Synthesis of block polyethers with various structures and their application in dispersing single-walled carbon nanotubes

Long-Term Stable Dispersion of Multiwalled Carbon Nanotubes by Peroxydisulfate upon Ultrasonication Activation

Poor dispersibility of carbon nanotubes greatly hinders their practical applications. Herein, a long-term stable dispersion of multiwalled carbon nanotubes (MWCNTs) in peroxydisulfate (PDS) is achieved. MWCNTs at 40 mg L-1 are completely dispersed by PDS upon ultrasonication (US/PDS) within 64 min and a stable dispersion is maintained at least 20 days. Mechanistically, US created defects on the nanomaterial and PDS-origin free radicals attacked these defects to introduce O-containing moieties (─OH and ─COOH). Interestingly, dispersion efficiency of MWCNTs by US/PDS initially at pH 7 and 3.8 is comparable, but lower than that initially at pH 12. Both •OH and SO4 •- are produced under alkaline condition, while SO4 •- is the dominant free radicals initially at pH 7 and 3.8 during the whole dispersion period. Stronger dispersion of MWCNTs initially at pH 12 resulted from greater amounts of O-containing moieties mainly in ─OH (46.32%) rather than ─COOH (24.19%) form. This differential more strongly promotes MWCNTs-water interaction via hydrogen bonding, thereby enhancing the dispersion. Notably, no significant mass loss of MWCNTs occurred during dispersion. Overall, the developed method achieves long-term stable dispersion of MWCNTs in a manner that can significantly extend their applications.

Preparation, film fabrication and gas-sensitive responsive properties of MWCNTs@PS-b-HTPB5-b-PS conductive polymer nanocomposites

Novel nanocomposites consisting of polystyrene-block-polybutadienyl polyhexamethylene dicarbamate-block-polystyrene (PS-b-HTPB5-b-PS) and multiwalled carbon nanotubes (MWCNTs) were designed and prepared via noncovalent interactions. Scanning electron microscopy and transmission electron microscopy observations showed that segregated networks of MWCNTs were formed due to the cladding of PS-b-HTPB5-b-PS, presenting a parallel-arranged topology of the MWCNTs in a continuous PS-b-HTPB5-b-PS phase, which improved the dispersibility of the MWCNTs. The nanocomposites were fabricated into vapor sensing elements to detect CH2Cl2 vapor in the environment, exhibiting excellent responsive sensitivity, reproducibility and a low limit of detection (LOD) of 1 ppm when exposed to CH2Cl2 vapor. The chain extension of HTPB overcame the fragility and improved the tenacity of the thin films, and the responsivity was optimized by adjusting the content of the MWCNTs and the length of the PS chains. The newly developed conductive composites can be applied as a promising vapor sensor to accurately monitor CH2Cl2 vapor in the environment.

Thermoplastic polyurethane/single-walled carbon nanotube composites with low electrical resistance surfaces

Thermoplastic polyurethane (TPU)/single-walled carbon nanotube (SWCNT) nanocomposite films were prepared using 1,6-hexane diisocyanate and hydroxyl-terminated polybutadiene (HTPB) in tetrahydrofuran with various concentrations of SWCNTs. The interaction between polyurethane (PU) and SWCNTs in nanocomposite was studied using different methods. The film turns yellowish to grayish-black in colour upon increasing the concentration of SWCNTs in PU matrix. This may be due to the formation of π–π interaction between polyurethane amide functional group and SWCNTs. Differential scanning calorimetric results show that the soft segment of nanocomposite interacts much stronger than hard segment, which results in lowering melting transition temperature of soft segments. The activation energy and thermal stability parameters were determined from thermogravimetric and differential scanning calorimetric analyses. The x-ray photoelectron spectroscopic results show the intermolecular interaction between HTPB-based PU and SWCNT. Mesoporous morphology of the nanocomposites was observed by scanning electron microscopy. The average diameter of the pores was calculated using Gaussian method. The TPU films exhibit about 3.5 times greater resistivity than nanocomposite films. All the analysed data prove that the SWCNTs were well distributed in PU matrix and exhibited as tough films with low electrical resistivity.

Aggregation behaviors of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO at an air/water interface: experimental study and molecular dynamics simulation

The block polyethers PEO-PPO-ph-PPO-PEO (BPE) and PPO-PEO-ph-PEO-PPO (BEP) are synthesized by anionic polymerization using bisphenol A as initiator. Compared with Pluronic P123, the aggregation behaviors of BPE and BEP at an air/water interface are investigated by the surface tension and dilational viscoelasticity. The molecular construction can influence the efficiency and effectiveness of block polyethers in decreasing surface tension. BPE has the most efficient ability to decrease surface tension of water among the three block polyethers. The maximum surface excess concentration (Γ(max)) of BPE is larger than that of BEP or P123. Moreover, the dilational modulus of BPE is almost the same as that of P123, but much larger than that of BEP. The molecular dynamics simulation provides the conformational variations of block polyethers at the air/water interface.

Effect of alcohols on aggregation behaviors of branched block polyether Tetronic 1107 at an air/liquid surface

The aggregation behaviors of branched block polyether Tetronic 1107 (T1107) at an air/liquid surface was investigated in mixed solvents consisting of water and one of the following polar cosolvents: ethanol, n-propanol, ethylene glycol (EG), or glycerol (GLY). Surface tension measurements provide information about the effects of cosolvents on the critical micellization concentration (cmc), the standard Gibbs energy (ΔG°(mic)), the maximum surface excess concentration (Γ(max)), the minimum area per polyether molecule at the air/liquid surface (A(min)), and the standard free energy of adsorption (ΔG°(ads)). The addition of ethanol and n-propanol to water disfavors the micellization and progressively increases the cmc of T1107, whereas the cmc decreases with the addition of EG and GLY. The values of ΔG°(mic) of T1107 are all negative in mixed solvents, and their absolute values become smaller as the ethanol or n-propanol content increases but become larger as the EG or GLY content increases. The cosolvents have a significant effect on the surface adsorption and cmc, and the order is as follows: n-propanol-water > ethanol-water > water > EG-water > GLY-water. The octanol/water partition coefficient (log P) of the cosolvent is used to correlate the effects, and it could capture the effect of cosolvents on the cmc qualitatively. The surface dilational rheological properties of T1107 in water and water-alcohol mixtures were also studied by surface dilational viscoelasticity and surface tension relaxation measurements. The dilational elasticity decreases monotonously in the presence of ethanol or n-propanol. With the increasing concentration of EG and GLY, the dilational elasticity of T1107 passes through a maximum that coincides with the change in Γ(max).