Kinetics of Homoallylic/Homobenzylic Rearrangement Reactions under Combustion Conditions

Homoallylic/homobenzylic radicals refer to typical radicals with the radical site located at the β position from the vinyl/phenyl group. These radicals are largely involved in combustion systems, such as the pyrolysis or oxidation of alkenes, cycloalkanes, and aromatics. The 1,2-vinyl/phenyl migration via two steps (cyclization/fission) is a peculiar reaction type for the homoallylic/homobenzylic radicals, entitled homoallylic/homobenzylic rearrangement, which has been studied by theoretical calculations including the Hirshfeld atomic charge analysis in the present work. With the help of rate constant calculations, the competition between this reaction channel and other possible pathways under combustion temperatures (500–2000 K) were evaluated. Analogous 1,3- and 1,4-vinyl/phenyl migration reactions for similar radicals with the radical sites located at the γ and δ positions from the vinyl/phenyl group were also computed. The results indicate that the 1,2-vinyl/phenyl migration is particularly important for the kinetics of unimolecular reactions of homoallylic radicals under 1500 K; nevertheless, it still has noticeable contribution at higher temperature. For those radicals with the radical site at the γ or δ positions, the respective 1,3- or 1,4-vinyl/phenyl migration channel plays an insignificant role under combustion conditions

Electrochemistry-Triggered Microscopic Wrinkle Patterns That Improve the Sensitivity of Hydrogel Sensors

To improve the signal-to-noise ratio of strain sensors, a critical factor involves improving the change ratio of resistance in response to an external force. Traditional methods such as templating, prestretching, or asymmetric swelling can construct wrinkles on hydrogel but do not alter its conductive characteristics and improve the change ratio of resistance. Herein, we report an electrochemical protocol that can trigger homogeneous hydrogel to form the gradient distribution of mechanical strength and induce microscopic wrinkle patterns at the surface of hydrogel. The electrode reactions produce metal ions (Fe3+) inside the hydrogel, in which the electric field-driven ion migration results in the gradient distribution of Fe3+ ions, the closer to the wrinkle patterning surface of hydrogel, the higher content of Fe3+ ions. Large amounts of Fe3+ ions concentrate at the wrinkle surface, which improves the conductive characteristics of hydrogel. Therefore, upon compression at the wrinkle surface, the hydrogel sensor shows the higher change ratio of resistance. We demonstrate this feature by testing the weak vibration such as motion of soft brush and rolling of glass rods at the wrinkle surface of hydrogel, which shows the wrinkle patterns can improve the signal intensity of hydrogel sensor by two times. These results highlight the potential of our method for the construction of microscopic wrinkle structures to improve the sensitivity of hydrogel sensors

Electrochemistry-Triggered Microscopic Wrinkle Patterns That Improve the Sensitivity of Hydrogel Sensors

To improve the signal-to-noise ratio of strain sensors, a critical factor involves improving the change ratio of resistance in response to an external force. Traditional methods such as templating, prestretching, or asymmetric swelling can construct wrinkles on hydrogel but do not alter its conductive characteristics and improve the change ratio of resistance. Herein, we report an electrochemical protocol that can trigger homogeneous hydrogel to form the gradient distribution of mechanical strength and induce microscopic wrinkle patterns at the surface of hydrogel. The electrode reactions produce metal ions (Fe3+) inside the hydrogel, in which the electric field-driven ion migration results in the gradient distribution of Fe3+ ions, the closer to the wrinkle patterning surface of hydrogel, the higher content of Fe3+ ions. Large amounts of Fe3+ ions concentrate at the wrinkle surface, which improves the conductive characteristics of hydrogel. Therefore, upon compression at the wrinkle surface, the hydrogel sensor shows the higher change ratio of resistance. We demonstrate this feature by testing the weak vibration such as motion of soft brush and rolling of glass rods at the wrinkle surface of hydrogel, which shows the wrinkle patterns can improve the signal intensity of hydrogel sensor by two times. These results highlight the potential of our method for the construction of microscopic wrinkle structures to improve the sensitivity of hydrogel sensors

Electrochemistry-Triggered Microscopic Wrinkle Patterns That Improve the Sensitivity of Hydrogel Sensors

To improve the signal-to-noise ratio of strain sensors, a critical factor involves improving the change ratio of resistance in response to an external force. Traditional methods such as templating, prestretching, or asymmetric swelling can construct wrinkles on hydrogel but do not alter its conductive characteristics and improve the change ratio of resistance. Herein, we report an electrochemical protocol that can trigger homogeneous hydrogel to form the gradient distribution of mechanical strength and induce microscopic wrinkle patterns at the surface of hydrogel. The electrode reactions produce metal ions (Fe3+) inside the hydrogel, in which the electric field-driven ion migration results in the gradient distribution of Fe3+ ions, the closer to the wrinkle patterning surface of hydrogel, the higher content of Fe3+ ions. Large amounts of Fe3+ ions concentrate at the wrinkle surface, which improves the conductive characteristics of hydrogel. Therefore, upon compression at the wrinkle surface, the hydrogel sensor shows the higher change ratio of resistance. We demonstrate this feature by testing the weak vibration such as motion of soft brush and rolling of glass rods at the wrinkle surface of hydrogel, which shows the wrinkle patterns can improve the signal intensity of hydrogel sensor by two times. These results highlight the potential of our method for the construction of microscopic wrinkle structures to improve the sensitivity of hydrogel sensors

Thermal Decomposition of 1‑Pentanol and Its Isomers: A Theoretical Study

Pentanol is one of the promising “next generation” alcohol fuels with high energy density and low hygroscopicity. In the present work, dominant reaction channels of thermal decomposition of three isomers of pentanol: 1-pentanol, 2-methyl-1-butanol, and 3-methyl-1-butanol were investigated by CBS-QB3 calculations. Subsequently, the temperature- and pressure-dependent rate constants for these channels were computed by RRKM/master equation simulations. The difference between the thermal decomposition behavior of pentanol and butanol were discussed, while butanol as another potential alternative alcohol fuel has been extensively studied both experimentally and theoretically. Rate constants of barrierless bond dissociation reactions of pentanol isomers were treated by the variational transition state theory. The comparison between various channels revealed that the entropies of variational transition states significantly impact the rate constants of pentanol decomposition reactions. This work provides sound quality kinetic data for major decomposition channels of three pentanol isomers in the temperature range of 800–2000 K with pressure varying from 7.6 to 7.6 × 10⁴ Torr, which might be valuable for developing detailed kinetic models for pentanol combustion

Theoretical Studies on the Unimolecular Decomposition of Propanediols and Glycerol

Polyols, a typical type of alcohol containing multiple hydroxyl groups, are being regarded as a new generation of a green energy platform. In this paper, the decomposition mechanisms for three polyol molecules, i.e., 1,2-propanediol, 1,3-propanediol, and glycerol, have been investigated by quantum chemistry calculations. The potential energy surfaces of propanediols and glycerol have been built by the QCISD­(T) and CBS-QB3 methods, respectively. For the three molecules studied, the H₂O-elimination and C–C bond dissociation reactions show great importance among all of the unimolecular decomposition channels. Rate constant calculations further demonstrate that the H₂O-elimination reactions are predominant at low temperature and pressure, whereas the direct C–C bond dissociation reactions prevail at high temperature and pressure. The temperature and pressure dependence of calculated rate constants was demonstrated by the fitted Arrhenius equations. This work aims to better understand the thermal decomposition process of polyols and provide useful thermochemical and kinetic data for kinetic modeling of polyols-derived fuel combustion

Toward High-Level Theoretical Studies of Large Biodiesel Molecules: An ONIOM [QCISD(T)/CBS:DFT] Study of the Reactions between Unsaturated Methyl Esters (C_<i>n</i>H_{2<i>n</i>–1}COOCH₃) and Hydrogen Radical

A two-layer ONIOM­[QCISD­(T)/CBS:DFT] method was proposed for the high-level single-point energy calculations of large biodiesel molecules and was validated for the hydrogen abstraction reactions of unsaturated methyl esters that are important components of real biodiesel. The reactions under investigation include all the reactions on the potential energy surface of C_<i>n</i>H_{2<i>n</i>–1}COOCH₃ (<i>n</i> = 2–5, 17) + H, including the hydrogen abstraction, the hydrogen addition, the isomerization (intramolecular hydrogen shift), and the β-scission reactions. By virtue of the introduced concept of chemically active center, a unified specification of chemically active portion for the ONIOM (ONIOM = our own <i>n</i>-layered integrated molecular orbital and molecular mechanics) method was proposed to account for the additional influence of CC double bond. The predicted energy barriers and heats of reaction by using the ONIOM method are in very good agreement with those obtained by using the widely accepted high-level QCISD­(T)/CBS theory, as verified by the computational deviations being less than 0.15 kcal/mol, for almost all the reaction pathways under investigation. The method provides a computationally accurate and affordable approach to combustion chemists for high-level theoretical chemical kinetics of large biodiesel molecules

Humidity- and Sunlight-Driven Motion of a Chemically Bonded Polymer Bilayer with Programmable Surface Patterns

We report a bilayer of sodium alginate/polyvinylidene fluoride (SA/PVDF) that is chemically bonded through a series of interfacial coupling reactions. The SA layer is hydrophilic in structure and is capable of strong interaction with water molecules, thus presenting high sensitivity to humidity, whereas the PVDF layer is hydrophobic, inert to humidity. This structural feature results in the bilayer having asymmetric humidity-responsive performances that can thus make its shape change with directionality, which cannot be achieved in an SA single layer. The responsive process to humidity can be adjusted by exposure of the bilayer to sunlight by means of a photothermal effect that accelerates dehydration of the bilayer to cause more rapid shape deformations. When the sunlight is removed, the bilayer adsorbs humidity again and returns to its original shape, indicating good reversibility. To exactly regulate the shape deformations of the bilayer with external stimuli, we employ Ca²⁺-treated filter paper to customize crosslinking reactions in the SA layer as desired patterns which are capable of causing different mechanical tensors and swellabilities in the bilayer so as to regulate and control the actuations for self-folding, curling, twisting, and coiling in response to sunlight and humidity.On the other hand, the chemically bonded bilayer has stronger interfacial toughness and is capable of reaching 300 J m^–2, which is around 12 times the interfacial toughness of the physically combined bilayer; as a result, the chemically bonded bilayer is capable of sustaining continuous shape deformations without interfacial failure. The directionally mechanical actuations can be utilized in designing an indicator to roughly indicate the range of intensity of sunlight by coupling the chemically bonded bilayer into a typical electric circuit, in which the range of intensity of sunlight can be easily estimated by visual observation of the light-emitting diodes

Theoretical Studies on the Unimolecular Decomposition of Ethylene Glycol

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H₂O-elimination channels have the lowest barriers, and the C–C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H₂O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C–C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500–2000 K, the calculated rate constant is expressed to be 7.63 × 10⁴⁷<i>T</i>^–10.38 exp(−42262/<i>T</i>) for the channel CH₂OHCH₂OH → CH₂CHOH + H₂O, and 2.48 × 10⁵¹<i>T</i>^–11.58 exp(−43593/<i>T</i>) for the channel CH₂OHCH₂OH → CH₃CHO + H₂O, whereas for the direct bond dissociation reaction CH₂OHCH₂OH → CH₂OH + CH₂OH the rate constant expression is 1.04 × 10⁷¹<i>T</i>^–16.16 exp(−52414/<i>T</i>)

Marangoni Effect-Driven Motion of Miniature Robots and Generation of Electricity on Water

The well-known Marangoni effect perfectly supports the dynamic mechanism of organic solvent-swollen gels on water. On this basis, we report a series of energy conversion processes of concentrated droplets of polyvinylidene fluoride/dimethyl formamide (PVDF/DMF) that can transfer chemical-free energy to kinetic energy to rapidly rotate itself on water. This droplet (22.2 mg) is capable to offer kinetic energy of 0.099 μJ to propel an artificial paper rocket of 31.8 mg to move over 560 cm on water at an initial velocity of 7.9 cm s^–1. As the droplet increases to 35.0 mg, a paper goldfish of 10.6 mg can be driven to swim longer at a higher initial velocity of 20 cm s^–1. The kinetic energy of the droplet can be further converted to electrical energy through an electromagnetic generator, in which as a 0.5 MΩ resistor is loaded, the peak output reaches 6.5 mV that corresponds to the power density of 0.293 μW kg^–1. We believe that this report would open up a promising avenue to exploit energies for applications in miniature robotics