Ice Nucleation of Confined Monolayer Water Conforms to Classical Nucleation Theory

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Dynamic Observation of Anisotropic Chainlike Structures during Nonclassical Two-Step Nucleation in Solid-State Iron Oxide Crystallization

The demonstration of the self-crystallization nucleation process from an amorphous precursor in a solid is crucial for understanding of interactions between atoms. We report a study of dynamic crystallization process of iron oxides by virtue of in situ measurement of transmission electron microscopy. At first, semiordered chainlike structures are observed with the increase of concentration, and when sufficient chains form, the crystalline lattice begins to grow. The two-step nucleation pathway has also been confirmed by performing a molecular dynamics simulation, where Lennard-Jones and magnetic dipole-dipole interaction potentials are both taken into account and take effect individually predominantly in different ranges of distance between atoms. Furthermore, the total free energy profile in the crystallization nucleation process is calculated to evidence the stabilization of intermediate state. This work advances our understanding of nonclassical nucleation theory.

Liquid-Liquid Phase Separation in Nucleation Process of Biomineralization

Biomineralization is a typical interdisciplinary subject attracting biologists, chemists, and geologists to figure out its potential mechanism. A mounting number of studies have revealed that the classical nucleation theory is not suitable for all nucleation process of biominerals, and phase-separated structures such as polymer-induced liquid precursors (PILPs) play essential roles in the non-classical nucleation processes. These structures are able to play diverse roles biologically or pathologically, and could also give inspiring clues to bionic applications. However, a lot of confusion and dispute occurred due to the intricacy and interdisciplinary nature of liquid precursors. Researchers in different fields may have different opinions because the terminology and current state of understanding is not common knowledge. As a result, our team reviewed the most recent articles focusing on the nucleation processes of various biominerals to clarify the state-of-the-art understanding of some essential concepts and guide the newcomers to enter this intricate but charming field.

Two-dimensional monolayer salt nanostructures can spontaneously aggregate rather than dissolve in dilute aqueous solutions

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

Aqueous solutions under nanoscale confinement exhibit interesting physicochemical properties. This work reports evidence on the spontaneous formation of two-dimensional alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement by computer simulations.

Effect of the Janus Amphiphilic Wall on the Viscosity Behavior of Aqueous Surfactant Solutions

The effects of the chemical nature of an interface are one of the key parameters which can affect self-assembly and rheological behavior. To date, several studies have reported self-assembled structures and rheological behaviors in the development of various functional materials. In this study, we investigated the self-assembly and viscosity behavior of aqueous surfactant solutions confined in three types of Janus amphiphilic nanotubes (JANTs), which have two, four, and eight sequential domains, respectively, using molecular simulation. We found that the viscosity behavior depends on the surfactant concentration and the chemical nature of the wall surface. For instance, although the concentration levels of the surfactants are the same (c = 10%), completely different viscosity behaviors were observed in the two sequential domains (Newtonian-like) and the four and eight sequential domains (strong shear-thinning) of the JANTs. Our simulations demonstrated how the rheological properties of aqueous surfactant solutions, including viscosity and velocity profiles, can be controlled by the chemical nature of the JANT wall surface, effect of confinement, and their self-assembly structures. Considering the foregoing, we hope that our study offers new knowledge on nanofluid systems.

Computational Prediction of Novel Ice Phases: A Perspective

Although computational prediction of new ice phases is a niche field in water science, the scientific subject itself is representative of two important areas in physical chemistry, namely, statistical thermodynamics and molecular simulations. The prediction of a variety of novel ice phases has also attracted general public interest since the 1980s. In particular, the prediction of low-dimensional ice phases has gained momentum since the confirmation of a number of low-dimensional "computer ice" phases in the laboratory over the past decade. In this Perspective, the research advancements in computational prediction of novel ice phases over the past few years are reviewed. Particular attention is placed on new ice phases whose physical properties or dimensional structures are distinctly different from conventional bulk ices. Specific topics include the (i) formation of superionic ices, (ii) electrofreezing of water under high pressure and in a high external electric field, (iii) prediction of low-density porous ice at strongly negative pressure, (iv) ab initio computational study of two-dimensional (2D) ice under nanoscale confinement, and (v) 2D ices formed on a solid surface near ambient temperature without nanoscale confinement. Clearly, the formation of most of these novel ice phases demands certain extreme conditions. Ongoing challenges and new opportunities for predicting new ice phases from either classical molecular dynamics simulation or high-level ab initio computation are discussed.

Electric Field Induced Dewetting of Hydrophobic Nanocavities at Ambient Temperature

The understanding of water dewetting in nanoporous materials is of great importance in various fields of science and technology. Herein, we report molecular dynamics simulation results of dewetting of water droplet in hydrophobic nanocavities between graphene walls under the influence of electric field. At ambient temperature, the rate of dewetting induced by electric field is significantly large. Whereas, it is a very low rate of dewetting induced by high temperature (423 K) due to the strong interaction of the hydrogen-bonding networks of water droplets in nanocavities. In addition, the electric filed induced formation of a water column has been found in a vacuum chamber. When the electric field is turned off, the water column will transform into a water droplet. Importantly, the results demonstrate that the rate of electric field-induced dewetting increases with growth of the electric field. Overall, our results suggest that electric field may have a great potential application for nanomaterial dewetting.