Nanocellulose extracted from wood pulps using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation and sulfuric acid hydrolysis methods was characterized by small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) techniques. The dimensions of this nanocellulose (TEMPO-oxidized cellulose nanofiber (TOCN) and sulfuric acid hydrolyzed cellulose nanocrystal (SACN)) revealed by the different scattering methods were compared with those characterized by transmission electron microscopy (TEM). The SANS and SAXS data were analyzed using a parallelepiped-based form factor. The width and thickness of the nanocellulose cross section were ∼8 and ∼2 nm for TOCN and ∼20 and ∼3 nm for SACN, respectively, where the fitting results from SANS and SAXS profiles were consistent with each other. DLS was carried out under both the V mode with the polarizer and analyzer parallel to each other and the H mode having them perpendicular to each other. Using rotational and translational diffusion coefficients obtained under the H mode yielded a nanocellulose length qualitatively consistent with that observed by TEM, whereas the length derived by the translational diffusion coefficient under the V mode appeared to be overestimated.
Mechanistic
behavior and flow properties of cellulose nanofibers
(CNFs) in aqueous systems can be described by the crowding factor
and the concept of contact points, which are functions of the aspect
ratio and concentration of CNF in the suspension. In this study, CNFs
with a range of aspect ratio and surface charge density (380–1360
μmol/g) were used to demonstrate this methodology. It was shown
that the critical networking point of the CNF suspension, determined
by rheological measurements, was consistent with the gel crowding
factor, which was 16. Correlated to the crowding factor, both viscosity
and modulus of the systems were found to decrease by increasing the
charge density of CNF, which also affected the flocculation behavior.
Interestingly, an anomalous rheological behavior was observed near
the overlap concentration (0.05 wt %) of CNF, at which the crowding
factor was below the gel crowding factor, and the storage modulus
(G′) decreased dramatically at a given frequency
threshold. This behavior is discussed in relation to the breakup of
the entangled flocs and network in the suspension. The analysis of
the mechanistic behavior of CNF aqueous suspensions by the crowding
factor provides useful insight for fabricating high-performance nanocellulose-based
materials.
CO2-responsiveness is imported into amphiphilic block copolymers, poly[(N,N-diethylaminoethyl methacrylate)-b-(N-isopropylacrylamide)] (PDEAEMA-b-PNIPAM), and a system dual-responsive to CO2 and temperature is constructed. The copolymer self-assembles in aqueous solution, and undergoes phase transition when CO2 and temperature stimuli occur, since the stimuli give rise to the conversion of the hydrophilicity of both blocks. Combining CO2 and temperature as triggers, schizophrenic micelle to vesicle morphological transition of the polymer assemblies is controlled.
Aryl trifluoromethoxylation by a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxylamine derivatives and intramolecular OCF3 migration is presented. This protocol allows easy access to a wide range of synthetically useful ortho-OCF3 aniline derivatives. In addition, it utilizes bench-stable reagents, is operationally simple, shows high functional-group tolerance, and is amenable to gram-scale as well as one-pot synthesis. A reaction mechanism of a heterolytic cleavage of the NOCF3 bond followed by recombination of the resulting nitrenium ion and trifluoromethoxide is proposed for the OCF3 -migration reaction.
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