Macroscopic mechanical polymer properties

Abiotic forces will not be in the focus of the discussion, but it is obvious that a polymeric material like PVAc or PVA exposed to outdoor conditions will undergo different alterations at the macroscopic and microscopic scales. Depending on its interaction with mechanical forces, thermal stress, radiation or chemical attack, the polymer properties might be changed in a way that is relevant for its interaction with biological systems. 

Yount WC, Loveless DM, Craig SL. SmaU-molecule dynamics and mechanisms underlying the macroscopic mechanical properties of coordinatively cross-hnked polymer networks. J Am Chem Soc 2005a 127 14488-14496. 

A number of PAL studies on polymers have attempted to correlate PAL parameters with macroscopic mechanical properties. The value of PAL in providing microscopic structural information for the observed macroscopic properties in polymer systems is illustrated by the examples bellow. 

The electrical conductivity of a material is a macroscopic solid-state property since even in high molecular-weight polymers there is not just one conjugated chain which spans the distance between two electrodes. Then it is not valid to describe the conductivity by the electronic structure of a single chain only, because intra- and interchain charge transport are important. As with crystalline materials, some basic features of the microscopic charge-transport mechanism can be inferred from conductivity measurements [83]. The specific conductivity a can be measured as the resistance R of a piece of material with length d and cross section F within a closed electrical circuit,... 

Molecular dynamics (MD) is an invaluable tool to study structural and dynamical details of polymer processes at the atomic or molecular level and to link these observations to experimentally accessible macroscopic properties of polymeric materials. For example, in their pioneering studies of MD simulations of polymers, Rigby and Roe in 1987 introduced detailed atomistic modeling of polymers and developed a fundamental understanding of the relationship between macroscopic mechanical properties and molecular dynamic events [183-186]. Over the past 15 years, molecular dynamics have been applied to a number of different polymers to study behavior and mechanical properties [187-193], polymer crystallization [194-196], diffusion of a small-molecule penetrant in an amorphous polymer [197-199], viscoelastic properties [200], blend [201,202] and polymer surface analysis[203-210]. In this article, we discuss MD studies on polyethylene (PE) with up to 120,000 atoms, polyethylproplyene (PEP), atactic polypropylene (aPP) and polyisobutylene (PIB) with up to 12,000 backbone atoms. The purpose of our work has been to interpret the structure and properties of a fine polymer particle stage distinguished from the bulk solid phase by the size and surface to volume ratio. 

A simple theory of free volume was formulated to explain the molecular motion and physical behavior of the glassy and liquid states of matter [87]. This theory has been widely accepted in polymer science because it is conceptually simple and intuitively plausible for understanding many polymer properties at the molecular level. The derived macroscopic properties from free volume perspective are fruitful with the assistance of quantum and statistical mechanical calculations. 

The remarkable properties of electrospun CNTs nanocomposites continue to draw attention in the development of multifunctional properties of nanostructures for many applications.. Multiscale model for calculation macroscopic mechanical properties for fibrous sheet is developed. Effective properties of the fiber at microscale determined by homogenization using modified shear-lag model, while on the second stage the point-bonded stochastic fibrous network at macroscale replaced by multilevel finite beam element net. Elastic modulus and Poisson s ratio dependence on CNT volume concentration are calculated. Effective properties fibrous sheet as random stochastic network determined numerically. We conclude that an addition of CNTs into the polymer solution results in significant improvement of rheological and structural properties. 

P-transition temperature. This brittle-to-tough P-transition is believed to be associated with the local segmental motion of polymer molecules. The proposed association between the macroscopic mechanical properties and molecular motion still remains a conjecture. An independent verification, especially by using molecular spectroscopy as a probe to elucidate the dynamics of segmental motion of polymers under dynamic deformation, is welcome once again. 

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