The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Reiner Mehnert - One of the best experts on this subject based on the ideXlab platform.
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UV Curable Acrylate Nanocomposites: Properties and Applications
Journal of Polymer Research, 2005Co-Authors: Frank Bauer, Reiner MehnertAbstract:Transparent nanocomposites were prepared from nano-sized silica and radiation curable acrylates. To improve the embedding of silica nanoparticles within the acrylate matrix the filler surface was modified by trialkoxysilanes. Instead of an expected monomeric silane grafting polysiloxane structures were anchored on the nanoparticle surface due to acid catalyzed pre-hydrolysis/condensation of trialkoxysilanes. The polysiloxanes structures covering the silica surface were characterized by temperature-programmed oxidation, infrared and multinuclear MAS NMR spectroscopy. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with more than 20 monomeric silane units. Ladder-like polysiloxane chains have been proposed and atomic force microscopy were used to visualize the structure of surface-anchored organosilanes. These ladder-like structures are assumed to build up a short range interpenetrating network with polyacrylate chains during UV or EB curing. Due to the organophilic modification of silica nanoparticles reinforced acrylate formulations can contain up to 50 wt.-% nanofiller maintaining satisfactory rheological properties. These formulations can be used as Coatings on substrates such as polymer films, paper, metal, wood, engineered wood, etc. After UV/EB curing nanoparticle reinforced polyacrylate Coatings are obtained which show markedly improved properties as compared to neat polymers, e.g., increased microhardness and modulus, improved scratch and abrasion resistance, higher gas barriers and temperature resistance. Due to the nano-sized silica filler the cured Coatings remain transparent, hazeless and glossy. On a pilot scale unit acrylate nanocomposite Coatings are manufactured for roll Coating, Curtain Coating and spray applications. Basic properties of acrylate nanocomposite Coatings are described.
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UV curable acrylate nanocomposites: Properties and applications
Journal of Polymer Research, 2005Co-Authors: Frank Bauer, Reiner MehnertAbstract:Transparent nanocomposites were prepared from nano-sized silica and radiation curable acrylates. To improve the embedding of silica nanoparticles within the acrylate matrix the filler surface was modified by trialkoxysilanes. Instead of an expected monomeric silane grafting polysiloxane structures were anchored on the nanoparticle surface due to acid catalyzed pre-hydrolysis/condensation of trialkoxysilanes. The polysiloxanes structures covering the silica surface were characterized by temperature-programmed oxidation, infrared and multinuclear MAS NMR spectroscopy. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with more than 20 monomeric silane units. Ladder-like polysiloxane chains have been proposed and atomic force microscopy were used to visualize the structure of surface-anchored organosilanes. These ladder-like structures are assumed to build up a short range interpenetrating network with polyacrylate chains during UV or EB curing. Due to the organophilic modification of silica nanoparticles reinforced acrylate formulations can contain up to 50 wt.-% nanofiller maintaining satisfactory rheological properties. These formulations can be used as Coatings on substrates such as polymer films, paper, metal, wood, engineered wood, etc. After UV/EB curing nanoparticle reinforced polyacrylate Coatings are obtained which show markedly improved properties as compared to neat polymers, e.g., increased microhardness and modulus, improved scratch and abrasion resistance, higher gas barriers and temperature resistance. Due to the nano-sized silica filler the cured Coatings remain transparent, hazeless and glossy. On a pilot scale unit acrylate nanocomposite Coatings are manufactured for roll Coating, Curtain Coating and spray applications. Basic properties of acrylate nanocomposite Coatings are described. [ABSTRACT FROM AUTHOR] Copyright of Journal of Polymer Research is the property of Springer Science & Business Media B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Frank Bauer - One of the best experts on this subject based on the ideXlab platform.
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UV Curable Acrylate Nanocomposites: Properties and Applications
Journal of Polymer Research, 2005Co-Authors: Frank Bauer, Reiner MehnertAbstract:Transparent nanocomposites were prepared from nano-sized silica and radiation curable acrylates. To improve the embedding of silica nanoparticles within the acrylate matrix the filler surface was modified by trialkoxysilanes. Instead of an expected monomeric silane grafting polysiloxane structures were anchored on the nanoparticle surface due to acid catalyzed pre-hydrolysis/condensation of trialkoxysilanes. The polysiloxanes structures covering the silica surface were characterized by temperature-programmed oxidation, infrared and multinuclear MAS NMR spectroscopy. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with more than 20 monomeric silane units. Ladder-like polysiloxane chains have been proposed and atomic force microscopy were used to visualize the structure of surface-anchored organosilanes. These ladder-like structures are assumed to build up a short range interpenetrating network with polyacrylate chains during UV or EB curing. Due to the organophilic modification of silica nanoparticles reinforced acrylate formulations can contain up to 50 wt.-% nanofiller maintaining satisfactory rheological properties. These formulations can be used as Coatings on substrates such as polymer films, paper, metal, wood, engineered wood, etc. After UV/EB curing nanoparticle reinforced polyacrylate Coatings are obtained which show markedly improved properties as compared to neat polymers, e.g., increased microhardness and modulus, improved scratch and abrasion resistance, higher gas barriers and temperature resistance. Due to the nano-sized silica filler the cured Coatings remain transparent, hazeless and glossy. On a pilot scale unit acrylate nanocomposite Coatings are manufactured for roll Coating, Curtain Coating and spray applications. Basic properties of acrylate nanocomposite Coatings are described.
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UV curable acrylate nanocomposites: Properties and applications
Journal of Polymer Research, 2005Co-Authors: Frank Bauer, Reiner MehnertAbstract:Transparent nanocomposites were prepared from nano-sized silica and radiation curable acrylates. To improve the embedding of silica nanoparticles within the acrylate matrix the filler surface was modified by trialkoxysilanes. Instead of an expected monomeric silane grafting polysiloxane structures were anchored on the nanoparticle surface due to acid catalyzed pre-hydrolysis/condensation of trialkoxysilanes. The polysiloxanes structures covering the silica surface were characterized by temperature-programmed oxidation, infrared and multinuclear MAS NMR spectroscopy. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with more than 20 monomeric silane units. Ladder-like polysiloxane chains have been proposed and atomic force microscopy were used to visualize the structure of surface-anchored organosilanes. These ladder-like structures are assumed to build up a short range interpenetrating network with polyacrylate chains during UV or EB curing. Due to the organophilic modification of silica nanoparticles reinforced acrylate formulations can contain up to 50 wt.-% nanofiller maintaining satisfactory rheological properties. These formulations can be used as Coatings on substrates such as polymer films, paper, metal, wood, engineered wood, etc. After UV/EB curing nanoparticle reinforced polyacrylate Coatings are obtained which show markedly improved properties as compared to neat polymers, e.g., increased microhardness and modulus, improved scratch and abrasion resistance, higher gas barriers and temperature resistance. Due to the nano-sized silica filler the cured Coatings remain transparent, hazeless and glossy. On a pilot scale unit acrylate nanocomposite Coatings are manufactured for roll Coating, Curtain Coating and spray applications. Basic properties of acrylate nanocomposite Coatings are described. [ABSTRACT FROM AUTHOR] Copyright of Journal of Polymer Research is the property of Springer Science & Business Media B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Marcio S Carvalho - One of the best experts on this subject based on the ideXlab platform.
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Dynamic wetting failure in shear-thinning and shear-thickening liquids
Journal of Fluid Mechanics, 2020Co-Authors: Vasileios Charitatos, Marcio S Carvalho, Wieslaw J Suszynski, Satish KumarAbstract:Dynamic wetting failure in shear-thinning and shear-thickening liquids is examined in this paper. Flow visualization experiments using a Curtain-Coating geometry suggest that shear thinning postpones the onset of wetting failure and the resulting air entrainment. To advance the fundamental understanding of the underlying physical mechanisms, a hydrodynamic model consisting of liquid displacing air in a rectangular channel in the absence of inertia is developed. Both shear thinning and shear thickening are considered by using Carreau-type models to describe the liquid rheology. Steady-state solutions are calculated using the Galerkin finite-element method and the critical capillary number where wetting failure occurs is identified. Shear thinning is found to postpone the onset of wetting failure whereas shear thickening is found to promote it. The underlying mechanism involves thickening/thinning of the air film as a consequence of shear thinning/thickening of the liquid and the tangential stress balance. The results can be interpreted in terms of an effective viscosity, and demonstrate that similar physical mechanisms govern dynamic wetting failure in Newtonian, shear-thinning and shear-thickening liquids.
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delaying breakup and avoiding air entrainment in Curtain Coating using a two layer liquid structure
Chemical Engineering Science, 2020Co-Authors: Alireza Mohammad Karim, Saswati Pujari, Lorraine F. Francis, Wieslaw J Suszynski, Marcio S CarvalhoAbstract:Abstract Successful Curtain Coating is limited by two flow instabilities, the breakup of the liquid Curtain below a critical flow rate and air entrainment above a maximum substrate speed. These limitations make thin film Coating at high speed a great challenge. Previous work has shown that the Curtain breakup can be delayed to lower flow rates if the flowing liquid has viscoelastic behavior. However, viscoelastic stresses near the dynamic contact line destabilize the flow in that region, leading to the onset of air entrainment at lower web speeds. We propose and experimentally validate the use of a two-layer Curtain Coating configuration, with a shear-thinning liquid as the bottom layer and a viscoelastic liquid as the top layer, that expands the processing window and enables thin Coating at high speeds.
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dynamic wetting failure in Curtain Coating comparison of model predictions and experimental observations
Chemical Engineering Science, 2019Co-Authors: Marcio S Carvalho, Satish KumarAbstract:Abstract In this work dynamic wetting failure of Newtonian liquids in a Curtain Coating geometry is studied using a hydrodynamic model developed in our prior work (Liu et al., 2016b). The model is used to predict the onset of wetting failure with Curtain heights consistent with prior experimental setups. In the model, a Navier-slip boundary condition and constant contact angle are used to describe the dynamic contact line (DCL). The governing equations are solved with the Galerkin finite-element method and the critical substrate speed is identified at which wetting failure occurs. A boundary of a Coating window is constructed which outlines the critical substrate speed for different flow rates of the liquid Curtain. The model predictions are compared with prior experimental observations reported by Blake et al. (1999) and Marston et al. (2009). The model reproduces the non-monotonic behavior of the critical speed as the liquid flow rate increases. When surfactants are absent, our results suggest that the experimental observations can largely be explained with a model that uses the simplest boundary conditions at the DCL (Navier-slip and constant contact angle) and accounts for the air stresses there to accurately calculate interface shapes. When surfactants are present, our results suggest that a decrease in the equilibrium surface tension may not be the only mechanism responsible for changes in the shape of the Coating window. In particular, Marangoni stresses may play an important role.
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Effect of viscoelasticity on liquid sheet rupture
Journal of Non-newtonian Fluid Mechanics, 2019Co-Authors: M.s. Bazzi, Marcio S CarvalhoAbstract:Abstract Thin liquid sheets are ubiquitous in many industrial processes, such as atomization and Curtain Coating. In the latter, the thickness of the deposited layer is limited by the breakup of the liquid Curtain below a critical flow rate. The stability of a liquid sheet depends on the disturbance characteristics, sheet thickness and fluid properties. Experimental analyses have shown that thinner stable liquid Curtains can be obtained with viscoelastic liquids; however, the underlining physical mechanisms associated with the increased stability are not fully understood. This work presents a numerical analysis of the effect of viscoelasticity on the stability of a thin liquid sheet. We first derive linear stability criteria for both planar and axisymmetric perturbations of Newtonian and Oldroyd-B liquids. The time evolution of planar and axisymmetric perturbations in an Oldroyd-B liquid sheet is evaluated using asymptotic expansion of the flow variables and a fully-implicit time integration scheme. The breakup time is calculated as a function of Deborah number and polymer to solvent viscosity ratio. The results show that the liquid rheological behavior does not change the linear stability criterion, however it has a strong effect on the growth rate of the disturbance and consequently on the breakup time.
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dynamic wetting failure and hydrodynamic assist in Curtain Coating
Journal of Fluid Mechanics, 2016Co-Authors: Eric Vandre, Marcio S Carvalho, Satish KumarAbstract:Dynamic wetting failure in Curtain Coating of Newtonian liquids is studied in this work. A hydrodynamic model accounting for air flow near the dynamic contact line (DCL) is developed to describe two-dimensional (2D) steady wetting and to predict the onset of wetting failure. A hybrid approach is used where air is described by a one-dimensional model and liquid by a 2D model, and the resulting hybrid formulation is solved with the Galerkin finite element method. The results reveal that the delay of wetting failure in Curtain Coating – often termed hydrodynamic assist – mainly arises from the hydrodynamic pressure generated by the inertia of the impinging Curtain. This pressure leads to a strong capillary-stress gradient that pumps air away from the DCL and thus increases the critical substrate speed for wetting failure. Although the parameter values used in the model are different from those in experiments due to computational limitations, the model is able to capture the experimentally observed non-monotonic behaviour of the critical substrate speed as the feed flow rate increases (Blake et al. , Phys. Fluids , vol. 11, 1999, p. 1995–2007). The influence of insoluble surfactants is also investigated, and the results show that Marangoni stresses tend to thin the air film and increase air-pressure gradients near the DCL, thereby promoting the onset of wetting failure. In addition, Marangoni stresses reduce the degree of hydrodynamic assist in Curtain Coating, suggesting a possible mechanism for experimental observations reported by Marston et al. ( Exp. Fluids , vol. 46, 2009, pp. 549–558).
Satish Kumar - One of the best experts on this subject based on the ideXlab platform.
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Dynamic wetting failure in shear-thinning and shear-thickening liquids
Journal of Fluid Mechanics, 2020Co-Authors: Vasileios Charitatos, Marcio S Carvalho, Wieslaw J Suszynski, Satish KumarAbstract:Dynamic wetting failure in shear-thinning and shear-thickening liquids is examined in this paper. Flow visualization experiments using a Curtain-Coating geometry suggest that shear thinning postpones the onset of wetting failure and the resulting air entrainment. To advance the fundamental understanding of the underlying physical mechanisms, a hydrodynamic model consisting of liquid displacing air in a rectangular channel in the absence of inertia is developed. Both shear thinning and shear thickening are considered by using Carreau-type models to describe the liquid rheology. Steady-state solutions are calculated using the Galerkin finite-element method and the critical capillary number where wetting failure occurs is identified. Shear thinning is found to postpone the onset of wetting failure whereas shear thickening is found to promote it. The underlying mechanism involves thickening/thinning of the air film as a consequence of shear thinning/thickening of the liquid and the tangential stress balance. The results can be interpreted in terms of an effective viscosity, and demonstrate that similar physical mechanisms govern dynamic wetting failure in Newtonian, shear-thinning and shear-thickening liquids.
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dynamic wetting failure in Curtain Coating comparison of model predictions and experimental observations
Chemical Engineering Science, 2019Co-Authors: Marcio S Carvalho, Satish KumarAbstract:Abstract In this work dynamic wetting failure of Newtonian liquids in a Curtain Coating geometry is studied using a hydrodynamic model developed in our prior work (Liu et al., 2016b). The model is used to predict the onset of wetting failure with Curtain heights consistent with prior experimental setups. In the model, a Navier-slip boundary condition and constant contact angle are used to describe the dynamic contact line (DCL). The governing equations are solved with the Galerkin finite-element method and the critical substrate speed is identified at which wetting failure occurs. A boundary of a Coating window is constructed which outlines the critical substrate speed for different flow rates of the liquid Curtain. The model predictions are compared with prior experimental observations reported by Blake et al. (1999) and Marston et al. (2009). The model reproduces the non-monotonic behavior of the critical speed as the liquid flow rate increases. When surfactants are absent, our results suggest that the experimental observations can largely be explained with a model that uses the simplest boundary conditions at the DCL (Navier-slip and constant contact angle) and accounts for the air stresses there to accurately calculate interface shapes. When surfactants are present, our results suggest that a decrease in the equilibrium surface tension may not be the only mechanism responsible for changes in the shape of the Coating window. In particular, Marangoni stresses may play an important role.
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dynamic wetting failure and hydrodynamic assist in Curtain Coating
Journal of Fluid Mechanics, 2016Co-Authors: Eric Vandre, Marcio S Carvalho, Satish KumarAbstract:Dynamic wetting failure in Curtain Coating of Newtonian liquids is studied in this work. A hydrodynamic model accounting for air flow near the dynamic contact line (DCL) is developed to describe two-dimensional (2D) steady wetting and to predict the onset of wetting failure. A hybrid approach is used where air is described by a one-dimensional model and liquid by a 2D model, and the resulting hybrid formulation is solved with the Galerkin finite element method. The results reveal that the delay of wetting failure in Curtain Coating – often termed hydrodynamic assist – mainly arises from the hydrodynamic pressure generated by the inertia of the impinging Curtain. This pressure leads to a strong capillary-stress gradient that pumps air away from the DCL and thus increases the critical substrate speed for wetting failure. Although the parameter values used in the model are different from those in experiments due to computational limitations, the model is able to capture the experimentally observed non-monotonic behaviour of the critical substrate speed as the feed flow rate increases (Blake et al. , Phys. Fluids , vol. 11, 1999, p. 1995–2007). The influence of insoluble surfactants is also investigated, and the results show that Marangoni stresses tend to thin the air film and increase air-pressure gradients near the DCL, thereby promoting the onset of wetting failure. In addition, Marangoni stresses reduce the degree of hydrodynamic assist in Curtain Coating, suggesting a possible mechanism for experimental observations reported by Marston et al. ( Exp. Fluids , vol. 46, 2009, pp. 549–558).
A. Jeffrey Giacomin - One of the best experts on this subject based on the ideXlab platform.
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Slip heating in die drool
Canadian Journal of Chemical Engineering, 2015Co-Authors: P. H. Gilbert, A. Jeffrey GiacominAbstract:When molten plastic is extruded from a die, it can collect on the open die face. Called die drool, this phenomenon costs plastics manufacturers by requiring shutdown for die cleaning. This has been attributed to cohesive failure within the fluid at an internal surface, where the fluid slips on itself; the corresponding isothermal analysis led to an analytical solution for the drool rate (Schmalzer and Giacomin, J. Polym. Eng. 2013, 33, 1). In this paper, we account for the frictional heating at the cohesive slip interface, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, Curtain Coating, and in many other chemical engineering unit operations. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solution for the temperature rise in pressure-driven slit flow subject to constant heat generation at the cohesive slip interface. We solve the energy equation in Cartesian coordinates for the temperature rise, for both the transient and steady temperature profiles, in both the drool layer and the bulk polymer. We then evaluate the effect of this temperature rise on the rate of die drool. For this simplest relevant non-isothermal problem, we neglect viscous dissipation and convective heat transfer in the melt and we model viscosity as an Arrhenius function of temperature. We conclude with three worked examples showing the relevance of slip heating in determining die drool flow rates. We find that slip heating diminishes die drool. We arrive at two sufficient dimensionless conditions for the accurate use of our results: Br ≪1 or Gi ≪1.
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Wall slip heating
Polymer Engineering and Science, 2014Co-Authors: P. H. Gilbert, A. Jeffrey GiacominAbstract:When molten plastic is extruded, the upper limiting throughput is often dictated by fine irregular distortions of the extrudate surface. Called sharkskin melt fracture, plastics engineers spike plastics formulations with processing aids to suppress these distortions. Sharkskin melt fracture is not to be confused with gross melt fracture, a larger scale distortion arising at throughputs higher than the critical throughput for sharkskin melt fracture. Sharkskin melt fracture has been attributed to a breakdown of the no slip boundary condition in the extrusion die, that is, adhesive failure at the die walls, where the fluid moves with respect to the wall. In this article, we account for the frictional heating at the wall, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, Curtain Coating, and when curvature can be neglected, slit flow is easily extended to pipe extrusion and film blowing. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solutions for the temperature rise in pressure-driven slit flow and simple shearing flow, each subject to constant heat generation at the adhesive slip interface, with and without viscous dissipation in the bulk fluid. We solve the energy equation in Cartesian coordinates for the temperature rise, for steady temperature profiles. For this simplest relevant nonisothermal model, we neglect convective heat transfer in the melt and use a constant viscosity. We arrive at a necessary dimensionless condition for the accurate use of our results: Pe≪1. We find that slip heating can raise the melt temperature significantly, as can viscous dissipation in the bulk. We conclude with two worked examples showing the relevance of slip heating in determining wall temperature rise, and we show how to correct wall slip data for this temperature rise. POLYM. ENG. SCI., 55:2042–2049, 2015. © 2014 Society of Plastics Engineers
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Sheet Coating by drawdown of extruded polymer
Journal of Coatings Technology, 2001Co-Authors: Fan Ding, A. Jeffrey Giacomin, John C. SlatteryAbstract:An approximate analytic solution for Coating a highly viscous Newtonian fluid ontoa substrate is developed (low Poiseuille number and high capillary number). Two particular extrusion angles are considered: parallel and perpendicular to the moving substrate. We obtain expressions for the Curtain shape, Coating thickness, contact length, contact pressure, drawing force, apparent contact angle, and contact convexity. In this paper, we identify a process indeterminacy that arises in the Curtain Coating employing a parallel slit. Weshow that, by orienting the extrusion slit perpendicular to the moving substrate, this indeterminacy vanishes. Thus, a unique solution for the contact length is always obtained. The extension to a viscoelastic fluid is also briefly considered.
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Angular plane Curtain Coating by drawdown of extruded polymer
Journal of Coatings Technology, 2000Co-Authors: Fan Ding, A. Jeffrey Giacomin, John C. SlatteryAbstract:An approximate analytic solution for an angular plane Curtain Coating of a highly viscous Newtonian fluid is developed. We obtain expressions for the melt Curtain shape, Coating thickness, contact length, contact pressure, drawing force, apparent contact angle, and contact convexity. Specially constructed examples enable practitioners to apply the results without advanced training in fluid mechanics. We identify a process indeterminacy that arises in Curtain Coating employing a parallel slit. We show that, with a rapidly converging extrusion slit, this indeterminacy vanishes. Thus, a unique solution for the contact length is always obtained. The extension to a viscoelastic fluid is also briefly considered.
