Rheology of polymer layered silicate nanocomposites

Layered silicate based polymer nanocomposites have gained significant technological interest because of the recent commercialization of nylon 6 and polypropylene based materials. Aside from the natural interests in understanding and improving the processing of these hybrids, viscoelastic measurements have also proven to be a sensitive tool to probe the mesoscale structure and the strength of polymer–nanoparticle interactions.     

Rheology of a miscible polymer blend

Difference spectra of blends of cis-1,4-polyisoprene and atactic poly(vinylethylene), obtained from the measured FTIR spectra of the pure components and the blends, indicate that mixing of these polymers is not accompanied by any specific chemical interactions. Miscibility in this system arises solely due to the small combinatorial entropy of mixing. The conformation and configuration of the polymer chains in the blends are, therefore, identical to those in the pure melts. As a consequence it was found that the entanglement density of the blends varied monotonically with composition. This variation, however, was not in accordance with predictions based simply on the mechanical interaction density. The principle rheological effect of miscible blending was a large change in the monomeric friction coefficient, which arises from the strong dependence of free volume on composition. The zero shear viscosity and the terminal relaxation time of the blends reflected this change in local chain mobility. Empirical relations, which have previously been proposed for the properties of miscible polymer mixtures, were found to be without merit in describing the obtained experimental results.     

Rheology of polymer melts and concentrated solutions

The basic concepts of entangled polymer dynamics, like that of ‘tube’ of constraints and of ‘reptation’, have not yet exhausted their momentum. Further progress has taken place recently with detailed calculations of tube length fluctuations and constraint release, not only for branched polymers but also for linear ones. Progress in the non-linear range has occurred with the concept of convective constraint release and, for branched polymers, with the so-called ‘pom-pom’ model. Lack of complete agreement between theory and experiments stimulates work to proceed along various lines.     

Rheology and morphology of compatibilized polymer blends

Research into the compatibilization of immiscible polymer blends has, during the past few years, begun to focus on the role of block co-polymers (bcp) on various morphological processes. Considerable advances have been made, from both a theoretical and an experimental point of view, in relating the presence of compatibilizers to structure development during flow.     

Rheology of concentrated alumina-polyelectrolyte systems

Rheological properties of concentrated alumina suspensions using a charged copolymer as the dispersant have been studied. The non-Newtonian behavior of these fluids was characterized and correlated to potential measurements and sedimentation column data, obtained with these dispersions. As a result, a clear relationship between dispersion stability and pseudoplastic/dilatant rheological behavior was established.     

Multifunctional polymer dispersions for biomedical assays obtained by heterophase radical polymerization

Methods for the preparation of multifunctional dispersions of polymer particles (DPP) in the course of free radical heterophase polymerization, which provides careful control of both macromolecular and colloidal properties, are considered. Approaches that, according to the polymerization technique, make it possible to control the particle diameter and shape, particle size distribution, colloidal stability, morphology, surface chemistry and functionality, as well as the formation of organo-inorganic hybrid particles, are demonstrated. The possibilities of DPP application in homogeneous and heterogeneous assays and cell labelling are reviewed. The use of DPP leads to decrease the reaction scales and costs and to increase the speed, sensitivity, selectivity, and reproducibility of assays.     

Specificity of the application of disperse and fibrous fillers in heterophase polymer materials

The mechanism of the reinforcing effect of fillers in polymer composition is studied and the relation between the properties and structure of materials is established. It is shown that, upon the addition of even a small amount of filler, properties of polymers change markedly due to intermolecular interactions. Variations in the composition of filled polymers and conditions of their preparation make it possibly to regulate properties of polymers within noticeably wide ranges. Specific features of polymer compositions filled with polymer fibers, the effect of fiber length, and the degree of orientation on the strength of composition are considered. For crosslinked epoxy urethane polymers, the effect of glass and polycaproamide (capron) fibers on the mechanical properties of polymer clutches in glassy and rubbery states is studied. The possibility to realize the shape memory effect for shrinkable filled polymer clutches is demonstrated.     

Rheology and morphology of polymer blends in melt and solid state

The rheological properties of polymer mixture melts containing polysulfone and LC-polyester have been investigated in this work in terms of the morphology and physical-mechanical characteristics of extrudates. The perculiarities of rheological behaviour are accounted for by morphology of stream which is maintained also in solid extrudates. The reinforcement of an isotropic mixture by LC-polymers as well as formation of an anisotropic surface layer lead to a specific change in the strength properties of compositions. An increase in strength and initial modulus was observed for blends containing not more than 10% LC-polymer.     

Polyferrocenylsilane-based polymer systems

The study of metallopolymers has blossomed into a mature field over the last few decades. Especially, polyferrocenylsilane (PFS) chemistry has taken a tremendous leap and continues to raise intense interest. Since the discovery of thermal ring-opening polymerization (ROP) of sila[1]ferrocenophanes, PFSs have been also accessed by anionic, cationic, transition-metal-catalyzed, and photolytic anionic ROP methodologies. A plethora of synthetic strategies have been devised, enabling access to a wide variety of copolymers, polyelectrolytes, and nanostructured materials. The distinctive physical properties and functions of many PFS-based polymers have been explored, leading to their apt exploitation in technical applications. Therefore, it is conceivable that PFS-related platforms might be indispensable nano-objects in the near future, as they stand on the verge of a new generation of sophisticated materials.     

Gas-chromatographic determination of mutual solubility of components in heterophase binary systems of organic solvents

A general gas-chromatographic method is proposed for determining mutual solubility of partially miscible organic solvents. The method involves gradual increase of the concentration of one component in the other component in the region below their mutual solubility limit, determining parameters of the linear regression c = aS + b (c is the concentration, and S is the peak area), analysis of saturated solutions of components of binary systems in each other (at S ≈ const), and calculating c values from the obtained equation. The method was tested by known data on mutual solubility of components of the hexane-acetonitrile and hexane-nitromethane binary systems. Data for the hexane-2,2,2-trifluoroethanol and perfluorodecalin-acetonitrile binary systems are obtained for the first time; in the latter case, abnormally low mutual solubility of components is revealed.     

Thermodynamics of polymer systems

This work gives an introduction into the thermodynamic modeling of polymer systems. After a short overview about the different basics of thermodynamic models, results obtained with the recently proposed PC-SAFT equation of state are discussed exemplarily for systems containing polymers as well as copolymers.     

Effect of a linear polymer on crosslinking heterophase copolymerization of maleic anhydride, styrene, and divinylbenzene

A polymeric porogene has been shown to promote the formation of a developed porous structure in network maleic anhydride-styrene-divinylbenzene copolymers synthesized through crosslinking free-radical alternating copolymerization in the presence of a solvating solvent (dioxane).     

Rheology and structure formation in diluted mixed particle-surfactant systems

In the present work, we focus on the bulk rheology of mixtures consisting of surfactant modified silica nanoparticles in water. Depending on the ratio of surfactant and nanoparticle concentrations, significant modifications in the measured rheology are evidenced. A domain where the dispersions behave like viscoelastic media is observed. Outside this domain, the dispersions exhibit viscous properties. The changes in the bulk rheology characteristics are discussed in terms of interaction effects between the surfactant and the particles. The results obtained are seen in the context of diluted emulsions' properties and characteristics.     

Rheology of viscoelastic solutions of cationic surfactant. Effect of added associating polymer

Rheological studies were performed with aqueous salt solutions of viscoelastic cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride (EHAC) and its mixtures with hydrophobically modified polyacrylamide. The solutions of surfactant itself above the concentration of crossover of wormlike micelles exhibit two regions of rheological response. In the first region, they behave like polymer solutions in semidilute regime characterized by viscoelastic behavior with a spectrum of relaxation times. In the second region, unlike polymer solutions their relaxation after shear is dominated by a single relaxation time. Being composed of "living" micelles, the EHAC solutions easily lose their viscosity at the variation of the external conditions. For instance, heating from 20 to 60 degrees C reduces viscosity by up to 2 orders of magnitude, while added hydrocarbons induce a sudden drop of viscosity by 3-6 orders of magnitude. Polymer profoundly affects the rheological properties of EHAC solutions. The polymer/surfactant system demonstrates a 10,000-fold increase in viscosity as compared to pure-component solutions, the effect being more pronounced for polymer with less blocky distribution of hydrophobic units. A synergistic enhancement of viscosity was attributed to the formation of common network, in which some subchains are made up of elongated surfactant micelles, while others are composed of polymer. At cross-links the hydrophobic side groups of polymer anchor EHAC micelles. In contrast to surfactant itself, the polymer/surfactant system retains high viscosity at elevated temperature; at the same time it keeps a high responsiveness to hydrocarbon medium inherent to EHAC.     

Nanostructures in polymer systems

General concepts concerning the formation, structure, and some properties of nanosized structural elements in polymers and polymeric materials are summarized from the standpoint of feasibility of formation of nanoparticles and nanoreactors in such systems and practical use of advantages offered by these structures. The familiar concepts are complemented with the results obtained recently. Examples are given to illustrate the implementation of elements of nanotechnology based on the principles of creation of nanostructures in amorphous and crystalline polymers, copolymers, and molecular composites. Practicable methods for the preparation of polymeric nanostructures by controlled crystallization, microphase and nanophase separation of components, and their dispersion, as well as the formation of interfaces, are discussed.     

Rheology of nanofibrillated cellulose/acrylate systems for coating applications

In this work, the suitability of nanofibrillated cellulose (NFC) as a novel component for wood coatings has been evaluated. NFC was prepared from two different wood pulps with a high pressure homogeniser and a grinder, depending on the initial fibre size of the two pulps. The fibrillation process was monitored using viscosity measurements and scanning electron microscopy. Viscosity measurements were found to be a suitable, reliable and especially fast and easy method for process monitoring, optimization and quality assessment of the NFC fibrillation process. NFC was mixed with four different waterborne acrylic polymer emulsions and analysed regarding its rheological behaviour. The viscosity of the acrylate–NFC suspensions was dominated by the NFC, whereas the polymer type was of minor importance at the tested concentrations. The viscosity increased exponentially after NFC addition and consequently the viscosity of such suspensions would be precisely adjustable in the considered shear range. During accelerated storage at elevated temperatures, the general flow behaviour did not change; only a slight viscosity increase was observed. The study shows that rheology is an important issue that has to be taken into account when applying NFC as additive in water based coating systems and that NFC is suitable as component for coating applications.     

Reactive surfactants in heterophase polymerization

The mechanism for the formation of polymer particles in the dispersion polymerization of methyl methacrylate and styrene in alcohol-water mixtures has been investigated. Methacrylic based poly(ethylene oxide) macromonomers and poly(vinyl-pyrrolidone) have been used as steric stabilizers. Dynamic light scattering as well as transmission electron microscopy have been applied to determine the evolution of the average particle size at the beginning of the polymerization. Stable nuclei from 80 to 400 nm in diameter size were detected. The nucleation process was quite rapid and completed within less thanca. 0.1% monomer conversion. The experimental results are compared with those predicted by the multibin kinetics model for coalescence developed by Paine [(1990) Macromolecules 23: 3109].A series of publication from the EU program Human Capital and Mobility (CHRX CT 93-0159)