Uniform nylon 6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon 6 in unconfined (i.e., as-electrospun) and a high T g (340 °C) polyimide confined nanofibers were studied. Similar to melt-spun nylon 6 fibers, electrospun nylon 6 nanofibers also exhibited predominant, meta-stable γ crystalline form, and the γ-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 °C, γ-form crystals gradually melted and recrystallized into the thermodynamically stable α-form crystals, which ultimately melted at 220 °C. Release of surface tension accompanied this meltrecrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; γ-form crystals did not melt and recrystallize into α-form crystals until 210 °C, only 10 °C below the T m at 220 °C. After complete melting of nano-confined crystals at 240 °C and recrystallization at 100 °C, only α-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic α-form to a high temperature monoclinic form) was observed at 180-190 °C, which was at least 20 °C higher than that in unconfined nylon 6 at approximately 160 °C. This, again, was attributed to the confinement effect.

Two diblock copolymers composed of polystyrene and a liquid crystalline azobenzenecontaining polymethacrylate were used as model systems to investigate the confinement effects on the photoalignment, photochemical phase transition, and thermochromic behavior of the azobenzene polymer. The study finds that when confined in the microphase-separated domains in the diblock copolymers, the azobenzene polymer behaves differently with respect to the homopolymer having no confinement. The confinement effects are manifested by (1) decreased photoinduced and thermally enhanced orientation of azobenzene mesogenic groups in different aggregation states, (2) slower transformation from a liquid crystalline phase to the isotropic state triggered by the trans-cis photoisomerization and slower recovery of the liquid crystalline phase after the thermally induced cis-trans back-isomerization, and (3) severely reduced and even suppressed changes in the aggregation states of azobenzene groups on heating, which is at the origin of the thermochromic property. The common cause of these confinement effects is the restriction imposed by the confining geometry on either an order-disorder or a disorder-order reorganization process involving the motion and rearrangement of azobenzene groups.

A new strategy for the preparation of azo-containing liquid crystalline polymers is presented. A polymethacrylate bearing an azopyridine group in the side chain was synthesized for the first time. The amorphous azopyridine polymer can easily be converted into liquid crystalline polymers through self-assembly with a series of commercially available, aliphatic and aromatic carboxylic acids including the acetic acid. The measurement of photoinduced birefringence reveals that these complexes may have very different behaviors. The study thus shows that azopyridine side chain polymers combine the photoactivity of azobenzene polymers with the capability of self-assembly promoted by the pyridyl group, which offers a new and robust approach toward the preparation and exploitation of photoactive liquid crystalline materials.

No abstract

A new series of liquid crystalline diblock copolymers composed of a polystyrene and a polymethacrylate with an azobenzene moiety in the side chain were synthesized through atom transfer radical polymerization and characterized by various techniques. Photoinduced birefringence of diblock copolymers and the azobenzene homopolymer was investigated and compared under different excitation conditions. The results show that the microdomain structures characteristic of diblock copolymers hinder the photoalignment of azobenzene mesogenic groups.

Co 3 O 4 nanorods have been successfully synthesized by thermal decomposition of the precursor prepared via a facile and efficient microwave-assisted hydrothermal method, using cetyltrimethylammonium bromide (CTAB) with ordered chain structures as soft template for the first time. The obtained Co 3 O 4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The results demonstrate that the as-synthesized nanorods are single crystalline with an average diameter of about 20 to 50 nm and length up to several micrometers. Preliminary electrochemical studies, including cyclic voltammetry (CV), galvanostatic chargedischarge, and electrochemical impedance spectroscopy (EIS) measurements, are carried out in 6 M KOH electrolyte.

Atom transfer radical polymerization (ATRP) was used to prepare a new series of ABA triblock copolymers that are photoactive thermoplastic elastomers. The samples synthesized have the same rubbery midblock of poly(n-butyl acrylate) (PnBA) but differ in the degree of polymerization of the end blocks of a methacrylate-based azobenzene-containing side-chain liquid crystalline polymer (Azo-SCLCP). The coupling between elasticity, liquid crystallinity and photoactivity imparts interesting features to this type of thermoplastic elastomers. When the solution-cast film is stretched at T > T g of the Azo-SCLCP whose microdomains act as physical cross-links, in contrast to conventional thermoplastic elastomers (such as styrene−butadiene−styrene triblock copolymer) that lose the elasticity, liquid crystalline microdomains can support part of the elastic extension of PnBA chains and, in the same time, deform to result in a long-range orientation of azobenzene mesogens. The liquid crystal orientation is retained in the relaxed film at T < T g, which creates a thermoplastic elastomer whose glassy microdomains contain oriented azobenzene mesogens. Moreover, the reversible trans−cis photoisomerization of the azobenzene chromophore can be used to modulate the mechanically induced orientation.

Activated carbon honeycomb supported manganese and cerium oxides (MnO x –CeO2/ACH) catalysts were investigated for selective catalytic reduction (SCR) of NO at low temperatures of 80–200 °C. Compared with ACH supported manganese oxide catalyst (MnO x /ACH), MnO x –CeO2/ACH catalysts show much higher SCR activity and higher selectivity to N2. NO conversion can be improved by the addition of CeO2 from less than 50% to 100% at 80–160 °C. The N2 selectivity of higher than 99.8% is obtained over the Ce(1)Mn/ACH catalyst at 80–200 °C. Results indicate that the addition of CeO2 improves the distribution of MnO x and enhances the oxidation of NO to NO2, producing more absorbed NO3 – on the catalyst surface, which is then reduced into N2 by NH3. These behaviors account for the promoting effect of CeO2 on the SCR activity.