Comment on “Rheological Properties of Polyethylene Glycol (PEG 35000): An Interpretation of a Negative Intrinsic Viscosity and a High Huggins Coefficient Value.” J. Macromol. Sci., Part B: Physics 2014 (53) 391”

It is shown that the recently reported negative intrinsic viscosity and the high Huggins coefficient value of polyethylene glycol (PEG 35000) water solutions [J. Macromol. Sci., Part B: Physics 2014, 53 (3) 391] is just the result of omitting some experimental data from the consideration. Viscometric studies, which we have performed on the PEG 35000 solutions, exclude an anomalous behavior of the viscosity and related quantities under the conditions of the discussed experiments.     

Hypercoiled structures in aqueous solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers at low metnacrylic acid content

The behavior of solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers in aqueous 2–8M urea was investigated at temperatures ranging from 10 to 50°C at pH from 3 to 8. The molar fraction of methacrylic acid in the copolymer was 0.045 at most. The values of the intrinsic viscosity and Huggins coefficient were determined. Under these conditions, the poly-(2-hydroxyethyl methacrylate) molecules are in a hypercoiled state. In copolymers at a low degree of dissociation, the methacrylic acid units make the degree of coiling even higher, but in the dissociated state this degree is much lower. Hypercoiling is interpreted as a consequence of the association of hydrophobic groups in the molecule of copolymers.     

Viscometric Studies of Interactions between Hydrophobically Modified Acrylamide Copolymer and Poly(N-isopropylacrylamide) in Dilute Solutions

The viscosity behavior of the dilute aqueous solutions of hydrophobically modified acrylamide copolymer (HMPAM) and poly(N-isopropylacrylamide) (PNIPAM) was investigated. A negative deviation of reduced viscosity of HMPAM + PNIPAM from the theoretical values was observed. Both a conventional viscometry method and a method using an aqueous solution of one polymer as the solvent for the other polymer were used to clarify the mechanism behind the observed viscosity behavior. With the conventional method, the theoretical predictions obtained by the Δb (or α) criterion are contradictory to the experimental results and cannot be applied to describe the interaction between HMPAM and PNIPAM, where Δb is the difference of experimental interspecific interaction coefficient b_m and theoretical b_m,i and α is the difference of experimental Huggins coefficient k_m and theoretical k_m,i. The change of Δ[η]/[η]_i suggests that there is only an attractive interaction between HMPAM and PNIPAM, where Δ[η] is the difference of experimental intrinsic viscosity [η]_m and theoretical [η]_i. Results from the method using an aqueous solution of one polymer as the solvent for the other polymer confirmed the attractive interaction between HMPAM and PNIPAM and indicated that the attachment of the PNIPAM molecules to the hydrophobic groups in HMPAM can disrupt both the initial intra- and intermolecular associations between HMPAM chains simultaneously. The disruption of the original intramolecular association of HMPAM leads to an increase in the intrinsic viscosity [η], while the disruption of the original intermolecular association of HMPAM yields a negative deviation of the reduced viscosity.     

Mass fabrication of size-controllable hydrogel microarrays by dip-pen nanolithography with viscosity-tunable ink

A method of mass fabricating poly(ethylene glycol) (PEG) hydrogel microarrays is demonstrated. Microarrays of poly(ethylene glycol) dimethacrylate (PEG-DMA) with photoinitiator were patterned by one-dimensional (1-D) parallel dip-pen nanolithography (DPN), and the microarrays were cross-linked to form PEG hydrogels by UV irradiation in N₂ air. As an ink material for DPN printing, solid and liquid phase of PEG-DMA were mixed and prepared to tune viscosity of the ink material by temperature. Thus, the diameter of the microarrays was able to be averagely controlled from 1.7 to 6.2 μm as temperature during printing was increased from 25 °C to 37 °C, respectively. The overall microarrays showed less than 16% coefficient of variation (C.V.). Moreover, small molecules, such as fluorescence dyes, were able to be embedded in the PEG hydrogel microarrays.     

Viscosity,Ultrasonic, and Refractometric Studies of Chitosan/Polyethylene Glycol Blend in Solution at 30, 40, and 50°C

Measurements of viscosity, ultrasonic velocity, refractive index, and density of chitosan (CS)/polyethylene glycol (PEG) blends in buffer solution (0.1 M acetic acid+0.2 M sodium acetate) were carried out for different blend compositions at 30, 40, and 50°C. Using the viscosity data, interaction parameters μ and α were computed to determine miscibility. These values revealed that the blend was miscible when the chitosan content was more than 60% of the blend. The results were further confirmed by ultrasonic velocity, density, and refractive index measurements. Further, the results revealed that the change in temperature has no significant effect on the miscibility of CS/PEG polymer blends.     

Effect of Temperature on Cononsolvency of Polyvinylpyrrolidone in Water/Methanol Mixture

The behavior of polyvinylpyrrolidone in mixed water/methanol solvents was studied by rheoviscosimetry over a temperature range of 20°C–40°C. For the lower temperatures of this range, the intrinsic viscosity variation of the polymer vs. methanol molar fraction shows structural transitions (coil–globule–coil). This transition, which is usually attributed to the cononsolvency phenomenon, agrees with our previously published results obtained by dynamic light scattering. For higher temperatures, near 40°C, the intrinsic viscosity increase shows an expansion of the polymer over the alcohol molar fraction range 0.2 < X _A < 0.5. This last result can be attributed to the water/alcohol complex destruction under temperature increase. The “excess viscosity” of the polymer-mixed solvents vanishes with increasing temperature and becomes positive at 40°C. So, the polymer chain tends to transit from a globular to an ideal chain in the middle composition range of the mixed solvents.     

Effect of temperature on the synthesis of silver nanoparticles with polyethylene glycol: new insights into the reduction mechanism

Polyethylene glycol (PEG) molecules act as a reducing and stabilizing agent in the formation of silver nanoparticles. PEG undergoes thermal oxidative degradation at temperatures over 70 °C in the presence of oxygen. Here, we studied how the temperature and an oxidizing atmosphere could affect the synthesis of silver nanoparticles with PEG. We tested different AgNO₃ concentrations for nanoparticles syntheses using PEG of low molecular weight, at 60 and 100 °C. At the higher temperature, the reducing action of PEG increased and the effect of PEG/Ag⁺ ratio on nanoparticles aggregation changed. These results suggest that different synthesis mechanisms operate at 60 and 100 °C. Thus, at 60 °C the reduction of silver ions can occur through the oxidation of the hydroxyl groups of PEG, as has been previously reported. We propose that the thermal oxidative degradation of PEG at 100 °C increases the number of both, functional groups and molecules that can reduce silver ions and stabilize silver nanoparticles. This degradation process could explain the enhancement of PEG reducing action observed by other authors when they increase the reaction temperature or use a PEG of higher molecular weight     

Molecular dynamics simulations on chitosan/graphene nanocomposites as anticancer drug delivery using systems

Several chitosan (CS) drug delivery systems (DDSs) were designed by molecular dynamics (MD) simulations. The systems were composed of pure graphene (G), P-doped (GP) or N-doped (GN) graphene nanosheets for the anticancer drug cyclophosphamide (CP) with the aim of discovering the most appropriate drug carrier. Furthermore, the temperature influence was investigated on the systems characteristics through performing the simulations at four different temperatures including 25, 35, 45 and 55 °C. The diffusion coefficients and mean square displacements (MSDs) were boosted with the temperature increase. At 55 °C, the CS-G-CP exhibited the greatest diffusion coefficient (0.0658 × 10^–5 cm²/s) but the CS-GN-CP had the smallest diffusion coefficient of 0.0553 × 10^–5 cm²/s and the CS-GP-CP illustrated a medium amount (0.0595 × 10^–5 cm²/s) indicating the most controlled/sustained drug diffusion could occur in the CS-GN-CP which could allow the most efficient drug delivery. Moreover, to evaluate the effects of PEG chains and VC molecule on the drug delivery capacity of the CS-GN-CP cell, they were added to the this system and the CS-GN-CP-PEG2-VC was nominated as the best DDS working at 35 °C (close to the human body temperature) due to it had a relatively high drug loading capacity as well as suitable CP diffusion coefficient and FV, FFV values.     

Rheological Investigations of Copolymers of N-(Substituted Maleimide)s with Styrene in Dimethylsulfoxide

The viscoelastic behavior of poly(N-(4-formylphenoxy-4′-carbonylphenyl)maleimide-co-styrene) and poly(N-(4-carboxyphenyl)maleimide-co-styrene) in dimethylsulfoxide is investigated. The rheological parameters (elastic modulus, viscous modulus, loss tangent) were determined at different temperatures in the range 20°C–80°C. Poly(N-(4-carboxyphenyl)maleimide-co-styrene) exhibits a Newtonian behavior in the frequency range from 0.05 to 700 rad/s at all temperatures. For poly(N-(4-formylphenoxy-4′-carbonylphenyl)maleimide-co-styrene), a shear thinning behavior was observed at temperatures below 40°C (pseudoplastic behavior), whereas at higher temperatures the sample exhibits Newtonian flow throughout the studied frequencies range. The activation energies of the flow (calculated by using the zero shear viscosity values) give indications about the intensity of polymer-polymer interactions as a function of the maleimide monomer structure.     

The Newtonian viscosity of polymer solutions: Scaling relationships

Scaling in terms of temperature, composition, and molecular weight variables has practical and fundamental significance. The viscosity of polymer solutions deviates from that predicted by the Huggins equation when the concentration is higher than a characteristic concentration c_ch. The value of c_ch depends on the molecular weight of the polymer and the thermodynamic conditions of the system. It is also a known fact that the deviations are due to the entanglements and interactions of polymer molecules. Therefore, we believe cch can be used as a concentration-reducing parameter to get the superposition curves. It can be shown that the concentration corresponding to a minimum value of η_sp/ch² (in the case of η_sp/c² vs concentration curves) is the value of c_ch of that system. Moreover, this c_ch is related to the intrinsic viscosity and molecular weight through the Huggins and Mark-Hauwink-Sakurada equations (c_ch = k′M^?a′). Using c_ch values for different systems and plotting log η_r versus C/C_ch, the superposition curves are obtained. In each case these curves are found to be linear, at least when concentrations approach zero. Master curves may be plotted by making use of the initial slopes of the curve (log η_r vs Bc/c_ch) and it is found that the data obtained at different thermodynamic conditions fit these (log η_r vs Bc/c_ch, B being the initial slope of log η vs c/c_ch) curves very well. The slopes are also compared to k′, a′, and the expansion coefficient of the system and the relationships are found to be linear. It is concluded that c_ch is a better parameter for the superposition of viscosity data, as well as being easy to obtain experimentally.     

On possibility of a structural transition in the vicinity of the melting point in liquid copper

The temperature dependence of the kinematic viscosity of liquid copper has been studied by the method of torsional vibrations during heating and cooling within the temperature range 1080–1500°C. A reversible structural transition was discovered in the vicinity of 1170°C. This transition manifests itself in a jumpwise change of viscosity and the activation energy of viscous flow at this temperature.     

Viscometric Study of the Gelatin Solutions Ranging from Dilute to Extremely Dilute Concentrations

The viscosity of gelatin solutions with concentrations between 10^?4 and 10^?5 g/cm³, covering the extremely dilute zones, was studied via a photoelectric viscometer, and the effects of the electrolyte, pH, surfactant, urea, and temperature were discussed. The results showed that the reduced viscosity (η_sp/C) of gelatin exhibited a drastic increase with dilution in the extremely dilute aqueous solutions, this being a typical polyelectrolyte effect. The reduced viscosity of gelatin underwent several oscillations with varying pH; the minimum value of the viscosity was at pH = 5.0, corresponding to its isoelectric point, where gelatin exhibited antipolyelectrolyte behavior. The reduced viscosity of gelatin decreased with increasing temperature, which was due to the helix–coil transition in the gelatin solution. The temperature of the helix–coil transition was 30.0°C in gelatin aqueous solution; however the temperature of helix–coil transition decreased to 20.0°C in urea. Upon cooling, the gelatin molecules in aqueous solution underwent a coil–helix transition. Hydrophobic interactions caused chain folding in the presence of the surfactant sodium dodecylsulphate.     

Effect of fast neutron irradiation on the structural and optical properties of Makrofol DE 1-1 CC polycarbonate

Samples from sheets of the polymeric material Makrofol DE 1-1 CC have been exposed to neutrons of incident energy in the range of 0.8–19.2 MeV. The modifications induced in Makrofol samples due to neutron irradiation have been studied through different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, intrinsic viscosity, refractive index and color difference studies. Infrared spectroscopy indicated that cross-linking is the dominant mechanism in the energy range of 2.3–19.2 MeV. The cross-linking reported by FTIR spectroscopy destroyed the degree of ordering in the Makrofol samples, as revealed by the XRD technique. Also, this cross-linking led to an increase in the values of intrinsic viscosity from 0.41 to 0.68 at 28 °C, indicating an increase in the average molecular mass, associated with an increase in the refractive index. Additionally, the non-irradiated Makrofol samples showed significant color sensitivity toward neutron irradiation. The sensitivity toward neutron irradiation can be seen by the change in the blue color component of the non-irradiated Makrofol film to yellow after the samples are exposed to neutrons up to 19.2 MeV. This is accompanied by a net increase in the darkness of the samples.     

Measurement of liquid surface properties using a He-Ne laser

The surface tension, viscosity, and damping coefficient of surface waves on a liquid sample have been determined by observing the diffraction of an optical beam. To achieve high accuracy, a He-Ne laser having a high brightness and coherence was used as a light source. Experiments illustrating and verifying the techniques are described.Values of the surface tension for different samples have been measured with a standard deviation of less than ±0.6% for frequencies of the ripple motion ranging from 500 to 3 000 Hz over the temperature range 20–45°C. The viscosity and damping coefficient of water were measured for frequencies in the range 600–1500 Hz. The values obtained agree with those available from the literature.     

Importance of poly(ethylene glycol) conformation for the synthesis of silver nanoparticles in aqueous solution

Silver nanoparticles (NPs) were prepared using silver nitrate (AgNO₃) as a precursor in an aqueous solution of poly(ethylene glycol) (PEG), which acted as both a reducing and stabilizing agent. The UV/Vis spectra showed that PEG 100 (100 kg/mol) has a remarkable capability to produce silver NPs at 80 °C, but the production of silver NPs by both PEG 2 (2 kg/mol) and PEG 35 (35 kg/mol) was negligible. This difference was explained by the conformation of PEG in the reaction solution: the entangled conformation for PEG 100 and the single-coiled conformation for PEG 2 and PEG 35, which were confirmed by pulse-field-gradient ¹H NMR and viscosity measurements. In an aqueous solution, the entangled conformation of PEG 100 facilitated the reduction reaction by caging silver ions and effectively prevented the agglomeration of formed NPs. The reaction in an aqueous PEG 100 solution was observed to be stable under the conditions of a prolonged reaction time or an increased temperature, while no reduction reaction occurred in the PEG 2 solution. The synthesis of silver NPs by PEG 100 was well controlled to produce fine silver NPs with 3.68 ± 1.03 nm in diameter, the size of which remained relatively constant throughout the reaction.     

Pyroelectric properties of BiFeO3 ceramics prepared by a modified solid-state-reaction method

BiFeO₃ (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T _cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T _sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm². The measured piezoelectric coefficient d ₃₃ was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m² K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.     

Diffusion of iron in lithium niobate: a secondary ion mass spectrometry study

Iron-doped X-cut lithium niobate crystals were prepared by means of thermal diffusion from thin film varying in a systematic way the process parameters such as temperature and diffusion duration. Secondary Ion Mass Spectrometry was exploited to characterize the iron in-depth profiles. The evolution of the composition of the Fe thin film in the range between 600°C and 800°C was studied, and the diffusion coefficient at different temperatures in the range between 900°C and 1050°C and the activation energy of the diffusion process were estimated.     

Microstructural Evolution and Its Effect on Mechanical Properties of Isotactic Polypropylene by Shear Plastic Deformation at Elevated Temperatures

Isotactic polypropylene (iPP) was plastically shear deformed by equal channel angular extrusion (ECAE) at extrusion temperatures varied from 45 to 125°C (25 mm/min). The evolutions of morphology and crystal orientation were studied by reflected optical microscopy (ROM), scanning electron microscopy (SEM), and X-ray diffraction. It was found that the original spherulites were deformed into nearly ellipsoids with their long axis tilted at an angle away from the flow direction. Azimuthal scanning results revealed that two preferred crystal orientations were formed after ECAE. The crystal plasticity was activated by increasing the extrusion temperature, followed by fast rotation of crystallites toward the shear direction. The thermal mechanical analysis (TMA) indicated that low extrusion temperature was favorable to fix the molecular orientation. The iPP samples processed at the investigated temperatures displayed a significant increase in the impact strength, especially for those extruded at 45°C and 65°C. The tensile results revealed a greater elongation at break in the samples deformed at low temperatures (45°C and 65°C) but not in those deformed at high temperatures (85°C or above).     

Structural transition in liquid cobalt

The temperature dependence of kinematic viscosity of liquid cobalt in the range 1490–1700°C and the influence of the degree of cobalt overheating on its overcooling were studied by viscometry and differential thermal analysis. It was found that liquid cobalt undergoes a structural transition near 1595°C, which manifests itself as a sharp change in the viscosity and the activation energy for viscous flow at this temperature and is accompanied by a considerable increase in crystallization ability.