Effect Of Solvent Quality Research Articles

Effect of solvent quality and sidechain architecture on conjugated polymer chain conformation in solution.

Conjugated polymers (CPs) are solution-processible for various electronic applications, where solution aggregation and dynamics could impact the morphology in the solid state. Various solvents and solvent mixtures have been used to dissolve and process CPs, but few studies have quantified the effect of solvent quality on the solution behavior of CPs. Herein, we performed static light scattering and small-angle X-ray scattering combined with molecular dynamics (MD) simulation to investigate CP solution behaviors with solvents of varying quality, including poly(3-alkylthiophene) (P3ATs) with various sidechain lengths from -C4H9 to -C12H25, poly[bis(3-dodecyl-2-thienyl)-2,2'-dithiophene-5,5'-diyl] (PQT-12) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-12). We found that chlorobenzene is a better solvent than toluene for various CPs, which was evident from the positive second virial coefficient A2 ranging from 0.3 to 4.7 × 10-3 cm3 mol g-2 towards P3ATs. For P3ATs in non-polar solvents, longer sidechains promote more positive A2, indicating a better polymer-solvent interaction, wherein A2 for toluene increases from -5.9 to 1.4 × 10-3 cm3 mol g-2, and in CB, A2 ranges from 1.0 to 4.7 × 10-3 cm3 mol g-2 when sidechain length increases from -C6H13 to -C12H25. Moreover, PQT-12 and PBTTT-12 have strong aggregation tendencies in all solutions, with an apparent positive A2 (∼0.5 × 10-3 cm3 mol g-2) due to multi-chain aggregates and peculiar chain folding. These solvent-dependent aggregation behaviors can be well correlated to spectroscopy measurement results. Our coarse-grained MD simulation results further suggested that CPs with long, dense, and branched sidechains can achieve enhanced polymer-solvent interaction, and thus enable overall better solution dispersion. This work provides quantitative insights into the solution behavior of conjugated polymers that can guide both the design and process of CPs toward next-generation organic electronics.

Solvent Quality and Aggregation State of Asphaltenes on Interfacial Mechanics and Jamming Behavior at the Oil/Water Interface.

The formation of highly stable water-in-oil emulsions results in complications in both upstream and downstream processing. Emulsion stability in these systems has been connected to the adsorption of surface-active asphaltenes that are assumed to form a rigidified film at the oil/water (o/w) interface. Full characterization of this behavior is needed to allow for engineered solutions for enhanced oil recovery. Interfacial properties, such as surface pressure and interfacial elasticity, are implicated in the stabilizing mechanism for these observed films. Asphaltenes are known to be interfacially active in both good solvents (aromatics) and poor solvents (high ratio of aliphatic to aromatic). However, due to inherent complexities present in asphaltene studies, the details of the mechanical properties of the interface remain poorly understood. Despite the widely accepted perception that asphaltenes form persistent rigid films at fluid-fluid interfaces, the connection between bulk solution properties and interfacial mechanics has not been resolved. Here, the effects of solvent quality on the interfacial properties of asphaltene dispersions are determined by using a well-defined asphaltene/solvent system. Interfacial rigidity is observed only under poor solvent conditions, while the good solvent system remains fluid-like. The interfacial rheology under good and poor solvent conditions is measured simultaneously with surface pressure measurements to track interfacial development. It is shown that surface pressure and dilatational modulus measurements are not indicators of whether an interface demonstrates rigid behavior under large compressions. Finally, conditions required for asphaltene-coated interfaces to exhibit the mechanical behavior associated with a rigidified interface are defined. This work provides a framework for quantifying the impact of the aggregation state of asphaltenes on the stability and mechanics at the o/w interface.

Effect of solvent quality on covalent bonds cleavage behaviors of lignite during pyrolysis/liquefaction processes

Effect of solvent quality on coal conversion and product distribution during lignite pyrolysis/liquefaction were investigated at the temperatures ranging from 180 to 460 °C, and the covalent bond cleavage behaviors in different solvents were comparatively elucidated. Results showed that at the temperatures below 280 °C, weak covalent bonds, such as methoxy and carboxyl groups, are cleaved to generate a small amount of gaseous products (mainly CO2) and liquefied oil. At the temperatures of 330–380 °C, ether bridges that connecting the aromatic clusters are cleaved and contributed significantly to the production of preasphaltene (PA). Meanwhile, oil yield and coal conversion increased to 27.50% and 64.58% in tetralin. At the temperatures of 430–460 °C, the cleavage of CH2 bridges, alkyl substituent groups and aromatic heterocyclic structures proceeded markedly, and the scission of CH2 bridges and some naphthenic CH2 bonds significantly contributed to oil production. Consequently, oil yield and coal conversion greatly increased to 43.90% and 84.13% in tetralin. Hydrogen donor solvent is conducive to the cleavage of strong covalent bonds, such as Car–O–Car and Car-Cal bonds, to realize the efficient liquefaction of coal.

Effects of solvent conditions on the self-assembly of heterotrimeric collagen-like peptide (CLP) triple helices: a coarse-grained simulation study.

We perform coarse-grained (CG) molecular dynamics (MD) simulations to investigate the self-assembly of collagen-like peptide (CLP) triple helices into fibrillar structures and percolated networks as a function of solvent quality. The focus of this study is on CLP triple helices whose strands are different lengths (i.e., heterotrimers), leading to dangling 'sticky ends'. These 'sticky ends' are segments of the CLP strands that have unbonded hydrogen-bonding donor/acceptor sites that drive heterotrimeric CLP triple helices to physically associate with one another, leading to assembly into higher-order structures. We use a validated CG model for CLP in implicit solvent and capture varying solvent quality through changing strength of attraction between CG beads representing the amino acids in the CLP strands. Our CG MD simulations show that, at lower CLP concentrations, CLP heterotrimers assemble into fibrils and, at higher CLP concentrations, into percolated networks. At higher concentrations, decreasing solvent quality causes (i) the formation of heterogeneous network structures with a lower degree of branching at network junctions and (ii) increases in the diameter of network strands and pore sizes. We also observe a nonmonotonic effect of solvent quality on distances between network junctions due to the balance between heterotrimer end-end associations driven by hydrogen bonding and side-side associations driven by worsening solvent quality. Below the percolation threshold, we observe that decreasing solvent quality leads to the formation of fibrils composed of multiple aligned CLP triple helices, while the number of 'sticky ends' governs the spatial extent (radius of gyration) of the assembled fibrils.

Effect of Solvent Quality on Structure and Dynamics of Lignin in Solution.

Due to its significant aromatic content, lignin is an attractive source of valuable organic chemicals. As most of the proposed lignin depolymerization processes are expected to be liquid-phase, it is necessary to understand the effect of solvent quality on the structure and dynamics of lignin. Here we use all-atom molecular dynamics simulations to understand the evolution of lignin structure as a function of methanol concentration in methanol/water solution at different temperatures. We utilize two different lignin models: softwood consisting of guaiacyl (G) monomer and hardwood consisting of heteropolymer containing guaiacyl/syringyl (S) with a 1.35:1 ratio. The presence of additional methoxy groups in the hardwood lignin leads to a more extended configuration than softwood lignin with increasing methanol concentration. Structural features (radius of gyration and solvent accessible surface area) of lignin correlate with the strength of intermolecular forces quantified using cohesive energy density. We find that methanol preferentially solvates the nonpolar segments of the lignin polymer while water molecules solvate the polar functional groups. Thus, as the methanol concentration increases, methanol can better solvate lignin polymer, leading to a more extended configuration suitable for catalytic transformation to value-added chemicals.

On the formation and stability of cellulose-based emulsions in alkaline systems: Effect of the solvent quality

With amphiphilic properties, cellulose molecules are expected to adsorb at the O/W interface and be capable of stabilizing emulsions. The effect of solvent quality on the formation and stability of cellulose-based O/W emulsions was evaluated in different alkaline systems: NaOH, NaOH-urea and tetrabutylammonium hydroxide (TBAH). The optimal solvency conditions for cellulose adsorption at the O/W interface were found for the alkaline solvent with an intermediate polarity (NaOH-urea), which is in line with the favorable conditions for adsorption of an amphiphilic polymer. A very good solvency (in TBAH) and the interfacial activity of the cation lead to lack of stability because of low cellulose adsorption. However, to achieve long-term stability and prevent oil separation in NaOH-urea systems, further reduction in cellulose's solvency was needed, which was achieved by a change in the pH of the emulsions, inducing the regeneration of cellulose at the surface of the oil droplets (in-situ regeneration).

Modeling short-chain branched polyethylenes in dilute solution under variable solvent quality conditions: Basic configurational properties

We perform molecular dynamics (MD) simulations of a coarse-grained model of linear low-density polyethylenes (LLDPEs) having short-chain branching in an implicit solvent and calculate basic configurational properties (radius of gyration Rg, hydrodynamic radius Rh, and intrinsic viscosity [η]) using the path-integration program ZENO. Solvent quality effects in our model are accounted for through the introduction of an attractive polymer-polymer interaction potential with solvent quality “strength” λ that is tuned from a “good” solvent limit, where the inter-polymer interactions are purely repulsive, to a “very poor” solvent regime, where the polymers collapse due to their self-attractive intermolecular interactions. We also identify a compensation condition or “θ point” in our model between these limits, where the polymers are “ideal” in the sense in which attractive interactions effectively nullify inter-polymer repulsions so that the chains behave akin to Gaussian polymer chains in their average conformational properties. In order to compare with experiments performed under variable solvent conditions, we define a dimensionless measure of excluded volume interaction parameter δ in terms of the mass scaling exponent ν for Rg or νh for Rh, which can be determined from both experiment and simulation. We illustrate our variable solvent approach to estimate polymer solution properties in the case of polyethylenes (PEs) and evaluate the δ value that corresponds to the experimental solvent conditions. Our combined use of MD and ZENO allows for the numerical estimation of polymer solution properties for polymers having general monomer structures and solvent qualities in a computationally tractable fashion and should be useful as a general computational tool for polymer structural characterization.

Effect of Solvent Quality on the Phase Behavior of Polyelectrolyte Complexes

The role of polyelectrolyte–solvent interactions, among other non-Coulomb interactions, in dictating the thermodynamics and kinetics of polyelectrolyte complexation is prominent yet sparingly studi...

Variable temperature asymmetric flow field-flow fractionation for the topology separation of poly(methyl methacrylate)

Size exclusion chromatography is the method of choice for the molar mass analysis of polymers, however, it is not selective towards polymer microstructure. Counterintuitively, asymmetric flow field-flow fractionation (AF4), a channel-based molar mass analysis technique, has been shown to be able to fractionate poly(methyl methacrylate (PMMA) according to tacticity. This was revealed by investigating the solution behaviour of syndiotactic- (s-PMMA), atactic- (a-PMMA) and isotactic (i-PMMA) poly(methyl methacrylate) of similar molecular masses in solvents with different thermodynamic properties. In addition to developing a selective fractionation method, the effects of solvent quality and channel temperature on the fractionation were investigated. It was concluded that the thermodynamic quality of the carrier liquid has a significant influence on the retention behaviour of polymers in AF4. It was shown that the separation of s-PMMA and i-PMMA can be improved by using a theta solvent (acetonitrile) as the carrier liquid instead of thermodynamically good solvents such as tetrahydrofuran and chloroform. In addition, it was found that by using a non-stereocomplexing solvent for PMMA, such as chloroform, blends of s-PMMA and i-PMMA can be separated. Lastly, it was established that the AF4 channel temperature has an influence on the retention behaviour of the PMMA samples. For THF as carrier liquid it was found that the maximum difference in retention between s-PMMA and i-PMMA can be achieved at a channel temperature of 35 °C. In the case of ACN being the carrier liquid, it was observed that the retention behaviour of i-PMMA was significantly more influenced by a change in temperature as compared to s-PMMA and a-PMMA.

Compression and swelling of hydrogels in polymer solutions: A dominant-mode model.

The swelling and compression of hydrogels in polymer solutions can be understood by considering hydrogel-osmolyte-solvent interactions which determine the osmotic pressure difference between the inside and the outside of a hydrogel particle and the changes in effective solvent quality for the hydrogel network. Using the theory of poroelasticity, we find the exact solution to hydrogel dynamics in a dilute polymer solution, which quantifies the effect of diffusion and partitioning of osmolyte and the related solvent quality change to the volumetric changes of the hydrogel network. By making a dominant-mode assumption, we propose a model for the swelling and compression dynamics of (spherical) hydrogels in concentrated polymer solutions. Osmolyte diffusion induces a biexponential response in the size of the hydrogel radius, whereas osmolyte partitioning and solvent quality effects induce monoexponential responses. Comparison of the dominant-mode model to experiments provides reasonable values for the compressive bulk modulus of a hydrogel particle, the permeability of the hydrogel network, and the diffusion constant of osmolyte molecules inside the hydrogel network. Our model shows that hydrogel-osmolyte interactions can be described in a conceptually simple manner, while still capturing the rich (de)swelling behaviors observed in experiments. We expect our approach to provide a roadmap for further research into and applications of hydrogel dynamics induced by, for example, changes in the temperature and the pH.

A correspondence between the Flory–Rehner theory for microgels and the Daoud–Cotton model for polymer-grafted nanoparticles

Poly(N-isopropyl acrylamide) (PNIPAM) is a commonly investigated thermoresponsive polymer that exhibits a number of interesting physical behaviors. Here, we use small-angle neutron scattering (SANS) measurements to determine the conformation of PNIPAM in two regions of the chain when it is grafted at moderate grafting densities to the surface of SiO2 nanoparticles (rNP ≈ 10 nm). At these grafting densities, polymer chains may adopt two primary conformations, depending on the specific value of the second virial coefficient, the molecular weight of the chains, and other properties. The nanoparticles are studied in D2O and ethanol-d6 to ascertain the effect of solvent quality on the chain conformation in both the inner and outer regions of the brush. The SANS measurements are interpreted using a modified Daoud–Cotton model that connects the Flory–Rehner theory of microgel thermodynamics to the structure of polymer-grafted nanoparticles.

Approaches to Understanding the Solution-State Organization of Spray-Dried Dispersion Feed Solutions and Its Translation to the Solid State

It is well established that polymers adopt a range of conformations and solution-state organization in response to varying solution environments, although very little work has been done to understand how these effects might impact the physical stability and bioavailability of spray-dried amorphous dispersions (SDDs). Potentially relevant solution-state polymer-solvent/cosolute interactions include preferential solvation, hydrodynamic size (i.e., polymer swelling or collapse), and solvent quality effects (i.e., attractive or repulsive self-interactions). Of particular interest is the investigation of preferential solvation, defined as the relative attraction or rejection of a cosolvent and/or cosolute from the local environment of a solvated macromolecule, which often occurs in multicomponent macromolecular solutions. As spray drying and other solvent-based dispersion processing necessitates the use of complex media consisting of at least three or more components (drug, polymer, solvent(s), and other possible excipients), the prevalence of this phenomenon is likely. This work characterizes largely unexplored solution-state properties in model spray-dried dispersion feed solutions using light scattering and viscometric techniques to add greater context and guidance in studying these information-rich materials. These systems are found to exhibit complex non-intuitive behavior, which serves to highlight the potential utility of preferential solvation in spray-dried dispersion processing and stability. It is hypothesized that solution-state organization of the liquid feed can be engineered and translated to the solid-state for the optimization of SDD properties.

The effect of solvent quality on pathway-dependent solution-state self-assembly of an amphiphilic diblock copolymer

The cholesterol-functionalized polycarbonate-based diblock copolymer, PEG113-b-P(MTC-Chol)30, forms pathway-dependent nanostructures via dialysis-based solvent exchange. The initial organic solvent that dissolves or disperses the polymer dictates a self-assembly pathway. Depending upon the initial solvent, nanostructures of disk-like micelles, exhibiting asymmetric growth and hierarchical features, are accessible from a single amphiphilic precursor. Dioxane and tetrahydrofuran (THF) molecularly dissolve the block copolymer, but THF yields disks, while dioxane yields stacked disks after dialysis against water. Dimethylformamide and methanol display dispersed disks and then form stacked disk structures after dialysis. The path-dependent morphology was correlated to solubility parameters, an understanding of which offers routes to tailor self-assemblies with limited sets of building blocks.

Electrostatic expansion of polyelectrolyte microgels: Effect of solvent quality and added salt

We report dynamic light scattering data for a PNIPAM based microgel copolymerised with 2% ionic groups. The hydrodynamic radius is measured as a function of temperature (which varies the solvent quality) and added salt concentration (cS) from salt-free conditions up to cS = 0.1 M. Incorporation of the ionic co-monomer leads to an increase of the volume phase transition temperature with respect to a non-ionic microgel from T≃306 K to T≃317 K in salt-free water. The hydrodynamic radius varies as RH∝cS-0.05 in good solvent (T≃278–298 K) and RH∝cS-0.15 in poor solvent (T≃313–319 K). Deep into the poor solvent regime the microgel is collapsed for all salt concentrations and RH∝cS0. Data are fitted to the Flory-Rehner model modified to account for the osmotic pressure of the counterions through the Donnan model. We find that the Flory-Rehner-Donnan (FRD) model does not fully account for the experimental observations, particularly at low ionic strengths, possibly due to the influence of electrostatic excluded volume. The disagreements between theory and experiments are greatly reduced if a cross-linking density three times lower than that expected from synthesis is assumed. The scaling theory exponents for the variation of gel size with temperature and added salt are not in agreement with the experimental results presented.

Effects of solvent quality and non-equilibrium conformations on polymer translocation.

The conformation and its relaxation of a single polymer depend on solvent quality in a polymer solution: a polymer collapses into a globule in a poor solvent, while the polymer swells in a good solvent. When one translocates a polymer through a narrow pore, a drastic conformational change occurs such that the kinetics of the translocation is expected to depend on the solvent quality. However, the effects of solvent quality on the translocation kinetics have been controversial. In this study, we employ a coarse-grained model for a polymer and perform Langevin dynamics simulations for the driven translocation of a polymer in various types of solvents. We estimate the free energy of polymer translocation using steered molecular dynamics simulations and Jarzynski's equality and find that the free energy barrier for the translocation increases as the solvent quality becomes poorer. The conformational entropy contributes most to the free energy barrier of the translocation in a good solvent, while a balance between entropy and energy matters in a poor solvent. Interestingly, contrary to what is expected from the free energy profile, the translocation kinetics is a non-monotonic function of the solvent quality. We find that for any type of solvent, the polymer conformation stays far away from the equilibrium conformation during translocation due to an external force and tension propagation. However, the degree of tension propagation differs depending on the solvent quality as well as the magnitude of the external force: the tension propagation is more significant in a good solvent than in a poor solvent. We illustrate that such differences in tension propagation and non-equilibrium conformations between good and poor solvents are responsible for the complicated non-monotonic effects of solvent quality on the translocation kinetics.

Effect of solvent quality on Poiseuille flow of polymer solutions in microchannels: A dissipative particle dynamics study

ABSTRACTThe Poiseuille flows of polymer solutions for varying quality solvents in microchannels have been simulated using dissipative particle dynamics. In particular, the velocity distributions and the polymer migration across the channel have been investigated for good, athermal, and poor solvents. The velocity profiles for all three kinds of solvent deviate from the parabolic profile, and the velocity profile of the athermal solvent falls in between the good solvent and the poor solvent. For the athermal solvent, a migration away from the wall due to the hydrodynamic interactions between the chains and the wall is observed, and a migration away from the channel center due to the different chain Brownian diffusivities is also observed. For the good solvent, because of the more stretched polymer chains, the migration away from the wall is stronger than that for the athermal solvent. However, the migration away from the channel center is not observed for good solvents. For the poor solvent, the hydrodynamic interaction within the chains is screened, and the polymer chains migrate toward the wall and appear to be absorbed by the wall. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47345.

Thermodynamic Analysis of Polymer Gel Elasticity

Elastomer and polymer gel have a three-dimensional polymer network structure and the characteristic of being soft and well extended (rubber elasticity). Many researches on rubber elasticity have been carried out mainly with elastomer since 1950's. Entanglement of network chains dominates the physical properties because elastomer contains almost no solvent, thus it is difficult to investigate the correlation between the structure and the physical properties in detail. On the other hand, polymer gel is a dilute system coexisting with solvent, thus it is possible to design various network structures with controlled entanglement. Recently, we developed Tetra-PEG gel, which is formed by AB-type polycondensation of tetra-armed prepolymers. Tetra-PEG gel has a highly homogeneous network structure, which is suitable for verifying the theory of polymer gel. In the previous study, Phantom network model, which is a rubber elasticity model, was verified. Phantom network model assumes that the crosslinks fluctuate with deformation, and elastic modulus (G) is described as G = ξk B T Here, k B is the Boltzmann constant, T is absolute temperature, and ξ is the number densities of independent cycles surrounded by the mesh chain. In tree-like approximation, ξ can be calculated from polymer concentration, polymer molecular weight, and connection probability between prepolymers. This equation indicates that one cycle has the influence of the thermal energy k B T on the elasticity. As a result of the verification using Tetra-PEG gel, it was confirmed for the first time in the world that the connection probability dependence of the elastic modulus and the calculated ξ (ξ th) was the same. This indicates that Phantom network model can describe the elasticity of polymer gel. However, the polymer concentration (C) dependence of them was different as shown in Figure 2. Here, the polymer concentration was normalized by the overlapping concentration (C*). The polymer concentration is a concept inherent to polymer gel, and it has not been considered so much in conventional researches. Therefore, we returned to thermodynamics, which is the origin of rubber elasticity models, and experimentally verified it. The elastic modulus from Helmholtz free energy is described as the following equation. G = U” + S”T The first term (U”) is referred to as energy elasticity, and the second term (S”T) as entropy elasticity. From this equation, it is shown that elastic modulus can be separated into energy elasticity and entropy elasticity by measuring temperature dependence of elastic modulus. Classical rubber elasticity theory ignores the energy elasticity and predicts that the elastic modulus is proportional to temperature (G ~ T). It has been experimentally confirmed that the proportional relationship is roughly correct in the case of elastomer. On the other hand, the elastic modulus of Tetra-PEG gel was not proportional to temperature, and the negative energy elasticity whose value cannot be ignored was measured (Figure 1). This result may indicate an essential difference between elastomer and polymer gel. Therefore, we further investigated the energy elasticity and entropy elasticity using Tetra-PEG gel with various network structures. When only the connection probability was changed, energy elasticity was proportional to entropy elasticity (U”~ S”T). Since in previous study it was shown that the connection probability dependence of the elastic modulus and ξ was the same, we found that the dependence of the entropy elasticity and the energy elasticity was also the same as ξ. Furthermore, the entropy elasticity had the same polymer concentration dependence as ξ, which shows that the entropy elasticity follows Phantom network model except the value. Therefore, this result also shows the different concentration dependence of the elastic modulus and ξ is derived from the energy elasticity (Figure 2). In the poster presentation, I will talk about the cause of energy elasticity and the effect of solvent quality of polymer gel, too. Figure 1

Effects of solvent quality on contact formation dynamics of polymer chain

We investigate the interplay effects of internal friction and solvent quality on the contact formation dynamics based on non-Markovian diffusion equation supplemented with an exponential sink term accounting for the electron transfer quenching. The mean contact formation time has been derived under Wilemski-Fixman approximation. We show that internal friction induces fractional viscosity dependence of looping time, which will be affected remarkably by solvent quality condition. Besides, internal friction promotes a diffusion-limited mechanism by slowing chain relaxation, while solvent quality being another key factor shifts the critical internal friction for the crossover of the transition from reaction to diffusion-limited regimes.

Nature and Extent of Solution Aggregation Determines the Performance of P(NDI2OD‐T2) Thin‐Film Transistors

AbstractHere the effect of solvent quality on the microstructure and organic field‐effect transistor (OFET) performance of thin films of the high mobility naphthalene‐diimide‐thiophene‐based n‐type semiconducting copolymer P(NDI2OD‐T2) is investigated. A strong correlation between OFET mobility and solvent quality is observed with average electron mobility increasing from 0.21 cm2 V−1 s−1 for samples prepared from tolerably good solvents to 0.56 cm2 V−1 s−1 for samples prepared from poor solvents, with a maximum electron mobility of 1.5 cm2 V−1 s−1 observed for transistors processed from toluene. The variation in transistor performance with solvent quality is linked to the nature and extent of the solution aggregation of P(NDI2OD‐T2) chains. Small angle X‐ray scattering measurements reveal elongated rod‐like aggregates up to 300 nm in length in solutions prepared using poor solvents, in contrast to more coil‐like chains with radius of gyration of ≈10–15 nm for solutions based on good to tolerably poor solvents. Thin films produced from decreasing solvent quality show an increase in the extent of correlated ordering of backbones and the degree of edge‐on orientation of polymer chains at the air/film interface. This work establishes the important link between solution‐phase chain aggregation behavior, thin‐film microstructure, and transistor performance in the P(DNI2OD‐T2) system.

Effect of solvent quality and humidity on the porous formation and oil absorbency of SAN electrospun nanofibers

ABSTRACTIn this study, nanofibrous mat with high oil sorption capability was prepared via one‐step electrospinning process without any further post‐treatments. For this purpose, the fabrication of styrene/acrylonitrile copolymer nanofibers was carried out using various dimethylformamide (DMF)/tetrahydrofuran and DMF/ethanol (DMF/EtOH) binary mixture ratios in an electrospining atmosphere with various relative humidity (RH) levels. Scanning electron microscope micrographs showed that DMF/tetrahydrofuran and DMF/EtOH ratio and RH value could considerably affect the diameter, surface, and interior morphology of the resultant nanofibers. The nanofiber morphology was dependent upon the polymer/solvent(s)/water ternary phase diagram behavior. In overall, the partial hydrophilicity of styrene/acrylonitrile copolymer resulted in electrospun nanofibers with wrinkled surface. In addition, the incorporation of nonsolvent in the spinning solution and using high RH atmosphere forced the polymeric solution jet to intensively phase separate and, therefore, produce the nanofibers with highly interior porous structure during drying process. The maximal capacity and rate of oil sorption (170 g/g) was observed for the nanofibrous mat prepared using EtOH/DMF (2/3: vol/vol) and RH value of 60% showing the highest internal porosity. The results showed that the oil sorption capability and mechanical strength of the fibrous mat are strongly dependent on nanofibers diameter and porous structure, which can be controlled through adjusting the RH and spinning solvent quality. The electrospun mat with highest Young's modulus (7.68 MPa) was prepared using EtOH/DMF (2/3) binary mixture and RH value of 45%. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45586.