Dopant‐induced microstructural,optical, and electrical properties of TiO2/PVA composite

The optical, electrical, and microstructurtal properties of pure and TiO₂/Poly(vinyl alcohol) (PVA) composite polymer films were carried out using FTIR, XRD, UV‐Visible, DC electrical conductivity, and Positron annihilation lifetime spectroscopy (PALS) techniques. The FTIR study reveals that the Ti⁺ ions of TiO₂ interacts with the OH groups of PVA via intra/inter molecular hydrogen bonding and forms charge transfer complex (CTC). These formed CTC will affect the optical property of the composite film, which is reflected from UV‐Visible study. Using the observed UV–Visible spectra, optical energy band gap is estimated and its value decreases with increasing dopant concentration. The positron annihilation studies show that the considerable effect on free volume related microstructure of the PVA due to doping and complex formation. These microstructural modifications are also enhances PVA crystallinity which is reflected from XRD studies. It is also observed that the TiO₂ particle forms cluster within the PVA due to the aggregation of particles and these particle cluster size increases with dopant concentration. These microstructural variations due to doping affects the DC electrical conductivity and its variations are understood based on the intra chain one‐dimensional interpolaron hopping conduction mechanism. POLYM. COMPOS. 37:987–997, 2016. © 2014 Society of Plastics Engineers     

Thermally induced microstructural changes and its influence on electrical conductivity of a polymer‐based bakelite RPC detector material: A positron lifetime study

Annealing studies have been carried out to understand the temperature induced microstructural changes in Bakelite (P‐120 NEMA LI‐1989 Grade XXX) Resistive Plate Chamber (RPC) detector material using Positron annihilation lifetime spectroscopy (PALS), Fourier transform infrared spectroscopy (FTIR), and XRD. The variation of positron lifetime parameters viz., ortho‐Positronium lifetime (τ₃) and free volume size (V_f) increases marginally above glass transition temperature T_g as a result of structural changes due to segmental mobility. The drastic increase of free volume parameters above 240°C attributed to the reduction in strength of C—H bond of the aliphatic bridges and cleavage of methylene bridges of the polymer network, which is supported by the FTIR results. The XRD results show the reduction in crystallinity and average crystallite size of Bakelite on annealing correlates well with the free volume and electrical conductivity. The temperature induced electrical conductivity and activation energy is also correlated with the positron lifetime parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 793‐800, 2013     

Free volume‐related microstructural properties of lithium perchlorate/sodium alginate polymer composites

The effect of salt (LiClO₄) on free volume‐related microstructural, optical, and dielectric properties of lithium perchlorate (LiClO₄)‐doped sodium alginate (NaC₆H₇O₆)_n solid polymer electrolyte were studied using Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), UV–Visible, dielectric measurements, and positron annihilation lifetime spectroscopy (PALS) techniques. The FTIR study reveal that the LiClO₄ interact with the O H groups of sodium alginate (NaAlg) and forms charge transfer complex (CTC). These formed CTC within the composite film affect the optical property of the polymer composite, which was reflected from UV–Visible study. The free volume was probed by the PALS technique, which uses the o‐Ps pickup lifetime τ _3, as an indication of local electron density and mean free volume radius. The o‐Ps pickup intensity I₃, reflects the probability of o‐Ps formation. The o‐Ps components τ₃ and I₃ increases with salt concentration, which shows microstructural modifications due to the decrease in the crystallinity of the NaAlg as observed from XRD studies. Therefore, electrical studies on the doped NaAlg reveal that the ionic movement in the composites is mainly due to the segmental motion of the polymer backbone. So, the complex formation due to doping affects the free volume‐related microstructure and hence the dielectric properties including the AC conductivity of the polymer composites. POLYM. COMPOS., 35:1267–1274, 2014. © 2013 Society of Plastics Engineers     

Hybrid organic inorganic nylon‐6/SiO2 nanocomposites: Transport properties

Organic‐inorganic hybrid membranes of nanosized SiO₂‐filled polyamide composites were prepared via film casting and their transport properties were studied. Gas permeation measurements were performed at room temperature, and the membrane exhibited an increase in membrane permeability performance. In contrast to the performance of traditional dense filled polymer systems, the permeability increased with an increased number of nanosilica particles. The nanocomposites were studied using positron annihilation lifetime spectroscopy (PALS). From the ortho‐positronium (o–Ps) lifetime (τ₃), the size of the local free volume (holes) was estimated. The increase in permeability is ascribed to the additional free volume obtained. This is created by the presence of nanoparticles that alter the PA chain packing. Furthermore, wide angle X‐ray diffraction (WAXD) patterns revealed that the incorporation of silica induced the structural modification of polymer chains by modifying the degree of crystallinity in comparison with the neat polymer. Polym. Eng. Sci. 44:1240–1246, 2004. © 2004 Society of Plastics Engineers.     

Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparations and properties of thermosensitive terpolymers of N‐isopropylacrylamide,sodium 2‐acrylamido‐2‐methyl‐propanesuphonate,and N‐tert‐butylacrylamide

Terpolymers based on N‐isopropylacrylamide, sodium 2‐acrylamido‐2‐methyl‐propanesulfonate, and N‐tert‐butylacrylamide were synthesized by free‐radical copolymerization with 2,2′‐azobisisobutyronitrile as an initiator. The lower critical solution temperatures (LCSTs) of the linear polymer aqueous solutions were determined by the measurement of the transmittance on UV at different temperatures. The influence of the polymer concentration, polymer composition, and ionic strength on the LCSTs of the linear polymers was investigated. The LCST decreased with increases in the hydrophobic monomer N‐tert‐butylacrylamide, polymer concentration, and ionic strength. The phase transition became sharp when the polymer concentration and ionic strength increased. Meanwhile, the crosslinked hydrogels were prepared with the same recipe used for the linear terpolymers, but a crosslinker was added to the reaction system. The swelling ratios of the hydrogels at various temperatures and salt solutions were determined. The hydrogels possessed both high swelling ratios and thermosensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Microstructural characterization of short glass fibre reinforced polyethersulfone composites

To explore the effect of short glass fiber reinforcement (SGFR) on the mechanical properties of polyethersulfone (PES), microstructural characterization has been performed by positron lifetime technique. The free volume distribution of SGFR‐PES composites derived from CONTIN‐PALS2 program exhibits the narrow full width at half maximum (FWHM) indicates the strong interaction between polymeric chains of PES matrix and SGF. The positron lifetime parameters of SGFR‐PES composites are correlated with the mechanical properties viz., Tensile strength (TS), Young's modulus (YM) and elongation at break (EB). The decreased positron lifetime parameters, improved mechanical properties and reduced crystallinity of SGFR‐PES composites are attributed to the improved chemical and physical interaction between the functional groups of both SGF and PES matrix. This is clearly evident from the FTIR (Fourier Transform Infrared Spectrometry) studies. The hydrodynamic interaction parameter (h) show negative values, suggest the improved interaction in SGFR‐PES composites by the generation of excess friction at the interface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43647.     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinylalcohol) films

Poly(vinylalcohol) (PVA) films filled with different filling levels of CrF₃ and MnCl₂ have been prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in structure properties that occur due to filling. The changes occurring in the measured parameters with increasing the filler content was been interpreted in terms of the structural modification of the PVA matrix. It was found that all studied samples had the main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. On the other hand, the samples of CrF₃‐filled PVA films with filling level W ≥ 10 wt % revealed another melting temperature, indicating the presence of a new crystalline phase besides the main crystalline phase. Changes occurring in the degree of crystallinity of the studied samples were discussed. The calculated degree of crystallinity was formulated numerically to be an exponential function of filling level. The X‐ray diffraction patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 516–521, 2003     

Gelation of a new hydrogel system of atactic‐poly(vinyl alcohol)/NaCl/H2O

a‐PVA/NaCl/H₂O hydrogels have been prepared by gelation of aqueous atactic‐poly(vinyl alcohol) (a‐PVA) solutions in the presence of NaCl. The gelling temperature, melting temperature and the preservation of water of the hydrogels have been measured. The effect of the addition of NaCl to the hydrogels on gelling temperature and melting temperature is marked when the NaCl concentration is over a certain value. High NaCl concentration favours high‐melting‐point hydrogels. When the NaCl concentration is high enough (such as 11%), high‐melting‐point and white turbid opaque a‐PVA/NaCl/H₂O hydrogels can be prepared, regardless of the PVA concentration. Similarly, the low gelling temperature of a‐PVA/NaCl/H₂O solutions comes from low NaCl concentration, while high gelling temperature ranges from 50 to 70 °C when the NaCl concentration is 11%. In appearance, the types of syneresis of a‐PVA/NaCl/H₂O are χ‐type or a mixture of χ‐ and n‐types; water release of the hydrogels is slowed down by the addition of NaCl. © 2002 Society of Chemical Industry     

Investigation of free volume distribution and mechanical properties of rectorite/nylon 6 nanocomposites

The effects of organophilic rectorite (OREC) content and interfacial interaction on the nanoscale free volume, the crystallinity, and the heat distortion temperature (HDT) have been studied for nylon 6/layered nanocomposites by positron annihilation lifetime spectroscopy (PALS) and dynamic mechanical analysis (DMA) etc. Experimental results indicated that both HDT and crystallinity increase with filled OREC due to the nucleating or epitaxial effect of nanoparticles filled and interfacial interaction between the OREC and matrix. A continuous positron lifetime analysis program based on maximum entropy lifetime method (MELT) was used to obtain the free volume distribution, which revealed the existences of two long‐lived lifetime components (τ₃ and τ₄) corresponding to two kinds of different free volumes. We introduced a new parameter A defined as A = Aτ₃/A (τ₃ + τ₄) and found a direct linearly relationship between the A and the crystallinity, which suggested that τ₃ is mainly attributed to ortho‐positronium pick‐off annihilation in the interstitial free volume of the crystalline region. Experimental results also found that the interfacial interaction has different effect on the free volume properties in the different temperature range, which can be explained by a model that describes the evolution of the interfacial interaction area with temperature. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Swelling characteristics of thermo‐ sensitive poly[(2‐diethylaminoethyl methacrylate)‐co‐(N,N‐dimethylacrylamide)] porous hydrogels

Temperature‐sensitive poly[(2‐diethylaminoethyl methacrylate)‐co‐(N,N‐dimethylacrylamide)] [P(DEAEMA‐co‐DMAAm)] hydrogels with five different DMAAm contents were synthesized with and without the addition of sodium carbonate as porosity generator. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observation and the determination of swelling ratio. The influence of the pore‐forming agent and content of DMAAm on swelling ratio and network parameters such as polymer–solvent interaction parameter (χ), average molecular mass between crosslinks (M?_c) and mesh size (ζ) of the cryogels are reported and discussed. The swelling and deswelling rates of the porous hydrogels are much faster than for the same type of hydrogels prepared via conventional methods. At a temperature below the volume phase transition temperature, the macroporous hydrogels also absorbed larger amounts water compared to that of conventional hydrogels and showed obviously higher equilibrated swelling ratios in aqueous medium. In particular, the unique macroporous structure provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling and swelling processes. These properties are attributed to the macroporous and regularly arranged network of the porous hydrogels. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying porosity generation methods during the polymerization reaction. Copyright © 2007 Society of Chemical Industry     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Mechanochemical modification of silica with poly(1‐vinyl‐2‐pyrrolidone) by grinding in a stirred media mill

The polymerization of 1‐vinyl‐2‐pyrrolidone (VP) mechanochemically initiated by grinding silica was investigated in a wet stirred media mill. The polymerization itself proceeds from the silica grinding without any additional initiator. We have found that the amount of grafted polymer increases with an increase in total ground silica surface. The suspension of polymer‐modified silica nanoparticles showed high colloidal stability in water because of the appearance of grafted hydrophilic PVP on the surface during the reactive grinding. Because the nanoparticles SiO₂‐graft‐PVP are biocompatible, the developed polymer nanocomposite material can be of particular interest for the performance of membranes and for the fabrication of biocompatible hydrogels with enhanced mechanical properties and porosity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3708–3714, 2007     

Positron Annihilation in Off‐Stoichiometric and Ta‐Doped Zn2TiO4

While Zn vacancies are regarded as the charge compensators in Ti‐rich Zn₂TiO₄, no evidence of cation vacancies in essentially single‐phase samples containing up to 13 wt% excess TiO₂ was evident from positron annihilation lifetime spectroscopy (PALS). Nor was there strong evidence of cation vacancies in Ta‐doped samples targeted to contain either tetrahedral or octahedral vacancies, although there was a small increase in the lifetime as the doping level increased and the structure changed from cubic to tetragonal.     

Preparation and characterization of dual responsive sodium alginate‐g‐poly(vinyl alcohol) hydrogel

Poly(vinyl alcohol) (PVA) was chosen as a controllable gelator to prepare sodium alginate (SA)‐based physically cross‐linked dual‐responsive hydrogel by three steps. First, polyvinyl acetate (PVAc) was grafted onto SA via radical copolymerization. Then, the copolymer was subsequently converted into SA‐g‐poly(vinyl alcohol) (SAPVA) by alcoholysis reaction. PVA content of SAPVA was tailored by controlling the graft percentage of PVAc, i.e. through varying the amount of vinyl acetate during copolymerization. Finally, SAPVA hydrogels were formed by freezing‐thawing cycles. The structure of the graft copolymers was verified with FTIR spectroscopy. X‐ray diffraction analysis results revealed that the crystallinity of SAPVA hydrogels depended on the PVA content of SAPVA. The swelling test showed that SAPVA hydrogels were pH‐responsive, and the swelling was reversible. SAPVA hydrogels also behaved electric‐responsive. In addition, the pH‐sensitivity of SAPVA hydrogels was able to be controlled with the composition of the hydrogels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermally crosslinked anionic hydrogels composed of poly(vinyl alcohol) and poly(γ‐glutamic acid): Preparation,characterization, and drug permeation behavior

pH‐sensitive anionic hydrogels composed of poly(vinyl alcohol) (PVA) and poly(γ‐glutamic acid) (γ‐PGA) were prepared by the freeze drying method and thermally crosslinked to suppress hydrogel deformation in water. The physical properties, swelling, and drug‐diffusion behaviors were characterized for the hydrogels. In the equilibrium swelling study, PVA/γ‐PGA hydrogels shrunk in pH regions below the pK_a (2.27) of γ‐PGA, whereas they swelled above the pK_a. In the drug‐diffusion study, the drug permeation rates of the PVA/γ‐PGA hydrogels were directly proportional to their swelling behaviors. The cytocompatibility test showed no cytotoxicity of the PVA/γ‐PGA hydrogels for the 3T3 fibroblast cell lines. The results of these studies suggest that hydrogels prepared from PVA and γ‐PGA could be used as orally administrable drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Determination of green‐bond strength in tacky poly(vinyl alcohol) hydrogels

Pressure‐sensitive tack is the adhesive property related to bond formation. It is a key issue when formulating hydrogel poultices for transdermal delivery, dressings, and bioelectrodes. Quantitative tack gives an indication of the potential ease and success of application when gels are brought into contact with skin. The effects of different dwell times and constant pressures on bond formation between tacky poly(vinyl alcohol) (PVA) hydrogels and a skin model were explored in the current study; these were correlated with viscoelastic properties in order to elucidate structure–function relationships. A rolling tack test was performed using a novel apparatus capable of simultaneously controlling the pressure and dwell time in a hydrogel/skin‐model‐probe system. PVA gels were formed via the freeze–thaw technique using Ca²⁺ ions. Lower calcium availability in PVA gels resulted in longer dwell times required to complete bond formation, decreased creep compliance (at 0.01 s) and a decreased G′_{(ω = 40)}/G′_{(ω = 0.01)} ratio, all three leading to a loss in tack strength. All tested gels were found to have pressure‐sensitive tack. The results of this study support the applicability of a rheological methodology and a novel tack‐testing procedure to quantify green‐bond formation in pressure‐sensitive‐adhesive PVA hydrogels. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2130–2135, 2003     

Changes in free volume and gas permeation properties of poly(vinyl alcohol) nanocomposite membranes modified using cage-structured polyhedral oligomeric silsesquioxane

The present work reports the effect of various organically functionalized polyhedral oligomeric silsesquioxane (POSS) particles on the gas transport properties (N₂, O₂, and CO₂ molecules) in poly(vinyl alcohol) (PVA) membranes. The incorporation of polyethylene glycol-POSS (PEG-POSS), octa-tetramethylammonium-POSS (Octa-TMA-POSS) and m-POSS (Octa-TMA-POSS molecule was modified using cetyltrimethyl ammonium bromide) led to the enhancement in CO₂ separation performance of PVA, among which, PEG-POSS exhibited highest CO₂ separation due to the dipole-quadrupolar interaction of CO₂ with ethylene oxide group in POSS. Octa-TMA-POSS and m-POSS reduced the O₂ and N₂ permeability of the PVA membrane due to the reduction in the number of permeating pathways as compared to pure PVA. Free volume of the membranes was evaluated by positron annihilation lifetime spectroscopic (PALS) and coincidence Doppler broadening measurements. PALS confirms the increase in polymer free volume in PVA/POSS system due to the presence of rigid and spherical POSS molecule, which could enter in the polymer chain and provide viable pathway for molecular transport. Maxwel–Wagner–Sillar and Higuchi models were applied for the theoretical prediction of permeability of the fabricated membranes.     

Preparation and antibacterial effects of PVA‐PVP hydrogels containing silver nanoparticles

The poly(vinyl alcohol)/poly(N‐vinyl pyrrolidone) (PVA–PVP) hydrogels containing silver nanoparticles were prepared by repeated freezing–thawing treatment. The silver content in the solid composition was in the range of 0.1–1.0 wt %, the silver particle size was from 20 to 100 nm, and the weight ratio of PVA to PVP was 70 : 30. The influence of silver nanoparticles on the properties of PVA–PVP matrix was investigated by differential scanning calorimeter, infrared spectroscopy and UV–vis spectroscopy, using PVA–PVP films containing silver particles as a model. The morphology of freeze‐dried PVA–PVP hydrogel matrix and dispersion of the silver nanoparticles in the matrix was examined by scanning electron microscopy. It was found that a three‐dimensional structure was formed during the process of freezing–thawing treatment and no serious aggregation of the silver nanoparticles occurred. Water absorption properties, release of silver ions from the hydrogels and the antibacterial effects of the hydrogels against Escherichia coli and Staphylococcus aureus were examined too. It was proved that the nanosilver‐containing hydrogels had an excellent antibacterial ability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 125–133, 2007     

Thermal properties of poly(vinyl alcohol)–solute blends studied by TMDSC

A thermal analysis study of blends of semicrystalline poly(vinyl alcohol) (PVA) with a pharmaceutical substance, buflomedil pyridoxal phosphate (BPP) is presented. Temperature‐modulated DSC (TMDSC) was used to determine the T_g as well as the crystallinity of blends with various polymer to drug ratios, for different annealing procedures. Positive deviations from a simple expression for the composition dependence of the glass transition of the blend were found. This result, together with the increased thermal stability of PVA–BPP blends, evidenced by TGA analysis, indicates the existence of specific interactions between the polar groups of the two components. The incorporation of dispersed BPP in the PVA matrix results in a composition‐dependent lowering of the polymer's T_m and degree of crystallinity. In addition, we found that, while melting of pure PVA is predominantly reversing, its melting in the blends acquires an increasingly higher nonreversing component with increasing BPP content in the blend. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1151–1156, 2004