Tensile actuation

The tensile actuation in polymer coil muscles is directly linked to torsional actuation derived from the twisted polymer fibre. To illustrate the link between fibre torsional actuation and coil tensile actuation, coils were fabricated as either homochiral or heterochiral , depending on whether the... 

Figure 13.4 (a) Optical images of a coiled fibre made by twist insertion into a 300 xm diameter nylon-6,6 fibre, a two-ply muscle made of the coiled fibres of (a), the braided structure made of 32 two-ply coiled nylon fibres made from a 100 pm diameter precuror fibre, and a 1.55 mm coil made from a 300 pm diameter precursor nylon fibre by twist insertion followed by mandrel coiling, (b) Optical images of coiled nylon-6,6 (300 pm) before and after heating, (c) Tensile actuation of coiled fibres as a function of the temperature. Inset shows the same data for untwisted fibres. 

SO as to push apart the adjacent turns in a heterochiral coil (Figure 13.7a) or draw closer together the adjacent turns in a homochiral coil (Figure 13.7b). Further evidence to support coupling between fibre torsion and coil tensile actuation is the near equivalence of work density in both modes 2.1 kj kg torsional work capacity was measured in twisted nylon-6,6 fibre and 2.5 kjkg was measured when the same fibre was formed into a coil and operated in the tensile contraction mode. 

Figure 13.8 Torsional actuation of twisted carbon nanotube yarns, (a) Twisted carbon nanotube yarn operating in 0.2 M tetrabutylam-monium hexafluorophosphate/acetonitrile electrolyte, (b) Paraffin impregnated carbon nanotube yarn operating in air. (c) Two-ply carbon nanotube yarn coated with a poly(vinylidene fluoride-co-hexafluoropropylene) based tetraethylammonium tetrafluoroborate (TEA.BF4) solid polyelectrolyte. (Panel (a) is from ref. 16 Foroughi et al. Torsional Carbon Nanotube Artificial Muscles , Science, 2011, 334, 494-497. Reprinted with permission from AAAS. Panel (b) is from ref. 17 Lima et al. Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles , Science, 2012, 338, 928-932. Reprinted with permission from AAAS. Panel (c) is reprinted with permission from ref. 18 Lee et al. All-Solid-State Carbon Nanotube Torsional and Tensile Artificial Muscles , Nano Lett, 2014, 14, 2664-2669. Copyright 2014 American Chemical Society.)...

Kosidlo U, et al (2013) Nanocarbon based ionic actuators-a review. Smart Mater Struct 22 104022 Li J, et al (2011) Superfest-response and ultrahigh-power-density electromechanical actuators based on hierarchal carbon nanotube electrodes and chitosan. Nano Lett 11 4636-4641 Lima MD, et al (2012) Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yam muscles. Science 338 928-932 Liu Q, et al (2014) Nanostructured carbon materials based electrothermal air pump actuators. Nanoscale 6 6932-6938... 

In this chapter, we review the methods used to fabricate CNT hybrid yams and describe configurations used to demonstrate and optimize both torsional and tensile actuation. Although actuation can be stimulated electrochemically, optically, chemically, and thermally, we here concentrate on the electrothermal method for actuating the CNT yams. 

Experimeiital data on tensile actuation versus twist insertion for neat non-coded MWNT yams shows the importance of twist on thermal contraction (Fig. 8). Although only small actuation strains of less than 0.1% were observed in diese neat, non-coiled Fermat yams, a clear increase in thermal contraetion was evident in yams prepared with higher twist. With increase of inserted twist from 9,650 to... 

Fig. 8 Tensile actuation as a function of inserted twist for a neat 13.5 )tm diameter Fermat yam. The amount of steady-state electrical power applied to obtain yam contraction was constant (85 2.6 mW/cm) when normalized to the measured yam length for each degree of twist, so the input power per yam weight was also constant. Mechanical load was constant and corresponded to 72 MPa. The lines are guides for the eyes (From Lima et al. (2012). Reprinted with permission from AAAS)...

Fig. 9 Thermal tensile aetuation for two-end-tethered homoehrral yams, (a) Tensile aetuation strain versus temperature before (black) and after (red) wax infiltration for a eoiled, dual-Archimedean yam having 130 pm initial diameter, an inserted twist of 4,000 turns/ m (per length of the precursor sheet stack), and an applied stress of 6.8 MPa. Inset corresponding actuation data before (black) and after (red) wax infiltration for a non-coiled Fermat yam having 16 pm initial diameter, 20,000 tums/m twist, and an applied stress of 4.8 MPa (b) The stress dependence of steady-state tensile actuation and contractile work (black and blue data points, respectively) produced by Joule heating (0.189 V/cm) for a 150 pm diameter, wax-filled dual-Archimedean yam having ditferent levels of inserted twist (From Lima et al. (2012). Reprinted with permission from AAAS)...

Fig. 10 Electrothermal tensile actuation for two-end-tethered, homochiral, wax-filled coiled CNT yams, (a) Tensile actuation strain versus time after 1,400,000 reversible cycles for an 11.5 (rai diameter, coiled Fermat yam having -25,000 tums/m twist when driven by a 18.3 V/cm, 20 Hz symmetric square-wave voltage while lifting a load that provided a 14.3 MPa stress, (b) Tensile actuation for the yam of (a) with 109 MPa pUed tensile stress when driven at 3 % duty cycle by 15 ms, 32 V/cm square-wave voltage pulses having a period of 500 ms. (c) Tensile strain versus time for a 150 pm diameter, diial-Aichimedean yam with 3,990 tums/m of inserted twist per preciusor sheet stack length, when supporting a 5.5 MPa tensile stress and driven by a 15 V/cm square wave having 50 ms pulse duration and 2.5 s period (From Lima et aL (2012). Reprinted with permission from AAAS)...

Tensile actuation was also demonstrated in all twisted CNT yams, while stroke, work, and power ou uts were dramatically increased by incorporation of yam guest and by overtwisting tire yam to form coils. Fast, highly reversible tensile actuation was demonstrated for parafBn-wax-filled yams. Strokes of up to 10 % were observed in coiled, wax-filled yams. For small diameter yams, actuation at 1,200 cycles per minute giving 3 % stroke was demonstrated for over 1.4 million eyeles. In the tensile mode, power outputs during contraction reached 27.9 kW/kg or 85 times that of skeletal muscle. 

Lima MD, Li N, Jung De Andrade M et al (2012) Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yam muscles. Science... 

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