Non-equilibrium chemical potential and polymer extraction from a porous matrix

The influence of a flow on the transfer of a polymer solution from a porous matrix to a flowing fluid is analysed. Since the flow modifies the free energy of the solution, through stretching and orientation of the macromolecules, the thermodynamic driving force for polymer transport is modified with respect to that of a quiescent fluid. The consequences of this modification for the extraction of a polymer from a porous matrix are explored in detail, and the formal results are explicitly illustrated by means of a specific solution. For the particular example analysed here, of possible interest in oil extraction or in microfluidic problems, the non-equilibrium effects may yield a reduction of the order of 10% of the extraction rate.     

Calculation of the effect of macromolecular architecture on structure and thermodynamic properties of linear-tri-arm polyethylene blends from Monte Carlo simulation

A Monte Carlo simulation formalism proposed recently [Peristeras et al. Macromolecules 2007;40:2904-14] is applied here to linear-tri-arm polyethylene blends using atomistic models. Elementary Monte Carlo moves for long chain and branched molecules are used and shown to result in efficient relaxation of long chains. The effect of chain and arm molecular weight and of temperature on the structure and thermodynamic properties of blends is examined. Chemical potential versus composition diagrams are drawn in order to assess the non-ideality of mixing that may lead to phase separation. All of the blends examined are shown to be fully miscible. The microscopic blend structure is examined by calculating the radial distribution function. Finally, the radii of gyration of linear and branched chains are calculated and scaling exponents are evaluated.     

A molecular thermodynamic model for binary lattice polymer solutions

A molecular thermodynamic model for binary lattice polymer solutions with concise and accurate expressions for the Helmholtz energy of mixing and other thermodynamic properties is established. Computer simulation results are combined with the statistical mechanics to obtain the expressions. Yan et al.'s model for Ising lattice and the sticky-point model of Cumming, Zhou and Stell are incorporated in the derivation. Besides the nearest neighbor cavity correlation function obtained from the Ising lattice, the long range correlations beyond the close contact pairs are represented by a parameter λ, the linear chain-length dependence of which is obtained by fitting the simulated critical parameters of two systems with chain lengths of 4 and 200. The predicted critical temperatures and critical compositions, spinodals and coexistence curves as well as internal energies of mixing for systems with various chain lengths are in satisfactory agreement in comparison with the computer simulation results and experimental data indicating the superiority of the model over other theories. The model can serve as a basis to develop more efficient models for practical applications.     

Molecular modeling and synthesis of polymers for use in applications requiring a low-k dielectric

As integrated circuits have become more and more complex and with smaller and smaller feature sizes several limitations have become apparent. One of these is the need for low-k dielectric materials as insulating layers. Recent work has reported promising materials for such insulators that include some fluorinated polymers. These dielectric materials were further improved by introducing porosity into the polymer films. One of the key factors in the dielectric constant of a material is its density. As the polarization of the material is related to the number of bonds, the dielectric constant will scale with the density. In this paper a series of molecular modeling calculations were conducted on various fluorine substituted polymers in order to predict their densities. A surprising result of these calculations was the prediction that some of the polymers would have densities less than 1 g/cm³. One of these polymers was synthesized and the density determined. The calculated density was in extremely good agreement with the experimental density. This paper will present the details of the molecular modeling technique as well as the synthesis and characterization of one of the polymers of interest.     

Non-equilibrium chemical potential and stress-induced migration of polymers in tubes

A non-equilibrium chemical potential depending on the viscous pressure tensor is used to describe shear-induced diffusion in polymer solutions flowing along cylindrical tubes. Our results generalize previous ones in three main aspects: a Flory-Huggins expression for the equilibrium contribution to the chemical potential is used instead of the ideal-gas like expression, the full expression for the steady-state compliance of the solution is taken into account instead of only the polymer contribution, and the influence of the solute molecular mass is explicitly considered. As a qualitatively new result of considerable practical interest, it stands the prediction that in some circumstances, a dynamical instability may appear, which accelerates and enhances the separation process.     

Specific interactions in blends containing Chitosan and functionalized polymers. Molecular dynamics simulations

Chitosan (CS)/poly(vinyl alcohol) (PVA) and Chitosan/poly(2-hydroxyethyl methacrylate) (P2HEM) blends have been studied through molecular dynamic simulations. In a previous work it was found miscibility between these polymers and it was attributed to hydrogen bonding formation. However, the experimental information obtained was not enough to know which of the interacting groups of Chitosan, i.e. -CH₂OH or -NH₂, are responsible of the interaction. Therefore, we have performed molecular dynamics simulation runs of 1 ns in order to calculate radial distribution functions (RDF) for the groups tentatively involved in the interaction. The results are correlated with our previous experimental data. This way, we have obtained a more precise conclusive information about the interactions involved as function of the blends composition. For low compositions of PVA and P2HEM the interaction is predominantly with the hydroxymethyl groups of CS while as the composition of PVA and P2HEM increases, the interaction with the amine groups increases.     

Wetting by polymer solutions

Very small droplets of polystyrene dissolved in toluene were placed on a glass slide and studied under a goniometer microscope. The drops were allowed to spread and dry and their extent of spreading is plotted as a variation of the concentration of the polymer in the solution. It was observed that drops of polystyrene in a volatile solvent such as toluene, spread to some extent and then gets dried up thus preventing the contact line from moving further. When liquid PDMS in non-volatile solvent, HMDS, and in volatile solvent, toluene, was used, the droplets continued to spread. One conclusion among others, is that even if the droplet dries but leaves behind a mobile contact line then the solution spreads out, on the other hand if the droplet dries and the contact line loses its mobility, the spreading automatically comes to a stop.     

Liquid crystalline (cyanoethylpropyl)cellulose and its optically anisotropic composites with acrylic polymers

Described herein are anisotropic polymer composites, made up of (cyanoethylpropyl)cellulose (CEPC) and acrylic polymer. A band texture (which can be seen with a polarisation microscope) forms in CEPC and its lyotropic solutions in acrylic monomer after orientation as a result of relaxation phenomena. The photopolymerisation of acrylic monomer (acrylic or methacrylic acid) in an oriented lyotropic solution of CEPC ‘freezes’ the orientation, and stable birefringent polymer composites are created. Thermooptical analysis shows that these composites exhibit thermally reversible anisotropy of optical properties. Molecular relaxations in such composites were investigated by means of dielectric and mechanical spectroscopies. The molecular relaxation processes, characteristic of pure components, are preserved in these composites. Two representations were used in dielectric spectroscopy: the temperature dependences of dielectric loss ε″ and of electric modulus M″. The latter was especially useful in the high temperature range, where ionic conductivity dominates the dielectric response.     

A molecular approach to bioseparations: Protein-protein and protein-salt interactions

Many bioprocess separations involve manipulating the solution conditions to selectively remove or concentrate a target protein. The selectivity is determined by the thermodynamics of the protein solution, which are governed, at the molecular level, by protein-protein interactions. Thus, to optimise these processes, one must understand the precise nature of these interactions, how they are affected by the control parameters (e.g., temperature, ionic strength, pH), and how they relate to the solution properties of interest (e.g., protein solubility, protein stability, crystal nucleation rates). Recently, studies of protein-protein interactions have been motivated by the discovery of a crystallisation window, which places bounds on the protein-protein attraction that is required for crystallisation to be possible. This review focuses on experimental and theoretical studies of protein-protein interactions and discusses the current gaps in understanding these forces. The first models for these interactions had been based on DLVO theory, which has proven useful for understanding protein-protein interactions in dilute electrolyte solutions. However, DLVO theory does not include such important effects as anisotropic interactions, solvation forces, and specific ion effects. Various approaches have been developed to include these phenomena although they are still not well understood. One outstanding issue concerns specific ion effects, which play a crucial role in biological systems. An initial step in understanding these effects might be to first rationalize protein-salt interactions.     

Coextrusion flow of two molten polymers between parallel plates: Non isothermal computation and experimental study

A theoretical study of the one-directional coextrusion flow of two molten polymers between parallel plates has been carried out using a non-isothermal power-law model. A numerical method has been used to solve simultaneously the momentum and energy balance equations, in order to obtain the evolutions of the interface position, the pressure gradient, and the temperature profiles all along the flow. The theoretical results are in good agreement with experimental values measured on an industrial coextrusion line.     

Insight into molecular interactions between constituents in polymer clay nanocomposites

The mechanisms responsible for the enhancement of physical properties of polymer clay nanocomposites (PCN) over pristine polymers are not well understood. This knowledge is important for obtaining a better control over the physical properties of PCN and designing PCN with tailored properties. The interactions among the different constituents of PCN may be a key factor for controlling physical properties of PCN. The interaction energy is an important measure of the interactions among different constituents of composites. Molecular dynamics (MD) is a useful tool for studying the nature and quantitative analysis of interaction energies of a molecular system. In this work, the interaction energies among different components of intercalated organically modified montmorillonite (OMMT) and PCN have been investigated. Here, the interaction of polymer or organic modifier with clay and polymer and modifier is studied. Also, the nature and quantitative contributions arising from functional groups or backbone chain have been assessed. This investigation provides important insight into the mechanism of intercalation, and specific information about the interactions of different constituents in the nanocomposites system. In this current work using MD, for the first time, we have provided a detailed quantitative picture of interactions among the different components of OMMT and PCN.     

Low-Reynolds-number motion of a heavy sphere between two parallel plane walls

A novel boundary-integral algorithm [Staben, M.E., Zinchenko, A.Z., Davis, R.H., 2003. Motion of a particle between two parallel plane walls in low-Reynolds-number Poiseuille flow. Physics of Fluids 15, 1711-1733; Erratum: Phys. Fluids 16, 4206] is used to obtain O(1)-nonsingular terms that are combined with two-wall lubrication asymptotic terms to give resistance coefficients for near-contact or contact motion of a heavy sphere translating and rotating between two parallel plane walls in a Poiseuille flow. These resistance coefficients are used to describe the sphere's motion for two cases: a heavy sphere driven by a Poiseuille flow in a horizontal channel and a heavy sphere settling due to gravity through a quiescent fluid in an inclined channel. When the heavy sphere contacts a wall in either system, which occurs when the gap between the sphere and the wall becomes equal to the surface roughness of the sphere (or plane), a contact-force model using the two-wall resistance coefficients is employed. For a heavy sphere in a Poiseuille flow, experiments were performed using polystyrene particles with diameters 10%-60% of the channel depth, driven through a glass microchannel using a syringe pump. The measured translational velocities for these particles show good agreement with theoretical results. The predicted translational velocity increases for increasing particle diameter, as the spheres extend further into the Poiseuille flow, except for particles that are so large (diameters of 80%-85% of the channel depth) that the upper wall has a dominant influence on the particle velocity. For a heavy sphere settling in a quiescent fluid in an inclined channel, the transition from the no-slip regime to slipping motion occurs for a larger inclination angle of the channel with respect to the horizontal for an increase in particle diameter, since the larger particles are more slowed by the second wall. Limited experiments were performed for Teflon spheres with diameters 64%-95% of the channel depth settling in a very viscous fluid along the lower wall of an inclined acrylic channel. The measured translational velocities, which are only about 15%-25% of the tangential component of the undisturbed Stokes settling velocity, are in close agreement with theory using physical parameters obtained from similar experiments with a single wall [Galvin, K.P., Zhao, Y., Davis, R.H., 2001. Time-averaged hydrodynamic roughness of a noncolloidal sphere in low Reynolds number motion down an inclined plane. Physics of Fluids 13, 3108-3119].     

DEVELOPMENT OF BATCH EMULSION POLYMERIZATION PROCESSES

Although emulsion polymerization has been used for a long time, relatively little attention has been paid to the technological issues of this polymerization technique. This paper describes the research on chemical engineering aspects of emulsion polymerization in (semi-)batchwise operated stirred tanks. The objective of this work was to improve the operation of current processes and to allow for improvements in the development of novel emulsion polymerization processes. For this purpose, different issues have shown to be important, for which the work described in this paper has been focused on four topics: emulsification, colloidal stability, rheology in high solids polymerization and heat transfer. These topics have been studied using the polymerization of styrene and vinyl acetate as two representative model systems

Our results reveal that sufficient emulsification is essential for proper control of the polymerization process. For the emulsifier used in this study, the colloidal stability of the polymer particles is mainly governed by the physico-chemical properties of the reaction mixture. During high solids emulsion polymerization, the particle size distribution of the polymer particles considerably influences the Theological properties of the reaction mixture and thereby the flow pattern in the reactor. Heat transfer to the reactor wall depends strongly on reactor geometry, impeller type and diameter as well as stirrer speed. Additionally, the physical properties of the reaction mixture, being related to solids content, conversion and monomer type, are important for heat transfer.     

DEVELOPMENT OF BATCH EMULSION POLYMERIZATION PROCESSES

Although emulsion polymerization has been used for a long time, relatively little attention has been paid to the technological issues of this polymerization technique. This paper describes the research on chemical engineering aspects of emulsion polymerization in (semi-)batchwise operated stirred tanks. The objective of this work was to improve the operation of current processes and to allow for improvements in the development of novel emulsion polymerization processes. For this purpose, different issues have shown to be important, for which the work described in this paper has been focused on four topics: emulsification, colloidal stability, rheology in high solids polymerization and heat transfer. These topics have been studied using the polymerization of styrene and vinyl acetate as two representative model systems

Our results reveal that sufficient emulsification is essential for proper control of the polymerization process. For the emulsifier used in this study, the colloidal stability of the polymer particles is mainly governed by the physico-chemical properties of the reaction mixture. During high solids emulsion polymerization, the particle size distribution of the polymer particles considerably influences the Theological properties of the reaction mixture and thereby the flow pattern in the reactor. Heat transfer to the reactor wall depends strongly on reactor geometry, impeller type and diameter as well as stirrer speed. Additionally, the physical properties of the reaction mixture, being related to solids content, conversion and monomer type, are important for heat transfer.     

超临界二氧化碳对聚合物的增塑作用及应用

简要介绍了超临界二氧化碳的性质及其与聚合物的相互作用 ,着重论述了超临界二氧化碳对聚合物的增塑作用及应用 ,包括小分子渗透、溶胀聚合、抽提分级、聚合物脱挥及微孔材料的制备等     

Specific binding of cholic acid by cross-linked polymers prepared by the hybrid imprinting method

A cholic acid-imprinted polymer has been prepared by a hybrid imprinting method involving the use of a template-containing monomer, 3α-methacryloyl cholic acid methyl ester. The removal of the template can afford the polymer with cavities and carboxylic acid groups well positioned in these cavities for the specific binding of cholic acid via hydrogen bonding. The maximum binding capabilities for the imprinted and non-imprinted polymers were determined to be 344.8 and 43.6 μmol/g, respectively. Scatchard analysis indicates the existence of two kinds of binding sites on the imprinted polymer. The imprinted polymers exhibit high affinity and good recognition selectivity for cholic acid in comparison to other compounds with similar molecular structures. The size-specific binding and hydrogen bonding may be both important for the binding of cholic acid by the imprinted polymers.     

Sheet formation during drop deformation and breakup in polyethylene/polycarbonate systems sheared between parallel plates

A polycarbonate drop was sheared inside a polyethylene matrix in a transparent rotating parallel plate device at 220 °C and low shear rates. A flat sheet was formed during the initial shearing of the drop. The drop then developed into either a thin thread or a sheet with a thin cylindrical tip. Sheet formation was found to occur at a critical strain or time. A stress ratio (S_r) between the matrix breakup stress, made up of the matrix normal stress and viscous stress, and the drop restoring stress, made up of the drop normal stress and the interfacial stress, is used to characterize the sheet formation during the drop deformation and breakup process. It was found that the viscosity ratio (η_r), stress ratio (S_r) and Deborah number (De) of the system could be used to predict the drop deformation and breakup.     

The investigation of the effects of two different polymers and three catalysts on pyrolysis of hazelnut shell

This study covers an investigation of three catalyst candidates namely; calcium carbonate (CaCO₃), Perlite and potassium dichromate (K₂Cr₂O₇) on pyrolysis of mixtures of hazelnut shell (HS) with ultra-high molecular weight polyethylene (UHMWPE) and polyethylene oxide (PEO) by measuring percentages of solid, liquid and gas products amounts gravimetrically. Pyrolysis processes were executed in a batch type tubular reactor at 500 and 650 °C for fifteen minutes. Catalysts have behaved differently on compounded mixtures. Especially the obtained liquid products from pyrolysis of mixtures shows smooth distribution compared to anomalous results of pure raw materials. The effect of catalysts on the pyrolysis of HS becomes more obvious in the presence of polymers which produces more gaseous product for K₂Cr₂O₇ case. The other catalysts (CaCO₃, Perlite) are more effective without addition of polymers which produce more liquid products. The ratio of HS should not be beyond the 0.5 for production of commercial materials and in their possible recycling process such as pyrolysis for acquisition of combustible liquids. These results may allow some clues for compounding of environmentally safe commercial materials, and easy and efficient recycling technologies.     

Secondary flow induced by inertia in a thin-fluid layer between two parallel plates

The present paper is concerned with the motion of fluid layer between two parallel concentric circular plates, when the inertia of fluid is not negligible. We consider the two specific problems to examine the inertia effects; one in which an incompressible Newtonian fluid is injected into the gap through the hole located at the center of each plate and the other in which two parallel plates rotate coaxially with arbitrary angular velocities. The method of solution is an asymptotic expansion which is usually employed for the thin-film lubrication problem in the limit of small but finite Reynolds number based on the gap height. The asymptotic solutions for the two problems considered here provide the inertia-induced secondary flow patterns, which in turn determine the inertia contributions to the flow parameters such as the pressure drop, injection flow rate, and torque required to sustain the rotation of each plate.