long-lived components (lifetimes: in the range of 1.4-3 ns) were found, which were attributed to ortho-positronium (o-Ps) pick-off annihilations in free volumes. Accordingly, free volume size determinations were carried out, considering shapes for free volumes as spherical as well as cylindrical. Further, utilizing such free volume data, results of hydrazine hydrate separation by pervaporation were interpreted leading to a better understanding of the process.     

正电子湮没在高聚物中的应用研究

正电子湮没技术是通过自由体积的研究,对聚合物结构探测和表征的1种新型技术。介绍了正电子湮没的实验原理、对寿命数据谱的处理方法并概括了它在高聚物中的应用。     

Investigation of free volume,interfacial, and toughening behavior for cyanate ester/bentonite nanocomposites by positron annihilation

Effects of filler on microstructure and toughening behavior of cyanate ester (CE)/bentonite (BT) nanocomposites with different content of BT have been studied by positron annihilation lifetime spectroscopy, X‐ray diffraction, transmission electron microscopy, dynamic mechanical analysis, etc. The interesting results found by PALS indicate that the size and concentration of the free volume holes and the apparent free volume fraction increased with increasing the content of BT, which indicates that adding nano‐layers to thermosetting materials can lead to the high crosslinking density structure “looser.” The experimental results reveal that the increases in size of free volume holes and apparent free volume fraction are related to the increasing conversion of cure reaction. On the other hand, the mechanism of toughening (by adding the nano‐clay to the thermosetting material) has been discussed by combining free volume and interfacial property. It is shown that, for the high crosslinking thermosetting material‐based nanocomposites, both the property of free volume and dispersion state of nano‐layers are the two key factors in determining toughening property. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1509–1515, 2006     

Characterization of methyl‐substituted polyamides used for reverse osmosis membranes by positron annihilation lifetime spectroscopy and MD simulation

Three kinds of polyamides were synthesized from three diamines and 1,3,5‐benzenetricarbonyl trichloride (TMC). The diamines used were m‐phenylene diamine, N‐methyl‐m‐phenylenediamine, and N,N′‐dimethyl‐m‐phenylenediamine. The average free volume sizes of the polyamides were measured by positron annihilation lifetime spectroscopy (PALS), and the free volume fractions were evaluated by molecular dynamics (MD) simulations. The methyl substitution on amino groups of diamines brought about an increase in interstitial space of molecular chains of the polyamides. In addition, reverse osmosis (RO) membranes were prepared by interfacial polymerization from the three diamines and TMC. The increase in the degree of methyl‐substitution of diamines led to increased chlorine resistance and decreased salt rejections of the polyamide RO membranes. Thus, the methyl‐substitution of diamines significantly influenced membrane performance. The vacancy sizes and fractional volumes in polyamides evaluated by PALS measurement and MD simulation were well correlated with salt rejection of polyamide RO membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Antiplasticization of a polyamide: a positron annihilation lifetime spectroscopy study

In order to modify the transport properties of the amorphous polyamide Trogamid-T™, several additives with structural characteristics that produce antiplasticization have been tested. Positron annihilation lifetime spectroscopy (PALS) has been used to determine both the size of free volume holes and the number of holes (free fractional free volume). Polyvinyl phenol (PVPh), 1,5 dihydroxy naphthalene (Ndiol) and a hexafluorinated Bisphenol A (HFBA) were chosen according to the results of a preliminary study based on density and PALS measurements with 15% of additive blends. Their blends with Trogamid show different behaviours: HFBA behaves clearly as a plasticizer while the polyvinyl phenol acts as an antiplasticizer. Ndiol has a more special effect: blend densities are greater than additive whereas the hole size decreases.     

Characterization of photodegradation of a polyurethane coating by positron annihilation spectroscopy: correlation with cross-link density

Photodegradation of a polyurethane coating by Xe arc-lamp irradiation as a function of time is studied by positron annihilation spectroscopy. Doppler broadening energy spectra (DBES) of annihilation irradiation is measured as a function of incident positron energy (0–30 keV). A significant decrease in the S-defect parameter from DBES is observed as a function of irradiation time. This is interpreted as a loss of free-volume and holes during the photodegradation process. The cross-link density in the same system is measured by a solvent (methylene chloride) swelling method and is found to increase as a function of irradiation time. A direct correlation between the increase in cross-link density and the decrease in the S-defect parameter from the DBES data is observed. These results are used to discuss the photodegradation process in terms of chemical and physical changes due to UV-irradiation in protective polymeric systems.     

Interdiffusion in a particle matrix system of two miscible polymers: An investigation by positron annihilation lifetime spectroscopy and differential scanning calorimetry

Positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC) were used to study the interdiffusion in a particle matrix system consisting of (styrene‐maleic anhydride) copolymer containing 24% maleic anhydride (SMA) and poly(methyl methacrylate) (50:50). Starting from the phase separated state of the miscible components, the transition to the mixed state due to interdiffusion during annealing at 160 and 180 °C was investigated. The diffused mass fractions of both components were estimated by DSC; they increase linearly with the logarithm of the annealing time. Both components show the same behavior, suggesting an average interphase composition of 50:50. For subsequent annealing, the kinetic behavior differs from the earlier behavior, probably because of the different diffusion coefficients of the two components. Experimental evidence is presented that the ortho‐positronium (o‐Ps) intensity correlates to the interdiffusion process. The response is due to the diffusion of inhibitors for Ps formation from one phase into the other. A semiquantitative model is developed that allows the estimation of the interphase volume fraction from the relative change of the annihilation parameters. The PALS results are discussed in relation to those obtained by DSC. The results show that PALS is a useful tool to study mixing and demixing processes in polymer blends with a three‐dimensional morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 654–664, 2002; DOI 10.1002/app.10362     

Free volume behavior in spincast thin film of polystyrene by energy variable positron annihilation lifetime spectroscopy

Free volume behavior in polystyrene thin films with thickness ranging from 22 to 1200 nm on silicon substrates was studied by energy variable positron annihilation lifetime spectroscopy (EVPALS). The films were prepared by spincasting from toluene solutions of 0.5-5.0 wt% polystyrene with M_w = 1?090?000 g/mol. Distinct deviations from bulk polystyrene in thermal expansion of the free volume holes and the glass transition temperature associated with free volume behavior were observed for the thinnest film with 22 nm thickness, indicating its exclusively high chain mobility. Comparison of the polystyrene concentration in the precursor solution around the overlap concentration suggests that the high chain mobility is due to less entangled chains caused by rapid removal of the solvent from the diluted solution in order to prepare very thin film.     

正电子湮没技术在橡塑共混体系中的应用

通过正电子湮没寿命谱技术(PALS)探测聚合物的自由体积特性,能够了解聚合物的微观性质。介绍了应用PALS在三元乙丙橡胶、丙烯酸酯类共聚物、丁苯橡胶与塑料共混体系中有关自由体积特性的研究现状。实验结果表明PALS作为一种微孔探针技术,能够在橡塑共混体系相容性研究方面发挥重要作用。     

聚苯胺溶解性研究

以苯胺氧化聚合和乳液聚合两种方法合成聚苯胺(PAn),研究了溶剂、聚合方法、反应温度、导电态、十二烷基苯磺酸用量等因素对聚苯胺溶解性的影响。结果表明,N-甲基吡咯烷酮是本征态聚苯胺的良溶剂,用乳液聚合法合成的聚苯胺其溶解性明显高于化学氧化法合成的聚苯胺,当乳液中十二烷基苯磺酸∶苯胺(摩尔比)=2.0∶1,聚合温度25℃时合成溶解率大的PAn。     

Free volume and the physico‐mechanical behaviour of polyurethane/polyacrylonitrile interpenetrating polymer networks: positron annihilation results

A series of semi‐interpenetrating polymer networks (SIPNs) of polyurethane (PU) and polyacrylonitrile (PAN) in the weight ratios 90/10, 70/30, 60/40 and 50/50 PU/PAN were prepared using polyethylene glycol, 4,4′‐diphenylmethane diisocyanate and acrylonitrile by sequential polymerization. Differential scanning calorimetry and scanning electron microscopy techniques were used to find the glass transition temperature and surface morphology of SIPNs. The tough and transparent SIPN films were characterized for physico‐mechanical properties such as density, surface hardness and tensile properties. Positron annihilation lifetime spectroscopy (PALS) was used to measure the free volume behaviour of the IPNs. The sorption behaviour of IPNs with benzene penetrant was also measured. An attempt was made to correlate the PALS results with the mechanical and sorption properties of the SIPNs. Copyright © 2005 Society of Chemical Industry