Morphology polymer mixtures

This document is organized into three sections. The first defines terms basic to the description of polymer mixtures. The second defines terms commonly encountered in descriptions of phase-domain behaviour of polymer mixtures. The third defines terms commonly encountered in the descriptions of the morphologies of phase-separated polymer mixtures. 

Fig. 37. Theoretical predictions for thin film morphology of a phase-separating polymer mixture. Case I yA where yA and yB are the surface tensions of components A and B, respectively, and yAB is the interfacial tension. Case II yA

The optical, mechanical, electrical, morphological and thermodynamic properties of various polymer mixtures are often used as evidence for establishing miscibility. The methods have been extensively reviewed by MacKnight et al. and Olabisi In this section we will attempt only to discuss the applicability of some of the methods to various types of blends. 

Bousfield DW, Keunings R, Marrucci G, Denn MM (1986). J Non-Newt Fluid Mech 21 79. Briber RM, Han CC, Peiffer DG (1996). Morphological Control in Multiphase Polymer Mixtures, MRS Symposium Proceedings 461. 

In a large part of what we have discussed above, we considered binary polymer mixtures. However, the situation is somewhat different, if instead of polymer blends, thin films of block copolymers are investigated. Due to the molecular connectivity of the different blocks, the inherent length scale is now determined by the size of the molecules. Early experiments focussed on the thin film morphology in symmetric diblock copolymers, where surface interactions tend to orient the block copolymer lamellae parallel to the boundary surfaces. In contrast to most bulk specimens, the planar interfaces lead to the formation... 

Therefore, at least in principle, the above process may represent a very easy way to produce polymer mixtures, blends and composites based on PCL, with som peculiar morphologies and properties. 

In Sect. 2 the coexistence conditions of high polymer mixtures are described. Here we focus on the internal interface between two coexisting phases with a bilayer morphology. The properties of this interface determine phase coexistence characteristics necessary to describe segregation phenomena discussed in Sects. 3 and 4. 

In Section 3.2 both external interfaces confining binary polymer mixture in a thin film geometry are explicitly considered. These interfaces specify the equilibrium morphologies of the coexisting phases. Finite size effects relevant for thin films with reduced thickness are also described. 

Coexistence conditions of high polymer mixtures may be determined directly with the advent of the novel approach [74,75] focused on two coexisting phases confined in a thin film geometry and forming a bilayer morphology. Such equilibrium situation is obtained in the course of relaxation of an interface between pure blend components or in late stages of surface induced spinodal decomposition. It is shown that both methods lead to equivalent results [107] (Sect. 2.2.1). 

A polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) system has been selected for an investigation of the process of phase separation in immiscible polymer mixtures. Within this system, studies are made of the XX, lx, xl, and the 11 forms. In recognition of the incompatibility of PBMA with even the oligomeric soft segment precursor of the PU, no attempt was made to equalize the rates of formation of the component linear and network polymers. Rather, a slow PU formation process is conducted at room temperature in the presence of the PBMA precursors. At suitable times, a relatively rapid photopolymerization of the PBMA precursors is carried out in the medium of the slowly polymerizing PU. The expected result is a series of polymer mixtures essentially identical in component composition and differing experimentally only in the time between the onset of PU formation and the photoinitiation of the acrylic. This report focuses on the dynamic mechanical properties cf these materials and the morphologies seen by electron microscopy. 

Morphology. Phase inversion in polymer mixtures occurs when the volume fraction of the dispersed phase becomes equal to or exceeds 0.5 (14). The driving force is to minimize the interfacial energy of the system. This is not the case here because the volume fraction of the rubber-rich phase at phase inversion is about 0.85. After inversion, the fraction of the continuous rubber-rich phase is only 0.28, and it increases to 0.63 at 12.5% rubber content. Initially, the components are fully soluble and compatible, but as the reactions proceed, the molecular weight of the products increases and phase separation results. The ability to separate and invert is dependent on the viscosity of the medium. The unsaturated polyester forms a gel at conversions as low as 2 to 5%, and both the ability to separate and to invert is impeded. Thus the morphology depends on the two competing effects of phase inversion and... 

For the better understanding of blend morphologies, the fundamental mechanisms of morphology development are discussed, viz. the liquid-solid phase transition (crystallization), the liquid-liquid phase separation e.g., spinodal decomposition under non-isoquench depth), as well as the complex mechanism of the morphology generation that results from the competition between these two transitions. The effects of chemical reactions and flow fields on morphology development have also been discussed. Finally, several evidences of a local structure in single-phase polymer-polymer mixtures are presented. 

The development of novel morphologies as well as the ability to predict morphology of polymer mixtures are areas of significant interest to both the industrial and academic researchers. Phase separation and the resultant morphology in block copolymers is reasonably well understood. The prediction of phase morphology of polymers in shear flow has been documented in papers several decades ago [Van Oene, 1972 1978] as well as more recent references [White and Min,... 

Nauman and He [1994] simulated two dimensional spinodal decomposition for ternary polymer mixtures. Variations in volume fraction and interaction parameters of the constituents yielded a multiplicity of different morphologies, some of which were verified in the film experiments. A phase classification was presented for the morphologies obtainable with ternary polymer blends. 

An immiscible polymer mixture with a modified interphase, interface and morphology. 

The third effect, i.e. the stabilization of fine dispersions of polymer mixtures, may be of great importance when blends of desidered morphology show a tendency to increase the particle... 

The above-mentioned scenario is greatly modified by the presence of chemical reactions. It has been shown recently by numerical as well as analytical calculations that chemical reaction can be used as a driver for these unstable modes (2-7). suggesting a novel method for morphology control of polymer mixtures. Experimentally, we have demonstrated that not only the characteristic length scales (S),but also the spatial symmetry of the morphology can be manipulated by taking advantages of photochemical reactions (9-10). 

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