Cohesive Energy Density Of Polymer Research Articles

Probing Contact Electrification: A Cohesively Sticky Problem.

Contact electrification and the triboelectric effect are complex processes for mechanical-to-electrical energy conversion, particularly for highly deformable polymers. While generating relatively low power density, contact electrification can occur at the contact-separation interface between nearly any two polymer surfaces. This ubiquitousness of surfaces enables contact electrification to be an important phenomenon to understand energy conversion and harvesting applications. The mechanism of charge generation between polymeric materials remains ambiguous, with electron transfer, material (also known as mass) transfer, and adsorbed chemical species transfer (including induced ionization of water and other molecules) all being proposed as the primary source of the measured charge. Often, all sources of charge, except electron transfer, are dismissed in the case of triboelectric energy harvesters, leading to the generation of the "triboelectric series", governed by the ability of a polymer to lose, or accept, an electron. Here, this sole focus on electron transfer is challenged through rigorous experiments, measuring charge density in polymer-polymer (196 polymer combinations), polymer-glass (14 polymers), and polymer-liquid metal (14 polymers) systems. Through the investigation of these interfaces, clear evidence of material transfer via heterolytic bond cleavage is provided. Based on these results, a generalized model considering the cohesive energy density of polymers as the critical parameter for polymer contact electrification is discussed. This discussion clearly shows that material transfer must be accounted for when discussing the source of charge generated by polymeric mechanical energy harvesters. Thus, a correlated physical property to understand the triboelectric series is provided.

The cohesive energy density of polymers and its relationship to surface tension, bulk thermodynamic properties, and chain structure

ABSTRACTThe cohesive energy density (CED) and the internal pressure (Pi) have similar values for most liquids at low pressures. For most polymers CED cannot be directly measured, unlike Pi which is readily obtained in the melt from PVT or other related data. Directly measured CED are available for the oligomer linear alkane series over a moderate molecular weight (MW) range. Scaling CED with measured surface tensions (ɣ) leads to separation into two universal scaling curves, which provides a measure of surface configurational entropy, as does the MW dependence of experimental surface tensions for two polymer series. A novel polymer scaling curve based on CED is shown to provide improved accuracy in the prediction of ɣ for any polymer or solvent. For polymers that interact predominately through Van der Waals forces, correlations between the average interchain separation distances and the magnitude of CED (or Pi), are shown to give a universal derivation of CED. In contrast, polymers like P4VP having strong polar interactions provide dramatic evidence of the different physical basis of CED and Pi. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44431.

Effect of OH group on the water vapor sorption property of adamantane-containing polymer membranes

The synthesis and characteristics of adamantane-containing acryl or methacryl polymers were investigated, focusing on the effects of the hydrophobic adamantyl unit and the hydrophilic OH group. The water vapor sorption property of adamantane polymer membranes was determined at 35°C. The membrane density which represents the packing of polymer segments increased with increasing the OH groups and the polymer cohesive energy density (CED), which reflects the polarity of polymers. The water vapor solubility in OH-containing adamantane polymer membranes was higher than that in non-OH-containing adamantanes due to the high interaction between the OH group and the water molecules. Therefore, the OH groups in the adamantane unit give the sorption site of the water molecules in the membranes. In addition, we found that the stronger interaction by OH groups between the water molecules and polymers can prevent the clustering of water molecules based on the Zimm–Lundberg analysis.

The interrelation among network structures, molecular transport of solvent, and creep behaviors of TiB2 ceramic containing butyl rubber composites

AbstractSwelling of polymer composites in solvents has become one of the major problems in the use of polymer composites exposed to petroleum products. As a possible solution to the problem, this experimental study was conducted to examine the potential application of TiB2 ceramic in butyl rubber (IIR) composites. The effect of TiB2 content on the curing kinetics of IIR composites was studied using a torque rheometer technique. The effect of TiB2 on the network structure was investigated in terms of the crosslinking density, interparticle distance between conducting particles, surface tension, glass transition temperature, degree of crystallinity, scanning electron microscopy, and X‐ray analysis. Moreover, the effect of TiB2 content on the molecular transport of solvent (kerosene) was examined by means of degree of swelling, solvent interaction parameters, volume fraction of rubber, interparticle distance after swelling, penetration rate of solvent, mean diffusion coefficient, cohesive energy density of polymer, standard entropy, standard enthalpy, and standard free energy of IIR composites. It was ascertained that with increasing TiB2 content the degree of swelling shifts to a lower value. The main reason was interpreted as the introduction of good interface adhesion of TiB2 with rubber matrix, which tends to block the diffusion of solvent molecules. The effect of TiB2 content on hardness, tensile strength, Young's modules, and elongation at break is discussed. An apparent steady‐state creep of butyl rubber IIR/TiB2 composites is evident under different constant stresses at room temperature. The strain rate of steady‐state creep showed a dependence on stress and TiB2 volume fraction. The stress sensitivity parameter, viscosity coefficient, and activation volume for samples loaded with different content of TiB2 were estimated. It is apparent that these new composites should be very useful for solvent permeation resistance at high TiB2 loading level with good mechanical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2226–2235, 2005

Surface Tension and Melt Cohesive Energy Density of Polymer Melts Including High Melting and High Glass Transition Polymers

Melt surface tensions and pressure−volume−temperature (PVT) data were obtained for many hydrophobic and hydrophilic polymers including high melting polyesters and polyamides such as poly(ethylene terephthalate) and nylon 66. A model is developed that uses surface tension to convert PVT data (from which the thermodynamic quantity “internal pressure” is calculated) into another thermodynamic bulk property, the cohesive energy density (CED). The errors inherent in assuming that the CED has the same proportionality factor to internal pressure independent of chemical structure are discussed. The results emphasize the difference between internal pressure and CED, where only internal pressure can be directly obtained from PVT data. The CED is the quantity that must be used for calculations of surface tension, and examples of the determination of melt surface tension are given for several polar or hydrogen-bonding polymers and semicrystalline or amorphous polymers of different molecular weights. Poly(2-vinyl pyridine) is contrasted with poly(4-vinyl pyridine), where the strong hydrogen bonding of the latter contributes to a large deviation of the proportionality factor between CED and internal pressure compared to that of the typical weakly interacting polymer. The results indicate that thermodynamic quantities, such as CED as a function of temperature in the melt, can be calculated for almost any molten liquid using these new models. The calculation of the CED for nylon 66 using structure/property relationships also provides a method for the determination of surface tensions for that polymer that cannot be directly measured.

The transport properties of CO2 and CH4 for brominated polysulfone membrane

The sorption and permeation properties of CO2 and CH4 for synthesized brominated polysulfone, BPSf (bromobisphenol A polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone), MPSf (bisphenol A methylated polysulfone) and TMSPSf (bisphenol A trimethylsilylated polysulfone) to investigate the structure-property relationships. Especially, the effect of polarity of substituents on the transport properties was studied. The effect of operating pressure on the permeation properties of polysulfones was examined. The permeation properties for a mixture of CO2 and CH4 were also measured, and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to the dual mode model. The permeability coefficients of each gas of a binary mixture are less than those of pure gases, and the extent of reduction in permeability coefficient is larger for less permeable polymer. The ideal separation factor for four polysulfones increases in the following order: TMSPSf< PSf< BPSf< MPSf. The ideal separation factor for BPSf is higher than other polysulfones having similar permeability coefficients of CO2 with BPSf. It can be explained that the strong polarity of bromine in BPSf increases cohesive energy density of polymer, and reduces the chain packing-inhibiting ability. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is not consistent with the permeability coefficient.

Solubility of Homopolymers and Copolymers in Carbon Dioxide

The cloud points of various amorphous polyether, polyacrylate, and polysiloxane homopolymers, and a variety of commercially available block copolymers, were measured in CO2 at temperatures from 25 to 65 °C and pressures of ca. 1000−6000 psia. Almost without exception, the solubility of amorphous polymers increases with a decrease in the cohesive energy density, or likewise, the surface tension of the polymer. With this decrease in surface tension, the polymer cohesive energy density becomes closer to that of CO2. Consequently, solubility is governed primarily by polymer−polymer interactions, while polymer−CO2 interactions play a secondary role. The solubility is strongly dependent upon molecular weight for the less CO2-philic polymers. The solubilities of high-molecular-weight poly(fluoroalkoxyphosphazenes) in CO2 were comparable to those of poly(1,1-dihydroperfluorooctylacrylate), one of the most CO2-soluble polymers known.

Prediction of gas barrier properties of high polymers

AbstractThis paper studies the correlation of polymer structure and morphology and gas permeability. A scale of numerical values based on polymer cohesive energy density and fractional free volume has been devised to predict permeability and also to estimate diffusion and solubility properties.

Cohesive Energy Density of Polystyrene

Bristow and Watson1 have recently described the determination of the cohesive energy densities of polymers by swelling and viscosity measurements. This communication summarizes the results of viscosity measurements on polystyrene solutions directed towards a similar end. The measurements cover a slightly different range of solvents from that of Bristow and Watson, and in some solvents a range of molecular weights has been investigated.

Cohesive energy densities of polymers. Part 1.—Cohesive energy densities of rubbers by swelling measurements

The first page of this article is displayed as the abstract.

Cohesive energy densities of polymers. Part 2.—Cohesive energy densities from viscosity measurements

The first page of this article is displayed as the abstract.

Some factors affecting the solubility of polymers

AbstractThe solubility of a polymer in a non‐polymeric liquid depends mainly on the heat of mixing. When no polar forces are concerned, the cohesive energy densities of polymer and solvent must be close; a method is given for estimating the cohesive energy densities of polymers from a set of additive constants, and it is shown that good agreement is found between values so calculated and values obtained by swelling measurements. The effects of dipole interactions and hydrogen bonding are also discussed. The solubility of polyvinyl chloride in a number of solvents is considered, and correlated with both the cohesive energy density of the solvent and its ability to form hydrogen bonds.