A series of novel azo polyelectrolytes have been synthesized based on an extremely reactive precursor polymer, poly(acryloyl chloride) (PAC), prepared from acryloyl chloride by radical polymerization. The precursor polymer was post-functionalized by the Schotten-Baumann reaction of PAC and several aromatic azo reactants containing hydroxyl end groups. The degrees of functionalization were controlled by selecting suitable feed ratios between the azo reactants and poly(acryloyl chloride) and the unreacted acyl chloride groups were hydrolyzed to obtain ionizable carboxyl groups. The products were characterized by elemental analysis, FT-IR, 1H NMR and UV−vis spectroscopy. Irradiated by 365 nm UV light, azo polyelectrolytes PPAPE, PEAPE and PCAPE showed a significant photochromic effect. The contact angles of water on the surfaces of spin-coated films of PPAPE and PEAPE decreased evidently upon UV irradiation. The extent of the photoinduced contact angle changes depends on the type of the azo chromophores and the degree of functionalization. Self-assembled multilayers of the azo polyelectrolytes were fabricated by a layer-by-layer adsorption method. A significant photochromic effect from cis−trans isomerization of the azo chromophores was observed for the multilayers. The photoinduced contact angle changes of water on the self-assembled multilayers were also observed.

The manipulation of nanobuilding blocks into a 3D macroscopic monolith with ordered hierarchical structures has been much desired for broad and large-scale practical applications of nanoarchitectures. In this paper, we demonstrate a fully bottom-up strategy for the preparation of aramid aerogel monoliths. The process starts from the synthesis of poly­(p-phenylene terephthalamide) (PPTA) through the polycondensation of p-phenylenediamine and terephthaloyl chloride, with the assistance of a nonreactive dispersing agent (polyethylene glycol dimethyl ether), which helps the dispersal of the as-synthesized PPTA in an aqueous medium for the formation of p-aramid nanofibers (ANF). Then the vacuum-assisted self-assembly (Vas) technique is skillfully connected with the ice-templated directional solidification (I) technique, and the combined VasI method successfully tailors the self-assembly of ANF to transform the 1D nanofibers into a 3D aerogel monolith with a specific long-range aligned, lasagna-like, multilaminated internal structure. The study of the aerogel microstructure revealed the dependence of the lamina orientation on the direction of the freezing front of ice crystals. This direction should be parallel to the deposition plane of the Vas process if a long-range aligned lamellar structure is desired. The anisotropy of the multilaminated aerogel was proven by the different results in the radial and axial directions in the compression and thermal conductivity tests. As a kind of organic aerogel, the ANF monolith has typical low density, high porosity, and low thermal conductivity. Additionally, the ANF monolith exhibits high compressive stress and excellent thermal stability. Considering its high performance and facile preparation process, potential applications of the ANF aerogel monolith can be expected.

Poly(p-phenylene terephthalamide) nanofibers were prepared via a polymerization induced self-assembly process with the assistance of methoxy polyethylene glycol (mPEG).

Aerogel has been widely known as a low-density and highly porous material and is closely connected with the complex processing methods, such as freeze−drying or supercritical drying. In this work, using the polymerization-induced aramid nanofiber (PANF) as a building block, we put forward a modified freezing−drying method for the high-efficiency preparation of all-para-aromatic-amide aerogels. In the preparation process, PANF hydrogel is first frozen at −18 °C and then dried at 20−150 °C for the formation of PANF aerogel. The PANF framework formed during the freezing process is crucial for the formation of the PANF aerogel. Moreover, the space-occupying effect of ice crystals is also helpful for the formation of the macroscopic pore structure in the aerogel. Aerogels with large size or well-controlled shape could be successfully obtained by this method. Through the variation of PANF concentration in the hydrogel and drying temperature, aerogels with different densities (20−185 mg/cm 3 ) could be achieved, and the lowest density is reached at 150 °C, with the PANF concentration of 0.7%. The low-density PANF aerogels show high specific compressive strengths and low thermal conductivities, which are comparable to those resulting from the freeze−drying or supercritical drying method. Furthermore, the shrinkage phenomenon in the drying process could be skillfully utilized for the preparation of PANF aerogel-coated objects. The PANF aerogels could be applied as a thermal insulating material or shock absorption material in practical applications.

Stable and uniform dispersions of para-aramid nanofibers have been prepared by adding methoxypolyethylene glycol (mPEG) in the polymerization process, followed by strong shear and dispersion. Aramid membranes are fabricated by vacuumassisted filtration of the nanofiber dispersion and assembled into batteries as separator. The membrane properties and battery performances are characterized in detail and the effect of mPEG content on these properties is explored. It is demonstrated that aramid membranes possess good electrolyte wettability, excellent mechanical properties, and superior thermal stability, which improve the safety of lithium ion batteries. The mPEG is critical to the formation of aramid nanofibers and improves the porosity and ionic conductivity of the membranes. These fascinating characteristics and facile papermaking method endow aramid membrane potential application as separator in lithium ion batteries with superior safety.