Phase separation characterizations

Urethane and urea Amide bands coupled with the N-H stretching bands have been studied by many investigators to explore the relationship between intermolecular and intramolecular interactions and morphologies of polyether-urethanes (16, 18-20, 23-32) and polyether-urethane-ureas (15,17,21,22,33-37). The N-H groups serve as proton donors in the interactions. The possible proton acceptors in polyether-urethanes initially were assumed to be only the urethane carbonyls or polyether oxygens (16, 19, 23-27). Under these assumptions, complete phase separation characterized... 

A. Hernandez, 0-26, Phase-separation characterization separation membranes, Proc. 2 Workshop on AppUcations of Synchrotron Light to Non-Crystalline Diffraction in Materials and Life Science, Madrid, 2007. 

Equation (A3.3.57) must be supplied with appropriate initial conditions describing the system prior to the onset of phase separation. The initial post-quench state is characterized by the order parameter fluctuations characteristic of the pre-quench initial temperature T.. The role of these fluctuations has been described in detail m [23]. Flowever, again using the renomialization group arguments, any initial short-range correlations should be irrelevant, and one can take the initial conditions to represent a completely disordered state at J = xj. For example, one can choose the white noise fomi (i /(,t,0)v (,t, 0)) = q8(.t -. ), where ( ) represents an... 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

The term compatibility is used extensively in the blend literature and is used synonymously with the term miscibility in a thermodynamic sense. Compatible polymers are polymer mixtures that do not exhibit gross symptoms of phase separation when blended or polymer mixtures that have desirable chemical properties when blended. However, in a technological sense, the former is used to characterize the ease of fabrication or the properties of the two polymers in the blend [3-5]. 

These solvents are characterized by a high affinity for aromatics, good thermal stability, and rapid phase separation. The Tetra extraction process by Union Carbide (Figure 2-2) uses tetraethylene glycol as a solvent. The feed (reformate), which contains a mixture of aromatics, paraffins. 

Synthesis and mechanical and morphological characterization of (AB)n, ABA and BAB type copolymers of m-phenylene-isophthalamide and polydimethylsiloxane have been reported241 242>. The effect of copolymer type, chemical composition and segment molecular weights on phase separation and the solution behavior of these systems have also been discussed. 

We have recently initiated our investigation of blends by examining the compatibility between our modified polymer sample 4 and poly(methyl methacrylate). Mixtures with a composition of between 10% and 30% of sample 4 yield compatible blends which are transparent under a polarized light microscope, and are characterized by a single Tg. Mixtures richer than 60% of 4 undergo complete phase separation. 

The dynamic mechanical behavior indicates that the glass transition of the rubbery block is basically independent of the butadiene content. Moreover, the melting temperature of the semicrystalline HB block does not show any dependence on composition or architecture of the block copolymer. The above findings combined with the observation of the linear additivity of density and heat of fusion of the block copolymers as a function of composition support the fact that there is a good phase separation of the HI and HB amorphous phases in the solid state of these block copolymers. Future investigations will focus attention on characterizing the melt state of these systems to note if homogeneity exists above Tm. 

There is now available a substantial amount of information on the principles and techniques involved in preparing evaporated alloy films suitable for adsorption or catalytic work, although some preparative methods, e.g., vapor quenching, used in other research fields have not yet been adopted. Alloy films have been characterized with respect to bulk properties, e.g., uniformity of composition, phase separation, crystallite orientation, and surface areas have been measured. Direct quantitative measurements of surface composition have not been made on alloy films prepared for catalytic studies, but techniques, e.g., Auger electron spectroscopy, are available. 

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