Density and crystallinity of poly (3-hydroxybutyrate/3-hydroxyvalerate) copolymers

Bacteria can produce a range of optically active copolymers of (R)-3-hydroxybutyrate (HB) and (R)-3-hydroxyvalerate (HV). These copolymers have aroused much scientific interest because of their high crystallinity at all HB ∶ HV compositions which suggests the possibility of inclusion of HB and HV in the same crystal. In this paper we look at the assessment of crystallinity by density measurements taking into account the possible changes in crystal and amorphous densities caused by the rejection or inclusion of HV from the crystallites. The approach developed is applicable to crystallization of copolymers and blends whatever the composition of the crystals and makes a distinction between mass fraction and mole fraction crystallinities for cases where the average molar mass of residues in the crystal and amorphous phases differs. While it is impossible to give values for crystallinity without knowing the degree of inclusion of HV into the crystals it is possible to say that the previous suggestions that the crystallinity remains constant independent of HV content and that there is equal concentration of HV in the crystal and amorphous phases are incompatible with the measured sample densities. We also show that the crystallization temperature is an important factor in the balance between the crystallinity and HV content of crystals.     

Investigation of crystallinity of germanium thin films vacuum deposited on GaAs

We investigated the cyrstalline quality of Ge thin films vacuum deposited on heated (100) GaAs substrates. Ge was evaporated using an electron beam and deposited to thicknesses of 100 and 500 nm, which were measured by a Dektak stylus-type instrument. These results were compared with the predictions of a cosine distribution law derived for the deposition system and found to be in relatively good agreement. The crystalline quality of the films was studied using scanning electron microscopy. Results have shown that epitaxy was strongly dependent on the substrate temperature, surface cleanliness and post-deposition annealing. Epitaxy was reproducibly achieved at a substrate temperature ofT _s=450 °C. All films deposited atT _s=350 or 400 °C were polycrystalline or amorphous, except one grown atT _s=350 °C, which proved to be monocrystalline. It is speculated that an anomalously clean and smooth substrate surface was responsible for this crystalline quality of films. In addition, it has been shown that post-deposition annealing of the films improved their crystallinity.     

Investigation on crystallinity and optical properties of l-tartaric acid single crystal at dynamic shocked conditions

Journal of Materials Science: Materials in Electronics - In this article, the authors demonstrate the experimental findings of the effect of dynamic shock waves on the crystallographic structural...     

The crystallinity of bone mineral

The degree of crystallinity of human femoral cortical bone from 16 to 83 years of age was determined by various X-ray and infra-red methods. It was established that an X-ray integral index method and an infra-red peak comparison method were the most reliable. Both methods indicated that the crystallinity of bone material varies between 51 and 59%, with no significant change with age. A new X-ray line was noted at 2=43° in bone of age greater than 50 years.     

Investigation on the properties of linear PLA-poloxamer and star PLA-poloxamine copolymers for temporary biomedical applications

The objective of this work was to develop and study new biodegradable thermoplastics with improved mechanical properties for potential use as temporary implantable biomaterials. Linear poloxamer and star-shaped poloxamine have been used as macroinitiators for the ring-opening polymerization (ROP) of lactide to yield high molecular weight PLA-based thermoplastic block copolymers. The influence of the nature of the macroinitiator, PLA crystallinity and initial molecular weight on the copolymers properties was investigated by performing a 7-week degradation test in PBS. The evaluation of water uptakes and molecular weights during the degradation pointed out an early hydrolytic degradation of the 100-kg?mol^? 1 copolymers compared to the 200-kg?mol^? 1 ones (molecular weight decrease of ca. 40% and 20%, respectively). A dramatic loss of tensile mechanical properties was also observed for the 100-kg?mol^? 1 copolymers, whereas the 200-kg?mol^? 1 copolymers showed stable or even slightly improved properties with Young's moduli around 500 MPa and yield strains around 3% to 4%. Finally, the cytocompatibility of the more stable 200 kg?mol^? 1 copolymers was confirmed by murine mesenchymal stem cells (MSCs) culture.     

Influence of the crystallinity on the transport properties of polyethylene

Transport properties of dichloromethane were analysed in high- and low-density polyethylene films, obtained with different thermal treatments, in order to correlate sorption and diffusion with the crystallinity of the samples. The crystalline fraction of all the analysed samples was evaluated from density and X-ray data; it ranged from 40%–85%. From the X-ray diffractograms the reciprocal of the width at half-height for the strongest reflection was derived for all the samples; it was considered as an order parameter. It was found that the sorption depends only on the fraction of amorphous phase; in fact, the specific sorption, normalized for the crystallinity of the sample, is constant for all the samples. However, the zero concentration diffusion coefficient,D ₀, varies with the sample crystallinity, but there is no simple correlation between these two parameters; rather a transition seems to separate two ranges in which the diffusion coefficient decreases with the crystallinity. At variance, a linear decrease of the diffusion parameter with the order parameter, derived from the X-ray diffractograms, was found in the whole range of crystallinity.     

Residual crystallinity of vapor-deposited tin films

Using transmission electron microscopy and selected-area electron diffraction techniques, the residual crystallinity of vapor-deposited tin thin films has been investigated. At substrate temperatures above about 0.8T_m, liquid-like particles were observed to be single crystals, with no evidence of grain boundaries or related crystallographic inhomogeneities. A significant portion of the single-crystal particles exhibited epitaxial features, and they appeared to have solidified by a liquid-solid phase transformation beginning at the particle-substrate interface and propagating in the [001] direction, with the (00$\text{1}$) plane facing the (001) NaCl substrate. The observation of crystal facets supports this model. For substrate temperatures of approximately 0.7T_m or below, the tin films were composed of island structures. An examination of the crystallographic and morphological features of the tin films suggests a coalescence mechanism consistent with that outlined by Pocza. For substrate temperatures greater than 0.8T_m, coalescence is dominated by liquid drops with liquid drops. Below 0.8T_m, the mechanism shifts from one of liquid drops with crystallites to one dominated primarily by the coalescence of crystallites with crystallites below 0.6T_m.     

Kinetics of the recovery of crystallinity in ground dolomite

The kinetics of the recovery of crystallinity, evidenced in the DSC curves of this carbonate by the presence of an exothermal peak, are studied by the analysis of isothermal and dynamic DSC traces. The correspondence between the values of the activation energy computed by the Arrhenius and Coats and Redfern plots and the slopes of the ln-ln plots shows that a three-dimensional growth of nuclei model describes the process. The low value of the activation energy allows classification of the process as a recovery of crystallinity. An increase in the activation energy with grinding time is also observed.     

Investigation of the aqueous dissolution of semicrystalline poly(ethylene oxide) using infrared chemical imaging: the effects of molecular weight and crystallinity

Fourier transform infrared (FT-IR) imaging was used to successfully explore several factors influencing the dissolution of poly(ethylene oxide). The effect of the degree of crystallinity on the rate of dissolution of mid-range molecular weight PEO was negligible over the temperature ranges studied. The influence of molecular weight on polymer dissolution was found to be much greater than the changes in morphology. An examination of the polymer and solvent images and absorbance profiles, compared with the results of the bulk polymer/solvent boundary movement, confirmed this relationship. An investigation of the bulk polymer/solvent boundary using a crystalline-sensitive polymer band showed the crystalline to amorphous phase change occurred over a short distance. Moreover, solvent diffusion ahead of the bulk polymer/solvent front was minimal, most likely a result of the required phase change, which in turn regulated the degree of solvent ingress. Modeling of the dissolution was performed using the Peppas (power law) model. Physical parameters of the dissolution process were obtained from fitting the release profiles to the power law (fraction released = k x t(n), where k is the dissolution rate constant and n is the release exponent). Results indicated the model worked well to describe dissolution at all molecular weights. By varying the number of data points input to the model and then comparing the generated graphs, it becomes clear that not only does the dissolution slow down over the course of the experiment, but an increase in molecular weight enhances this effect. The effect of different types of drug on the rate of polymer dissolution was also studied. The dissolution of neat polymer was compared to the dissolution of polymer containing 10% (by weight) of theophylline, etophylline, or testosterone. The general trend of all the dissolution curves was the same, with the addition of etophylline and testosterone tracing almost the same route in terms of movement of the bulk polymer/solvent front.     

Effect of crystallinity in the thermal behaviour of nickel hydroxide

The textural and structural characteristics of nickel hydroxide condition the properties of its thermal decomposition product. The thermal behaviour is also affected. Thus, the differential scanning calorimetry traces of a sample of low crystallinity shows an exothermal peak which is indicative of a process of release of the energy stored as defects. This interpretation is evidenced by a loss of microstrains in the temperature interval of the exotherm.     

退火对氧化锌薄膜结晶性能的影响

采用射频磁控溅射法在(001)硅片上制备了ZnO薄膜,利用X射线衍射对薄膜的制备工艺进行了研究,结果表明,基板温度、溅射功率、氩氧比、总气压在一个较大的范围内变化时都可实现薄膜的c轴择优取向生长.随后对薄膜进行了空气退火并利用摇摆曲线表征薄膜的结晶质量,摇摆曲线的半高宽随退火温度的提高而减小,700℃退火后FWHM为2.5°.     

Surfactant-induced postsynthetic modulation of Pd nanoparticle crystallinity

Modulation of Pd nanoparticle (NP) crystallinity is achieved by switching the surfactants of different binding strengths. Pd NPs synthesized in the presence of weak binding surfactants such as oleylamine possess polyhedral shapes and a polycrystalline nature. When oleylamine is substituted by trioctylphosphine, a much stronger binding surfactant, the particles become spherical and their crystallinity decreases significantly. Moreover, the Pd NPs reconvert their polycrystalline structure when the surfactant is switched back to oleylamine. Through control experiments and molecular dynamics simulation, we propose that this unusual nanocrystallinity transition induced by surfactant exchange was resulted from a counterbalance between the surfactant binding energy and the nanocrystal adhesive energy. The findings represent a novel postsynthetic approach to tailoring the structure and corresponding functional performance of nanomaterials.     

Surface chemistry controls crystallinity of ZnS nanoparticles

Combined small-angle and high energy wide-angle X-ray scattering measurements of nanoparticle size and structure permit interior strain and disorder to be observed directly in the real-space pair distribution function (PDF). PDF analysis showed that samples of ZnS nanoparticles with similar mean diameters (3.2-3.6 nm) but synthesized and treated with different low-temperature procedures possess a dramatic range of interior disorder. We used Fourier transform infrared spectroscopy to detect the surface species and the nature of surface chemical interactions. Our results suggest that there is a direct correlation between the strength of surface-ligand interactions and interior crystallinity.     

Enhancing the stability and crystallinity of CsPbIBr2 through antisolvent engineering

All inorganic lead-based perovskites containing bromine-iodine alloys, such as CsPbIBr_2, have arisen as one of the most attractive candidates for absorber layers in solar cells. That said, there remains a large gap when it comes to film and crystal quality between the inorganic and hybrid perovskites. In this work, antisolvent engineering is employed as a simple and reproducible method for improving CsPbIBr₂ thin films. We found that both the antisolvent used and the conditions under which it was applied have a measurable impact on both the quality and stability of the final product. We arrived at this conclusion by characterising the samples using scanning electron microscopy, X-ray diffraction, UV–visible and photoluminescence measurements, as well as employing a novel system to quantify stability. Our findings, and the application of our novel method for quantifying stability, demonstrate the ability to significantly enhance CsPbIBr₂ samples, produced via a static one-step spin coating method, by applying isopropanol 10 s after commencing the spin programme. The antisolvent quenched CsPbIBr₂ films demonstrate both improved crystallinity and an extended lifespan.

     

Control of hydroxyapatite crystallinity by mechanical grinding method

Crystallinity of hydroxyapatite reflecting crystal size and crystal elastic strain was controlled by the mechanical grinding (MG) technique using a set of container and balls made of SUS304 stainless steel or agate. Variation in the crystallinity through MG was monitored by the XRD method and represented by the broadening of the diffraction peak. Effect of changes in crystallite size and strain on the crystallinity was also examined using the Hall-plot method.Crystallinity rapidly decreased with milling time. Significant crystallographic diffraction peaks disappeared and a broad diffraction around 2=32° was observed after MG for 72 h. The broadening was dominantly due to an increase in crystal strain in addition to fine crystallite size. Contamination from the container and balls during MG was more suppressed using agate than SUS304 stainless steel.The recovery process of crystallinity during heating between 300 °C and 1200 °C was examined focusing on the decrease in residual elastic strain. Low crystallinity was maintained at annealing temperatures below 800 °C but lattice defects were recovered above 1000 °C.© 2001 Kluwer Academic Publishers     

The effect of crystallinity on the fracture of polytetrafluoroethylene (PTFE)

The extremely low coefficient of friction and biocompatibility provided by the inert nature of polytetrafluoroethylene (PTFE) have lead to its application in a wide range of biological implants ranging from single component PTFE structures to sliding contact pads in complex joints. In vivo fracture has been identified as a major cause of failure in these implants. It has recently been shown that the fracture behavior of PTFE undergoes transitions from brittle-fracture below 19 °C to ductile-fracture with fibril formation and large-scale plasticity over 30 °C associated with crystalline phase transformations. In this paper the formation of fibrils and an associated increase in J_IC fracture toughness are revealed to be restricted by an increase in crystalline content in PTFE. [LAUR 05-2223]