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We have studied the dynamic scanning of liquid-crystalline (LC) poly(_{2}SO_{4}) solution, and its blend with single-walled carbon nanotubes (SWNTs), by using a flat plate rotational rheometer. The effects of weight concentration and molecular weight of PPTA, as well as operating temperature, on dynamic viscoelasticity of the PPTA-H_{2}SO_{4} LC solution system are discussed. The transition from a biphasic system to a single-phase LC occurs in the weight concentration range of SWNTs from 0.1% to 0.2%, in which complex viscosity reaches the maximum at 0.2 wt% and the minimum at 0.1 wt%, respectively, of SWNTs. With increasing SWNT weight concentration, the endothermic peak temperature increases from 73.6 to 79.9 °C. The PPTA/SWNT/H_{2}SO_{4} solution is in its plateau zone and storage modulus (^{−1}, then when ω > 1 s^{−1} G″ increases faster than

A liquid-crystalline (LC) solution is an orientationally ordered liquid that displays fluidic characteristics of the liquid state while the molecules still maintain a directional order. There are three main classes of LC phases, _{2}SO_{4}) and hence form LC phases [_{2}SO_{4}. Nematic sulfuric acid LC solution of PPTA, referred to as PPTA-H_{2}SO_{4}, with a weight concentration range of 19–20% when heated to 80–95 °C has been used to fabricate high-strength fibers by dry-jet wet-spinning process [_{2}SO_{4} LC solution have been reported [_{2}SO_{4} LC solution system in the spinning process. We then carried out the dynamic scanning of the PPTA-H_{2}SO_{4} LC solution system with a flat plate rotational rheometer and discussed the effects of weight concentration and molecular weight of PPTA, as well as temperature, on such viscoelastic properties as complex viscosity (^{*}), storage modulus (

Single-walled carbon nanotubes (SWNTs) have been shown to possess extraordinary mechanical, electrical and thermal properties [_{2}SO_{4} solution has been evidenced by birefringence and rheological curves [_{2}SO_{4} was prepared, and its thermal and rheological behaviors were studied accordingly. Our study aims to assess the effects of SWNTs on the properties of the spinning solution. Through our studies, we are able to identify the optimal range of SWNTs concentration and spinning temperature for dry-jet wet-spinning process of PPTA fibers.

Effects of the variation of weight concentrations of PPTA (PPTA wt%: 18.5, 19 and 19.5%) and temperatures (75, 80, 85, 90 °C) on rheological curves of the PPTA-H_{2}SO_{4} LC solution are shown in ^{*} decreases as _{2}SO_{4} LC solution would increase as ^{*}, ^{*},

Supramolecular structure is key to affecting the rheological characterization of the polymer system. _{2}SO_{4} LC solution at 19.5 wt% of PPTA as a function of _{w}^{*}, _{w}_{w}_{w}_{w}

Variation of complex viscosity as a function of SWNT weight concentration (SWNT wt%) in PPTA/SWNT/H_{2}SO_{4} dopes is plotted in ^{*} first gradually increases with increasing SWNT wt%, and then decreases abruptly when beyond ∼0.1 SWNT wt%, and arises again when beyond 0.2 SWNT wt% to reach about the same viscosity for three temperature-dependent curves. In general, this concentration dependent viscosity behavior of PPTA/SWNT/H_{2}SO_{4} solution resembles that of SWNT/H_{2}SO_{4} solution. As the SWNT concentration was below 0.1 wt%, the solution viscosity increased accordingly with increasing SWNT wt%. This can be considered as normal behavior of an isotropic solution. When SWNT concentration was exceeded 0.1 wt%, the viscosity decrease at increasing SWNT concentration can be considered as a unique behavior of anisotropic solution. It is caused by the liquid crystal behavior where SWNT are aligned upon shear and form domains of highly ordered structures.

It has been revealed in rheology and microscopy studies that SWNTs in H_{2}SO_{4} exhibit roughly similar phase behavior as rod-like polymer solutions [_{2}SO_{4} system. A biphasic region of mixed isotropic and anisotropic phase existed between 0.1 wt% and 0.2 wt%. Beyond 0.2 wt%, the solution became an increasingly anisotropic-rich phase, and the solution viscosity increased again with increasing SWNT wt%.

Temperature effect on complex viscosity (^{*}) as opposed to shearing frequency (_{2}SO_{4} dope is shown in

All three samples composed of pure PPTA and PPTA coupled with different portion of SWNT exhibit an obvious shear-thinning behavior through the entire ^{*} decreases in direct proportion to _{2}SO_{4} dopes are more highly shear-sensitive. (1) The ^{*} of PPTA/H_{2}SO_{4} dope decreases as temperature increases from 75 to 85 °C. Such behavior is often observed among conventional polymers. (2) The ^{*} of PPTA/SWNT (98/2 wt%)/H_{2}SO_{4} dope decreases as temperature increases from 80 to 85 °C, while it becomes nearly independent of temperature ranging between 75 °C and 80 °C. (3) The ^{*} of PPTA/SWNT (97/3 wt%)/H_{2}SO_{4} dope decreases slightly as temperature increases from 80 to 85 °C, but increases slightly as temperature increases from 75 to 80 °C.

To determine possible phase changes from 75 to 85 °C, we carried out thermal analysis on PPTA/SWNT/H_{2}SO_{4} dopes. The DSC thermogram (^{*} vs.

_{2}SO_{4} dopes over _{2}SO_{4} dope is a dominant factor within the frequency range from 0.1 to 10 rad/s. As ^{−1}), the ^{−1}),

According to the relative magnitude of _{2}SO_{4} dope is in its plateau zone within the frequency range from 0.1 to 10 rad/s [^{®}, for example, supports this argument [_{2}SO_{4} dope seems to exhibit more intermolecular interaction and chain rigidity, thus giving rise to the plateau-zone behavior [

Sulfuric acid with 0.2 wt% excess SO_{3} was prepared by mixing the fuming sulfuric acid (25 wt%) with concentrated sulfuric acid (98 wt%). The concentration of sulfuric acid was measured by acid-base titration. The SWNTs used in this study was acquired from Shenzhen Nanotechnologies Co., Ltd. and an average diameter of <2 nm. Finally, SWNTs were dried under vacuum overnight at 80–100 °C. Dispersions were prepared by mixing with a magnetic stir bar for 3 days in an anhydrous environment in a glovebox which was nitrogen atmosphere at room temperature [

The PPTA-H_{2}SO_{4} LC solutions were prepared with four different molecular weight polymers _{w}_{2}SO_{4} at 75 °C. The mixture was then stirred for 2.5 h and opalescence was observed during this step. Likewise, the LC solutions of PPTA/SWNT/H_{2}SO_{4}, in which PPTA was kept at 19.5 wt% and PPTA/SWNT is 99/1 wt%, were prepared in a 250 mL three-neck flask. SWNTs (0.3401 g) were dispersed in H_{2}SO_{4} (140.4 g) under an inert and anhydrous atmosphere with mechanical stirring and at room temperature for at least 3 days [

Subsequently, the PPTA-H_{2}SO_{4} LC and PPTA/SWNT/H_{2}SO_{4} dope solutions were performed with dynamical scanning on an ARES rotational rheometer (TA Instruments, New Castle, DE, USA) at four temperatures (75, 80, 85, 90 °C) in the frequency range of 0.01–100 rad·s^{−1} and 0.1–10 rad·s^{−1}, respectively. Testing fixtures parallel plates (50 mm) were made of stainless steel 316 to avoid corrosion. In order to prevent water exchange between the sample and environment, the sample surface between the plate and the cone was coated with a mineral oil [^{*},

Thermal analysis on the PPTA/SWNT/H_{2}SO_{4} dope was carried out on a differential scanning calorimeter (DSC) (Mettler Toledo 822) under a N_{2} atmosphere at a heating rate of 5 °C/min ranging from 25 to 90 °C.

We have shown that PPTA-H_{2}SO_{4} LC solution exhibits a typical shear-thinning behavior. Our rheology studies are summarized as follows. (1) As PPTA wt% increases, rheological curves of ^{*}, ^{*}, ^{*}, _{w}

When SWNTs are added into PPTA-H_{2}SO_{4} LC solution, the protonation of SWNTs in superacids enables their good dispersion to form homogeneous PPTA/SWNT/H_{2}SO_{4} dope solution. The dope solution exhibits a remarkable nematic LC phase. Our findings are multi-folds. (1) For all temperature and concentration of SWNT, the complex viscosity of PPTA/SWNT/H_{2}SO_{4} dope shows an obvious shear-thinning behavior, and the slope of complex viscosity _{2}SO_{4} dope is a dominant factor within the frequency range from 0.1 to 10 rad/s. At sufficiently high concentrations of SWNT, approximately 0.2 wt%, and at 85 °C, a novel type of single-phase nematic liquid crystal is formed. This allows the dope solution to produce superior-performance fibers by dry-jet wet-spinning process.

We are grateful for valuable discussions with Zhusheng Zhou, Qingji Wu, Xingsheng Zhu. This work was supported by Industrial Technology Development Foundation of National Development and Reform Commission of China.

_{2}O solution system

Rheological curves dependences of PPTA-H_{2}SO_{4} LC solution on shearing frequency (

Effect of PPTA molecular weight of PPTA-H_{2}SO_{4} LC solution on rheological curves

Dependence of complex viscosity (^{*}) of PPTA/SWNT/H_{2}SO_{4} dopes on temperature and SWNT wt% at a shear frequency (^{−1}, (^{−1} and (^{−1}.

Temperature dependence of complex viscosity (^{*}) of (_{2}SO_{4}, (_{2}SO_{4}, and (_{2}SO_{4} as a function of shearing frequency (

DSC heating curves of PPTA/SWNT/H_{2}SO_{4} dope with different weight ration of PPTA and SWNT.

Dynamic modulus (_{2}SO_{4} dope as a function of shearing frequency (

Molecular structure of poly(