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Electrorheology of nanofiber suspensions.

Yin J, Zhao X - Nanoscale Res Lett (2011)

Bottom Line: Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances.In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers.Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

View Article: PubMed Central - HTML - PubMed

Affiliation: Smart Materials Laboratory, Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710129, China. jbyin@nwpu.edu.cn.

ABSTRACT
Electrorheological (ER) fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

No MeSH data available.


Related in: MedlinePlus

Yield stress as a function of electric field strength for N-CT suspension (square symbol) and heat treated granular PANI suspension by the same process (circle symbol) (T = 23°C, 15 vol.%) [134].
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Figure 11: Yield stress as a function of electric field strength for N-CT suspension (square symbol) and heat treated granular PANI suspension by the same process (circle symbol) (T = 23°C, 15 vol.%) [134].

Mentions: Very recently, a kind of nanotube-like nitrogen-enriched carbonaceous nanofibers (N-CTs) were prepared by the heat treatment of conducting PANI nanofibers and then were used as new carbonaceous ER materials [134]. The heat treatment temperature was found to be important to obtain N-CTs with the optimal ER effect. The heat treatment at the temperature lower than 500°C easily transformed PANI nanofibers into thermally degraded PANI nanofibers whose conductivities were too low to induce a strong ER effect, while the heat treatment at temperature higher than 600°C transformed PANI nanofibers into the partially graphitized nitrogen-containing nanotubes whose conductivities were too high to finish ER measurements because of the electrical short circuit. When PANI nanofibers were treated in vacuum at the temperature range of 500 to 600°C, the obtained N-CTs were suitable to be used as ER dispersal phase because they had the moderate conductivity. After heat treatment, the nanofiber morphology was found to be well preserved except that the diameters showed shrinkage and the aspect ratio of nanotubes slightly decreased with increasing heat treatment temperatures [134]. Figure 10 showed the morphology and Raman spectra of N-CTs obtained at 550°C. The N-CTs possessed the uniform nanotubular morphology with a diameter of 90 to 150 nm and a length of 1 to 2 μm. The Raman spectra of the N-CTs showed two broad bands centered at about 1588 cm-1 (G band) and 1345 cm-1 (D band), characteristic of amorphous carbon or disordered graphites. The N-CTs mainly contained C (77.5 wt%), N (12.6 wt%), and other elements (such as H and O). These indicated that the heat treatment at 550°C had transformed the PANI nanofibers into the amorphous nitrogen-enriched carbonaceous nanotubes [135]. Under electric fields, the rheological results showed that the N-CT suspension possessed versatile ER performance including high ER efficiency, good dispersion stability, and temperature stability. Especially, compared to the corresponding suspension of heat treated granular PANI, the N-CT suspension showed better dispersion stability and higher ER effect (see Figure 11). The analogical result was also observed in the dilute ER fluid containing commercial CNTs [132]. When a power-law relation τy ∝ Eα was used to fit the correlation of yield stresses and electric fields, it was also found that the exponent of the N-CT suspension was smaller than that of granular suspension. This was mainly related to the particle morphology because other factors such as particle concentration, particle's conductivity, liquid phase, and so on were the same for N-CTs and heat treated granular PANI. The similar result was also observed in the PANI nanofiber suspension [96,98] and in the whisker-like inorganic aluminum borate suspension [67]. Furthermore, the ER effect of N-CT suspension could be adjusted by varying heat treatment temperatures and the N-CTs obtained at around 600°C exhibited the maximum ER effect (see Figure 12). This was explained by the polarization response, which originated from the regular change of conductivity of N-CTs as a function of heat treatment temperatures [134]. It showed that under electric fields the N-CT suspension showed good temperature stability in ER effect though its off-field viscosity decreased with elevated temperatures. Meanwhile, the flow curve of shear stress vs. shear rate also maintained a stable level and the critical shear rate shifted toward high values as the operating temperature increased. The dynamic viscoelastic measurement showed that the storage modulus slightly increased with increasing operating temperature, also confirming the good temperature stability of ER effect of N-CT suspension. The dielectric spectra of N-CT suspension and the dielectric parameters calculated by the Cole-Cole equation could explain the temperature dependence of ER effect of N-CT suspension [135].


Electrorheology of nanofiber suspensions.

Yin J, Zhao X - Nanoscale Res Lett (2011)

Yield stress as a function of electric field strength for N-CT suspension (square symbol) and heat treated granular PANI suspension by the same process (circle symbol) (T = 23°C, 15 vol.%) [134].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211318&req=5

Figure 11: Yield stress as a function of electric field strength for N-CT suspension (square symbol) and heat treated granular PANI suspension by the same process (circle symbol) (T = 23°C, 15 vol.%) [134].
Mentions: Very recently, a kind of nanotube-like nitrogen-enriched carbonaceous nanofibers (N-CTs) were prepared by the heat treatment of conducting PANI nanofibers and then were used as new carbonaceous ER materials [134]. The heat treatment temperature was found to be important to obtain N-CTs with the optimal ER effect. The heat treatment at the temperature lower than 500°C easily transformed PANI nanofibers into thermally degraded PANI nanofibers whose conductivities were too low to induce a strong ER effect, while the heat treatment at temperature higher than 600°C transformed PANI nanofibers into the partially graphitized nitrogen-containing nanotubes whose conductivities were too high to finish ER measurements because of the electrical short circuit. When PANI nanofibers were treated in vacuum at the temperature range of 500 to 600°C, the obtained N-CTs were suitable to be used as ER dispersal phase because they had the moderate conductivity. After heat treatment, the nanofiber morphology was found to be well preserved except that the diameters showed shrinkage and the aspect ratio of nanotubes slightly decreased with increasing heat treatment temperatures [134]. Figure 10 showed the morphology and Raman spectra of N-CTs obtained at 550°C. The N-CTs possessed the uniform nanotubular morphology with a diameter of 90 to 150 nm and a length of 1 to 2 μm. The Raman spectra of the N-CTs showed two broad bands centered at about 1588 cm-1 (G band) and 1345 cm-1 (D band), characteristic of amorphous carbon or disordered graphites. The N-CTs mainly contained C (77.5 wt%), N (12.6 wt%), and other elements (such as H and O). These indicated that the heat treatment at 550°C had transformed the PANI nanofibers into the amorphous nitrogen-enriched carbonaceous nanotubes [135]. Under electric fields, the rheological results showed that the N-CT suspension possessed versatile ER performance including high ER efficiency, good dispersion stability, and temperature stability. Especially, compared to the corresponding suspension of heat treated granular PANI, the N-CT suspension showed better dispersion stability and higher ER effect (see Figure 11). The analogical result was also observed in the dilute ER fluid containing commercial CNTs [132]. When a power-law relation τy ∝ Eα was used to fit the correlation of yield stresses and electric fields, it was also found that the exponent of the N-CT suspension was smaller than that of granular suspension. This was mainly related to the particle morphology because other factors such as particle concentration, particle's conductivity, liquid phase, and so on were the same for N-CTs and heat treated granular PANI. The similar result was also observed in the PANI nanofiber suspension [96,98] and in the whisker-like inorganic aluminum borate suspension [67]. Furthermore, the ER effect of N-CT suspension could be adjusted by varying heat treatment temperatures and the N-CTs obtained at around 600°C exhibited the maximum ER effect (see Figure 12). This was explained by the polarization response, which originated from the regular change of conductivity of N-CTs as a function of heat treatment temperatures [134]. It showed that under electric fields the N-CT suspension showed good temperature stability in ER effect though its off-field viscosity decreased with elevated temperatures. Meanwhile, the flow curve of shear stress vs. shear rate also maintained a stable level and the critical shear rate shifted toward high values as the operating temperature increased. The dynamic viscoelastic measurement showed that the storage modulus slightly increased with increasing operating temperature, also confirming the good temperature stability of ER effect of N-CT suspension. The dielectric spectra of N-CT suspension and the dielectric parameters calculated by the Cole-Cole equation could explain the temperature dependence of ER effect of N-CT suspension [135].

Bottom Line: Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances.In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers.Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

View Article: PubMed Central - HTML - PubMed

Affiliation: Smart Materials Laboratory, Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710129, China. jbyin@nwpu.edu.cn.

ABSTRACT
Electrorheological (ER) fluid, which can be transformed rapidly from a fluid-like state to a solid-like state under an external electric field, is considered to be one of the most important smart fluids. However, conventional ER fluids based on microparticles are subjected to challenges in practical applications due to the lack of versatile performances. Recent researches of using nanoparticles as the dispersal phase have led to new interest in the development of non-conventional ER fluids with improved performances. In this review, we especially focus on the recent researches on electrorheology of various nanofiber-based suspensions, including inorganic, organic, and inorganic/organic composite nanofibers. Our goal is to highlight the advantages of using anisotropic nanostructured materials as dispersal phases to improve ER performances.

No MeSH data available.


Related in: MedlinePlus