Molecular Dynamics of Polyisoprene/Polystyrene Oligomer Blends: The role of self-concentration and fluctuations on blend dynamics

The effect of self-concentration and intermolecular packing on the dynamics of polyisoprene (PI)/polystyrene (PS) blends is examined by extensive atomistic simulations. Direct information on local structure of the blend system allows a quantitative calculation of self- and effective composition terms at various length scales that are introduced to proposed models of blend dynamics. Through a detailed statistical analysis, the full distribution of relaxation times associated with reorienation of carbon-hydrogen bonds was extracted and compared to literature experimental data. A direct relation between relaxation times and local effective composition is found. Following an implementation of a model involving local composition as well as concentration fluctuations the relevant length scales characterizing the segmental dynamics of both components were critically examined. For PI the distribution of times becomes narrower for the system with the lowest PS content and then broadens as more PS is added. This is in contrast to the slow component (PS), where an extreme breadth is found for relaxation times in the 25/75 system prior to narrowing as we increase PI concentration. The chain dynamics was directly quantified by diffusion coefficients as well as the terminal (maximum) relaxation time of each component in the mixed state. Strong coupling between the friction coefficients of the two components was predicted that leads to very similar chain dynamics for PI and PS, particularly for high concentrations of PI. We anticipate this finding to the rather short oligomers (below the Rouse regime) studied here as well as to the rather similar size of PI and PS chains. The ratio of the terminal to the segmental relaxation time, τterm/τseg,c, presents a clear qualitative difference for the constituents: for PS the above ratio is almost independent of blend composition and very similar to the pure state. In contrast, for PI this ratio depends strongly on the composition of the blend; i.e. the terminal relaxation time of PI increases more than its segmental relaxation time, as the concentration of PS increases, resulting into a larger terminal/segmental ratio. We explain this disparity, based on the different length scales characterizing dynamics. The relevant length for the segmental dynamics of PI is about 0.4-0.6 nm, smaller than chain dimensions which are expected to characterize terminal dynamics, whereas for PS associated length scales are similar (about 0.7-1.0 nm) rendering a uniform change with mixing

Local Structure and Dynamics of Trans-polyisoprene oligomers

Mono- and poly-disperse melts of oligomers (average length 10 monomers) of trans-1,4-polyisoprene are simulated in full atomistic detail. The force-field is developed by means of a mixture of ab initio quantum-chemistry and an automatic generation of empirical parameters. Comparisons to NMR and scattering experiments validate the model. The local reorientation dynamics shows that for C$-$H vectors there is a two-stage process consisting of an initial decay and a late-stage decorrelation originating from overall reorientation. The atomistic model can be successfully mapped onto a simple model including only beads for the monomers with bond springs and bond angle potentials. End-bridging Monte Carlo as an equilibration stage and molecular dynamics as the subsequent simulation method together prove to be a useful method for polymer simulations.Comment: 25 pages, 15 figures, accepted by Macromolecule

Η ψήφος των εκτός επικρατείας εκλογέων

Η παρούσα διπλωματική εργασία εξετάζει το ζήτημα της ψήφου των εκτός επικρατείας εκλογέων, νοούμενης ως δυνατότητας των εκλογέων που την ημέρα διεξαγωγής των εκλογών ή του δημοψηφίσματος βρίσκονται εκτός της εδαφικής επικράτειας της χώρας της ιθαγένειάς τους να ασκούν από εκεί το ενεργητικό εκλογικό τους δικαίωμα, Παρ' ότι συνιστά σχετικά πρόσφατο φαινόμενο, η ανωτέρω δυνατότητα καθιερώνεται σήμερα στη συντριπτική πλειονότητα των ανά τον κόσμο εννόμων τάξεων, συμπεριλαμβανομένης πλέον και της ελληνικής. Αντίθετα, το διεθνές δίκαιο κατά κανόνα δεν παρέχει στους εκτός επικρατείας εκλογείς αντίστοιχη προστασία. Τούτο οφείλεται εν μέρει στις δικαιοπολτικές αντιρρήσεις που εκφράζονται ως προς τη συμμετοχή των εκτός επικρατείας εκλογέων στις εκλογικές αναμετρήσεις της χώρας καταγωγής τους, αντιρρήσεις ωστόσο που δεν συνεκτιμούν ιδίως τις θεμελιώδεις για μία δημοκρατική πολιτεία αρχές της καθολικότητας και της ισότητας της ψήφου. Στο επίπεδο του θετού δικαίου, τόσο ενωσιακοί όσο και ελληνικοί κανόνες δικαίου εμποδίζουν τη στέρηση του δικαιώματος ψήφου από τους εκτός επικρατείας εκλογείς και οριοθετούν τους περιορισμούς του. Περαιτέρω, η ειδικότερη διαμόρφωση της εκτός επικρατείας ψηφοφορίας (σε ποιες εκλογικές αναμετρήσεις θα εφαρμοστεί, με ποια μέθοδο θα διεξαχθεί, πώς θα ενσωματωθεί το αποτέλεσμά της στο συνολικό εκλογικό αποτέλεσμα) εναπόκειται στο εκάστοτε κράτος, το οποίο, στον βαθμό που δεν προκαλείται σύγκρουση με τις θεμελιώδεις ή άλλες, συνταγματικά προβλεπόμενες, αρχές της ψήφου και της ψηφοφορίας αρχές, την προσαρμόζει ελεύθερα στις απαιτήσεις και στις ανάγκες της έννομης τάξης της.The present Master thesis addresses the issue of voting as an out-of-country elector, understood as the ability of electors, who are situated abroad on election/referendum day, to exercise their right to vote from there. Despite it being a relatively recent phenomenon, the aforementioned ability is enshrined today in the vast majority of legal orders across the world, including the greek one. On the contrary, international law has yet to (consistently) offer expatriate electors similar protection. This is in part due to the theoretical objections raised against the participation of expatriate electors in home country elections and referenda. Those objections, however, do not take into consideration mainly the fundamental for a democratic polity principles of universality and equality of vote. De lege lata, rules of European Union law, as well as rules of greek law prohibit the disenfranchisement of electors abroad and set limits to the restrictions of the right to vote. Furthermore, the specific arrangement of out-of-country voting (i.e. the elections concerned, the voting method applied, the assignment of external votes to electoral districts) is determined by each state, which, to the extent that no conflict with the fundamental or other, constitutionally provided, principles of vote and voting arises, is free to adapt it to the demands and needs of the respective legal order

Local viscoelastic properties and shear stress propagation in bulk and confined polymer melts and low-molecular weight liquids

Through the analysis of the spatial correlations of local stress, we detect the propagation of long-ranged liquid-elasticity-mediated shear stress waves in polymeric and low-molecular weight liquids. The propagation of shear waves is effectively planar; i.e., σαβ propagates in the αβ plane. The autocorrelation functions of the local stress of a region are affected by both the relaxation of stress in that region and the propagation of stress from the region to the rest of the sample. However, due to the planar propagation of shear waves, the transfer of σαβ from those slices of the simulation box that are periodic in the αβ plane is negligible. This allows direct probing of the position-dependent local stress relaxation modulus of liquid in the vicinity of a confining surface.Goodyear Tire & Rubber Company Horizon 2020 (European Union)11 página

Automatic Coarse Graining of Polymers

Several recently proposed semi--automatic and fully--automatic coarse--graining schemes for polymer simulations are discussed. All these techniques derive effective potentials for multi--atom units or super--atoms from atomistic simulations. These include techniques relying on single chain simulations in vacuum and self--consistent optimizations from the melt like the simplex method and the inverted Boltzmann method. The focus is on matching the polymer structure on different scales. Several ways to obtain a time-scale for dynamic mapping are discussed additionally. Finally, similarities to other simulation areas where automatic optimization are applied as well are pointed out.Comment: 17 pages, 5 figure

Optimization of formulation and process of Australian sweet lupin (ASL)-wheat bread

This study aimed to optimise formulation and process factors of Australian sweet lupin (ASL)-refined wheat bread bun to maximise the ASL level whilst maintaining bread quality using response surface methodology (RSM) with a central composite face-centered design. Statistical models were generated that predicted the effects of level of ASL flour incorporation (g/100 g of ASL-wheat composite flour), ASL flour volume weighted mean particle size (mm), water incorporation level (g/100 g ASL-wheat composite flour), mixing time of sponge and dough (min) and baking time (min) on crumb specific volume (CSV), instrumental texture attributes and consumer acceptability of the breads. Verification experiments were used to validate the accuracy of the predictive models. Optimisation of the formulation and process parameters using these models predicted that formulations containing ASL flour at 21.4e27.9 g/100 g of ASL-wheat composite flour with volume weighted mean particle size of 415e687 mm, incorporating water at 59.5e71.0 g/100 g ASL-wheat composite flour, with sponges and dough mixed for 4.0e5.5 min and bread baked for 10e11 min would be within the desirable range of CSV, instrumental hardness and overall consumer acceptability. Verification experiments confirmed that the statistical models accurately predicted the responses