Interchain Interactions Research Articles

Theoretical investigation of solvation and inter-chain interactions for phosphate ester dispersants on tetragonal BaTiO3 (0 0 1) in non-aqueous solvents: An ab initio molecular dynamics simulation approach

Tetragonal BaTiO3 is a key material for manufacturing multi-layer ceramic capacitors (MLCCs), and a highly dispersed BaTiO3 suspension, where the surfaces are conjugated by phosphate ester dispersants, is an essential technology for the production of ultra-thin films and small-sized ceramic capacitors. Therefore, understanding the interactions of conjugated polymers with solvents is critical to designing improved dispersants and solvents for commercial MLCC applications. In this work, we theoretically investigate the solvation and inter-chain interactions of mono-alkyl and ethoxy phosphate esters under methanol, ethanol, isopropanol, 1-butanol, and toluene, on tetragonal BaTiO3 (001) using the ab initio molecular dynamics (AIMD) simulations. Our results show that the total number of solvent molecules surrounding mono-alkyl and ethoxy phosphate esters decreases in the order of methanol > ethanol > isopropanol > 1-butanol > toluene, indicating that solvation via van der Waals forces and hydrogen bonding declines with increasing the hydrophobicity of solvent molecules. Also, the solvation interaction energy has a linear correlation with the experimental differential of zeta potential, suggesting that the calculated energy is associated with electrostatic environment at the dispersant/solvent/BaTiO3 interface. Therefore, the solvation interaction energy is an important factor that describes the liquid–solid interfaces as well as a dispersion stability of BaTiO3 suspension.

Cyanide-Bridged Rope-like Chains Based on Trigonal-Bipyramidal [Fe2Cu3] Subunits.

Extending a selected cyanometalate block into a higher dimensional framework continues to present intriguing challenges in the fields of chemistry and material science. Here, we prepared two rope-like chain compounds of {[(Tp*Me)Fe(CN)3]2Cu2X2(L)}·sol (1, X = Cl, L = (MeCN)0.5(H2O/MeOH)0.5, sol = 2MeCN·1.5H2O; 2, X = Br, L = MeOH, sol = 2MeCN·0.75H2O; Tp*Me = tris(3, 4, 5-trimethylpyrazole)borate) in which the cyanide-bridged trigonal-bipyramidal [Fe2Cu3] subunits were linked with the adjacent ones via two vertex Cu(II) centers, providing a new cyanometallate chain archetype. Direct current magnetic study revealed the presence of ferromagnetic couplings between Fe(III) and Cu(II) ions and uniaxial anisotropy due to a favorable alignment of the anisotropic tricyanoiron(III) units. Moreover, compound 1 exhibits single-chain magnet behavior with an appreciable energy barrier of 72 K, while 2 behaves as a metamagnet, likely caused by the subtle changes in the interchain interactions.

The effect of physical aging on the viscoelastoplastic response of glycol modified poly(ethylene terephthalate)

For most amorphous polymers, their long term viscoelastic behaviour is greatly affected by physical aging, referring to the transition of their non-equilibrium structure towards equilibrium. This, in turn, affects their thermomechanical properties. In this study, we successfully applied a constitutive model, originally developed for semi-crystalline polyesters to assess the impact of physical aging on stress relaxation and creep in two glycol modified poly(ethylene terephthalate) grades, (poly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate) (PECT) and poly(ethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PETT). Both copolyesters are subject to annealing at Tg-20 °C for up to 504 h and subsequent uniaxial stress relaxation tests and, for PECT, creep tests. The results show that the annealing time has a significant influence on the viscoelastic behaviour increasing the resistance to creep and stress relaxation. The effect of physical aging on model parameters is described and analysed while it is found that the concentration of active polymer junctions decreases exponentially with annealing time. Generally, PETT and PECT showed almost identical viscoelastic behaviours at 30 °C, suggesting that the chemical structure of the glycol unit (2,2,4,4-tetramethyl-1,3-cyclobutanediol and 1,4-cyclohexylenedimethanol) does not have significant effect on their viscoelasticity. However, when stress relaxation is tested at increased temperatures, the structural effects are more apparent, demonstrating higher activation energies for PECT than those for PETT, describing the rate of the rearrangement of interchain interactions. Physical aging is also found to decrease these activation energies from 326.6 to 128.1 kJ mol−1 for PECT and from 262.7 to 78.5 kJ mol−1 for PETT.

Spatial Organization of Slit-Confined Melts of Ring Polymers with Nonconserved Topology: A Lattice Monte Carlo Study.

We present Monte Carlo computer simulations for melts of semiflexible randomly knotted and randomly concatenated ring polymers on the fcc lattice and in slit confinement. Through systematic variation of the slit width at fixed melt density, we explore the influence of confinement on single-chain conformations and interchain interactions. We demonstrate that confinement makes chains globally larger and more elongated while enhancing both contacts and knottedness propensities. As for multichain properties, we show that ring-ring contacts decrease with the confinement, yet neighboring rings overlap more as confinement grows. These aspects are accompanied by a marked decrease in the links formed between pairs of neighboring rings. In connection with the quantitative relation between links and entanglements in polymer melts recently established by us [Ubertini M. A.; Rosa A.Macromolecules2023, 56, 3354-3362], we propose that confinement can be used to set polymer networks that act softer under mechanical stress and suggest a viable experimental setup to validate our results.

A new shear stress model of magnetorheological gels considering interchain interactions

A new shear stress model of magnetorheological gels considering interchain interactions

Dynamic acylhydrazone bonds cross-linked chromotropic photonic-ionic skin with self-healing and high resilience for interactive human-machine interface

Advanced skin systems realize perception and interaction with the environment through synergistic electrical and color signals generated by transmitting ions and manipulating photonic structures. Here, inspired by chameleon skins, a novel self-healing and resilient photonic-ionic skin (PI-skin) with electro-optical dual response is ingeniously constructed integrating the ordered micro-nano array and the dynamically covalently cross-linked ionogel. The elaborately designed polycation network with weak inter-chain interactions can promote the uniform distribution of high-content low-viscosity ionic liquid (IL), effectively eliminating energy dissipation and resulting in high resilience. Dynamic acylhydrazone bonds are served as reversible chemical crosslinking to realize high-efficiency self-healing and further enhance resilience. Notably, the artificially manipulated transition of the photonic array from dense packing to non-dense packing endows sensitive chromotropic properties synchronized with electrical response under stretched (Δλ > 130 nm) and compressed (Δλ > 160 nm). Furthermore, by harnessing the correspondence between electrical and optical signals, the control of optical signals over electrical signals is achieved for inputting complex coded information and constructing interactive human–machine interfaces. This work not only inspires the design and construction of high-level artificial skins but also stimulates the development of visual interactive devices and smart electronic/ionic products.

Anisotropy-Driven Crystallization of Dimensionally Resolved Quasi-1D Van der Waals Nanostructures.

Unusual behavior in solids emerges from the complex interplay between crystalline order, composition, and dimensionality. In crystals comprising weakly bound one-dimensional (1D) or quasi-1D (q-1D) chains, properties such as charge density waves, topologically protected states, and indirect-to-direct band gap crossovers have been predicted to arise. However, the experimental demonstration of many of these nascent physics in 1D or q-1D van der Waals (vdW) crystals is obscured by the highly anisotropic bonding between the chains, stochasticity of top-down exfoliation, and the lack of synthetic strategies to control bottom-up growth. Herein, we report the directed crystallization of a model q-1D vdW phase, Sb2S3, into dimensionally resolved nanostructures. We demonstrate the uncatalyzed growth of highly crystalline Sb2S3 nanowires, nanoribbons, and quasi-2D nanosheets with thicknesses in the range of 10 to 100 nm from the bottom-up crystallization of [Sb4S6]n chains. We found that dimensionally resolved nanostructures emerge from two distinct chemical vapor growth pathways defined by diverse covalent intrachain and anisotropic vdW interchain interactions and controlled precursor ratios in the vapor phase. At sub-100 nm nanostructure thicknesses, we observe the hardening of phonon modes, blue-shifting of optical band gaps, and the emergence of a new high-energy photoluminescence peak. The directional growth of weakly bound 1D ribbons or chains into well-resolved nanocrystalline morphologies provides opportunities to develop ordered nanostructures and hierarchical assemblies that are suitable for a wide range of optoelectronic and quantum devices.

A superstable, flexible, and scalable nanofluidic ion regulation composite membrane

Two-dimensional layered membranes with high and stable ion transport properties have various applications in nanofluidic devices; however, their construction remains a considerable challenge. Herein, we develop a superstable aramid nanofiber/graphite composite membrane with numerous one-dimensional and two-dimensional nano-confined interspaces for ultrafast ion transport. The fabricated flexible and scalable membrane exhibits high tensile strength (∼115.3 MPa) even after immersion in water for 90 days. Further, the aramid nanofiber/graphite conductor features the surface-charge-governed ion transport behavior. The ionic conductivity of the membrane at a low potassium chloride concentration of 10−4 mol/L can be enhanced by 16 times that of the bulk counterpart. More importantly, its structure and ionic conductivity remain unchanged even after immersion in different harsh solutions (e.g., acid, base, and ethanol) for over 30 days. Molecular dynamics simulations reveal that the superstability of the membrane is attributable to the robust interchain interactions within the aramid nanofibers and the strong interfacial interactions between the aramid nanofibers and graphite nanosheets. This study highlights the superior structural stability of the proposed flexible and scalable aramid nanofiber/graphite composite membrane, which could be employed in advanced nanofluidic devices for application under extreme working environments.

One-Dimensional Van Der Waals Helical Crystals with an Irrational Twist

Long-range helicity in condensed materials has sternly relied on the precise ordering of cooperative intra- and inter-molecular bonding interactions. The exclusivity of these interactions in natural, organic, or molecular systems has limited the conclusive demonstration of aperiodic helical motifs in densely packed solid state lattices. In this talk, we will present a class of 1D van der Waals solids that crystallize as weakly bound helical chains that possess atomic scale order consistent with an aperiodic tetrahelix. We will describe how precise atomic level control of the local coordination environment in these 1D vdW lattices induces helical aperiodicity in periodic helical motifs based on repeating screw axis symmetry motifs. We will also highlight herein that the modularity of vdW lattices allows for the systematic engineering of helical attributes (radius, rise, and twist angle) and band gap energies across the visible to the near-UV spectral window. Owing to the intrinsic non-centrosymmetry of aperiodic helices, we will show that these 1D vdW tetrahelices exhibit visible range second harmonic generation in freestanding crystals from the bulk down to the nanoscale. Lastly, we will demonstrate that the weak vdW interchain interactions in these 1D vdW tetrahelices enables the micromechanical exfoliation into single ~1 nm diameter chiral helical chains. The realization of exfoliable 1D vdW tetrahelices presents a unique materials platform towards understanding the synthetic design rules towards helicity and chirality in low-dimensional solids. Atomically-precise helicity along these length scales will facilitate new opportunities in designing solid state materials towards sub-nanoscale nonlinear chiroptics, long-range spin polarization via chiral-induced spin selectivity, and 1D topological helicoid quantum states.

Interchain Hydrodynamic Interaction and Internal Friction of Polyelectrolytes.

Polyelectrolytes (PE) are polymeric macromolecules in aqueous solutions characterized by their chain topology and intrinsic charge in a neutralizing fluid. Structure and dynamics are related to several characteristic screening length scales determined by electrostatic, excluded volume, and hydrodynamic interactions. We examine PE dynamics in dilute to semidilute conditions using dynamic light scattering, neutron spinecho spectroscopy, and pulse field gradient NMR spectroscopy. We connect macroscopic diffusion to segmental chain dynamics, revealing a decoupling of local chain dynamics from interchain interactions. Collective diffusion is described within a colloidal picture, including electrostatic and hydrodynamic interactions. Chain dynamics is characterized by the classical Zimm model of a neutral chain retarded by internal friction. We observe that hydrodynamic interactions are not fully screened between chains and that the internal friction within the chain increases with an increase in ion condensation on the chain.

Structure of Strongly Adsorbed Polymer Systems: A Computer Simulation Study.

The structure of very thin polymer films formed by strongly adsorbed macromolecules was studied by computer simulation. A coarse-grained model of strictly two-dimensional polymer systems was built, and its properties determined by an efficient Monte Carlo simulation algorithm. Properties of the model system were determined by means of Monte Carlo simulations with a sampling algorithm that combines Verdier-Stockmayer, pivot and reputation moves. The effects of temperature, chain length and polymer concentration on the macromolecular structure were investigated. It was shown that at low temperatures, the chain size increases with the concentration, that is, inversely with high temperatures. This behavior should be explained by the influence of inter-chain interactions.

Accelerated Design of Ultra-High-Performance Aramid Copolymers via a High-Throughput Screening Approach.

Developing advanced materials, such as functional polymers, poses a significant challenge as a result of the vastness of the material space that needs to be explored, which could potentially be infinite in principle. We propose a data-driven high-throughput screening approach coupled with molecular dynamics (MD) simulations to address this issue in the design of high-performance co-polymerized aramid fibers. We aimed to identify diamine monomers that could replace 3,4'-oxydianiline in Technora from a large-scale set (1 920 304) of possible monomers that were prepared from the PubChem database. We initially screened these monomers using a cheminformatics-based approach, considering four criteria: complexity, neutrality, linearity, and gyration radius of the molecule. Then, we performed subsequent screening based on MD simulations to estimate interchain interaction energies under both stretched and melted conditions and tensile strength simulations. Our screening approach successfully identified 31 promising and novel diamine monomers for aramid copolymers. This demonstrates the potential and effectiveness of our approach as a promising protocol for exploring targeted chemical spaces in designing novel monomers for high-performance aramid fibers and possibly other advanced polymers.

Optimizing BiOCl concentration for enhanced LDPE performance: Investigation of structure, thermal stability, and optical characteristics

This research article presents a comprehensive study on enhancing the structural, thermal alongside optical properties of LDPE by incorporating BiOCl nanoparticles. LDPE nanocomposites were synthesized using the solvent casting technique, employing different concentrations of BiOCl (3, 5, and 7 wt.%) nanoparticles. BiOCl demonstrated crystalline anisotropic growth along the (110) plane under solvothermal treatment, enhancing the interfacial interaction with LDPE chains. This interaction reduces electrostatic inter-chain interactions, promoting alignment and crystallization of molecular chains and yielding a smooth morphology. The optimal BiOCl concentration is determined to be 5 wt.%, as higher concentrations lead to nanoparticle aggregations and weak interactions. Raman spectroscopy shows broadened intensity peaks in the nanocomposite with increasing BiOCl concentrations, indicating the presence of defects and oxygen vacancies. These findings offer promising prospects for photocatalytic applications. The thermal analysis reveals enhanced thermal stability, fire resistance, and insulation in the nanocomposites compared to pure LDPE. The incorporation of BiOCl increases activation energy, melting, and glass transition temperatures, highlighting their positive impact on enhancing the thermal properties of LDPE. The red shift in absorption peaks of LDPE nanocomposites indicates π-delocalization, suggesting small band gaps. Additionally, higher weight percentages of BiOCl nanoparticles in the LDPE matrix result in increased absorption intensities in the UV region, providing enhanced UV radiation protection, with a maximum absorption of 96% of UV light. The results include improved interaction, morphology, alignment, thermal stability, fire resistance, and UV protection of BiOCl: LDPE nanocomposite, with potential for diverse industries.

Deep transfer learning for inter-chain contact predictions of transmembrane protein complexes

Membrane proteins are encoded by approximately a quarter of human genes. Inter-chain residue-residue contact information is important for structure prediction of membrane protein complexes and valuable for understanding their molecular mechanism. Although many deep learning methods have been proposed to predict the intra-protein contacts or helix-helix interactions in membrane proteins, it is still challenging to accurately predict their inter-chain contacts due to the limited number of transmembrane proteins. Addressing the challenge, here we develop a deep transfer learning method for predicting inter-chain contacts of transmembrane protein complexes, named DeepTMP, by taking advantage of the knowledge pre-trained from a large data set of non-transmembrane proteins. DeepTMP utilizes a geometric triangle-aware module to capture the correct inter-chain interaction from the coevolution information generated by protein language models. DeepTMP is extensively evaluated on a test set of 52 self-associated transmembrane protein complexes, and compared with state-of-the-art methods including DeepHomo2.0, CDPred, GLINTER, DeepHomo, and DNCON2_Inter. It is shown that DeepTMP considerably improves the precision of inter-chain contact prediction and outperforms the existing approaches in both accuracy and robustness.

Copper(II) halide complexes of aminopyridines: Synthesis, structure, and magnetic behavior of neutral compounds of 5-IAP: (5-IAP)2CuCl2·H2O, [(5-IAP)2CuBr2]2, (5-IAP)2CuBr2 and (5-IAP)3CuCl2·nH2O (5IAP = 2-amino-5-iodopyridine)

Reaction of 2-amino-5-iodopyridine (5IAP) with copper(II) bromide or chloride in alcoholic solution led to four coordination complexes: [(5-IAP)2CuCl2](H2O) (1), (5-IAP)2CuBr2 (2), [(5-IAP)2CuBr2]2 (3) and [(5-IAP)3CuCl2](H2O)n (4). The compounds were characterized by single crystal X-ray diffraction and variable temperature magnetic susceptibility measurements. 1 crystallizes as monomeric units with the 5IAP ligands in the syn-conformation and one lattice water molecule. 2 also exhibits syn-conformation 5IAP ligands, but forms a common bromide bibridged dimer structure. 3 is a conformational polymorph of 2 with anti-oriented 5IAP ligands. Long Cu⋯Br contacts link the molecules into chains. 4 crystallizes with 1.67 lattice water molecules, disordered over three positions. All four compounds exhibit strong halogen bonding. Variable field and temperature magnetic data were obtained on 1–3. 1 is paramagnetic, with no indication of magnetic exchange down to 1.8 K. 2 is well modeled as an antiferromagnetic dimer (J/kB = −22 K) with significant antiferromagnetic interactions between the dimers. 3 is well modeled as a uniform antiferromagnetic chain (J/kB = −6 K) with weak interchain interactions.

A physically-based hydrostatic strain energy model for rubber-like materials inspired by Flory-Orwoll-Vrij equation of state theory

In a compressible hyperelastic model for rubber-like materials, the strain energy function is generally composed of the hydrostatic part corresponding to changes in interchain interactions and the compressible elastic part attributable to the network structure. It is well known that the hydrostatic part dominates the compressibility of the material. In this study, inspired by the Flory-Orwoll-Vrij (FOV) equation of state (EOS) theory for pure polymer liquids (note: a cell-like EOS theory), we assume that (i) the compressibility of rubber-like materials corresponds to changes in free volume of polymer chain segments; (ii) the hydrostatic strain energy of a rubber-like solid is attributable to changes in interchain interaction energy and chain segments’ external motion degrees of freedom (the latter solely depends on interchain forces). With a focus on the reversible isothermal deformation process, we construct a physically-based hydrostatic strain energy function based on the Helmholtz free energy formulation in FOV EOS theory. With a view towards applications, we provide a specific compressible hyperelastic model by incorporating the new hydrostatic strain energy function and compressible eight-chain model, where the latter is utilized as the elastic part of the strain energy function. Our model is capable of predicting various volume data of rubber-like materials from the literature, such as the nonlinear pressure-volume response at finite volume changes in hydrostatic compression (HC), the volume change-stretch and stress-stretch data in uniaxial tension (UT), and the stress-volume data in constrained uniaxial compression (CUC). Given the severely limited volume change data for finite stretches in UT and other modes of deformation, we simulate the volume change-volume modulus-stretch responses in UT, equibiaxial tension (ET), pure shear (PS), and uniaxial compression (UC) over their respective theoretical range of stretch and successfully predict some available (qualitative) experimental observations. Together with the simulations of the volume change-stretch responses in UT, ET, PS, and UC based on the Ogden’s and Bischoff et al.’s compressible models, we summarize the characteristics of these responses and analyze the possible deformation mechanisms. These simulations can provide some guidance for future corresponding experiments. Finally, we analyze the deformation mechanisms of HC, CUC, UT, ET, PS, and UC by simulating the responses for total strain energy and its components. This study provides a new physical picture and corresponding theoretical model for the hydrostatic strain energy function of rubber-like materials and finally proposes the general research strategy for constructing new hydrostatic strain energy functions based on the EOS theories for pure polymer liquids.

Cobalt-nickel coordinated polyaniline as electrodes for high performance flexible asymmetric supercapacitor

Polyaniline (PANI) is commonly employed as a material for supercapacitor electrodes. However, its molecular structure is susceptible to disruption due to high volume expansion, leading to a significant decline in cycling performance. Enhancing the cyclic stability of PANI is of utmost importance. In here, a one-step electrodeposition method is utilized to produce cobalt-nickel coordinated PANI (PCN) on a carbon cloth (CC) substrate. By coordinating the intra- and inter-chain interactions of PANI molecules with Co2+ and Ni2+, the expansion of PANI volume during charging and discharging can be significantly reduced, resulting in enhanced cycle performance. The CC/PCN electrode exhibits a high capacitance of 592.5 F g−1 at 1 A g−1. The assembled asymmetric device, comprising PCN as the positive electrode and MXene as the negative electrode (PCN//MXene), demonstrates a capacitance of 131.8 F g−1 at 1 A g−1. Moreover, the asymmetric device exhibits a remarkable capacitance retention of 85.9 % at 5 A g−1 even after 5000 cycles, and exhibits an energy density of 799.89 W kg−1 at a power density of 46.86 W h kg−1. Additionally, the supercapacitor demonstrates exceptional flexibility by maintaining its excellent capacitance even after undergoing 1000 bending cycles. The research presented herein showcases that PCN//MXene asymmetric supercapacitor exhibits great potential for applications in the field of next-generation flexible energy storage devices.

Plasticization, Antiplasticization, and Fragility in Blends of Polyvinyl Butyral and Polyethylene Glycol Dimethyl Ether

AbstractBlends of polyvinyl butyral (PVB) and polyethylene glycol dimethyl ether (PEGDME) with low molecular weight (= 250 g mol−1) show two calorimetric (for PEGDME content higher than 11% by weight) and mechanical glass transitions. Their substantial changes in the relative content of the two components are explained by considering the self‐concentrations of both polymers determined by the connectivity of their own chains. Increasing content of PEGDME lower the glass transition temperature Tg of PVB (the component with the highest Tg) by about 100 K, also causing a progressive and significant increase of its fragility (following the Angell's strong/fragile liquids classification scheme). Strengthening of polymer blends is observed in the fully glassy region, quite below the Tg's of both the components, with the storage modulus E′ becoming more than a factor 2 higher than that of neat PVB. The progressive increase of E′, without any change of slope, points to structural homogeneity of blends determined by compatibility of components, as a result of interchain interactions activated by the polar groups of both polymers. The present results reveal that PEGDME plasticizes PVB when the blend is in the fully rubbery state while acting as an anti‐plasticizer in the fully glassy state.

OPTICAL AND DIELECTRIC PROPERTIES OF EPOXY RESIN FILLED WITH TITANIUM DIOXIDE PARTICLES

This work studies the electrical properties for pure epoxy, and epoxy with (0, 1, 1.5, 2 wt%) titanium dioxide powder composites. The effects of titanium dioxide contents on optical and dielectrically properties of the epoxy/ titanium dioxide have investigated by several techniques were used to characterize the epoxy/titanium dioxide: UV-visible spectrophotometer reveals a new absorption band in the wavelength range (350-600) nm. The findings of this investigation show that when the proportion of titanium dioxide added increases, the absorbance increases which are ascribed to interchain interaction. The absorption coefficient (α), extinction coefficient (k), refractive index (n), the real and imaginary permittivity (εr, εi), and energy gap (Eg) of epoxy/titanium dioxide samples were effectively determined from the recorded data optical transmission technique. In addition, these epoxy have been examined in the wavenumber range (4000-500 cm-1) using an FT-IR spectrometer and also a dielectric constant measurement. The thickness of all the samples is 1.2 mm ± 0.1 mm.

Spontaneous Magnetization in the Finite-Size Two-Leg Ising Ladder in the External Magnetic Field

This paper considers a finite-sized two-leg ladder of spin-1/2 particles with local inter-chain Ising interaction. We include the effects of an external magnetic field by incorporating a Zeeman-type coupling between the magnetic field and the spins localized on the lattice sites. To analyze the system, we utilize the transfer-matrix formalism to calculate the partition function. We compute the magnetization for different configurations by varying the system's parameters. We observe the presence 3of spontaneous magnetization within the system. As the inter-chain Ising interaction changes its sign, the magnetization value changes from negative to positive values. Furthermore, we identify a phase transition from diamagnetic to ferromagnetic states when examining the temperature dependence of the magnetization at zero magnetic fields. We observe a step-like behavior in the magnetization curve in the low temperature limit.