Multi-walled carbon nanotubes acting as antioxidant for fluorosilicone rubber

Rational Design of Oil-Resistant and Electrically Conductive Fluorosilicone Rubber Foam Nanocomposites for Sensitive Detectability in Complex Solvent Environments

Recent years have witnessed the explosive development of highly sensitive smart sensors based on conductive polymer foam materials. However, the design and development of multifunctional polymeric foam composites as smart sensors applied in complex solvent and oil environments remain a critical challenge. Herein, we design and synthesize vinyl-terminated polytrifluoropropylmethylsiloxane through anionic ring-opening polymerization to fabricate fluorosilicone rubber foam (FSiRF) materials with nanoscale wrinkled surfaces and reactive Si-H groups via a green and rapid chemical foaming strategy. Based on the strong adhesion between FSiRF materials and consecutive oxidized ketjen black (OKB) nano-network, multifunctional FSiRF nanocomposites were prepared by a dip-coating strategy followed by fluoroalkylsilane modification. The optimized F-OKB@FSiRF nanocomposites exhibit outstanding mechanical flexibility in wide-temperature range (100 cycle compressions from -20 to 200 °C), structure stability (no detached particles after being immersed into various aqueous solutions for up to 15 days), surface superhydrophobicity (water contact angle of 154° and sliding angle of ∼7°), and tunable electrical conductivity (from 10-5 to 10-2 S m-1). Additionally, benefiting from the combined actions of multiple lines of defense (low surface energy groups, physical barriers, and "shielding effect"), the F-OKB@FSiRF sensor presents excellent anti-swelling property and high sensitivity in monitoring both large-deformation and tiny vibrations generated by knocking the beaker, ultrasonic action, agitating, and sinking objects in weak-polar or nonpolar solvents. This work conceivably provides a chemical strategy for the fabrication of multifunctional polymeric foam nanocomposite materials as smart sensors for broad applications.

Preparation and characterization of high molecular weight vinyl-containing poly[(3,3,3-trifluoropropyl)methylsiloxane

Prior to crosslinking and vulcanization, fluorosilicone rubber is a linear polymer. This linear polymer contains 3,3,3,-trifluoropropyl methyl siloxane links, a few methyl vinyl siloxane links, and is formed by co-polymerization of 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl) cyclotrisiloxane (D3F) with 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4) under alkaline conditions. To improve the performance of fluorosilicone rubber, three key points should be considered during the synthesis of vinyl-containing high-molecular-weight linear fluorosilicone polymers (fluorosilicone raw rubber): first, avoid the generation of low molecular weight equilibrium by-products; second, eliminate the influence of impurities; and third, increase the copolymerization participation rate of monomer V4. From the three aspects above, this study optimized the reaction conditions for the synthesis of high-molecular-weight linear fluorosilicone polymers containing vinyl. Various factors influencing polymerization were thoroughly investigated. These factors include the initiation system, accelerator, equilibrium reaction, feeding ratio, feeding sequence, neutralization mode, impurity content, etc.

Improving the thermal stability of poly[methyl(trifluoropropyl)siloxane] by introducing diphenylsiloxane units

A series of poly(methyl(trifluoropropyl)-diphenyl siloxane) (P(MTFPS-co-DPS)) was synthesized by polycondensation of diphenylsilanediol and methyltrifluoropropylsiloxanediol. Their chemical structures were investigated by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and differential scanning calorimeter (DSC). The effect of diphenylsiloxane (DPS) units on the thermal stability of poly[methyl(trifluoropropyl)siloxane] (PMTFPS) was studied by thermogravimetric analysis (TGA), isothermal degradation tests, and pyrolysis-gas chromatography-mass spectrometry (Py-GCMS). The results showed that the thermal stability of PMTFPS improved with the introduction of DPS units into the chain. In particular, the temperature for 5% mass loss in PMTFPS increased by 72 °C under a nitrogen atmosphere. In addition, the mechanism by which the DPS units improve the thermal stability of PMTFPS was also investigated.

Pristine, carboxylated, and hybrid multi-walled carbon nanotubes exert potent antioxidant activities in in vitro-cell free systems

Multi-walled carbon nanotubes (MWCNTs) are tubular-shaped carbon allotropes, composed of multiple concentric graphene cylinders. The extended systems of conjugated double bonds, that MWCNTs are constituted by, provide them with high electron affinities, enabling them to act as electron donors or acceptors. Consequently, their potential biomedical applications, as synthetic antioxidant agents, are of particular interest. Based on the above, the purpose of the present study was to evaluate the intrinsic antioxidant properties of pristine and carboxylated MWCNTs, as well as of novel hybrid nanocomposites of MWCNTs and inorganic nanoparticles. To this end, after the synthesis and characterization of MWCNTs, their antiradical, reducing, and antigenotoxic properties were assessed in cell-free assays, using a methodological approach that has been recently proposed by our research group. According to our results, most of the tested MWCNTs exhibited strong antioxidant activities. More elaborately, the hybrid material of MWCNTs and ferrous oxide nanoparticles, i.e., CNTs@Fe₃O₄, showed robust scavenging capacities in all free-radical scavenging assays examined. As regards reducing properties, the pristine MWCNTs, i.e., CNTs-Ref, exhibited the greater electron donating capacity. Finally, in terms of antigenotoxic properties, the hybrid material of MWCNTs and silicon carbide nanoparticles, i.e., CNTs@SiC, exhibited potent ability to inhibit the formation of peroxyl radicals, thus preventing from the oxidative DNA damage. Conclusively, our findings suggest that the MWCNTs of the study could be considered as promising broad-spectrum antioxidants, however, further investigations are required to evaluate their toxicological profile in cell-based and in vivo systems.

Improving the Mechanical/Anticorrosive Properties of a Nitrile Rubber-Based Adhesive Filled with Cerium Oxide Nanoparticles Using a Two-Step Surface Modification Method

To prepare a nanocomposite adhesive based on nitrile rubber (NBR) with excellent mechanical/anticorrosion properties, cerium oxide (CeO₂) nanoparticles were grafted with bis-[3-(triethoxysilyl)propyl]tetrasulfide silane (TESPT) at different concentrations (i.e., 1, 5, 10, and 20 times the stoichiometric content). The surface-modified nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), ζ-potential, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM) techniques. The results showed that the steaming process resulted in an increase in the grafting ratio (R _g) by 2.35 times. Pure and modified cerium oxide nanoparticles were added at 1.5, 4.5, and 7.5 wt % to a mixture of a phenolic resin and NBR compound to prepare adhesive samples. The prepared adhesives were evaluated for curing behavior and thermomechanical properties. The morphology of the adhesives was also characterized using SEM analysis. The bonding of adhesives to steel plates was measured by a cathodic disbonding test. The adhesive-coated steel plates were evaluated for anticorrosion performances using a salt spray test. It was found that surface-modified hydrothermally steamed CeO₂ nanoparticles that had the highest silane grafting ratio enhanced the anticorrosion properties and cathodic disbonding of NBR-based adhesives. The curing rate index (CRI) and crosslinking of the NBR compound were enhanced using the modified and steamed nanoparticles. This also improved the interfacial interactions between rubber chains and nanoparticle surface, resulting in a 6 °C increase in the glass-transition temperature (T _g) of NBR compared to the pristine rubber.

Green and Rapid Preparation of Fluorosilicone Rubber Foam Materials with Tunable Chemical Resistance for Efficient Oil-Water Separation

Polydimethylsiloxane (PDMS) foam materials with lightweight, excellent oil resistance and mechanical flexibility are highly needed for various practical applications in aerospace, transportation, and oil/water separation. However, traditional PDMS foam materials usually present poor chemical resistance and easily swell in various solvents, which greatly limits their potential application. Herein, novel fluorosilicone rubber foam (FSiRF) materials with different contents of trifluoropropyl lateral groups were designed and fabricated by a green (no solvents used) and rapid (<10 min foaming process) foaming/crosslinking approach at ambient temperature. Typically, vinyl-terminated poly(dimethyl-co-methyltrifluoropropyl) siloxanes with different fluorine contents of 0−50 mol% were obtained through ring-opening polymerization to effectively adjust the chemical resistance of the FSiRFs. Notably, the optimized FSiRF samples exhibit lightweight (~0.25 g/cm−3), excellent hydrophobicity/oleophilicity (WCA > 120°), reliable mechanical flexibility (complete recovery ability after stretching of 130% strain or compressing of >60%), and improved chemical resistance and structural stability in various solvents, making them promising candidates for efficient and continuous oil−water separation. This work provides an innovative concept to design and prepare advanced fluorosilicone rubber foam materials with excellent chemical resistance for potential oil−water separation application.

Study on Thermal-Oxidative Aging Properties of Ethylene-Propylene-Diene Monomer Composites Filled with Silica and Carbon Nanotubes

In this work, a small amount of carbon nanotubes (CNTs) was used to partially replace the silica in ethylene-propylene-diene monomer (EPDM) to prepare EPDM composites via mechanical blending. The mechanical properties, thermal-oxidative aging properties and thermal stability of the composites were systematically investigated. The results showed that with the increase of CNTs content, the Shore A hardness and stress at 100% strain of the composites increased, while the elongation at break decreased. With the aging time increasing, the aging coefficient and elongation at break of composites decreased while hardness increased due to the raise of crosslinking density. In addition, evidences were found to demonstrate the improved aging resistance by adding CNTs in the EPDM composites, including the less change in Shore A hardness, the smaller change ratio of elongation at break and the lower aging coefficient. When the content of CNTs reached 10 phr, the aging coefficient of the EPDM composite aged for 168 h was nearly twice that of the composite without CNTs, and the thermal stability of the EPDM composite with CNTs was improved as demonstrated by thermal analysis.

Straightforward preparation of highly loaded MWCNT-polyamine hybrids and their application in catalysis

Multiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state ¹³C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), potentiometric titration, and temperature programmed desorption of carbon dioxide (CO₂-TPD). One of the prepared materials was tested as a heterogeneous base catalyst in C-C bond forming reactions such as the Knoevenagel condensation and Henry reaction. Furthermore, two examples concerning a sequential one-pot approach involving two consecutive reactions, namely Knoevenagel and Michael reactions, were reported.

Aggregation Behavior of "Linear" Trisiloxane Surfactant with Different Terminal Groups (CH3-, ClCH2-, and CF3-) in Aqueous Solution

Novel "linear" trisiloxane surfactants with different terminal groups (CH₃-, ClCH₂-, CF₃-) and two polyether hydrophilic groups were successfully synthesized and confirmed using ¹H NMR, ¹³C NMR, ²⁹Si NMR, and FT-IR spectroscopy. The aggregation and adsorption behavior of the "linear" trisiloxane surfactants in aqueous solution was studied by surface tension, dynamic light scattering (DLS), transmission electron microscopy (FF-TEM), and TEM. Owing to the introduction of two polyether hydrophilic groups in the terminal positions of the trisiloxane hydrophobic part, "linear" trisiloxane surfactants (Me-Si₃-EO₈, Cl-Si₃-EO₈, and F-Si₃-EO₈) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC ( γ_CMC) and single trisiloxane surfactant molecule at the air/water interface ( A _min) values. Following the difference in the intermolecular forces and molecular volumes (CH₃- < ClCH₂- < CF₃-), the γ_CMC values decrease following the order Me-Si₃-EO₈ > Cl-Si₃-EO₈ > F-Si₃-EO₈, and the adsorption efficiency ( p C₂₀), surface pressure at the CMC ( π_CMC), CMC/ C₂₀ , and A _min values increase following the order Me-Si₃-EO₈ < Cl-Si₃-EO₈ < F-Si₃-EO₈. As comparison, fluorinated trisiloxane surfactant (F-Si₃-EO₈) has greater surface activity attributed to the terminal CF₃- group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.