Hydrogels have been widely used in biomedical and environmental applications, yet precise control of mechanical properties (quantified by elastic modulus, G') over a broad range remains essential for expanding their functionality. While pressure treatment typically enhances hydrogel strength through pressure-induced crosslinking, we report a counterintuitive phenomenon in locust bean gum (LBG) hydrogels: High-pressure processing induces softening rather than stiffening. Under repeated compression-decompression cycles up to 1.2 GPa, LBG hydrogels undergo progressive softening, with elastic modulus decreasing to approximately 31% of the initial value. Conversely, repeated freeze-thaw cycles enhance the modulus by approximately 2.3-fold. Scanning electron microscopy reveals a structural transition from a porous network to a flocculent morphology, corresponding to substantial alterations in elastic modulus and viscoelastic behavior. Mechanistic analysis suggests that pressure-induced disruption of hydrogen bonding, water redistribution, and structural rearrangement drive these changes. These findings demonstrate that pressure modulation can serve as a complementary method to conventional freeze-thaw treatment, offering precise control over hydrogel mechanical properties across a wide range.

Energetic materials have closely correlated safety and high-pressure chemical reaction kinetics. While extensive research has typically focused on structural evolution and reversible phase transitions at high pressures, chemical decomposition pathways remain underexplored. Here, we report a novel pressure-induced chemical reaction in CL-20 during decompression from a peak pressure of 26.2 GPa under nonhydrostatic compression. Infrared spectroscopy confirmed chemical bond cleavage, yielding gaseous decomposition products primarily composed of N2O and CO2. Molecular dynamics simulations revealed that the initial decomposition steps involved H migration, OH transfer, β-scission of the C-C bridge, and cleavage of C-N bonds. Notably, under improved hydrostatic conditions (using KBr as the pressure-transmitting medium), the reaction threshold pressure increased to 30.1 GPa, highlighting the critical roles of shear stress in the diamond anvil cell environment. This study represents the first clear demonstration of decompression-induced chemical reactions in condensed explosives, providing fundamental insights into their intrinsic safety mechanisms as well as their initiation and detonation behaviors.

Amorphous solids, as long-range disorder materials, have complex order on multiple length scales. The regulation of the degree of order is generally achieved through annealing or static compression. Unlike previous studies, this work has triggered the disorder-to-order transition in amorphous selenium (a-Se) by cyclic compression-decompression in a dynamic diamond anvil cell. We found that the degree of order in the directionally bonded a-Se positively correlates with the number of compression cycles, and long-range order was achieved in a relatively low-pressure range. The possible transformation mechanism is discussed on the basis of medium-range structural parameter regulation. This work provides an understanding of the relaxation and extension of the order length scale by unconventional mechanical stimulation.

In the quasi-free electron model, the Fermi surface spreads into a sphere in the Brillouin zone, i.e., the Fermi sphere. The Fermi sphere exists widely in metal systems, no matter whether the crystal is in a body-center cubic, face-center cubic, or hexagonal close-packed lattice. Here, we report a class of compounds stabilized at high pressure with Rubik's cubic Fermi surface, in which the representative example is Pm3((sic))n-CaCl3. Our quantum-mechanical variable-composition evolutionary simulations predict the thermal stabilities of CaCl3, and the tight-binding model reveals that its unique Fermi surface originates from the quasi-one-dimensional interaction, structural symmetric protection, and particle-hole symmetry breaking. Furthermore, by its flat and steep band structure, CaCl3 has a huge span of effective mass from 9.08 x 10(3)m(e) (super-heavy) to 5.13 x 10(-4)me on the Fermi level, which supplies an interesting platform for quasiparticle research.

The molecular stacking mode of organic luminescent materials directly affects the mechanoresponsive luminescence (MRL) properties. Although crystallization-enhanced emission applies to most organic luminescent materials, the emission of the amorphous phase in MRL materials with two-state switching is generally redder and weaker. Herein, the amorphization-enhanced emission (AEE) phenomenon from tetraphenylethylene (TPE) was observed by the rapid compression of its melt caused by the transformation of the TPE from a liquid to an amorphous solid. The fluorescence emission of amorphous TPE was significantly stronger than that of crystalline TPE throughout the depressurization process. As pure hydrocarbons, intermolecular interactions rely more on C-Hpi, and amorphous aggregates attributed to enhance this interaction, leading to increased efficiency. The experimental approach provided in this paper is universally applicable to organic luminescent materials that remain stable after melting, which perfectly inherits the liquid phase's properties and helps further investigate the luminescence mechanism of AEE materials.

It is well known that atoms of the same element in different valence states show very different chemical behaviors. Calcium is a typical divalent metal, sharing or losing both of its valence electrons when forming compounds. Attempts have been made to synthesize compounds of monovalent calcium ions for decades, but with very little success (e.g., in clusters). Pressure can result in substantial changes in the properties of atoms and chemical bonding, creating an extensive variety of unique materials with special valence states. In this study, using the ab initio evolutionary algorithm USPEX, we search for stable calcium–chlorine (Ca–Cl) system compounds at pressures up to 100 GPa. Besides the expected compound CaCl2, we predict three new compounds with monovalent Ca to be stable at high pressures, namely, CaCl, Ca5Cl6, and Ca3Cl4. According to our calculations, CaCl is stable at pressures above 18 GPa and is predicted to undergo a transition from nonmagnetic Fm-3m-CaCl to ferromagnetic Pm-3m-CaCl at 40 GPa. Ca5Cl6 and Ca3Cl4 are stable at pressures above 37 and 73 GPa, with space groups P-1 and R-3, respectively. Following these predictions, we successfully synthesized Pm-3m-CaCl in laser-heated diamond anvil cell experiments. The emergence of the unusual valence state at high pressures reveals exciting opportunities for creating entirely new materials in sufficiently large quantities for a variety of potential applications.

Pressure-induced polymerization (PIP) of crystalline and amorphous 3-nitrophenylacetylene (3-NPA), formed by controlling the average compression rate, was investigated by using in situ Raman spectra and Fourier transform infrared spectroscopy. The results suggest that the threshold pressure for the alkynyl polymerization reaction found in the crystalline phase was about 11.8 GPa, whereas polymerization occurred at 6.2 GPa in the amorphous phase. The hydrogen transfer reaction was observed during these decompression processes. The crystal structure of 3-NPA at 12.0 GPa was solved, and the distances between alkynyl groups were calculated. Our research demonstrates that one poly(phenylacetylene) derivative can be synthesized at lower pressures from the amorphous phase, providing some inspiration for future pressure-induced polymerization.

Isotropic materials are required to adhere to various mechanical principles due to their limited thermal stability. For instance, it is essential for Poisson's ratio to be within the range of -1 to 0.5, and the longitudinal wave velocity must exceed the transverse wave velocity. Nevertheless, perfect crystals, as anisotropic materials, have the ability to defy conventional rules. Through the integration of high-throughput processes and first-principles calculations, a comprehensive exploration of known materials was conducted, resulting in the establishment of a database featuring an extreme anisotropic mechanism. This included the identification of abnormal Poisson's ratios (with the directional Poisson's ratio ranging from -3.00 to 3.67), the discovery of extreme negative linear compressibility, the determination of the upper and lower limits of the sound velocity, and other associated properties. Several materials with abnormal Poisson's ratios (<-1 or >0.5) were listed, and their peculiar mechanical behavior, wherein the volume decreased counterintuitively with uniaxial tension, was discussed. Finally, this study focused on the velocities of longitudinal and transverse waves, with specific emphasis on materials exhibiting transverse wave velocities that exceeded the longitudinal wave velocities.

The Grüneisen parameter (γ) is crucial for determining many thermal properties, including the anharmonic effect, thermostatistics, and equation of state of materials. However, the isentropic adiabatic compression conditions required to measure the Grüneisen parameter under high pressure are difficult to achieve. Thus, direct experimental Grüneisen parameter data in a wide range of pressures is sparse. In this work, we developed a new device that can apply pressure (up to tens of GPa) with an extremely short time of about 0.5 ms, confidently achieving isentropic adiabatic compression. Then, we applied our new technique to sodium chloride and measured its Grüneisen parameter, which conforms to previous theoretical predictions. According to our obtained sodium chloride Grüneisen parameters, the calculated Hugoniot curve of the NaCl B1 phase appears up to 20 GPa and 960 K, which compares very well with the shock compression experimental data by Fritz et al. and other calculation works. Our results suggest that this new method can reliably measure the Grüneisen parameter of even more materials, which is significant for researching the equation of state in substances.

Conventionalhigh-pressure chemical reactions that are initiatedby manual compression or decompression face critical challenges inreproducibility, as different research groups often obtain differentresults. In this study, we developed a new high-pressure techniquetermed programmable compression and decompression (PCD) in order tosolve this problem. This versatile method allows us to arbitrarilyadjust the pressure loading modes, including the compression and decompressionrates, the amplitude, and the number of compression-decompressioncycles, to explore their effects on chemical reactions. Using thepolymerization of methyl methacrylate (MMA) as a model reaction, ourPCD technique shows that the characteristic of the pressure-inducedpolymerization (PIP) of MMA is "high-pressure initiation andlow-pressure polymerization". The effects of the initiationpressure, polymerization pressure, and holding time at low pressurewere confirmed by simple compression and decompression experiments.Furthermore, using the PCD technique, we set several pressure loadingmodes to explore the effects of the number of compression-decompressioncycles, amplitude, and rate on MMA polymerization. The results showthat the number of compression-decompression cycles and theamplitude significantly affect the conversion yield (CY). Our resultsdemonstrate that the PCD technique is a convenient method for controllinghigh-pressure reaction conditions and provide some inspiration forfuture high-pressure technology.

The high-pressure polymorphism of pyridine has attracted great attention. Herein, the crystallization process of pyridine at different compression rates was investigated in detail. When the compression time was <= 1 s, pyridine crystallized into phase III, while phase I occurred when the compression time was >= 10 s, although both phases were compressed from 0.30 to similar to 1.20 GPa. In situ time-resolved ruby fluorescence and optical micrographs of the pyridine compression process revealed that the compression rate affected the initial crystallization pressure and resulted in different crystalline phases. Phase I slowly transformed to phase III at 1.55 GPa, while the reverse transformation occurred rapidly upon decompression to 1.0 GPa. In situ Raman spectroscopy and synchrotron X-ray diffraction results demonstrated that phase III did not undergo any further phase transition up to 17 GPa. Our results proved that the compression rate could selectively control the nucleation pathway to achieve different final products even when the final pressure was the same. The findings will enable a better understanding of the high-pressure crystallization kinetics of the materials.

Mechanoluminescence (ML) has promising applications such as stress sensors and many other fields, which raises intensive research attention and enthusiasms in the past few decades. However, accurate characterizations of the ML process with high temporal and spectral resolution remain a considerable challenge for the current scientific community. Here, an advanced ML characterization system based on the dynamic diamond anvil cell (dDAC) is developed to achieve flexible modulations of ML performances. Upon compression, the ML spectra of manganesedoped zinc sulfide (ZnS:Mn) show a large red-shift (similar to 45 nm) and a volcano-trend of the ML intensity, where the cumulative ML intensity is solely dependent on the pressure change. DFT calculations identify the coupling of Mn-doping and surface vacancies is playing a crucial role in contributing to the improvement of ML through the band offset. The suppression of the vacancies formation on the surface by the applied pressure over 4 GPa leads to the decreases of the ML intensity. This work provides a brand new ML color and intensity tuning strategy and offers a promising method to explore the ML mechanism.

We study the stability of Li-O compounds as a function of pressure, with rich phase diagram, diverse properties, and fundamental chemical interest in mind. Using the ab initio evolutionary algorithm USPEX, we predict the stability of compounds LiO4, Li5O3, and Li6O under pressure. Unexpectedly, LiO2 will decompose to Li2O2 + LiO4 in the pressure range 6-18 GPa. LiO4, formed at the pressure of just 6 GPa, can be seen as epsilon-O-8 accepting two electrons from two Li atoms. This phase is superconducting, with T-c up to 12.2 K at 10 GPa. This is remarkable, because elemental oxygen becomes superconducting at much higher pressure (96 GPa) and has much lower T-c (<0.6 K), and suggests that chemical alloying with other elements has the potential of not only decreasing metallization pressure, but also of increasing T-c. Since epsilon-O-8 is called red oxygen, LiO4 can be identified as "lithium red-oxide", and is distinct from superoxide. Additionally, Li5O3 is stable at pressures above 70 GPa and can be represented as a hybrid structure 4Li(2)O center dot Li2O2, and electride suboxide Li6O is stable above 62 GPa.