Microscopic structure of polymers

It has been shown that polymer properties change over time, as a result of the combined action of numerous external factors. The microscopic structure of polymers also changes over time, even in the absence of external factors. Indeed, the arrangement of macromolecules is not fixed, and their mobility is responsible for several property changes. 

As for bulk condensed matter in general, analysis of the microscopic structure of polymer systems is mostly carried out by scattering experiments. This chapter in the Appendix is meant to provide the reader with a summary of results of scattering theory, including both general and specific equations, in a selection suggested by the needs of the considerations in this book. 

Figure 7.16 (a, b) Comparison of several microscopic structures of polymer scaffolds. 

Porosity and surface area are routinely measured by nitrogen absorption-desorption, mercury intrusion, and low-angle X ray. The electron microscope (EM) provides direct visual evidence of pore size and pore-size distribution. Thus, a combination of EM and conventional methods of pore-size measurement should provide reliable information on the pore structure of polymers. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

The microscopic structure of the undercooled melt has been a subject of great interest in studies of polymer crystallization. There have been long arguments in favor of the presence of mesoscopic local order in the melt or at the crystal-... 

Polarized Luminescence. The polarized luminescence technique gives information about local mobility of polymer sequences, and so about microscopic structure of the system (18-21. ... 

However, the long range effectiveness of polymer additives remains, due to the mechanical degradation, a hitherto unsolved problem. By application of the above-mentioned theoretical approaches and the influence of laminar and elongational flow on polymer stability described in Sect. 6.3.4, it seems possible to retain the flow features over a longer period. It is therefore necessary to reinforce investigations which enable a more quantitative description of turbulent flow, so that in the future structure-property relationships can be established which permit a correlation of the microscopic structure of the macromolecules with the observed flow phenomena. 

Many polymer blends or block polymer melts separate microscopically into complex meso-scale structures. It is a challenge to predict the multiscale structure of polymer systems including phase diagram, morphology evolution of micro-phase separation, density and composition profiles, and molecular conformations in the interfacial region between different phases. The formation mechanism of micro-phase structures for polymer blends or block copolymers essentially roots in a delicate balance between entropic and enthalpic contributions to the Helmholtz energy. Therefore, it is the key to establish a molecular thermodynamic model of the Helmholtz energy considered for those complex meso-scale structures. In this paper, we introduced a theoretical method based on a lattice model developed in this laboratory to study the multi-scale structure of polymer systems. First, a molecular thermodynamic model for uniform polymer system is presented. This model can... 

In the previous sections, theories were reviewed where the optical properties of polymer liquids were cast in terms of the microscopic properties of the constituent chains. The dynamics of polymer chains subject to external fields that orient and distort these complex liquids are considered in this section for a variety of systems ranging from dilute solutions to melts. Detailed descriptions of theories for the dynamics and structure of polymer fluids subject to flow are found in a number of books, including those by Bird et al. [62], Doi and Edwards [63], and Larson [64],... 

Although the microscopic theory remains to be the real foundation of the theory of relaxation phenomena in polymer systems, the mesoscopic approach has and will not lose its value. It will help to understand the laws of diffusion and relaxation of polymers of various architecture. The information about the microstructure and microdynamics of the material can be incorporated in the form of constitutive relation, thus, allowing to relate different linear and non-linear effects of viscoelasticity to the composition and chemical structure of polymer liquid. 

In Sections 2.2 and 2.3, it is described that the network structures of polymer gels, especially microscopic inhomogeneity, may be detected through the diffusion behaviour of probe molecules of different sizes, which can be obtained by using time-dependent diffusion NMR spectroscopy. In this section, it will be... 

For studying structure of polymer and influence of introduction of additives HZ-1 HZ-2 HZ-4 the method of micro photographing has been applied. Cuts of polymeric fibers photographed at 40 multiple increase, on a microscope "Polar" which had a special nozzle for photographing. 

Infrared spectroscopy provides information on the microscopic structure of hydrated polymers which is not easily available by other means. Nafion is a new material and so far only four infrared studies on it have been reported (L-4). The scope of these studies is summarized in Table I they are of preliminary nature and do not exhaust the possibilities of the infrared technique. In the present chapter the structural information which has been so far derived from infrared studies of Nafion will be collected, and some additional results from the author1s laboratory will be presented. 

Spectroscopic techniques are valuable in studies of the structure of polymers because they give information about the environment of the probe atom on a microscopic scale. Mossbauer spectroscopy is particularly useful because the absorption spectrum is entirely due to one isotope of a single chemical element, most commonly 57Fe. By introducing iron into polymers containing acid groups, it is possible therefore to examine the ionic phase specifically. Its structure can be defined to some extent, and interactions of the cations with their surroundings can be determined. 

In this work we propose a model for ionic clustering, which we have called the cluster-network model (2), to account for hydroxyl rejection in nNafionM perfluorinated membranes. In developing this model we have been guided by two requirements 1. the model should be consistent with the available data on the microscopic structure of the polymer (1-5) 2. the model should... 

Only a few studies about aqueous films of amphiphilic random polyelectrolytes are reported in the literature. Millet et al. [239-241] have investigated by x-ray reflectivity the behavior of vertical free-standing films (Figure 29) of a series of hydrophobically modified poly(acrylic acid) sodium salt (HMPAANa) and poly(acrylic acid) (HMPAAH). The chemical structure of the polymer was presented in Sec. II.C (Eq. 2a). One of the aims of this work was to determine the microscopic structure of the films to explain the (macroscopic) stability behavior of the dodecane-in-water emulsions studied by Perrin et al. [188,189], who used the same series of amphiphilic polyelectrolytes as primary emulsifiers. The aqueous polyelectrolyte films have been used as model systems for the interstitial films separating two neighboring oil droplets of an emulsion creamed layer. The authors have assumed that the oil/water interface encountered in emulsions was suitably described by the air/water interface of the films. The HMPAANa and HMPAAH co-... 

A dilute polymer solution is a system where polymer molecules are dispersed among solvent molecules. An assumption common to any existing theory for flow properties of polymer solutions is that the structure of solvent molecules is neglected and the solvent is assumed to be replaced by a continuous medium of a Newtonian nature. Thus, macroscopic hydrodynamics may be used to describe the motion of the solvent. Recently, some ordering or local structure of solvent molecules around a polymer chain has been postulated as an explanation of the stress-optical coefficient of swollen polymer networks (31,32) so that the assumption of a solvent continuum may not apply. The high frequency behavior shown in Chapter 4 could possibly due to such a microscopic structure of the solvent molecules. Anyway, the assumption of the continuum is employed in every current theory capable of explicit predictions of viscoelastic properties. In the theories of Kirkwood or... 

During the first operation hydrogel elements often shows a poor repeatability and a drift of the parameters. This is caused by changes in the microscopic structure of the polymer network. By swelling and shrinking the too short polymer chains have to be cracked and the chains in general have to find their optimal moving way and position. 

We saw in the last chapter that, under a wide variety of circumstances, polymers will not mix at a molecular level at equilibrium. If we take such a pair of polymers and mix them mechanically, we will get domains of one polymer in the other what will be the nature of the interface between the two coexisting phases and what determines the interfacial energy The morphology of our mixture will be greatly influenced by the interfacial energy, which will control the domain size, while the microscopic structure of this interface will... 

Fergg F, Keil FJ, Quader H (2001) Investigations of the microscopic structure of poIy(vinyI alcohol) hydrogels by confocal laser scanning microscopy. Colloid Polym Sci 279 61... 

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