Free Volume Analysis and Transport Mechanisms of PVC Modified with Fluorothiophenol Compounds. A Molecular Simulation Study

Thermomechanical Properties of Nontoxic Plasticizers for Polyvinyl Chloride Predicted from Molecular Dynamics Simulations

Environmental and toxicity concerns dictate replacement of di(2-ethylhexyl) phthalate (DEHP) plasticizer used to impart flexibility and thermal stability to polyvinyl chloride (PVC). Potential alternatives to DEHP in PVC include diheptyl succinate (DHS), diethyl adipate (DEA), 1,4-butanediol dibenzoate (1,4-BDB), and dibutyl sebacate (DBS). To examine whether that these bio-based plasticizers can compete with DEHP, we need to compare their tensile, mechanical, and diffusional properties. This work focuses on predicting the effect these plasticizers have on T_g, Young's modulus, shear modulus, fractional free volume, and diffusion for PVC-plasticizer systems. Where data was available, the results from this study are in good agreement with the experiment; we conclude that DBS and DHS are most promising green plasticizers for PVC, since they have properties comparable to DEHP but not the environmental and toxicity concerns.

Diffusion Behavior of VOC Molecules in Polyvinyl Chloride Investigated by Molecular Dynamics Simulation

Due to the threats posed by many volatile organic compounds (VOCs) to human health in indoor spaces via air, the mass transfer characteristics of VOCs are of critical importance to the study of their mechanism and control. As a significant part of the mass transfer process, diffusion widely exists in emissions from floors (e.g., PVC floors) and in sorption in porous materials. Molecular simulation studies by can provide unparalleled insights into the molecular mechanisms of VOCs. We construct the detailed atomistic structures of PVC blend membranes to investigate the diffusion behavior of VOC molecules (n-hexane) in PVC by molecular dynamics (MD). The variation in the diffusion coefficient of n-hexane in PVC with respect to temperature is in line with Arrhenius' law. The effect of temperature on the diffusion mechanism was investigated from the perspectives of free volume, cavity distribution and polymer chain mobility. It was found that the relationships between the diffusion coefficients of n-hexane in the polymer and the inverse fractional free volume are exponential and agree well with the free volume theory. Hopefully, this study will offer quantitative insights into the mass transport phenomena of VOCs within polymeric materials.

Large Transconductance of Electrochemical Transistors Based on Fluorinated Donor-Acceptor Conjugated Polymers

Organic electrochemical transistors (OECTs) have enormous potential for use in biosignal amplifiers, analyte sensors, and neuromorphic electronics owing to their exceptionally large transconductance. However, it is challenging to simultaneously achieve high charge carrier mobility and volumetric capacitance, the two most important figures of merit in OECTs. Herein, a method of achieving high-performance OECT with donor-acceptor conjugated copolymers by introducing fluorine units is proposed. A series of cyclopentadithiophene-benzothiadiazole (CDT-BT) copolymers for use in high-performance OECTs with enhanced charge carrier mobility (from 0.65 to 1.73 cm²·V^-1·s^-1) and extended volumetric capacitance (from 44.8 to 57.6 F·cm^-3) by fluorine substitution is achieved. The increase in the volumetric capacitance of the fluorinated polymers is attributed to either an increase in the volume at which ions can enter the film or a decrease in the effective distance between the ions and polymer backbones. The fluorine substitution increases the backbone planarity of the CDT-BT copolymers, enabling more efficient charge carrier transport. The fluorination strategy of this work suggests the more versatile use of conjugated polymers for high-performance OECTs.

Simulation Study on the Screening of Hydrophobic Surface Materials for Pipeline Drag Reduction Based on Adsorption Properties

Hydrophobic surface drag reduction techniques are effective in reducing the frictional resistance of fluids, the adsorption of liquid molecules on hydrophobic surfaces can reflect the resistance to fluid flow through such solid surfaces. Based on molecular simulation technology, we investigate the adsorption characteristics of water molecules on hydrophobic surfaces to achieve rapid screening of hydrophobic materials in fire-fighting water supply systems. The Monte Carlo method was used to simulate the adsorption process of polymers and to analyze the effects of temperature and fixed adsorption quantity. Contact angle tests were also done to verify polymer hydrophobicity. The isothermal adsorption heat, water molecule distribution, and energy distribution were studied by molecular mechanics and molecular dynamics methods. Then, adsorption localization simulations and electrostatic potential distributions were used to predict possible adsorption sites on hydrophobic surfaces and single-molecule chains. Finally, the interaction energy, diffusion coefficient, and free volume were investigated to explain the adsorption mechanism at the molecular level. Simulation results show that, overall, PTFE was more hydrophobic and PES was more hydrophilic and at 298 K, the number of adsorbed water molecules was ranked as follows: PTFE < PVDF < PVC < PMMA < PPS < CSM < BD-HDI < BD-MDI < BD-TDI < PES. Furthermore, PTFE, PVDF, PVC, PES, and PPS have more stable adsorption configurations on the (0 -1 0) surface. According to the findings, hydrogen bonding dominates the interaction between water molecules and hydrophilic polymers, whereas π-π interactions increase water molecules' diffusion resistance in polymers with benzene rings. In addition, PES contains many sulfone groups and ether bonds, which disorganize the chain arrangement to provide more free volume, whereas the water adsorption rate of PTFE is reduced because its molecular chains are less convoluted and more organized.

Accelerated Diffusion Following Deprotection in Chemically Amplified Resists

Polymeric chemically amplified resists (CARs) are critical materials for high-throughput lithographic processes. A photoactivated acid-anion catalyst changes the polymer's solubility via a deprotection reaction, which enables pattern development through selective dissolution. To capture observed reaction kinetics, reaction-diffusion models employ a catalyst diffusivity that is accelerated by reaction. However, the microscopic origin and factors contributing to this phenomena remain unclear. Herein, we employ detailed atomistic molecular dynamics simulations to examine the impact of protecting group removal and material relaxation on catalyst mobility. We report data on polymer density, catalyst dispersion, excess free volume, and segmental dynamics with increasing time/extent of deprotection. We then propose simple kinetic Monte Carlo algorithms that can describe both molecular dynamics simulations of deprotection reactions and experimental data.

Study of the Effects of the Structure of Phthalazinone’s Side-Group on the Properties of the Poly(phthalazinone ether ketone)s Resins

The application of poly(phthalazinone ether ketone)s (PPEKs) resin containing phthalazinone moiety is limited, due to its poor thermoforming processability. To investigate the effects of the phthalazinone’s side-group on the thermal stability and processability of the resin, a series of PPEKs resins with different side-group (–H/–CH₃/–Ph) were prepared by nucleophilic aromatic substitution polymerization. The properties of the obtained resins were investigated by differential scanning calorimetry analysis (DSC), thermogravimetric analysis (TGA), dynamic thermomechanical analysis (DMA), and rheogoniometer. The results show that the introduction of methyl or phenyl into the PPEKs resin, significantly reduced the melting viscosity of the resin, but resulted in a slight decrease in the thermal stability of it. This might be due to the presence of methyl or phenyl, which enhanced the free volume of the molecule and reduced the entanglement between the chains; the results of the computer simulation confirmed it. Moreover, the resin films displayed excellent tensile strength with the introduction of methyl or phenyl. In a word, a novel poly(phthalazinone ether ketone)s resin with thermal resistance, easy processing and excellent mechanical properties could be obtained by introducing appropriate bulk-rigid side-groups into the phthalazinone moiety.

Effect of Hindered Phenol Crystallization on Properties of Organic Hybrid Damping Materials

Organic hybrid damping materials have achieved sustainable development in recent years for superior damping properties due to the hydrogen bonding of hindered phenol. However, the aggregation and crystallization of hindered phenol in the matrix can lead to a sharp decline in material properties. Thus, a series of hindered phenol hybrid carboxylated nitrile rubber (XNBR) composites with different types and contents of hindered phenol were prepared by melt blending to study the effects of different hindered phenol on the properties of organic hybrid damping materials. A dynamic mechanical analyzer (DMA) and scanning electron microscope (SEM) were used to study the dynamic mechanical properties and cross-section morphology of composites. X-ray diffraction (XRD) was used to study the crystallization of hindered phenol. The results show that the properties of organic hybrid damping materials were affected by the structure of hindered phenol, and that hindered phenol molecules with a linear structure had better performances. The greater the number of hydrogen bonds between hindered phenol and the XNBR matrix, the more difficult it was for the hindered phenol to crystallize.