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Self-Assembling Protein Nanomaterials – Design, Production and Characterization
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Bhuvana K. Shanbhag, Victoria S. Haritos, Lizhong He
On the other hand, the addition of an external stimulus can trigger a quicker and spontaneous self-assembly by providing the required driving force. From a fundamental point of view, the free energy of a spontaneous process is negative, and for this, the enthalpy must be negative and exceed the entropy term (O’Mahony et al., 2011). Therefore, in a self-assembly system, external stimuli such as pH and salt can increase the enthalpy of the system through electrostatic screening or salting in/out effects to favor intermolecular interactions between monomeric units (Mason et al., 2017). As a result, the external stimuli reduce the energy barrier leading to spontaneous or faster self-assembly process. A detailed review on the self-assembly mechanism has been reported by Löwik et al. (2010); examples of stimuli and their mechanisms are summarized in Table 16.1. Depending on the type of interactions involved, the assembly process may be reversible or irreversible. For example, the P11 peptide family is based on non-covalent interactions and can be switched between monomeric and assembled state by a change of pH. On the contrary, application of enzymatic stimulus in the form of peptide bond cleavage is a permanent change and thus irreversible.
Phase Transition and Thermodynamic Diagrams
Published in John Newman, Vincent Battaglia, The Newman Lectures on Thermodynamics, 2019
John Newman, Vincent Battaglia
The condition for a spontaneous process is that the entropy change of the universe be positive: () ΔSuniverse>0.
Thermodynamic Fundamentals
Published in Roger T. Haug, of Compost Engineering, 2018
In any spontaneous process, whether endothermic or exothermic, the entropy must increase and the free energy decrease. Final realization of this concept was one of the crowning achievements of 19th century thermodynamics.
Alteration mechanisms of carbonated steel slag product under hydrochloric acid attack
Published in Journal of Sustainable Cement-Based Materials, 2021
Yangyang Gu, Yangyang Zhang, Jun Chang, Tingting Zhang, Caijun Shi
Table 4 listed the standard molar thermodynamic parameters of phases at 25 °C including the Gibbs free energy change Δf Go, the enthalpy change Δf Ho and the entropy S° used in this study. The negative or positive value of ΔHo represents a process is an exothermic or endothermic reaction respectively. ΔGo is a key parameter to establish the spontaneity degree of a process. If the characteristic of a process is to reduce the total free energy of the system (ΔGo<0), it is categorized into a spontaneous process, which means at a specified temperature the reaction happens favorably and spontaneously. On the contrary, the process is defined as infeasible and non-spontaneous if ΔGo>0. Thus, the two parameters can be used to analyze the reactions of constituents in the specimen with acid from the thermodynamic aspect.
A hydrophobic bio-adsorbent synthesized by nanoparticle-modified graphene oxide coated corn straw pith for dye adsorption and photocatalytic degradation
Published in Environmental Technology, 2020
Juan Chen, Shanshan Liu, Heyi Ge, Yu Zou
To deeply study the adsorption characteristic of CSP-5GO-TiO2, several thermodynamic parameters were calculated from adsorption isotherms at three different temperatures. The standard free energy change (ΔG) is the main criterion for a spontaneous process. This value can be expressed by the following equation:where R is the universal gas constant (8.314 J mol−1 k−1), T is the absolute temperature (K). K is the sorption equilibrium constant related to temperatures, which is calculated by the intercept of the line of ln (qe/Ce) vs. qe (Fig. S8a). The standard enthalpy change (ΔH) and the standard entropy change (ΔS) are calculated from the following equation: and are the slope and intercept of line of ln K vs. (Fig. S8b). The values of The ΔG, ΔH and ΔS are listed in Table 2. The ΔG values are −0.038, −0.027 and −0.026 kJ/mol according to 298, 318 and 338 K, respectively, which indicates that the removal MB procedure was a spontaneous reaction. The ΔH and ΔS values are −0.127 kJ/mol and −0.304 Jmol−1 K−1, respectively. The results indicate that the adsorption was an exothermic and randomness decrease process.