Solvent-induced Crystallization Research Articles

Controllable Conformation Transfer of Conjugated Polymer toward High Photoelectrical Performance: The Role of Solvent in Induced-Crystallization Route

In the present work, polyimides with different conformation (dendritic, spherulitic, and laminar) were synthesized in different solvents. The strong solvent-dependent conformation variation is found intimately related to the specific interactions between the polymer chain and solvent molecules that have a primary driving force for the chain diffusion and rearrangement. Moreover, the photoelectrical properties of polyimide were sensitively influenced by the crystal structure and polymer morphology. In laminar conformation with strong intermolecular π–π interactions, the light absorption as well as the mobility and separation of photoinduced carriers were greatly improved compared with similar values of dendritic and spherulitic ones. For photocatalytic hydrogen evolution from water splitting, polyimide with laminar conformation exhibits 16 times enhancement in activity than the dendritic. This work provides further insight into the intrinsic interacting mechanism of solvent-induced crystallization of conju...

Image analysis as a useful tool for fast detection of dimensional and structural changes of poly(ethylene terephthalate) containers

The aim of this paper is to present image analysis as a useful technique for fast, reliable and non-destructive detection of dimensional and structural changes in polymers. The possibility of applying image analysis was demonstrated in the case of solvent-induced crystallization of poly(ethylene terephthalate) (PET) containers filled with commonly used organic solvents: chlorobenzene, isophorone, xylene, Espesol, Shellsol A 100, Solvesso 150, propylene glycol, glycerin and water and subjected to the storage stability test at 54 ?C for 14 days (CIPAC 1-MT 46.1.3). In addition, the obtained results were analyzed using one-step analysis of variance (ANOVA) combined with the Duncan?s statistical test (p<0.05). According to the achieved results, three main impacts of the presented paper could be distinguished: 1) dimensional and transparency changes could be precisely followed by image analysis in both following cases: for small changes in water, as well as for significant ones in chlorobenzene; 2) a correlation between the changes in the degree of crystallinity and transparency could be obtained without the continuous material testing by DSC; 3) image analysis is potentially applicable for assessment of other crystalline polymers.

Tracking free volume changes in bisphenol-a based polycarbonate sheets after treatment with liquid acetone

Free volume properties, size and distribution, in the bisphenol-a based polycarbonate (PC) sheets were investigated as a function of the treatment duration by liquid acetone using the positron annihilation lifetime (PAL) spectroscopy. Along with increasing the PC treatment duration, the free volume sizes decreased and the holes-distribution broadened, which in turns led to the polymer crystallization induction. From the PAL and WAXD data, it has been confirmed that the crystallization capability of the amorphous PC tremendously enhanced, with a rapid increase of the PC crystallinity along with increasing the treatment duration by liquid acetone. These findings were further confirmed by the surface chemistry and topography characterization techniques which revealed the formation of crystalline structure after liquid acetone treatment. The solvent-induced crystallization of PC sheets promoted restrictions to the infrared induced molecular vibrations the surface functional groups which was reflected as drop in peaks intensities and shift of the carbonyl peak of the Fourier transform infrared (FTIR) spectrum.

Solvent-induced crystallization for hybrid perovskite thin-film photodetector with high-performance and low working voltage

Organometal trihalide perovskites have emerged as a class of solution-processed semiconductors exhibiting remarkable optoelectronic properties. Using a high-quality perovskite thin film prepared by solvent-induced crystallization method and adopting a novel device configuration based on photon recycling effect, a perovskite thin-film photodetector has been constructed with the highest external quantum efficiency of 4.1 × 104% and responsivity of 219 A W−1 at a low bias of 1 V so far. The device working mechanism was further disclosed based on energy band bending model. The high-performance and low working-voltage perovskite thin-film photodetector will find potential applications in photodetection and optoelectronic integrated circuits.

Heat Transfer and Fluid Flow Characteristics in a Sessile Droplet on Oil-Impregnated Surface Under Thermal Disturbance

The present study examines the flow field and heat transfer inside a sessile droplet on oil-impregnated surface when subjected to a small temperature difference at the droplet–oil interface. Temperature and flow fields inside the droplet are predicted and the flow velocities predicted are validated through the data obtained from a particle image velocimetry (PIV). Several images of droplets in varying sizes are analyzed and the droplet geometric features and experimental conditions are incorporated in the simulations. A polycarbonate wafer is used to texture the surface via incorporating a solvent-induced crystallization method. Silicon oil is used for impregnation of the textured surfaces. It is found that two counter-rotating circulation cells are formed in the droplet because of the combined effect of the Marangoni and buoyant currents on the flow field. A new dimensionless number (Merve number (MN)) is introduced to assess the behavior of the Nusselt and the Bond numbers with the droplet size. The Merve number represents the ratio of the gravitational force over the surface tension force associated with the sessile droplet and it differs from the Weber number. The Nusselt number demonstrates three distinct behaviors with the Merve number; in which case, the Nusselt number increases sharply for the range 0.8 ≤ MN ≤ 1. The Bond number increases with increasing the Merve number, provided that its values remain less than unity, which indicates the Marangoni current is dominant in the flow field.

Structural Study of Solvent-induced Crystallization Phenomenon of PET for the Economical Production of PET Bottles

Structural Study of Solvent-induced Crystallization Phenomenon of PET for the Economical Production of PET Bottles

Solvent-induced crystallization of electrospun syndiotactic polystyrene nanofibers and its reversible desorption/sorption of volatile organic vapors

Electrospun fiber mats are promising media for chemical separation because of their porous interior and high surface area, which enhance penetrant permeation and provide a large number of active sites. The application of this technology was fulfilled in the present study, wherein syndiotactic polystyrene (sPS) fibers were prepared by high-temperature solution electrospinning to absorb volatile organic compounds. The as-spun sPS fibers had an average radius of ~360 nm and were amorphous as revealed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction. When the electrospun fibers were exposed to different solvent vapors, solvent-induced crystallization occurred in these submicron-sized fibers to form δ- or γ-form sPS crystals, depending on the solvent used. To trace the microstructure transformation of sPS chains induced by the solvent vapors, in situ FTIR spectral measurements were performed. The absorbance of crystallization-sensitive IR bands was plotted against time, from which the crystallization kinetics were analyzed based on the Avrami equation. Results showed that the rate of solvent-induced crystallization was higher for solvents with a higher saturated vapor pressure. Subsequent solvent desorption from the crystallized sPS fibers was also studied under ambient conditions by monitoring the absorbance variation of the solvent-sensitive IR band. Two-stage solvent desorption was observed in the δ-form sPS fibers; this process consisted of initial rapid desorption from the amorphous region, followed by slow desorption from the crystalline region. Notably, all the solvent molecules in the treated fibers can be completely removed in this manner, thereby leading to the formation of δ e-form crystals for repetitive sorption/desorption applications.

High dielectric permittivity and improved mechanical and thermal properties of poly(vinylidene fluoride) composites with low carbon nanotube content: effect of composite processing on phase behavior and dielectric properties

The composite processing technique and nanofiller concentration and its functionalization significantly alter the properties of polymer nanocomposites. To realize this, multi-walled carbon nanotubes (CNT) were dispersed in a poly(vinylidene fluoride) (PVDF) matrix at carefully selected CNT concentrations by two illustrious methods, such as solution-cast and melt-mixing. Notwithstanding the processing method, CNTs induced predominantly the γ-phase in PVDF, instead of the commonly obtained β-phase upon nanofiller incorporation, and imparted significant improvements in dielectric properties. Acid-treatment of CNT improved its dispersion and interfacial adhesion significantly with PVDF, and induced a higher γ-phase content and better dielectric properties in PVDF as compared to pristine CNT. Further, the γ-phase content was found to be higher in solution-cast composites than that in melt-mixed counterparts, most likely due to solvent-induced crystallization in a controlled environment and slow solvent evaporation in the former case. However, interestingly, the melt-mixed composites showed a significantly higher dielectric constant at the onset of the CNT networked-structure as compared to the solution-cast composites. This suggests the possible role of CNT breakage during melt-mixing, which might lead to higher space-charge polarization at the polymer–CNT interface, and in turn an increased number of pseudo-microcapacitors in these composites than the solution-cast counterparts. Notably, PVDF with 0.13 vol% (volume fraction, fc = 0.0013) of acid-treated CNTs, prepared by melt-mixing, displayed the relative permittivity of ∼217 and capacitance of ∼5430 pF, loss tangent of ∼0.4 at 1 kHz and an unprecedented figure of merit of ∼105. We suggest a simple hypothesis for the γ-phase formation and evolution of the high dielectric constant in these composites. Further, the high-dielectric composite film showed marked improvements in mechanical and thermal properties over the neat PVDF film. These composites with exceptional dielectric properties and concomitant improvement in mechanical and thermal properties offer a great promise for use in flexible and mechanically robust charge storage devices.

Compact low-field NMR: Unmasking morphological changes from solvent-induced crystallization in polyethylene

It is accepted knowledge that solvents diffuse in the amorphous phase of semi-crystalline polymers. Yet these solvents may trigger swelling that affects segmental chain mobility and gives rise to changes of the polymer. This study explores compact low-field NMR as a fast, simple, and low-cost method of analysis to detect such swelling-induced morphological changes. Here, 1H NMR relaxation, 1H wide-line NMR spectroscopy, and DSC were employed to investigate the morphological changes of a commercial-brand low-density polyethylene (LDPE) induced by swelling for different durations in different solvents and at three different temperatures. The analysis of the phase composition and relaxation times T2eff reveals that solvent-induced crystallization (SINC) is accompanied by structural rearrangements in the soft domain that, in turn, increase the amount of the rigid fraction. The variations in the chain mobility of LDPE samples identified by NMR prove that the SINC proceeds faster at higher swelling temperature. Moreover, the changes in the relaxation time of LDPE samples swollen in different solvents suggest that thermodynamic and kinetic factors govern the SINC process. This agrees well with the variations in the degree of crystallinity evaluated by DSC. The NMR data show that short-chain branching may accelerate the SINC process. This study also proves, that compact low-field NMR is an adequate tool for detecting the morphological changes in polyethylene invoked by solvent-induced crystallization.

Vapochromic Behaviour of Polycarbonate Films Doped with a Luminescent Molecular Rotor.

We report on vapochromic films suitable for detecting volatile organic compounds (VOCs), based on polycarbonate (PC) doped with 4-(triphenylamino)phthalonitrile (TPAP), a fluorescent molecular rotor sensitive to solvent polarity and viscosity. PC films of variable thickness (from 20 up to 80 µm) and containing small amounts of TPAP (0.05 wt.%) were prepared and exposed to a saturated atmosphere of different VOCs. TPAP/PC films showed a gradual decrease and red-shift of the emission during the exposure to solvents with high polarity index and favourable interaction with the polymer matrix such as THF, CHCl3, and acetonitrile. In the case of the most interacting solvents (THF and CHCl3), TPAP/PC films also showed a fluorescence increase at longer exposure times, as a consequence of an irreversible, solvent-induced crystallization process of the polymeric matrix. The vapochromism of TPAP/PC films is rationalized on the basis of alterations of the rotor intramolecular motion upon solvent uptake by PC and polarity effects of the microenvironment. Interestingly, the fluorescence response of the TPAP/PC films shows a non-trivial, tuneable dependence on film thickness during the second solvent-exposure stage. The latter effect is attributed to a variable extent of the crystallization process occurring in the PC films. This observation promptly suggests, in turn, an effective procedure to modulate the spectroscopic response in such functionalized polymeric materials through the precise control of the film thickness.

Rice husk ash as a renewable source for synthesis of sodium metasilicate crystal and its characterization

The objective of the present work is to develop an environmentally friendly ("green") and economically effective process to synthesize sodium metasilicate crystal from cheap rice husk ash (RHA). We made full use of the silica in RHA as raw material, extracting the silica liquid via an alkali dissolving method and using it to prepare sodium metasilicate crystal by solvent-induced crystallization. The as-synthesized samples were characterized by X-ray diffraction, infrared spectra, optical microscopy and thermal gravimetric analysis. As per the results, we concluded that the optimum condition for the maximum dissolution rate of silica was sodium hydroxide and RHA after acid pre-treatment at a solid/liquid ratio of 1:8 with 10 wt% of NaOH at 90 °C for 2.5 h. Meanwhile, we can prepare sodium metasilicate pentahydrate qualified with silica under the mild condition.

Novel Flow Field with Superhydrophobic Gas Channels Prepared by One-step Solvent-induced Crystallization for Micro Direct Methanol Fuel Cell

The CO2-induced capillary blocking in anode flow field is one of the key adverse factors to reduce the performance of a micro-direct methanol fuel cell (μDMFC). In order to solve this problem, new polycarbonate (PC) flow field plates with nested arrangement of hydrophilic fuel channels and superhydrophobic gas channels were designed, fabricated, and tested in this work. The gas channels were treated with solvent-induced crystallization using acetone solution. The superhydrophobicity with 160° water contact angle and 2° tilting angle was obtained on the PC substrates. A dummy cell using hydrogen peroxide decomposition reaction and a test loop were separately set up to evaluate the flow fields’ performance. It was found that a 37 % pressure drop decrease can be obtained in the new serpentine flow field compared with that of the conventional one. The benefit of the new flow field to remove gas bubbles was also confirmed by an in situ visualization study on the dummy cell. Results show that the auxiliary superhydrophobic gas channels can speed up the discharge of the gas bubbles from the flow field, which will in turn improve the μDMFC performance.

Solvent-induced crystallization behaviors of PLLA ultrathin films investigated by RAIR spectroscopy and AFM measurements.

The crystallization of poly(L-lactide acid) (PLLA) ultrathin films induced by different solvents was investigated using reflection-absorption infrared (RAIR) spectroscopy and atomic force microscopy (AFM). Irregular PLLA dendrite lamellae grew in the flat-on orientation with dichloromethane solvent before being redissolved after longer induction times owing to the strong interaction between the PLLA segments and solvent molecules. Faster formation of PLLA spherulites was induced with acetone than with dichloromethane, and these remained unchanged with increasing induction time because of the polarity difference between the PLLA segments and acetone molecules. PLLA ultrathin films could not be induced to crystallize using chloroform because of the very strong interactions between the chloroform (CHCl3) molecules and PLLA amorphous chains, which caused the CHCl3 solvent molecules to rapidly permeate the PLLA random coils and dissolve the amorphous chains. These phenomena are attributed to solvent-specific competition between solvent-induced crystallization and dissolution effects in PLLA ultrathin films, which ultimately leads to the higher degree of crystallinity obtained with acetone than with dichloromethane.

Robust polythiophene nanowires cross-linked with functional fullerenes

Poly(3-hexyl thiophene) (P3HT)-block-poly(3-(3-aminopropyl)oxymethyl thiophene) (P3AmT) diblock copolymers were synthesized and assembled into nanowires by solvent-induced crystallization. Bis(4-[1,6-hexyldiisocyanate]benzylpyrrolidine)-C60 was synthesized and used to covalently cross-link the structures, affording robust p-type/n-type nanowires. These cross-linked nanowires proved stable to solvents and temperatures that would disrupt conventional P3HT-nanowires, as characterized by transmission electron microscopy (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. Photoluminescence spectroscopy showed quenching of the PL signal of the fullerene-crosslinked material, suggesting electronic communication between the polymer and fullerene in these novel donor/acceptor assemblies. Grazing incidence X-ray diffraction (GIXD) showed a similar crystal structure for nanowires before and after cross-linking, while field effect transistor transfer measurements of the cross-linked nanowires showed hole and electron mobilities of 3.5 × 10−5 cm2 V−1 s−1 and 4.6 × 10−5 cm2 V−1 s−1, respectively.

Reversible, self cross-linking nanowires from thiol-functionalized polythiophene diblock copolymers.

Poly(3-hexylthiophene)-block-poly(3-(3-thioacetylpropyl) oxymethylthiophene) (P3HT)-b-(P3TT) diblock copolymers were synthesized and manipulated by solvent-induced crystallization to afford reversibly cross-linked semiconductor nanowires. To cross-link the nanowires, we deprotected the thioacetate groups to thiols and they subsequently oxidized to disulfides. Cross-linked nanowires maintained their structural integrity in solvents that normally dissolve the polymers. These robust nanowires could be reduced to the fully solvated polymer, representing a novel, reversible cross-linking procedure for functional P3HT-based nanowire fibrils. Field-effect transistor measurements were carried out to determine the charge transport properties of these nanostructures.

Preparation of Low Band Gap Fibrillar Structures by Solvent-Induced Crystallization.

Solvent-induced crystallization of the low band gap polymer poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) was shown to give fibril-like structures of 40-60 nm width and ∼0.5 μm length. These structures, formed by heating and cooling PCDTBT in a marginal solvent for the polymer, were characterized by AFM, TEM, GI-WAXS, and steady state absorption and emission spectroscopy. The width of the PCDTBT structures suggests that the polymer chains are oriented perpendicular to the fiber axis, while the observed undulated structure, as revealed by AFM, suggests that the nanostructures may be composed of smaller crystalline units that associate preferentially on specific faces of the crystals. The spectroscopic signatures of the suspended PCDTBT fibrils resembled that of the polymer in solution, in contrast to features associated with the fibril formation of the well-known conjugated polymer poly(3-hexyl thiophene) (P3HT). The solution-based crystallization of PCDTBT reported herein offers insight into the self-assembly of conjugated polymers toward better understanding of their role in photovoltaic devices.

The effect of crystallization on hydrolytic stability of polycarbonate

Bisphenol A polycarbonate (PC) was chosen as the representation of polyester resins for investigating the effect of aggregative state on hydrolytic stability of this kind of materials. Surface-crystallized PC was prepared by solvent-induced crystallization method. Moreover, a comparative study on hydrolytic stability of amorphous PC and surface-crystallized PC had been carried out by means of mechanical performance testing, static water contact angle, IR, GPC and DSC measurements. The results indicated that the surface-crystallized PC had better hydrolytic stability than amorphous PC, manifesting as: (1) the hydrophobicity of PC was enhanced obviously when the surface of material crystallizes via solvent-induced method; (2) the reduced rate of the elongation at break of surface-crystallized PC was much smaller than that of amorphous PC during hydrolysis; (3) the impact strength of amorphous PC reduced rapidly in the early stage of hydrolysis, while that of surface-crystallized PC firstly increased, following by a slightly decrease; (4) the reduced rate of weight-average molecular weight of surface-crystallized PC was smaller than that of amorphous PC; and (5) the stability of the chemical structures of surface-crystallized PC was much higher than that of amorphous PC during hydrolysis, resulting in fewer changes in the glass transition temperature (Tg), as well as less cleavage of polycarbonate linkage after hydrolysis in 65 °C water for 36 days. This investigation clearly shows that solvent-induced crystallization on surface can be an efficient way to enhance the hydrolytic stability of polycarbonate.

Development of Solvent-Induced Crystallization Method Using Toluene for the Improvement of Thermal Shrinkage of Poly (Ethylene Terephthalate) (PET) Film

Development of Solvent-Induced Crystallization Method Using Toluene for the Improvement of Thermal Shrinkage of Poly (Ethylene Terephthalate) (PET) Film

Polyethersulfone polymers and oligomers — Morphology and crystallization

Crystal forms of polyethersulfones (PES) were investigated by using a model compound and a low molecular weight oligomer. These are amorphous as-synthesized, and can undergo solvent-induced crystallization under the appropriate conditions. The model compound, 4,4′-bis(p-methoxyphenoxy)diphenyl sulfone, yielded monocrystals, and its structure was solved using X-ray diffraction. Conformational disorder is present, two conformers cohabiting in 55:45 proportions. This model compound, combined to previous structural studies published in the literature, served as a basis for conformational studies of polyethersulfone. Low molecular weight polymers submitted to solvent-induced crystallization resulted in a PES crystal form different from that previously published in the literature, as shown by powder X-ray diffraction.

Manipulating poly(lactic acid) surface morphology by solvent-induced crystallization

Here, we report some unique crystalline morphologies of poly(lactic acid) (PLA) via organic solvent-induced crystallization. It was revealed that the surface morphology of PLA can be fine tuned by simply varying the volume ratio of a mixed solvent (acetone/ethanol). By increasing the ethanol content in the mixed solvent, we observed a morphological evolution of PLA surface from spherulite to shish–kebab and bamboo-cage-like structure. It was also interesting to find that the initial surface structure of PLA plays an important role to determine the final solvent-induced crystalline morphology. This work provides a new method for manipulating PLA crystal morphology through a simple solvent-induced crystallization.