Self-assembly properties of carboxylated tunicate cellulose nanocrystals prepared by ammonium persulfate oxidation and subsequent ultrasonication.

Tunicate cellulose, extracted from the marine animal, has drawn increasing attention as the high crystallinity and aspect ratio. However, it is hard to prepare tunicate cellulose nanocrystals (tCNCs) with narrow size distribution in the traditional way, especially for the carboxylated samples, which also affects their lyotropic liquid crystal behavior to a certain extent. Herein, carboxylated tCNCs with uniform nanoscale dimensions and high surface charges density were prepared through ammonium persulfate (APS) oxidation and ultrasonic post-processing. Of particular interest, the formation of carboxylated tCNCs lyotropic chiral nematic liquid crystals was observed for the first time, which displayed obvious birefringence and fingerprint texture. Meanwhile, it was found that the critical concentration of phase separation for tCNCs suspension was around 3.5 wt% from the phase diagram. This study provides an efficient way to fabricate carboxylated tCNCs, and the self-assembly properties may lead to great potential applications in constructing advanced functional materials.

Control over Tuning Fullerene Microcrystals by Means of Engineering Charge-Transfer Interactions.

Multifunctional fullerene microcrystals have been prepared by the involvement of water in the liquid-liquid interfacial precipitation. The resulting microcrystals were characterized microscopically and spectroscopically. The role of water in engineering charge-transfer interactions between fullerenes and electron-donating solvents has been corroborated through thermogravimetric and transient absorption spectroscopy analyses.

Optically active polyaniline film based on cellulose nanocrystals.

Chiral transfer from cellulose nanocrystals (CNCs) chiral nematic liquid crystal to polyaniline (PANI) is successfully achieved through co-assembly method for the first time, affording the PANI film based on CNCs optical activity. Meanwhile, the CNCs/PANI composite film displays notable Cotton effect ascribed to the polaron band transitions of PANI in circular dichroism (CD) spectrum. Hydrogen bond and electrostatic attraction favor the combination of two molecular chains in the mixed aqueous suspension and will lead to the chiral assembly of the PANI in the host chiral nematic film. However, the CD signal disappears when cholesteric phase collapse by acid protonation, and which demonstrates the chiral nematic ordering of the CNCs is essential to the chiral transfer. With the assistance of CNCs, PANI chains form a helically stacked structure. Thus, the optical activity of PANI originates from its long range organization.

Lyotropic liquid crystal behavior of carboxylated cellulose nanocrystals.

In this work, the lyotropic liquid crystal (LC) behavior of carboxylated cellulose nanocrystals (CNs) has been studied for cotton cellulose prepared by TEMPO-mediated oxidation of cellulose nanocrystals (TOCNs). It is found that suspensions of TOCNs at a critical concentration of 4.1wt% form anisotropic phase with clear optical birefringence. Furthermore, fingerprint texture is clearly observed when the concentration is 9.0wt% under a polarizing optical microscope. Fingerprint texture is characteristic of chiral nematic liquid crystal (N*-LC) phase. The band-spacing corresponds to half the helical pitch, and thus, the helical pitch of N*-LCs (9.0wt%) is about 6.0µm. The degree of oxidation (DO) and zeta potential of TOCNs in suspension are 0.15 and -59.5mV, respectively. Relatively larger aspect ratio and higher surface charges density of TOCNs make the critical concentration of LC formation decreased and the helical pitch increased compared to that of the LC prepared by H2SO4 hydrolysis system. The interparticle electrostatic repulsion between CNs with different surface charges influence the helical pitch of N*-LCs.

The structural transitions of C60 nanowhiskers under an electric field characterized by in situ transmission electron microscopy and electron energy-loss spectroscopy.

In situ electrical transport measurements for individual C60 nanowhiskers are performed using a transmission electron microscope which monitors the crystal and electronic structural changes of the C60 nanowhiskers simultaneously. Electron diffraction combined with electron energy-loss spectroscopy shows that under the external electric current, the C60 nanowhiskers first transform from a face-centered-cubic structure to a disordered arrangement of C60 molecules. The cage structure of the C60 molecules then collapses to an amorphous carbon and finally, the amorphous carbon turns into graphene stacks. This process indicates the hybridization transformation from sp(2.278) to sp(2), which is different from the transition process of C60 materials under high pressure. The obtained results also suggest that the stability of the C60 nanowhiskers should be of crucial concern when they work as electrical devices.

Electron holography characterization as a method for measurements of diameter and mean inner potential of hollow nanomaterials.

In this paper, we provide a method for the simultaneous measurement of the inner diameter of nanotubes with a regular shape and calculation of their mean inner potential (MIP) using electron holography. This method contains 4 steps: (i)phase profile characterization from electron holography; (ii) shape assumption from prepared data; (iii) thickness simulation from a shape assumption and fitting method; (iv) calculation of MIP of the simulated and fitted parameters. By this method, as an example, the shape and the outer and inner diameters of a tube formed from C(60) molecules were characterized. The MIP of the tube was also calculated through this method. The MIP calculation from another nano whisker formed from C(60) molecules supports the feasibility of our method and it could be extended to other nanomaterials. This work provides a convenient method for morphology characterization of hollow nanomaterials, such as diameter measurements and cross-sectional shape determination, which are the most basic and important characteristics of the nanomaterials. In addition, it also provides a method for MIP calculation without a thickness measurement if the samples have relatively regular shapes. Thus this method should be more convenient for closely combining the tomography and physical properties of samples, which could be essential for in situ TEM studies of nanomaterials.

Simultaneous Alignment and Micropatterning of Organic Crystallites under a Modulated Magnetic Field.

In a previous paper, we reported the micropatterning of magnetically isotropic particles using a microscopically modulated magnetic field. In this paper, we report that the alignment occurs simultaneously if the particles have magnetic anisotropy. An oil-in-water emulsion of p-terphenyl or anthracene was subjected to the modulated magnetic field and allowed to evaporate the solvent to obtain a line pattern consisting of the crystallites with alignment. The patterned samples exhibited an emission strongly polarized in the direction of the applied magnetic field that is perpendicular to the patterning lines.

Synthesis of helical polyacetylene in chiral nematic liquid crystals using crown ether type binaphthyl derivatives as chiral dopants.

A series of crown ether type binaphthyl derivatives (CEBDs) were synthesized and used as chiral dopants to induce chiral nematic (N*) liquid crystals (LCs). The twisting powers of the CEBDs for phenylcyclohexane (PCH)-derived nematic LCs were evaluated. It was found that the twisting powers of the CEBDs increased with decreasing ring size of the crown ether. Helical polyacetylenes were synthesized in the N*-LCs induced by the CEBDs. The relationship between the morphology of the helical polyacetylene and the helical structure of the N*-LC was investigated. The result showed that the interdistance between the fibril bundles of the helical polyacetylene was equal to a half-helical pitch of the N*-LC and the screw direction of the polyacetylene fibrils was opposite to that of the N*-LC.