Controlled condensation by liquid contact-induced adaptations of molecular conformations in self-assembled monolayers.

Surface condensation control strategies are crucial but commonly require relatively tedious, time-consuming, and expensive techniques for surface-chemical and topographical engineering. Here we report a strategy to alter surface condensation behavior without resorting to any molecule-type or topographical transmutations. After ultrafast contact of liquids with and removal from surfaces, the condensation rate and density of water droplets on the surfaces decrease, the extent of which is positively correlated with the polarity of the liquid and the duration of contact. The liquid contact-induced condensation rate/density decrease (LCICD) can be attributed to the decrease of nucleation site density resulted from the liquid contact-induced adaption of surface molecular conformation. Based on this, we find that LCICD is applicable to various surfaces, on condition that there are flexible segments capable of shielding at least part of nucleation sites through changing the conformation under liquid contact induction. Leveraging the LCICD effect, we achieve erasable information storage on diverse substrates. Furthermore, our strategy holds promise for controlling condensation of other substances since LCICD is not specific to the water condensation process.

Reversible Stacking and Delamination-Regulation of MXene via Controlled Freezing.

MXene's configuration, whether it is aggregated or dispersed in a monolayer, determines the specific application areas and even greatly influences the intrinsic properties of MXene. However, how to desirably control MXene's configuration is challenging. Here, a simple, additive-free, chemical reaction-free, and scalable strategy to optionally and reversibly regulate MXene's ordered stacking and delamination of MXene aggregates (AM) is reported. Just by controlled freezing of MXene aqueous dispersions, the aggregation percentage, delamination percentage, and interlayer spacing of AM can be finely tuned. Experimental results reveal that the freezing-induced aggregation and delamination effects can be explained by the squeezing action of growing ice grains on the MXene excluded/concentrated between ice grains and the expanding action caused by the ice formation between AM lamellae, respectively. The dominance between them depends on the freezing parameter-influenced ice nucleation sites, numbers, and ice grain sizes. This work not only contributes to the preparation, storage, and practical applications of MXene, but also opens a new and green avenue for controlling materials' assembly structures.

Graphene Oxide Inhibits Calcium Carbonate Nucleation.

Formation of minerals such as calcium carbonate often causes energy consumption and even safety risk increase due to the hindrance on heat/mass transfer. However, the current antiscalants are not efficient enough because of the poor understanding of the scale inhibition mechanisms. Here, we report an ultrahigh-performance antiscalant, graphene oxide (GO), which exhibits an outstanding nucleation inhibition effect far better than the current state-of-the-art antiscalants even on a subppm dosage. Our experiments reveal that the superior nucleation inhibition effect of GO is attributed to its limiting effect on the nucleation kinetics of ions and its ability to increase the nucleation barrier of calcium carbonate by altering the normal pathway of calcium carbonate polymorph formation. Further analysis indicates that the ion-limiting effect and the polymorph control ability of GO may stem from its oxygen functional group-rich surface chemistry and two-dimensional (2D) planar features, which endow GO with a Ca2+ binding ability and additional steric hindrance for CO32- diffusion, respectively.

Probing the critical nucleus size in tetrahydrofuran clathrate hydrate formation using surface-anchored nanoparticles.

Controlling the formation of clathrate hydrates is crucial for advancing hydrate-based technologies. However, the microscopic mechanism underlying clathrate hydrate formation through nucleation remains poorly elucidated. Specifically, the critical nucleus, theorized as a pivotal step in nucleation, lacks empirical validation. Here, we report uniform nanoparticles, e.g., graphene oxide (GO) nanosheets and gold or silver nanocubes with controlled sizes, as nanoprobes to experimentally measure the size of the critical nucleus of tetrahydrofuran (THF) clathrate hydrate formation. The capability of the nanoparticles in facilitating THF clathrate hydrate nucleation displays generally an abrupt change at a nanoparticle-size-determined specific supercooling. It is revealed that the free-energy barrier shows an abrupt change when the nanoparticles have an approximately the same size as that of the critical nucleus. Thus, it is inferred that THF clathrate hydrate nucleation involves the creation of a critical nucleus with its size being inversely proportional to the supercooling. By proving the existence and determining the supercooling-dependent size of the critical nucleus of the THF clathrate hydrates, this work brings insights in the microscopic pictures of the clathrate hydrate nucleation.

Protocol for cryopreservation of red blood cells that controls ice crystal formation by fulvic acid.

The development of biocompatible ice-controlling materials for non-vitreous cryopreservation of cells is of great importance to the field of biomedicine. Here, we present a protocol to use fulvic acid (FA) for efficient non-vitreous cryopreservation of red blood cells (RBCs) that both promotes the melting of ice crystals and retards their growth/recrystallization. We describe steps for FA fractionation and performing tests for ice recrystallization and ice freezing/thawing. We then detail the freezing/thawing of RBCs, recovering RBCs, and testing their viability. For complete details on the use and execution of this protocol, please refer to Bai et al. (2022).1.

Quantitative Structure-Activity Relationship Studies on Alkane Chemistry Tuning Ice Nucleation.

Understanding how surface chemistry influences ice nucleation is essential for both forecasting icing phenomena and designing surfaces with desired ice-control abilities. Although alkylating is one of the most common and simplest ways for surface chemical modification, the effect of alkane chemistry on ice nucleation remains ambiguous as a result of the usually accompanying interferences of substrate morphology or heat transfer. Here, we decouple the effect of alkane chemistry on ice nucleation by investigating the ice nucleation behaviors on alkane self-assembled monolayers (SAMs) with atomic-level roughness and (sub)nanoscale thickness. Our results indicate that the introduction of alkane chemistry leads to decreased ice nucleation activities, i.e., increased anti-icing abilities, and the longer alkyl chain endows the SAM surface with the more inert ability to promote ice nucleation. The alkyl-chain-length-dependent ice nucleation activities are found to be correlated with the surface polarity. This work sheds light on a long-standing question of how alkane chemistry influences ice nucleation and offers a useful strategy for tuning ice nucleation.

Small-molecule fulvic acid with strong hydration ability for non-vitreous cellular cryopreservation.

The exploitation of biocompatible ice-control materials especially the small molecules for non-vitreous cryopreservation remains challenging. Here, we report a small molecule of fulvic acid (FA) with strong hydration ability, which enables non-vitreous cellular cryopreservation by reducing ice growth during freezing and reducing ice recrystallization/promoting ice melting during thawing. Without adding any other cryoprotectants, FA can enhance the recovery of sheep red blood cells (RBCs) by three times as compared with a commercial cryoprotectant (hydroxyethyl starch) under a stringent test condition. Investigation of water mobility reveals that the ice-control properties of FA can be ascribed to its strong bondage to water molecules. Furthermore, we found that FA can be absorbed by RBCs and mainly locates on membranes, suggesting the possible contribution of FA to cell protection through stabilizing membranes. This work bespeaks a bright future for small-molecule cryoprotectants in non-vitreous cryopreservation application.

Influences of Oxidation Degree and Size on the Ice Nucleation Efficiency of Graphene Oxide.

Figuring out the influences of carbonaceous particle properties on ice nucleation is important to atmospheric science, but it is still a challenge, especially for experimental investigations due to the coupling effect of multiple properties. Here we separately investigate the effects of oxidation degree and size, two typical and debated factors, on ice nucleation efficiency by choosing graphene oxide (GO) as the model. The results show that with the decrease of oxidation degree, ice nucleation efficiency increases through decreasing the ice nucleation free energy barrier (ΔGheter*) on GO surface. Interestingly, although the chosen GO sizes are sufficiently large compared with the sizes of critical ice nuclei, the increase of GO size leads to the increase of ΔGheter* and thus the decrease of ice nucleation efficiency, unlike the general thought that ΔGheter* is not affected by the particle size any more when the size of particle increases to several times that of the critical ice nucleus.

Spontaneous Freezing of Water between 233 and 235 K Is Not Due to Homogeneous Nucleation.

The spontaneous freezing of microdroplets around 233 K has long been regarded as the occurrence of homogeneous ice nucleation. The corresponding temperature has been directly regarded as the homogeneous ice nucleation temperature, which is an intrinsic character of water. However, many recent investigations indicate that the spontaneous freezing may be still induced by surfaces of the water microdroplets or the residual impurities inside. Therefore, it is highly desired to reveal with solid evidence the exact origin of the spontaneous freezing. Here we show with no ambiguity that the spontaneous freezing between 233 and 235 K is actually triggered by the surface of microdroplets, as the nucleation rate is found to be proportional to the surface area of droplets, via systematically investigating the freezing of water droplets with varying sizes under various cooling rates followed by a new approach in data analysis. The conclusion is further consolidated by published experimental data from other groups when using our data analysis approach. This study is critical for understanding the sources of "no-man's land" and features of homogeneous nucleation, as well as studying the structure and properties of deeply supercooled liquid water.

Probing the critical nucleus size for ice formation with graphene oxide nanosheets.

Water freezing is ubiquitous and affects areas as diverse as climate, the chemical industry, cryobiology and materials science. Ice nucleation is the controlling step in water freezing1-5 and has, for nearly a century, been assumed to require the formation of a critical ice nucleus6-10. But there has been no direct experimental evidence for the existence of such a nucleus, owing to its transient and nanoscale nature6,7. Here we report ice nucleation in water droplets containing graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our experimental data and theoretical calculations that the critical size of the graphene oxide reflects the size of the critical ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behaviour consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the critical ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide11. The results provide experimental information on the existence and temperature-dependent size of the critical ice nucleus, which has previously only been explored theoretically and through simulations12-16. As pinning of a pre-critical nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the critical nuclei in other nucleation processes.

Tuning Ice Nucleation and Propagation with Counterions on Multilayer Hydrogels.

Ice formation on solid surfaces includes heterogeneous ice nucleation and ice propagation processes. However, no study has been focused on tuning of both ice nucleation and ice propagation via a simple anti-icing coating method. In this work, we have prepared multilayer hydrogels based on simple layer-by-layer (LBL) deposition approach and discover the ion-specific effect on both ice nucleation and ice propagation. A large ice nucleation temperature window of 11 °C is controlled via changing different counterions; meanwhile, the differences in ice propagation time can be tuned up to 4 orders of magnitude. Through synergistically controlling of ice nucleation and propagation delay times, we can tune the freezing delay time of water droplets on multilayer hydrogel surfaces up to 3 orders of magnitude via changing various counterions. Considering the application requirements, these multilayer hydrogels are stable under different conditions and can be coated on various materials without destroying the existing surface. This new insight can inspire the design of anti-icing surfaces based on regulating both ice nucleation and ice propagation.

Size Fractionation of Graphene Oxide Nanosheets via Controlled Directional Freezing.

The properties and functions of graphene oxide (GO)-based materials strongly depend on the lateral size and size distribution of GO nanosheets; therefore, GO and its derivatives with narrow size distributions are highly desired. Here we report the size fractionation of GO nanosheets by controlled directional freezing of GO aqueous dispersions. GO nanosheets with a narrow size distribution can be obtained by controlling the growth rate of the freezing front. This interesting phenomenon can be explained by the adsorption of GO nanosheets on the ice crystal surface in combination with the stratification of GO nanosheets at the ice growth front. Such a convenient size fractionation approach will be essential for practical applications of chemically modified graphene, including GO, reduced GO, and their assemblies or composites.

Size Controllable, Transparent, and Flexible 2D Silver Meshes Using Recrystallized Ice Crystals as Templates.

Ice templates have been widely utilized for the preparation of porous materials due to the obvious advantages, such as environmentally benign and applicable to a wide range of materials. However, it remains a challenge to have controlled pore size as well as dimension of the prepared porous materials with the conventional ice template, since it often employs the kinetically not-stable growing ice crystals as the template. For example, there is no report so far for the preparation of 2D metal meshes with tunable pore size based on the ice template, although facile and eco-friendly prepared metal meshes are highly desirable for wearable electronics. Here, we report the preparation of 2D silver meshes with tunable mesh size employing recrystallized ice crystals as templates. Ice recrystallization is a kinetically stable process; therefore, the grain size of recrystallized ice crystals can be easily tuned, e.g., by adding different salts and changing the annealing temperature. Consequently, the size and line width of silver meshes obtained after freeze-drying can be easily adjusted, which in turn varied the conductivity of the obtained 2D silver film. Moreover, the silver meshes are transparent and display stable conductivity after the repeated stretching and bending. It can be envisioned that this approach for the preparation of 2D conducting films is of practical importance for wearable electronics. Moreover, this study provides a generic approach for the fabrication of 2D meshes with a controllable pore size.

Oxidized Quasi-Carbon Nitride Quantum Dots Inhibit Ice Growth.

Antifreeze proteins (AFPs), a type of high-efficiency but expensive and often unstable biological antifreeze, have stimulated substantial interest in the search for synthetic mimics. However, only a few reported AFP mimics display thermal hysteresis, and general criteria for the design of AFP mimics remain unknown. Herein, oxidized quasi-carbon nitride quantum dots (OQCNs) are synthesized through an up-scalable bottom-up approach. They exhibit thermal-hysteresis activity, an ice-crystal shaping effect, and activity on ice-recrystallization inhibition. In the cryopreservation of sheep red blood cells, OQCNs improve cell recovery to more than twice that obtained by using a commercial cryoprotectant (hydroxyethyl starch) without the addition of any organic solvents. It is shown experimentally that OQCNs preferably bind onto the ice-crystal surface, which leads to the inhibition of ice-crystal growth due to the Kelvin effect. Further analysis reveals that the match of the distance between two neighboring tertiary N atoms on OQCNs with the repeated spacing of O atoms along the c-axis on the primary prism plane of ice lattice is critical for OQCNs to bind preferentially on ice crystals. Here, the application of graphitic carbon nitride derivatives for cryopreservation is reported for the first time.

Graphene Oxide Restricts Growth and Recrystallization of Ice Crystals.

We show graphene oxide (GO) greatly suppresses the growth and recrystallization of ice crystals, and ice crystals display a hexagonal shape in the GO dispersion. Preferred adsorption of GO on the ice crystal surface in liquid water leads to curved ice crystal surface. Therefore, the growth of ice crystal is suppressed owing to the Gibbs-Thompson effect, that is, the curved surface lowers the freezing temperature. Molecular dynamics simulation analysis reveals that oxidized groups on the basal plane of GO form more hydrogen bonds with ice in comparison with liquid water because of the honeycomb hexagonal scaffold of graphene, giving a molecular-level mechanism for controlling ice formation. Application of GO for cryopreservation shows that addition of only 0.01 wt % of GO to a culture medium greatly increases the motility (from 24.3 % to 71.3 %) of horse sperms. This work reports the control of growth of ice with GO, and opens a new avenue for the application of 2D materials.