In thermodynamics a quasistatic process is a process that happens infinitely slowly. In practice, such processes can be approximated by performing them "very slowly".
A quasistatic process often ensures that the system will go through a sequence of states that are infinitesimally close to equilibrium, in which case the process is typically reversible. An example of a quasistatic process that is not reversible is the slow heat exchange between two bodies at two finitely different temperatures, where the heat exchange rate is controlled by an approximately adiabatic partition between the two bodies (Sears and Salinger, 1986) — in this case, no matter how slowly the process takes place, the states of the two bodies are never infinitesimally close to equilibrium, since thermal equilibrium requires that the two bodies be at precisely the same temperature.
Some ambiguity exists in the literature concerning the distinction between quasistatic and reversible processes, as these are sometimes taken as synonyms (Lavenda, 1978). The above definition is closer to the intuitive understanding of the word "quasi-" (almost) "static", while remaining technically different from reversible processes.
A process is called quasi-static when it follows a succession of equilibrium states; the surroundings may be irreversibly altered during the process so that after a return path, the system ends up in a final state which differs from its initial state.
In a quasistaticprocess, or equilibrium process, a sufficiently slow transition of a thermodynamic system from one equilibrium state to another occurs such that at every moment in time the state of the system is close to an equilibrium state.
A quasistaticprocess is not necessarily a reversible one.
Process is relatively slow, and the inertial effects of fluid flow and polymer network are negligible.
Process is solvent diffusion-limited into the gel network, and the effects of surrounding fluid convection is negligible.
The process from state 1 to state 2 is therefore entropy generating run-down mixing process, and the changes in thermodynamic properties of control volume due to such mixing process are described by Flory.
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