Studies on the miscibility and effect of the addition of urea to poly(acrylic acid) and poly(sodium styrene sulfonate) blends by dilute solution viscometry method

The miscibility of poly(acrylic acid) (PAA) and poly(sodium styrene sulfonate) (PSSNa), in H₂O was investigated by a dilute solution viscometry method (DSV). The miscibility of the polymer blend was investigated on the basis of the signs of the interaction parameters Δ[b]_m, Δ[η]_m, ΔB and μ. The results from the viscosity method were correlated with the miscibility data obtained for the same blend by Fourier transform infrared and differential scanning calorimetry. These investigation indicated that the examined blend was miscible for all composition ratios examined (w₂ = 0.10, 0.25, 0.50, 0.75, and 0.90).The addition of urea to the polymer mixture H₂O (1)/PAA (2)/PSSNa (3) decreased the miscibility.     

Viscometric study on the miscibility of polystyrene/brominated polystyrene blends

The miscibility of polystyrene/brominated polystyrene blends (PS/PBrS) was investigated by using dilute-solution viscometry (DSV) method. The intrinsic viscosity and the viscometric parameters of this system have been determined at 20 ± 0.1 °C for prepared several PS/PBrS compositions (85/15, 75/25, 50/50, 25/75, 10/90). The binary systems were prepared in chloroform at five different concentrations; 0.15, 0.30, 0.60, 0.90, 1.20 g 100 ml⁻¹. The miscibility criteria on the basis of the sign of Δ[η] _m, Δb and Δb′, which are based on the difference between experimental and ideal values of [η]_m, and b_m were calculated by applying the Garcia et al., Catsiff-Hewett and Krigbaum-Wall theoretical equations. The thermodynamic parameter, α, modified thermodynamic parameter, β, and interaction parameter, μ, were also estimated. The data obtained from the viscometry studies showed that the examined blends were immiscible in all the compositions range besides the composition (10/90). The results from the DSV method are correlated with the miscibility data obtained for the same blend by differential scanning calorimetry (DSC) find.     

The miscibility of poly(vinyl alcohol)/poly(N-vinylpyrrolidone) blends investigated in dilute solutions and solids

Poly(vinyl alcohol) (PVA) (polymer A) and poly(N-vinylpyrrolidone) (PVP) (polymer B) are known to form a thermodynamically miscible pair. In the present study the conclusion on miscibility of PVA/PVP solid blends, confirmed qualitatively (DMTA, FTIR) and quantitatively (DSC, χ_AB = − 0.69 at 503 K) is compared with the miscibility investigations of PVA/PVP solution blends by the technique of dilute solution viscometry. The miscibility of the ternary (polymer A/ polymer B/ solvent) system is estimated on the basis of experimental and ideal values of the viscosity parameters k, b and [η]. It is found that the conclusions on miscibility or nonmiscibility drawn from viscosity measurements in dilute solution blends depend: (i) on the applied extrapolation method used for the determination of the viscosity interaction parameters, (ii) on the assumed definition of the ideal values and (iii) on the thermodynamic quality of the solvent, which in the case of PVA depends on its degree of hydrolysis. Hence, viscometric investigations of dilute PVA/PVP solution blends have revealed that viscometry, widely used in the literature for estimation of polymer-polymer miscibility can not be recommended as a sole method to presume the miscibility of a polymer pair.     

Conductance study of the thermodynamics of micellization of 1-hexadecylpyridinium bromide in mixed solvents containing dilute electrolyte solutions

The critical micelle concentration (CMC) of hexadecylpyridinium bromide (HDPB) is determined conductometrically in binary mixtures of water + cosolvent at various temperatures and at low concentrations of sodium bromide, ranging from 0 to 2.4 × 10^?2 M. Dimethylsulfoxide (DMSO) and acetonitrile (AN) were used as cosolvents added to water. The ability of NaBr to lower the CMC of HDPB in water is inhibited by DMSO and AN. Thermodynamic parameters of micellization ΔH_m ^o, ΔS_m ^o, and ΔG_m ^o are evaluated according to the pseudo-phase model. The contribution of DMSO and AN in the micellization process of HDPB in aqueous electrolyte solutions are discussed in terms of the observed thermodynamic properties.     

微量量热法研究阴离子表面活性剂在DMA/长链醇体系中CMC和热力学函数

在N,N-二甲基乙酰胺(DMA)/长链醇非水溶液体系中, 利用微量量热仪, 研究阴离子表面活性剂十二烷基羧酸钠(SLA)、十二烷基硫酸钠(SDS)的临界胶束浓度(CMC)和热力学函数. 本文在十二烷基羧酸钠, 十二烷基硫酸钠的N,N-二甲基乙酰胺溶液中, 分别加入长链醇(庚醇、辛醇、壬醇、癸醇), 测定体系的热功率-时间曲线. 借助热力学理论, 由测得曲线, 进一步得到临界胶束浓度和热力学函数(ΔH_m⁰, ΔG_m⁰和ΔS_m⁰). 讨论了温度、醇的碳原子数目、醇的浓度与热力学参数之间的关系. 结果表明, 对十二烷基羧酸钠或十二烷基硫酸钠的DMA溶液, 在含有相同浓度的各种醇的体系中, CMC, ΔH_m⁰和ΔS_m⁰的值随着温度的升高而增加, 而ΔG_m⁰的值随着温度的升高而降低. 在相同温度及相同浓度的醇体系中, CMC, ΔH_m⁰,ΔG_m⁰和ΔS_m⁰的值都随着醇中碳原子数目的增加而降低. 在相同温度及相同醇的体系中, CMC, ΔG_m⁰的值随着醇的浓度的增加而增大, 而ΔH_m⁰, ΔS_m⁰的值随着醇的浓度的增加而减少.     

Viscometric Analysis of Miscibility and Interactions for Binary,Ternary Polycarbonate/Brominated Polystyrene + Chloroform Systems at Different Temperatures

Viscosities of ternary systems consist of polycarbonate (PC)/brominated polystyrene (PBrS) in chloroform and their corresponding binary systems were measured at different temperatures (20, 25, and 30°C). All the measurements were carried out at the concentration ranges of 0.1–0.6 g·dL^?1. The mass ratio of PC to PBrS was selected as 75:25, 50:50, and 25:75 in the ternary solutions. Two empirical expressions of Huggins and Kraemer equations with three-parameters were used for reproducing of the experimental viscosity data. The fitting parameters were obtained for the corresponding temperatures. The miscibility criteria on the basis of the sign of Δ[η]_m based on the difference between experimental and ideal values of [η]_m, was calculated by applying the Garcia et al., theoretical equation. The effect of temperature on the viscosity data was also studied. The results from this method were correlated with the miscibility data obtained for the same system by differential scanning calorimeter (DSC) findings.     

Evaluation of the flory-huggins interaction parameter for poly(styrene-co-acrylo-nitrile) and poly(methyl-methacrylate) blend from enthalpy of mixing measurements

A direct determination of enthalpy of mixing (ΔH _mix) is of interest in predicting miscibility in polymer—polymer systems. Such measurements present, however, working difficulties, so a reliable indirect approach has been attempted. The enthalpy of mixing ΔH _m is obtained by application of Hess law to heat of solution measurement for blends and their components in a common solvent. For SAN/PMMA blend, corresponding to the weight ratio 50∶50, the experiments were performed by the Hess law approach at 29.4 and 49.3°C on dilute polymer solutions, for various concentrations, getting very good correlation data. This leads to a negative value of the interaction parameterFH _χ(1,2) and by ΔG _mix diagram it is possible to make a comparison for each temperature in accordance with the LCST behaviour of these mixtures.     

Miscibility studies on the blends of collagen/chitosan by dilute solution viscometry

The viscosity behavior of collagen, chitosan and their blends at several compositions (2/8, 4/6, 5/5, 6/4, 8/2) has been studied. The miscibility of this polymer system was investigated on the basis of the sign of the criteria ΔB, Δb, Δ[η], α and β determined by dilute solution viscosity. These investigations indicate that collagen/chitosan is miscible at any composition in HAc at 25 °C. According to the “memory effect”, we can conclude that collagen/chitosan is also miscible in the solid state.     

Miscibility studies on blends of poly(phenylene oxide)/brominated polystyrene by viscometry

The viscosity behavior of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), brominated polystyrene (PBrS) and their blends at several compositions (25/75, 50/50, 75/25, 85/15) has been studied. The miscibility of this polymer system was investigated on the basis of the sign of the criteria Δb, α, ΔK, μ, and Δ[η] determined by viscosity. These investigations indicate that PPO/PBrS is miscible at the compositions of (75/25), (85/15) and completely immiscible at the compositions of (25/75), (50/50) in chloroform at 20 °C. Results from viscometry match very well those of DSC results cited in the literature.     

Effects of Electron Beam Irradiation on the Structural Properties of PVA/PAM/CMC Ternary Polymer Blends

Ternary miscible blends based on various ratios of poly(vinyl alcohol) (PVA), poly(acrylamide) (PAM) and carboxymethyl cellulose (CMC) were prepared by solution casting in the form of thin films. The structure‐property behavior of the ternary PVA/PAM/CMC blends, before and after they had been exposed to various doses of electron beam irradiation, was investigated by FT‐IR spectroscopy, SEM, XRD and stress‐strain curves. The visual observation showed that the cast films of the individual polymers PVA, PAM, and CMC and their blends over a wide range of composition are clear and transparent indicating the miscibility of PVA/PAM/CMC ternary blends. The FT‐IR analysis of pure polymers or their ternary blends before or after electron beam irradiation proved the formation of hydrogen bonding. In addition, it was found that the intensity of the different absorption bands depends on the ratio of PAM and CMC in the ternary blend. The XRD patterns showed that the peak position for the ternary blends decreases with increasing the ratio of CMC in the blend. However, the peak position for the ternary blend based on equal ratios of pure polymers was not affected by blending and was found in the same position as in the XRD pattern of pure PVA. The SEM micrographs give support to the visual observation indicating the complete miscibility of PVA/PAM/CMC ternary blends. The improvement in morphology leads to improvement in the tensile mechanical properties of the ternary polymer blends.     

Hexadecyltrimethylammonium bromide micellization in glycine,diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg^?1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔG _HP ^○ , free energy associated with the surface contributions, ΔG _S ^○ , standard free energy, ΔG _m ^○ , enthalpy, ΔH _m ^○ , and entropy, ΔS _m ^○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I ₁/I ₃ ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.     

A thermodynamic approach to study hydrogen-bonding interactions in solvent/solvent/polymer ternary systems

A thermodynamic approach based on both the classical Flory-Huggins (FH) formalism and the association equilibria (AE) theory has been developed to study the solubility properties of a system formed by a proton-donor solvent (A), a proton-acceptor solvent (B) and a proton-acceptor polymer (C). The miscibility of this ternary system is attained by competitive specific interactions via hydrogen-bonding established between the hydroxyl and carbonyl interacting groups of either solvent-solvent (AB) or solvent-polymer (AC) system components. The binary AB and AC specific interactions and their dependence with the system composition as well as with the extent of the association equilibrium have been quantified by means of two new parameters, Δg_AB and Δg_AC. These excess functions have appeared to be equivalent to the combinatorial or entropic term of the Gibbs free energy of the complex formation process, which accounts for the entropy of mixing plus the intermolecular specific interactions. The theoretical predictions have reasonablely agreed with experimental data on preferential solvation of two systems taken from literature: methanol(A)/1,4-dioxane(B)/poly(alkyl methacrylate)(C) and n-alcohol(A)/heptan-3-one(B)/poly(vinyl pyrrolidone)(C).     

Octadecylamine cobalt(III) dimethyl glyoximato complexes: synthesis,thermodynamics of micellization,steady-state photolysis and biological activities

A new class of surfactant–cobalt(III) complexes of the type trans-[Co(DH)₂(OA)X], where DH = dimethylglyoxime, OA = octadecylamine, X = Cl^?, Br^?, I^?, N₃ ^?, NO₂ ^?, SCN^? or OA, were synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in ethanol solution were obtained by measuring absorption at ~250 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG _m ⁰ , ΔH _m ⁰ and ΔS _m ⁰ ). Steady-state photolysis and cyclic voltammetry of the complexes were studied. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms.     

Assembly and characterization of Ag nanoparticles in PAM-g-PVA/PVP semi-interpenetrating network hydrogels

Polyacrylamide grafted poly(vinyl alcohol)/polyvinylpyrrolidone (PAM-g-PVA/PVP) semi-interpenetrating network (semi-IPN) hydrogels were designed and prepared via a simple free radical polymerization reaction process initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox system. The structure of the PAM-g-PVA/PVP semi-IPNs was characterized by a Fourier transform infrared spectroscopy. The morphologies of PAM-g-PVA/PVP hydrogels and PAM-g-PVA/PVP/Ag nanocomposite hydrogels were examined by scanning electron microscopy and transmission electron microscopy (TEM). The experimental results indicated that the PAM, PVA or PVP chains can efficiently act as stabilizing agents for Ag nanoparticles. TEM investigation of sample morphology showed the presence of nearly spherical-, square- or rectangular-shaped Ag nanoparticles with diameters ranging from 10 to 60 nm. The characteristic surface plasmon resonance band appeared at 390–400 run as a result of the immobilization of Ag nanoparticles within the hydrogel matrices. The self-assembly of Ag nanoparticles and the swelling behavior of the resulting nanocomposites can be controlled and modulated by altering the mole fraction of PVP in the PAM-g-PVA/PVP semi-IPNs.     

Synthesis of cross-linked carboxymethyl cellulose and poly (2-acrylamido-2-methylpropane sulfonic acid) hydrogel for sustained drug release optimized by Box-Behnken Design

This research aims to fabricate and characterize chemically crosslinked CMC/PVP-co-poly (AMPS) based hydrogel for the sustained release of model drug metoprolol tartrate through the free radical polymerization technique. Box-Behnken Design was used to optimize CMC/PVP-co-poly (AMPS) hydrogel by varying the content of reactants such as; polymers (CMC and PVP), monomer (AMPS), and crosslinker (EGDMA). Carboxymethyl cellulose (CMC) was crosslinked chemically with AMPS with a constant ratio of PVP by the ethylene glycol dimethacrylate as the crosslinker in the presence of sodium hydrogen sulfite (SHS)/ammonium peroxodisulfate (APS) as initiators. After developing CMC-based hydrogels using different polymers, monomer, and crosslinker concentrations, this study encompassed dynamic swelling, sol–gel fraction, drug release and chemical characterizations such as FTIR, XRD, TGA, DSC, and SEM. In vitro drug release and swelling were performed at 1.2 and 6.8 pH to determine the sustained release pattern and pH-responsive behavior. These parameters depended on the crosslinker, polymer, and monomer ratios used in the formulation development. XRD, SEM, and FTIR showed the successful grafting of constituents resulting in the formation of a stable hydrogel. DSC and TGA confirmed the thermodynamic stability of the hydrogel. Hydrogel swelling was increased with an increase in the ratio of monomer; however, an increase in the ratio of polymer and crosslinker decreased the hydrogel swelling. In vitro gel fraction and drug release also depended on polymer, monomer, and crosslinker ratios. The fabricated CMC/PVP-co-poly (AMPS) hydrogels constituted a potential system for sustained drug delivery.     

Miscibility and volume changes of mixing in the polystyrene/poly(2-chlorostyrene) blend system

The specific volume-temperature relationships of polystyrene, poly(2-chlorostyrene), and their polymer blends as well as the volume change of mixing Δv_m of the blends were obtained in the liquid state by dilatometry. The equation of state parameter and the molecular parameter of each homopolymer and blends were determined according to the lattice fluid theory of Sanchez and Lacombe. The experimental Δv_m obtained agreed quite well with that predicted from theory, and the enthalpy of mixing ΔH_m was also predicted using the pair molecular parameter. These two values were negative, indicative of miscibility of polystyrene and poly(2-chlorostyrene) in the liquid state. The absolute values of Δv_m and ΔH_m were about twice those for polystyrene and poly(phenylene oxide) blend, suggesting a specific interaction between the two polymers.     

Miscibility and orientation behavior of poly(vinyl alcohol) / poly(vinyl pyrrolidone) blends

The miscibility of poly(viny1 alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) blends is investigated by differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD). The molecular orientation induced by uniaxial stretching of the blends is also examined by WAXD and birefringence measurements. It is shown by the DSC thermal analysis that the polymer pair is miscible, since a single glass transition temperature (T_g) is situated between the T_gs of the two homopolymers at every composition. The T_g versus composition curve does not follow a monotonic function but exhibits a cusp point at a PVP volume fraction of a little under 0.7, as in a case predicted by Kovacs' theory. The presence of a specific intermolecular interaction between the two polymers is suggested by an observed systematic depression in the melting point of the PVA component. A negative value of the polymer-polymer interaction parameter, χ₁₂ = 0.35 (at 513 K), is estimated from a thermodynamic approach via a control experiment using samples crystallized isothermally at various temperatures. The extent of optical birefringence (Δn) of the drawn blends decreases drastically with increasing PVP content up to 80 wt %, when compared at a given draw ratio, and ultimately Δn is found to change from positive to negative at a critical PVP concentration of a little over 80 wt %. Discussion of the molecular orientation behavior takes into consideration a birefringence compensation effect in the miscible amorphous phase due to positive and negative contributions of oriented PVA and PVP, respectively.     

Characterization,optical, and nanoscale free volume properties of Na‐CMC/PAM/CNT nanocomposites

Polyblend and nanocomposite films of sodium salt of carboxymethylcellulose (Na‐CMC)/polyacrylamide (PAM) and Na‐CMC/PAM modified with carbon nanotubes (CNT) were synthesized by the solution casting technique. The effect of PAM and CNT loading on the structural, optical, and nanoscale free volume properties of Na‐CMC was studied. X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy exhibited the existence of strong interactions between Na‐CMC and PAM and the non‐destructive effect of CNT on Na‐CMC/PAM structure. The HR‐TEM revealed the multi‐walled structure of CNT with a 7.06‐nm wall thickness and a 6.92‐nm wall inner diameter. Positron annihilation lifetime spectroscopy (PALS) was done, in a vacuum and at 30°C to 200°C, to investigate the nanoscale free volume properties by using a conventional fast‐fast coincidence spectrometer. It was found that the o‐Ps lifetime (τ₃ ) and free volume (V_h) increase with increasing CNT percentage in the Na‐CMC/PAM blend. The distribution of the o‐Ps lifetime was broadened with increasing CNT ratios. Furthermore, the glass transition temperature (T_g) increases with increasing loads of CNT. For the first time, a correlation was done between Urbach energy (E_U) and V_h. Finally, the results were represented and discussed in the frame of free volume properties. Optical measurements showed that the transmittance T% of Na‐CMC/PAM was 91.12% and decreased to 68.42% and 36.45% after loading with 1.0 and 2.0 wt % CNT. In addition, the blend shows higher insulating properties compared with the individual polymers. The CNT incorporation reduces the band gap significantly and increases the E_U in the films.     

Surface activity of diphilic substances at different liquid interfaces

Systematic high-precision (±0.02 mJ m⁻²) measurements of surface tension were performed on aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium desoxycholate (DChNa) in order to study the effect of the non-polar phase (air, octane, perfluorodecaline, perfluorotributylamine) on surface activity (J) of the diphilic substance and the solution concentration (C_m) corresponding to the ultimate occupation of a monolayer at the interface. In the systems investigated, C_m proved to be 40–70% lower than the CMC, as was also confirmed by surface potential measurements. Analysis of the calculated standard thermodynamical functions of adsorption (ΔG⁰, ΔH⁰ and ΔS⁰) indicates that for substances with flexible hydrophobic radicals, the surface activity is higher at interfaces where the entropy gain is higher, primarily on account of the conformation entropy. In the case of surfactants with a rigid hydrocarbon radical, J increases with the exothermicity of adsorption due to considerable adhesion of the adsorbate to the non-polar phase.     

VISCOMETRIC STUDY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE BLENDS IN DIFFERENT SOLVENTS

The intermolecular interaction between poly(methyl methacrylate) (PMMA) and polystyrene (PS) intetrahydrofuran (THF) and N,N'-dimethyl formamide (DMF) solvents was studied at 28℃ using a dilute solution viscometrymethod. Solvent is believed to play a key role in characterizing the viscosity behavior of the polymer solution. The intrinsicviscosity and viscosity interaction parameter were experimentally measured for the binary (solvent/polymer) and for theternary systems in two solvents. The compatibility of the polymer mixture was discussed in terms of the sign of △b_m. Theresults show that the compatibility of PMMA/PS blend in DMF is larger than that in THF.