Enhanced DNA repair through droplet formation and p53 oscillations.

Living organisms are constantly exposed to DNA damage, and optimal repair is therefore crucial. A characteristic hallmark of the response is the formation of sub-compartments around the site of damage, known as foci. Following multiple DNA breaks, the transcription factor p53 exhibits oscillations in its nuclear concentration, but how this dynamics can affect the repair remains unknown. Here, we formulate a theory for foci formation through droplet condensation and discover how oscillations in p53, with its specific periodicity and amplitude, optimize the repair process by preventing Ostwald ripening and distributing protein material in space and time. Based on the theory predictions, we reveal experimentally that the oscillatory dynamics of p53 does enhance the repair efficiency. These results connect the dynamical signaling of p53 with the microscopic repair process and create a new paradigm for the interplay of complex dynamics and phase transitions in biology.

Hierarchical bubble size distributions in coarsening wet liquid foams.

Coarsening of two-phase systems is crucial for the stability of dense particle packings such as alloys, foams, emulsions, or supersaturated solutions. Mean field theories predict an asymptotic scaling state with a broad particle size distribution. Aqueous foams are good model systems for investigations of coarsening-induced structures, because the continuous liquid as well as the dispersed gas phases are uniform and isotropic. We present coarsening experiments on wet foams, with liquid fractions up to their unjamming point and beyond, that are performed under microgravity to avoid gravitational drainage. As time elapses, a self-similar regime is reached where the normalized bubble size distribution is invariant. Unexpectedly, the distribution features an excess of small roaming bubbles, mobile within the network of jammed larger bubbles. These roaming bubbles are reminiscent of rattlers in granular materials (grains not subjected to contact forces). We identify a critical liquid fraction [Formula: see text], above which the bubble assembly unjams and the two bubble populations merge into a single narrow distribution of bubbly liquids. Unexpectedly, [Formula: see text] is larger than the random close packing fraction of the foam [Formula: see text]. This is because, between [Formula: see text] and [Formula: see text], the large bubbles remain connected due to a weak adhesion between bubbles. We present models that identify the physical mechanisms explaining our observations. We propose a new comprehensive view of the coarsening phenomenon in wet foams. Our results should be applicable to other phase-separating systems and they may also help to control the elaboration of solid foams with hierarchical structures.

Phase separation and ripening in a viscoelastic gel.

The process of phase separation in elastic solids and viscous fluids is of fundamental importance to the stability and function of soft materials. We explore the dynamics of phase separation and domain growth in a viscoelastic material such as a polymer gel. Using analytical theory and Monte Carlo simulations, we report a domain growth regime in which the domain size increases algebraically with a ripening exponent [Formula: see text] that depends on the viscoelastic properties of the material. For a prototypical Maxwell material, we obtain [Formula: see text], which is markedly different from the well-known Ostwald ripening process with [Formula: see text]. We generalize our theory to systems with arbitrary power-law relaxation behavior and discuss our findings in the context of the long-term stability of materials as well as recent experimental results on phase separation in cross-linked networks and cytoskeleton.

Thermal Stability of High-Entropy Alloy Nanoparticles Evaluated by In Situ TEM Observations.

High-entropy alloy (HEA) nanoparticles (NPs) have attracted attention in several fields because of their fascinating properties. The high mechanical strength, good thermal stability, and superior corrosion resistance of HEAs, which are derived from their high configurational entropy, are attractive features. Herein, we investigated the thermal stability of FeCoNiCuPd HEA NPs on reduced graphene oxide via in situ transmission electron microscopy observations at elevated temperatures. The HEA NPs maintained their structure, size, and composition at 700 °C, and their size gradually decreased accompanied by the preferential sublimation of Cu. On the contrary, the deterioration of the monometallic Pd NPs begins at temperatures greater than 700 °C according to Ostwald ripening, which involves the migration of adatoms or mobile molecular species. Theoretical calculations revealed that the detachment of adatoms from clusters (i.e., the first step of Ostwald ripening) was suppressed in the case of HEA NPs because of the high-configuration-entropy effect.

Iron-Catalyzed Laser-Induced Graphitization - Multiscale Analysis of the Structural Evolution and Underlying Mechanism.

The transition to sustainable materials and eco-efficient processes in commercial electronics is a driving force in developing green electronics. Iron-catalyzed laser-induced graphitization (IC-LIG) has been demonstrated as a promising approach for rendering biomaterials electrically conductive. To optimize the IC-LIG process and fully exploit its potential for future green electronics, it is crucial to gain deeper insights into its catalyzation mechanism and structural evolution. However, this is challenging due to the rapid nature of the laser-induced graphitization process. Therefore, multiscale preparation techniques, including ultramicrotomy of the cross-sectional transition zone from precursor to fully graphitized IC-LIG electrode, are employed to virtually freeze the IC-LIG process in time. Complementary characterization is performed to generate a 3D model that integrates nanoscale findings within a mesoscopic framework. This enabled tracing the growth and migration behavior of catalytic iron nanoparticles and their role during the catalytic laser-graphitization process. A three-layered arrangement of the IC-LIG electrode is identified including a highly graphitized top layer with an interplanar spacing of 0.343 nm. The middle layer contained γ-iron nanoparticles encapsulated in graphitic shells. A comparison with catalyst-free laser graphitization approaches highlights the unique opportunities that IC-LIG offers and discuss potential applications in energy storage devices, catalysts, sensors, and beyond.

Entropy-Driven Ostwald Ripening Reversal Promotes the Formation of Low-Platinum Intermetallic Fuel Cell Catalysts.

Strain engineering has been widely used to optimize platinum-based oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs). PtM3 (M is base metals), a well-known high-compressive-strain intermetallic alloy, shows promise as a low platinum ORR catalyst due to high intrinsic activity. However, during the alloying of Pt with a threefold amount of M, a notable phase separation between Pt and M may occur, with M particles rapidly sintering while Pt particles grow slowly, posing a challenge in achieving a well-defined PtM3 intermetallic alloy. Here, an entropy-driven Ostwald ripening reversal phenomenon is discovered that enables the synthesis of small-sized Pt(FeCoNiCu)3 intermetallic ORR catalysts. High entropy promotes the thermodynamic driving force for the alloying Pt with M, which triggers the Ostwald ripening reversal of sintered FeCoNiCu particles and facilitates the formation of uniform Pt(FeCoNiCu)3 intermetallic catalysts. The prepared Pt(FeCoNiCu)3 catalysts exhibit a high specific activity of 3.82 mA cm-2, along with a power density of ≈1.3 W cm-2 at 0.67 V and 94 °C with a cathode Pt loading of 0.1 mg cm-2 in H2-air fuel cell.

Coarsening of Quasi Two-Dimensional Emulsions Formed by Islands in Free-Standing Smectic Films.

We study the coarsening behavior of assemblies of islands on smectic A freely suspended films in ISS microgravity experiments. The islands can be regarded as liquid inclusions in a two-dimensional fluid in analogy to liquid droplets of the discontinuous phase of an emulsion. The coarsening is effectuated by two processes, predominantly by island coalescence, but to some extend also by Ostwald ripening, whereby large islands grow at the expense of surrounding smaller ones. A peculiarity of this system is that the continuous and the discontinuous phases consist of the same material. We determine the dynamics, analyze the self-similar aging of the island size distribution and discuss characteristic exponents of the mean island growth.

Unveiling the Molecular Dynamics, Anticancer Activity, and Stability of Spearmint Oil Nanoemulsions with Triglycerides.

Although spearmint oil (SMO) has various pharmacological properties, especially for cancer treatment, its low water solubility results in poor bioavailability. This limits its application as a medicine. One possible solution is to the use of SMO in the form of nanoemulsion, which has already been shown to have anticancer effects. However, the mechanism of SMO nanoemulsion formation remains unclear. The objective of this study was to use molecular dynamics (MD) for clarifying the formation of SMO nanoemulsion with triglycerides (trilaurin, tripalmitin, and triolein) and Cremophor RH40 (PCO40). Nanoemulsions with different SMO:triglyceride ratios and triglyceride types were prepared and analyzed for anticancer activity, droplet size, droplet morphology, and stability. Despite switching the type of carrier oil, SMO nanoemulsions retained strong anticancer effects. A ratio of 80SMO:20triglycerides produced the smallest droplets (<100 nm) and exhibited excellent physical stability after a temperature cycling test. MD simulations showed that polyoxyethylenes of PCO40 are located at the water interface, stabilizing the emulsion structure in an egglike layer. Droplet size correlated with triglyceride concentration, which was consistent with the experimental findings. Decreasing triglyceride content, except for the 90SMO:10triglyceride ratio, led to a decrease in droplet sizes. Hydrogen bond analysis identified interactions between triglyceride-PCO40 and carvone-PCO40. Geometry analysis showed PCO40 had an "L-like" shape, which maximizes the hydrophilic interfaces. These findings highlight the value of MD simulations in understanding the formation mechanism of SMO and triglyceride nanoemulsions. In addition, it might also be beneficial to use MD simulations before the experiment to select the potential composition for nanoemulsions, especially essential oil nanoemulsions.

Unveiling Hierarchical Dendritic Co3O4-SnO2 Heterostructure for Efficient Water Purification.

The construction of a desirable, environmentally friendly, and cost-effective nanoheterostructure photoanode to treat refractory organics is critical and challenging. Herein, we unveiled a hierarchical dendritic Co3O4-SnO2 heterostructure via a sequential hydrothermal process. The time of the secondary hydrothermal process can control the size of the ultrathin SnO2 nanosheets on the basis of the Ostwald solidification mass conservation principle. Ti/Co3O4-SnO2-168h with critical growth size demonstrated a photoelectrocatalysis degradation rate of ∼93.3% for a high dye concentrate of 90 mg/L with acceptable long-term cyclability and durability over reported Co3O4-based electrodes because of the large electrochemically active area, low charge transfer resistance, and high photocurrent intensity. To gain insight into the photoelectric synergy, we proposed a type-II heterojunction between Co3O4 and SnO2, which prevents photogenerated carriers' recombination and improves the generation of dominant active species •O2-, 1O2, and h+. This work uncovered the Ti/Co3O4-SnO2-168 as a promising catalyst and provided a simple and inexpensive assembly strategy to obtain binary integrated nanohybrids with targeted functionalities.

Viscosity Flow Curves of Agar and the Bounded Ripening Growth Model of the Gelation Onset.

The gelation kinetics of agar aqueous solutions were studied by means of the viscosity flow curves using a coaxial Couette cylinder viscometer. The viscosity curves show an unusual sigmoidal trend or an exponential decay to a viscous steady state. An original theory of gelation kinetics was developed considering the coarsening of increasingly larger and more stable clusters due to Ostwald ripening and the breakup of clusters that were too large due to the instability of rotating large particles induced by the shear rate. The developed Bounded Ripening Growth model takes into account the trend of the viscosity curves by means of an autocatalytic process with negative feedback on aggregation according to the logistic kinetic equation, in which the constants k1(γ) and k-(ν) are governed by the surface tension and shear rate, respectively. A dimensionless equation based on the difference between the Weber number and the ratio of the inverse kinetic constant to forward constant, accounts for the behavior of the dispersed phase in equilibrium conditions or far from the hydrostatic equilibrium.

Ostwald ripening for designing time-dependent crystal hydrogels.

Ostwald ripening (OR), a classic solution theory describing molecular transfer from metastable crystal to stable one, is applied to design time-dependent crystal hydrogels that can automatically change their mechanical properties. Using a system made from crosslinked polyacrylamide (PAM) and sodium acetate (NaAc), we demonstrate that metastable fibrous crystal networks of NaAc preferably form in PAM hydrogels via a polymer-involving mismatch nucleation. These fibrous crystals would undergo OR and evolve into isolated bulk crystals, leading to a significant reduction in material rigidity (179 folds) and interfacial adhesion (20 folds). This transformation can be applied to program time-dependent self-recovery in shape and self-delamination. Since OR is a ubiquitous, robust feature of various crystals, the approach reported here represents a new direction for designing advanced transient soft materials.

Ostwald-Ripening Induced Interfacial Protection Layer Boosts 1,000,000-Cycled Hydronium-Ion Battery.

Collapsing and degradation of active materials caused by the electrode/electrolyte interface instability in aqueous batteries are one of the main obstacles that mitigate the capacity. Herein by reversing the notorious side reactions include the loss and dissolution of electrode materials: as we applied Ostwald ripening (OR) in the electrochemical cycling of a copper hexacyanoferrate electrode in a hydronium-ion batteries, the dissolved Cu and Fe ions undergo a crystallization process that creates a stable interface layer of cross-linked cubes on the electrode surface. The layer exposed the low-index crystal planes (100) and (110) through OR-induced electrode particle growth, supplemented by vacancy-ordered (100) superlattices that facilitated ion migration. Our design stabilized the electrode-electrolyte interface considerably, achieving a cycle life of one million cycles with capacity retention of 91.6%, and a capacity retention of 91.7% after 3000 cycles for a full battery.

Metal Nanocatalyst Sintering Interrogated at Complementary Length Scales.

Metal nanoparticle (NP) sintering is a prime cause of catalyst degradation, limiting its economic lifetime and viability. To date, sintering phenomena are interrogated either at the bulk scale to probe averaged NP properties or at the level of individual NPs to visualize atomic motion. Yet, "mesoscale" strategies which bridge these worlds can chart NP populations at intermediate length scales but remain elusive due to characterization challenges. Here, a multi-pronged approach is developed to provide complementary information on Pt NP sintering covering multiple length scales. High-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation show that the size evolution of individual NPs depends on the number of coalescence events they undergo during their lifetime. In its turn, the probability of coalescence is strongly dependent on the NP's mesoscale environment, where local population heterogeneities generate NP-rich "hotspots" and NP-free zones during sintering. Surprisingly, advanced in situ synchrotron X-ray diffraction shows that not all NPs within the small NP sub-population are equally prone to sintering, depending on their crystallographic orientation on the support surface. The demonstrated approach shows that mesoscale heterogeneities in the NP population drive sintering and mitigation strategies demand their maximal elimination via advanced catalyst synthesis strategies.

Shaping Copper Oxide Layers on Gold Nanoparticle Ensembles by Controlled Electrodeposition with Single Particle Scatterometry.

Electrodeposition of copper on gold nanoelectrode ensembles result in the formation of uniform copper oxide layers on individual nanoparticles. A linear sweep of voltammetric change induces three distinct morphologies dependent upon particle density. Ex situ imaging and in situ scatterometry at a single-particle level identifies multi-step electrochemical growth sequences that deviated from classical nucleation and growth pathways. In addition, the study demonstrated the possibility of synthesizing sophisticated structures based on the symmetry of nanoelectrodes. This result guides the nanoscale morphology control of electrode ensembles with potential application in electrocatalysis and sensing.

In-Situ Transmission Electron Microscopy Observation of Germanium Growth on Freestanding Graphene: Unfolding Mechanism of 3D Crystal Growth During Van der Waals Epitaxy.

Breakthroughs in cutting-edge research fields such as hetero-integration of materials and the development of quantum devices are heavily bound to the control of misfit strain during heteroepitaxy. While remote epitaxy offers one of the most intriguing avenues, demonstrations of functional hybrid heterostructures are hardly possible without a deep understanding of the nucleation and growth kinetics of 3D crystals on graphene and their mutual interactions. Here, the kinetics of such processes from real-time observations of germanium (Ge) growth on freestanding single layer graphene (SLG) using in-situ transmission electron microscopy are unraveled. This powerful technique provides a unique opportunity to observe new and yet unexplored phenomena, which are not accessible to the standard ex situ characterizations. Through direct observations, remote interactions are elucidated between Ge crystals through the graphene layer in double heterostructures of Ge/graphene/Ge. Notably, the data show real-time evidence of vertical Ge atoms diffusion through the graphene layer. This phenomenon is attributed to the remote interactions of Ge atoms through the graphene lattice, due to its interatomic interaction transparency. Additionally, key mechanisms governing nucleation and initial growth in graphene were systematically determined. These findings enlighten the growth mechanism of graphene and provide a new pathway for disruptive hybrid semiconductor-graphene devices.

Process-Specific Effects of Sulfate on CaCO3 Formation in Environmentally Relevant Systems.

Additives, such as ions, small molecules, and macromolecules, have been found to regulate the formation of CaCO3 and control its morphologies and properties. However, a single additive usually affects dominantly one process in CaCO3's formation and is seldom found to significantly affect multiple CaCO3 formation processes. Here, we used in situ grazing incidence X-ray techniques to observe the heterogeneous formation of CaCO3 and found that a series of formation processes (i.e., nucleation, growth, and Ostwald ripening) were modulated by sulfate. In the nucleation process, increased interfacial free energy and bulk free energy cooperatively increased the nucleation barrier and decreased nucleation rates. In the growth process, sulfate reduced the electrostatic repulsion between CaCO3 precursors and nuclei, promoting CaCO3 growth. This influence on the growth counteracted the inhibition effect in the nucleation process, causing a nearly 100% increase in the volume of heterogeneously formed CaCO3. Meanwhile, adsorbed sulfate on CaCO3 nuclei may poison the surface of smaller CaCO3 nuclei, inhibiting Ostwald ripening. These revealed sulfate's active roles in controlling CaCO3 formation advance our understanding of sulfate-incorporated biomineralization and scaling phenomena in natural and engineered aquatic environments.

Intralayered Ostwald Ripening-Induced Self-Catalyzed Growth of CNTs on MXene for Robust Lithium-Sulfur Batteries.

The distinguishable physicochemical properties of MXenes render them attractive in electrochemical energy storage. However, the strong tendency to self-restack owing to the van der Waals interactions between the MXene layers incurs a massive decrease in surface area and blocking of ions transfer and electrolytes penetration. Here, in situ generated Ti3 C2 Tx MXene-carbon nanotubes (Ti3 C2 Tx -CNTs) hybrids are reported via low-temperature self-catalyzing growth of CNTs on Ti3 C2 Tx nanosheets without the addition of any catalyst precursors. With combined spectroscopic studies and theoretical calculation results, it is certified that the intralayered Ostwald ripening-induced Ti3 C2 Tx nanomesh structure contributes to the uniform precipitation of ultrafine metal Ti catalysts on Ti3 C2 Tx , thus giving rise to the in situ CNTs formation on the surface of Ti3 C2 Tx with high integrity. Taking advantages of intimate electrolyte penetration, unobstructed 3D Li+ /e transport, and rich electroactive sites, the Ti3 C2 Tx -CNTs hybrids are confirmed to be ideal 3D scaffolds for accommodating sulfur and regulating the polysulfides conversion for high-loaded lithium-sulfur batteries.

Real-Time Fluorescence Visualization of Nanoparticle Aggregation and the Polymorph-Transition Process of a Mechanofluorochromic Difluoroboron-ß-Diketone Derivative.

The use of organic nanomaterials in biomedical and optical devices has been widely studied. The key to improving the performance and stability of these devices is to control the fabrication process, which determines the phase stability and photophysical properties. In this study, fluorescence changes were observed during the reprecipitation process of mechanofluorochromic molecules of dibenzoyl(methanato)boron difluoride. The cyan-emission phase (C-phase) was first identified. The time evolution of the resolved fluorescence spectra revealed that the green-emission phase (G-phase) was formed from the amorphous phase with yellow emission via the C-phase, in addition to the direct formation of the G-phase. Combined with the results of the investigation into the thermal properties, the fluorescence changes clearly indicate a two-step nucleation process and Ostwald's rule of stages for polymorph transition, which enables us to not only provide guidance for controlling the fabrication process but also propose the ripening process for organic nanoparticle formation.

The disappearance and return of nanoparticles upon low energy ion irradiation.

Ion irradiation of bulk and thin film materials is tightly connected to well described effects such as sputtering or/and ion beam mixing. However, when a nanoparticle is ion irradiated and the ion range is comparable to the nanoparticle size, these effects are to be reconsidered essentially. This study investigates the morphology changes of silver nanoparticles on top of silicon substrates, being irradiated with Ga+ions in an energy range from 1 to 30 keV. The hemispherical shaped nanoparticles become conical due to an enhanced and curvature-dependent sputtering, before they finally disappear. The sputter yield and morphology changes can be well described by 3D Monte Carlo TRI3DYN simulations. However, the combination of sputtering, ion beam mixing, ion beam induced diffusion, and Ostwald ripening at ion energies lower than 8 keV results in the reappearance of new particles. These newly formed nanoparticles appear in various structures depending on the material and ion energy.

Ostwald ripening in the presence of simultaneous occurrence of various mass transfer mechanisms: an extension of the Lifshitz-Slyozov theory.

The Ostwald ripening stage of a phase transformation process with allowance for synchronous operation of various mass transfer mechanisms (volume diffusion and diffusion along the block boundaries and dislocations) and the initial condition for the particle-radius distribution function is theoretically studied. The initial condition is taken from the analytical solution describing the intermediate stage of a phase transition process. The present theory focuses on relaxation dynamics from the beginning of the ripening process to its final asymptotic state, which is described by the previously constructed theories (Slezov VV. et al. 1978 J. Phys. Chem. Solids 39, 705-709. (doi:10.1016/0022-3697(78)90002-1) and Alexandrov & Alexandrova 2020 Phil. Trans. R. Soc. A 378, 20190247. (doi:10.1098/rsta.2019.0247)). An evolutionary behaviour of particle growth rates dependent on various mass transfer mechanisms and time is analytically described. The boundaries of the transition layer, which surround the blocking point, are found. The fundamental and relaxation contributions to the particle-radius distribution function are derived for the simultaneous occurrence of various mass transfer mechanisms. The left branch of this function is shifted to smaller particle radii whereas its right branch extends to the right of the blocking point as compared with the asymptotic universal distribution function. The theory under consideration well agrees with experimental data. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.