Atomistic Molecular Dynamics Simulations for the Morphology and Property Relationship of Poly (Trimethylene Terephthalate) fibers

We performed a series of atomistic molecular dynamics simulations to study the relation between the properties and the conformation of poly (trimethylene terephthalate), PTT. In the first part of this work, we investigate the dependence of properties on the degree of polymerization (DP) and number of PTT molecules in the system. We find that there is an apparent change of such dependences in both structure (end-to end distance, aspect ratio) and energetic properties as the DP of PTT is greater than 54. This indicates that simulation models with DP equal to or larger than 54 are capable of representing the polymeric material.
In the second part of this work, we discuss the relation between the infrared (IR) spectrum and the degree of crystallization of PTT fibers. The IR spectrum are calculated from the Hessian matrix (0 K) and the Fourier transform of the velocity autocorrelation function (elevated temperatures). We find that the calculated IR frequencies are constantly greater than the experimental values by 10 to 15%. We have also identified the characteristic peaks of PTT fibers in the pure crystalline and pure amorphous states. We observe an increase and decrease in the intensity of crystalline and amorphous characteristic peaks respectively as an amorphous PTT is heated (from 300K to 473K) or stretched (up to 100% extension). This indicates the enhancement of crystillinity of PTT in the heating or drawing process.