Ion implant-induced change in polyimide films monitored by variable energy positron annihilation spectroscopy

6FDA-pMDA polyimide membranes were implanted with 140 keV N⁺ ions to fluences between 2 × 10¹⁴ and 5 × 10¹⁵ cm⁻². Variable energy positron annihilation spectra were taken and spectral features compared to previously reported changes in gas permeability and permselectivity of these membranes as a function of ion fluence. Positron data corroborate the explanation of these changes in terms of molecular damage caused by the implant: for fluences up to about 1 × 10¹⁵ cm⁻², the concentration of irradiation-induced defects merely increases with implant fluence; while fluences exceeding this threshold value create a second type of positron annihilation site, thereby marking a distinct change in the structure of the polymer, which is responsible for the vast improvement of gas permselectivity data found at the same threshold fluence. PACS codes: 78.70.Bj—positron annihilation; 61.82.Pv—polymers, organic compounds; 61.72.Ww—doping and impurity implantation. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2413–2421, 1998     

Experimental comparison of the relative yield of 3γ/2γ positron annihilation using semiconductor and scintillation detectors

The yield of three photon positron annihilation is measured using semiconductor and scintillation detectors in a comparison for applications in positron emission tomography, particularly in the exploitation of three photon positron annihilation imaging where good energy resolution and good efficiency are required. In this experimental study four detectors, High-purity Germanium (HPGe), Sodium Iodide (NaI(Tl)), Lanthanum Chloride (LaCl₃:10%Ce³⁺) and Lanthanum Bromide (LaBr₃:5%Ce³⁺) were used. The peak-to-peak method was used with a ²²Na source to determine these yields. Aluminium was employed as a reference material as its high electron density reduces positronium formation and lifetimes. Teflon was also used in order to enhance the formation of ortho-positronium, since quenching is low, leading to increased three photon positron annihilation. The relative 3γ/2γ yields obtained were (3.04±0.11)·10⁻², (2.17±0.11)·10⁻², (3.26±0.10)·10⁻² and (2.03±0.11)·10⁻² for LaBr₃:Ce, LaCl₃:Ce, NaI(Tl) and HPGe detectors, respectively. Among these detectors LaBr₃:Ce proved to be the detector of choice for three photon imaging applications as it has both good energy resolution and efficiency.     

The polyurethane membranes with temperature sensitivity for water vapor permeation

The size and shape of free-volume holes available in membrane materials control the rate of gas diffusion and its permeability. Based on this principle, two segmented thermo-sensitive polyurethane (TSPU) membranes with functional gates, i.e. the ability to sense and respond to external thermo-stimuli, were synthesized and used for water vapor controllable permeation. Differential scanning calorimetry (DSC), positron annihilation lifetimes (PAL), water swelling and water vapor permeability (WVP) were used to evaluate how the structure of the polyurethane (PU) and the temperature influence the free-volume holes size and the water vapor permeability (WVP) of the PU membranes. DSC study reveals that TSPU with a glass transition or a crystalline transition reversible phase shows an obvious phase-separated structure and a phase transition temperature (defined as switch temperature, T_s). PAL study indicates that the free-volume holes size of TSPU is closely related to the T_s. When the temperature is higher than the T_s, the ortho-positronium (o-Ps) lifetime (τ₃) and the average radius (R) of free-volume holes of TSPU membrane increase dramatically. As a result, the WVP of TSPU membrane shows a dramatic increase. Additionally, the water swelling and the WVP of TSPU membrane are found to depend on the inner structure of the polymer, and they also give different responses to temperature variation. When the temperature is higher than the T_s, there is a significant increase of WVP from 3.80 kg/m² day to 7.63 kg/m² day for TSPU(a) and from 4.30 kg/m² day to 8.58 kg/m² day for TSPU(b), respectively. Phase transition accompanying significant changes in free-volume holes size and WVP can be used to develop “smart membranes” with functional gates and controllable gas permeation.     

Positronium annihilation data and actual free-volume distribution in polymers

Determination of the size distribution of free-volume holes in solids, in particular, polymers, is an important physicochemical problem. The positron annihilation technique has been proposed for this purpose. The central point in this technique is the quantitative interpretation of data, especially, for substances with a high specific surface area. A developed free-volume system in open-pore membrane materials, such as poly(trimethylsilylpropyne) PTMSP and the spirocyclically bound benzodioxane polymer PIM-1, and polymeric sorbents (hypercrosslinked polystyrenes) makes it possible for the first time to compare the sorption characteristics and positron annihilation data on the character of size distribution of nanopores in these polymers. In combination with the results of mathematical simulation of the structure and radiothermoluminescence measurements, the array of data indicate the structural inhomogeneity of the test amorphous materials. It was shown that this inhomogeneity in relation to the positron annihilation technique is expressed in the insufficiency of the representation of the orthopositronium decay curve by one component that takes into account the Gaussian lifetime distribution (symmetrical pore size distribution) and in the necessity of use of several decay components. The feasibility of revealing a nonrandom character of pore size distribution gives the positron annihilation technique an advantage over other approaches (inverse gas chromatography, ¹²⁹Xe NMR) to investigation of nanopores in polymers.     

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     

The Spin Probe Dynamics and the Free Volume in a Series of Amorphous Polymer Glass-Formers

We report the results of a combined study of the local structure and the reorientation dynamics in a series of five amorphous polymers of different fragility: cis-trans-1,4-poly(butadiene) (c-t-1,4-PBD), cis-1,4-poly(isoprene) (cis-1,4-PIP), poly(isobutylene) (PIB), poly(vinyl methylether)(PVME) and poly (propylene glycol) (PPG) by using two different probe methods. The reorientation dynamics of the molecular spin probe 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) from electron spin resonance (ESR) is related to the annihilation behaviour of the atomic ortho-positronium (o-Ps) one as obtained by positron annihilation lifetime spectroscopy (PALS). It was found that a slow to fast transition in the spin probe rotation mobility at the operationally defined spectral temperature parameter, T_50G, is connected with the mean o-Ps lifetime, τ₃ (T_50G) = (2.04 ± 0.26) ns. Consequently, using the free-volume concept of the o-Ps annihilation in terms of a quantum-mechanical model of o-Ps lifetime this transition can be connected with the occurrence of the mean free volume hole, V_h (T_50G) = (102 ± 17) ų, nearly independent of the chemical composition and the basic structural relaxation parameters of the amorphous polymers investigated. Finally, the free volume hole distribution aspect of the slow to fast transition indicates the presence of a sufficient free volume fluctuation at T_50G for both typical fragile PVME and strong PIB polymer and emphasizes the essential role of free volume in the spin probe dynamics.     

On the expansion of hole in main chain polymers determined by positron annihilation

The temperature dependence of positron annihilation characteristics, ₃ andI ₃, has been studied on sample of poly(butadiene), poly(isobutylene) and poly(chloroprene). The temperature range was between 15 and 470 K. The rate of expansion of holes or free-volume in all samples was deduced belowT _g as well aboveT _g as appr. 3·10^–3 K^–1 and 2·10^–2 K^–1, respectively. These values are very close to the rate of the mean squared displacement of scatterer<r ²>observed in neutron scattering experiments. A possibility to use an inverse value of free-volume,V _f ^–1 for study of viscoelastic state of polymers is demonstrated.     

Diffusion of gold and silver in bisphenol trimethylcyclohexanen polycarbonate

Diffusion coefficients between 5 × 10^-14 and 1 × 10^-16 cm² s^-1 have been measured for diffusion of gold and silver in the glassy state of bisphenol trimethylcyclohexanen polycarbonate in the temperature range between T_g = 507 K and 420 K using the radiotracer technique in combination with ion-beam sputtering for serial sectioning. The Arrhenius plot exhibits a downward curvature, which is interpreted within an extension of the free-volume theory to the glassy state by Vrentas and Duda. The very small metal diffusivities in comparison to values for gas molecules of comparable size suggest substantial interaction energies. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 :1043–1048, 1997     

Diffusivity enhancement of water vapor in poly(vinyl alcohol)–fumed silica nano-composite membranes: Correlation with polymer crystallinity and free-volume properties

The diffusion coefficients of water vapor in poly(vinyl alcohol)–fumed silica (PVA–FS) nano-composite membranes were determined using the gravimetric method. Water vapor was observed to diffuse more rapidly in membranes with increased FS content. The vapor diffusion coefficient was determined as 1.2 × 10⁻¹³ m²/s in pure PVA and was observed to increase to 3.0 × 10⁻¹³ m²/s in PVA composites containing 30% FS nano-particles. The free-volumes of PVA–FS membranes were characterized using positron annihilation lifetime (PAL) spectroscopy. PAL results showed that both the ortho-positronium (o-Ps) lifetime and intensity increased with the addition of FS. The intensity (I₃) was found to be higher than the estimated value determined from the linear combination of the data from pristine PVA and FS, and correlated excellently with the polymer amorphous content. The PAL results indicate that a higher FS content in PVA increases the free-volume hole size (a volume increase from 40 to 55 Å³) and free-volume hole density (an I₃ increase from 23 to 28%), resulting in a higher fractional free-volume in the nano-composites. The increase in the relative polymer free-volume with higher FS content was associated with a decrease in the PVA crystallinity, as determined from differential scanning calorimetry measurements. It is postulated that the incorporated FS nano-particles interrupt polymeric chain packing and retard crystallization during membrane formation. More crystalline segments were transformed into amorphous regimes in the nano-composites containing more FS. A correlation between water diffusivity and the fractional free-volume was obtained, and the water diffusivity was successfully expressed by the free-volume theory.     

Molecular fragmentations: Part II. Structures and energies of molecular fragments derived from formamide and its molecular cation

Molecular geometries and heats of formation have been calculated, using MINDO/3, for mass spectral fragment pairs (A⁺ + B) derived from formamide. There are five stable isomeric forms of the molecular ion: [H₂NC(OH)]⁺, (H₃NCO)⁺, [HNC(OH₂)]⁺, [NCH(OH₂)]⁺, and (NCOH₃)⁺ (in order of increasing

, but no isomer (H₂NCHO)⁺. There are three isomeric forms of (M—H)⁺: (H₂NCO)⁺ (HNCOH)⁺, and (NCOH₂)⁺: the only stable form of (M—2H)⁺ is (NCOH)⁺. Other (A/B)⁺ fragment pairs calculated are (CO/NH₃)⁺, (HCO/NH₂)⁺, (H₂O/HCN)⁺, (H₂O/HNC)⁺ [HO^. + (HCNH)⁺], and [HO^. + (H₂NC)⁺]. The structure of the doubly charged ion M²⁺ is also reported.     

Degradation of polymer coating systems studied by positron annihilation spectroscopy. II. Correlation with free radical formation

The photo‐degradation of polymer coating systems due to irradiation by UV and Xenon light sources is studied using positron annihilation spectroscopy and electron spin resonance (ESR). Doppler broadened spectra of positron annihilation, as a function of slow positron implantation energy and ESR spectra, are measured in two types of polyurethane which were exposed, ex situ, to UV irradiation for up to 800 h. The UV irradiation systematically decreases the S parameter as a function of exposure duration and increases the ESR signals. Thus, significant S parameter decrease is correlated with the ESR signal increase resulting from photo‐degradation of polymers due to UV irradiation. Parallel in situ positron annihilation and ESR experiments are performed as a function of Xenon light exposure for up to 100 min. These results show that the photo‐degradation of the polyurethane coatings involves initial free‐radical formation, which is correlated with the subnanometer defects detected by positron annihilation spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1289–1305, 1999     

A study of time dependence of ortho-positronium annihilation in a poly(butadiene) at different temperatures: a meaning of I3 parameter

Positron annihilation measurements as a function of temperature and time have been carried out on a poly(butadiene). The measurements were performed at several temperature points from 14 to 225 K. The measurement time was several hours to four days. The analysis of data shows the following features:

(i) the value of τ₃ does not depend on the rate of cooling or time,

(ii) the value of I₃ depends on the rate of cooling and the history of thermal treatment,

(iii) the dependence of I₃ on time can be described by Debye function. But the rise in I₃ is observed at very low temperatures,

(iv) the I₃ decays to value of I₃ observed during very slow cooling.

Selective and Sensitive Two New Macroacyclic Schiff base Fluorescent Turn-Off Receptors for Fe3+, DFT Calculation and Their Antibacterial Activity

Two new Macroacyclic Schiff base chemosensors (L₁ and L₂) were synthesized by the one pot condensation reaction of 2-[3-(2-formyl phenoxy)propoxy]benzaldehyde and aminophenol in a 1:2 molar ratio and were characterized by IR, NMR spectroscopy. Both Schiff bases displayed high selectivity and sensitivity towards Fe³⁺ over other metal ions in H₂O-DMF solution (Ag⁺,Cu²⁺, Ni²⁺, Zn²⁺, Mg⁺², Mn⁺², Pb⁺², Co⁺², Hg⁺², Cr⁺³, Na⁺, Ba⁺² and Cd²⁺) due to their structure including oxygen donor atoms. The test results showed fluorescence quenching of the fluorophores when Fe³⁺ was bound to the recognition units. From test results, a high selectivity for Fe³⁺ were discovered in this type of sensors, especially, the probe based on 2-aminophenol exhibited more significant quenching in fluorescence intensity compared with 4-aminophenol-based due to its rigidity structure. In addition, the structure of ligands and their antibacterial properties was investigated.     

Synthesis of a novel poly(para‐phenylene ethynylene) for highly selective and sensitive sensing mercury (II) ions

A new poly(p‐phenylene ethynylene) derivative with pendant 2,2′‐bipyridyl groups and glycol units (PPE‐bipy) has been prepared, and its metal ion sensing properties were investigated. The polymer of PPE‐bipy exhibited high selectivity for Hg²⁺ as compared with Li⁺, Na⁺, K⁺, Ba²⁺, Ca²⁺, Mg²⁺, Al³⁺, Mn²⁺, Ag⁺, Zn²⁺, Pb²⁺, Ni²⁺, Cd²⁺, Cu²⁺, Co,²⁺ and Fe³⁺ in THF/EtOH (1:1, v/v) solution. The fluorescence of PPE‐bipy was efficiently quenched by Hg²⁺ ions, and the detection limit was found to be 8.0 nM in a THF/EtOH (1:1, v/v) solvent system. PPE‐bipy also showed a selective chromogenic behavior toward Hg²⁺ ions by changing the color of the solution from slight yellow to colorless, which can be detected with the naked eye. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1998–2007, 2008     

The validities of centrifugal sudden approximations in chemical reaction dynamics

In this review article, we discuss and analyze the validities of centrifugal sudden (CS) approximations in chemical reactions, with emphasis on the recent progress in the comparison studies of close‐coupling and CS approximations in chemical dynamics both adiabatically and nonadiabatically. All these relevant studies are performed using the time‐dependent wave packet approach, focusing on several typical and benchmark chemical reactions, for example, the triatomic adiabatic ion–molecule reactions of Ne + , He + HeH⁺, O⁺ + H₂, O⁺ + D₂, and O⁺ + HD, the triatomic nonadiabatic reactions of N + NH and O + N₂, and the tetraatomic and polyatomic adiabatic reactions of H₂ + D₂ and H + CHD₃. © 2015 Wiley Periodicals, Inc.     

Synthesis of new Azo‐based liquid crystalline polymers and their selective sensing behaviors to alkali metal ions

We report novel liquid crystalline (LC) polymers containing pendant azobenzene moieties with n‐dodecyl substituents and ethyleneoxy spacers of different lengths and describe their selective detection behaviors to alkali metal ions. The new azopolymers produce homogenous smectic phases with a typical fan‐shaped texture. UV‐Vis and ¹H NMR studies confirm that the azopolymers selectively bind to Li⁺ and Na⁺, but do not complex with K⁺, Ba²⁺, Mg²⁺, or Ca²⁺. Both the ethyleneoxy spacer and azobenzene units participate in binding to Li⁺ and Na⁺ cations in solution. Interestingly, after formation of the complexed structure, the ratio of cis to trans conformer is considerably increased suggesting stronger interactions of the cis conformer with alkali metal ions. Irradiation of the complexed structure with 365 nm UV induces conversion of the uncomplexed trans to the cis. These findings suggest a great potential of the LC azopolymers as selective sensors or separation membranes for alkali metal ions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1713–1723     

Fourier transform infrared spectroscopy study of the effect of pH on anion and cation adsorption onto poly(acrylo‐amidino diethylenediamine)

The role of hydrogen bonding in the chemistry of transition‐metal complexes remains a topic of intense scientific and technological interest. Poly(acrylo‐amidino diethylenediamine) was synthesized to study the effects of hydrogen bonding on complexes at different pHs. The polymer was synthesized through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl₃ · 6H₂O addition. The adsorption capacity of this polymer was 11.4 mequiv/g. The ions used for the adsorption test were CrO, PO, Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺. All experiments were confirmed with Fourier transform infrared. In the study of anion adsorption, at low pHs, only ionic bonds existed, whereas at high pHs, no bonds existed. However, in the middle pH region, both ionic bonds and hydrogen bonds formed between poly(acrylo‐amidino diethylenediamine) and the chromate ion or phosphate ion. When poly(acrylo‐amidino diethylenediamine) and metal ions (Cu²⁺, Ni²⁺, Fe²⁺, and Ag⁺) formed complexes, a hydrogen‐bonding effect was not observed with Fourier transform infrared. The quantity of metal ions adsorbed onto poly(acrylo‐amidino diethylenediamine) followed the order Ag⁺ > Cu²⁺ > Fe²⁺ > Ni²⁺. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2010–2018, 2004     

Studies on the equilibrium among poly(sodium 4‐styrenesulfonate), Cu2+, and iminodiacetic acid by ultrafiltration at constant ionic strength

The ultrafiltration technique evaluates the interactions of water‐soluble polymers with metal ions. Aqueous solutions containing poly(sodium 4‐styrenesulfonate) (PSS), Cu(NO₃)₂, NaNO₃, and iminodiacetic acid (IDAA) are examined by this technique. Cu²⁺ undergoes complex formation with IDAA and intreracts electrostatically with PSS. On the other hand, Na⁺ ions are in competition with Cu²⁺ for the electrostatic binding to PSS. The solutions are ultrafiltered keeping the ionic strength constant, so their compositions are allowed to change continuously. The concentration of Cu²⁺ bound to the polymer showed an exponential decay during filtration. The concentration of Cu²⁺ bound to the polymer before ultrafiltration is calculated by extrapolation. The concentration of the different species in solution is proposed as a function of the filtration factor. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2587–2593, 2002     

Relation of gas-transport parameters of amorphous glassy polymers to their free volume: Positron annihilation study

Correlations of transport parameters (diffusion coefficients D and permeabilities P of gases) and thermodynamic parameters (solubility coefficients S and parameters C′ _H of sorption isotherms) with the sizes of free-volume elements, v _h, as estimated via positron annihilation lifetime spectroscopy are analyzed for the first time on the basis of the data array obtained for glassy polymers. Correlations of logD and logP with 1/v _h that agree with the free-volume model under the condition of a weak change in the concentration of free-volume elements in different polymers are ascertained. Certain deviations from linear correlations with 1/v _h for polymers with high free volumes are interpreted as evidence that the connectivity (openness) of pores increases with the sizes of free-volume elements. For solubility coefficients and Langmuir parameters of sorption capacity C′ _H , good linear correlations with the value of v _h are demonstrated.     

5,5′‐Hydrazinebistetrazole: An Oxidation‐stable Nitrogen‐rich Compound and Starting Material for the Synthesis of 5,5′‐Azobistetrazolates

All 5,5′‐hydrazinebistetrazoles reported in the literature are sensitive to oxidation and react with atmospheric oxygen to yield the corresponding 5,5′‐azobistetrazolates on time. Herewith, we report on the synthesis of the free acid 5,5′‐hydrazinebistetrazole (HBT) which showed to be stable on air for extended periods of time. The compound was fully characterized by analytical and spectroscopic methods and its X‐ray structure was determined by diffraction techniques. Besides, we determined its explosive properties by BAM methods and calculated its heat of formation (+414 kJ mol^?1), detonation velocity (8523 m s^?1) and detonation pressure (27.7 GPa). HBT proved to be very safe to handle (impact sensitivity: >30 J, friction sensitivity: ～108 N) and was used as a starting material for the synthesis of some already reported 5,5′‐azobistetrazolates: NH₄⁺, NH₂NH₃⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺.