Heterogeneous Polymer Systems Research Articles

Materials Technology for Heterogeneous Polymer Systems : Part II. Investigation of Motional Heterogeneity in Rubber Vulcanizates

For rubber vulcanizates or crosslinked rubbers, inherent characteristics of rubber elasticity are well known to be mainly controlled by the change in conformational entropy under deformation, causing constrained molecular mobility of rubbery network chains. In this part II of special lecture, 1H-pulsed NMR method is applied to observe the motional heterogeneity in the crosslinked rubbers, related to effects of crosslink density and incorporation of reinforcing carbon black fillers on the tensile failure behaviors under various conditions. Furthermore, as for analysis of thermo-oxidative aging behaviors for the crosslinked rubbers, the relationships between the breaking stretch ratio in tensile measurements, λb, and NMR relaxation properties such as spin-spin relaxation time, T 2, and residual dipolar coupling constant , D res, were discussed to predict the failure properties of small pieces sampled from engineering rubber parts, for which tensile tests could not be easily performed.

Deformation and Failure Mechanism of Particulate Filled and Short Fiber Reinforced Thermoplastics: Detection and Analysis by Acoustic Emission Testing.

Acoustic emission, the detection of signals during deformation, is a frequently used method for the study of local deformation processes occurring in heterogeneous polymer systems. Most of these processes result in the evolution of elastic waves which can be detected by appropriate sensors. The analysis of several parameters characterizing the waves offers valuable information about the possible deformation mechanism. The acoustic emission testing of composites may yield very different number of signals from a few hundred to more than 100,000. This latter was proved to be affected mainly by particle size, interfacial adhesion and composition, but other factors, such as matrix modulus and specimen size, also influence it. Local deformation processes are claimed to have a strong effect on macroscopic properties. Indeed, a close correlation was found between the initiation stress of the dominating particle related process derived from acoustic emission testing and the tensile strength in both polypropylene (PP) and poly(lactic acid) (PLA) composites. However, in polyamide (PA)-based heterogeneous polymer systems, deformations related to the matrix dominated composite properties. Besides forecasting failure, the method makes possible the determination of the inherent strength of lignocellulosic fibers being around 40 MPa as well as the quantitative estimation of adhesion strength for composites in which interactions are created by mechanisms other than secondary forces. The proposed approach based on acoustic emission testing proved that in PP/CaCO3 composites, the strength of adhesion can be increased by ten times from about 100 mJ/m2 to almost 1000 mJ/m2 in the presence of a functionalized polymer.

Sensing the melting transition of semicrystalline polymers via a novel fluorescence technique

The melting point (Tm) is an important parameter that dictates the physical properties and thereby applications of semicrystalline thermoplastics. Conventional melting transition characterization techniques, e.g., differential scanning calorimetry, ellipsometry, optical microscopy, and X-ray based methods, probe Tm by monitoring temperature (T)-dependent thermal properties, morphologies, and microstructures. Although these techniques have been well developed, they tend to have their own limitations, e.g., X-ray based techniques require X-ray beams and most previous techniques can only measure spatially averaged properties throughout a film cross section or an entire bulk sample. Here, we have developed a new, simple, and versatile fluorescence technique for probing the melting transitions of semicrystalline thermoplastics. With this approach, fluorescent probes are incorporated into a semicrystalline polymer, either by physical doping or covalent labeling, and their T-dependent fluorescence intensity data exhibit a stepwise decrease nearby Tm because of the reduced restriction of intramolecular motion when crystals start to melt. Interestingly, the first derivative of the obtained T-dependent fluorescence intensity data can reveal more details of the underlying melting transition, e.g., the onset and endset of the melting transition as well as the peak melting temperature. The melting point values determined by fluorescence agree well with those characterized by conventional differential scanning calorimetry, confirming the validity of our fluorescence technique for probing melting transitions. In addition, this fluorescence technique can be applied with various types of fluorescent probes (e.g., fluorophores exhibiting either aggregation-induced emission or aggregation-caused quenching effects) and generalized to many semicrystalline thermoplastics (e.g., poly(l-lactic acid), poly(caprolactone), and poly(ethylene oxide)), while maintaining excellent sensitivity to melting transitions. Overall, our fluorescence technique represents an easy and contact-free melting point characterization approach that may allow for novel location-specific Tm investigations within heterogeneous polymeric systems (e.g., multilayer films, blends, and composites). Such a novel fluorescence technique can expand the toolbox for Tm determination and potentially lead to unprecedented insights into the design principles for semicrystalline thermoplastics.

Ionic liquids: From a solvent for polymeric reactions to the monomers for poly(ionic liquids)

Ionic liquids (ILs) have created their niche as a solvent of choice in the realm of synthetic chemistry. More specifically, in polymer chemistry, these designer solvents are utilized as the potential media for carrying out the polymeric reactions and sometimes as reactive constituents of polymeric materials. None of the polymeric reactions is left to explore the ability of ILs as a solvent for homogeneous/ heterogeneous polymerization systems to develop specialty polymers making use of their versatile properties viz. non-toxicity, high thermal stability, negligible vapor pressure, and large electrochemical window. Interestingly, over some time, another aspect of these ILs has been explored i.e. their ability of getting polymerized, and their inherent properties are further enhanced in this form. Such polymerized ionic liquids (PILs) exhibit particular properties and find many newer applications such as in electrochemical devices as polyelectrolyte, development of nanocomposites, optoelectronics, gas membranes, smart materials, building blocks in materials science, and also in other areas such as environment, energy, analytical chemistry, and catalysis. A comprehensive review of both the aspects of ILs i.e. solvent of choice in the polymeric reactions and various aspects of its polymeric form i.e. [poly(ionic liquids)] is presented in this article.

Rheological Measurements and Structural Analysis of Polymeric Materials.

Rheological measurements of polymer melts are widely used for quality control and the optimization of processing. Another interesting field of rheology is to provide information about molecular parameters of polymers and the structure build-up in heterogeneous polymeric systems. This paper gives an overview of the influence of molar mass, molar mass distribution and long-chain branching on various rheological characteristics and describes the analytical power following from established relations. With respect to applications, we discuss how rheological measurements can be used to gain insight into the thermal stability of a material. A special impact lies in the demonstration, how long-chain branching can be analyzed using rheological means like the zero-shear viscosity as a function of molar mass and strain hardening occurring in elongation. For contributions to branching analysis, the thermorheological behavior and activation energies are particularly discussed. The use of elastic quantities in the case of mechanical pretreatment effects is briefly addressed. The influence of fillers on recoverable properties in the linear range of deformation is analyzed and the role of their specific surface area for interactions described. It is shown how the fundamental results can be applied to study the state of nanoparticle dispersions obtained under special conditions. Furthermore, it is demonstrated that the findings on polymer/filler systems are the base of structure analyses in heterogeneous polymeric materials like polyvinylchloride (PVC) and acrylonitrile–butadiene–styrene copolymers (ABS).

Novel tetraphenylethylene (TPE)-functionalized nitroxide/alkoxyamine for nitroxide-mediated homogeneous and heterogeneous polymerizations

Tetraphenylethylene (TPE)-functionalized nitroxide/alkoxyamine realized the “in situ observation” of the NMP process for both homogeneous and heterogeneous polymerization systems.

Melting Behavior of Heterogeneous Polymer Bulk Solids Related to Flood Fed Single Screw Extruders.

Melting models for flood fed single screw extruders, like the Tadmor model, describe the melting of pure thermoplastic polymers. However, the melting behavior of heterogenous polymer systems is of great interest for recycling issues, for example. In this work, the melting of polymer mixtures and that of pure bulk polymers by the drag induced melt removal principle is examined both theoretically and experimentally. The applied model experiments represent the melting of the solid bed at the barrel in single screw extruders. As polymer pellet mixtures, polypropylene-homopolymer mixed with polypropylene-block-copolymer, high density polyethylene, polyamide 6, and polymethylmethacrylate were studied using different mixing ratios. The melting rate and the shear stress in the melt film were evaluated dependent on the mixing ratio. The results show that when processing unfavorable material combinations, both shear stress and melting rate can be far below that of pure materials, which was also confirmed by screw extrusion and screw pull-out experiments. Furthermore, approaches predicting the achievable melting rate and the achievable shear stress of polymer mixtures based on the corresponding values of the pure materials are presented.

Comprehensive Characterization of Neat Polymers and Compositional Imaging Heterogeneous Polymer Systems with AFM Based Mechanical, Electric and Spectroscopic Methods

ABSTRACTComprehensive characterization of materials suggests measuring their different properties for optimal use in technological applications and this task becomes more challenging as size of related structures decreases and their complexity increases. At smaller scales Atomic Force Microscopy (AFM) enables visualization of structures and quantitative measurements of their mechanical and electric properties. So far, several properties such as elastic modulus and work of adhesion, surface potential and dielectric permittivity can be extracted from the results obtained in various AFM modes. More complicated are the AFM experiments and their analysis in case of viscoelastic, piezoelectric and thermoelectric properties. Several examples of quantitative characterization of neat polymers will be given. In many cases the dissimilarity of the components’ properties is employed for their recognition in heterogeneous systems such as polymer blends, block copolymers and metal alloys. The confined geometries, which are common for small-scale structures, might restrict such identification and a combination of AFM with spectral methods such as Raman scattering will be helpful. Achievements and challenges of compositional mapping will be illustrated on several complex materials.

Integrated compositional and nanomechanical analysis of a polyurethane surface modified with a fluorous oxetane siliceous-network hybrid.

Investigating the surface characteristics of heterogeneous polymer systems is important for understanding how to better tailor surfaces and engineering specific reactions and desirable properties. Here we report on the surface properties for a blend consisting of a major component, a linear polyurethane or thermoplastic elastomer (TPU), and a minor component that is a hybrid network. The hybrid network consists of a fluorous polyoxetane soft block and a hydrolysis/condensation inorganic (HyCoin) network. Phase separation during coating formation results in surface concentration of the minor fluorous hybrid domain. The TPU is H12MDI/BD(50)-PTMO-1000 derived from bis(cyclohexylmethylene)-diisocyanate and butane diol (50 wt %) and poly(tetramethylene oxide). Surface modification results from a novel network-forming hybrid composed of poly(trifluoroethoxymethyl-methyl oxetane) diol) (3F) as the fluorous moiety end-capped with 3-isocyanatopropylriethoxysilane and bis(triethoxysilyl)ethane (BTESE) as a siliceous stabilizer. We use an integrated approach that combines elemental analysis of the near surface via X-ray photoelectron microscopy with surface mapping using atomic force microscopy that presents topographical and phase imaging along with nanomechanical properties. Overall, this versatile, high-resolution approach enabled unique insight into surface composition and morphology that led to a model of heterogeneous surfaces containing a range of constituents and properties.

Particle Responses to Flow Field Oscillations in Heterogeneous Polymerizations Performed in Tank Reactors

This work analyzes the possible influence of the inevitable temperature and concentration fluctuations that take place inside typical stirred tank heterogeneous polymerization reactors on the evolution of kinetic variables. Preliminary analyses regarding the characteristic time constants for heat and mass transfer inside polymer particles that are suspended in a continuous phase are performed in order to evaluate how fast particles respond to perturbations along a dynamic trajectory inside the reactor. It is concluded that particles of typical heterogeneous systems can respond almost immediately to operation changes. For this reason, simulations are performed to evaluate the influence of the varying temperature and concentration fields on the evolution of kinetic variables. It is concluded that the effects caused by the inevitable fluctuations of temperature and concentration inside the vessel can be neglected in usual conditions of reaction of heterogeneous polymerization systems.

Dynamics of a heterogeneous polymer system obtained as a result of a conductor explosion

The performed studies allowed us to obtain a composite with regulated structure formation at φ ≥ 0.06 vol % of copper and directed changes of the electrophysical properties in a dielectric using the explosion of a conductor.

Food Packaging Permeability Behaviour: A Report

The use of polymer materials in food packaging field is one of the largest growing market area. Actually the optimization behaviour of packaging permeability is of crucial importance, in order to extend the food shelf-life and to reach the best engineering solution. Studying the permeability characterization of the different polymer material (homogeneous and heterogeneous polymer system) to the different packaging gases, in different environmental condition, is crucial to understand if the selected material is adapted to the chosen food contact field. Temperature and humidity parameters are of crucial importance for food quality preservation, especially in real life situations, like food market, and house long-life use. The aim of this report was to collect information about the state of the art on the permeability characteristics of the polymer packages used on food field.

Internal Reorganization of Agglomerates as an Explanation of Energy Dissipation at Very Low Strain for Heterogeneous Polymer Systems

AbstractThe addition of a new mechanism to the Leonov model is described to capture the energy dissipation observed for highly filled systems even at very low strain values. By considering that flocs can undergo deformation before rupture, an internal reorganization within the agglomerates is introduced as a dissipative mechanism. The present improved model describes both oscillatory and strain sweep experimental results with only one additional, physically meaningful parameter: the number of hopping particles in the flocs which may be obtained from microscopic observations. Consistent values of this number are found in agreement with the histograms of the particle dispersion.magnified image

Determination of structural and dynamic characteristics of biodegradable polymers by the NMR relaxation method

A theory of the NMR spectra of heterogeneous polymer systems is proposed that makes it possible to simulate signals observed over a wide temperature range with account of spectral diffusion. Based on this theory, a technique of rapid analysis of molecular structure parameters, including the degree of crystallinity and NMR line shape, is developed. The degree of crystallinity is demonstrated to be a linear function of the area under the NMR spectrum. It is shown that this dependence, universal for a given substance, makes it possible to reliably determine the degree of crystallinity over a wide temperature range (or the fraction of low-molecular additives in composites). The NMR spectra of chitosan is simulated and compared to experimental data. The universal dependence of the degree of crystallinity on the area under the spectrum of chitosan is calculated. A comparison with experimental signals allowed determining the degree of crystallinity.

Viscoelastic properties of filled polyethylene glycol in the megahertz frequency band

For heterogeneous polymeric systems obtained on the basis of polyethylene glycol and containing multi- layer carbon nanotubes as a filler, we consider the behavior of composites in temperature and ultrasonic fields at a frequency of 0.4 MHz. It is shown that the viscoelastic properties of these materials depend on the content of carbon nanotubes, temperature, and the linear sizes of structural formations participat- ing in the dissipative processes. High-molecular compounds are often characterized by specific viscoelastic properties caused by the struc- ture of the materials (1). Moreover, they exhibit the properties of both elastic bodies and liquids (2). The com- prehensive analysis of the viscoelastic properties of polymers and, hence, their structural features, can be per- formed by using the acoustic methods. Thus, in particular, the data on changes in the velocity and absorption of the stress waves enable us to directly observe the relaxation processes, study the properties of heterogeneous polymeric systems (HPS) in broad temperature ranges, and investigate the effects of structure formation and their kinetics under the action of various factors (3). The investigations carried out within the region of ultrason- ic frequencies prove to be especially promising because the relationship between the structure of a polymer and its viscoelastic properties (moduli of elasticity and internal friction) manifests itself in this case most completely (4). The results of recent investigations demonstrate that the structure of polymers can be especially intensely and purposefully changed with the help of nanoparticles among which an especially important role is played by carbon nanotubes (CNT) (5). It is shown that the presence of CNT in the HPS based on polymethylmethacrylate (2), polystyrene (1), polypropylene (3), and other compounds (5) affects the properties of materials. However, at present, the researchers focus their attention mainly on the possibility of purposeful changes in the acoustic properties of polyethylene glycol (PEG) with the help of CNT. This can be explained by the fact that systems of this sort are now extensively used for the practical purposes (6). The aim of the present work is to study the influence of CNT on the viscoelastic properties of PEG by using elements of the theory of molecular acoustics (7). The behavior of HPS containing 0-1.0 vol.% CNT is ana- lyzed by the dilatometric method and according to the temperature dependences of the modulus of relaxation and damping decrement.

Aqueous Dispersion Polymerization of 2-Methoxyethyl Acrylate for the Synthesis of Biocompatible Nanoparticles Using a Hydrophilic RAFT Polymer and a Redox Initiator

Aqueous dispersion polymerization systems mediated by reversible addition–fragmentation chain transfer (RAFT) process have been less studied in comparison with other heterogeneous polymerization systems due to limited number of monomer/polymer pairs that are suitable for such a condition. We report a novel dispersion polymerization system based on 2-methoxyethyl acrylate (MEA) which is highly water-soluble, but its polymer is not. Using a hydrophilic polymer, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA), as the macromolecular chain transfer agent (Macro-CTA), both solution and dispersion polymerization of MEA were studied. Chain extension by MEA from PPEGMA was successfully realized in DMF solution polymerization. In dispersion polymerization of MEA in water, PPEGMA was used as both a RAFT mediating species and a steric stabilizer for the formed nanoparticles. The dispersion polymerization of MEA in water was highly efficient using a redox initiator, potassium persulfate/sodium ascorbate, at low temperatures. Simultaneous control of both colloidal stability and RAFT process was realized. Block copolymers with small polydispersity indices were efficiently produced up to complete monomer conversion at solids content up to 32% w/v, in the form of nanoparticles of 40–60 nm diameter.

Synchrotron IR microspectroscopy: Opportunities in polymer science

The last decade has seen a spectacular growth in the use of synchrotron-based IR sources for infrared microspectroscopy. The unique features of coupling synchrotron radiation into commercial IR microscopes at IR beamlines gives access to spatially resolved infrared spectra with superior signal-to-noise characteristics. Specific features of the technique are discussed with particular emphasis on its application to the study of polymeric materials, with examples from a series of heterogeneous polymeric systems, including semicrystalline polymers and blends, reinforced composites and microstructured polymer membranes.

Statistical theory of NMR line shape for heterogeneous polymeric systems

Statistical theory of NMR line shape for heterogeneous polymeric systems

Glass transition of heterogeneous polymeric systems studied by calorimetry

This personal review focuses on two aspects. First, glass transition dynamics and hence also calorimetry is connected to dynamic heterogeneity. This results in an interplay of the corresponding dynamic length scales and length scales from structural heterogeneities in polymeric samples. Second, the complexity of the dynamic glass transition itself results in different effects of this interplay for different experimental observables. Hence the comparison of results from calorimetry with other relaxation methods gives important clues to an understanding of the complex glass transition phenomenon.

Evolution of the structure and phase state in nonequilibrium heterogeneous polymer systems

Structural and phase transformations in the course of the multistage physical aging of semi-inter-penetrating polymer networks based on crosslinked polyurethane and linear polystyrene are studied. Dynamic mechanical and thermophysical studies make it possible to assume that, as a result of the physical aging, a heterogeneous polymer system experiences structural rearrangements and the fraction of the inter-facial region increases.