Intermolecular Interaction Forces Research Articles

Structural and computational insights into two completely unanticipated Cu(II) and Ni(II) complexes derived from a bifunctional salamo-type bis(pyridine)-arm ligand

A bifunctional Salamo-type bis(pyridine)-arm ligand H2L (4,4′-Methyl-6,6′-pyridinenitrilomethylidyne-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) was designed and synthesized, which can react with Cu(II) and Ni(II) nitrates to hydrolyze & break the C = N double bonds of new ligand H2L′ (4,4′-Methyl-6,6′-formal-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol). The ligand reacted with Cu(II) and Ni(II) salts to form respectively complexes [Cu(L′)] (1) and [Ni2(L′)(H2O)2](NO3)2 (2). They were elucidated by single crystal X-ray method. Many important noncovalent interactions, such as intramolecular hydrogen bonding, intermolecular hydrogen bonding and π···π stacking interactions, can be observed in the crystal structures of the two complexes. IR & UV–Vis absorbent spectroscopic analysis showed that the ligand unit is involved in the coordination with copper(II) and nickel(II) atoms, and ultraviolet titration and fluorescence titration spectra verified that the coordinating radios of the two complexes formed in liquid phase are in accordance with those of single-crystal X-ray diffraction. Through DFT theoretical calculations and electrostatic potential analyses (MESP) of the ligand and its complexes, the configuration of the ligand at the lowest energy were deeply understood, and it was demonstrated that the coordination reaction at salamo sites requires a great torsional force, and the weak intermolecular interaction force and the energy gaps of HOMO-LUMO orbitals were profoundly discussed, and the Cu(II) and Ni(II) complexes exhibit anomalous fluorescence enhancement behaviors.

Optimizing carbon sources regulation in the biochemical treatment systems for coal chemical wastewater: Aromatic compounds biodegradation and microbial response strategies

The complex composition of coal chemical wastewater (CCW), marked by numerous highly toxic aromatic compounds, induces the destabilization of the biochemical treatment system, leading to suboptimal treatment efficacy. In this study, a biochemical treatment system was established to efficiently degrade aromatic compounds by quantitatively regulating the dosage of co-metabolized substrates (specifically, the chemical oxygen demand (COD) Glucose: COD Sodium acetate = 3:1, 1:3, and 1:1). The findings demonstrated that the system achieved optimal performance under the condition that the ratio of COD Glucose to COD Sodium acetate was 3:1. When the co-metabolized substrate was added to the system at an optimal ratio, examination of pollutant removal and cumulative effects revealed that the removal efficiencies for COD and total organic carbon (TOC) reached 94.61 % and 86.40 %, respectively. The removal rates of benzene series, nitrogen heterocyclic compounds, polycyclic aromatic hydrocarbons, and phenols were 100 %, 100 %, 63.58 %, and 94.12 %, respectively. Research on the physiological response of microbial cells showed that, under optimal ratio regulation, co-metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, the contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) for proteins in the optimal group were 7.12 mg/g-SS and 152.28 mg/g-SS, respectively. Meanwhile, the ratio of α-Helix / (β-Sheet + Random coil) and the proportion of intermolecular interaction forces were also increased in the optimal group. At system completion, the ratio of α-Helix / (β-Sheet + Random coil) reached 0.717 (LB-EPS) and 0.618 (TB-EPS), respectively. Additionally, the proportion of intermolecular interaction forces reached 74.83 % (LB-EPS) and 55.03 % (TB-EPS). An in-depth analysis of the metabolic regulation of microorganisms indicated that the introduction of optimal ratios of co-metabolic substrates contributed to a noteworthy upregulation in the expression of Catechol 2,3-dioxygenase (C23O) and Dehydrogenase (DHA). The expression levels of C23O and DHA were measured at 0.029 U/mg Pro·g MLSS and 75.25 mg TF·(g MLSS·h)−1 (peak value), respectively. Correspondingly, enrichment of aromatic compound-degrading bacteria, including Thauera, Saccharimonadales, and Candidatus_Competibacter, occurred, along with the upregulation of associated functional genes such as Catechol 1,2-dioxygenase, Catechol 2,3-dioxygenase, Protocatechuate 3,4-dioxygenase, and Protocatechuate 4,5-dioxygenase. Considering the intricate system of multiple coexisting aromatic compounds in real CCW, this study not only obtained an optimal ratio for carbon source addition but also enhanced the efficient utilization of carbon sources and improved the capability of the system to effectively degrade aromatic compounds. Additionally, this paper established a theoretical foundation for metabolic regulation and harmless treatment within the biochemical treatment of intricate systems, exemplified by real CCW.

Preparation and adsorption behavior investigation of polypropylene/organically modified saponite nanocomposites fiber membrane with strong oil‐adsorption

AbstractTo improve the adsorption and reusability of polypropylene (PP) fiber membranes, the organically modified saponite (Sap@P(St‐co‐MMA)) was prepared by solution polymerization. Furthermore, PP‐based nanocomposite fiber membranes with strong oil adsorption, thermal stability, and reusability were prepared via melt‐blown technology. The increased specific surface area of PP‐based nanocomposite fiber membranes (PP‐1.5%) provided more active sites for the oil adsorption. Simultaneous rheology and Fourier transform infrared measurements tests showed that Sap@P(St‐co‐MMA) enhanced the crystallinity of PP matrix, promoted the regular arrangement of molecules, and improved the intermolecular interaction force, which was beneficial for the oil adsorption. The adsorption of PP‐1.5% (1.5 wt% addition of Sap@P(St‐co‐MMA)) fiber membrane for xylene and kerosene reached a maximum of 15.84 and 22.84 g g−1, respectively. In the treatment of coal tar wastewater, the removal rate of oil can reach 62.9%, and the removal rate can still reach 51.17% after five cycles of experiments. In summary, PP‐1.5% fiber membrane does not produce secondary pollution to the environment, and is a kind of oil removal material with good application prospect.Highlights PP‐based nanocomposites fiber membrane with strong oil adsorption was prepared. Organically modified saponite had strong heterogenous nucleation for PP matrix. Sap@P(St‐co‐MMA) increased the specific surface area of PP‐based fiber membrane.

Fabrication strategies for chiral self-assembly surface.

Chiral self-assembly is the spontaneous organization of individual building blocks from chiral (bio)molecules to macroscopic objects into ordered superstructures. Chiral self-assembly is ubiquitous in nature, such as DNA and proteins, which formed the foundation of biological structures. In addition to chiral (bio) molecules, chiral ordered superstructures constructed by self-assembly have also attracted much attention. Chiral self-assembly usually refers to the process of forming chiral aggregates in an ordered arrangement under various non-covalent bonding such as H-bond, π-π interactions, van der Waals forces (dipole-dipole, electrostatic effects, etc.), and hydrophobic interactions. Chiral assembly involves the spontaneous process, which followed the minimum energy rule. It is essentially an intermolecular interaction force. Self-assembled chiral materials based on chiral recognition in electrochemistry, chiral catalysis, optical sensing, chiral separation, etc. have a broad application potential with the research development of chiral materials in recent years.

Improving the dielectric properties of polypropylene for metallised film capacitors based on cyclic olefin copolymer blending

AbstractHigh conductivity loss and low breakdown strength of traditional polypropylene (PP) film in the high‐temperature environment are the key factors limiting the application of metallised film capacitors (MFCs). The effect of cyclic olefin copolymers (COCs) with different glass transition temperatures (Tgs) on the dielectric performance of PP/COC composites at high temperature are studied. The results showed that the addition of COC enhanced the intermolecular interaction force, which led to the reduction of defects in the films. In addition, COC with high Tg inhibits the movement of molecular chains and enhances the thermal stability of the film, which limits the transport of carriers at high temperatures. The conductivity and breakdown strength of the modified films (with a Tg of 134°C for COC) at 125°C are 91.6% lower and 45.7% higher, respectively, than that of pure PP. This method shows great potential in improving the dielectric properties of PP at high temperatures.

Molecular Crystals Constructed by Polar Molecular Cages: A Promising System for Exploring High-performance Infrared Nonlinear Optical Crystals.

Polar molecular crystals, with their densely stacked polar nonlinear optical (NLO) active units, are favored for their large second harmonic generation (SHG) responses and birefringence. However, their potential for practical applications as Infrared (IR) NLO materials has historically been underappreciated due to the weak inter-molecular interaction forces that may compromise their physicochemical properties. In this study, we propose molecular crystals with polar molecular cages as a treasure-house for the development of superior IR NLO materials and a representative system, binary chalcogenide molecular crystals, composed of [P4 Sn ] (n=3-9) polar molecular cages, is introduced. These crystals may not only achieve wide band gap, large SHG response, and birefringence in a single structure, but also exhibit favorable physicochemical properties. We subsequently obtained a polar molecular crystal, α-P4 S5 , which demonstrated exceptional IR optical properties, including a strong SHG response (1.1×AGS), wide band gap (3.02 eV), large birefringence (0.134@2050 nm), and a broad transmission range (0.41-14.7 μm). Moreover, it showed excellent water resistance and hardness. These findings highlight the potential of polar molecular crystals as a promising platform for the development of high-performance IR NLO materials.

Effect of subcritical water temperature on the structure, antioxidant activity and immune activity of polysaccharides from Glycyrrhiza inflata Batalin

In this study, the polysaccharide from Glycyrrhiza inflata Batalin extracted by hot water (HW-GP) was further physically modified with subcritical water to obtain novel polysaccharides (SW-GP). Comparative analysis was conducted to examine the disparities in conformation and bioactivity between HW-GP and SW-GP, aiming to precisely regulate the structure of the polysaccharides and enhance their bioactivity by controlling subcritical water temperature. The results showed that, compared with HW-GP, subcritical water modification (100–160 °C) not only significantly reduced the molecular weight of polysaccharides (from 5.586 × 105 g/mol to 1.484 × 105 g/mol), but also modulated the intermolecular interaction forces, which maintain the conformation of the polysaccharides, including electrostatic and hydrophobic interactions, thereby dynamically transforming the polysaccharide chain conformation from triple helix to random coil, and the strength of the chain conformation shifted from rigid to flexible. In addition, the modification of the SW-GP structure by subcritical water also enhanced its biological activity. SW-GP (140 °C) with low molecular weight and semi-rigid triple helix conformation showed the best scavenging effect on the DPPH, ABTS, and hydroxyl radicals, and exhibited excellent antioxidant activity. SW-GP (130 °C) with medium molecular weight and semi-rigid triple helix conformation significantly promoted the proliferation and phagocytosis of RAW264.7 cells, as well as increased the release levels of NO, TNF-α, IL-6, and IL-1β, and the immunomodulatory activity was much higher than that of other polysaccharides. These findings confirmed the feasibility of using subcritical water temperature as a regulatory feature for the structure and bioactivity of glycyrrhiza polysaccharides, which may have reference significance for the modification of polysaccharides with heightened bioactivity.

Acrylonitrile‐styrene‐acrylate particles with different acrylonitrile contents for improving the toughness of poly(vinyl chloride) resin

AbstractPoly(butyl acrylate) grafted styrene and acrylonitrile copolymer (PBA‐g‐SAN, ASA) with core–shell structures were prepared by emulsion polymerization technology to improve the toughness of the poly(vinyl chloride) (PVC). The mechanical properties of the PVC/ASA blends were investigated. The notch impact strength of the PVC/ASA blend could reach 1200 J/m when the 13 phr ASA was added to the PVC. This was several times more than pure PVC resin. Scanning electron microscopy analysis results indicated that the improvement in impact strength of the PVC/ASA blend was attributed to shear yielding induced by ASA particles. Additionally, subtle changes in the ratio of monomers in the shell layer led to significant fluctuations in the mechanical properties of the composites. Dynamic mechanical analysis showed that the intermolecular interaction forces between ASA particles and PVC resins played a key role in improving the toughness of PVC/ASA blend.

Effect of electrothermopolarization on thermal properties of compositions based on polypropylene and MnO2

Information about the internal structure can also be obtained by studying the thermal properties of composites with low molecular weight additives in the low and high temperature range.In this work, by studying the thermophysical properties of PP-based MnO2 composites after exposure to an electric field, we will look at how the additive changes the properties and determine the processes of thermal degradation after aging. Differential thermal analysis (DTA) or thermospectroscopy method is based on measuring the thermal effect when heating or cooling the test substance depending on the temperature. This method makes it possible to quantify the temperature of various transitions with high accuracy. Also that polymer and polymer composite aging relate to the high local anisotropy of force field due to sharp difference of intramolecular and intermolecular interaction forces. By derivatographic method polypropylene films (PP) exposed to electrothermoplarization filled by MnO2 to the extent of 0.5 and 1vol.% have been investigated. By electrothermoplarization E=7×106V/m as a result of aging PP matrix crystals part amorphism is taken place and thermal stability. It is established that electric intensity leads as to the complete amorphism of PP+0.5vol.%MnO2 composition so the complete depolymerization followed by volatilization of formed intermediate products to the extent of 100%.

An ultrasensitive electrochemical sensor for detecting Cd(II) in aquatic products based on CS/COFs/PEDOT: PSS modified acupuncture needle electrode

The use of low-cost working electrodes is of great importance for the development of sensor industrialization. Acupuncture needles electrode (ANE) was selected as working microelectrode, a sensor was designed based on poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT: PSS) and chitosan (CS) modified covalent organic frameworks (COFs) (CS/COFs) for detection of cadmium (Cd(II)). First, a mixture of PEDOT and PSS was electrodeposited on the surface of the acupuncture needles to synthesize a PEDOT: PSS as conductive polymeric film to support the electron transfer capability and enhance the conductive efficiency of the sensor. Then, CS/COFs was self-assembled and attached to the PEDOT: PSS/ANE surface by π-π stacking intermolecular interaction forces and the viscosity of CS, thus increasing the specific surface area of the electrode. Differential pulse anodic stripping voltammetry (DPASV) was used as the electrochemical method for detection of Cd(II). And the results indicated that the CS/COFs/PEDOT: PSS/ANE was linearly responsive in the range of 400 μg/L to 2400 μg/L, and the LOD was 13.8 ng/L for Cd(II). The constructed sensor also showed great selectivity, reproducibility, and stability. Additionally, the sensor demonstrated outstanding recovery in the detection of Cd(II) in real sample scallops. This sensing construction method based on acupuncture needles as working electrodes is of great significance to the development of sensor industrialization and aquatic product safety detection.

SIMULATION OF OSCILLATIONS OF WATER MOLECULES USING THE MODEL OF A TWO-FREQUENCY PENDULUM IN THE JAHN-TELLER POTENTIAL

The interaction potential for water molecules is considered, which corresponds to the presence of bends in hydrogen bonds in it. To explain the nature of this phenomenon, the theory of the Jahn-Teller effect (JTE) is applied. A model of the Jahn–Teller potential (JTP) was constructed, which has a minimum at a certain angle Θ. To simulate oscillations of water molecules in JTP using a pendulum, a correction of the angular potential U1 in the potential of directed forces (PDF) of intermolecular interaction is proposed using a wavelet type additive ΔU1 = c cos(mΘ)/exp(sΘ2). The parameters for the wavelet are selected based on the magnitude of the bending of hydrogen bonds in water (m=s=8, c=0…0.1). Modeling of rotational oscillations of molecules in JTP was carried out using the model of a two-frequency pendulum, which takes into account the ratio of the moments of inertia of the molecule (pendulum) along the axes k=3 and the PDF index n=8 in JTP Un =U1n. New types of pendulum oscillations in the JTP are determined in comparison with the original PDF (c=0) and their features. It is established that several types of oscillations are observed for this potential. These are new: sector, rotation of the pendulum in the potential trough – disordered or ordered, as well as types for PDF: two-frequency independent oscillations (IO) along the axes and ellipse-like oscillations (ELO) at one frequency. Oscillations in the JTP chute are observed for the main range of initial velocities inside an elliptical ring compressed along the Y axis, and only for the ELO, in an elliptical region elongated along the Y axis, as in the PDF. The methodology for calculating and analyzing the oscillation parameters of a two-frequency pendulum has been improved. The boundaries of oscillation types are determined for given parameters of the potential and a number of initial data. The difference between the patterns of oscillations is established for cases when the initial displacement of the pendulum is greater or less than the position of the minimum of the JTP. It is shown that the velocities at the boundary of the transition from the rotation of the pendulum in the potential trough to the IO correlate with the magnitude of the JTP maximum on the axis of the pendulum. The presence of stable transverse vibrations in the JTP for the case of protons of water molecules can apparently be considered as a new degree of freedom for vibrations of water molecules, which can lead to an explanation of the large contribution of rotational vibration modes to its heat capacity.

Intermolecular Non-Bonded Interactions from Machine Learning Datasets

Accurate determination of intermolecular non-covalent-bonded or non-bonded interactions is the key to potentially useful molecular dynamics simulations of polymer systems. However, it is challenging to balance both the accuracy and computational cost in force field modelling. One of the main difficulties is properly representing the calculated energy data as a continuous force function. In this paper, we employ well-developed machine learning techniques to construct a general purpose intermolecular non-bonded interaction force field for organic polymers. The original ab initio dataset SOFG-31 was calculated by us and has been well documented, and here we use it as our training set. The CLIFF kernel type machine learning scheme is used for predicting the interaction energies of heterodimers selected from the SOFG-31 dataset. Our test results show that the overall errors are well below the chemical accuracy of about 1 kcal/mol, thus demonstrating the promising feasibility of machine learning techniques in force field modelling.

Identification and Verification of Novel Umami Peptides Isolated from Hybrid Sturgeon Meat (Acipenser baerii × Acipenser schrenckii).

To explore the umami mechanism in sturgeon meat, five peptides (ERRY, VRGPR, LKYPLE, VKKVFK, and YVVFKD) were isolated and identified by ultrafiltration, gel filtration chromatography, and UPLC-QTOF-MS/MS. The omission test confirmed that the five umami peptides contributed to the umami taste of sturgeon meat. Also, the peptides had the double effective role of enhancing both umami and saltiness. The threshold of ERRY was only 0.031, which exceeded most umami peptides in the last 3 years. Molecular docking results showed that five peptides could easily bind to Gly167, Ser170, and Try218 residues in T1R3 through hydrogen bonds and electrostatic interactions. Furthermore, molecular dynamics simulations indicated that hydrogen bonds and hydrophobic interactions were the main intermolecular interaction forces. This study could contribute to revealing the umami taste mechanism of sturgeon meat and provide new insights for effective screening of short umami peptides.

Polyimide films with ultralow dielectric loss for 5G applications: Influence and mechanism of ester groups in molecular chains

Polyimides are ideal candidates for 5G high-frequency communications due to their good thermal stability, mechanical properties and processability. However, the exploration of how to reduce their high-frequency dissipation factor (Df) remains an urgent and alluring challenge. Inspired by the molecular structure of liquid crystal polyester, which is insensitive to high-frequency electric fields, here we design two series of polyimides derived from diamines with multiple ester groups (AXEB, X = 1, 2 or 3) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or p-phenylene bis (trimellitate anhydride) (TA2EB). We investigated the effects of ester number on the aggregation structure, water absorption, dielectric properties, heat resistance and mechanical properties of the polyimides and find that the Df of the multiple ester-containing polyimides decreases rapidly with increasing frequency and number of ester groups. Wide-angle X-ray diffraction analysis, polarized optical microscopy observations and molecular dynamics simulations show that the unique properties of these polyimides benefit from the tight packing of the molecular chain and the strong intermolecular interaction force caused by the ester group, as well as the resulting prolonged dipole relaxation time and the greatly reduced water absorption. Therefore, the polyimide films show extremely low Df values of 0.0030 for AXEB-6FDA and 0.0013 for AXEB-TA2EB. Furthermore, AXEB-TA2EB also shows excellent thermal stability, mechanical properties, electrical properties and permittivity. More importantly, their ultralow moisture rate (<0.83 %) ensures that the high-frequency Df remains stable in different humid environments, even after soaking in water. This method can also be extended to other polymers, thus providing a new strategy for the design of low dielectric loss materials.

Highly conductive anion-exchange membrane based on poly(acenaphthylenyl aryl piperidinium) π-π self-assembly

The use of strong intermolecular interaction force to promote the formation of ion transport channels is one of the common methods to increase the conductivity of AEMs. In this work, a series of poly(acenaphthylenyl aryl piperidinium) membranes and ionomer were prepared by ultra-strong acid-catalyzed polymerization. The π-π self-assembly of acenaphthylene monomer promoted the aggregation of piperidinium cation and the formation of efficient ion transport channel, which was confirmed by well aggregated transmission electron micrographs of the ion clusters. Therefore, the prepared membrane had desirable conductivity (173.38 mS cm−1 at 80 °C). Meanwhile, the membrane exhibited excellent alkaline stability (99 % retention of conductivity in 3 M NaOH solution immersed at 80 °C for 1000 h), acceptable dimensional stability (swelling rate < 27.78 % at 80 °C), and high mechanical properties (tensile strength >33.9 MPa). The H2/O2 fuel cell assembled based on the prepared QPANTP-20 membrane and ionomer exhibited peak power density of 266 mW cm−2 at 80 °C.

Influence on the volatilization of ethyl esters: Nonnegligible role of long-chain fatty acids on Baijiu flavor via intermolecular interaction

Long-chain fatty acids (LCFAs) are commonly presented in Baijiu, but their influence on flavor is ambiguous. The interaction between LCFAs and volatiles was systematically investigated in terms of chemometrics, sensory, and chemical-physical perceptions. The static-headspace-gas-chromatography-mass-spectrometry results demonstrated LCFAs suppressed the volatilizations of most volatiles. According to Phase-ratio-variation analysis, partition coefficients of ethyl acetate (EA) and ethyl hexanoate (EH) decreased 4%–31% and 27%–74%, while those of ethyl butyrate (EB) increased. Calculated by molecular dynamic simulation, the attractive intermolecular forces related to EA/EH increased with oleic acid (OA) addition, while those related to EB decreased. Sensory evaluation confirmed the olfactory threshold of EA and EH increased by 2.4 and 2.7 times respectively, but the threshold of EB decreased from 0.36 to 0.05 mg/L in the presence of OA. Overall, LCFAs altered the intermolecular interaction forces related to esters and ethanol, subsequently affecting the volatile profile and modifying Baijiu flavor's sensory perception.

Relationship between physical, mechanical and thermal properties of flexible chain polymers

The results of the study on the relationship between the physical, mechanical and thermal properties of linear flexible polymers due to the harmonic and anharmonic components of the interatomic and intermolecular interaction force are presented. Using the example of polyvinyl chloride (PVC), polyvinyl butyral (PVB), polystyrene (PS), it is shown that in the region of 300 K &lt; = T &lt; = 400 K, the relaxation state of the system is realized due to the mobility of the structural elements, which makes it possible to apply the terms of thermodynamics and statistics of small systems to the properties of the material, and to treat the polymeric state as a special form of condensation of matter. The quantitative relationship between the properties of systems has been established, which is of interest for creating scientific foundations for predicting, obtaining and operating materials under the action of external fields of various nature.

Changes in Intermolecular Interaction Forces Inducing Glass Transition Determined by Three-Dimensional Aggregated Structural Models of Coal

Changes in Intermolecular Interaction Forces Inducing Glass Transition Determined by Three-Dimensional Aggregated Structural Models of Coal

Molecular simulation of the effect of dioctyl phthalate on the properties of nitrile rubber

The mechanical and tribological properties of pure nitrile rubber (NBR) and dioctyl phthalate/nitrile rubber (DOP/NBR) composite materials with mass ratios of 5/95, 10/90, 15/85, 20/80, 25/75, and 30/70 were studied through molecular dynamics simulations at the molecular level. The root mean square displacement (RMSD) and gyration radius of the composite materials were investigated to explore the mechanism of DOP plasticizing NBR. Different models of pure NBR and DOP/NBR composite materials with different mass ratios were established, and the mechanical properties of the materials were calculated by using the constant strain method. The tribological properties of the materials were studied by applying shear velocity on the surface of the materials. The research results showed that the shear resistance of the DOP/NBR composite material increased and then decreased with the increase of the DOP mass ratio, and the same pattern was observed for the shear modulus. Compared with pure NBR materials, DOP/NBR composite materials demonstrated better mobility and flexibility, and the RMSD and gyration radius of the material increased and then decreased with the increase of the DOP mass ratio. The DOP plasticization of NBR reduced the intermolecular interaction forces and changed the molecular conformation, increasing the softness and plasticity of the polymer chains.

Phenomenological Interactions during CVT Synthesis of Large Scale MoS2

In the Chemical Vapor Transport (CVT), for deposition of MoS2, sulfur and MoO3 powder is evaporated at 200 0C and 650 0C respectively. The Ar flow directs the sulfur atoms to Mo species so as to react chemically as specified in the reactions in Equation-1. During the CVT process there is adsorption of MoS2 on Si/SiO2 substrate associated with the exhuast of SO2 as chemical reaction by-product. The MoS2 is deposited on the substrate by physisorption. Thus, in CVT, the nucleation and growth is a combined effect of chemisorption and physisorption. The three types of nucleation and growth theories for deposition of 2D thin films are presented by a. Volmer–Weber b.Frank–van der Merwe, c. Stranski–Krastanov in Figure 1.Figure 1[Equation 1]The mechanism for MoS2 nucleation and growth during CVT involves the evaporation of powdered precursors at a high temperature which leads to decomposition as well, followed by a chemical reaction. Temperature ramping-up rate, positioning of precursors, type and flow rate of carrier gases, Cooling rate, and pressure simultaneously determine the morphology, thickness, and crystallinity of the physisorbed MoS2. The highly simplified resolution of forces acting during the nucleation process is represented in Figure 2. The σF refers to the forces due to surface tension along the droplet, σS is the force exerted due to the energy associated with the substrate surface, and σFS is the force due to the interface energy between the droplet and the substrate. A little consideration of the comparison of the magnitude of these three forces leads to the determination of Growth Kinetics. When σS is smaller than the sum of σF and σFS, it favors Weber-Volmer theory; when σS is greater than the sum of σF and σFS, it favors Frank van der Merwe theory, and when the balance of this comparison fluctuates or is equal, it favors the Stranski–Krastanov growth model. In practice, the several parameters other than temperature, pressure, flow rate, and precursor flux that influence the nucleation and growth mechanism involve substrate surface texture, functionalization, availability of active cites, steric hindrance, Columbic interactions etc.Figure 2 Interactions in CVT on the basis of Scientific Theories : Considering that CVT involves the gas phase chemical reaction of precursors and physisorption for the MoS2 adsorption on the Si/SiO2 substrate, the modified ideal gas law can be applied more realistically with the introduction of the van der Waals parameters for intermolecular interaction forces ‘a’ and molecular size ‘b’. The modified gas law is stated by van der Waals equation as,[Equation 2]a – Constant for Intermolecular forces and b – Constant for Molecular size for the specified gas under consideration. Thus, if studies related to variation in temperature are carried out, Volume being physically constant and significantly large space in case of CVT may be considered as independent parameter. Thus, from relation 2, pressure is directly affected with the change in temperature.Further, the pressure in accordance with Amonton’s law affects the adsorption and mean free path of the Mo and S atoms that determines the reaction between the chemical species [3].The mean free path for the atomized precursor is expressed as follows.[Equation 3]The dependence of the mean free path λ on T – temperature and P – the pressure is conclusive for the parametric interactions resulting in accordance with the Amonton’s law for constant volume affect the CVT process. In the equation, is the Boltzman’s constant.As referred to in the beginning, physisorption is the mechanism for depositing 2D thin films in CVT. Physisorption is caused by adsorption and thus, the variation in process parameters will have impact on Langmuir’s adsorption [4]given by[Equation 4]Langmuir’s adsorption isotherm explains the interfacial interaction of the gas phase molecules with the substrate. The Figure 3. depicts the variation in corresponding to the KP at a constant temperature. As is evident the Langmuir’s adsorption is derived at isothermal conditions for variation in pressure. Thus, it is implied that during the CVT synthesis of MoS2 if the variation in temperature is studied, it will inherently affect the adsorption.Arrhenius equation [5] governs the reaction rate based on A- pre-exponent rate factor, Ea – activation energy, R – gas constant and temperature.[Equation 5]Considering the van der Waals equation and Amontons law, the temperature is going to affect the pressure. The rate constant will be affected by Ar flow rate. These phenomological interactions occur and influence the nucleation and large scale growth of MoS2 during CVT synthesis. Figure 1