Wide-angle X-ray Diffraction Measurements Research Articles

Mechanical Stabilization of Deoxyribonucleic Acid Solid Films Based on Hydrated Ionic Liquid.

Solid films of deoxyribonucleic acid (DNA) containing a hydrated ionic liquid, choline dihydrogen phosphate (CDP), were prepared by a solvent-casting method. Thermal properties, aggregation structure, thermal molecular motion, and tensile properties of CDP-containing DNA films were examined by thermogravimetry (TG), wide-angle X-ray diffraction (WAXD) measurement, dynamic mechanical analysis (DMA), and tensile tests, respectively. The water retentivity of the films at room temperature was much improved with CDP. The packing density of DNA helical chains clearly depended on the amount of CDP in the film. A small amount of CDP contributed to the suppression of the BI → BII conformational transition and the cooperative motion of the DNA duplex in the film. The tensile properties of the film drastically changed in the presence of CDP. When the amount of hydrated CDP in the film increased, the mechanical response of the film changed from glassy-like to rubbery-like via a semicrystalline-like state. The above results make it clear that CDP plays two major roles as a water absorber and plasticizer in the DNA film. Thus, it can be concluded that the use of an ionic liquid as an additive significantly increases the possibility of using a DNA solid film as a structural material.

Crystallization-driven microstructure changes during microphase separation for environment-friendly thermoplastic triblock copolymer elastomers

A study on the crystallization-driven microstructure changes during microphase separation for a series of high transparent semicrystalline thermoplastic triblock copolymer elastomers (TBCPEs), polylactide-b-polyisoprene-b-polylactide (PLA-b-PI-b-PLA) was conducted in this work. A series of PLA-b-PI-b-PLA TBCPEs with different molecular masses of PI midblock and same molecular mass of PLA end blocks were synthesized. Differential scanning calorimetry was applied to demonstrate the microphase separation and crystallization behaviors of these samples. Small-angle X-ray scattering and ultra-small-angle X-ray scattering techniques were employed to investigate the different microphase-separated structures between solvent-cast and melt quenched PLA-b-PI-b-PLA films. It was disclosed that crystallization of the PLA end blocks could obviously enlarge the interdomain distance if the microphase-separated structures in PLA-b-PI-b-PLA took lamella or cylinder formats, while much less effect was noticed if the structures took sphere format. Wide-angle X-ray diffraction measurement demonstrated that PLA end blocks in PLA-b-PI-b-PLA could crystallize and eventually form α-form crystals with relatively high crystallinity values. The α-form crystals stay clear with high transparency even with high crystallinity values, because the initially formed microphase-separated structures could confine crystallization of PLA end blocks, preventing the growth of any large PLA crystals eventually.

Enhanced mechanical and oxygen barrier performance in biodegradable polyurethanes by incorporating cellulose nanocrystals with interfacial polylactide stereocomplexation

Using bio-derived cellulose nanocrystals (CNCs) to reinforce the mechanical properties of biodegradable polyurethanes (PUs) is a promising approach especially when attempting to fabricate fully sustainable materials with high performance. However, the way to efficiently improve the dispersion and interfacial strength of CNCs in PU matrices is still an open question. In the current work, poly-l-lactide (PlLA) grafted CNCs (CNC-g-l) and a PU elastomer with poly-d-lactide as partial soft segments (d-PU) were first prepared separately, and then the fully biodegradable PU nanocomposites were fabricated by solution blending of CNC-g-l and d-PU. The surface grafting of PlLA can improve the thermal stability of CNCs, but has marginal effect on that of the nanocomposites. The improved dispersion of CNCs and enhanced interfacial strength, as evidenced by scanning electron microscopy, wide-angle X-ray diffraction and rheology measurements, are achieved by the construction of interfacial polylactide stereocomplexation (sc-PLA). The optimal improvement in mechanical properties of the nanocomposites is realized when only 1 wt% CNC-g-l is incorporated in the d-PU matrix. With the assistance of interfacial sc-PLA, the nanocomposite can gain 40% reduction in oxygen transmission rate at the optimal CNC-g-l content of 5 wt%. This study may provide a new method to improve the dispersion and interfacial strength of CNCs in biodegradable PUs and achieve simultaneously mechanical and barrier performance enhancement.

Synthesis and characterization of thermally stable bio-based poly(ester amide)s from sustainable feedstock

Aromatic poly(ester amide)s comprising of α-amino acids and lignin-derived building blocks were synthesized and their thermal properties assessed. The polymers, which were prepared by melt polycondensation with p-toluenesulfonic acid as the catalyst, all possessed high thermal stability in N2; the onsets of thermal degradation (Td onset) were >320 °C, the percent char yields ranged from 40 to 65% at 800 °C, and the glass transition temperatures (Tg) ranged from 136 °C–238 °C. Remarkably, the polymers were also thermally stable in air, with the Td onsets >330 °C and Td 50% >520 °C. Interestingly, the size of the R-group on the amino acids greatly affected the Tg, but only minimally affected the Td; perhaps due to the variation in polymer size. Wide angle x-ray diffraction measurements (WAXS) revealed semi-crystalline polymers, with similar diffraction patterns for all the polymers. The polymers mostly maintain their thermal stability after being subjected to various pH media for 6 days at 50 °C. Altogether, these characteristics make our bio-based PEAs worthwhile candidates for continued investigation as alternatives to petrochemical-derived thermoplastics for high performance materials.

Structural Evolution Mechanism of Crystalline Polymers in the Isothermal Melt-Crystallization Process: A Proposition Based on Simultaneous WAXD/SAXS/FTIR Measurements.

Time-resolved simultaneous measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) (and FTIR spectra) were performed for various kinds of crystalline polymers in isothermal melt-crystallization processes, from which the common features of the structural evolution process as well as the different behaviors intrinsic to the individual polymer species were extracted. The polymers targeted here were polyethylene, isotactic polypropylene, polyoxymethylene, aliphatic nylon, vinylidene fluoride copolymer, trans-polyisoprene, and poly(alkylene terephthalate). A universal concept of the microscopically viewed structural evolution process in isothermal crystallization may be described as follows: (i) the small domains composed of locally regular but more or less disordered helical chain segments are created in the melt (this important information was obtained by the IR spectral data analysis); (ii) these domains grow larger as the length and number of more regular helical segments increase with time; (iii) the correlation among the domains becomes stronger and they approach each other; and (iv) they merge into the stacked lamellar structure consisting of the regularly arranged crystalline lattices. The inner structure of the domains is different depending on the polymer species, as known from the IR spectral data.

Diversified α-phase nanostructure of isotactic polypropylene under cylindrical confinement via cross diffraction analysis

Understanding polymer nanostructures is a prerequisite to manipulate their physical properties. Molecular self-assembly under confinement effectively generates novel polymer nanostructures. However, in one confined system, diffraction signals of different nanostructures are merged in a typical two-dimensional (2D) wide-angle X-ray diffraction (WAXD) measurement. For comparison, selected-area electron diffraction (SAED) of transmission electron microscopy can precisely capture the “local” diffraction signal of an individual nanoscale entity. Here, using isotactic polypropylene (i-PP) as a model polymer, we have demonstrated a cross-analysis of global X-ray and local electron diffraction results to fully reveal the structural details of i-PP nanorods. For the first time, we have decomposed completely the “mixed” 2D WAXD patterns of i-PP nanorods into five types of α-phase nanostructures: (a). Left-tilted daughter crystals; (b) Right-tilted daughter crystals; (c) Double-tilted daughter crystals; (d) a*-axis oriented crystals; (e) b-axis oriented crystals.

Advantages of bulge testing and rupture mechanism of glassy polymer films

The advantages of bulge testing as a method of mechanical property analysis for polymer films was described. Deformation and rupture mechanisms of glassy polymer films during bulge testing were investigated by in situ molecular aggregation structure analyses. Heat-pressed polycarbonate (PC, weight-average molecular weight (Mw) = 38k) and poly(methyl methacrylate) (PMMA, Mw = 70k and 1.2 M (PMMA-70k and PMMA-1.2 M)) films were employed as transparent glassy polymers. Evaluations of molecular aggregation structures during bulge testing were conducted by polarized high-speed camera observation and wide-angle X-ray diffraction (WAXD) measurements. PC and PMMA-1.2 M films showed a yield point in their stress-strain curves, indicating ductility, while PMMA-70k film showed brittleness. WAXD measurements revealed that the distances between the main chains slightly increased with increasing strain. With increasing film strain above the yield point, a craze-like morphology with thinning of the film was seen for the PC film, likely due to the flexible PC molecules. Although it is difficult for PMMA molecules to orient along applied stress, a transition to the thinner state with the formation of wrinkled structures occurred for the PMMA-1.2 M film above the yield point. The transition to the thinner state, which corresponds to a discontinuous decrement of the cross-section area by deformation, might be categorized as two-dimensional crazing and/or shear deformation. PMMA-70k did not show such behavior because of the small number of entanglements. The use of a small amount of films in terms of thickness and size and the capability of observation of the entire film were given as advantages of the bulge test.

Zirconium phosphate changing hygroscopicity of polyamide-6 in nanocomposites PA-6/ZrP

Hygroscopicity can be understood as ability of any material to absorb water. This investigation aims to study the effect of lamellar zirconium phosphate (ZrP) in the hygroscopicity of poliamide-6 (PA-6). In situ (PA-6/ZrP) nanocomposites were prepared during the polymerization of caprolactam. Structural, thermal, crystallographic and rheological characteristics were assessed by infrared spectroscopy (FTIR), thermogravimetry, differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), rheological and water absorption measurements. FTIR evidenced strong interaction between polymer/nanofiller. According to the kind of nanofiller, changes in PA-6 thermal stability and crystallinity degree were noticed. Formation of PA-6 α-crystal, microcomposite and possibly exfoliated nanocomposite was predicted by WAXD. Rheological measurements evidenced great interaction between PA-6 and nanofillers. PA-6 hygroscopicity was strongly influenced by ZrP-attained value almost 40% lesser as compared to neat PA-6.

High-performance polyurethane nanocomposites based on UPy-modified cellulose nanocrystals

Densely H-bonding assemblies are the key strategy found by nature to enhance the rupture strength of natural polymers without sacrificing their toughness, such as spider silk, while it still remains a great challenge using such intriguing strategy to prepare high-performance synthesized polymer or biopolymer enhanced polymer nanocomposites. To address this challenge, we report here a bio-inspired strategy using densely H-bonding assembly for facile fabrication of high performance polyurethane (PU) nanocomposites reinforced by hydroxyl-rich cellulose nanocrystals (CNCs) functionalized with 2-ureido-4-[1 H]-pyrimidinone motifs (CNC-UPy) containing self-complementary hydrogen bonds. These PU/CNC-UPy nanocomposites showed remarkably improved mechanical strength without sacrificing the elongation at break and toughness compared to pure PU matrix. Differential scanning calorimetry(DSC) results indicated that CNC-UPy could induce the formation of long range ordering of hard segment domains, due to the strong hydrogen bonding interactions between UPy motifs attached on CNC-UPy and PU matrix. Furthermore, wide angle X-ray diffraction (WAXD) measurements demonstrated that the strain-induced crystallization (SIC) was enhanced significantly by introducing CNC-UPy into PU, leading to a large stress at break. The enhanced interfacial H-bonding interactions between CNC and PU though UPy anchoring could overcome the inherent trade-off between the stiffness and toughness of polymer composites. The proposed bio-inspired strategy using densely H-bonding assembly will be with more extensive application prospects.

Synergistic effect of alkyl lactate functional groups on properties of methacrylate polymers

In this work, four novel different alkyl lactate methacrylate monomers were synthesized through azeotropic esterification method by reacting methyl, ethyl, propyl and butyl lactates with methacrylic acid. The prepared monomers were polymerized through solution polymerization technique and both monomers and polymers were analyzed by FTIR, 1H NMR and 13C NMR spectroscopy techniques to elucidate the structure and to confirm their formation. Increasing the number of methylene units in alkyl lactate side chain decreases the glass transition temperature (Tg) of the polymers. Average molecular interchain spacing (〈R〉) of polymers was obtained from the wide-angle X-ray diffraction measurement and the values ranged from 6.26 to 7.18 A based on the length of alkyl lactate group. The prepared polymers showed hygroscopic property and their moisture absorption was in the range of 10–24% (w/w) depending upon the length of alkyl lactate moiety, relative humidity and time. These polymers have the potential for hydrogel applications owing to their increased moisture absorption capacity. Both polymethyl and propyl lactate methacrylate showed two distinct and prominent thermal degradations whereas polyethyl and butyl lactate methacrylates showed only a single distinct and prominent thermal degradation step. An interesting result of as-synthesized polymers showed odd–even chain length effect in the properties of 〈R〉, moisture uptake and thermal stability.

On the enthalpy of melting of poly(l-lactide)

Poly(l-lactide) (PLLA) is an extensively employed biodegradable semicrystalline polymer with usage from implantable medical devices and drug release matrices to environmentally friendly packaging materials. Since the morphology and crystallinity considerably determine the application field, PLLA samples with a large variation in crystallinity (going from below 20% to over 70%) were prepared by different procedures. Subsequent differences in morphology, crystallinity and thermal properties were followed by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) measurements and differential scanning calorimetry (DSC). The value of the enthalpy of melting of a perfectly (100%) crystalline PLLA was determined (ΔHf = 115.7 J/g).

INFLUENCE OF STRAIN-INDUCED CRYSTALLIZATION ON STRESS SOFTENING OF SULFUR CROSS-LINKED UNFILLED GUAYULE AND DANDELION NATURAL RUBBERS

ABSTRACT The stress softening behaviors of sulfur cross-linked unfilled guayule natural rubber (S-GR) and sulfur cross-linked unfilled dandelion natural rubber (S-DR) under cyclic deformation were characterized by simultaneous wide angle X-ray diffraction and tensile measurements under cyclic deformation. The behaviors were found to be affected by their strain-induced crystallization (SIC) phenomena and aggregated nonrubber components. The stress softening degree at stretching ratio = 8.0 of S-DR was almost two times larger than that of S-GR. Additionally, the hysteresis loss and residual strain of S-DR were much higher than those of S-GR in the same cycle. The key factors that caused the increase in their degree of stress softening were the increase in average volume and the decrease in average number of strain-induced crystallites upon cyclic deformation, not the insignificant decrease in crystallinity. The breakage of the aggregated nonrubber components is a main origin of stress softening behaviors for S-GR and S-DR because their SIC behaviors also were significantly influenced by the aggregates of nonrubber components in the rubber matrixes. Both the effects of nonrubber components and SIC on stress softening were more dominant in S-DR than in S-GR, probably owing to the larger amount of aggregated nonrubber components in the former than in the latter. The results will be useful in effectively using guayule and dandelion natural rubbers as alternatives to Hevea natural rubber in the rubber industry.

Direct Evaluation of Local Dynamic Viscoelastic Properties of Isotactic Polypropylene Films Based on a Dynamic μ-Beam X-ray Diffraction Method.

The local mechanical properties of crystalline polymer were evaluated using synchrotron radiation X-ray diffraction with 10 μm lateral resolution. A nonoriented isotactic polypropylene (iPP) film with isolated spherulites in a crystallized matrix was used as a model sample. In situ wide-angle X-ray diffraction (WAXD) measurement was performed on the iPP film using a microbeam synchrotron radiation X-ray under sinusoidal strain. The lattice spacing of the crystal planes increased and decreased in response to the applied sinusoidal strain. Local dynamic viscoelastic functions (dynamic storage and loss moduli (E' and E″)) were calculated at room temperature from the relationship between the calculated applied stress and the response strain obtained by dynamic μ-beam WAXD measurement inside and outside of the spherulites. The E' values inside and outside of spherulite obtained from the change in spacing of the (110) plane were 1.8 and 1.1 GPa, respectively. Furthermore, the E' value inside of spherulite obtained from the change in spacing of the (1̅13) plane was 6.0 GPa. These values can be explained by the deformation of crystallite, which depends on the direction of crystal planes. The results obtained here revealed that synchrotron radiation X-ray diffraction measurement gives not only structural information but also the local mechanical properties of the materials E'.

Waterborne polyurethane-silica nanocomposite adhesives based on castor oil-recycled polyols: Effects of (3-aminopropyl)triethoxysilane (APTES) content on properties

Waterborne castor oil-recycled polyol based polyurethane-silica nanocomposite adhesives (WPU) with polymer matrix and silica nanoparticles chemically bonded have been successfully prepared through a sol-gel process. A series of waterborne polyurethane adhesives with hard segment contents from 71.3 to 74.5 wt%, were synthesized using an isophorone diisocyanate, 2-bis(hydroxymethyl) propionic acid, recycled castor oil-based as soft segments and (3-aminopropyl)triethoxysilane (APTES) as chain extender. The depolymerized oligoester obtained from glycolysis of poly(ethylene terephthalate) (PET) waste using triethylene glycol (TEG), was transesterified with castor oil (CO) which resulted in the formation of hydroxyl-functional polyester polyol, with hydroxyl value of 414 mgKOH g−1. The molecular structures and mass of glycolyzed PET oligoesters, castor oil-based polyol and castor oil-based polyurethane-silica nanocomposite adhesives were estimated by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The structure and properties of the resulting films were investigated by FTIR, wide angle X-ray diffraction measurement (XRD), thermogravimetry (TG) and differential scanning calorimetry (DSC). TG analysis indicated that APTES can improve the thermal stability of WPU. XRD showed that the crystallinity of WPU decreased with the increase alkoxysilane content. The extent of crosslinking was investigated to show a dependence on silica concentration, which increased the glass transition temperature and particle size of polyurethane nanocomposites with increasing alkoxysilane content due to the condensation of the alkoxysilane groups. The hardness, adhesion and gloss quality of the polyurethane films were also determined considering the effect of APTES content, so this paper confirmed the suitability of using these castor oil-based waterborne polyurethane-silica nanocomposites as new adhesive materials with high performance coatings materials. The experimental results reveal that the APTES and the hard segment content play a key role in controlling the structure and properties of the PU cast films based on castor oil-recycled polyols.

Molecular orientation and stability of poly(3-hexylthiophene) nanogratings affected by the fabricated solvent vapor.

During the nanoimprinting lithography (NIL) process, the role of solvent vapor in fabricating the pattern structure and inducing the molecular alignment of nanoimprinted polymer film has been attracting significant attention. We demonstrate here that the molecular orientation and thermal stability of poly(3-hexylthiophene) (P3HT) nanograting film can be affected obviously by the fabricated solvent vapor. A solvent-vapor nanoimprinting lithography (SV-NIL) technique based on a polydimethylsiloxane (PDMS) template is employed to fabricate a P3HT nanograting structure film successfully and solvent vapor is offered by chlorobenzene, chloroform and carbon disulphide, respectively. The molecular orientation of the polymer film is carefully characterized by grazing incidence wide angle X-ray diffraction (GIWAXD) measurements to investigate the effect of various solvent vapors on the molecular orientation of the P3HT nanograting film. For the P3HT nanograting film fabricated by chloroform and chlorobenzene solvent, the edge-on molecular orientation of the typical form II crystallographic structure is induced. However, this indicates that there are both the face-on molecular orientations of the form II and form I crystallographic conformation present for the P3HT nanograting film fabricated by carbon disulphide solvent. Therefore, the fabricated solvent vapor plays a significant role in determining the formation of the molecular orientation of the polymer nanostructure. Then, the role of thermal annealing in the stability of the molecular orientation was investigated for the P3HT nanograting film after a fixed temperature. As for the annealed nanograting film fabricated by chlorobenzene and chloroform solvent vapor, a single edge-on molecular orientation mode of the form I crystallographic structure has been obtained. However, for the annealed nanograting film fabricated by the carbon disulphide solvent, the edge-on and face-on molecular orientations of the form I crystallographic structure are still retained. This indicates that the stability of the form II crystallographic conformation is mainly dependent on the thermal annealing process. Therefore, after the annealing process, the final determining of the molecular alignment and crystallographic conformation depends significantly on the orientation type of the nanograting film before the annealing history, and it can be further inferred that the molecular orientation of the annealed polymer film is still affected by the fabricated solvent vapor significantly. Thus this will provide new understanding and guidance for the research of the topographical structure and molecular alignment of conjugated polymers.

Pore formation mechanism of oriented β polypropylene cast films during stretching and optimization of stretching methods: In-situ SAXS and WAXD studies

In this article, the relationship between the initial microvoids or cavities variations and lamellar structures evolutions of oriented β-PP cast films along different tensile directions was mainly investigated via In-situ small-angle X-ray (SAXS) and wide-angle X-ray diffraction (WAXD) measurements. The pore formation mechanism, initial cavities were directly originated from the lamellar separation and its specific positions were at the weak boundary between β lamellae and adjacent amorphous phase, was proposed. Although the pore formation mechanism of both different stretching directions was consistent, the separation process of β lamellae was greatly different during stretching. Lamellae on β-transcrystals (β-TCs) were preferred to be separated along machine direction, while twisted and inter-crosslinked β lamellae were more likely to separate along transverse direction. Both stretching directions mainly affected the stage of microvoids growth that could be promoted along transverse direction. Moreover, for the sample of stretching along transverse direction, microporous membranes with higher porosity and more homogeneous micropores distribution could be obtained through subsequent biaxial stretching. Therefore, the suitable stretching methods were optimized for β-TCs to prepare PP microporous membranes with excellent performance.

Understanding structure-mechanics relationship of high density polyethylene based on stress induced lattice distortion

The relationship between the macroscopic non-linear mechanics and the microscopic crystal structural evolution of pre-oriented high-density polyethylene (HDPE) is investigated by in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) measurement over a wide temperature range from −10 to 130 °C. With the concept of stress-induced disordering of crystal, the ratio (φa/b) of lattice parameters a to b is defined as a new structural variable, which can reflect the lattice distortion and then the microscopic stress state of orthorhombic crystal (O-crystal). According to the temperature-dependent non-linear variation of φa/b with strain, the contributions of O-crystal and monoclinic crystal (M-crystal) to the macroscopic mechanics including linear elasticity, yielding, stress softening and strain hardening are clarified. It is found that M-crystal bears the main extensional stress once formed, although it survives within a limited strain window relying on temperature. By further combining the extensional phase diagram constructed in strain-temperature space, the HDPE deformation is recognized to undergo successively one-dimensional (1D) chain segments rotation of crystal, two-dimensional (2D) crystal plan shearing or slipping and three-dimensional (3D) recrystallization along with increasing strain or stress, demonstrating a multiscale structural transition and energy dissipation mechanism.

Isothermal crystallization of poly(glycolic acid) studied by terahertz and infrared spectroscopy and SAXS/WAXD simultaneous measurements

Isothermal crystallization of poly(glycolic acid) (PGA) has been studied using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. Changes in the intermolecular interactions in PGA during the isothermal crystallization were monitored using THz spectroscopy, which is an efficient technique for analyzing the higher-order structure of polymers. In the THz spectra, the temporal difference in the intensity observed in the isothermal crystallization is due to the difference in the vibrational origins of two bands at 192 and 65 cm−1. The band at 192 cm−1 primarily originates from the intramolecular vibrational mode (twisting of the local structure of the PGA molecular chain). Furthermore, the band at 65 cm−1 exists due to the intermolecular vibration mode (C = O···H-C hydrogen bonds between polymer chains). In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks. When a lamellar structure is formed and the molecular chains are oriented, the THz band originating from the intermolecular vibration is observed. It is highly possible that the intermolecular vibration appearing in the THz spectra requires the molecular chains to be oriented. Isothermal crystallization of poly(glycolic acid) (PGA) was carried out using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. The intensity of the absorption peak at 192 cm−1 increased before the increase in intensity of the peak at 65 cm−1 during the isothermal melt-crystallization process at 185 °C. This is due to a difference in the vibrational origins of these two bands. In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks

Multi-responsive red solid emitter: Detection of trace water and sense of relative humidity

A multi-responsive D-A type compound ( CYQ ) based on pyrone and triphenylamine was designed and successfully synthesized. The target compound exhibited distinct aggregation-enhanced emission (AEE) effect. Solvatochromic experiment and density functional theory (DFT) indicated CYQ possessed excellent intramolecular charge transfer (ICT) ability. Besides, its mechanofluorochromic property (MFC) was found with a 37 nm red-shift. Powder wide-angle X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) measurements were performed to demonstrate the transformation from the crystalline to amorphous states upon grinding. Surprisingly, CYQ displayed a hypersensitive response to trace water in organic solvents with an excellent detection limit as low as 0.0096% in tetrahydrofuran (THF). Furthermore, it was found that the fluorescent intensity of CYQ declined progressively upon humidity rise, and its color change can be witnessed by naked eyes. Therefore, the relative humidity (RH) sensing strategy guarantees the AIEgen to become a colorimetric sensor under various conditions.

Structural Formation of UHMWPE Film Tracked by Real-Time Retardation Measurements during Uniaxial/Biaxial Stretching.

This work reports on an experimental study of the stretching of ultra-high molecular weight polyethylene (UHMWPE) film in various uniaxial/biaxial stretching modes at various temperatures and stretching speeds. We examined the stress-birefringence relationship as a stress-optical rule (SOR) under uniaxial stretching and evaluated the stress-optical coefficient (SOC). Wide-angle X-ray diffraction (WAXD) measurements were applied to evaluate the contribution to birefringence of the crystalline and amorphous phases and to characterize stretching modes. In simultaneous biaxial stretching, the melting temperature (Tm) proved critical to structural formation. We applied thermal analysis techniques and tensile testing to evaluate higher order structures after each stretching mode.