The effect of molecular weight (MW) on the polymorphous crystallization and melting behavior of poly(l-lactide) (PLLA) were systemically studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), and time-resolved Fourier transform infrared (FTIR) spectroscopy. It was found that the polymorphism of PLLA is not influenced much by MW, and the α‘- and α-form crystals are produced at low and high crystallization temperature (T c), respectively, regardless of the MW. However, MW significantly affects the crystallization kinetics, and the crystallization rate reduces greatly with MW increasing. Moreover, the T c- and MW-dependent melting behavior of PLLA was clarified with combining the DSC and FTIR results. It was found that the α‘- to α-crystalline phase transition occurs prior to the dominant melting in both the low- and high-MW PLLA crystallized at low T c. Unlike the high-MW PLLA, in low-MW PLLA crystallized at low T c, the α‘-form crystals only partially transform into the α-one, and some amounts of α‘-form crystals melt directly without transition during the heating process. With increasing T c, the melting of PLLA with various MWs changes from the phase transition + melting mechanism to the usual melt−recrystallization mechanism.

The elastic modulus of single microfibrils from tunicate (Halocynthia papillosa) cellulose was measured by atomic force microscopy (AFM). Microfibrils with cross-sectional dimensions 8 × 20 nm and several micrometers in length were obtained by oxidation of cellulose with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) as a catalyst and subsequent mechanical disintegration in water and by sulfuric acid hydrolysis. The nanocellulosic materials were deposited on a specially designed silicon wafer with grooves 227 nm in width, and a three-point bending test was applied to determine the elastic modulus using an AFM cantilever. The elastic moduli of single microfibrils prepared by TEMPO-oxidation and acid hydrolysis were 145.2 ± 31.3 and 150.7 ± 28.8 GPa, respectively. The result showed that the experimentally determined modulus of the highly crystalline tunicate microfibrils was in agreement with the elastic modulus of native cellulose crystals.

Effects of annealing conditions and molecular weight (MW) on the crystalline phase transition in poly(L-lactide) (PLLA) were studied by wide-angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The disordered crystal (R′-form) of PLLA was found to transform into the R one during annealing process at elevated temperatures. The R′-to-R transition is quite dependent on the annealing period (t a : 0-1440 min) and annealing temperature (T a : 120-160°C). With increasing T a , the polymorphic transition progresses much more rapidly. The R′-to-R transition is mainly involved by the slight rearrangement of the chain conformation (especially related to the side groups) and packing manner in the unit cell to the more energy-favorable state, corresponding to the reduction of unit cell dimension. Besides, it was proposed that the R′-to-R transformation mainly proceeds by the direct solid-solid transition mechanism. Moreover, it was found that MW affects the crystalline phase transition significantly. In the low-MW PLLA sample, the R′-to-R transition becomes much faster, and it can proceed prominently even when annealed at relatively lower temperature.

A convenient, fast and selective water analysis method is highly desirable in industrial and detection processes. Here a robust microporous Zn-MOF (metal–organic framework, Zn(hpi2cf)(DMF)(H2O)) is assembled from a dual-emissive H2hpi2cf (5-(2-(5-fluoro-2-hydroxyphenyl)-4,5-bis(4-fluorophenyl)-1H-imidazol-1-yl)isophthalic acid) ligand that exhibits characteristic excited state intramolecular proton transfer (ESIPT). This Zn-MOF contains amphipathic micropores (<3 Å) and undergoes extremely facile single-crystal-to-single-crystal transformation driven by reversible removal/uptake of coordinating water molecules simply stimulated by dry gas blowing or gentle heating at 70 °C, manifesting an excellent example of dynamic reversible coordination behaviour. The interconversion between the hydrated and dehydrated phases can turn the ligand ESIPT process on or off, resulting in sensitive two-colour photoluminescence switching over cycles. Therefore, this Zn-MOF represents an excellent PL water-sensing material, showing a fast (on the order of seconds) and highly selective response to water on a molecular level. Furthermore, paper or in situ grown ZnO-based sensing films have been fabricated and applied in humidity sensing (RH<1%), detection of traces of water (<0.05% v/v) in various organic solvents, thermal imaging and as a thermometer.

The crystalline structure of poly(L-lactide) (PLLA) have been found to quite depend on the crystallization temperatures (T c s), especially in the range of 10021208C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide-angle X-ray diffraction and Fourier transformed infrared spectroscopy revealed that 1108C is a critical temperature for PLLA crystallization. At T c < 1108C and T c 1108C, the a 0 and a crystals were mainly produced, respectively. Besides, the structural feature of the a 0 -form was illustrated, and it was found that the a 0 -form has the larger unit cell dimension than that of the a-form. Moreover, the crystallization kinetics of the a 0 and a crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus T c and the half time in the melt-crystallization (t 1/2 ) versus T c investigated by Polarized optical microscope and Differential scanning calorimetry, respectively.