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Thermodynamics memory effect

Zwanzig R 1961 Memory effects in irreversible thermodynamics Phys. Rev. 124 983... [Pg.715]

The fact that mbber shows mbber elasticity was discovered more than 100 years earlier than professor H. Staudinger s proposal. The memory effect acquired by vulcanization, so-called Gough-Joule effect, and its thermodynamic explanation were the great achievements in the nineteenth century. As seen in many textbooks, this thermodynamic approach was the easiest one to gain consistency between ever-performed experiments and theory. In fact, thermodynamics of mbbery material can be treated in parallel with thermodynamics of gas. One could show experimentally that... [Pg.580]

Just above the melting point the polymer is visually quite viscous and numerous observations have been made that the polymer exhibits a memory effect, that is to say, on recooling the melt crystallites will appear in the same sites where they had been before melting the polymer. Hartley, Lord and Morgan (1954) state It is reasonable to suppose that there will be a few localities in the crystalline polymer which have a very high degree of crystalline order, and therefore the melt can contain, even at considerable temperatures above the observed melting or collapse point, thermodynamically stable minute crystals of the polymer . Especially if the polymer has been irradiated so as to contain a few crosslinks as in irradiated polyethylene, then flow is inhibited and spherulites can be made to appear on recrystallization in the same sites that they had before the polymer was melted, Hammer, Brandt and Peticolas (1957). However, as mentioned above, the specific heat of irradiated polyethylene in the liquid state is identical with that of the unirradiated material, within the limits of experimental error. Dole and Howard (1957). [Pg.261]

Zimm BH (1956) Dynamics of polymer molecules in dilute solution viscoelasticity, flow birefringence and dielectric loss. J Chem Phys 24 269-278 Zwanzig R (1961) Memory effects in irreversible thermodynamics. Phys Rev 124(4) 983-992... [Pg.252]

While enzymes, as a rule, essentially lose their normal activity and specificity, they possess new useful features 1) utilization of substrates non-soluble in water 2) their ability to change substrate and inhibitor selectivity and specificity 3) they alternate of reactions thermodynamics and kinetics reactions so that desirable products are favoured 4) improvements of enzyme stability and 5) the possibility to fix enzymes and reaction intermediates at states of certain pH and ionic strength in both solution and crystal form ( molecular memory effects ). [Pg.166]

One must note that the balance equations are not dependent on either the type of material or the type of action the material undergoes. In fact, the balance equations are consequences of the laws of conservation of both linear and angular momenta and, eventually, of the first law of thermodynamics. In contrast, the constitutive equations are intrinsic to the material. As will be shown later, the incorporation of memory effects into constitutive equations either through the superposition principle of Boltzmann, in differential form, or by means of viscoelastic models based on the Kelvin-Voigt or Maxwell models, causes solution of viscoelastic problems to be more complex than the solution of problems in the purely elastic case. Nevertheless, in many situations it is possible to convert the viscoelastic problem into an elastic one through the employment of Laplace transforms. This type of strategy is accomplished by means of the correspondence principle. [Pg.697]

The inhibition effects of type-III AFP and trehalose, two cryoprotecting materials produced in animals, on type-I CO2 clathrate-hydrates were examined. For comparison with the results of a previous study in which the lateral growth rates of COi-hydrate film were dependent on temperature, pressure and NaCl concentration, the solution droplet was observed in a high pressure vessel filled with CO2. Type-III AFP was found to increase the induction period and to reduce the lateral growth rate of C02-hydrate films. It worked well at low concentrations, indicating that AFP works as a kinetic inhibitor. It was also indicated that AFP would weaken the memory effect of C02-hydrate formation. Trehalose had similar inhibition effects on both the induction period and the lateral growth rate, but it had little apparent concentration-dependence on them. Since trehalose also causes the equilibrium conditions of the CO2 hydrate to shift to lower temperatures, it works not only as a thermodynamic inhibitor but also as a kinetic inhibitor, especially as an anti-agglomerant. [Pg.617]

The present chapter is organized in three sections the first section is devoted to basic theoretical backgroimd concerning the spin-crossover phenomenon, viz ligand field theory, thermodynamics and cooperativity the second section reports on some examples that we feel are particularly relevant to illustrate the main directions in which research on synthetic aspects of cooperativity is being directed finally, the third section describes three approaches, up to now reported, concerning spin bistability in supramolecular and molecular systems and memory effect. [Pg.54]

There is a lot to explain here. It looks very odd that syn-66 is preferred and even more so that alkylation of the enolate 67 occurs on the same face as the undoubtedly large /-butyl group. Both these issues matter as the original chiral centre in proline is destroyed in 67 and only the newly introduced chiral centre in 66 retains the stereochemical information from proline. This centre acts as a relay for the stereochemical information. Others call this a memory effect. The acid-catalysed formation of the N, O-acetal 66 is under thermodynamic control (acetal formation is reversible) and the conformation 66a shows that the molecule folds about the necessarily cis ring junction and the /-butyl group prefers to be on the outside (or exo- face).8 The enolate 67 has a flattened conformation 67a (probably more flattened than this ) and its alkylation is under kinetic control. Attack is preferred on the outside, exo-face. Note that this happens to restore the original configuration at the ex-proline chiral centre. [Pg.606]

It reveals the structural feature of the non-stoichiometric phase and the memory effect of the a-phase in the thermodynamic data [52, 53]. In these electron diffraction patterns the strong diffraction spots of the (110) and (112) orientations correspond to the fluorite structure. From a to e and f to j the diffraction patterns show that ... [Pg.81]

In thermodynamic parameters, the thermal-responsive shape memory effect can be explained by the fact that at a temperature higher than the shape transition temperature (Ttrans). thc blcud material tanporarily changes its shape when cooling below the Ttrans) thc material retains the deformed shape and it can return to the initial nonde-formed shape by reheating at more than... [Pg.92]

The situation that we have just described is known as bistability. The solid lines in Figure 2.6 indicate stable branches, while the dashed line is an unstable branch of steady states. In a flow system, the lower branch is called the equilibrium or thermodynamic branch, because it extends from the thermodynamic equilibrium point at zero flow rate. The upper or flow branch is so named because it can be accessed from high flow rate. Typically, the composition of steady states on the equilibrium branch resembles that of the products, while states on the flow branch look more like the reactants in the input flow. Obviously, in the limits of zero or infinite flow, we obtain the compositions of the equilibrium state and the pure reactants, respectively. The arrows in Figure 2.6b indicate the direction that the system will take when the flow rate reaches a particular value. Notice that the system remembers its history. Which state the system resides in depends on where it came from—that is, low or high flow rate. This memory effect, associated with the switching between branches of states in a bistable system, is known as hysteresis. [Pg.33]

The model of the shape memory effect is based on thermodynamic laws of phase transitions in solids. Due to inner friction and losses of the phase transformation, the simulation of the hysteresis by means of the Preisach-model [83] must be modified and linked with the thermodynamic equations. [Pg.156]

This introductory text assumes no familiarity with thermodynamics. For this reason we have excluded a number of interesting problems often associated with extended thermodynamics. Interested readers are invited to consult more specialized texts in the bibliographies. These are the questions which deal with strong gradients or with very long timescales when memory effects have to be... [Pg.500]

Within the frameworks of this formalism to account for consistently nonlinear phenomenon complex nature is a success, such as memory effects and spatial correlations. In addition the earlier known solutions are not only reproduced, but their nontrivial generalization is given. Another important feature is connected with fractal structures self-similarity using. Unlike the traditional methods of system description on the basis of averaging different procedures, when microscopic level erasing occurs, in fractal conception medium self-affine structure and thus within the frameworks of this conception system micro and macroscopic description levels are united. Exactly such method is important for complex multicomponent systems, discovered far from thermodynamic equilibrium state [35], which are polymers [12], The authors of Refs. [31, 32] are attempted two indicated trends combination. [Pg.278]


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