Metal ion permeation properties of silk fibroin/chitosan blend membranes

Silk fibroin/chitosan (SF/CS) blend membranes were prepared and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy. It was found that SF and CS were compatible in the blend membranes and that the membranes were dense without microscopic phase separation. Swelling experiments showed that the swelling ratio of the blend membranes increased with CS content and reached the highest value when CS content was 70 wt%. Experiments indicated that the permeability coefficient of K⁺ through the blend membrane was 2–4 times higher than that of pure CS membrane, and 10 times higher than that of pure SF membrane. The permeation rate of K⁺ increased linearly with CS content in the blend membrane for the lower concentration feeding solution. For different metal ions, the permeability through SF/CS blend membranes was in the sequence K⁺ > Ca²⁺ > Cd²⁺ > Pb²⁺ > Cu²⁺ > Ni²⁺. Copyright © 2006 Society of Chemical Industry     

Processable aromatic polyesters based on bisphenol derived from cashew nut shell liquid: synthesis and characterization

The miscibility of chitosan/poly(ethylene oxide) (CS/PEO) blends was investigated by a combination of experiment and molecular simulation. Results from X-ray diffraction (WAXD) and thermal analysis (DSC) suggest that the maximum miscibility was seen at the PEO weight fraction (w _PEO) =0.2; the optimum stoichiometric ratio for CS and PEO functional groups. The change in vibrational frequencies from infrared spectra was attributed to the specific interaction between PEO ether oxygen with the amino and hydroxyl groups of CS. Radial distribution functions (RDF) from MD simulation suggest that all CS functional groups (NH₂, C3-OH, and C6-OH) can interact with PEO ether groups for which NH₂ has the highest activity. For CS hydroxyl groups, a more significant contribution of C6-OH rather than C3-OH groups that interact with PEO ether oxygen was observed. The interaction parameter (χ) determined from MD simulation was in good agreement with that of the DSC experiment (χ_CS-PEO?=?-0.21). Based on a comparison between χ and χ _critical , CS/PEO blend was predicted to be miscible for w _PEO <0.58 with a maximum at w _PEO =0.2. In addition, the order parameter from the mesoscale simulation was employed to monitor the phase separation in these blends. From MesoDyn simulation, the miscibility was decreased with increasing PEO content, and miscible CS/PEO blends were obtained only with w _PEO <0.58, in good agreement with MD simulation and experiment.     

Miscibility with positive deviation in Tg-composition relationship in blends of poly(2-vinyl pyridine)-block-poly(ethylene oxide) and poly(p-vinyl phenol)

Phase behavior and miscibility with positive deviation from linear T_g-composition relationship in a copolymer/homopolymer blend system, poly(2-vinyl pyridine)-block-poly(ethylene oxide) (P2VP-b-PEO)/poly(p-vinyl phenol) (PVPh), were investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR), optical microscopy (OM), and scanning electron microscopy (SEM). Optical and electron microscopy results as well as NMR proton spin-lattice relaxation times in laboratory frame () all confirmed the miscibility as judged by the T_g criterion using DSC. In comparison to the literature result on a homopolymer/homopolymer blend of P2VP/PVPh, fitting with the Kwei equation on the T_g-composition relationship for the block-copolymer/homopolymer blend of P2VP-b-PEO/PVPh blend system yielded a smaller q value (q = 120) for P2VP-b-PEO/PVPh than that for P2VP/PVPh blend (q = 160). The FT-IR and ¹³C NMR results revealed hydrogen-bonding interactions between the pendant pyridine group of P2VP-b-PEO and phenol unit in PVPh, which is responsible for the noted positive deviation of the T_g-composition relationship. Comparison of the shifts of hydroxyl IR absorbance band, reflecting the average strength of H-bonding, indicates a decreasing order of P2VP/PVPh > P2VP-b-PEO/PVPh > PEO/PVPh blends. The PEO block in the copolymer segment tends to defray the interaction strength in the P2VP-b-PEO/PVPh blends because of relative weaker interaction between PEO and PVPh than that between P2VP and PVPh pairs. A comparative ternary (P2VP/PEO)/PVPh blend was also studied as the controlling experiments for comparison to the P2VP-b-PEO/PVPh blend. The thermal behavior and interaction strength in (P2VP/PEO)/PVPh ternary blends are discussed with those in the P2VP-b-PEO/PVPh copolymer/homopolymer blend.     

Impact of the cation field strength on physical properties and structures of alkali and alkaline-earth borosilicate glasses

The impact of the cation field strength (CFS) of the glass network-modifier cations on the structure and properties of borosilicate glasses (BS) were examined for a large ensemble of mixed-cation (R/2)M₍₂₎O–(R/2)Na₂O–B₂O₃–KSiO₂ glasses with M⁺ ={Li⁺, Na⁺, K⁺, Rb⁺} and M²⁺ ={Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺} from four series of {K, R} combinations of K = n(SiO₂)/n(B₂O₃) = {2.0, 4.0} and R =[n(M₍₂₎O) ?+ ?n(Na₂O)]/n(B₂O₃) = {0.75, 2.1}. Combined with results from La³⁺ bearing glasses enabled the probing of physical-property variations across a wide CFS range, encompassing the glass transition temperature (T_g), density, molar volume and compactness, as well as the hardness (H) and Young's modulus (E). We discuss the inferred composition–structure/CFS–property relationships. Each of T_g, H, and E revealed a non-linear dependence against the CFS and a strong T_g/H correlation, where each property is maximized for the largest alkaline-earth metal cations, i.e., Sr²⁺ and Ba²⁺, along with the high-CFS La³⁺ species. The ¹¹B MAS NMR-derived fractional BO₄ populations decreased linearly with the average M^z+/Na⁺ CFS within both K–0.75 glass branches, whereas the NBO-rich K–2.1 glasses manifested more complex trends. Comparisons with results from RM₂O–B₂O₃–KSiO₂ glasses suggested no significant “mixed alkali effect”.     

The solubility of selenate-AFt (3CaO·Al2O3·3CaSeO4·37.5H2O) and selenate-AFm (3CaO·Al2O3·CaSeO4·xH2O)

The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO·Al₂O₃·3CaSeO₄·37.5H₂O), and selenate-AFm (3CaO·Al₂O₃·CaSeO₄·xH₂O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 °C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K_so=61.29±0.60 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·3CaSeO₄·37.5H₂O+12 H⁺⇔6Ca²⁺+2Al³⁺+3SeO₄²⁻+43.5H₂O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log K_so=73.40±0.22 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·CaSeO₄·xH₂O+12 H⁺⇔4Ca²⁺+2Al³⁺+SeO₄²⁻+(x+6)H₂O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.     

Blend membranes from carboxymethylated chitosan/alginate in aqueous solution

The blend membranes were satisfactorily prepared by coagulating a mixture of O‐carboxymethylated chitosan (CM‐chitosan) and alginate in aqueous solution with 5 wt % CaCl₂, and then by treating with 1 wt % HCl aqueous solution. Their structure and miscibility were characterized by scanning electron micrograph, X‐ray diffraction, infrared spectra, differential thermal analysis, and atomic absorption spectrophotometer. The results indicated that the blends were miscible, when the weight ratio of CM‐chitosan to alginate was in the range from 1 : 1 to 1 : 5. The polymers interpenetration including a Ca²⁺ crosslinked bridge occurred in the blend membrane, and leads to high separation factor for pervaporation separation of alcohol/water and low permeation. The tensile strength in the wet state (σ_b = 192 kg cm⁻² for CM‐chitosan/alginate 1 : 1) and thermostability of the blend membranes were significantly superior to that of alginic acid membrane, and cellulose/alginate blend membranes, owing to a strong electrostatic interaction caused by —NH₂ groups of CM‐chitosan with —COOH groups of algic acid. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 610–616, 2000     

Investigation on interfacial interaction of flame retarded and glass fiber reinforced PA66 composites by IGC/DSC/SEM

The interfacial interaction of flame retarded and glass fiber reinforced PA66 composites is a very important issue due to one of the key factors influencing the mechanical properties of materials. In this article, the interfacial interaction among the components in the composites has been studied by IGC/DSC/SEM techniques. The experimental data demonstrated that Zn²⁺-modified melamine polyphosphate (Zn-MpolyP) flame retardant could obviously enhanced the mechanical properties of the composites compared with melamine polyphosphate (MpolyP). SEM results proved that Zn-MpolyP could well disperse in the composites, and effectively improve the interfacial compatibility of the composites. Based on DSC results, Zn-MpolyP and MpolyP promoted the crystallization enthalpy (ΔH_c) and temperature (T_c) of PA66 to increase. Zn-MpolyP showed more effect in increasing the crystallization degree of PA66 than MpolyP. They exhibited the nucleating effect in PA66. The Lewis acid-base numbers (K_a and K_b) and their ratio (K_b/K_a) obtained by inverse gas chromatography (IGC) further proved that the strongest Lewis acid-base interaction between PA66 and Zn-MpolyP existed in the composites. This result is probably due to the strong complex between Zn²⁺ in Zn-MpolyP and lone pair electrons at O and N atoms of PA66 and glass fiber. Therefore, the all results of IGC/DSC/SEM techniques demonstrated that the interfacial compatibility of components in composites was better improved by Zn-MpolyP than MpolyP.     

Polymer electrolytes based on a ternary miscible blend of poly(ethylene oxide), poly(bisphenol A-co-epichlorohydrin) and poly(vinyl ethyl ether)

Ternary blends of poly(ethylene oxide) (PEO), poly(bisphenol A-co-epichlorohydrin) (PBE) and poly(vinyl ethyl ether) (PVEE) were obtained as films and characterized by differential scanning calorimetry (DSC) and vibrational spectroscopy (FTIR). From the DSC results, phase diagrams for the ternary blends were determined, where the variation of the viscoelastic phase extent as a function of the polymers composition was determined. The DSC results also indicated miscibility of the system, exhibiting only one glass transition temperature (T_g) and decrease in the crystallinity of the system, as well as decrease in the crystallinity of PEO present in the blends. Vibrational spectroscopy (FTIR) provided information on the intermolecular interactions between the pairs PBE/PEO and PBE/PVEE, via hydrogen bond interaction. From the FTIR analyses, molecular model systems of equilibrium among the interacting structures were proposed as a molecular basis for the miscibility of the system.Polymer electrolytes based on the ternary blend containing 60/25/15 (PEO/PBE/PVEE) mass percent and lithium perchlorate (LiClO₄) were obtained and characterized by DSC, FTIR, optical microscopy and electrochemical impedance spectroscopy (EIS). Solid electrolytes containing up to 10 wt% LiClO₄ exhibited a single-phase behavior, evidenced by the DSC results. For these electrolytes, FTIR spectra indicated the formation of polymer-ion complexes, in which the cation (Li⁺) acts favoring the polymer-polymer miscibility. Electrolytes containing LiClO₄ higher than 10 wt% exhibit a multiple phase behavior, in which a PEO-rich, salt-containing phase is present in equilibrium with PBE or PVEE-rich phases. Maximum ionic conductivity at room temperature, for the electrolyte containing 20 wt% LiClO₄, reached 4.23 × 10⁻³ Ω⁻¹ cm⁻¹, while all samples exhibited conductivity of approximately 10⁻¹ Ω⁻¹ cm⁻¹ at 80 °C.     

Sequence distribution affect the phase behavior and hydrogen bonding strength in blends of poly(vinylphenol-co-methyl methacrylate) with poly(ethylene oxide)

Experimental results indicate that the PEO was miscible with PVPh-r-PMMA copolymers as shown by the existence of single composition-dependent glass transition temperature over the entire compositions. However, the PVPh-b-PMMA copolymer with PEO shows a like closed loop phase-separated region in this copolymer/homopolymer blend system. Furthermore, FTIR reveals that at least three competing equilibrium are present in these blends; self-association (hydroxyl-hydroxyl), interassociation (hydroxyl-carbonyl) of PVPh-co-PMMA, and hydroxyl-ether interassociation between PVPh and PEO. Based on the Painter-Coleman Association Model (PCAM), a value for inter-association, K_C=300 is obtained in PVPh-b-PMMA/PEO blend system at room temperature. Although the relative ratio of interassociation equilibrium constant of PEO to PMMA is larger in PVPh-b-PMMA/PEO blend system, the PVPh-r-PMMA/PEO blend system has greater Δν and greater homogeneity at the molecular scale than the PVPh-b-PMMA/PEO blend system because of the ΔK effect.     

A polymeric solid electrolyte based on a binary blend of poly(ethylene oxide), poly(methyl vinyl ether-maleic acid) and LiClO4

A new polymeric solid electrolyte based on a PEO/PMVE-MAc blend, complexed with LiClO₄, was obtained and characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), polarized light optical microscopy, electrochemical impedance and cyclic voltammetry. DSC traces indicated miscibility for all the PSE samples. Crystallinity was suppressed for samples with LiClO₄ concentrations higher than 2.5 wt%. FTIR associated with DSC studies indicated that there is a preferential formation of complexes PEO/Li⁺/PMVE-MAc in all PSE samples studied here. The ionic conductivity of PSE reaches a maximum of about 10⁻⁵ S/cm at ambient temperature and 7.5 wt% LiClO₄. The electrochemical stability window is 4.5 V and associated with the other characteristics, make the PSE studied here suitable for applications in ‘smart-windows’, batteries, sensors, etc.     

Multicomponent ion exchange isotherms in NaX zeolite: evaluation of Cr/Ca/Mg,Cr/Ca/K and Cr/Mg/K systems

BACKGROUND: One of the most important heavy metals is Cr³⁺, which is commonly found together with Ca²⁺, Mg²⁺ and K⁺ ions in tannery wastewaters. Such metals can be removed through ion exchange process using zeolite NaX. Unfortunately, with single exchange mechanisms it is impossible to predict muti‐component and competitive interactions. This work is aimed at overcoming this problem. Ion exchange isotherms of Cr³⁺, Mg²⁺, Ca²⁺ and K⁺ in ternary mixtures (Cr/Mg/Ca, Cr/Ca/K, Cr/Mg/K) using NaX zeolite at 30 °C, 45 °C and 60 °C are studied and reported. RESULTS: Ion exchange is dependent on temperature, and on the nature and interaction of ingoing cations. Sequential ion exchange occurs where one cation is able to displace another already located in the site. Values of the equilibrium constant of all cations investigated are close to each other, which indicates a weak preference for Cr⁺³. The affinity order is as follows: for Cr/Ca/Mg–NaX isotherms, Cr³⁺ > Ca²⁺ > Mg²⁺ at 30 °C, Ca²⁺ > Cr³⁺ > Mg²⁺ at 45 °C and Ca²⁺ > Mg²⁺ > Cr³⁺ at 60 °C. For Cr/Ca/K–NaX isotherms the sequence is Cr³⁺ > Ca²⁺ > K⁺ for the three temperatures and for Cr/Mg/K–NaX isotherms, Cr³⁺ > Mg²⁺ > K⁺ at 30 and 45 °C and Mg²⁺ > K⁺ > Cr³⁺ at 60 °C. CONCLUSION: It can be concluded that ions with a high charge such as Cr³⁺ are not always preferentially removed from multi‐component solution. Therefore, exchanges in NaX zeolite are useful when there is no need to have high chromium removal when compared to the competitive cations investigated here. Copyright © 2008 Society of Chemical Industry     

Ion—solvent interaction: viscosity of ternary electrolytes in dioxane-water mixtures at 35°

The viscosities of the chlorides, bromides and nitrates and perchlorates of Mg²⁺ and Ba²⁺, of the chlorides and nitrates of Ca²⁺ and Sr²⁺, and of the sulphates of Na⁺ and K⁺ at mass fraction of dioxane, 10, 20 and 30% have been measured at 35°. The values of the constant A and B of the viscosity equation indicate ion—ion and ion—solvent interaction respectively. The ion-solvent interaction is found to be of the order NO^?₃ > ClO^?₄ > Br^? > Cl^? and K⁺ > Na⁺.     

Novel blend microspheres of poly(vinyl alcohol) and succinyl chitosan for controlled release of nifedipine

Water-soluble succinyl chitosan (SCS) was synthesized by reacting succinic anhydride with –OH and –NH₂ reactive groups of chitosan (CS). The blend hydrogel microspheres were prepared from SCS with poly(vinyl alcohol) (PVA) by water-in-oil (w/o) emulsion cross-linking using glutaraldehyde (GA) as the cross-linking agent. Nifedipine (NFD), an antihypertensive drug having a plasma half-life of 2 h, was encapsulated giving encapsulation efficiency up to 92 % and its release was extended up to 12 h. Scanning electron microscopy (SEM) confirmed the spherical nature and smooth surfaces of the microspheres, while Fourier transform infrared spectroscopy (FTIR) confirmed succinylation of CS and chemical stability of NFD in the matrix. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) characterized the SCS and the blend hydrogel microspheres. X-ray diffraction (XRD) and DSC were also used to study the crystalline or amorphous nature of NFD. Swelling and in vitro release experiments performed in pH 1.2 and 7.4 buffer media showed a dependence of blend composition, extent of cross-linking and pH of the media. The mechanism of drug release as analyzed by an empirical equation, suggested non-Fickian trends.     

Crystallographic studies on the site selectivity of Ca<Superscript>2+</Superscript>, K<Superscript>+</Superscript>, and Rb<Superscript>+</Superscript> ions within zeolite Y (Si/Al = 1.56)

The single-crystals of Ca²⁺, K⁺-exchanged zeolite Y, and Ca²⁺, Rb⁺-exchanged zeolite Y were prepared by using flow method with mixed ion-exchange solution, whose Ca(NO₃)₂:KNO₃ mole ratios were 1:1 (crystal 1) and 1:100 (crystal 2), and Ca(NO₃)₂:RbNO₃ mole ratios were 1:1 (crystal 3) and 1:100 (crystal 4), respectively, with a total concentration of 0.05 M. They were fully dehydrated by vacuum dehydration at 723 K and 1 × 10^?6 Torr for 2 days. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group \(Fd \overline{3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.057/0.196, 0.073/0.223, 0.055/0.188, and 0.049/0.175 for crystals 1, 2, 3, and 4, respectively. In the structure of crystal 1 (|Ca₂₃K₂₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 23 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 29 K⁺ ions per unit cell are at sites II′, II, and III′. In the structure of crystal 2 (|Ca_18.5K₃₈|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18.5 Ca²⁺ ions per unit cell occupy sites I, I′, and II; 38 K⁺ ions are at sites I′, II, and III′. In the structure of crystal 3 (|Ca₂₇Rb₂₁|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 27 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 21 Rb⁺ ions per unit cell are at sites II′, II, and III. In the structure of crystal 4 (|Ca₁₈Rb₃₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18 Ca²⁺ ions per unit cell occupy sites I and II; 39 Rb⁺ ions per unit cell are at sites I′, II′, II, III, and III′. In the four crystals, the Ca²⁺ ion which has much smaller size and higher charge than other cations such as K⁺ and Rb⁺ energetically preferred at site I and so the first to be filled on it. Unlike Ca²⁺ ion, no K⁺ and Rb⁺ ions are found at site I, which are clearly less favorable for K⁺ and Rb⁺ ions.     

Synthesis and properties of a cellulose exchanger with the crown ether diaminodibenzo-17-crown-5 as anchor group

A new cellulose exchanger was synthesized from “o-aminophenolcellulose” by diazotation and coupling with diaminodibenzo-17-crown-5. The distribution coefficients for Ca²⁺, Sr²⁺, Ba²⁺, Na⁺ and K⁺ were determined in water/methanol mixtures as a function of the water content. Separation of Ca²⁺, Na⁺ and K⁺ and fractionation of the calcium isotopes ⁴⁸Ca and ⁴⁰Ca were investigated. The enrichment factor ε = 4.9 · 10^?3 for ⁴⁸Ca²⁺ is appreciably higher than that found for cation exchange resins with ? SO₃H groups, but lower than that reported for certain cryptands.     

Oxidized pea starch/chitosan composite films: Structural characterization and properties

In this article, a series of oxidized pea starch/chitosan (OPS/CS) blend films were prepared by a casting and solvent evaporation method. The structure, thermal behavior, and mechanical properties of the films were investigated by means of Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and tensile testing. The results suggested that, in addition to hydrogen bonding, the interactions between OPS and CS molecules were enhanced by the formation of electrostatic interaction between the negatively charged carboxyl groups on OPS and the positively charged amino groups on CS. Compared with the pea starch/chitosan (PS/CS) blend films, OPS/CS blend films exhibited significantly higher tensile strength with significantly lower elongation at break. Moreover, incorporation of CS into the OPS matrix also led to a decrease in moisture uptake by the composite film. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of ion‐imprinting chitosan/PVA crosslinked membrane for selective removal of Ag(I)

A novel ion‐imprinted membranes were synthesized for selective removal and preconentration for Ag(I) ions from aqueous solutions. The membranes were obtained via crosslinking of chitosan (CS), PVA, and blend chitosan/PVA using glutaraldehyde (GA) as crosslinker. The FTIR spectra were used to confirm the membrane formation. Comparing with the nonimprinted membranes, Ag(I)‐imprinted CS and CS/PVA has higher removal capacity and selectivity for Ag⁺ ions. An enhancement in the Ag⁺ removal capacity by ～ 20% (from 77.8 to 94.4 mg g^–1) and ～ 50% (from 83.9 to 125 mg g^–1) was found in the Ag(I)‐imprinted CS and Ag(I)‐imprinted CS/PVA membranes, respectively, when compared with the nonimprinted membranes. Removal equilibra was achieved in about 40 min for the non‐ and ion‐imprinted CS/PVA. The pH and temperature significantly affected the removal capacity of ion‐imprinted membrane. The relative selectivity coefficient values of Ag⁺/Cu²⁺ and Ag⁺/Ni²⁺ are 9 and 10.7 for ion‐imprinted CS membrane and 11.1 and 15 for ion‐imprinted CS/PVA membrane when compared with nonimprinted membranes. The imprinted membranes can be easily regenerated by 0.01M EDTA and therefore can be reused at least five times with only 15% loss of removal capacity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Correlation between interactions, miscibility, and spherulite growth in crystalline/crystalline blends of poly(ethylene oxide) and polyesters

Crystalline/crystalline blend systems of poly(ethylene oxide) (PEO) and a homologous series of polyesters, from poly(ethylene adipate) to poly(hexamethylene sebacate), of different CH₂/CO ratios (from 3.0 to 7.0) were examined. Correlation between interactions, miscibility, and spherulite growth rate was discussed. Owing to proximity of blend constituents' T_g's, the miscibility in the crystalline/crystalline blends was mainly justified by thermodynamic and kinetic evidence extracted from characterization of the PEO crystals grown from mixtures of PEO and polyesters at melt state. By overcoming experimental difficulty in assessing the phase behavior of two crystalline polymers with closely spaced T_g's, this work has further extended the range of polyesters that can be miscible with PEO. The interaction parameters (χ₁₂) for miscible blends of PEO with polyesters [poly(ethylene adipate), poly(propylene adipate), poly(butylene adipate), and poly(ethylene azelate) with CH₂/CO = 3.0-4.5] are all negative but the values vary with the polyester structures, with a maximum for the blend of PEO/poly(propylene adipate) (CH₂/CO = 3.5). The values of interactions are apparently dependent on the structures of the polyester constituent in the blends; interaction strength for the miscible PEO/polyester systems correlate in the same trend with the PEO crystal growth rates in the blends.     

Ionic conductivity in polyethylene-b-poly(ethylene oxide)/lithium perchlorate solid polymer electrolytes

The ionic conductivity and phase arrangement of solid polymeric electrolytes based on the block copolymer polyethylene-b-poly(ethylene oxide) (PE-b-PEO) and LiClO₄ have been investigated. One set of electrolytes was prepared from copolymers with 75% of PEO units and another set was based on a blend of copolymer with 50% PEO units and homopolymers. The differential scanning calorimetry (DSC) results, for electrolytes based on the copolymer with 75% of PEO units, were dominated by the PEO phase. The PEO block crystallinity dropped and the glass transition increased with salt addition due to the coordination of the cation by PEO oxygen. The conductivity for copolymers 75% PEO-based electrolyte with 15 wt% of salt was higher than 10⁻⁵ S/cm at room temperature and reached to 10⁻³ S/cm at 100 °C on a heating measurement. The blend of PE-b-PEO (50% PEO)/PEO/PE showed a complex thermal behavior with decoupled melting of the blocks and the homopolymers. Upon salt addition the endotherms associated with PEO domains disappeared and the PE crystals remained untouched. The conductivity results were limited at 100 °C to values close to 10⁻⁴ S/cm and at room temperature values close to 3 × 10⁻⁶ S/cm were obtained for the 15 wt% salt electrolyte. Raman study showed that the ionic association of the highly concentrated blend electrolytes at room temperature is not significant. Therefore, the lower values of conductivity in the case of the blend with 50% PEO can be assigned to the higher content of PE domains leading to a morphology with lower connectivity for ionic conduction both in the crystalline and melted state of the PE domains.