Volume 55 Issue 6, June 2023

Various in situ measurement techniques have been applied to investigate changes in the three-dimensional structures and the physical properties of polyimides (PIs) generated at high pressures using a custom-built optical cell (up to 4,000 atm) or a diamond anvil cell (up to 80,000 atm). Moreover, the structural changes in the PI chain repeating units and interchain distances induced by the ultrahigh pressures were observed with WAXD, and they were compared with optical absorption, fluorescent and phosphorescent emission spectra, infrared absorption spectra, and refractive indexes observed under the same conditions.

This focus review summarized current adhesives that are capable of macroscopic adhesion in seawater. The design strategies and performance of these adhesives were reviewed based on their bonding methods. Some future research directions and perspectives for under-seawater adhesives were discussed.

A series of amphiphilic diblock copolymers (PVA_m-b-PVPi_n: m/n = 82/6, 72/26, and 70/74) with different block lengths of hydrophilic poly(vinyl alcohol) (PVA) and hydrophobic poly(vinyl pivalate) (PVPi) blocks were prepared. PVA_m-b-PVPi_n was synthesized from poly(vinyl acetate)-b-PVPi (PVAc_m-b-PVPi_n) diblock copolymer via selectively hydrolysis. In water, PVA_m-b-PVPi_n formed spherical polymer micelles with a PVPi core and a PVA shell. The hydrodynamic radius, light scattering intensity, and aggregation number of PVA_m-b-PVPi_n increased with increasing PVPi block length. In contrast, the critical micelle concentration was reduced because of stronger hydrophobic interactions.

The modification of cellulose nanocrystal film using glycidyl silane compounds was performed with a coating process. Control of the surface structure and functionalization by silylation was achieved. Postmodification using glycidyl groups in silane-modified cellulose nanocrystal was demonstrated.

The conformational relaxation of ethylene-propylene-diene terpolymer (EPDM) chains at the interface with a model filler of quartz was examined by sum frequency generation (SFG) spectroscopy in conjunction with molecular dynamics (MD) simulations. We found that the glass transition temperature (T_g) of EPDM was higher at the interface than in the bulk. Also, the conformational relaxation beyond the T_g was significant for ethylene units, but not for propylene units. This information might be useful in controlling the local conformation and dynamics of polymer chains at the interface.

Microstructure-free strong all-wooden nanocomposites (AWNC) was directly made from the weak raw wood (RW) of paulownia, in which microscale wood fibers and void structures were dismantled into a fully consolidated structure containing nanofibrils (as the reinforcing phase) and noncrystalline cellulose, lignin, and hemicelluloses (as the matrix phase). This direct conversion was carried out through simultaneous chemomechanical densification/downsizing in three steps, including (1) partial delignification, (2) partial dissolution with IL or oxidation with TEMPO and ammonium persulfate (APS), and (3) hot pressing with cyclic pressurizing-depressurizing conditions.

The grazing incidence diffracted X-ray blinking was proposed to evaluate the molecular motions occurring at polymer surfaces by measuring X-ray diffraction patterns near the total reflection angle over small time periods. When the crystallized polymer poly{2-(perfluorooctyl)ethyl acrylate}(PC₈FA) film was measured, the results of the decay constants, which are indexes of molecular motions, suggested that the PC₈FA surface is mobile compared to the bulk.

PVDF forms β- and γ-phases in the presence of alkylammonium salts. We investigated crystal polymorphism obtained by various crystallization processes using FT-IR in PVDF added with two different alkylammonium salts. The fractions of crystalline phase changed with crystallization processes and ionic salts, which is attributed to the different crystallization mechanisms depending on the strengths of the ion-dipole interactions between alkylammonium salts and PVDF chains.

Two types of polyimide nanofibers (PINFs) were prepared. PINF-I (lengths = 305 ± 152 nm and diameters = 12 ± 2 nm) was prepared via crystallization of PI dissolved in a concentrated sulfuric acid solution. Adding t-butanol to a PINF-I aqueous dispersion and subsequent freeze–drying produced PINF-II (diameters = 105 ± 99 nm) with PINF-I aggregated into a fibrous form. The PI crystalline unit cell parameters were orthorhombic, a = 1.21 nm, b = 0.88 nm, and c = 2.23 nm (molecular chain axis direction).