Segmental dynamics of atactic polypropylene as revealed by molecular simulations and quasielastic neutron scattering

Ahumada, O; Theodorou, DN; Triolo, A; Arrighi, V; Karatasos, C; Ryckaert, J-P

dc.contributor.author	Ahumada, O	en
dc.contributor.author	Theodorou, DN	en
dc.contributor.author	Triolo, A	en
dc.contributor.author	Arrighi, V	en
dc.contributor.author	Karatasos, C	en
dc.contributor.author	Ryckaert, J-P	en
dc.date.accessioned	2014-03-01T01:18:20Z
dc.date.available	2014-03-01T01:18:20Z
dc.date.issued	2002	en
dc.identifier.issn	0024-9297	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/14938
dc.subject	Activation Energy	en
dc.subject	Atomistic Simulation	en
dc.subject	Dynamic Structure Factor	en
dc.subject	Exponential Decay	en
dc.subject	Exponential Function	en
dc.subject	Gaussian Distribution	en
dc.subject	Molecular Dynamic Simulation	en
dc.subject	Molecular Simulation	en
dc.subject	Momentum Transfer	en
dc.subject	Neutron Scattering	en
dc.subject	Oscillations	en
dc.subject	Polypropylene	en
dc.subject	Relaxation Time	en
dc.subject	Standard Deviation	en
dc.subject	Time Window	en
dc.subject	Incoherent Scatter	en
dc.subject.classification	Polymer Science	en
dc.subject.other	Atomistic simulation trajectories	en
dc.subject.other	Gaussian distribution	en
dc.subject.other	Methyl torsional transitions	en
dc.subject.other	Momentum transfer	en
dc.subject.other	Relaxation times	en
dc.subject.other	Time decay	en
dc.subject.other	Activation energy	en
dc.subject.other	Glass transition	en
dc.subject.other	Mechanical properties	en
dc.subject.other	Molecular dynamics	en
dc.subject.other	Neutron scattering	en
dc.subject.other	Nuclear magnetic resonance spectroscopy	en
dc.subject.other	Polypropylenes	en
dc.title	Segmental dynamics of atactic polypropylene as revealed by molecular simulations and quasielastic neutron scattering	en
heal.type	journalArticle	en
heal.identifier.primary	10.1021/ma011807u	en
heal.identifier.secondary	http://dx.doi.org/10.1021/ma011807u	en
heal.language	English	en
heal.publicationDate	2002	en
heal.abstract	The dynamics of atactic polypropylene has been explored with quasielastic neutron scattering (QENS) measurements in the temperature range 4-460 K and momentum transfer range q = 0.2-2.25 Angstrom(-1). In parallel, molecular dynamics simulations of the same polymer have been conducted in the temperature range 260-600 K, using both a fully atomistic model and a model with united-atom methyl groups. In conjunction with the second model, a computational procedure for introducing the motion of methyl hydrogens a posteriori is proposed and tested against the fully atomistic simulation results. Simulated intermediate incoherent scattering functions I(q,t) reveal an initial exponentially decaying regime of duration ca. 1 ps, which is dominated by bond angle bending vibrations and torsional oscillations, as well as features attributable to torsional transitions of the methyl groups and to correlated conformational transitions of the backbone bonds at longer times. The time decay of I(q,t) beyond 1 ps is well-described by stretched exponential functions, the stretching exponent being around 0.5 at 600 K and decreasing with decreasing temperature. Analysis of the atomistic simulation trajectories yields distributions of relaxation times with a distinct log-Gaussian peak characteristic of methyl motion, from which a Gaussian distribution of activation energies for methyl torsional transitions with mean around 15 kJ/mol and standard deviation around 3 kJ/mol is extracted, in excellent agreement with QENS estimates. Torsional transitions of different methyls occur essentially independently of each other. QENS experiments reveal a nondecaying elastic contribution to the scattering over the time window of the measurement, which is not seen in the simulations. Apart from this, computed I(q,t) and incoherent dynamic structure factor S(q,w) curves are in very favorable agreement with the measured QENS spectra and with earlier NMR, data on atactic polypropylene.	en
heal.publisher	AMER CHEMICAL SOC	en
heal.journalName	Macromolecules	en
dc.identifier.doi	10.1021/ma011807u	en
dc.identifier.isi	ISI:000177688800052	en
dc.identifier.volume	35	en
dc.identifier.issue	18	en
dc.identifier.spage	7110	en
dc.identifier.epage	7124	en