Abstract
Scattering data for polymers in the non-crystalline state, i.e., the glassy state or the molten state, may appear to contain little information. In this work, we review recent developments in the use of scattering data to evaluate in a quantitative manner the molecular organization of such polymer systems. The focus is on the local structure of chain segments, on the details of the chain conformation and on the imprint the inherent chemical connectivity has on this structure. We show the value of tightly coupling the scattering data to atomistic-level computer models. We show how quantitative information about the details of the chain conformation can be obtained directly using a model built from definitions of relatively few parameters. We show how scattering data may be supplemented with data from specific deuteration sites and used to obtain information hidden in the data. Finally, we show how we can exploit the reverse Monte Carlo approach to use the data to drive the convergence of the scattering calculated from a 3d atomistic-level model with the experimental data. We highlight the importance of the quality of the scattering data and the value in using broad Q scattering data obtained using neutrons. We illustrate these various methods with results drawn from a diverse range of polymers.
Highlights
Amorphous polymers are characterised by the absence of long-range order, leading to a level of order that is essentially associated with the inherent atomic connectivity and is concentrated in the vicinity of the polymer chain
Based on our previous discussion, we can clearly see that the extent, resolution and quality of the experimentally observed structure factor will have an influence on the outcome of the reverse Monte Carlo (RMC) modelling procedure
We have presented an overview of the possibilities for structural analysis offered by intimately coupling high-quality broad Q neutron scattering data with atomistic models
Summary
Amorphous polymers are characterised by the absence of long-range order, leading to a level of order that is essentially associated with the inherent atomic connectivity and is concentrated in the vicinity of the polymer chain. In a neutron scattering experiment over a thermal average and Q is the scattering vector commonly expressed as Q = 4π sin θ/λ, where 2θ is broad Q range, we can obtain information about bond lengths and segmental interactions at distances the scattering angle and λ is the incident wavelength [3,4]. The experimentally observed structure factor S(Q) is defined as the broad Q range, we can obtain information about bond lengths and segmental interactions at distances spatial Fourier transform of the atomic pairwise correlation functions of approximately 0.1–100 Å. We will discuss the advantages of neutron scattering at small angles and deuterium labelling, and how this offers an approach to unlocking the secrets of the chain conformation and revealing the polymer structure on a multitude of length scales. We will discuss the role of the intimate coupling of the experimental data with computer-generated models that are centred on a range of different approaches originating from the RMC method that allows for the creation of realistic three-dimensional models of amorphous and semi-crystalline polymers
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