Evaporation Of Residual Solvent Research Articles

Modulating secondary growth of perovskite grains through residual solvent evaporation

Modulating secondary growth of perovskite grains through residual solvent evaporation

Establishing Self‐Dopant Design Principles from Structure–Function Relationships in Self‐n‐Doped Perylene Diimide Organic Semiconductors

Self-doping is a particular doping method that has been applied to a wide range of organic semiconductors. However, there is a lack of understanding regarding the relationship between dopant structure and function. A structurally diverse series of self-n-doped perylene diimides (PDIs) is investigated to study the impact of steric encumbrance, counterion selection, and dopant/PDI tether distance on functional parameters such as doping, stability, morphology, and charge-carrier mobility. The studies show that self-n-doping is best enabled by the use of sterically encumbered ammoniums with short tethers and Lewis basic counterions. Additionally, water is found to inhibit doping, which concludes that thermal degradation is merely a phenomenological feature of certain dopants, and that residual solvent evaporation is the primary driver of thermally activated doping. In situ grazing-incidence wide-angle X-ray scattering studies show that sample annealing increases the π-π stacking distance and shrinks grain boundaries for improved long-range ordering. These features are then correlated to contactless carrier-mobility measurements with time-resolved microwave conductivity before and after thermal annealing. The collective relationships between structural features and functionality are finally used to establish explicit self-n-dopant design principles for the future design of materials with improved functionality.

Exploiting the full advantages of colloidal perovskite nanocrystals for large-area efficient light-emitting diodes.

Cost-effective, high-throughput industrial applications of metal halide perovskites in large-area displays are hampered by the fundamental difficulty of controlling the process of polycrystalline film formation from precursors, which results in the random growth of crystals, leading to non-uniform large grains and thus low electroluminescence efficiency in large-area perovskite light-emitting diodes (PeLEDs). Here we report that highly efficient large-area PeLEDs with high uniformity can be realized through the use of colloidal perovskite nanocrystals (PNCs), decoupling the crystallization of perovskites from film formation. PNCs were precrystallized and surrounded by organic ligands, and thus they were not affected by the film formation process, in which a simple modified bar-coating method facilitated the evaporation of residual solvent to provide uniform large-area films. PeLEDs incorporating the uniform bar-coated PNC films achieved an external quantum efficiency (EQE) of 23.26% for a pixel size of 4 mm2 and an EQE of 22.5% for a large pixel area of 102 mm2 with high reproducibility. This method provides a promising approach towards the development of large-scale industrial displays and solid-state lighting using perovskite emitters.

Solid-state analysis of amorphous solid dispersions: Why DSC and XRPD may not be regarded as stand-alone techniques

Amorphous solid dispersions (ASDs) are single-phase amorphous systems, where drug molecules are molecularly dispersed (dissolved) in a polymer matrix. The molecular dispersion of the drug molecules is responsible for their improved dissolution properties. Unambiguously establishing the phase behavior of the ASDs is of utmost importance. In this paper, we focused on the complementary nature of (modulated) differential scanning calorimetry ((m)DSC) and X-ray powder diffraction (XRPD) to elucidate the phase behavior of ASDs as demonstrated by a critical discussion of practical real-life examples observed in our research group. The ASDs were manufactured by either applying a solvent-based technique (spray drying), a heat-based technique (hot melt extrusion) or mechanochemical activation (cryo-milling). The encountered limiting factors of XRPD were the lack of sensitivity for small traces of crystallinity, the impossibility to differentiate between distinct amorphous phases and its impossibility to detect nanocrystals in a polymer matrix. In addition, the limiting factors of (m)DSC were defined as the well-described heat-induced sample alteration upon heating, the interfering of residual solvent evaporation with other thermal events and the coinciding of enthalpy recovery with melting events. In all of these cases, the application of a single analytical technique would have led to erroneous conclusions, whilst the combination of (m)DSC and XRPD elucidated the true phases of the ASD.

Structural evolution from poly(amic acid) to polyimide fibers during thermal imidization process

In this study, poly(amic acid) (PAA) precursor fiber was prepared via a two-step wet spinning method and subsequently heat-treated to obtain the polyimide fiber by thermal imidization. The structural evolution of the PAA precursor during the imidization was traced using various measurements. The imidization degree of the PAA fibers treated at different temperatures was calculated by Fourier transform infrared analysis, and the cyclization reaction occurred accompanied by the decomplexation of the H-bonded N, N′-dimethylacetamide (DMAc). The thermogravimetry test illustrated that the residual solvent evaporation took place prior to imidization. Moreover, in situ wide-angle X-ray diffraction and small-angle X-ray scattering measurements were employed to investigate the development of the aggregation structure and microvoids in PAA fibers. The results indicated that molecular chains were thermally extended during the thermal imidization, resulting in the increase of Hermans’ orientation factor and the increased strain. The thermal imidization process also led to the orientation and elongation of microvoids along the molecular chains.

Ultrasonication-Mediated Self-Assembly in Polythiophene Films via Control of Residual Solvent Evaporation

We have developed a facile ultrasonication method for the preparation of ordered polymer films. This method was tested by determining the structural, morphological, and electrical characteristics of poly(3-hexylthiophene) films ultrasonicated for various periods under various solvent vapor pressures. Ultrasonic irradiation for short periods under solvent vapor conditions intensifies the interactions between the polymer molecules and the solvent, which results in decreased polymer chain entanglement and in turn promotes polymer association and reorganization. The resulting improved molecular order and favorable morphologies were found to enhance the charge transport in organic transistors prepared with these films. The correlation between the molecular structural order and the electrical characteristics of the films was used to determine the appropriate ultrasonication time and solvent vapor pressure.

Metallized Nonwoven Electrospun Polyamide-6 Nanofibers for Energy Production and Storage

Nonwoven polymer materials based on polyamide-6 coated with stainless steel that are used as electrodes to produce energy and batteries to store it were investigated. Nanofibers were prepared by capillary-free electrospinning. The metal coating was applied using vacuum magnetron sputtering. Continuous metallized nonwoven material coated with sputtered stainless steel was formed after 4-10 min of magnetron sputtering. The resistance of the metallized nonwoven material was seven orders of magnitude less than that of uncoated material and five orders less than that of heat-treated nonwoven material. It was found that vacuum sputtering of the conducting stainless-steel coating reduced the nanofiber diameter by an average of 1.5 times due to evaporation of residual solvent.

From CsPbBr3 Nano-Inks to Sintered CsPbBr3-CsPb2Br5 Films via Thermal Annealing: Implications on Optoelectronic Properties.

CsPbBr3 nanocrystals passivated with short molecular ligands and deposited on a substrate were annealed from room temperature to 400 °C in inert atmosphere. Chemical, structural, and morphological transformations were monitored in situ and ex situ by different techniques, while optoelectronic properties of the film were also assessed. Annealing at 100 °C resulted in a 1 order of magnitude increase in photocurrent and photoresponse as a result of partial sintering of the NCs and residual solvent evaporation. Beyond 150 °C the original orthorhombic NCs were partially transformed into tetragonal CsPb2Br5 crystals, due to the desorption of weakly bound propionic acid ligands. The photocurrent increased moderately until 300 °C although the photoresponse became slower as a result of the formation of surface trap states. Eventually, annealing beyond 350 °C removed the strongly bound butylamine ligands and reversed the transition to the original orthorhombic phase, with a loss of photocurrent due to the numerous defects induced by the stripping of the passivating butylamine.

Production of Fluconazole-Loaded Polymeric Micelles Using Membrane and Microfluidic Dispersion Devices.

Polymeric micelles with a controlled size in the range between 41 and 80 nm were prepared by injecting the organic phase through a microengineered nickel membrane or a tapered-end glass capillary into an aqueous phase. The organic phase was composed of 1 mg·mL−1 of PEG-b-PCL diblock copolymers with variable molecular weights, dissolved in tetrahydrofuran (THF) or acetone. The pore size of the membrane was 20 μm and the aqueous/organic phase volumetric flow rate ratio ranged from 1.5 to 10. Block copolymers were successfully synthesized with Mn ranging from ~9700 to 16,000 g·mol−1 and polymeric micelles were successfully produced from both devices. Micelles produced from the membrane device were smaller than those produced from the microfluidic device, due to the much smaller pore size compared with the orifice size in a co-flow device. The micelles were found to be relatively stable in terms of their size with an initial decrease in size attributed to evaporation of residual solvent rather than their structural disintegration. Fluconazole was loaded into the cores of micelles by injecting the organic phase composed of 0.5–2.5 mg·mL−1 fluconazole and 1.5 mg·mL−1 copolymer. The size of the drug-loaded micelles was found to be significantly larger than the size of empty micelles.

Effect of solvent evaporation on the self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) and on the film morphology during electrospray deposition

AbstractA high‐voltage rectangular pulse was applied to the electro‐spray deposition (ESD) to control the evaporation‐induced self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). Two groups of P3HT thin films were deposited by a series of high‐voltage rectangular pulses. Compared with the ESD driven by a constant voltage, the pulse‐driven ESD enables to probe the effect of solvent evaporation on the self‐assembly of P3HT molecules. The droplet size and the evaporation of residual solvent in the droplet determine the film morphology. Ultraviolet–visible absorption spectroscopy was used to identify the ordering of P3HT molecules in the films. The self‐assembly of P3HT molecules took place during the solvent evaporation which can be controlled by a combination of the pulse amplitude and the pulse interval. With an appropriate combination of the amplitude and the interval, the ESD produced a P3HT thin film with high chain ordering.magnified image(© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evolution of Structure, Optoelectronic Properties, and Device Performance of Polythiophene:Fullerene Solar Cells During Thermal Annealing

AbstractWe use spectroscopic ellipsometry to study the evolution of structure and optoelectronic properties of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) photovoltaic thin film blends upon thermal annealing. Four distinct processes are identified: the evaporation of residual solvent above the glass transition temperature of the blend, the relaxation of non‐equilibrium molecular conformation formed through spin‐casting, the crystallization of both P3HT and PCBM components, and the phase separation of the P3HT and PCBM domains. Devices annealed at 150 °C for between 10 and 60 min exhibit an average power conversion efficiency of around 4.0%. We find that the rate at which the P3HT/PCBM is returned to room temperature is more important in determining device efficiency than the duration of the isothermal annealing process. We conclude that the rapid quenching of a film from the annealing temperature to room temperature hampers the crystallization of the P3HT and can trap non‐equilibrium morphological states. Such states apparently impact on device short circuit current, fill factor and, thus, operational efficiency.

Optical bonding with fast sol-gel

We investigate here the properties of fast sol-gel for optical bonding. The precursors of the fast sol-gel material are organically modified alkoxides generating a transparent hybrid (organic-inorganic) substance with silica glass-like properties whose index of refraction can be modified by the addition of various metal-oxides. The fast sol-gel method consists of rapid fabrication of a viscous resin and its subsequent dilution for long shelf life use. This material, when used as an adhesive offers the option of either a thermal or UV curing procedure. We demonstrate a bonding strength of ~ 10 MPa when a 15 µm layer is applied between two glass elements. The bonding remained stable after an extensive -40ºC – 120ºC temperature cycling with minimal residual solvent evaporation at 150ºC. The fast sol-gel material was tested for optical bonding between silica bulks, between silica bulk and silicon wafers and as an adhesive in silica fibre couplers.

Calibration system and analytical considerations for quantitative sesquiterpene measurements in air

Sesquiterpenes (C 15H 24, SQT) are semi-volatile organic compounds emitted from vegetation and are of interest for air quality considerations because of their suspected contribution to the formation of secondary aerosol. This article investigates the application of a capillary diffusion method for the generation of standard atmospheres of 16 SQT and four other related semi-volatile compounds. This instrument subsequently has been used in the testing of analytical materials, protocols and calibration of air sampling methods. SQT DB-1 retention indices, vapor pressures at 25 and 75 °C, and diffusion coefficients were determined. A quantitative, on-line GC method yielded improved results (median relative standard deviation of 5.0–6.1%) for the diffusion rate determination in comparison to a gravimetric approach (median relative standard deviation 18%). The GC method also allowed identifying errors in the gravimetric method stemming from residual solvent evaporation, impurities, and chemical analyte losses. Stainless steel, glass, nickel and PTFE tubing that were tested for transfer lines and a sampling loop had to be kept at temperatures in excess of ∼110 °C in order to prevent significant analytical errors from the stickiness of SQT to these materials. In addition to SQT analysis, results from this research provide general guidelines for gas-phase analysis of related compounds in the C 14–C 16 volatility range.

Effects of harvesting and cooling on crystallization and transformation of orthorhombic paracetamol in ethanolic solution

Orthorhombic paracetamol (form II) can be obtained from ethanolic solution when seeding technique is applied although it converts to monoclinic (form I) upon contact with the solvent. In the present work different cooling temperature T C (−20, −10 and 0 °C) was applied under fixed agitation (700 rpm) and the crystalline product was harvested after different crystallization time t H (20, 30 and 40 min). Crystal yield ( Y%), micromeritic properties and orthorhombic content of the crystalline product were evaluated and related to T C and t H. Conditions for optimal crystal yield and orthorhombic content were elucidated and kinetic parameters of solvent mediated transformation (induction times, t it, and activation energy, E a) were determined. It was found that crystal yield ( Y%) increases with t H and decreases with T C. The mean crystal size and size distribution is affected linearly by T C, probably due to alterations in the nucleation and growth processes. The effects on the crystal shape can be elucidated only after size classification. As the crystals grow, they become more elongated, with rougher surface due to secondary nucleation and alteration in growth rate of different crystal faces. Induction times for solvent mediated transformation ( t it), were remarkably longer than those corresponding to appearance of monoclinic form, when large scale collection and drying of crystalline product was applied, probably due to residual solvent evaporation. The activation energy of solvent mediated transformation ( E a=62.9 kJ/mol) is between those for nucleation in the solid state and in a solvent, indicating the operation of a mixed mechanism.

Lithographic Characteristics and Thermal Processing of Photosensitive Sacrificial Materials

Previously, a novel method for fabricating microfluidic and microelectromechanical devices with buried microchannel structures using thermally sacrificial polymers was reported. These previous methods required separate lithographic and etching sequences to pattern the sacrificial polymer. In this work, a more advanced approach in which the sacrificial material is radiation sensitive and can be patterned directly using standard lithographic techniques is explored. The lithographic performance of a new class of photosensitive polynorbornene (PNB) sacrificial materials has been characterized. The effect of soft bake and postexposure bake (PEB) on the cross-linking of photodefinable PNB has also been investigated. It was found that significant cross-linking of PNB occurs after exposure during the subsequent postexposure bake. However, this phenomenon is strongly dependent on the soft bake conditions used in preparing the sample, presumably due to varying levels of residual solvent content. This may be due to the high mass transport of the reactive species because of evaporation of residual solvent and shrinking of polymer matrix during the PEB process. No noticeable influence of residual solvent on cross-linking has been found during exposure. © 2002 The Electrochemical Society. All rights reserved.

Size analysis of a pressurized metered dose inhaler-delivered solution formulation by an Aerosizer-LD time-of-flight aerosol particle size spectrometer.

In a previous study, an Aerosizer-LD time-of-flight (TOF) aerosol spectrometer was shown to underestimate significantly the aerodynamic size of airborne particles produced following actuation of a suspension-based formulation delivered from a pressurized metered-dose inhaler (pMDI) via a nonelectrostatic valved holding chamber (VHC). It was postulated that the nonspecific nature of the particle detection system in terms of chemical composition was responsible for the inclusion of smaller non-drug-containing excipient particles in the measured size distribution data from this analyzer. This limitation may not apply to certain solution formulations in which the only particles remaining after the evaporation of propellant and volatile excipient (solubilizer) are composed of pure drug substance. Such a formulation (QVAR, HFA-formulated beclomethasone di-propionate [BDP]) has recently become available, and the present investigation was therefore designed to test this hypothesis. Aerosizer-LD measured mass-weighted size distribution data for QVAR had a mass median aerodynamic diameter (MMAD) close to 1.1 microm, very similar to published data for this parameter, based on measurement of the aerosol by cascade impactor followed by drug-specific assay. However, the Aerosizer-LD underestimated the spread of the size distribution significantly. The causes are believed to be a combination of two separate effects: (1) lack of sensitivity of the particle detection system to particles finer than about 0.7 microm aerodynamic diameter and (2) preferential removal of particles larger than the MMAD, either by evaporation of residual solvent (ethanol) or by inertial/gravitational deposition in the sampling arrangement upstream of the measurement zone.

Imidization processes of aromatic polyimide by temperature modulated DSC

Processing of polyimide (PI) from precursor polyamic acid (PAA) involves simultaneous imidization, evaporation of residual solvent and crystallization. These overlapped processes were analyzed by temperature modulated differential scanning calorimetry (T-MDSC). Glass transition temperature ( T g) of precursor PAA was manifested by T-MDSC, and it was 107°C for pyromellitic dianhydride–oxidianiline (PMDA–ODA) PAA cast from N-methyl-2-pyrrolidone (NMP) solution. The thermal cyclization reaction from PAA to PI is considered to progress randomly. The solvent system for casting PAA, influenced the conversion to PI, which is found to affect the T g of PAA.

Conversion mechanism of perhydropolysilazane into silicon nitride-based ceramics

The pyrolysis of perhydropolysilazane in anhydrous ammonia has been studied up to 1000 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, Fourier transform-infrared analysis. X-ray photoelectron spectroscopy, X-ray diffraction and 29Si cross-polarization magic angle spinning-nuclear magnetic resonance. The pyrolysis mechanism involves three main steps: (1) below 400 °C, evaporation of residual solvent; (2) from 400–600 °C, reaction with ammonia leading to an increase of nitrogen content and formation of preceramic polymer-ceramics intermediate solid with a three-dimensional network; (3) from 600–1000 °C, completion of the formation of an amorphous hydrogenated solid with composition close to silicon nitride.