Pure Amorphous Phase Research Articles

Molecular Miscibility of Polymer−Fullerene Blends

The device function of polymer bulk heterojunction (BHJ) solar cells has been commonly interpreted to arise from charge separation at discrete interfaces between phase-separated materials and subsequent charge transport through these phases without consideration of phase purity. To probe composition, the miscibility of poly(3-hexylthiophene) (P3HT) and poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) with phenyl-C61-butyric acid methyl ester (PCBM) has been determined, while the effects of polymer crystallinity on miscibility are probed using P3HT grades of varying regioregularity. It is found that, while no intercalation occurs in P3HT crystals, amorphous portions of P3HT and MDMO-PPV contain significant concentrations of PCBM, calling into question models based on pure phases and discrete interfaces. Furthermore, depth profiles of P3HT/PCBM bilayers reveal that even short annealing causes significant interdiffusion of both materials, showing that under no conditions do pure amorphous phases exist in BHJ or annealed bilayer devices. These results suggest that current models of charge separation and transport must be refined.

Nanostructural characterization of TiN-Ni films: A XAFS study

Abstract We report on the nanostructure of Ni and N in nanocomposite TiN-Ni films using extended (EXAFS) and near-edge (NEXAFS) X-Ray absorption fine structure spectroscopies at the Ni-K and N-K edges, respectively. The Ni content in the films, as determined by Rutherford backscattering analysis, varies between 0 and 21.5 at%. The Ni-K-edge EXAFS measurements disclose that the bonding environment of Ni is amorphous in all studied films. However, the local coordination of Ni changes as a function of the chemical composition. More specifically, Ni belongs both to a pure amorphous Ni phase, where the Ni–Ni bondlength is equal to 2.46–2.47 A (±0.01), while it also forms intermetallic TiNi bonds and the respective Ni–Ti bondlength is equal to 2.60–2.62 A (±0.02). The Ni–Ni and Ni–Ti bondlengths are equal among all studied samples and they are independent of the Ni content and the deposition temperature. On the contrary, the total coordination number of Ni in the 1st nearest neighbor shell, i.e. the sum of Ni and Ti atoms that comprise this shell, increases linearly with the Ni content and varies between 5.4 ± 0.7 and 13.1 ± 1.1. Finally, the N-K-NEXAFS results reveal that Ti forms crystalline TiN in all studied samples, independently of the N and Ti content in the films.

Structure and mechanical properties of impact modified poly(butylene terephthalate)/poly(ethylene terephthalate) blends

AbstractTwo poly(butylene terephthalate) (PBT)‐rich compositions of PBT/poly(ethylene terephthalate) (PET) blends (5/1 and 2/1) were mixed with up to 30 wt% of a maleinized poly(ethylene‐octene) copolymer (mPEO). The blends were composed of a PBT/PET amorphous phase, a pure mPEO amorphous phase, and the crystalline phases of PBT and mPEO. The average size of the dispersed mPEO particles was larger in the (PBT/PET 5/1)/mPEO blends than in the (PBT/PET 2/1)/mPEO blends, but in both cases larger than that of PET/mPEO blends and smaller than that of PBT/mPEO blends from previous works. The Young's modulus and the yield stress decreased with increasing mPEO contents and the ductility of the 2/1‐based blends remained constant at higher mPEO contents compared to the 5/1‐based blends. Super‐toughness was obtained in both blends, but only the critical interparticle distance (IDc) of the (PBT/PET 5/1)/mPEO blends was used for comparison with those of PET/mPEO, poly(trimethylene terephthalate) (PTT)/mPEO and PBT/mPEO blends in terms of adhesion, because the (PBT/PET 2/1)/mPEO blends showed a simultaneous change in matrix modulus and adhesion. This comparison provided additional support to the proposed “saturation” of the interactions between the ester and maleic groups in this series and to the role of adhesion on IDc (higher adhesion, lower IDc). POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Comparison of Nanomechanical Behavior of the Amorphous and Crystalline Phases of ALD HfO2

HfO2 films were deposited using atomic layer deposition (ALD) at temperatures ranging from 100oC to 250oC. We report detailed nanoindentation measurements on the pure amorphous, mixed-phase and polycrystalline phase of HfO2. We use nanoindentation techniques for determining the important mechanical properties such as hardness and effective modulus. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) to determine the structural properties of the various phases of these ALD HfO2 films. We measured the effective modulus to be 370 GPa for amorphous low temperature ALD HfO2 and 240 GPa after crystallization with rapid thermal annealing (RTA). Similarly, the hardness measurements revealed a value of 18 GPa for amorphous HfO2 and a lower value of 15 GPa following the transition temperature from amorphous to polycrystalline HfO2.

Structural and conformational changes during thermally‐induced crystallization of poly(trimethylene terephthalate) by infrared spectroscopy

AbstractConformational changes occurring during thermally‐induced crystallization of poly(trimethylene terephthalate) (PTT) by annealing have been studied using density measurement, differential scanning calorimetry (DSC), and mid‐infrared spectroscopy (MIR). Infrared spectra of amorphous and semicrystalline PTT were obtained, and digital subtraction of the amorphous contribution from the semicrystalline PTT spectra provided characteristic MIR spectra of amorphous and crystalline PTT. The normalized absorbance of 1577, 1173, and 976 cm−1 were plotted against the crystallinity showing that these bands can be used unambiguously to represent the trans conformation while the band at 1358 cm−1 can be used to represent gauche conformation of methylene segment. The presence of a weak band at 1358 cm−1 in the amorphous spectrum suggested that a small amount of gauche conformation is present in the amorphous phase. Infrared spectroscopy has been used for the first time as a means to estimate the trans and gauche conformations of methylene segments in PTT as a function of Ta. The amount of gauche conformation was plotted against the crystalline fraction and the extrapolation of this plot to zero crystalline fraction provided a value of 0.07, suggested that the pure amorphous phase consist of ∼ 7% gauche conformation. It was found that the amorphous and crystalline gauche conformation increases at the expense of amorphous trans conformation during thermally induced crystallization of PTT. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1497–1504, 2008

Structure and mechanical properties of blends of poly(ε‐caprolactone) with a poly(amino ether)

AbstractPoly(ε‐caprolactone) (PCL)/poly(amino ether) (PAE) blends were obtained by injection molding without any previous extrusion step in an attempt to (i) contribute to the knowledge of the relation between structure and mechanical properties in these type of blends composed of a rubbery and a glassy polymer and (ii) to find out to which extent are the PCL/PAE blends compatible, and therefore whether the biodegradability of PCL can be added as a characteristic of PAE‐based applications. PCL/PAE blends are composed of a crystalline PCL phase, a pure amorphous PCL phase, and a PAE‐rich phase where some PCL is present. The presence of some dissolved and probably unreacted PCL in the PAE‐rich phase led to a low interfacial tension as observed by the small size of the dispersed particles and the large interfacial area. The dependence on composition of both the modulus of elasticity and the yield stress of the blends was parallel to that of the orientation level. The elongation at break showed values similar to those of PAE in PAE‐rich blends, and was slightly synergistic in very rich PCL compositions; this behavior reflects a change in the nature of the matrix, from glassy to rubbery. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of thickness on the crystallinity and Curie transition behavior in P(VDF/TrFE) (72/28) copolymer thin films using FTIR-transmission spectroscopy

The effect of thickness on the ferroelectric behavior in spin-cast poly(vinylidene fluoride/trifluoroethylene) (P(VDF/TrFE)) (72/28 mol%) random copolymer films with varying degree of crystallinity was analyzed qualitatively and quantitatively using Fourier transform infrared-transmission spectroscopy (FTIR-TS) data. From the qualitative analysis of raw IR data, the critical thickness of crystallization was observed near 130 nm, below which the films exhibited significant changes in crystalline peak (1292 cm −1) absorption. Using factor analysis (FA) of their raw IR data, we have isolated the pure crystalline and amorphous phase spectra, and also quantitatively calculated their degree of crystallinity as a function of thickness. FA of the mixture spectra obtained at varying temperatures during a heating–cooling cycle (30 °C → 140 °C → 30 °C) was conducted to isolate the pure spectra of the low-temperature (ferroelectric) and high-temperature (paraelectric) crystalline phases and to determine the content of each phase quantitatively as functions of thickness and temperature. Curie transition temperature during heating ( T c ↑ ) and cooling ( T c ↓ ) decreased and increased, respectively, resulting in reduced temperature range between T c ↑ ↔ T c ↓ with decreasing film thickness used in our study and the quantitative data obtained from FA were quite comparable with the qualitative data obtained from raw IR analysis.

Phase transitions in amorphous calcium phosphates with different Ca/P ratios

The phase transitions occurring during calcination of flame-made calcium phosphates with Ca/P ratios between 1.00 and 1.54 were investigated by thermal analysis and powder X-ray diffraction from room temperature to 1350 °C. The as-prepared samples were amorphous and crystallized into metastable, low-temperature α LT polymorphs of Ca 3(PO 4) 2 (TCP) and Ca 2P 2O 7 (CPP) between 600 and 700 °C, depending on the Ca/P ratio. The enthalpy changes during crystallization amounted to 26.1 and 58.5 J/g for TCP and CPP, respectively. The metastable α LT TCP and CPP phases were at first transformed into stable β polymorphs between 870 and 950 °C and, later, between 1140 and 1200 °C, into high-temperature α phases. The enthalpy changes during these processes were small and lay in the range of 6–11 J/g. The composition of the eutectic formed in the system α-(TCP–CPP) was determined from the Tamman triangle, the melting enthalpy amounted to 197 J/g and the molar eutectic composition was 0.68 TCP and 0.32 CPP. The use of DSC analyses allowed to determine the composition of the precursor mixture during flame-made process which resulted in the synthesis of pure TCP amorphous phase.

In Silico Prediction of Drug Solubility. 3. Free Energy of Solvation in Pure Amorphous Matter

The solubility of drugs in water is investigated in a series of papers. In this work, we address the process of bringing a drug molecule from the vapor into a pure drug amorphous phase. This step enables us to actually calculate the solubility of amorphous drugs in water. In our general approach, we, on one hand, perform rigorous free energy simulations using a combination of the free energy perturbation and thermodynamic integration methods. On the other hand, we develop an approximate theory containing parameters that are easily accessible from conventional Monte Carlo simulations, thereby reducing the computation time significantly. In the theory for solvation, we assume that DeltaG* = DeltaGcav + ELJ + EC/2, where the free energy of cavity formation, DeltaGcav, in pure drug systems is obtained using a theory for hard-oblate spheroids, and ELJ and EC are the Lennard-Jones and Coulomb interaction energies between the chosen molecule and the others in the fluid. The theoretical predictions for the free energy of solvation in pure amorphous matter are in good agreement with free energy simulation data for 46 different drug molecules. These results together with our previous studies support our theoretical approach. By using our previous data for the free energy of hydration, we compute the total free energy change of bringing a molecule from the amorphous phase into water. We obtain good agreement between the theory and simulations. It should be noted that to obtain accurate results for the total process, high precision data are needed for the individual subprocesses. Finally, for eight different substances, we compare the experimental amorphous and crystalline solubility in water with the results obtained by the proposed theory with reasonable success.

Influence of compatibilization on the mechanical behavior of poly(trimethylene terephthalate)/poly(ethylene–octene) blends

Poly(trimethylene terephthalate) (PTT) based blends toughened with up to 30 wt.% of a partially maleinized poly(ethylene–octene) copolymer (mPEO) were obtained by melt mixing. The blends were composed of two pure amorphous phases and a partially crystalline PEO phase. The rubber modification clearly compatibilized the blends leading to a decrease in the dispersed phase size. The decrease was not enough to attain the brittle–tough transition, but an increase in the shear rate gave rise to an additional decrease in the dispersed phase size and in the interparticle distance (IDc) that led to very high toughness values (15-fold the notched impact strength of the matrix) at rubber contents above 25 wt.%. The critical interparticle distance of the blends was 0.17 μm. A comparison between this IDc and those of PBT/mPEO and PET/mPEO blends was explained in terms of their interfacial tensions.

Insights into the Fracture Mechanisms and Strength of Amorphous and Nanocomposite Carbon

Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs intergrain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.

Morphology and phase behaviour of poly(propylene oxide) containing copoly(ether ester)s

Abstract The morphology and phase behaviour of six different copoly(ether ester) elastomers, based on poly(butylene terephthalate) (PBT) hard blocks and poly- (ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b- PPO-b-PEO) soft blocks, differing in soft-block content and molecular weight of the soft block, have been investigated using various analytical techniques such as DSC, dynamic mechanical thermal analysis, dielectric spectroscopy, 13C CP-MAS NMR, AFM, TEM, and optical microscopy. The PBT blocks were found to crystallize in lamellar structures that form a continuous highly interconnected architecture. No crystalline regions for the PEO-b-PPO-b-PEO triblock could be observed, whereas no indications of a separate pure amorphous PBT phase were found. It is further shown that the amorphous phase is not a homogeneous mixture of amorphous PBT and soft segments. Based on the combined results of the analytical techniques used it is concluded that the PPO segments form an almost pure amorphous phase, whereas the PEO segments form a mixed phase with amorphous PBT. It is believed that the presence of this pure amorphous PPO phase provides the PEO-b-PPO-b-PEO containing copoly(ether ester)s with their excellent coldtemperature properties.

Structure and mechanical properties of polyamide‐6,6/poly(ethylene terephthalate) blends

AbstractPolyamide‐6,6 (PA)/poly(ethylene terephthalate) (PET) blends were obtained by direct injection molding over the whole composition range. Besides the two crystalline phases, the blends were composed of a pure amorphous PET phase, and a probably pure PA amorphous phase. The crystallinity of PA and PET did not change in the blends, although PA nucleated the crystallization of PET. The morphological heterogeneity was low because, although large particles were seen, they mostly contained many small (typically 0.3 μm) occlusions. This fairly homogeneous structure is attributed to the reactions observed during melt blending. The Young's modulus and yield stress of the blends followed the rule of mixtures, in good agreement with the lack of change of the crystallinity content, specific volume and orientation of the two components of the blends when they are mixed. The ductility values were also very close to those predicted by the rule of mixtures, with an absolute synergism in the 10/90 blend indicating compatibility. This positive mechanical behavior contrasts with that observed in previous works, and is attributed to the way PET crystallizes, to the highly dispersed morphology, and to the highly amorphous character of the blends obtained in this study. The ductile nature of the blends after annealing at either 80°C for one day or 100°C for 30 min indicated the considerable temperature resistance of these highly dispersed and partially reacted blends. Polym. Eng. Sci. 44:1405–1413, 2004. © 2004 Society of Plastics Engineers.

Compatibility in immiscible polysulfone/poly(ethylene terephthalate) blends

AbstractPolysulfone (PSU)/poly(ethylene terephthalate) (PET) blends were obtained by direct injection molding across the composition range. Their phase behavior, thermal properties, morphology, and mechanical properties were measured. The blends were composed of a pure PSU amorphous phase and either a pure PET phase in PSU‐poor blends, or a PET‐rich phase with some dissolved PSU in PSU‐rich blends. The morphology of the dispersed phase was mostly spherical with some elongated particles in the PET‐rich blends. A slight synergistic behavior was observed in the Young's modulus, mainly in the 90/10 blend, which is probably due to orientation effects. The presence of some broken particles indicated some interfacial adhesion. The ductility values were approximately linear with composition. This was generally the case in PSU‐rich blends, and was attributed to the higher level of PSU in the PET‐rich phase. Although embrittlement was seen in blends with 30% of the second component, the ductility of the two pure components did not significantly decrease after annealing due to the presence of low amounts (up to 10%) of another component of the blend. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2193–2200, 2004

Structure and mechanical properties of polysulfone‐based in situ composites

AbstractComposites based on the polysulfone of bisfenol A (PSF) and a liquid‐crystalline copolyester (Rodrun 5000) were obtained by two processing methods, (1) direct injection moulding (DI) and (2) extrusion followed by injection moulding (PI), across the whole composition range. The blends were immiscible and showed two pure amorphous phases. The inferior mechanical properties of PI blends, and their more difficult processing, meant that the PI procedure is not suitable in these blends. The generally linear relationship of the Young's modulus of the DI blends is due to the counteracting effects of the large orientation of the skin and its low thickness. The improvement in notched impact strength of PSF on the addition of small amounts of LCP indicated an important reduction in its notch sensibility. The tensile strength behaviour was close to linearity, with the exception of the 20/80 blend in which it was synergistic. This had been seen in previous thermoplastic/LCP blends, and depicts a behaviour reminiscent of rubber‐toughened blends. Copyright © 2004 Society of Chemical Industry

Processability, morphology and mechanical properties of glass fiber reinforced poly(ether sulfone) modified by a liquid crystalline copolyester

AbstractTernary composites based on glass fiber reinforced polyethersulfone (gPES) modified by a liquid crystalline copolyester (R5) were obtained by injection molding at different nozzle temperatures and at LCP contents up to 20%. The blends showed two pure amorphous phases. The ability of R5 to improve processing was seen mainly in the increase in the MFI of the blends on 5% LCP addition, which was more than 75% and 16% with respect to that of pure gPES and PES, respectively. The best processing temperature appeared to be 330°C, as it led to the maximum skin fibrillation and provided both the best small strain and fracture mechanical properties. The blend processed at 330°C with 5% R5 showed the best balance of properties because, besides the highest relative processability increase, it led to maximum values in all mechanical properties measured. This was due to both the overall fibrillation of the skin and to its having the highest ductility.

Reinforced poly(ether sulfone) materials by blending with a semiaromatic liquid crystalline copolyester

AbstractBlends based on poly(ether sulfone) (PES) and a semiaromatic liquid crystalline copolyester (R5) were obtained by injection molding across the entire composition range. The blends showed two pure amorphous phases. The fibrillar structure of the skin led to enhancements in the stiffness. The break properties, however, decreased at low LCP contents, due to the expected lack of adhesion between the phases. The increase in the modulus at increasing LCP content led to improvements in tensile strength. The notch sensitivity of PES decreased after the addition of low LCP levels, giving rise to enhancements of almost 600% in the notched impact strength. The unusually enhanced performance of the 20/80 blend, which has been seen previously in another thermoplastic/LCP blend, suggests that the dispersed PES phase in this blend may act as rubber particles do in rubber toughened thermoplastics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 52–59, 2004

Super‐toughness in compatibilized poly(butylene terephthalate)/poly(ethylene‐octene) copolymer blends

AbstractPoly(butylene terephthalate) (PBT)/poly(ethylene‐octene) (PEO) blends containing 1.0 wt% epoxy and from 0 to 30 wt% PEO were obtained by extrusion and injection molding. The blends were composed of two pure amorphous phases. The observed torque increases showed that epoxy reacted with PBT, leading to a fine and homogeneous morphology up to 15 wt% PEO content, which appeared larger and more heterogeneous at higher PEO contents. Toughness values fifteen‐fold those of pure PBT were obtained with only 13 wt% PEO. The tensile properties, including ductility, decreased with increasing PEO content, indicating that the adhesion level necessary for high ductility is higher than that necessary for super‐toughness. The inter‐particle distance (τ) was the main parameter that controlled toughness. The comparison of the results of this work with those of the same PBT/PEO blends with two different compatibilizers provides additional strong evidence of the adhesion at the interphase as the main parameter that controls the critical τ in these modified thermoplastic/rubber blends.

New super‐tough poly(butylene terephthalate) materials based on compatibilized blends with metallocenic poly(ethylene‐octene) copolymer

AbstractNew super‐tough poly(butylene terephthalate) (PBT)/poly(ethylene‐octene) copolymer (PEO) blends containing 2 wt% poly(ethylene‐co‐glycidyl methacrylate) (EGMA) as a compatibilizer were obtained by extrusion and injection molding. The blends comprised of an amorphous PBT‐rich phase with some miscibilized EGMA, a pure PEO amorphous phase, and a crystalline PBT phase that was not influenced by the presence of either PEO or EGMA. The blends showed a fine particle size up to 20 wt% PEO content. Super‐tough blends were obtained with PEO contents equal to or higher than 10%. The maximum toughness was very high (above 710 J/m) and was attained with 20% PEO without chemical modification of the commercial components used. Copyright © 2003 John Wiley & Sons, Ltd.

The effect of processing on the properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers

Semi-crystalline poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers are biodegradable systems with potential as substrates for use in tissue regeneration. Previous studies have shown that severe embrittlement occurs on storage at room temperature restricting their application possibilities. Concepts such as secondary, advancing crystallisation causing changes in the amorphous/crystalline ratio have been mooted as the cause of the embrittlement. Using films prepared by extrusion and compression moulding procedures we have attempted to probe not only the pure amorphous and crystalline phases but also the interfacial region. Interpretation of dynamic mechanical and dielectric data highlights the changes in the nature of the interfacial region on processing. Moreover, the use of the Thermally Stimulated Discharge technique is a powerful probe for highlighting the morphological changes induced in multiphase systems by the processing step.