Repositorio Institucional del la Universidad de Burgos Comunidad : Ofrece acceso a artículos de revista, comunicaciones de congresos, libros y otros trabajos de investigación del personal investigador de la UBU
http://hdl.handle.net/10259/2604
Ofrece acceso a artículos de revista, comunicaciones de congresos, libros y otros trabajos de investigación del personal investigador de la UBU2018-10-17T05:55:14ZAnisotropy in thermal conductivity and changes in heat capacity induced by deformation in polymers: experimental methods, current understanding and application to numerical methods
http://hdl.handle.net/10259/4972
Título : Anisotropy in thermal conductivity and changes in heat capacity 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.2018-01-01T00:00:00ZKinetics 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].2018-01-01T00:00:00ZPredictions 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 processing2018-01-01T00:00:00ZDeformation induced changes in the thermal properties of elastomers: experimental methods, current understanding and application to finite elements methods
http://hdl.handle.net/10259/4969
Título : Deformation induced changes in the thermal properties of elastomers: experimental methods, current understanding and application to finite elements methods
Autor : Nieto Simavilla, David; Venerus, David C. .; Verbeeten, Wilco M.H.
Resumen : Deformation-induced molecular orientation of polymeric materials affects thermo-physical properties such as thermal conductivity and heat capacity. These properties influence not only the optimization of fabrication processes, but also the performance of polymeric materials during use. We introduce two complementary experimental methods to characterize the anisotropy in thermal conductivity and its relationship to stress and deformation in elastomers 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 this rule extends beyond finite extensibility [1]. Additionally, we present a transient method for Infrared Thermography technique to investigate the dependence of heat capacity on deformation [3]. We find that the heat capacity increases with stretching in lightly crosslinked natural rubber. Using a simple thermodynamic analysis based on classical rubber elasticity, we discuss the implications of our findings for the assumption of purely entropic elasticity, and the presence of an energetic contribution to the stress in deformed polymers. A growing trend in the design and tuning of polymer manufacturing processes is the use of finite elements simulations for the complex 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 that are connected to the micro-structural orientation remains a challenge. This 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 manufacturing2018-01-01T00:00:00Z