Solvent-induced Crystallization Research Articles

Multifunctional polymeric microfibers with prolonged drug delivery and structural support capabilities

The strength and stability of hybrid fiber delivery systems, ones that perform a mechanical function and simultaneously deliver drug, are critical in the design of surgically implantable constructs. We report the fabrication of drug-eluting microfibers where drug loading and processing conditions alone increase microfiber strength and stability partially due to solvent-induced crystallization. Poly(l-lactic acid) microfibers of 64±7μm diameter were wet spun by phase inversion. Encapsulation of a model hydrophobic anti-inflammatory drug, dexamethasone, at high loading provided stability to microfibers which maintained linear cumulative release kinetics up to 8weeks in vitro. In our wet spinning process, all microfibers had increased crystallinity (13–17%) in comparison to unprocessed polymer without any mechanical stretching. Moreover, microfibers with the highest drug loading retained 97% of initial tensile strength and were statistically stronger than all other microfiber formulations, including control fibers without drug. Results indicate that the encapsulation of small hydrophobic molecules (<400Da) may increase the mechanical integrity of microfilaments whose crystallinity is also increased as a result of the process. Multifunctional drug-eluting microfibers can provide an exciting new opportunity to design novel biomaterials with mechanical stability and controlled release of a variety of therapeutics with micron-scale accuracy.

Transitions of morphological patterns of crystallizing polycarbonate in thin films

AbstractThis article reports the transitions of morphological patterns of polycarbonate crystals in thin films by solvent‐induced crystallization (SINC). As a substrate (silica glass) deposited with an amorphous and micron‐thick bisphenol A polycarbonate polymer film is partially dipped into a liquid acetone bath, acetone penetrated rapidly through the polymer film. The rate of acetone penetration is significantly higher than the predicted by Fickian diffusion or anomalous diffusion model, indicating that the capillary force through stress‐induced cracks may have played a major role in the upward transport of acetone through the polymer films. The morphologies of polycarbonate at different vertical positions on a substrate surface were analyzed by scanning electron microscopy and atomic force microscopy. It was observed that depending on the local acetone concentration the polymer morphologies showed quite diverse patterns ranging from stress‐induced cracks to fully developed three‐dimensional spherulites. The diverse morphologies developed during the thin film SINC may serve as a useful platform for further detailed mechanistic analysis of structures and crystallization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Nanoporous Crystalline Phases of Poly(2,6-Dimethyl-1,4-phenylene)oxide

Crystalline modifications, exhibiting largely different X-ray diffraction patterns, have been obtained for poly(2,6-dimethyl-1,4-phenylene)oxide (PPO), by gel desiccation procedures as well as by solvent-induced crystallization of amorphous films. The choice of the solvent allows controlling the nature of the crystalline phase. Both amorphous and semicrystalline samples of this commercial thermoplastic polymer exhibit a high uptake of large guest molecules (like, e.g., benzene or carbon tetrachloride), both from vapor phases and from diluted aqueous solutions. Surprisingly, the semicrystalline PPO samples present guest solubility much higher than fully amorphous PPO samples. These sorption experiments, as well as density measurements and classical Brunauer–Emmett–Teller (BET) experiments, clearly indicate that the obtained PPO crystalline phases are nanoporous. For these thermally stable PPO-based materials exhibiting nanoporous crystalline and amorphous phases, many applications are predictable.

Solvent-Induced Crystallization of Poly(3-dodecylthiophene): Morphology and Kinetics

We report on the self-assembly of poly(3-dodecylthiophene) (P3DDT) into nanowhiskers for the first time via addition of the marginal solvent anisole into its well-dissolved solution. By controlling the solvent composition and aging time, we observed a morphology evolution from nanowhiskers to two-dimensional nanoribbons and foliated aggregates, which was ascribed to diverse driving forces for self-assembly in the process of crystallization. UV-vis absorption spectroscopy and dynamic lighting scattering (DLS) measurements were employed to in situ monitor crystallization kinetics of P3DDT induced by mixed solvents. It has been shown that conformational transition serves as a critical factor for P3AT to perform π-π stacking to form nanowhiskers. From a thermodynamic point of view, P3AT dispersion dissolved in mixed solvents is actually not a thermodynamic equilibrium system, but a multicomponent and multiphase case whose phase composition and properties evolve with time. The understanding in morphology transition mechanisms and crystallization kinetics of P3DDT can provide guidelines for optimization of processing parameters and enhance performance of photovoltaic devices.

Orienting Semiconducting Nanocrystals on Nanostructured Polycarbonate Substrates: Impact of Substrate Temperature on Polymorphism and In-Plane Orientation

This paper reports a systematic investigation of the growth mechanism of zinc phthalocyanine, a p-type semiconductor, on oriented polymer substrates of bisphenol A polycarbonate (PC). It focuses on the impact of the substrate temperature on the polymorphism and the in-plane orientation of the ZnPc nanocrystals. The study combines transmission electron microscopy, X-ray diffraction, atomic force microscopy, UV–vis absorption spectroscopy, and force field-based molecular calculations. Large areas of oriented PC substrates are prepared by a simple process that combines mechanical rubbing and solvent-induced crystallization. The PC substrates show a smooth semicrystalline morphology with a preferential (a,c) surface of crystalline lamellae with a high in-plane orientation of the polymer chains. These substrates induce a unidirectional orientation of ZnPc nanocrystals with a preferred contact plane. The selection of the preferred ZnPc in-plane growth direction relies on a “self-amplified“ mechanism whereby a f...

Organic solvent-induced controllable crystallization of the inorganic salt Na3[Au(SO3)2] into ultralong nanobelts and hierarchical microstructures of nanowires

The present paper reports an organic solvent-induced controllable crystallization of a water-soluble inorganic salt Na(3)[Au(SO(3))(2)] into ultralong nanobelts and hierarchical microstructures of one-dimensional (1D) nanowires. It was found that the morphology of the resulting crystals can be fine tuned by simply varying the experimental parameters, such as the ratios of water to organic solvent and gold salt to organic solvent, as well as the type of organic solvent.

Applied Study of Solvent-Induced Crystallization Method for the Reduction of Thermal Shrinkage of Poly(Ethylene Terephthalate) (PET) Film

Solvent-induced crystallization effect has been found to be quite useful for the reduction of the thermal shrinkage of oriented poly(ethylene terephthalate) (PET) film． This method involves dipping of amorphous PET film into acetaldehyde for only a short time, which causes a drastic increase in the film crystallinity. The thus-dipped and dried-up film was stretched at near the glass transition temperature (Tg) to obtain the sample with relatively high degree of chain orientation. This oriented sample has been found to show negligibly small thermal shrinkage even when the sample was heated up to 95 o C, much higher than Tg. This new method has a potential to open a new and simple technology for the mass production of PET bottles without any thermal shrinkage even for the supply of boiling water into them．The origin of thus-obtained high thermal resistivity of acetaldehyde-immersed and oriented PET film has been clarified on the basis of infrared ATR (attenuated total reflection) spectral measurement．

Effect of chain-length of n-alkane on solvent-induced crystallization and solvent exchange phenomenon in syndiotactic polystyrene

The effect of molecular size and the vapor pressure of a series of n-alkanes as a solvent on solvent-induced crystallization of amorphous sPS and also the solvent exchange phenomenon in the δ form of syndiotactic polystyrene (sPS) were investigated by means of FT-IR spectroscopy and X-ray diffraction. The crystallization of amorphous sPS was found to be very much influenced by the molecular size and the vapor pressure of the n-alkanes used. At room temperature, n-alkanes with six and seven carbon atoms crystallize the sPS into the δ form, whereas the longer n-alkanes did not induce the crystallization of the amorphous sPS. By increasing the crystallization temperature to 50 °C, the vapor pressure of n-alkanes increases and as a result n-alkanes with eight to ten carbon atoms crystallize the amorphous sPS into the γ form unlike the cases of n-hexane and n-heptane. On further increasing the chain-length of n-alkanes to n-tridecane and n-hexadecane, no crystallization of amorphous sPS was observed even at 50 °C. By keeping the crystallization behavior in mind, we used these n-alkanes to exchange the existing solvent in the δ form of sPS/chloroform complex. n-Alkanes with six and seven carbon atoms easily replace the chloroform enclosed in the crystal lattice at room temperature and the d 010 lattice spacing was found to increase according to the molecular size of the solvent used in the exchange process. n-Alkanes with eight to ten carbon atoms could also replace the chloroform enclosed in the crystal lattice at room temperature. But in this case the d 010 lattice spacing was found to be similar or lower than that of the δ form of sPS/chloroform complex and a new reflection was observed 2 θ = 6.6°, indicating the formation of the ɛ form. On the other hand, longer n-alkanes (C13 and C16) did not intrude into the cavities of the δ form at room temperature. By increasing the solvent exchange temperature to 50 °C, the longer n-alkanes (C13 and C16) also replaced the existing chloroform in the δ form and structure transformed to the ɛ form. In this way, we found that the crystallization and solvent exchange process of sPS using n-alkanes is quite complicated and depends strongly on the chain-length of n-alkane molecule.

Solvent-Induced Crystallization of PS-b-PEO-b-PS Block Copolymer Films

Solvent-induced crystallization and dewetting behaviors of polystyrene-b-poly (ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) block copolymer films deposited on three different substrates, silicon, mica, and carbon-coated mica have been studied by atomic force microscope (AFM). When the common solvent dichloromethane was used for annealing, the films on all three of the substrates exhibited dewetting behavior; the dendritic crystallization patterns were found in the dewetted regions for the films on silicon and mica substrates, while for the films on carbon-coated mica, no crystallization pattern appeared. According to the observation of the crystallization patterns formed in the films with different initial thicknesses, it is shown that the width of the dendritic branches decreases with the increase of film thickness and solvent annealing time. When the PS-selective solvent toluene was used for annealing, the dewetting process was absent, and the crystallization patterns were observed on the surface of the films on all three kinds of substrates.

Syndiotactic Polystyrene Nanofibers Obtained from High-Temperature Solution Electrospinning Process

Electrospun syndiotactic polystyrene (sPS) fibers with a diameter of 150−400 nm were successfully prepared via high-temperature electrospinning of solutions with different concentrations in an o-dichlorobenzene solvent. From the polarized FTIR spectra, the sPS chains in the as-spun fibers were amorphous and exhibited a preferential chain orientation along the fiber axis. Upon thermal annealing at a temperature lower than 270 °C, sPS crystals with the α-form modification were developed, as revealed by the electron diffraction patterns of the individual fiber segments. The orientation factor of the (002) plane was determined to be 0.94−0.97, relatively independent of the annealing temperature. Solvent-induced crystallization readily took place in these submicrometer-sized fibers, giving rise to the δ-form sPS crystals, as revealed by the FTIR spectra and WAXD patterns. The absorbed solvents could subsequently be expelled by boiling in ethanol, leaving the cavities available for the next solvent treatment. I...

Investigation of liquid sensing mechanism of poly(lactic acid)/multi-walled carbonnanotube composite films

The liquid sensing mechanism of melt-processed poly(lactic acid) (PLA)/multi-walledcarbon nanotube (MWNT) composite films was investigated for the influence of MWNTloading, solubility parameters of solvents used, solvent transport behaviours, resultantelectrical resistance changes, as well as crystallization of the PLA matrix. Thediffusion, sorption and permeation coefficients of neat PLA and the composites wereestimated, indicating that MWNT network structures block solvent moleculesfrom penetrating into the polymer matrix. Solvent-induced crystallization of thepolymer matrix was observed. Isothermally crystallized composites showed reducedresistances, a significant decrease of sorbed solvent content and a reduction of theresulting resistance changes on the solvent contact. In the context with sensingresults on MWNT mats, it was proposed that the liquid sensing mechanism ofPLA/MWNT composites consists of the overall electrical resistance changes causedby the structural variation of the conductive MWNT network in the polymermatrix and additional interactions between the MWNT and solvent molecules.

Facile Creation of Biomimetic Systems at the Interface and in Bulk

AbstractNature always gives us inspiration for the fabrication of functional materials by mimicking the structural design or stimuli‐responsive capability of biomaterials. However, the strict preparation conditions, multistep processes, and high cost of the methods to create biomimetic systems at the interface and in bulk limit their practical applications. Therefore, development of a simple, cheap, but effective method has become the focus of our research in this field. In this feature article, facile methods for creating lotus‐leaf‐like micro‐nano‐binary structured superhydrophobic or superamphiphobic surfaces based on different mechanisms, i.e., solvent‐induced phase separation of a polymer blend solution, self‐assembly of a copolymer micelle solution, and solvent‐induced crystallization, are summarized. Moreover, progress into the investigation on the special microstructures that induce unique wetting properties are also introduced. As an effective biomimetic bulk system, a unique swift stimuli‐responsive gel actuator has been developed under a non‐contact electronic field in air. Artificial muscles with path‐controlled or self‐governing long‐range locomotion can be realized by using these stimuli‐responsive polymer gels on the basis of the extraordinary driving mechanisms.magnified image

Effect of Solvent on the Characteristics of Electrospun Regenerated Silk Fibroin Nanofibers

Nonwoven nanofiber matrices were prepared by electrospinning a solution of silk fibroin (SF) dissolved either in formic acid or in 1,1,1,3,3,3-hexafluoro-2-isopropyl alcohol (HFIP). The mean diameter of the electrospun nanofibers prepared from SF dissolved in formic acid was 80 nm with a unimodal size distribution, which was smaller than those prepared from HFIP (380 nm). SF nanofibers were then treated with an aqueous methanol solution, and structural changes due to solvent-induced crystallization of SF were investigated using IR and 13C solid-state CP/MAS NMR spectroscopy. SF nanofibers prepared from formic acid were found to have a higher proportion of β-sheet conformations than those prepared from HFIP. Methanol treatment provided a fast and effective means to alter the secondary structure of both types of SF nanofibers from a random coil form to a β-sheet form. As demonstrated in the present study, this approach to controlling the dimensions and secondary structure of proteins using various solvents may be useful for the design and tailoring of materials for biomedical applications, especially for tissue engineering applications.

Multi-Zone Drying Schemes for Lowering the Residual Solvent Content during Multi-Component Drying of Semicrystalline Polymers

The development of a glassy skin in multicomponent semicrystalline polymer systems limits the diffusion of solvents out of the system and increases residual solvent levels. Based on the results of a mathematical model that we had previously developed, we have proposed a multi-zone drying scheme aimed at lowering the residual solvent levels by taking into account the effect of interactions between the various solvents as predicted by the model. This article focuses on the application of this model to develop optimal drying schemes and to verify the effectiveness of these predictions using experimental techniques. The mathematical model developed previously to study the diffusion of multiple solvents and changes in the crystallinity of semicrystalline polymer systems during drying incorporates many features including Vrentas-Duda diffusion theory, solvent-induced crystallization kinetics, as well as glass transition effects and skinning of the film. The multi-zone drying system was developed by varying the drying temperature in each zone as well as changing the partial pressure of individual solvents during the drying process. The effectiveness of the multi-zone drying schemes predicted by the model was validated experimentally using thermogravimetric methods. The polymer-solvent system chosen was a poly(vinyl alcohol)-water-methanol system. Our experimental data suggested that the multi-zone drying schemes were superior to a single-zone drying system through direct comparison. Further examination of the mathematical model yielded individual solvent profiles and these data reaffirmed our conclusions that a multi-zone drying scheme has the ability to reduce the effect of solvent trapping and thus lower the overall residual solvent content.

Dynamic Interconversion of Amorphous Microparticles and Crystalline Rods in Salen-Based Homochiral Infinite Coordination Polymers

This paper describes a new class of homochiral salen-based infinite coordination polymers (ICPs) and the discovery of a novel and pseudo-reversible solvent-induced crystallization process. The solvent, methanol in this case, induces such a transformation through a change in the coordination environment around the metal bridging the metallo-salen portion of the complex. This transformation has allowed us to use X-ray methods to structurally characterize the crystalline product and through spectroscopic comparisons better understand the connectivity and structure of the amorphous ICP particles from which it is derived.

Solvent-Induced Crystallization of Spherical Micelles Formed by Copolymer Blends

We have followed the morphological evolution and crystallization process of spherical micelles formed by the mixture of polystyrene-b-poly(acrylic acid) (PS-b-PAA) and polystyrene-b-poly(2-vinylpyridine)b-poly(ethylene oxide) (PS-b-P2VP-b-PEO) (the core of the spherical micelles was made of P2VP and PAA blocks through hydrogen bonding in neutral solvent N,N-dimethylformamide, DMF) via DMF vapor treatment. Different phenomena, such as rupture of the film, formation of cylinder aggregates and regular square lamellae, were observed when the micelle film was treated in DMF for different times. At the early stage of annealing in DMF vapor, the micelle film became unstable and ruptured. Cylinder aggregates, within which the PEO blocks achieved the association and primary chain folding, formed as the mesophases before the nucleation of the PEO single crystals at this stage. Further treatment in DMF vapor resulted in the nucleation of the PEO blocks at the corners of quasi-square lamellae. Then a quite regular sandwich lamellar structure, constructed by a PEO single-crystal layer covered by two tethered layers of other amorphous blocks on the top and bottom crystal basal surfaces, formed when the film of micelles was annealed in DMF vapor for sufficient times.

Thermal analysis, X-ray and electron diffraction studies on crystalline phase transitions in solvent-treated poly(hexamethylene terephthalate)

The crystal polymorphism, transformation, and morphologies in chloroform solvent-cast poly(hexamethylene terephthalate) (PHT) were examined by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and temperature in situ transmission electron microscopy (TEM). Solvent-induced crystallization of PHT at room temperature yielded an initial crystal of γ-form, as confirmed by WAXD. Upon DSC scanning, the original γ-form in PHT exhibited three endothermic peaks, whose origins and association were carefully analyzed. The first peak, much smaller than the other two, is in the temperature range of ca. 100–120°C. It was found that the solvent-induced γ-form was transformed to β-form at 125°C via a solid-to-solid transformation mechanism. In addition, WAXD showed that γ- and β-forms co-existed in the temperature range of 100–125°C. These mixed crystal forms were further identified using TEM, and the selected-area electron diffraction (ED) patterns revealed that both γ- and β-form crystals co-existed and were packed within the same spherulite. Solid–solid transformation from the solvent-induced γ-form to β-form in PHT upon heat scanning was presented with evidence and discussed.

Structural Evolution Process in Solvent‐Induced Crystallization Phenomenon of Syndiotactic Polystyrene

AbstractStructural change has been traced in the solvent‐induced crystallization phenomenon of syndiotactic polystyrene through the time‐resolved measurements of infrared and Raman spectra and X‐ray diffraction. Immediately after the solvent is supplied to the glassy sample, the random coils start a micro‐Brownian motion and locally change to short regular helical segments after some induction time. These segments grow longer and gather together to form the crystal lattice. This crystallization occurs even at room temperature far below the original glass transition temperature (Tg = ca. 100°C), because Tg is shifted to ca. −90°C (in the case of chloroform) due to the plasticizing effect, as revealed by the temperature‐dependent infrared spectral measurement and the molecular dynamics calculation. The thus‐created sPS‐solvent complex was found to show a fast and reversible solvent exchange phenomenon between the originally‐existing solvent (toluene, for example) and the newly‐supplied different type of solvent (chloroform, for example). The time‐dependent measurement of wide‐angle and small‐angle X‐ray scatterings using a synchrotron radiation source revealed that the solvent exchange occurs with keeping both the columnar structure of the crystal and the stacked lamellar structure, and that the solvent exchange rate is in the order of chloroform &gt; benzene &gt; toluene, reflecting the difference in diffusion rate of solvent molecules and polymer‐solvent interaction.

Study of Solvent Diffusion and Solvent-Induced Crystallization in Syndiotactic Polystyrene Using FT-IR Spectroscopy and Imaging

Kinetics of solvent diffusion (chloroform) and solvent-induced crystallization in syndiotactic polystyrene (sPS) were investigated by Fourier transform infrared (FT-IR) transmission imaging and sin...

Effect of compression and thickness on acetone transport in polycarbonate

We investigated the kinetics of acetone transport in polycarbonate (PC) under compression and with different thicknesses using the sorption experiment technique. A model combining Case I transport arising from concentration gradient and Case II transport driven by stress relaxation was employed to analyze the transport process. The sorption data are in good agreement with the theoretical prediction. Both the diffusion coefficient D of Case I and the velocity v of Case II transport satisfy the Arrhenius equation. The activation energies of D and v are higher in the stress-free PC than in PC subjected to compression. The activation energies increase with decreasing specimen thickness. The calculated heat of mixing is −5.1 kJ/mol for both the stress-free sample and the sample subjected to compression at 196 MPa, and −8.4 kJ/mol for the sample subjected to compression at 294 MPa. However, the calculated mixing heats are almost the same regardless of specimen thickness. FTIR spectra show no new absorbance peak when the PC is exposed to acetone. The solvent-induced crystallization is confirmed using FTIR spectra. A periodical stripe pattern is observed on the surface when a sample of thickness less than 0.8 mm is exposed to acetone at temperatures greater than 20°C. POLYM. ENG. SCI., 45:687–693, 2005. © 2005 Society of Plastics Engineers