Liquid crystal surface anchoring of mesophase pitch

Jian, Kengqing; Shim, Hongsuk; Tuhus-Dubrow, D.; Bernstein, S.; Woodward, Christine; Pfeffer, Michael; Steingart, Daniel Artemus; Gournay, Thibault; Sachsmann, Suzanne; Crawford, Gregory P.; Hurt, Robert H.

doi:10.1016/s0008-6223(03)00203-3

Cited by 48 publications

(22 citation statements)

References 31 publications

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“…In Kundu and Ogale's study [42] on the flow-induced microstructural evolution of mesophase pitch in both the counterbore and capillary sections, enhanced orientation in the capillary was observed with a high shear rate from the counterbore with a low shear rate, and this was attributed to the high shear stress experienced in the capillary. Jian et al [43] experimentally determined the surface anchoring states of mesophase pitches on free surfaces and solid substrates, and they reported that edge-on anchoring is the most common state for various materials, including the stainless steel used as the capillary wall material in this study. Such edge-on orientation of discotic mesogens would preferentially provide radial orientation of layer planes in the capillary.…”

Section: Relationship Between Structural Parameters and The Propertiementioning

confidence: 73%

The effect of the spinning conditions on the structure of mesophase pitch-based carbon fibers by Taguchi method

Jiang¹,

Ouyang²,

Yao³

et al. 2016

Carbon letters

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Taguchi's experimental design was employed in the melt spinning of molten mesophase pitch to produce carbon fibers. The textures of the obtained carbon fibers were radial with varied crack angles, as observed by scanning electron microscopy and polarized optical imaging. The diameter, crack angle, preferred orientation, and tensile modulus of the produced samples were examined to investigate the influence of four spinning variables. The relative importance of the variables has been emphasized for each characteristic. The results show that thicker carbon fiber can be obtained with a smaller entry angle, a higher spinning temperature, a reduced winding speed, and an increased extrusion pressure. The winding speed was found to be the most significant factor in relation to the fiber diameter. While it was observed that thicker carbon fiber generally shows improved preferred orientation, the most important variable affecting the preferred orientation was found to be the entry angle. As the entry angle decreased from 120° to 60°, the shear flow was enhanced to induce more ordered radial alignment of crystallite planes so as to obtain carbon fibers with a higher degree of preferred orientation. As a consequence, the crack angle was increased, and the tensile modulus was improved.

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Section: Relationship Between Structural Parameters and The Propertiementioning

confidence: 73%

The effect of the spinning conditions on the structure of mesophase pitch-based carbon fibers by Taguchi method

Jiang¹,

Ouyang²,

Yao³

et al. 2016

Carbon letters

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Section: Governing Equationsmentioning

confidence: 99%

“…32,33 The edge-on anchoring (see Figure 5) is the more frequently found, and is the result of strong non-covalent interactions involving aromatic π clouds. 32,33 In the analytical equations derived in our previous studies to describe the orientation field in capillary flow the average molecular orientation at the boundaries are assumed to be planar, and this also will be the case in this study. 20,31,[34][35][36] A detailed discussion about the viscoelastic properties involved in the small amplitude oscillatory shear of discotic nematics can be found in our previous papers, 20,31,[34][35][36] here we briefly present the essential features of the material properties.…”

Section: Governing Equationsmentioning

confidence: 99%

Linear viscoelasticity of textured carbonaceous mesophases

Lima¹,

Rey²

2006

J. Braz. Chem. Soc.

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Fibras de carbono de alto desempenho podem ser produzidas a partir de piche de petróleo anisotrópico usando o processo de extrusão-fiação. O piche mesomórfico é um cristal líquido discótico nemático termotrópico, que possui ordem na orientação das moléculas. Cristais líquidos são materiais que possuem textura, anisotropia e visco-elasticidade. Um fenômeno importante que é encontrado em cristais líquidos é a interação entre a textura devido à orientação das moléculas e o comportamento reológico, no qual a textura ocorre devido à presença de defeitos na orientação das moléculas. O processo de extrusão-fiação usado na fabricação de fibras de carbono a partir de precursores nemáticos usa uma cascata de escoamentos que incluem fluxo capilar convergente e extensional, os quais promovem a formação de uma variedade de estruturas, incluindo radial, concêntrica, randômica e bipolar, que darão propriedades especificas para as fibras de carbono resultantes. Portanto, a compreensão fenomenológica da interação entre a textura e a reologia do precursor nemático é necessária para o controle do processo e para a otimização do produto. Neste artigo, a interação entre a reologia e a textura de cristais líquidos discóticos nemáticos será enfocada e um modelo anisotrópico será desenvolvido para descrever o regime linear visco-elástico de piches mesofásico com textura. O modelo é capaz de prever todas as características observadas experimentalmente, incluindo a dependência dos módulos de armazenamento e de perda com a freqüência de oscilação e a sua dependência com a temperatura, assim como promover uma melhor compreensão do papel dos defeitos e da anisotropia no comportamento visco-elástico do piche anisotrópico.High performance carbon fibers can be produced from anisotropic petroleum pitch using the fiber spinning process. The mesophase pitch is a thermotropic discotic nematic liquid crystal possessing orientational order. Liquid crystals are textured, anisotropic, viscoleastic materials. An important phenomenon of liquid crystals is the interaction between orientational textures and rheology, where the texture is due to the presence of orientational defects. The fiber spinning process used in the carbon fiber manufacture from nematic precursors uses a cascade of processing flows that involves capillary, convergent, and extensional flows, which promotes the formation of a variety of textures that will give specific properties to the resultant carbon fiber. Hence a fundamental understanding of the impact of textures on rheology is needed for eventual process control and product optimization. In this paper we study the interaction of rheology and texture and develop a model of anisotropic linear viscoelasticity of textured mesophases. The model is able to predict all the features observed experimentally, including the frequency dependency of the loss and storage modulus and their temperature sensitivity, and provides a better understanding of the role of defects and anisotropy on pitch viscoelasticity.

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“…5. Both carbon precursors exhibit a non-graphitic carbon microstructure with broad maxima around 2q ¼ 26 and [40][41][42][43][44][45] corresponding to the interlayer and intralayer scattering of the graphene stacks, but the maxima are more distinct for the mesophase pitch based carbon. The more diffuse maxima in the XRD pattern of the sucrose based carbon indicate a low degree of structural order being correlated with the microporosity.…”

mentioning

confidence: 99%

“…40,41 Preservation of this orientation during carbonization would -after etching of the SiO 2 -directly lead to a favorable orientation of the graphenes towards the surface and hence to facilitated lithium insertion/deinsertion.…”

mentioning

confidence: 99%

Towards commercial products by nanocasting: characterization and lithium insertion properties of carbons with a macroporous, interconnected pore structure

et al. 2012

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Carbon materials with defined porosity are prepared using the nanocasting approach. The structural properties of the prepared carbon materials are examined by SEM, XRD, XPS, elemental analysis, nitrogen physisorption and Hg porosimetry. The materials exhibit an interconnected porous network with spherical pores in the macropore range, being a replica of spherical SiO 2 particles. The average macropore size (300-700 nm) and surface area (35-470 m 2 g À1 ) can be tailored by the choice of template and carbon precursor. More importantly, based on silica templates prepared by flame pyrolysis, the whole process, including HF etching of the template, can be easily industrialized. Lithium storage measurements are used to demonstrate the beneficial transport properties of the porous carbon materials which are referenced against non-porous carbons. The porous carbon materials exhibit high capacity (550 mA h g À1 at C/5) and excellent rate capability (90 mA h g À1 at 60C). Surprisingly, the excellent lithium storage properties are related to the macroporous framework rather than high surface area and/or micro-and mesoporosity.

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Liquid crystal surface anchoring of mesophase pitch

Cited by 48 publications

References 31 publications

The effect of the spinning conditions on the structure of mesophase pitch-based carbon fibers by Taguchi method

The effect of the spinning conditions on the structure of mesophase pitch-based carbon fibers by Taguchi method

Linear viscoelasticity of textured carbonaceous mesophases

Towards commercial products by nanocasting: characterization and lithium insertion properties of carbons with a macroporous, interconnected pore structure

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