Unraveling Dynamic Transitions in Time-Resolved Biomolecular Motions by A Dressed Diffusion Model

Traversing the nucleation-growth landscape through heterogeneous random walks

The nucleation-growth process is a crucial component of crystallization. While previous theoretical models have focused on nucleation events and postnucleation growth, such as the classical nucleation theory and Lifshitz-Slyozov-Wagner model, recent advancements in experiments and simulations have highlighted the inability of classical models to explain the transient dynamics during the early development of nanocrystals. To address these shortcomings, we present a model that describes the nucleation-growth dynamics of individual nanocrystals as a series of reversible chain reactions, with the free energy landscape extended to include activation-adsorption-relaxation reaction pathways. By using the Monte Carlo method based on the transition state theory, we simulate the crystallization dynamics. We derive a Fokker-Planck formalism from the master equation to describe the nucleation-growth process as a heterogeneous random walk on the extended free energy landscape with activated states. Our results reveal the transient quasiequilibrium of the prenucleation stage before nucleation starts, and we identify a postnucleation crossover regime where the dynamic growth exponents asymptotically converge towards classical limits. Additionally, we generalize the power laws to address the dimension and scale effects for the growth of large crystals.

The selective heating effect of microwave irradiation on a binary mixture of water and polyethylene oxide: a molecular dynamics simulation approach

In this study, we investigate the molecular mechanisms of a microwave-driven selective heating process by performing molecular dynamics simulations for three different systems including pure water, pure polyethylene oxide (PEO), and water-PEO mixed systems in the presence of a microwave with two different intensities of electric field such as 0.001 V Å^-1 and 0.01 V Å^-1 at a frequency of 100 GHz. First, from performing molecular dynamics simulations of CO and CO₂ in the presence of the microwave, it is confirmed that the molecular dipole moment is responsible for the rotational motion induced by the oscillating electric field. Second, by analyzing the MD simulations of the pure water system, we discover that the dipole moment of water exhibits a time lag with respect to the microwave. During the heating process, however, the temperature, kinetic, and potential energies increase synchronously with the oscillating electric field of the microwave, showing that the heating of the water system is caused by the molecular reaction of water to the microwave. Comparing the water-PEO mixed system to the pure water and pure PEO systems, the water-PEO mixed system has a higher heating rate than the pure PEO system but a lower heating rate than the pure water system. Therefore, we conclude that heating the water-PEO mixed system is driven by water molecules selectively activated by microwave irradiation. We also calculate the diffusion coefficients of water molecules and PEO chains by describing their mean square displacements, demonstrating that the diffusion coefficients are increased in the presence of microwaves for both water and PEO in pure and mixed systems. Lastly, during the microwave heating process, the structures of the water-PEO mixed system are altered as a function of the intensity of electric field, which is mainly driven by the response of water molecules.

Generalization of Langevin Dynamics from Spatio-Temporal Dressed Dynamics Perspective

Understanding multiscale dynamics characteristics has been the holy grail in a broad range of scientific disciplines from physics, chemistry, to biology, and beyond. The seminal Langevin equation successfully unravels remarkable details of Brownian motion dynamics involving stochastic collisions from the fluidic medium. However, extraordinary phenomena beyond the scope of Langevin dynamics were observed to exhibit a series of multiscale dynamic features in recent years. Here, an explicit spatio-temporal coupled kernel is developed to provide the microscopic account for delicate dynamic coupling between particle and medium in the dressed dynamics perspective. This methodology is applied to investigate an aqueous solvation shell model with an explicit spatial boundary to illustrate the significance of spatial and temporal coupling, leading to a general temporal profile of dressed dynamics over 12 orders of magnitude in time In particular, the time-resolved viscosity is formulated to address the remarkable enhancement of viscosity measured by the liquid cell electron microscopy. The understanding of dressed dynamics processes will be greatly enriched by further studies on the detailed dynamics that manifests the microscopic inhomogeneity of medium.