Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics

Predicting Polymer Brush Behavior in Solvents Using the Steepest-Entropy-Ascent Quantum Thermodynamic Framework

The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is utilized to study the effects of temperature on polymer brushes. The brushes are represented by a discrete energy spectrum, and energy degeneracies obtained through the replica-exchange Wang-Landau algorithm. The SEAQT equation of motion is applied to the density of states to establish a unique kinetic path from an initial thermodynamic state to a stable equilibrium state. The kinetic path describes the brush's evolution in state space, as it interacts with a thermal reservoir. The predicted occupation probabilities along the kinetic path are used to determine the expected thermodynamic and structural properties. The polymer density profile of a polystyrene brush in cyclohexane solvent is predicted using the equation of motion, and it agrees qualitatively with the experimental density profiles. The Flory-Huggins parameter chosen to describe brush-solvent interactions affects the solvent distribution in the brush but has a minimal impact on the polymer density profile. Three types of nonequilibrium kinetic paths with differing amounts of entropy production are considered: a heating path, a cooling path, and a heating-cooling path. Properties such as tortuosity, radius of gyration, brush density, solvent density, and brush chain conformations are calculated for each path.

Predicting non-equilibrium folding behavior of polymer chains using the steepest-entropy-ascent quantum thermodynamic framework

The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is used to explore the influence of heating and cooling on polymer chain folding kinetics. The framework predicts how a chain moves from an initial non-equilibrium state to stable equilibrium along a unique thermodynamic path. The thermodynamic state is expressed by occupation probabilities corresponding to the levels of a discrete energy landscape. The landscape is generated using the Replica Exchange Wang-Landau method applied to a polymer chain represented by a sequence of hydrophobic and polar monomers with a simple hydrophobic-polar amino acid model. The chain conformation evolves as energy shifts among the levels of the energy landscape according to the principle of steepest entropy ascent. This principle is implemented via the SEAQT equation of motion. The SEAQT framework has the benefit of providing insight into structural properties under non-equilibrium conditions. Chain conformations during heating and cooling change continuously without sharp transitions in morphology. The changes are more drastic along non-equilibrium paths than along quasi-equilibrium paths. The SEAQT-predicted kinetics are fitted to rates associated with the experimental intensity profiles of cytochrome c protein folding with Rouse dynamics.

Time-Energy and Time-Entropy Uncertainty Relations in Nonequilibrium Quantum Thermodynamics under Steepest-Entropy-Ascent Nonlinear Master Equations

In the domain of nondissipative unitary Hamiltonian dynamics, the well-known Mandelstam–Tamm–Messiah time–energy uncertainty relation τFΔH≥ℏ/2 provides a general lower bound to the characteristic time τF=ΔF/|d〈F〉/dt| with which the mean value of a generic quantum observable F can change with respect to the width ΔF of its uncertainty distribution (square root of F fluctuations). A useful practical consequence is that in unitary dynamics the states with longer lifetimes are those with smaller energy uncertainty ΔH (square root of energy fluctuations). Here we show that when unitary evolution is complemented with a steepest-entropy-ascent model of dissipation, the resulting nonlinear master equation entails that these lower bounds get modified and depend also on the entropy uncertainty ΔS (square root of entropy fluctuations). For example, we obtain the time–energy-and–time–entropy uncertainty relation (2τFΔH/ℏ)2+(τFΔS/kBτ)2≥1 where τ is a characteristic dissipation time functional that for each given state defines the strength of the nonunitary, steepest-entropy-ascent part of the assumed master equation. For purely dissipative dynamics this reduces to the time–entropy uncertainty relation τFΔS≥kBτ, meaning that the nonequilibrium dissipative states with longer lifetime are those with smaller entropy uncertainty ΔS.

CH₄ Adsorption Probability on GaN(0001) and (000-1) during Metalorganic Vapor Phase Epitaxy and Its Relationship to Carbon Contamination in the Films

Suppression of carbon contamination in GaN films grown using metalorganic vapor phase epitaxy (MOVPE) is a crucial issue in its application to high power and high frequency electronic devices. To know how to reduce the C concentration in the films, a sequential analysis based on first principles calculations is performed. Thus, surface reconstruction and the adsorption of the CH₄ produced by the decomposition of the Ga source, Ga(CH₃)₃, and its incorporation into the GaN sub-surface layers are investigated. In this sequential analysis, the dataset of the adsorption probability of CH₄ on reconstructed surfaces is indispensable, as is the energy of the C impurity in the GaN sub-surface layers. The C adsorption probability is obtained based on steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic ensemble-based, non-phenomenological framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium. This framework is suitable especially when one studies the adsorption behavior of an impurity molecule because the conventional approach, the chemical potential control method, cannot be applied to a quantitative analysis for such a system. The proposed sequential model successfully explains the influence of the growth orientation, GaN(0001) and (000-1), on the incorporation of C into the film. This model can contribute to the suppression of the C contamination in GaN MOVPE.

SrFexNi1-xO3-δ Perovskites Coated on Ti Anodes and Their Electrocatalytic Properties for Cleaning Nitrogenous Wastewater

Perovskites (ABO₃), regarded as the antioxidative anode materials in electrocatalysis to clean nitrogenous wastewater, show limited oxygen vacancies and conductivity due to their traditional semiconductor characteristic. To further improve the conductivity and electrocatalytic activity, the ferrum (Fe) element was first doped into the SrNiO₃ to fabricate the SrFexNi1-xO3-δ perovskites, and their optimum fabrication conditions were determined. SrFexNi1-xO3-δ perovskites were coated on a titanium (Ti) plate to prepare the SrFexNi1-xO3-δ/Ti electrodes. Afterward, one SrFexNi1-xO3-δ/Ti anode and two stainless steel cathodes were combined to assemble the electrocatalytic reactor (ECR) for cleaning simulated nitrogenous wastewater ((NH₄)₂SO₄ solution, initial total nitrogen (TN) concentration of 150 mg L⁻¹). Additionally, SrFexNi1-xO3-δ materials were characterized using Fourier Transform Infrared (FT-IR), Raman spectra, X-Ray Diffraction (XRD), Energy Dispersive X-ray (EDX), Electrochemical Impedance Spectroscopy (EIS) and Tafel curves, respectively. The results indicate that SrFexNi1-xO3-δ materials are featured with the perovskite crystal structure and Fe is appreciably doped into SrNiO₃. Moreover, the optimum conditions for fabricating SrFexNi1-xO3-δ were the reaction time of 120 min for citrate sol-gel, a calcination temperature of 700 °C, and Fe doping content of x = 0.3. SrFe0.3Ni0.7O2.85, and perovskite performs attractive electrocatalytic activity (TN removal ratio of 91.33%) and ECR conductivity of 3.62 mS cm-¹ under an electrocatalytic time of 150 min. Therefore, SrFexNi1-xO3-δ perovskites are desirable for cleaning nitrogenous wastewater in electrocatalysis.