Repositorio Institucional del la Universidad de Burgos Colección :
http://hdl.handle.net/10259/4202
2019-01-23T22:36:23ZA Combination of the eXtended Pom-Pom Model and the Stress-Thermal Rule to Predict Anisotropy in Thermal Conductivity in Non-Linear Polymeric Flows
http://hdl.handle.net/10259/5000
Título : A Combination of the eXtended Pom-Pom Model and the Stress-Thermal Rule to Predict Anisotropy in Thermal Conductivity in Non-Linear Polymeric Flows
Autor : Nieto Simavilla, David; Verbeeten, Wilco M.H.
Resumen : Advances in polymer processing enables more affordable technologies and significantly impacts the global plastics market which is expected to reach 654 billion USD by 2020. The cost/energy required to manufacture, recycle and dispose polymers is strongly affected by the thermo-physical properties and their dependence on state variables such as temperature and stress. The viscoelastic behavior of polymeric flows under isothermal conditions has been extensively researched. However, most of the processing of polymeric materials occurs under non-isothermal conditions and their implementation in simulations remains a challenge. In particular, flow-induced anisotropy in the thermal conductivity of polymers has been previously omitted in the study of industrially relevant flows. Our work combines evidence of a universal relationship between thermal conductivity and stress tensors (i.e. the stress-thermal rule) with differential constitutive equations for the viscoelastic behavior of polymers to provide predictions for the anisotropy in thermal conductivity in uniaxial, planar, equibiaxial and shear flow in commercial polymers. Special focus is placed on the eXtended Pom-Pom model which captures the non-linear behavior in both shear and elongation flows. The predictions provided by this approach are easily implemented in finite elements packages since the viscoelastic and thermal behavior is described by a single equation. Our results include predictions for the flow-induced anisotropy in thermal conductivity for low density polyethylene as well as validation of the method by comparison with available measurements. Remarkably, this approach allows universal predictions of anisotropy in thermal conductivity to be used in simulations of complex flows in which only the most fundamental rheological behavior of the material has been previously characterized (i.e. no adjusting parameters are needed in addition to those in the constitutive model
Descripción : Trabajo presentado en: 33rd International Conference of the Polymer Processing Society, Cancún, 10 a 14 de diciembre de 20172017-01-01T00:00:00ZAnsiotropy in k and cp induced by deformation in polymers: experimental methods, current understanding and application to numerical methods
http://hdl.handle.net/10259/4972
Título : Ansiotropy in k and cp induced by deformation in polymers: experimental methods, current understanding and application to numerical methods
Autor : Nieto Simavilla, David; Venerus, David C. .; Verbeeten, Wilco M.H.
Resumen : The thermo-physical properties of polymers such as thermal conductivity and heat capacity are affected by molecular orientation induced by deformation. These properties influence the optimization of fabrication processes and the performance of polymeric materials during use. In this talk, we introduce two complementary experimental methods to characterize the anisotropy in thermal conductivity and its relationship to stress and deformation in polymers subjected to uniaxial extension. The first method, Forced Rayleigh Scattering (FRS) [1], allows directional measurement of thermal diffusivity. The second method, Infrared Thermography (IRT) [2], allows characterization of the deviations from the un-deformed value of different components of the thermal conductivity tensor. Surprisingly, we find: 1) universality of a linear relationship between anisotropy in thermal conductivity and stress known as the stress-thermal rule and 2) that, in contrast to the analogous stress-optic rule, the validity of the stress-thermal rule extends beyond finite extensibility [1]. Additionally, we present a transient method using Infrared Thermography to investigate the dependence of heat capacity on deformation [3]. We find that the heat capacity increases with stretching in lightly cross-linked natural rubber. Using a simple thermodynamic analysis based on classical rubber elasticity an energetic contribution to the stress is found to be responsible for the changes in heat capacity. We discuss the implications of our findings for the assumption of purely entropic elasticity. A growing trend in the design and tuning of polymer manufacturing processes is the use of numerical simulations for the complex non-homogeneous and non-isothermal flows involved. However, while there has been a significant amount of work to include more complete rheological constitutive models into these simulations [4], the characterization and implementation of material thermo-physical properties and their connection to the micro-structural orientation remains a challenge. Our work is presented as a stepping-stone for the development of a molecular-to-continuum methodology for the simulation of industrially relevant flows in polymer manufacturing.
Descripción : Trabajo presentado en: 13th International Meeting on Thermodiffusion, Londres, 11 a 14 de 20182018-01-01T00:00:00ZKinetics of irreversible adsorption: thermodynamics versus molecular mobility
http://hdl.handle.net/10259/4971
Título : Kinetics of irreversible adsorption: thermodynamics versus molecular mobility
Autor : Nieto Simavilla, David; Huang, Weide .; Housmans, Caroline .; Vandestrick, Philippe .; Ryckaerts, Jean-Paul .; Sferrazza, Michele .; Napolitano, Simone .
Resumen : Irreversibly adsorbed polymer layers represent an intriguing class of novel nanomaterials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. These extremely thin layers (thickness < few tens of nanometers) are obtained via a small number of successive steps, easily reproducible in a laboratory environment: a polymer melt is placed in contact with an adsorbing substrate and nonadsorbed chains are washed away by soaking the sample in a good solvent. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying the performance of polymer coatings without affecting the interfacial chemistry [1]. Here, we discuss on the physics behind the formation of irreversibly adsorbed layers onto solid substrate [2,3], highlighting the differences between measurements performed via dielectric spectroscopy and those via ellipsometry or atomic force microscopy. By analyzing the outcome of experiments and simulations, we show how changes in thermal energy and interaction potential affect the equilibrium and the nonequilibrium components of the kinetics. We identify a universal linear relation between the growth rates at short and long adsorption times, suggesting that the monomer pinning mechanism is independent of surface coverage, while the progressive limitation of free sites significantly limits the adsorption rate. We show that the equilibrium adsorbed amount is given by thermodynamics and depends on the interface interaction only (i.e. it is temperature independent in experiments). Importantly, in neat disagreement with current ideas on surface science, the equilibrium adsorbed amount – and, hence, interfacial interaction potential – is affected by nanoconfimenent [4].
Descripción : Trabajo presentado en: 10th Conference on Boroadband Dielectric Spectroscopy and its Applications, Bruselas, 26 a 31 de agosto de 20182018-01-01T00:00:00ZPredictions of anisotropic thermal transport in non-linear-non-isothermal polymeric flows
http://hdl.handle.net/10259/4970
Título : Predictions of anisotropic thermal transport in non-linear-non-isothermal polymeric flows
Autor : Nieto Simavilla, David; Verbeeten, Wilco M.H.; Venerus, David C. .; Schieber, Jay D. .; Theodorou, Doros N. .
Resumen : Over the last decades, significant efforts have been dedicated to include more complete rheological constitutive models into finite elements methods to simulate the complex flows in polymer manufacturing. However, while a remarkable portion of these processes are intrinsically non-isothermal, the study and implementation of non-isothermal flows has been very limited. The degree of complexity of such calculations is considerably increased by: 1) the addition to the problem of the energy equation; 2) a strong coupling to the momentum balance due to a highly temperature-dependent rheological behavior and 3) the strong influence that deformation-induced molecular orientation has on the thermo-physical properties of polymeric materials. Experimental evidence has shown that thermal conductivity becomes anisotropic in polymers subjected to deformation. Furthermore, a linear relationship between the thermal conductivity and stress tensors has been found to be universal (i.e. independent of polymer chemistry) and to extend beyond the finite extensibility limit. We make use of molecular simulation techniques to gain insights into the transport mechanisms behind these surprising results. On a more practical level, our work combines the thermal conductivity/stress response with two recent constitutive equations proposed for linear (Rolie Poly) and branched (eXtended Pom-Pom) polymers to venture predictions for the anisotropy in thermal conductivity in a number of interesting flows. These two constitutive models provide accurate descriptions of the available non-linear rheology and thermal transport data. Remarkably, our approach allows implementation of anisotropy in thermal conductivity into finite elements simulations without adding any adjusting parameters to those of the viscoelastic model. Our work represents a first step towards a molecular-to-continuum methodology for the simulation of industrially relevant non-isothermal flows to predict flow characteristics and the material final properties after processing
Descripción : Trabajo presentado en: 90th Annual Meeting of The Society of Rheology, 14 a 18 de ocubre de 2018, Houston2018-01-01T00:00:00Z