Wide-angle X-ray Diffractometry Research Articles

Structure and stability of columnar cyclomaltohexaose (α-cyclodextrin) hydrate

Rapid recrystallization of cyclomaltohexaose (α-cyclodextrin, α-CD) from aqueous solution resulted in formation of the columnar crystal structure of α-CD containing only water as the guest molecule. Complementary water vapor sorption and wide-angle X-ray diffractometry (WAXD) experiments were performed on the α-CD columnar structure to elucidate the crystal structure present at varying sorption levels. Equilibrium isothermal water vapor sorption experiments at 40 °C revealed that the α-CD columnar structure is unstable above a water activity of approximately 0.67. This was confirmed by WAXD diffractograms collected over time, which further revealed that α-CD columnar structure undergoes a phase transformation to the cage structure after approximately 0.25 h at 40 °C and a water activity of 1.0.

Characterization of cellulosic hot-melt extruded films containing lidocaine

Hot-melt extrusion technology was used to produce thin films containing a model drug, lidocaine, and the cellulosic polymers hydroxypropyl cellulose (HPC) and hydroxypropyl methyl cellulose (HPMC). Two film formulations were extruded and compared, one containing only HPC and the other containing HPC:HPMC (80:20). Thermal analysis of the films using differential scanning calorimetry (DSC) suggested that the drug existed in the amorphous condition, which was confirmed by wide angle X-ray diffractometry. Sustained release of the drug was observed from both of the polymer matrices. Dissolution profiles suggested that HPMC retarded the drug release from HPC:HPMC (80:20) films. However, the mechanism of drug release from both of the films was predominantly diffusion of the drug through the polymer matrices. Incorporation of HPMC also increased both adhesive strength and work of adhesion as compared to the HPC-only films.

The Effect of Aging on the Impact Strength of β-Polypropylenes

This work focuses on the time stability of the β-phase and the impact strength of β-nucleated injection-molded polypropylenes. For the purposes of the study, various amounts of a specific β nucleating agent based on N, N'-dicyclohexyl-2,6-naphtalenedicarboxamide have been added to commercially available isotactic polypropylene. From the prepared blends standard impact testing specimens have been injection-molded. The structure has been characterized with the aid of wide-angle X-ray diffractometry, differential scanning calorimetry and polarized light microscopy, and toughness has been characterized by Charpy impact testing. At first, a measurement of impact strength and β-phase content was carried out immediately after injection molding, and as a second step the same values were measured after 2 years. The results suggest that the β-phase is time-stable, and that the notch impact strength of the samples does not significantly change with time. Furthermore, it was confirmed that the β-phase has a positive influence on impact strength but it is not the only one important factor. There are other positive effects such as creation of structural heterogeneity, elongated chains in the skin layer, specific size of spherulites and their continuity with the amorphous phase.

Improvement of the biocompatibility of chitosan dermal scaffold by rigorous dry heat treatment

We have developed a rigorous heat treatment method to improve the biocompatibility of chitosan as a tissue-engineered scaffold. The chitosan scaffold was prepared by the controlled freezing and lyophilizing method using dilute acetic acid and then it was heat-treated at 110°Cin vacuo for 1∼3 days. To explore changes in the physicochemical properties of the heat-treated scaffold, we analyzed the degree of deacetylation by colloid titration with poly(vinyl potassium sulfate) and the structural changes were analyzed by scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, wide-angle X-ray diffractometry (WAXD), and lysozyme susceptibility. The degree of deacetylation of chitosan scaffolds decreased significantly from 85 to 30% as the heat treatment time increased. FT-IR spectroscopic and WAXD data indicated the formation of amide bonds between the amino groups of chitosan and acetic acids carbonyl group, and of interchain hydrogen bonding between the carbonyl groups in the C-6 residues of chitosan and theN-acetyl groups. Our rigorous heat treatment method causes the scaffold to become more susceptible to lysozyme treatment. We performed further examinations of the changes in the biocompatibility of the chitosan scaffold after rigorous heat treatment by measuring the initial cell binding capacity and cell growth rate. Human dermal fibroblasts (HDFs) adhere and spread more effectively to the heat-treated chitosan than to the untreated sample. When the cell growth of the HDFs on the film or the scaffold was analyzed by an MTT assay, we found that rigorous heat treatment stimulated cell growth by 1.5∼1.95-fold relative to that of the untreated chitosan. We conclude that the rigorous dry heat treatment process increases the biocompatibility of the chitosan scaffold by decreasing the degree of deacetylation and by increasing cell attachment and growth.

In vitro hydrolysis of poly( l-lactide) crystalline residues as extended-chain crystallites. Part I: long-term hydrolysis in phosphate-buffered solution at 37°C

Poly( l-lactide) (PLLA) crystalline residues or extended-chain crystallites containing a trace amount of chains in an amorphous state were prepared by hydrolysis of crystallized PLLA films in a phosphate-buffered solution (PBS) at 97°C for 40 h. Their in vitro hydrolysis behavior and mechanism were investigated in PBS at 37°C for the periods of time up to 512 days using gel permeation chromatography (GPC), gravimetry, differential scanning calorimetry, and wide angle X-ray diffractometry. The GPC results showed that the hydrolysis of the crystalline residues proceeded from their surface composed of very short chains with a free end along the chain direction but the hydrolysis from their lateral surface could not be traced. The average hydrolysis rates of PLLA crystalline residues estimated from the changes of number-average and peak top molecular weights ( M n and M t, respectively) were 5.31 and 5.01 g mol −1 day −1, respectively. Such low hydrolysis rates mean that the PLLA crystalline residues can remain for a long period such as ca. 2×10 3 days (ca. 5.5 years) in the human body even after PLLA loses its functions as biomaterials. The increased melting temperature ( T m) and crystallinity ( X c) (in 320 days), and the decreased half-widths of X-ray diffraction peaks (in 320 days) during hydrolysis were attributed to the decreased lattice disorder of the PLLA crystalline residues. On the other hand, the decreased X c for the hydrolysis period exceeding 320 days was ascribed to the decreased thickness or M n of the crystalline residues, which increased the effect of the surface having a large surface energy.

Histochemical and supramolecular studies in determining quality of hemp fibres for textile applications

The composition and supramolecular structure of hemp primary bast fibres have been assessed using microscopy, compositional analysis, wide-angle X-ray diffractometry and CP-MAS 13C-NMR, in order to unambiguously define some quality parameters. The main components of the fibre wall were detected by histochemical reactions and modifications occurring during the plant growth have been pointed out. Some differences in fibre lignification degree were recorded among cultivars and confirmed by means of compositional and structural analysis. As for flax and kenaf, X-ray patterns revealed semicrystalline structure of hemp cellulose. NMR spectra and their probabilistic elaboration by MaxEnt method gave further insight on the presence of paracrystalline and amorphous phases and provided an accurate evaluation of polymeric components.

Effect of Crystal Melting on Water Vapor Permeability of Shape-Memory Polyurethane Film

Crystal melting of shape memory polyurethane (SMPU) film is investigated using polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, and temperature variable wide-angle x-ray diffractometry. Water vapor permeability (wvp) at different temperatures is measured. The results show that the SMPU film is dense with crystalline soft segments. Crystal melting of soft segments takes place when the temperature increases from 10 to 50°C. At the same temperature range, the wvp of SMPU film increases significantly. After investigating the relationship between the relative changes in amorphous area and temperature, we can conclude that crystal melting of soft segments leads to increases in the amorphous area, resulting in a significant increase in water vapor permeability.

Formation of the Liquid Crystalline Glassy Phase and Cold Crystallization of a New Crystal Form from the Glassy Phase for Thermotropic Liquid Crystalline Polyether

The formation of the liquid crystalline (LC) glassy phase and phase transitions including cold crystallization associated with this phase have been investigated for main-chain thermotropic LC polyether (EDMB-10), which is composed of 3,3’-dimethyl-4,4’-biphenyl units as mesogen and 10 methylene sequences as spacer, by mainly using DSC, wide angle X-ray diffractometry, and solid–state 13C NMR spectroscopy. When the sample is quenched from the isotropic melt to ice-water, the LC glassy phase is really produced as suggested by the previous finding that the liquid crystallization temperature is almost independent of the cooling rate whereas the crystallization temperature rapidly decreases with increasing cooling rate. The liquid crystalline glass thus formed is found to undergo cold crystallization above Tg and to produce a new type of crystal form (form β) which is significantly different in structure from form α ordinarily crystallized on cooling from the isotropic melt through the nematic phase. In particular, the highest crystallinity of form β can be obtained by annealing the LC glass at 130°C for 30 min–about 2 d and then quenching to 0°C. This fact suggests that the stable nematic phase associated with the crystallization of form β may appear on rapid heating around 130°C. In addition, form α is also crystallized even on heating when the LC glass is annealed at 132–134°C and also quenched to 0°C, implying the appearance of the stable nematic phase preferentially producing form α at this temperature range. Additional phase transitions are also observed for the form β sample with the highest crystallinity and their origins are briefly discussed.

Effect of evaporation temperature on the crystalline properties of solution-cast films of poly(vinylidene fluoride)s

The crystalline properties of poly(vinylidene fluoride) (PVdF) and its copolymer films, prepared from the solvent (N-methyl-2-pyrrolidone) evaporation at different temperatures and subsequent slow cooling to ambient temperature, were investigated by using polarized optical microscopy, differential scanning calorimetry, wide-angle X-ray diffractometry, and Fourier-transform infrared spectroscopy. The results can provide helpful data for determining the optimal processing conditions of PVdFs as the polymer binder materials in making the electrodes of rechargeable lithium batteries. The morphology analysis gives useful information that the residual solvent remaining after the evaporation shows distinguishable amounts with respect to the temperature regions dividing by the crystallization (Tc) and melting (Tm) points of original PVdF samples. It is also proved that smallest spherulitic state coexisting with dominant α- and minor γ-phase crystals, simultaneously showing the lowest heat of fusion (e.g., the lowest crystallinity), can be obtained when the solvent is evaporated at a temperature between Tc andT m. Letting the minor γ-phase crystals exist by controlling the evaporation temperature like this can be one of the best drying (evaporation) conditions of PVdF-containing slurry in lithium rechargeable battery system.

Synthesis and properties of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites

AbstractPMMA/MMT nanocomposites were successfully synthesized via in situ intercalative polymerization, and characterized by means of wide‐angle X‐ray diffractometry, transmission electron microscopy, thermal gravimetric analysis, dynamic mechanical analysis and Fourier‐transform infrared analysis. The nanocomposites possess partially exfoliated and partially intercalated structure, in which the silicate layers are exfoliated into nanometre secondary particles with thickness of less than 20 nm and uniformly dispersed in the polymer matrix. In comparison with pure PMMA, the thermal stability, glass transition temperature, and mechanical properties of the polymer are notably improved by the presence of the nanometric silicate layers. It was found that part of the PMMA chains in the nanocomposites are well immobilized inside and/or onto the layered silicates and, therefore, the unique properties of the nanocomposites result from the strong interactions between the nanometric silicate layers and the polymer chains. Copyright © 2003 Society of Chemical Industry

Synthesis and characterization of ABA type tri‐block copolymers derived from p‐dioxanone, L‐lactide and poly(ethylene glycol)

AbstractA series of triblock co‐polymers, consisting of a poly(ethylene glycol) (PEG) central block joined to two blocks of random p‐dioxanone‐co‐L‐lactide copolymers were synthesized by ring‐opening polymerization of p‐dioxanone (PDO) and L‐lactide (LLA) initiated by PEG in the presence of stannous 2‐ethylhexanoate catalyst. The resulting copolymers were characterized by various techniques including 1H and 13C NMR and FTIR spectroscopies, gel permeation chromatography, inherent viscosity, wide‐angle X‐ray diffractometry (WAXD) and differential scanning calorimetry (DSC). The conversion of PDO and L‐lactide into the polymer was studied various mole ratios and at different polymerization temperature from 1H NMR spectra. Results of WAXD and DSC showed that the crystallinity of PEG macroinitiator was greatly influenced by the composition of PDO and L‐lactide in the copolymer. The triblock copolymers with low molecular weight were soluble in water at below room temperature.© 2003 Society of Chemical Industry

Synthesis and characterization of polypropylene/clay nanocomposites

Polypropylene/clay (PP/clay) nanocomposites were synthesized via intercalative polymerization. The nanostructure of the composites was investigated by wide-angle X-ray diffractometry (WAXD) and transmission electron microscopy (TEM). The WAXD patterns of the PP/clay nanocomposites indicated that the characteristic diffraction peak of the clay disappeared. The TEM image showed the clay was exfoliated into nanometer size and dispersed uniformly in the PP matrix. The composites exhibited much higher storage modulus compared to that of pure PP. At temperatures higher than Tg, the storage modulus of the PP/clay nanocomposites with 8.1 wt % clay content increased three times that of the pure PP. Additionally, the thermal stability of the nanocomposites significantly increased. The maximum decomposition temperature was increased by 44°C with the introduction of about 10 wt % clay. The heat-distortion temperatures (HDTs) of the nanocomposites also increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3611–3617, 2001

Synthesis and characterization of polypropylene/clay nanocomposites

AbstractPolypropylene/clay (PP/clay) nanocomposites were synthesized via intercalative polymerization. The nanostructure of the composites was investigated by wide‐angle X‐ray diffractometry (WAXD) and transmission electron microscopy (TEM). The WAXD patterns of the PP/clay nanocomposites indicated that the characteristic diffraction peak of the clay disappeared. The TEM image showed the clay was exfoliated into nanometer size and dispersed uniformly in the PP matrix. The composites exhibited much higher storage modulus compared to that of pure PP. At temperatures higher than Tg, the storage modulus of the PP/clay nanocomposites with 8.1 wt % clay content increased three times that of the pure PP. Additionally, the thermal stability of the nanocomposites significantly increased. The maximum decomposition temperature was increased by 44°C with the introduction of about 10 wt % clay. The heat‐distortion temperatures (HDTs) of the nanocomposites also increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3611–3617, 2001

Combined Type Liquid Crystalline Poly(oxy-1,4-phenyleneoxyterephthaloyl)s Bearing Cholesterol Pendants Attached through Polymethylene Spacers

A series of combined type thermotropic liquid crystalline (LC) poly(oxy-1,4-phenyleneoxyterephthaloyl)s bearing pendant cholesterol moieties attached to the backbone through oxyalkyleneoxy groups (hexamethylene, octamethylene, decamethylene, and dodecamethylene) of varying length, have been synthesized anew. And their LC properties and, especially, the dependence of mesophase morphology on the spacer length were studied by differential scanning calorimetry (DSC), optical microscopy, and small (SAXD)- and wide-angle X-ray diffractometry (WAXD). All the polymers were found to be amorphous, but thermotropic. And they formed layered morphologies in their mesophase when the spacer group is long. According to SAXD analysis the layered structure becomes better defined as the length of spacers increases. They exhibit two thermal transitions before isotropization. The lower temperature occurs between 34 and 56 °C, and the high-temperature ones between 94 and 156 °C, both of which decrease with increasing the lengt...

High temperature internal friction of engineering ceramics

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.

Preparation and solubility in acid and water of partially deacetylated chitins.

Partially deacetylated chitins with different degrees of deacetylation (DD) were prepared by alkaline treatment under homogeneous conditions, and the effect of DD on their solubility was discussed in terms of crystal structure and mode of hydrogen bonding. With an increase in the treatment time, the DD of chitin increased proportionally. The chitin became soluble in dilute acetic acid at the DD of ca. 28% or over and soluble in water at the DD of ca. 49%. The solubility of the partially deacetylated chitins had a close relationship with their crystal structure, crystallinity, and crystal imperfection as well as the glucosamine content. The wide-angle X-ray diffractometry (WAXD) revealed that the chitin with ca. 28% DD retained the crystal structure of alpha-chitin with significantly reduced crystallinity and perfection of the crystallites. The water-soluble chitin of ca. 49% DD had a new crystal structure similar to that of beta-chitin rather than either alpha-chitin or chitosan, suggesting that the homogeneous deacetylation transformed the crystal structure of chitin from the alpha to the beta form. Some hydrogen bonds existing in raw alpha-chitin were found to be missing at a DD of ca. 49%.

Nonisothermal crystallization behavior of SPS/APS blends

The nonisothermal crystallization behavior of syndiotactic polystyrene (SPS)/atactic polystyrene (APS) blends was studied with differential scanning calorimetry to investigate the effects of APS on the crystallization behavior of SPS. Polarized optical microscopy and wide-angle X-ray diffractometry were also used to observe the morphology of the SPS crystalline structure. From a cyclic heating/cooling temperature program, we obtained found that APS retarded the crystallization (and recrystallization) of SPS and made the crystal less perfect, but the ultimate crystallinity of SPS did not change with the addition of APS. We also observed that APS was disposed in the interfibrillar region of SPS spherulites and did not change the crystalline form of SPS. This result will be helpful for improving SPS applications through blending with rubber-toughened APS. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3001–3008, 2000

Synthesis and Characterization of New Chiral Side Chain Liquid Crystalline Polyoxetanes

Two series of the side chain liquid crystalline polyoxetanes were synthesized via cationic ring-opening polymerization of oxetane monomers bearing pendant mesogenic units including two chiral carbons. The first two polymers have only one pendant group in the repeating unit, whereas the second polymers have two mesogenic groups per repeating unit. The oxetane monomer bearing one mesogenic unit produced high molecular weight polymers, whereas the ones bearing two mesogenic units at the same carbon in the ring produced only oligomeric products. Thermal and liquid crystalline properties of the polymers were investigated by optical polarizing microscopy, differential scanning calorimetry (DSC), and small- and wide-angle X-ray diffractometry. All of the polymers, with the exception of only one polymer, formed liquid crystalline phases such as S A , S C * , and S 1 * phases in melts. The molecular arrangement in the smectic phases was interpreted as an intercalated bilayer structure. An attempt to study the ferroelectric properties of the polymers was made, but the results obtained were not satisfactory.

Crystal Transformation Behavior and Structural Changes of the Planar Zigzag Form for Syndiotactic Polypropylene

Crystal transformation behavior and structural changes for the planar zigzag form (form III) of syndiotactic polypropylene, which is spontaneously crystallized at 0 °C from the melt, have been investigated in the heating process by DSC, wide-angle X-ray diffractometry, and high-resolution solid-state 13C NMR spectroscopy. The DSC curve for the sample containing only form III crystallites, which is crystallized at 0 °C for 5000 h, shows an evident endothermic peak at about 20 °C and an additional exothermic peak at about 100 °C prior to melting at about 150 °C. The endothermic peak, which is shifted up to about 40 °C by annealing at room temperature, is found to be ascribed to the crystal transformation from form III with the planar zigzag conformation to form II composed of isochiral helices with the ttgg conformation by wide-angle X-ray diffractometry. Moreover, the CH3 resonance lines of the dipolar decoupling/MAS 13C NMR spectra measured at different temperatures for the sample with almost the same str...

Spontaneous Crystallization Process of the Planar Zigzag Form at 0 °C from the Melt for Syndiotactic Polypropylene

The spontaneous crystallization process of the planar zigzag form (form III) of syndiotactic polypropylene has been investigated at 0 °C for samples quenched from the melt by real-time wide-angle X-ray diffractometry and high-resolution solid-state 13C NMR spectroscopy. The X-ray diffraction profile just after quenched from the melt is in good accord with that of the melt, indicating that the sample is in the noncrystalline state. With increasing crystallization time, broad diffraction peaks assignable to form III are found to evidently appear for the diffraction profile obtained after the subtraction of the noncrystalline contribution. The spontaneous crystallization of form III is also confirmed by high-resolution solid-state 13C NMR spectroscopy; for example, the CH3(I) line assigned to the tt conformation really increased in intensity with increasing crystallization time in concomitancy with the decrease of the CH3(II) line ascribed to the tg conformation. The line shape analysis of these CH3 lines re...