- Università degli Studi di Padova
Dipartimento di Fisica e Astronomia "G. Galilei" -DFA
Via Francesco Marzolo, 8
35131 Padova (PD)
Italy
For each thermodynamic system, it is possible to determine a relation between energy, entropy, and the work parameters (the volume only in the case of simple systems) that is called the Fundamental Relation of the system. We start first... more
For each thermodynamic system, it is possible to determine a relation between energy, entropy, and the work parameters (the volume only in the case of simple systems) that is called the Fundamental Relation of the system. We start first with closed systems with no chemical reactions for which the Equilibrium State Postulate determines, in general, the number of degrees of freedom and then it is generalized to open systems with variable chemical composition. The Fundamental Relation describes the set of all stable and metastable equilibrium states that the system can reach and the geometrical properties of the surface described by it determines the conditions of stability of equilibrium states. It can be represented in various forms according to the external constraints. The representations commonly used, in addition to that of Energy and of Entropy, are the Free Energy, the Enthalpy, and the Gibbs Potential and the general properties of isothermal, isobaric and isochoric transformations are discussed. The definition of the chemical potential is given and its physical meaning as the thermodynamic potential responsible of phase equilibria is shown.
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The handling of yield‐stress fluids typically involves a jammed‐to‐flow transition that is pivotal for many injection and transport technologies on different scales, such as additive manufacturing, injection molding, food rheology, and... more
The handling of yield‐stress fluids typically involves a jammed‐to‐flow transition that is pivotal for many injection and transport technologies on different scales, such as additive manufacturing, injection molding, food rheology, and oil transport. For all of these applications, it is crucial to be able to tune the fluidization under constant load. The pressure‐driven flow of emulsions is reported within a microfluidic channel, one wall of which is patterned by a herringbone‐riblet roughness comprising a regular array of V‐shaped grooves. With respect to the pressure gradient, this pattern displays a convergent (divergent) orientation that provides a forward (backward) direction. At the tip of the herringbone pattern, the forward and backward flows are almost identical for a viscous Newtonian fluid and a diluted emulsion, whereas a surprising flow boost in the forward direction is observed as the emulsion approaches a jammed state. The flow boost is more effective at small herring...
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Extracellular vesicles (EVs) are double-layered lipid membrane vesicles released by cells. Currently, EVs are attracting a lot of attention in the biological and medical fields due to their role as natural carriers of proteins, lipids,... more
Extracellular vesicles (EVs) are double-layered lipid membrane vesicles released by cells. Currently, EVs are attracting a lot of attention in the biological and medical fields due to their role as natural carriers of proteins, lipids, and nucleic acids. Thus, they can transport useful genomic information from their parental cell through body fluids, promoting cell-to-cell communication even between different organs. Due to their functionality as cargo carriers and their protein expression, they can play an important role as possible diagnostic and prognostic biomarkers in various types of diseases, e.g., cancers, neurodegenerative, and autoimmune diseases. Today, given the invaluable importance of EVs, there are some pivotal challenges to overcome in terms of their isolation. Conventional methods have some limitations: they are influenced by the starting sample, might present low throughput and low purity, and sometimes a lack of reproducibility, being operator dependent. During th...
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We report on a comprehensive study of the unique adhesive properties of mats of polymethylmethacrylate (PMMA) nanofibers produced by electrospinning.
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Within the approximation of discontinuous systems, the entropy production is calculated in a variety of nonequilibrium situations in open/closed systems and for chemical and electrochemical reactions. The definition of generalized fluxes... more
Within the approximation of discontinuous systems, the entropy production is calculated in a variety of nonequilibrium situations in open/closed systems and for chemical and electrochemical reactions. The definition of generalized fluxes and forces is widely discussed. The dependence of fluxes on forces is explored and for near to equilibrium configurations this dependence is linearized. The linearization leads to the Onsager relations which give the quantitative characterization of the cross-interference of different irreversible processes. The non-unique determination of the fluxes and of the relative forces is widely discussed and the limits of validity for the linear relations between fluxes and forces are examined with particular reference to chemical reactions.
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The van der Waals equation of state is obtained as the first- order correction to the ideal gas equation and some observational consequences are discussed: the correlation of the critical parameters, the Joule–Thomson coefficient, the... more
The van der Waals equation of state is obtained as the first- order correction to the ideal gas equation and some observational consequences are discussed: the correlation of the critical parameters, the Joule–Thomson coefficient, the inversion curve, and the determination of the vapor pressure. The Law of Corresponding States is formulated and discussed in several aspects. The notion of generalized charts is introduced with particular reference to the compressibility chart. The behavior in the proximity of the critical point is briefly examined.
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The extension of the fundamental equations of Thermodynamics to a description of macroscopic systems in terms of continuous state variables is developed. All the basic relations as mass conservation in the presence of chemical reactions,... more
The extension of the fundamental equations of Thermodynamics to a description of macroscopic systems in terms of continuous state variables is developed. All the basic relations as mass conservation in the presence of chemical reactions, the equation of motion and the equations for energy and that for entropy which express, in the new formalism, the First and the Second Principles, respectively, must be reformulated. The correct expression for the entropy production and the consequent expressions for the fluxes and the corresponding generalized forces are obtained. In the linear regime, the general relation between the mobility of ionic species and the coefficient of diffusion (Einstein relation) is demonstrated. The thermoelectric phenomena (Seebeck, Peltier, and Thomson effects) are discussed together with the thermodiffusion processes. An appendix concerning the Gibbs–Duhem relation closes the Chapter.
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This book offers a comprehensive overview of thermodynamics. It is divided into four parts, the first of which equips readers with a deeper understanding of the fundamental principles of thermodynamics of equilibrium states and of their... more
This book offers a comprehensive overview of thermodynamics. It is divided into four parts, the first of which equips readers with a deeper understanding of the fundamental principles of thermodynamics of equilibrium states and of their evolution. The second part applies these principles to a series of generalized situations, presenting applications that are of interest both in their own right and in terms of demonstrating how thermodynamics, as a theory of principle, relates to different fields. In turn, the third part focuses on non-equilibrium configurations and the dynamics of natural processes. It discusses both discontinuous and continuous systems, highlighting the interference among non-equilibrium processes, and the nature of stationary states and of fluctuations in isolated systems. Lastly, part four introduces the relation between physics and information theory, which constitutes a new frontier in fundamental research. The book includes step-by-step exercises, with solutions, to help readers to gain a fuller understanding of the subjects, and also features a series of appendices providing useful mathematical formulae. Reflecting the content of modern university courses on thermodynamics, it is a valuable resource for students and young scientists in the fields of physics, chemistry, and engineering
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The impossibility of realizing the perpetual motion is universally accepted as a fundamental principle of Physics. This postulate defines two main categories, where physical processes can be placed: natural processes and unnatural... more
The impossibility of realizing the perpetual motion is universally accepted as a fundamental principle of Physics. This postulate defines two main categories, where physical processes can be placed: natural processes and unnatural processes. The former includes all the observed processes and the hypothesized processes that do not violate the fundamental principle and are, therefore, possible. The latter includes all the hypothesized processes that violate the principle of the impossibility of perpetual motion, and therefore they cannot occur. This is the starting point for formulating an evolutionary criterion for all-natural processes. To achieve this, a suitable mathematical tool must be developed. The fundamental step is the definition of entropy and of absolute temperature. These are complementary quantities and constitute the basis of the Second Principle, which must be formulated, first, in the frame of closed systems. Before the extension of the fundamental equations of Thermodynamics to continuous systems, the approximation of discontinuous systems and the problem of the conversion of heat into work both for reversible and irreversible engines are discussed. The coefficients of performance of refrigerators and of heat pumps are defined and the problem of the maximum work obtainable from a given configuration immersed in a given environment is briefly treated.
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The Onsager symmetry relations are applied to the study of electrokinetic effects and of thermomechanical effects. In the latter case the relation between thermomolecular pressure difference and the heat of transfer is calculated, for... more
The Onsager symmetry relations are applied to the study of electrokinetic effects and of thermomechanical effects. In the latter case the relation between thermomolecular pressure difference and the heat of transfer is calculated, for comparison, also for Knudsen gases in a classical kinetic model. The characterization of stationary states as states of minimum entropy production are studied. The determination of stationary states, their stability and the principles of Le Chatelier and of Le Chatelier–Braun, find their correct explanation within the context of the thermodynamical theory of stationary states. The model by Prigogine and Waime is presented as an example. Within the theory of fluctuations in an isolated thermodynamical system, the decay of fluctuations are treated with the formalism of linear irreversible processes and the symmetry properties of the linear phenomenological matrix is derived from the postulate of time reversal symmetry for microscopic physics.
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The structural evolution of polytetrafluoroethylene (PTFE) crystalline polymer latex films is studied at hundreds nanometer length scale by atomic force microscopy and Brillouin light scattering. In a controlled sintering process the... more
The structural evolution of polytetrafluoroethylene (PTFE) crystalline polymer latex films is studied at hundreds nanometer length scale by atomic force microscopy and Brillouin light scattering. In a controlled sintering process the transition is observed from the original particle distribution towards a ‘fibrillar’ structure of crystalline regions embedded in a disordered matrix. This transition is accompanied by a cross-over from localized acoustic excitations to propagating acoustic phonons, related to mesoscopic elastic properties. After sintering, a ‘mark’ of the original particulate structure persists, suggesting that filming of crystalline polymers may be analogous to sintering of ceramic powders. Films of crystalline polymers can thus be exploited as model systems to study the elasto-optical properties of granular and disordered media.
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Biomimetic surfaces with special wetting properties are attracting a lot of attention because of their fundamental and industrial applications. By tuning surface micro-nano structures and composition, it is possible to fabricate... more
Biomimetic surfaces with special wetting properties are attracting a lot of attention because of their fundamental and industrial applications. By tuning surface micro-nano structures and composition, it is possible to fabricate superhydrophobic surfaces exhibiting extreme water repellence and self-cleaning properties like the famous Lotus leaves or strong water adhesion as found on rose petals. Here we report results of a comprehensive study of the static and dynamic wetting properties of hairy surfaces produced by polymer replica molding of porous alumina matrices which are able to pin large water drops. The hairs, which have a characteristic diameter of 80 nm and height between 200 and 600 nm, are fabricated by imprinting an alumina (AAO) stamp into hard poly(dimethylsiloxane) (h-PDMS) and polypropylene (PP) samples. These polymers have similar contact angles for water drops on flat surfaces, but have an elastic modulus that differs by a factor of approximately 100. Hairy surfaces significantly increase drop stickiness with respect to the flat ones for either polymer, with the h-PDMS samples capable of holding water drops about 20% larger than those of the more rigid PP. We also imprinted micropatterned stamps covered by the porous alumina layer to produce multi-scale polymer surfaces consisting of a nanometric hairy layer superposed onto micrometric grooves. Water drops are suspended by the micrometric pillars and the resulting adhesion is intermediate between that on flat and on hairy surfaces. Finally, for nanoimprint with extremely deep AAO pores we saw a complete inversion of drop stickiness to the PP surface: long, collapsed hairs assembled a secondary micrometer scale network exhibiting non-stick hydrophobic wetting properties superior even to the hairy micro-patterned surface. This results in a robust technique to tailor the wetting behavior of polymeric surfaces.
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Magnetic beads (or particles) having a size between 1 and 5 µm are largely used in many biochemical assays devoted to both purification and quantification of cells, nucleic acids, or proteins. Unfortunately, the use of these beads within... more
Magnetic beads (or particles) having a size between 1 and 5 µm are largely used in many biochemical assays devoted to both purification and quantification of cells, nucleic acids, or proteins. Unfortunately, the use of these beads within microfluidic devices suffers from natural precipitation because of their size and density. The strategies applied thus far to cells or polymeric particles cannot be extended to magnetic beads, mainly due to their magnetization and their higher densities. We report an effective shaking device capable of preventing the sedimentation of beads that are stored in a custom PCR tube. After the characterization of the operating principle, the device is validated for magnetic beads in droplets, leading to an equal distribution between the droplets, barely affecting their generation.
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Droplet microfluidics is widespread in many chemical and biological applications where each droplet can be considered as a single, independent reactor unaffected by the presence of channel walls. This compartmentalization is facilitated... more
Droplet microfluidics is widespread in many chemical and biological applications where each droplet can be considered as a single, independent reactor unaffected by the presence of channel walls. This compartmentalization is facilitated by the addition of surfactants to increase the emulsion stability. However, the presence of surfactants is expected to strongly affect the dynamics and shape of flowing droplets. We report a systematic experimental study of the curvature of the front and the rear menisci of confined droplets flowing in a circular channel, with and without surfactants. In detail, the role played by surfactants on the droplet shape is investigated by dispersing them either in the droplet or in the continuous phases. The curvatures are evaluated by varying droplet speed, interfacial tension, and surfactant concentration. The curvature of the droplet front is found to scale with the capillary number (Ca) regardless of the presence or absence of surfactants. Differently, the curvature of the rear meniscus strongly depends on the surfactant concentration and whether surfactants are dispersed in the droplet or continuous phases. The surfactant accumulation at concentrations higher than the critical micelle concentration leads to an unexpected increase in the curvature in the former case and to droplet breakup in the latter.
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The first Principle defines, for every system, a property named energy which is a conserved quantity and this means that its variations in a process, can be due only to the interaction with the external world. The latter interactions are... more
The first Principle defines, for every system, a property named energy which is a conserved quantity and this means that its variations in a process, can be due only to the interaction with the external world. The latter interactions are divided into two groups. On one side, we consider all the interactions which are described within some theoretical contexts developed up to now. We say that these are the interactions controlled by the observer. In the second group, we place all those interactions which are unknown to the observer or which are treated as such. The cumulative effect of these unknown interactions gives rise to one term which is currently called quantity of heat. After having defined the meaning of adiabatic transformation, experimental evidence shows that in the latter case the amount of work delivered by the interactions controlled by the observer in a change of state depends only on the initial and final states and does not depend on the transformation used. This defines energy and, as a consequence, the contribution of the unknown interactions in a generic transformation, that is the amount of heat, is defined by the difference between the variation of energy and the amount of work carried out in that transformation. All this needs to be formulated for closed (with respect to mass) systems.
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We study the dynamic behaviour of concentrated colloidal hard spheres using Time Resolved Correlation, a light scattering technique that can detect the slow evolution of the dynamics in out-of-equilibrium systems. Surprisingly,... more
We study the dynamic behaviour of concentrated colloidal hard spheres using Time Resolved Correlation, a light scattering technique that can detect the slow evolution of the dynamics in out-of-equilibrium systems. Surprisingly, equilibrium is reached a very long time after sample initialization, the non-stationary regime lasting up to three orders of magnitude more than the relaxation time of the system. Before reaching equilibrium, the system displays unusual aging behaviour. The intermediate scattering function decays faster than exponentially and its relaxation time evolves non-monotonically with sample age.
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The sliding of non-Newtonian drops down planar surfaces results in a complex, entangled balance between interfacial forces and non linear viscous dissipation, which has been scarcely inspected. In particular, a detailed understanding of... more
The sliding of non-Newtonian drops down planar surfaces results in a complex, entangled balance between interfacial forces and non linear viscous dissipation, which has been scarcely inspected. In particular, a detailed understanding of the role played by the polymer flexibility and the resulting elasticity of the polymer solution is still lacking. To this aim, we have considered polyacrylamide (PAA) solutions of different molecular weights, suspended either in water or glycerol/water mixtures. In contrast to drops with stiff polymers, drops with flexible polymers exhibit a remarkable elongation in steady sliding. This difference is most likely attributed to different viscous bending as a consequence of different shear thinning. Moreover, an "optimal elasticity" of the polymer seems to be required for this drop elongation to be visible. We have complemented experimental results with numerical simulations of a viscoelastic FENE-P drop. This has been a decisive step to unrav...
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The actuation of droplets on a surface is extremely relevant for microfluidic applications. In recent years, various methodologies have been used. A promising solution relies on iron-doped lithium niobate crystals that, when illuminated,... more
The actuation of droplets on a surface is extremely relevant for microfluidic applications. In recent years, various methodologies have been used. A promising solution relies on iron-doped lithium niobate crystals that, when illuminated, generate an evanescent electric field in the surrounding space due to the photovoltaic effect. This field can be successfully exploited to control the motion of water droplets. Here, we present an experimental method to determine the attractive force exerted by the evanescent field. It consists of the analysis of the elongation of a pendant droplet and its detachment from the suspending syringe needle, caused by the illumination of an iron-doped lithium niobate crystal. We show that this interaction resembles that obtained by applying a voltage between the needle and a metallic substrate, and a quantitative investigation of these two types of actuation yields similar results. Pendant droplet tensiometry is then demonstrated to offer a simple solutio...
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We use dynamic light scattering and numerical simulations to study the approach to equilibrium and the equilibrium dynamics of systems of colloidal hard spheres over a broad range of density, from dilute systems up to very concentrated... more
We use dynamic light scattering and numerical simulations to study the approach to equilibrium and the equilibrium dynamics of systems of colloidal hard spheres over a broad range of density, from dilute systems up to very concentrated suspensions undergoing glassy dynamics. We discuss several experimental issues (sedimentation, thermal control, non-equilibrium aging effects, dynamic heterogeneity) arising when very large relaxation times are measured. When analyzed over more than seven decades in time, we find that the equilibrium relaxation time, tau_alpha, of our system is described by the algebraic divergence predicted by mode-coupling theory over a window of about three decades. At higher density, tau_alpha increases exponentially with distance to a critical volume fraction phi_0 which is much larger than the mode-coupling singularity. This is reminiscent of the behavior of molecular glass-formers in the activated regime. We compare these results to previous work, carefully dis...
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We perform a joint numerical and experimental study to sistematically characterize the motion of drops sliding over a periodic array of alternating hydrophobic and hydrophilic stripes with large wettability contrast, and typical width of... more
We perform a joint numerical and experimental study to sistematically characterize the motion of drops sliding over a periodic array of alternating hydrophobic and hydrophilic stripes with large wettability contrast, and typical width of hundreds of μm. The fraction of the hydrophobic stripes has been varied from about 20 patterning can be described by a renormalized value of the critical Bond number, i.e. the critical dimensionless force needed to depin the drop before it starts to move. Close to the critical Bond number we observe a jerkily motion characterized by an evident stick-slip dynamics. As a result, dissipation is strongly localized in time, and the mean velocity of the drops can easily decrease by an order of magnitude compared to the sliding on homogeneous surface. Lattice Boltzmann (LB) numerical simulations are crucial for disclosing to what extent the sliding dynamics can be deduced from the computed balance of capillary, viscous and body forces at varying the Bond n...
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The introduction of slippery lubricated surfaces allows the investigation of the flow of highly viscous solutions which otherwise will hardly move on standard solid surfaces. Here we present the study of the gravity induced motion of... more
The introduction of slippery lubricated surfaces allows the investigation of the flow of highly viscous solutions which otherwise will hardly move on standard solid surfaces. Here we present the study of the gravity induced motion of small viscoelastic drops deposited on inclined lubricated surfaces. The viscoelastic fluids exhibit shear thinning and, more importantly, a significant first normal stress difference N1. Despite the homogeneity of the surface and of the fluids, drops of sufficiently high N1 move down with an oscillating instantaneous speed whose frequency is found to be directly proportional to the average speed and inversely to the drop volume. The oscillatory motion is caused by the formation of a bulge at the drop rear that starts rolling around the moving drop.
The first Principle defines, for every system, a property named energy which is a conserved quantity and this means that its variations in a process, can be due only to the interaction with the external world. The latter interactions are... more
The first Principle defines, for every system, a property named energy which is a conserved quantity and this means that its variations in a process, can be due only to the interaction with the external world. The latter interactions are divided into two groups. On one side, we consider all the interactions which are described within some theoretical contexts developed up to now. We say that these are the interactions controlled by the observer. In the second group, we place all those interactions which are unknown to the observer or which are treated as such. The cumulative effect of these unknown interactions gives rise to one term which is currently called quantity of heat. After having defined the meaning of adiabatic transformation, experimental evidence shows that in the latter case the amount of work delivered by the interactions controlled by the observer in a change of state depends only on the initial and final states and does not depend on the transformation used. This de...
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This chapter deals with the general properties of gases starting from their isothermal behavior and the definition of the virial coefficients. The Joule–Thomson experiment (throttling experiment) is discussed together with the subsequent... more
This chapter deals with the general properties of gases starting from their isothermal behavior and the definition of the virial coefficients. The Joule–Thomson experiment (throttling experiment) is discussed together with the subsequent calorimetric measurements which prove the proportionality of the first virial coefficient to the absolute temperature T. The latter fact allows us to have a further tool for defining the absolute scale once an arbitrary value for T at one reference state is chosen. The Joule–Thomson coefficient and the inversion curve are defined and the problem of gases liquefaction is shortly outlined. The expression of the chemical potential for dilute gases is also shown. The heat capacities of gases are widely discussed starting from the theorem of energy equipartition.
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Within the approximation of discontinuous systems, the entropy production is calculated in a variety of nonequilibrium situations in open/closed systems and for chemical and electrochemical reactions. The definition of generalized fluxes... more
Within the approximation of discontinuous systems, the entropy production is calculated in a variety of nonequilibrium situations in open/closed systems and for chemical and electrochemical reactions. The definition of generalized fluxes and forces is widely discussed. The dependence of fluxes on forces is explored and for near to equilibrium configurations this dependence is linearized. The linearization leads to the Onsager relations which give the quantitative characterization of the cross-interference of different irreversible processes. The non-unique determination of the fluxes and of the relative forces is widely discussed and the limits of validity for the linear relations between fluxes and forces are examined with particular reference to chemical reactions.
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The Onsager symmetry relations are applied to the study of electrokinetic effects and of thermomechanical effects. In the latter case the relation between thermomolecular pressure difference and the heat of transfer is calculated, for... more
The Onsager symmetry relations are applied to the study of electrokinetic effects and of thermomechanical effects. In the latter case the relation between thermomolecular pressure difference and the heat of transfer is calculated, for comparison, also for Knudsen gases in a classical kinetic model. The characterization of stationary states as states of minimum entropy production are studied. The determination of stationary states, their stability and the principles of Le Chatelier and of Le Chatelier–Braun, find their correct explanation within the context of the thermodynamical theory of stationary states. The model by Prigogine and Waime is presented as an example. Within the theory of fluctuations in an isolated thermodynamical system, the decay of fluctuations are treated with the formalism of linear irreversible processes and the symmetry properties of the linear phenomenological matrix is derived from the postulate of time reversal symmetry for microscopic physics.
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The extension of the fundamental equations of Thermodynamics to a description of macroscopic systems in terms of continuous state variables is developed. All the basic relations as mass conservation in the presence of chemical reactions,... more
The extension of the fundamental equations of Thermodynamics to a description of macroscopic systems in terms of continuous state variables is developed. All the basic relations as mass conservation in the presence of chemical reactions, the equation of motion and the equations for energy and that for entropy which express, in the new formalism, the First and the Second Principles, respectively, must be reformulated. The correct expression for the entropy production and the consequent expressions for the fluxes and the corresponding generalized forces are obtained. In the linear regime, the general relation between the mobility of ionic species and the coefficient of diffusion (Einstein relation) is demonstrated. The thermoelectric phenomena (Seebeck, Peltier, and Thomson effects) are discussed together with the thermodiffusion processes. An appendix concerning the Gibbs–Duhem relation closes the Chapter.
The definitions of the macroscopic system and of empirical temperature are discussed. At the first step of the theory, a definition of the state of equilibrium must be given for isolated systems and the definition of mutual equilibrium... more
The definitions of the macroscopic system and of empirical temperature are discussed. At the first step of the theory, a definition of the state of equilibrium must be given for isolated systems and the definition of mutual equilibrium between closed systems put in contact comes as a consequence. The property of being in mutual equilibrium is, by definition, denoted by saying that the two systems have the same temperature. Empirical observation shows that the property of having the same temperature, i.e., of being in mutual equilibrium, is transitive and this statement is assumed to be true in general. This is the content of the Zeroth Principle of Thermodynamics, and it is the necessary postulation which allows us to define the concept of empirical temperature as a physical quantity.