Polymer blends, component dynamics

Ono, T. Nobori, T. Lehn, J.-M. Dynamic polymer blends Component recombination between neat dynamic covalent polymers at room temperature. Chem. Commun. 2005,1522-1524. 

Neuutn scattering is often perftrmed as a function cf particle concentration to determine specific interactions between components. Blends cf metallocene synthesized polyolefins (32) and efi ds cf solvent on dendrima- size (33) have been studied using SANS. Interface widths between two polymer blend components in the melt have been studied by neuu-on reflectivity (34). Dynamic studies have been undertaken on bimodal melts (35) using neutron spin echo techniques. Some of these recent developments will be reported in ttie following chrqiters. 

The flow behavior of the polymer blends is quite complex, influenced by the equilibrium thermodynamic, dynamics of phase separation, morphology, and flow geometry [2]. The flow properties of a two phase blend of incompatible polymers are determined by the properties of the component, that is the continuous phase while adding a low-viscosity component to a high-viscosity component melt. As long as the latter forms a continuous phase, the viscosity of the blend remains high. As soon as the phase inversion [2] occurs, the viscosity of the blend falls sharply, even with a relatively low content of low-viscosity component. Therefore, the S-shaped concentration dependence of the viscosity of blend of incompatible polymers is an indication of phase inversion. The temperature dependence of the viscosity of blends is determined by the viscous flow of the dispersion medium, which is affected by the presence of a second component. 

Polymer blends have been categorized as (1) compatible, exhibiting only a single Tg, (2) mechanically compatible, exhibiting the Tg values of each component but with superior mechanical properties, and (3) incompatible, exhibiting the unenhanced properties of phase-separated materials (8). Based on the mechanical properties, it has been suggested that PCL-cellulose acetate butyrate blends are compatible (8). Dynamic mechanical measurements of the Tg of PCL-polylactic acid blends indicate that the compatability may depend on the ratios employed (65). Both of these blends have been used to control the permeability of delivery systems (vide infra). 

Simulation Study of Relaxation Processes in the Dynamical Fast Component of Miscible Polymer Blends. 

In the future we will witness a drive towards more complexity. In this review, we have discussed a number of preliminary experiments pointing in this direction. In polymer blends, the question of dynamic mixing on a local scale was addressed and the Rouse dynamics in miscible polymer blends was studied. How the tube confinement evolves in blends where the two components have different tube diameters is a completely open question. Also, the question of how... 

The glass transition (Ta) and melting (Tm) temperature of the pure component polymers and their blends were determined on a Perkin-Elmer (DSC-4) differential scanning calorimeter and Thermal Analysis Data Station (TADS). All materials were analyzed at a heating and cooling rate of 20°C min-1 under a purge of dry nitrogen. Dynamic mechanical properties were determined with a Polymer Laboratories, Inc. dynamic mechanical thermal analyzer interfaced to a Hewlett-Packard microcomputer. The... 

Tihe technological properties and the commercial application of several polymer blends have been studied extensively. Investigations of the basic principles, however, relating the phase structure of the blends to the properties of the individual components have not been carried out to an extent justified by the industrial value of these materials. Several methods have been used, the most successful being optical and electron microscopy and dynamic-mechanical measurements. Critical factors and difficulties in the morphological studies of polymer blends have been... 

In this case study, which is extracted from reference 184, infrared dichroism is described as a means of separating the component dynamics in multicomponent polymer melts. What is necessary is the existence of distinct absorption peaks for at least one of the components. In the present problem, however, where two chains of identical chemistry but different molecular weights are mixed, there will not be any intrinsic differences in their absorption spectra. In this case it is necessary to label one of chains with a tag that will allow its presence in the blend to be revealed. For this purpose, deuteration of one of the chains is often used. This provides the labeled chain with an absorption of infrared light at the symmetric stretching vibration of the C-D bond, which occurs in the vicinity of 2180 cm-1. Fortunately, the unlabeled polymer contains no absorption peak at this location. It is important, however, to determine that the presence of a label on one species will not alter the physical response of the sample at a level that will affect the phenomena under study. For example, the labeling should not induce phase separation or cause unwanted specific interactions. 

J. A. Zawada, Component contributions to the dynamics of miscible polymer blends, Ph J). Thesis, Stanford University (1993). 

J. Zawada, C. Ylitalo, G. Fuller, R. Colby, and T. Long, Component relaxation dynamics in a miscible polymer blend Polyethylene oxide)/poly(methyl methacrylate), Macromolecules, 25,2896 (1992). 

The final chapter on applications of optical rheometric methods brings together examples of their use to solve a wide variety of physical problems. A partial list includes the use of birefringence to measure spatially resolved stress fields in non-Newtonian flows, the isolation of component dynamics in polymer/polymer blends using spectroscopic methods, the measurement of the structure factor in systems subject to field-induced phase separation, the measurement of structure in dense colloidal dispersions, and the dynamics of liquid crystals under flow. 

In this example of model reactive polymer processing of two immiscible blend components, as with Example 11.1, we have three characteristic process times tD,, and the time to increase the interfacial area, all affecting the RME results. This example of stacked miscible layers is appealing because of the simple and direct connection between the interfacial layer and the stress required to stretch the multilayer sample. In Example 11.1 the initially segregated samples do create with time at 270°C an interfacial layer around each PET particulate, but the torsional dynamic steady deformation torques can not be simply related to the thickness of the interfacial layer, <5/. However, the initially segregated morphology of the powder samples of Example 11.1 are more representative of real particulate blend reaction systems. 

Covalent dynamers may also present a range of unusual properties such as crossover component recombination between neat films in dynamic polymer blends [61], soft-to-hard transformation of polymer mechanical properties through component incorporation [62], and dynamic modification of optical properties (Fig. 6) [63],... 

Anomalous component dynamics in blends and mixtures have been observed which cannot be explained by the models of Fischer et al., Kumar et al., and Lodge and McLeish [329]. A recent example is the anomalous dynamics of d4PEO found in the d4PEO/PMMA polymer blends [336], While this anomaly cannot be understood by the other models, it has an immediate explanation from the CM [337],... 

Here ( )j and Rj are, respectively, the volume fraction and the drop radius. The main feamre of this model is the inclusion of a contribution from the interfacial tension to the viscoelastic properties and the inclusion of the effect of particles size polydispersity. For example, knowing G. (co) of the two main components of the blend, one can predict the dynamic moduli of the emulsion (as well as dilute polymer blends) from the knowledge of the interfacial tension coefficient and distribution of drop size. Note that the theory is applicable to low strains, and to the concentration range where the yield stress is absent [Graebling and Muller, 1990, 1991 Graebling et ai, 1993]. 

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