Showing papers on "Miscibility published in 2015"

High thermal conductivity in amorphous polymer blends by engineered interchain interactions

Abstract: A high density of strong hydrogen bonds connecting two polymers that are homogeneously mixed in a thin film is shown to enhance the intrachain thermal conductance, boosting thermal transport in fully organic layers. Thermal conductivity is an important property for polymers, as it often affects product reliability (for example, electronics packaging), functionality (for example, thermal interface materials) and/or manufacturing cost1. However, polymer thermal conductivities primarily fall within a relatively narrow range (0.1–0.5 W m−1 K−1) and are largely unexplored. Here, we show that a blend of two polymers with high miscibility and appropriately chosen linker structure can yield a dense and homogeneously distributed thermal network. A sharp increase in cross-plane thermal conductivity is observed under these conditions, reaching over 1.5 W m−1 K−1 in typical spin-cast polymer blend films of nanoscale thickness, which is approximately an order of magnitude larger than that of other amorphous polymers.

Determining the role of polymer molecular weight for high-performance all-polymer solar cells: its effect on polymer aggregation and phase separation.

Abstract: The molecular weight of a conjugated polymer is one of the key factors determining the electrical, morphological, and mechanical properties as well as its solubility in organic solvents and miscibility with other polymers. In this study, a series of semicrystalline poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) polymers with different number-average molecular weights (Mn’s) (PPDT2FBTL, Mn = 12 kg/mol; PPDT2FBTM, Mn= 24 kg/mol; PPDT2FBTH, Mn= 40 kg/mol) were synthesized, and their photovoltaic properties as electron donors for all-polymer solar cells (all-PSCs) with poly[[N,N′-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) acceptor were studied. The Mn effect of PPDT2FBT on the structural, morphological, electrical, and photovoltaic properties was systematically investigated. In particular, tuning the Mn induced dramatic effects on the aggregation behaviors of the polyme...

Halide-Free Synthesis and Tribological Performance of Oil-Miscible Ammonium and Phosphonium-Based Ionic Liquids

Abstract: Due to their low vapor pressures, nonflammability, high thermal stabilities, and excellent tribological properties ionic liquids (ILs) are highly attractive lubricant base oils and additives. However, for practical applications of ILs in lubrication, two requirements are often limiting, the required miscibility with standard mineral oils (≥5 wt %) and the complete absence of corrosive halide ions in the ionic liquid. Moreover, the need for full compatibility with standard oil additives reduces the number of potential IL-based lubricant additives even further. In this contribution, an economic halide-free synthesis route to oil-miscible ionic liquids is presented, and very promising tribological properties of such ILs as base oil or additive are demonstrated. Therefore, sliding tests on bearing steel and XPS analysis of the formed surface films are shown. Corrosion test results of different bearing metals in contact with our halide-free ILs and (salt) water prove their applicability as real life lubricants...

Miscibility of Itraconazole-Hydroxypropyl Methylcellulose Blends: Insights with High Resolution Analytical Methodologies.

Abstract: Drug–polymer miscibility is considered to be a prerequisite to achieve an optimally performing amorphous solid dispersion (ASD). Unfortunately, it can be challenging to evaluate drug–polymer miscibility experimentally. The aim of this study was to investigate the miscibility of ASDs of itraconazole (ITZ) and hydroxypropyl methylcellulose (HPMC) using a variety of analytical approaches. The phase behavior of ITZ-HPMC films prepared by solvent evaporation was studied before and after heating. Conventional methodology for miscibility determination, that is, differential scanning calorimetry (DSC), was used in conjunction with emerging analytical techniques, such as fluorescence spectroscopy, fluorescence imaging, and atomic force microscopy coupled with nanoscale infrared spectroscopy and nanothermal analysis (AFM-nanoIR-nanoTA). DSC results showed a single glass transition event for systems with 10% to 50% drug loading, suggesting that the ASDs were miscible, whereas phase separation was observed for all of...

Aggregation Behavior and Total Miscibility of Fluorinated Ionic Liquids in Water

Abstract: In this work, novel and nontoxic fluorinated ionic liquids (FILs) that are totally miscible in water and could be used in biological applications, where fluorocarbon compounds present a handicap because their aqueous solubility (water and biological fluids) is in most cases too low, have been investigated. The self-aggregation behavior of perfluorosulfonate-functionalized ionic liquids in aqueous solutions has been characterized using conductometric titration, isothermal titration calorimetry (ITC), surface tension measurements, dynamic light scattering (DLS), viscosity and density measurements, and transmission electron microscopy (TEM). Aggregation and interfacial parameters have been computed by conductimetry, calorimetry, and surface tension measurements in order to study various thermodynamic and surface properties that demonstrate that the aggregation process is entropy-driven and that the aggregation process is less spontaneous than the adsorption process. The novel perfluorosulfonate-functionalize...

Plasticizing effect of poly(ethylene glycol)s with different molecular weights in poly(lactic acid)/starch blends

Abstract: Binary and ternary blends composed of poly(lactic acid) (PLA), starch, and poly(ethylene glycols) (PEGs) with different molecular weights (weight-average molecular weights = 300, 2000, 4000, 6000, and 10, 000 g/mol) were prepared, and the plasticizing effect and miscibility of PEGs in poly(lactic acid)/starch (PTPS) or PLA were intensively studied. The results indicate that the PEGs were effective plasticizers for the PTPS blends. The small-molecule plasticizers of PEG300 (i.e., the Mw of PEG was 300g/mol) and glycerol presented better plasticizing effects, whereas its migration and limited miscibility resulted in significant decreases in the water resistance and elongation at break. PEG2000, with a moderate molecular weight, was partially miscible in sample PTPS3; this led to better performance in water resistance and mechanical properties. For higher molecular weight PEG, its plasticization for both starch and PLA was depressed, and visible phase separation also occurred, especially for PTPS6. It was also found that the presence of PEG significantly decreased the glass-transition temperature and accelerated the crystallization of the PLA matrix, depending on the PEG molecular weight and concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41808.

Effects of nano‐tio2 on the performance of high‐amylose starch based antibacterial films

Abstract: The purpose of this article is to investigate the effects of nano-tianium dioxide (nano-TiO2) on the high-amylose starch/polyvingl alcohol (PVA) blend films prepared by a solution casting method. The results show that at the concentration of 0.6% of nano-TiO2, the film demonstrated the best tensile strength at 9.53 MPa, and the elongation at break was noted as 49.50%. The optical transmittance of the film was decreased and the water resistance was improved with further increase of the concentration of nano-TiO2. Using the techniques of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and field-emission scanning electron microscopy (SEM), the molecular and the crystal structures of the films were characterized. The results indicate that the miscibility and compatibility between high-amylose starch and PVA were increased with the addition of nano-TiO2 into the films due to the formation of hydrogen and COTi bonds. The antimicrobial activities of the blend films were also explored. The results show that there were inhibitory zones around the circular film disc, which is attributable to the addition of nano-TiO2. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42339.

Investigation of Chitosan-PVA Composite Films and Their Adsorption Properties

Abstract: Viscous aqueous solutions of chitosan and polyvinyl alcohol (PVA) were blended to enhance miscibility and avoid polymer phase separation. The mixtures were drop-casted and air dried to yield composite film materials that were characterized by equilibrium water uptake, physical stability in aqueous solution, and thermal stability. Chitosan/PVA blends have greater thermal stability, unique morphology, and reduced solubility in acidic solution, thus extending the useful pH range for chitosan as a sorbent material. The uptake properties of the films was investigated using methylene blue (MB) and a p-nitrophenol (PNP) dyes, where it was found that each single component polymer has greater uptake toward MB than PNP. A direct relationship between film composition (chitosan:PVA) with solution pH and the uptake of MB was observed. The results are in agreement with electrostatic interactions and contributions due to the hydrophobic effect for such composite materials.

Molecular Modeling as a Predictive Tool for the Development of Solid Dispersions

Abstract: In this study molecular modeling is introduced as a novel approach for the development of pharmaceutical solid dispersions. A computational model based on quantum mechanical (QM) calculations was used to predict the miscibility of various drugs in various polymers by predicting the binding strength between the drug and dimeric form of the polymer. The drug/polymer miscibility was also estimated by using traditional approaches such as Van Krevelen/Hoftyzer and Bagley solubility parameters or Flory–Huggins interaction parameter in comparison to the molecular modeling approach. The molecular modeling studies predicted successfully the drug–polymer binding energies and the preferable site of interaction between the functional groups. The drug–polymer miscibility and the physical state of bulk materials, physical mixtures, and solid dispersions were determined by thermal analysis (DSC/MTDSC) and X-ray diffraction. The produced solid dispersions were analyzed by X-ray photoelectron spectroscopy (XPS), which confirmed not only the exact type of the intermolecular interactions between the drug–polymer functional groups but also the binding strength by estimating the N coefficient values. The findings demonstrate that QM-based molecular modeling is a powerful tool to predict the strength and type of intermolecular interactions in a range of drug/polymeric systems for the development of solid dispersions.

Controlling the Formation of Ionic‐Liquid‐based Aqueous Biphasic Systems by Changing the Hydrogen‐Bonding Ability of Polyethylene Glycol End Groups

Abstract: The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modifying the hydrogen-bond-donating/-accepting ability of the polymer end groups. It is shown that the miscibility/immiscibility in these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the anion of the salt. The removal of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in the region of the phase diagram in which all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen-bond-donating ability of PEG results in greater immiscibility, and thus, in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups.

An Improved CO2-Crude Oil Minimum Miscibility Pressure Correlation

Abstract: Minimum miscibility pressure (MMP), which plays an important role in miscible flooding, is a key parameter in determining whether crude oil and gas are completely miscible. On the basis of 210 groups of CO2-crude oil system minimum miscibility pressure data, an improved CO2-crude oil system minimum miscibility pressure correlation was built by modified conjugate gradient method and global optimizing method. The new correlation is a uniform empirical correlation to calculate the MMP for both thin oil and heavy oil and is expressed as a function of reservoir temperature, C7

Enhanced stability of the model mini-protein in amino acid ionic liquids and their aqueous solutions

Abstract: Using molecular dynamics simulations, the structure of model mini-protein was thoroughly characterized in the imidazolium-based amino acid ionic liquids and their aqueous solutions. Complete substitution of water by organic cations and anions further results in hindered conformational flexibility of the mini-protein. This observation suggests that amino acid-based ionic liquids are able to defend proteins from thermally induced denaturation. We show by means of radial distributions that the mini-protein is efficiently solvated by both solvents due to a good mutual miscibility. Amino acid-based anions prevail in the first coordination sphere of positively charged sites of the mini-protein whereas water molecules prevail in the first coordination sphere of negatively charged sites of the mini-protein.

Unusual Fragility and Cooperativity in Glass-Forming and Crystalline PVDF/PMMA Blends in the Presence of Multiwall Carbon Nanotubes

Abstract: Poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) are completely miscible below 50 wt % PVDF in the blends. In this work, an attempt was made to understand the fragility/cooperativity relation in glass-forming and crystalline blends of PVDF/PMMA and in the presence of a heteronucleating agent, multiwall carbon nanotubes (CNTs). Hence, three representative blends were chosen: a completely amorphous (10/90 by wt, PVDF/PMMA), on the verge of amorphous miscibility (50/50 by wt, PVDF/PMMA), and crystalline (60/40 by wt, PVDF/PMMA) blends. The intermolecular cooperativity/coupling, fragility, and configurational entropy near the glass transition temperature (T-g) were studied using differential scanning calorimetry (DSC) and broadband dielectric relaxation spectroscopy (DRS). It was observed that the blends with higher concentration of PMMA were more fragile (fragility index m = 141) and those with higher concentration of PVDF were more strong (m = 78). Interestingly, the coupling was less in the glass-forming blends (10/90 by wt, PVDF/PMMA) than the crystalline blends as manifested from DRS. This observation was also supported by DSC measurements which reflected that the cooperative rearranging region (CRR) existed over a smaller length scales in fragile blends as compared to strong blends, possibly due to restricted amorphous mobility. This effect was more prominent in the presence of CNTs, in particular for 50/50 (by wt) and 60/40 (by wt) PVDF/PMMA blends. Further, the configurational entropy, as manifested from DRS, decreased significantly in the strong blends in striking contrast to the fragile blends, supported by DSC, which manifested in an increase in the volume of cooperativity in the strong blends. The higher coupling in the crystalline blends can be attributed to good packing of the amorphous regions. While this is understood for crystalline blends (60/40 by wt, PVDF/PMMA), it is envisaged that enhanced dynamic heterogeneity is accountable for increased coupling in the case of blends which are on the verge of amorphous miscibility (50/50 by wt, PVDF/PMMA). The latter is also supported by broad relaxations near the T-g in DRS. Interestingly, the intermolecular coupling in the blends in the presence of CNTs has reduced, though the potential energy barrier hindering the rearrangement of CRR is lower than the blends without CNTs. In addition, the amorphous packing is not as effective as the blends without CNTs. This is manifested from reduced volume of cooperativity in particular, for 50/50 (by wt) and 60/40 (by wt) blends.

The Use of Cooling Crystallization in an Ionic Liquid System for the Purification of Pharmaceuticals

Abstract: The application of ionic liquids (ILs) as solvents is frequently discussed in the context of their tunability, with the potential to tailor the solvent system uniquely to the process being investigated. Instead, here we study the potential for a single IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2C1Im][NTf2]), to be used for the cooling crystallization of a wide range of active pharmaceutical ingredients (APIs). [C2C1Im][NTf2] was selected on the basis of its thermal stability, low reactivity, and miscibility with solvents of moderate polarity, which suggests that it is miscible with liquids that possess polarities comparable to those of many API molecules. The overwhelming majority of APIs tested were soluble at >50 wt % within [C2C1Im][NTf2] at elevated temperatures despite their relatively poor solubility at room temperature. This dramatic effect was ascribed to the miscibility of most of the molten APIs with the IL. The solubility curves for nine APIs were measured, which est...

Tensile Properties of Polylactide/Poly(ethylene glycol) Blends

Abstract: The blends of polylactide (PLA) and poly(ethylene glycol) (PEG) with different contents (0, 5, 10, 15, and 20 wt%) and molecular weights (\( \overline{M}_{w} \) 6000, 10,000 and 20,000, called respectively as PEG 6000, PEG 10,000, and PEG 20,000) were prepared by means of melt blending method. The effects of tensile speed, content and molecular weight of the PEG on the tensile properties of the PLA/PEG blends were investigated using a universal testing machine at 24 °C. With increasing tensile speed, the tensile modulus, strength and stress at break of the PLA/PEG blends marginally increased, while the tensile modulus and stress at break declined non-linearly, and the tensile strength dropped nearly linearly with increasing PEG 10,000 content. When the PEG 10,000 content was 5–15 wt%, the tensile strain at break of the PLA/PEG 10,000 blend markedly increased, and then decreased as the PEG 10,000 content exceeded 15 wt%. With increasing the molecular weight of PEG, tensile modulus and strength increased, whereas the tensile strain at break decreased. This showed that the application of right amount of lower molecular weight PEG was more conducive to improving the tensile toughness of the PLA/PEG blends, which was attributed to its better miscibility with PLA and increased mobility of PLA molecular chains.

Application of mean-field theory in PP/EVA blends by focusing on dynamic mechanical properties in correlation with miscibility analysis

Abstract: Multi frequency measurement of dynamic mechanical properties including storage modulus, loss modulus and loss tangent of binary blends of an isotactic polypropylene (PP) and ethylene/vinyl acetate copolymer (EVA) at varying blending ratios was performed. Molecular mechanisms of various transitions were explained. The effect of blend ratio on miscibility of the blends using different approaches was studied. It was found that miscibility of blends increases at around 60 wt. % of EVA loading. Also, molecular origins of this phenomenon were proposed. The Arrhenius relationship was used in order to calculate the apparent activation energy (Ea) for the glass transitions of blend components. The Ea were compared at different compositions. The composition dependency of Ea could be explained based on miscibility of the blend components. Morphological parameters such as particle size and its distribution were obtained from SEM micrographs. The differences observed in morphological parameters and also morphological evidence of increased miscibility near 60 wt.% of EVA loading could be explained. In order to predict the dynamic mechanical properties of blends from those of their pure components, mean-field theories developed by Kerner were applied and theoretical values were calculated by solving of the appropriate equations using iteration method. Comparatively, a good agreement between theoretical and experimental data, especially in the upper and lower temperature zones was obtained. It was found that differences between experimental and theoretical values are significant in transition zone. Finally, the different causes of deviations between theoretical and experimental results were discussed.

An investigation of nifedipine miscibility in solid dispersions using Raman spectroscopy.

Abstract: Raman spectroscopy is potentially an extremely useful tool for the understanding of drug-polymer interactions in solid dispersions. This is examined and demonstrated for the case of solid dispersions of nifedipine in a polymeric substrate. Solid dispersions consisting of nifedipine and polyvinyl caprolactam - polyvinyl acetate - polyethylene glycol graft copolymer (Soluplus®) were prepared by freeze drying, melting and solvent evaporation at drug loadings of 10, 30, 50, 70 and 90% w/w. Drug-polymer interactions in the amorphous solid dispersion were estimated by Raman spectroscopy. The correlation between the solid state stability of the drug in a solid dispersion and the extent of drug-polymer interaction was monitored by X-ray diffractometry. The miscibility limit of nifedipine-Soluplus® was found to be 30% w/w drug loading for all preparation methods. The drug was found to interact with Soluplus®, through a hydrophilic interaction identified by infrared spectroscopy and a hydrophobic interaction which could be quantified by Raman spectroscopy. The average extent of the drug-polymer interaction in the studied amorphous samples at equivalent drug loading was similar, regardless of the preparation method. Inhomogeneities in samples prepared by melting contributed to a wider variation in drug-polymer interaction and poorer solid state stability, in terms of its crystallization tendency. Raman spectroscopy was shown to be a useful technique in classifying miscibility levels based on the hydrophobic interaction between the drug and the polymer. Different drug loadings showed varying degrees of drug-polymer interaction, and hence variable solid state stability of the solid dispersion.