Small-angle neutron scattering study on the miscibility and concentration fluctuation of hydrogen-bonded polymer blends

Thermal concentration fluctuation in the blends of deuterated poly(ethylene oxide) (dPEO) and poly(vinyl acetate-co-vinyl alcohol) [P(VAc-VOH)] with various VOH contents f_OH were examined by small angle neutron scattering techniques at a fixed blend composition, dPEO/P(VAc-VOH) = 20/80 which is close to the critical composition. Blends at the highest f_OH (=0.35) showed a non-Lorentzian scattering profile: specifically the scattering intensities at the low q (angle) region were suppressed compared to those expected from the random phase approximation (RPA) theory. However, for the blends at lower f_OH (≤0.28), the profiles could be represented by the RPA. Using the RPA we determined effective values of the Flory-Huggins interaction parameter χ_eff as a function of f_OH (=0–0.28). The χ_eff showed the minimum around f_OH = 0.1–0.18 meaning the highest miscibility of the blend at these f_OH. On the basis of the random copolymer theory, we evaluated the three interaction parameters χ_Ac–EO, χ_EO–OH, and χ_Ac–OH separately from the χ_eff(f_OH) and found the order of magnitude; χ_Ac–EO < 0 < χ_EO–OH < χ_Ac–OH. The largest positive χ_Ac–OH showing intrachain interaction in the P(VAc-VOH) copolymer was concluded to be the origin of the enhanced miscibility at around f_OH = 0.1–0.18. On the basis of the Coleman and Painter's theory, the effects of hydrogen bonding on these three χ_A-B were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2556–2565, 2008     

Etude des systemes ternaires: polymere-polymere-solvant. Application au systeme polystyrene-polydimethylsiloxane-benzene

The ternary system benzene-polydimethylsiloxane-polystyrene has been investigated by light scattering. Apparent molecular weight and solvation coefficient have been determined by applying the relations established for the ternary system of polymer in mixed solvents. The range of validity of these relations for our system has been discussed. We have also determined the χ₂₃ parameter (interaction between the both polymers), following the variations of apparent molecular weight or the compositions at the spinodal.     

Block copolymer-homopolymer blends in the disordered state: Determination of the interaction parameter using small angle neutron scattering

The aim of this study was to determine the interaction parameter x_AB and its variation with temperature from the intensity scattered By pure block copolymer (A-B) and block copolymer-homopolymer (B) blends where A is polydeuteratedstyrene and B polybutadiene. SANS experiments on pure copolymers of low molecular weight have shown that the scattering curve exhibits a peak of intensity related to the correlation hole effect. χ_AB was determined by fitting the experimental curves using Leibler's theory and the law of variation of χ_AB versus temperature was established. In the case of copolymer-homopolymer blends, the scattering spectrum is modified because of a new and additional long range correlation effect (mixing effect) which dominates in the low q range and leads to strong forward scattering. We have not found any significant variation of χ with blend composition.     

Characterization of the interactions in polymer/silica systems by inverse gas chromatography

Authors propose to express the magnitude of modified filler/polymer interactions by Flory ‐ Huggins χ₂₃ parameter. We investigated polyether‐urethane/modified silica systems containing different amounts of filler (5, 10,20%wt). Moreover, information on the physicochemical properties of oligomer and modified silicas were presented with the use of the following parameters: • solubility parameter δ₂, describing properties of the polymer layer; • Flory‐Huggins parameter χ₁₂^∞ which describes polymer‐solute or mixture polymer/silica‐solute interactions. These parameters δ₂ and χ₁₂^∞ are obtained from Inverse Gas Chromatography experiments. The influence of the IGC experiment temperature, the content of modified silica, the nature of test solute on the evaluated parameters are presented and discussed.     

Thermodynamic study of poly(vinyl chloride)/polyester blends by inverse-phase gas chromatography at 120°C

Polymer/polymer interaction parameters χ′₂₃ have been measured at 120°C as a function of polymer concentration for six different poly(vinyl chloride)/linear aliphatic polyester blends. The technique used is inverse-phase gas chromatography with several molecular probes. The polymers investigated are poly(DL-lactide), poly(ethylene succinate), poly(ethylene adipate), poly(butylene adipate), poly(δ-valerolactone), poly(ε-caprolactone) and poly(hexamethylene sebacate). Probe/polymer interaction parameters χ₁₂ and polymer/polymer interaction parameters χ′₂₃ values are dependent upon the methylene to carbonyl ratio of the polyester, reaching a minimum for a value of 5, this ratio corresponding to poly(ε-caprolactone) blends. Results are interpreted in terms of pairwise interactions between carbonyl, methylene, and [CHCl] groups.     

Crystallization and melting of poly(2,6-dimethyl-1,4-phenylene oxide) in ternary mixtures with toluene and polystyrene

The crystallization and melting temperatures of an unfractionated poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) sample, PM2, were determined at 0.25°C/min cooling and heating rates in five binary toluene—PM2 and fifteen ternary toluene—polystyrene—PM2 solutions. The total polymer weight fraction range studied was 0.12–0.40 and the PM2 weight fraction range was 0.026–0.40. The heat of fusion H_f of the PM2 was computed to be 10.1 cal/g from the melting point depressions. A toluene—PM2 pair interaction parameter χ13 = 0.890 – 223.5/T was found. Although a reliable polystyrene–PM2 interaction parameter could not be computed, the data are consistent with χ23 = 0. Setting χ23 = 0 we calculate the toluene—polystyrene interaction parameter to be χ12 = 0.495 – 15.46/T. This χ12 is in remarkable agreement with values reported in osmotic pressure studies.     

Stimulated Raman scattering from H2+ ions

The observation of optical signals due to light scattering from H₂⁺ molecular ions is reported and discussed. By focusing Q-switched 1064 nm Nd : YAG laser light in H₂ at 20 bar, optical frequencies have been generated. They are assigned partly to stimulated Raman scattering from H₂⁺ and partly from H₂ molecules. The scattered radiation (Stokes-shifted 1064 nm beam) was transformed into visible light via higher-order four-wave mixing processes. The frequencies thus obtained could be observed with the naked eye if the scattered light was dispersed and projected on a white screen. The temperature of the gas in the focal region of the laser beam was estimated to be 1030 ± 300 K.     

Distribution of chain defects and microstructures of melt crystallized polyethylene. II. Influence of defect size and of plastic deformation

Unit cell expansion data for (a) melt-crystallized polyethylene (PE) containing known amounts of methyl, ethyl, and butyl branches and for (b) plastically deformed samples, are examined in the light of a model which takes into account the penetration of constitutional defects (branches) at interstitial crystal sites by means of a generation of 2g1 step chain defects (kink isomers). The present analysis complements previous results obtained for melt-crystallized PE samples with a widely varying number concentration ? of butyl or longer branches. An estimation of the concentration of chain defects incorporated into the crystal lattice is carried out. The results reveal that the fraction χ_c of defects which are accomodated within the lattice depends on both the amount and size of the chain defects and on the mechanical deformation of the sample. For PE chains with methyl and ethyl groups, χ_c ≈ 50%, whereas for butyl and longer branches, χ_c does not exceed 20% of the total concentration of defects. In addition, after cold drawing, PE with low amounts (? < 1%) of butyl or longer chain branching, χ_c turns out to be zero; i.e., during deformation single molecular chain rearrangements leading to a chain segregation of defects into the amorphous phase must occur.     

Etude du parametre d'interaction polymere-polymere pour le systeme ternaire solvant-polydimethylsiloxane-polystyrene. Influence de la concentration et de la masse moleculaire

This paper presents the results of a study of the thermodynamic properties of a ternary system viz. solvent (ethylacetate or benzene)-polydimethylsiloxane-polystyrene. The interaction parameter between the two polymers χ₂₃, determined both from light scattering and studies of the critical conditions of phase separation, has been studied as a function of the molecular weights of the two polymers. Using a polystyrene of fixed molecular weight, we observe a large decrease in χ₂₃ for increasing molecular weight of polydimethylsiloxane. When the molecular weights of the two polymers are very high, the parameter χ₂₃ becomes very small (of the order of 0.01). The values of χ₂₃ obtained for these two polymers are compared to those found for comparable systems, viz. polystyrene-polyisobutene and polydimethylsiloxane-polyisobutene.     

Incompatibility of polymer solutions. III. Critical opalescence in the system polystyrene + polyisobutylene + toluene

The angular dependence of light scattering from the homogeneous ternary system polystyrene + polyisobutylene + toluene was measured at a fixed (critical) concentration as a function of temperature. On approaching the critical temperature the scattering becomes very large and strongly angle-dependent. The experiments show that the interaction range r_G is of the same order of magnitude as the molecular radius of gyration of the polymer, but cannot be set equal to it as in the case of a binary system of one polymer in a single solvent. The temperature dependence of the various interaction parameters does not depend on the molecular weights of the polymers.     

The excited-state absorption of Ru(bpy)2+3 reexamined

The excited-state absorption of Ru (bpy)₃²⁺ ( RBY ) in the range 240 to 2200 nm is reported, extending the range and improving the resolution of previous measurements. The excitation power dependence of the excited-state populations are quantified and absorption measurements made in H₂O and D₂O solutions at 300 K and in poly (vinyl-alcohol) (PVA) films at 20 K. No evidence is found for an intervalence charge-transfer type transition in the near IR, but the Ψ→ χ ligand excitation transition is clearly seen near 11000 and 9000 cm⁻¹ in solution and in PVA respectively. The visible and UV excited-state spectra are similar in the two environments and differences are attributed to the effects of photoselection in PVA. The Ψ→ χ transition shows a marked shift in passing from a rigid to a fluid medium, indicating the possibility of a change in ligand geometry.     

b 1Σ+ Emissions from group V–VII diatomic molecules: bO+ → X1 O+ emission of Pl

Chemilluminescence of the bO⁺ → X₁O⁺ band system of P1 has been observed in a discharge flow system. Thirty-eight bands of the sequences, δν = +2, +1, 0, ?1, ?2 and ?3 were recorded photoelectrically at medium resolution. Evidence is presented that the vibrational numering assigned to the bands in the recently published first analysis of this system has to be modified. The re-analysis leads to the new constants (in cm ^?1) T_e = 11135 ± 5, ω′_e 400 ± 2, ω_e′_e = 1.4 ± 0.3, ω″_e = 372 ±2 and ωχ″_e, 1.4 ± 0.3 for the bO⁺ and χ₁ states, respectively. An upper limit of 0.01 was found for the ratio of the (0.0) band intensifies of the two sub-systems bO⁺ → χ₂ 1 and bO⁺ → χ₁O⁺.     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Correlation of the prigogine-flory theory with isothermal compressibility and excess enthalpy data for benzene +n-alkane mixtures

Isothermal compressibilitiesκ _T for benzene + n-alkane systems at 25, 35, 45, and 60°C have been used to check the Prigogine-Flory theory using the van der Waals and Lennard-Jones potentials in order to study the energy-volume dependence. The Flory interaction parameter χ₁₂ has also been calculated for those set of systems at four temperatures. The variation of χ₁₂ with the number of carbon atoms in the n-alkane was studied. Three excess functions have been obtained from χ₁₂ for the equimolecular mixture: (?V ^E/?p)_T which is related toκ _T ^E , the excess enthalpy H ^E , and the excess volume V ^E . Except for H ^E theoretical predictions using a Lennard-Jones potential are in good agreement with the experimental data. A similar treatment has been performed for the same set of systems but using H ^E data at 25°C. The theory, using a van der Waals potential, predicts correctly the variation of the three excess functions with the chain length of the n-alkane but using a Lennard-Jones potential results in better agreement for the order in the magnitude of these excess functions.     

Thermodynamic interaction parameter of star–star polybutadiene blends

The value of the thermodynamic interaction parameter, χ_eff, for star–star polybutadiene blends was determined with small‐angle neutron scattering. Blends in which the stars have the same number of arms and blends in which the stars have different numbers of arms are investigated. For star–star isotopic blends with components having the same number of arms, the presence of the junction point of the star leads to a value of χ_eff that is larger than that for an analogous linear–linear isotopic blend. However, changes in the value of χ_eff resulting from small dissimilarities in the number of arms of the two components in the isotopic star–star blends were too small to resolve. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 247–257, 2003     

Stability of coordination compounds of Co2+ and Ni2+ ions with maleic acid anion in aqueous isopropanol solutions

Composition and stability of coordination compounds of nickel(II) and cobalt(II) ions with maleic acid anion in aqueous isopropanol solutions (H₂O-IPA) of composition χ_IPA = 0–0.5 mole fraction was studied by potentiometric titration at ionic strength of 0.1 maintained with sodium perchlorate at 298.15 K. Monoligand complexes of Ni²⁺ and Co²⁺ ions with maleic acid anion become stronger when isopropanol content rises. In the solvent of the studied composition, Co²⁺ ions form less stable complexes than Ni²⁺ ions that corresponds to the Irving-Williams series established for aqueous solutions. Variations in complex stability are more expressed at small IPA content and differ within experimental error at χ_IPA = 0.5 mole fraction. Obtained results were compared with literature data for akin compounds.     

Estimating the segregation strength of microphase‐separated diblock copolymers from the interfacial width

The ever‐growing catalog of monomers being incorporated into block polymers affords exceptional control over phase behavior and nanoscale structure. The segregation strength, χN, is the fundamental link between the molecular‐level detail and the thermodynamics. However, predicting phase behavior mandates at least one experimental measurement of χN for each pair of blocks. This typically requires access to the disordered state. We describe a method for estimating χN from small‐angle X‐ray scattering measurements of the interfacial width between lamellar microdomains, t_x, in the microphase‐separated melt. The segregation strength is determined by comparing t_x to self‐consistent field theory calculations of the intrinsic interfacial width, t_i, as a function of the mean‐field χN. The method is validated using a series of independent experimental measurements of t_x and χN, measured via the order–disorder transition temperature, T_ODT. The average absolute relative difference between χN calculated from t_x and the value calculated from T_ODT is a modest 11%. Corrections for nonplanarity of the interfaces are investigated but do not improve the agreement between the experiments and theory. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J. Polym. Sci., Part B: Polym. Phys. 2019 © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 932–940     

Diamagnetic anisotropy of quadruple MoMo bonds: α-Mo2Cl4(diphosphine)2 complexes

Two components (χ_xV — χ′_hu and χ_xV — χ″_hu) of magnetic anisotropy of MoMo quadruple bonds have been obtained by using the X-ray crystallographic molecular structure and the low temperature ¹H NMR spectrum of α-Mo₂Cl₄[(C₆H₅)₂PCH₂CH₂P(p-RC₆H₄)₂]₂ [R  H (dppe), CH₃ (dpdt) and tert-C₄H₉ (dpdbp)]. The values of χ_xV — χ′_hu and χ_xV — χ″_hu for the dpdbp case are −(8470 ± 200) x 10⁻³⁶ and −(5540 ± 70) x 10⁻³⁶ m³ molecule⁻¹, respectively, which are several times as large as χ_xV — χ_hu (Mo³Mo). Through detailed examination of the ¹H NMR signals of the ethylene protons, conformational flexing of the chelate rings of α-Mo₂Cl₄(dpdbp)₂ has been recognized.     

Thermodynamic analysis of the phase separation during the polymerization of a thermoset system into a thermoplastic matrix. I. Effect of the composition on the cloud‐point curves

The cloud‐point curves of polystyrene (PS) mixed with reactive epoxy monomers based on diglycidyl ether of bisphenol A with stoichiometric amounts of 4,4′‐methylenebis(2,6‐diethylaniline) were experimentally studied. A thermodynamic analysis of the phase‐separation process in these epoxy‐modified polymers was performed that considered the composition dependence of the interaction parameter, χ(T,Φ₂) (where T is the temperature and Φ₂ is the volume fraction of polystyrene), and the polydispersity of both polymers. In this analysis, χ(T,Φ₂) was considered the product of two functions: one depending on the temperature [D(T)] and the other depending on the composition [B(Φ₂)]. For mixtures without a reaction, the cloud‐point curves showed upper critical solution temperature behavior, and the dependence of χ(T,Φ₂) on the composition was determined from the threshold point, that is, the maximum cloud‐point temperature. During the isothermal reactions of mixtures with different initial PS concentrations, the dependence of χ(T,Φ₂) on the composition was determined under the assumption that, at each conversion level, the D(T) contribution to the χ(T,Φ₂) value had to be constant independently of the composition. For these mixtures, it was demonstrated that the changes in the chemical structure produced by the epoxy–amine reaction reduced χ(T,Φ₂). This effect was more important at lower volume fractions of PS. Nevertheless, the decrease in the absolute value of the entropic contribution to the free energy of mixing was the principal driving force behind the phase‐separation process. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1351–1360, 2004     

Evidence for a long-lived excited state of CH4+ from a beam scattering study of the collision-induced dissociation of CH4+ to CH2+ at low energy

A crossed-beam study of the collision-induced dissociation of CH₄⁺ by Ar was carried out at a center-of-mass (c.m.) collision energy of 5.5 eV. The scattering shows three patterns for the formation of CH₂⁺, (1) large-angle scattering at preferred impact parameters with little internal excitation of the products, (2) scattering near the c.m. with nearly all collision energy transferred into products internal energy and (3) superelastic scattering, i.e. conversion of internal energy to translational energy, implying the reaction is initiated by a long-lived excited state of CH₄⁺ generated by electron impact ionization of methane. No previous evidence exists, to our knowledge, that excited states of CH₄⁺ thus generated may have microsecond lifetimes.