Amorphous Phase Transition Research Articles

Probing hydrogen-bond networks in plastic crystals with terahertz and infrared spectroscopy

A molecular-level understanding of phase changes in hydrogen-bonded solid-state systems is of great importance in fields spanning thermal science to medical therapeutics. Polyols have recently emerged as prime targets for deployment, given their versatility in phase-induced changes, and occupy a deep space in eutectic solvents. Here, we explore the hydrogen-bond network of neopentyl glycol (NPG) with terahertz time-domain spectroscopy, attenuated total reflection spectroscopy in the far- and mid-infrared regions augmented by electronic structure calculations. A picture emerges where vibrational spectroscopy can exquisitely probe a crystalline to amorphous solid-solid phase transition while spectroscopy in the mid-infrared region provides a molecular picture of the phase transition. These methods are then applied to understand the thermal properties and phase changes in NPG upon incorporation of bis(trifluoromethane)-sulfonimide lithium salt, to demonstrate that vibrational spectroscopy can directly probe the disruption of hydrogen-bond networks in plastic crystals.

Enthalpy relaxation of unconstrained and constrained amorphous phase for low isotacticity polypropylene

The influence of crystallization on the amorphous phase of low isotacticity polypropylene (LT-PP) was studied by analyzing the enthalpy relaxation behavior using fast scanning calorimetry (FSC) and temperature modulated FSC. The high temperature shift of the enthalpy recovery peak and the glass transition temperature during crystallization was interpreted as a transformation of the unconstrained amorphous (UCA) to constrained amorphous (CA) phase. Enthalpy relaxation approach had the same result as the conventional heat capacity analysis of mobile amorphous (MA) phase as proposed by Wunderlich. Our study revealed that successive glass transition of rigid amorphous (RA) phase in a three-phase model and the gradual increase in the heat capacity of the MA phase in a two-phase model are experimentally indistinguishable above the crystallization temperature.

Effects of tool geometry on tungsten removal behavior during nano-cutting

Although the researches in effects of tool geometry on the removal behavior of many metals have been studied, the deformation and removal mechanisms of tungsten have changed greatly due to the higher brittleness of tungsten compared with other metals and the research on the removal behavior of tungsten involved changing of tool geometry during nano-cutting has not been reported, which limits the development of high precision manufacturing of tungsten components. Herein, molecular dynamics (MD) simulation model of nano-cutting tungsten was established, and the material removal behavior induced by changing of tool geometry was comprehensively studied. The results showed that a larger positive rake angle or larger clearance angle or smaller edge radius of the tool was beneficial to reduce the surface roughness, elastic recovery, thickness of subsurface damage layer, cutting force, cutting temperature, friction coefficient, and maximum stress while the surface presented less residual compressive stress or even tensile stress. In the plastic deformation dominated by phase transition and dislocation slip, the region of 1/2<111> dislocation line presented compressive stress state whereas the region of <100> dislocation line presented tensile stress state during nano-cutting tungsten. Meanwhile, there was no phase transition from BCC structure to other crystal structures, but rather from ordered structure to disordered structure (amorphous structure). The correlation between amorphous phase transition and dislocation slip was affected by the tool geometry owing to the fact that the temperature and stress were different under different tool geometries. The research findings provide a comprehensive theoretical basis for the micro removal behavior of tungsten and technical reference for the design of tools in nano-cutting.

Effect of Twin Boundary Density on Mechanical Behavior of Al0.1CoCrFeNi High-Entropy Alloy by Molecular Dynamics Simulation

Molecular dynamics simulation method was used to study the influence of co-lattice twin boundary (TB) spacing on the deformation behavior of Al0.1CoCrFeNi high-entropy alloy single crystal under uniaxial tension. Studies have shown that there is a “critical distance” between the twin boundaries, and the sensitivity of the two sides to the change of the twin spacing is different, and the influence of the evolution of the deformation mechanism of the different twin spacing is analyzed from the number of defects and the evolution of the dislocation density. The results show that as the distance between twins decreases, the deformation mechanism gradually transforms from dislocation slip accompanied by defects, such as stacking faults and secondary twins, to a deformation mode of amorphous phase transition. The research aims to provide guidance and reference for the design of high-performance high-entropy alloys.

Pyrolytic Behavior of Long-Chain Alkyl Quaternary Ammonium Bromide Inside Nanopores

The pyrolytic behavior of organic matter inside nanopores was studied by simultaneous thermogravimetric/differential scanning calorimetry analyzer coupled with Fourier transform infrared spectroscopy (STA/TG-FTIR). Nanoporous silica was prepared by a hydrothermal method using long-chain alkyl quaternary ammonium bromide (CnTAB, n = 12, 14) as a template. The pyrolytic behavior of CnTAB inside nanopores with different diameters was investigated and compared with that of CnTAB inside and outside nanopores. The results showed that the pyrolytic removal process consisted of the following features: 1) CnTAB underwent carbon chain decomposition and oxidation; 2) the DSC exothermal peak of CnTAB came mainly from its oxidative combustion, and the oxidative combustion temperature decreased with increasing pore size; 3) the CnTAB inside nanopores underwent crystallization–amorphous state phase transition, and CnTAB got trapped inside the calcined nanopores. In addition, the pyrolytic behavior of CnTAB inside the calcined nanopores was found to be similar to that of the uncalcined nanopores. This study aims to understand the storage and transformation processes of organic hydrocarbons under nanopore-confinement effect.

Efficient Phase-Change Polymer Composite Film from Emulsion Gels Stabilized by Cellulose Nanofiber-Based Amphiphiles

Phase-change polymers (PCPs), exhibiting solid–solid phase transition, bring advancement to the conventional solid–liquid system for thermal energy storage. Such a system obtained as an aqueous dispersion is recommended for application as a surface coating. However, achieving good colloidal stability with efficient energy-storage performance requires precise process designing. Herein, we developed a film-forming PCP that was synthesized from emulsion gels stabilized by cellulose nanofiber-based amphiphiles (CLAm’s). The CLAm was obtained by grafting an amphiphile at a significantly higher degree (0.2–2.4). Depending on the degree of substitution and type of oil, the CLAm was able to efficiently stabilize o/w emulsion gels containing a very high oil phase (>90.0%) at a concentration of about 0.1 wt %. The PCPs were produced by the copolymerization of stearyl methacrylate (SMA) and methyl methacrylate used as the oil phase in emulsion gels. The composite film obtained from the colloidal dispersion of P(SMA-co-MMA) exhibited a solid–solid (crystalline–amorphous) phase transition involving high latent heat of upto ∼98 J/g for the melting and crystallization of SMA segments at ∼35 and ∼25 °C, respectively. This approach provides significant advancement in designing an efficient energy-storage material using plant-derived biocompatible nanomaterials.

Structural and Electrochemical Properties of the Type VIII Ba8Ga16–δ Sn30+δ (δ ≈ 1)clathrate during Lithiation

Clathrates of the Tetrel (Tt = Si, Ge, Sn) elements are host-guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16–δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis.The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (Li x Ba0.17Ga0.33Sn0.67, x = 2 – 3) with local structures similar to those in the crystalline binary Li-Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs. Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The clathrate structure is hypothesized to kinetically circumvent the formation of Li-Sn or Li-Ga crystalline phases, which results in better cycling and a lower reaction voltage.The electrochemical lithiation pathway of Ba8Ga16–δSn30+δ (δ ≈ 1) is similar to that of the previously investigated type I Ba8Ge43 1 suggesting that the amorphous lithiation could be a common mechanism for guest-filled Tetrel clathrates. As amorphous phase transformations are a beneficial property for alloying anodes, Tetrel clathrates could act as precursors for obtaining amorphous phases with tunable electrochemical properties. With this assumption of a common mechanism for guest-filled clathrates, we will then discuss design rules for clathrate based alloying anodes in terms of optimizing the gravimetric capacity and reaction voltage. References (1) Dopilka, A.; Childs, A.; Bobev, S.; Chan, C. K. Understanding the Amorphous Lithiation Pathway of the Type I Ba8Ge43 Clathrate with Synchrotron X-Ray Characterization. Chem. Mater. 2020, 32, 9444–9457.

Structural and Electrochemical Properties of Type VIII Ba8Ga16-δSn30+δ Clathrate (δ ≈ 1) during Lithiation.

Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host–guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16−δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (LixBa0.17Ga0.33Sn0.67, x = 2–3) with local structures similar to those in the crystalline binary Li–Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li–Sn or Li–Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.

Representation of Multiphase OH Oxidation of Amorphous Organic Aerosol for Tropospheric Conditions.

Organic aerosol (OA) is ubiquitous in the atmosphere and, during transport, can experience chemical transformation with consequences for air quality and climate. Prediction of the chemical evolution of OA depends on its reactivity with atmospheric oxidants such as the OH radical. OA particles undergo amorphous phase transitions from liquid to solid (glassy) states in response to temperature changes, which, in turn, will impact its reactivity toward OH oxidation. To improve the predictability of OA reactivity toward OH oxidation, the reactive uptake coefficients (γ) of OH radicals reacting with triacontane and squalane serving as amorphous OA surrogates were measured at temperatures from 213-293 K. γ increases strongest with temperature when the organic species is in the liquid phase, compared to when being in the semisolid or solid phase. The resistor model is applied, accounting for the amorphous phase state changes using the organic species' glass transition temperature and fragility, to evaluate the physicochemical parameters of the temperature dependent OH uptake process. This allows for the derivation of a semiempirical formula, applicable to models, to predict the degree of oxidation and chemical lifetime of the condensed-phase organic species for typical tropospheric temperature and humidity when OA particle viscosity is known.

The liquid-amorphous phase transition, slow dynamics and dynamical heterogeneity for bulk iron: a molecular dynamics simulation.

Based on molecular dynamics (MD) simulations, we investigate the liquid–amorphous phase transition, slow dynamic and dynamical heterogeneity (DH) for bulk iron in temperatures ranging 300–2300 K. The structure of obtained models is explored through the pair radial distribution function (PRDF) and simplex statistics. It was shown that the splitting of a PRDF second peak appears when the liquid transforms to an amorphous solid. This feature is originated from the transformation of simplexes from strongly-to weakly-distorted tetrahedron type. Further, we reveal that the diffusivity in the liquid is realized through the local density fluctuations (LDF) which are strongly correlated with each other. The diffusion coefficient is found to be a product of the rate of LDF act and mean square displacement of particles per LDF act. The later quantity mainly contributes to the slow dynamics and DH in the liquid. We found that the mobile atom clusters move during relaxation time, but mobile atoms do not tend to leave their cluster. Our work is expected to contribute a pathway to determine the liquid–amorphous phase transition and DH heterogeneity of bulk metal.

Effect of twin boundary on mechanical behavior of Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy by molecular dynamics simulation

The high-entropy alloys break through the traditional alloy structure and present unique and superior mechanical properties. However, the potential deformation mechanism of high-entropy alloy, which is regarded as a new member of alloy families in recent years, needs to be further investigated. In this paper, the mechanical properties of the nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy under tensile loading are studied by molecular dynamics simulation, and the effect of twin boundary on the deformation behavior of nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy is studied on an atomic level. The results show that the yield strength of the nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy increases with twin boundary spacing decreasing, presenting a Hell-Petch relationship. However, there is a critical value of the twin boundary spacing, which makes the sensitivity of the yield strength of the high-entropy alloy to the twin boundary spacing change significantly before and after this value. The results also indicate that the deformation mechanism of nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy changes from dislocation slip to amorphous phase transition with the decrease of twin boundary spacing. The research results of this paper have a certain reference value and guidance significance for designing and preparing high-performance high-entropy alloys.

Analysis of the influence of tool radius on mechanical state of monocrystalline silicon during nano-cutting

Molecular dynamics (MD) was used to build a simulation model for skiving single crystal silicon (SCS) with different tool radius. Through the analysis of phase change, instantaneous atomic position, temperature, Wigner–Seitz defects, stress and other variables, and the mechanical state distribution of SCS during processing is studied. The results show that the amorphous phase transition process occurs in the process of skiving SCS with different tool radii, the difference is that amorphous atoms use chips during sharp corner cutting. The form is removed, and the amorphous atoms in the rounded tool are further compressed directly under the tool, causing subsurface damage. The removal mechanism of sharp corner cutter chips is shear, and the removal mechanism of round corner cutter chips is shear and extrusion. And as the radius of the tool increases, the number of compressed atoms below the tool increases directly, resulting in a decrease in the quality of the processed surface.

Tricolor Ho^{3+} Photoluminescence Enhancement from Site Symmetry Breakdown in Pyrochlore Ho_{2}Sn_{2}O_{7} after Pressure Treatment.

The photoluminescence (PL) characterization spectrum has been widely used to study the electronic energy levels. Ho^{3+} is one of the commonly used doping elements to provide the PL with concentration limited to 1% atomic ratio. Here, we present a tricolor PL achieved in pyrochlore Ho_{2}Sn_{2}O_{7} through pressure treatment at room temperature, which makes a non-PL material to a strong multiband PL material with Ho^{3+} at the regular lattice site with 18.2% concentration. Under a high pressure compression-decompression treatment up to 78.0GPa, the Ho_{2}Sn_{2}O_{7} undergoes pyrochlore (Fd 3m), to cotunnite (Pnma), then amorphous phase transition with different Ho^{3+} coordinations and site symmetries. The PL emerged from 31.2GPa when the pyrochlore to cotunnite phase transition took place with the breakdown of site symmetry and enhanced hybridization of Ho^{3+} 4f and 5d orbitals. Upon decompression, the materials became an amorphous state with a partial retaining of the defected cotunnite phase, accompanied with a large enhancement of red-dominant tricolor PL from the ion pair cross-relaxation effect in the low-symmetry (C_{1}) site, in which two distinct Ho^{3+} emission centers (S center and L center) are present.

Atomic-scale structural evolution and welding deformations of laser welded joints in Ag nanowire connectors on homogeneous substrates

The formation mechanism and the influence of laser power on welding deformations of welded joints in Ag nanowire connectors were investigated using molecular dynamic simulations. Simulation results revealed that some regions of voids in the welded joint were filled due to the heat in the heat affected zone. The laser irradiation with the appropriate power can decrease dislocations and phase transitions generated by cold welding. The welding strength possessed an upward trend with the increase in laser power. With the increase of the laser power, the shear resistance of the welded joint improved. However, the welded joint after the laser with the excessive power weakened. Furthermore, by comparing the laser welding and the thermal annealing welding, we found that the laser welded joint possesses fewer amorphous atoms, phase transitions, dislocations, residual stress, and possibility of the shear deformation via simulation.

Synthesis and Characterization of Maleic Anhydride Modified Poly (Ethylene Glycol) as Polymeric Solid-Solid Phase Change Materials

In this study, a novel type of polymeric solid-solid phase change materials (SSPCMs) and Maleic anhydride (MA) modified poly (ethylene glycol) PEG. MAM-PEG polymers were synthesized from different moleculer weight PEG (Mw: 4000, 6000) .On the other hand two different catalyst system was used; para toluene sulfonic acid (PTSA) and 1,8-Diazabicyclo [5.4.0] undec-7-ene (DBU).The PEG bound to the backbone of the polymers formed crystalline regions responsible from latent heat storage with reversible crystalline to amorphous phase transition as linked unit prevented total melting of the structure. Also MAM-PEG polyester polymers acid and hydroxyl values were determined for number of average molecular weight (Mn) and calculated as 36232 and 49020. Characterization and thermal properties of SSPCMs were performed by using fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) techniques mainly. DSC results showed that solid-solid transitions 36-54 °C temperature range and 163-153 Jg-1 enthalpy. As a result, MAM-PEG polymers were found potential for thermal energy storage (TES) applications.

Correlation of Structure with Crystalline to Amorphous Phase Transitions of 1,3,6-Substituted Fulvene-Derived Molecular Glasses.

An investigation into the crystalline to amorphous phase transitions of prepared 1,3,6-substituted pentafulvenes showed the expected reversible heated melt and cooling recrystallization in only a few examples. Systematic incorporation of bulky substituents at the 6-position of the fulvene ring led to the nonreversible thermal behavior, rendering phases that were locked into glassy, vitrified states. These molecular glasses produced physically translucent and amorphous features with glass transition temperatures in the range of 61-77 °C, comparable with high-strength plastics such as polyethylene terephthalate. Additionally, the melting point transitions and the resulting heat of fusion values were found to be directly influenced by the nature of the 6-position substituent. Single crystal X-ray crystallography showed that in some cases, fulvenes possessing fused aromatics exhibited a high degree of intermolecular π-π stacking. These results point to a class of molecular glass formers as host materials possessing tunable bulk properties for potentially new optical applications.

Li2TiS3: Lithium Metal Sulphide Rocksalt As New Cathode Material for High Energy Batteries without Critical Materials

Most of the current Li-Ion cathodes use cobalt/nickel-based layered oxides as active materials. Due to the increasing demand of these critical and scarce elements in the coming years, it becomes urgent to develop new materials based on abundant elements. In 2014, Sakuda et al. introduce new sulphide rocksalt materials which can deliver a capacity higher than 400 mAh/g at 2.2 Volts.1 In 2019, a project named Spider funded by the European Union's Horizon 2020 research and innovation programme started with the objective to develop and use these materials in Li-Ion batteries. Several synthesis methods have been evaluated to produce Li2TiS3 materials. High capacities are obtained with these materials but they suffer from a poor cycle life.Several characterizations and experiments have been performed in order to obtain a better understanding of the material evolution during cycling. Ex-situ XRD are in good agreement with previous results reported by Sakuda et al. and we completed the investigation thanks to Ex-situ SEM and XPS characterizations.2 We highlight that the material is partially oxidized during the cathode manufacturing process which lead to a loss of the lithium content in the materials structure. Our conclusions will be helpful to overcome these issues.References(1) Sakuda, A.; Takeuchi, T.; Okamura, K.; Kobayashi, H.; Sakaebe, H.; Tatsumi, K.; Ogumi, Z. Rock-Salt-Type Lithium Metal Sulphides as Novel Positive-Electrode Materials. Sci. Rep. 2014, 4, 4883. https://doi.org/10.1038/srep04883.(2) Sakuda, A.; Ohara, K.; Kawaguchi, T.; Fukuda, K.; Nakanishi, K.; Arai, H.; Uchimoto, Y.; Ohta, T.; Matsubara, E.; Ogumi, Z.; et al. A Reversible Rocksalt to Amorphous Phase Transition Involving Anion Redox. Sci. Rep. 2018, 8 (1), 1–6. https://doi.org/10.1038/s41598-018-33518-4. Figure 1

Calorimetric investigation of the low temperature specific heat of the amorphous RE-Cu-Y metallic glasses

The specific heat, Cp of the RE0.40Cu0·37Y0.23 (RE = Gd, Tb, Dy, Ho, Er, and Lu) metallic glasses have been measured from liquid helium to liquid nitrogen temperatures using the traditional pulse and continuous heating techniques. The average values of the electronic and lattice specific heat coefficients, γ and β were estimated to be of order of 2.35 mJ/mol,K2, and 0.62 mJ/mol,K4 respectively. The corresponding average Debye temperature, θD(0) was estimated to be 145 K. The magnetic contributions to the specific heat, Cm are quite apparent in all samples. Cm has been separated from the nonmagnetic terms with an acceptable accuracy method; by subtracting the nonmagnetic specific heat, of the amorphous Lu0.40Cu0·37Y0.23 sample, which has been prepared with Lu rather than RE. The magnetic phase transition in these magnetic amorphous has been confirmed by the ac susceptibility results, which exhibits quite sharp maximum at the freezing temperature Tf, the spin glass freezing temperature. The magnetic specific heats were characterized by the quite broad maximum at temperature Tm and by the low-temperature linear term in Cm. Values of Tm are higher than Tf values for most of the samples. The magnetic entropy changes, Sm in the temperature range T = 0 K to T = Tf have also been estimated. Values of Sm and the effective value of the magnetic spin number J were found to be less than the expected maximum values of Sm(max) = Rℓn(2J + 1) and the well-known value of the magnetic number J of the rare earth metal respectively. The apparent features of the present amorphous magnetic samples agree quite well with traditional behaviors of the condensed spin glass systems.

Phenothiazine-Based Mechano-Fluorochromic Gels and Solids: Superhydrophobic Surface Formation and Crystal-to-Crystal Phase Transition

Organic materials exhibiting mechano-fluorochromic behavior in their gel state are extremely rare in the literature. Similarly, examples of mechano-fluorochromic organic materials with crystal-to-crystal phase transitions have not been reported until date. Herein, we achieved these two remarkable properties in phenothiazine derivatives S1 and S2[(E)-N′-((10-ethyl-10H-phenothiazin-3-yl)methylene)-3,4,5-tris(hexadecyloxy)benzohydrazide and (E)-N′-((10-ethyl-10H-phenothiazin-3-yl)methylene)isonicotinohydrazide)], where S1 formed mechano-luminescent xerogel and S2 exhibited the rare feature of crystal-to-crystal phase transition with mechano-luminescence behavior. Study of the photophysical properties of S1 and S2 indicated the suppression of twisted intramolecular charge transfer (TICT) upon self-assembly, leading to blue-shifted emission from S1 and S2. While both S1 and S2 exhibited the propensity to aggregate and disclosed the aggregation induced emission (AIE) behavior in a binary solvent (THF/H2O) mixture, only S1 resulted in a robust gel, which was further utilized for developing a superhydrophobic surface with a contact angle of 157.56°. Upon mechanical grinding, both pristine sample and xerogel of S1 showed an emission color change from light green (505 nm) to yellowish green (530 nm), whereas S2 exhibited an emission color change from cyan blue (480 nm) to green (535 nm). Furthermore, both fluorophores exhibited red-shifted emission under application of increased pressure. Mechanistic studies indicated that grinding resulted in crystal to amorphous phase transition in S1, whereas grinding in S2 demonstrated the rare feature of crystal-to-crystal phase transition. The mechano-fluorochromic (MFC) natures of S1 and S2 were supported by single point energy calculations using density functional theory (DFT).

Topological phase transitions in glassy quantum matter

Amorphous systems have rapidly gained promise as novel platforms for topological matter. In this work we establish a scaling theory of amorphous topological phase transitions driven by the density of lattice points in two dimensions. By carrying out a finite-size scaling analysis of topological invariants averaged over discrete and continuum random geometries, we discover unique critical properties of Chern and $\mathbb{Z}_2$ glass transitions. Even for short-range hopping models the Chern glass phase may persist down to the fundamental lower bound given by the classical percolation threshold. While the topological indices accurately satisfy the postulated one-parameter scaling, they do not generally flow to the closest integer value in the thermodynamic limit. Furthermore, the value of the critical exponent describing the diverging localization length varies continuously along the phase boundary and is not fixed by the symmetry class of the Hamiltonian. We conclude that the critical behaviour of amorphous topological systems exhibit characteristic features not observed in disordered systems, motivating a wealth of new research directions.