Dissertations and Theses
Date of Award
Random sequential adsorption, Gibbs Adsorption isotherm, phase transition, glassy dynamics, binary mixture, asphaltene, equation of state, ordering
The ability to predict the adsorption dynamic, phase behavior, and surface pressure of a monolayer of adsorbed particles in two-dimensional systems are key aspects of many current research areas. Examples include phase transitions in amphiphilic monolayers, emulsion stability due to particle adsorption at interfaces, and melting at an interface.
In this thesis, a new approach for deriving the equation of state for a two-dimensional lattice gas is proposed, based on arguments similar to those used in the derivation of the Langmuir-Szyszkowski equation of state for localized adsorption. This work aims to predict the adsorption kinetics and phase behavior of a system composed of many hard-core particles based on kinetic arguments and the Gibbs adsorption isotherm. To that purpose, the random sequential adsorption with a surface diffusion model is used to samples the configuration of the system at different coverage. This configuration is used to calculate the thermodynamic properties of the system where many interesting collective phenomena are observed.
The determination of phase behavior and, in particular, the nature of phase transitions in two-dimensional systems is often clouded by finite-size effects and by access to the appropriate thermodynamic regime. We address these issues using our new model. Insight into coexistence regions and phase transitions is obtained through direct visualization of the system at any fractional surface coverage via local bond orientation order. The analysis of the bond orientation correlation function for each individual configuration confirms that first-order phase transition occurs in a two-step liquid-hexatic-solid transition at high surface coverage.
The next part of this work concentrates on reversible adsorption by introducing a desorption process into our model and varying the equilibrium rate constant as a control parameter. We find that an exact prediction of the temporal evolution of fractional surface coverage and the surface pressure dynamics of reversible adsorption can be achieved by the use of the blocking function of a system with irreversible adsorption of highly mobile particles. For systems out of equilibrium, we observe several features of glassy dynamics, such as slow relaxation dynamics, the memory effect, and aging. In particular, the analysis of our system in the limit of small desorption probability shows simple aging behavior with a power-law decay. A detailed discussion of Gibbs adsorption isotherm for non-equilibrium adsorption is given, which exhibits a hysteresis between this system and its equilibrium counterpart.
The next chapter focus on the adsorption kinetics and the thermodynamic properties of a binary mixture on a square lattice are studied using the random sequential adsorption with surface diffusion (RSAD). We compare the adsorption of binary species with different equilibrium rate constants and effective rates of adsorption to a surface and find that the temporal evolution of surface coverages of both species can be obtained through the use of the blocking function of a system with irreversible adsorption of highly diffusive particles. Binary mixtures, when one of the components follows the random sequential adsorption (RSA) without surface diffusion and the other follows the RSAD model, display competitive adsorption in addition to cooperative phenomena. Specifically, (i) species replacement occurs over a long period of time, while the total coverage remains unchanged after a short time, (ii) the presence of the RSAD component shifts the jamming coverage to the higher values, and (iii) the maximum jamming coverage is obtained when the effective adsorption of the RSA type components is lower than the other adsorbing particles.
Then our new approach is used to analyze the interfacial behavior of asphaltenes at the water/oil interface. RSAD method reveals the phase transition of asphaltenes at the interface from disordered to ordered phase at high coverage due to the steric hindrance effect. This ordered phase is consistent with the observation of birefringence within asphaltenes laden interfaces upon contracting the aged droplet. Corresponding surface pressure obtained from this model is equal to the surface pressure that a droplet containing asphaltenes solution loses its Laplacian shape over the contraction experiment. Another outcome of this model is the observation of dynamic frustration within the dense interfacial layers due to the fast increase of surface coverage in comparison with interfacial diffusion either during spontaneous adsorption or during interfacial area reduction. As a result, the interfacial layer could enter into a metastable glass state that would slowly relax towards a crystalline state with time.
Finally, we investigated the phase behavior of particles adsorbed at the liquid/vapor interface using molecular dynamic simulations (MD). The results obtained from these simulations provide complementary insight about the orientation of particles at the interface and the formation of micelles in a real experiment such as pendant drop and Langmuir trough.
Darjani, Shaghayegh, "Adsorption Kinetics and Phase Behavior of Particles Adsorbed at an Interface" (2021). CUNY Academic Works.