Solutions In Good Solvents Research Articles

Nanoprecipitation through solvent-shifting using rapid mixing: Dispelling the Ouzo boundary to reach large solute concentrations

HypothesisThe addition of a non-solvent to a solute in good solvent solution leads to nanoprecipitation, which is the spontaneous formation of nanodomains. Yet, increasing solute concentration usually leads to the formation of macrodomains that quickly separate into a bulk phase, which is a severe process limitation. The corresponding concentration threshold, often termed as the Ouzo boundary, remains a mystery that could find its origin in the complex interplay between nanoprecipitation and mixing. ExperimentsWe performed a systematic investigation of nanoprecipitation thermodynamics and kinetics as well as its interplay with mixing hydrodynamics for the hexadecane-acetone-water system, in the presence of the non-ionic C16EO8 surfactant. The binodal curve and its underlying tie-lines were obtained using Raman spectroscopy, allowing the computation of the spinodal curve. Kinetics were probed using a continuous flow setup that combines two sequential rapid mixers. The impact of mixing efficiency was probed systematically by varying the oil concentration for respectively slow and rapid mixing, while the uncoupling from mixing and nanoprecipitation was quantified by modifying systematically the flow rate in a continuous flow approach. FindingsWe elucidate the nature of the Ouzo boundary that marks the maximal solute concentration leading to nanoobjects. Rather than a thermodynamic boundary, as evidenced by its uncorrelation to the spinodal curve, it results from the coupling of nanoprecipitation and mixing when both processes occur within the same time range, leading to heterogeneous conditions and the escape of some objects to the macroscale. Increasing the solute concentration speeds up nanoprecipitation and thus requires increasingly faster mixing times to uncouple both processes. Accordingly, if the mixing efficiency is large enough, it is possible to dispel the Ouzo boundary and reach very large solute concentrations. Implementing rapid mixing strategies in continuous flow approaches is thus the solution to overcome the most stringent condition of nanoprecipitation and open the way to scale-up, while also providing efficient means to probe its fast mechanism. Overall, the simultaneous control of hydrodynamics and physical chemistry is thus key to boost up the Ouzo effect.

Conformation and Structure of Hydroxyethyl Cellulose Ether with a Wide Range of Average Molar Masses in Aqueous Solutions

The solution properties of a water-soluble chemically modified cellulose ether, hydroxyethyl cellulose (HeC), were examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide-angle neutron scattering (S-WANS), small-to-wide-angle X-ray scattering (S-WAXS) and viscometric techniques at 25 °C. The examined HeC samples had average molar substitution numbers ranging from 2.36 to 2.41 and weight average molar masses (Mw) that fell within a wide range from 87 to 1500 kg mol-1. Although the relationship between the determined radius of gyration (Rg) and Mw was described as Rg ∝ Mw~0.6, as is observed usually in flexible polymer solutions in good solvents, the observed scattering vector (q) dependencies of excess Rayleigh ratios were well interpreted using a rigid rod particle model, even in high-Mw samples. Moreover, the ratios of the formed particle length (L) evaluated assuming the model for rigid rods to the determined Rg showed the relationship LRg-1 ~ 3.5 irrespective of Mw and were close to those theoretically predicted for rigid rod particle systems, i.e., LRg-1 = 12. The observed SLS behavior suggested that HeC molecules behave just like rigid rods in aqueous solution. As the L values were not simply proportional to the average molecular contour length calculated from the Mw, the chain conformation or structure of the formed particles by HeC molecules in aqueous solution changed with increasing Mw. The q dependencies of excess scattering intensities observed using the S-WANS and S-WAXS experiments demonstrated that HeC molecules with Mw less than 200 kg mol-1 have a diameter of ~1.4 nm and possess an extended rigid rod-like local structure, the size of which increases gradually with increasing Mw. The observed Mw dependencies of the translational and rotational diffusion coefficients and the intrinsic viscosity of the particle suspensions strongly support the idea that the HeC molecules behave as rigid rod particles irrespective of their Mw.

Photophysical properties of a coumarin amide derivative and its sensing for hypochlorite

A coumarin amide-pyrene derivative 1 as fluorescence probe for hypochlorite ions (ClO−) was developed. The UV–vis absorption and fluorescent properties of the compound in various microenvironment including different solvents and solid state were discussed. The compound has obvious yellow fluorescence in powder state, poor solvent H2O and weak fluorescence in good solvent solution. The weak fluorescence may be derived from weak intramolecular charge transfer process. The compound could specifically recognize ClO−) in aqueous solution with high selectivity and anti-interference. The sensing mechanism is that amide bond is hydrolyzed by ClO− to give 1-amino pyrene with bright blue fluorescence. The probe also can detect ClO− in 84 liquid disinfectant and actual water samples.

Universal Equation of State Describes Osmotic Pressure throughout Gelation Process.

The equation of state of the osmotic pressure for linear-polymer solutions in good solvents is universally described by a scaling function. We experimentally measure the osmotic pressure of the gelation process via osmotic deswelling. We find that the same scaling function for linear-polymer solutions also describes the osmotic pressure throughout the gelation process involving both the sol and gel states. Furthermore, we reveal that the osmotic pressure of polymer gels is universally governed by the semidilute scaling law of linear-polymer solutions.

Synthesis of Polymer Single-Chain Nanoparticle with High Compactness in Cosolvent Condition: A Computer Simulation Study.

Polymeric single-chain nanoparticles (SCNPs) are soft nano-objects synthesized by intramolecular crosslinking of isolated single polymer chains. Syntheses of such SCNPs usually need to be performed in a dilute solution. In such a condition, the bonding probability of the two active crosslinking units at a short contour distance along the chain backbone is much higher than those which are far away from each other. Such a reaction condition often results in local spheroidization and, therefore, the formation of loosely packed structures. How to inhibit the local spheroidization and improve the compactness of SCNPs is thus a major challenge for the syntheses of SCNPs. In this study, computer simulations are performed and the fact that a precollapse of the polymer chain conformation in a cosolvent condition can largely improve the probability of the crosslinking reactions at large contour distances is demonstrated, favoring the formations of closely packed globular structures. As a result, the formed SCNPs can be more spherical and have higher compactness than those fabricated in ultradilute good solvent solution in a conventional way. It is believed this simulation work can provide a insight into the effective syntheses of SCNPs with spherical conformations and high compactness.

Communication: A comparison between the solution properties of knotted ring and star polymers.

We computationally investigate the good solvent solution properties of knotted ring and star polymers by combining molecular dynamics (MD) simulation and path-integral calculations. We consider knotted rings having a minimal crossing number m c in the range, 0 ≤ m c ≤ 9, and star polymers having a range of f star arms, 2 ≤ f ≤ 20, attached to a common core monomer particle. After generating configurational ensembles of these polymers by MD, we use the path-integration program ZENO to calculate basic configurational properties, i.e., radius of gyration, hydrodynamic radius, intrinsic viscosity, as well as fluctuations in these properties. Our simulations indicate that the configurational properties of knotted rings and star polymers in solution show a similar decrease with increasing m c and f. Moreover, fluctuations in these properties also decrease with increasing topological complexity. Our findings should be helpful in polymer characterization and more generally for understanding the role of polymer topology in polymer material properties.

Kinetics of Light-Induced Concentration Patterns in Transparent Polymer Solutions.

When exposed to weak visible laser light, solutions of common polymers like poly(isoprene) and poly(butadiene) respond by local concentration variations, which in turn lead to refractive index changes. Various micropatterns have been recently reported, depending mostly on the solvent environment and the irradiation conditions. Here, we focused on the simpler case of single polymer-rich filaments and we employed phase contrast microscopy to systematically investigate the influence of laser illumination and material parameters on the kinetics of the optically induced local concentration increase in the polydiene solutions. The refractive index contrast of the formed filaments increased exponentially with the laser illumination time. The growth rate exhibited linear dependence on the laser power and increased with polymer chain length in semidilute solutions in good solvents. On the contrary, the kinetics of the formed filaments appeared to be rather insensitive to the polymer concentration. Albeit the origin of the peculiar light field-polymer concentration coupling remains yet elusive, the new phenomenology is considered necessary for the elucidation of its mechanism.

Blue-emitting poly(1,1′-binaphthol butyl ether) nanospheres via the nonsolvent vapor method

Under nonsolvent vapor atmospheres, poly(1,1′-binaphthol butyl ether) nanospheres can be self-assembled from various good solvent solutions. To obtain the optimized assembling parameters, the factors such as the solvents and the polymer concentrations, on the formation of polymeric nanospheres were investigated. The choice of good solvent and nonsolvent is an important factor. The well-ordered nanospheres with the sizes of hundreds nm can be easily obtained from the preparation combinations such as CH2Cl2/MeOH vapor, CHCl3/MeOH vapor, CHCl3/EtOH vapor, and THF/EtOH vapor. Moreover, the increasing polymer concentration leads to the increasing spherical agglomerations. The static water contact angles of the films with polymeric spheres were measured to be above 130°. With the excitation wavelength of 371 nm, the polymeric nanospheres showed the blue emission with the peak at 480 nm. The nonsolvent vapor method is a facile way to prepare polymeric nanospheres.

Quantification of Nanoparticle Interactions in Pure Solvents and a Concentrated PDMS Solution as a Function of Solvent Quality

Using turbidity measurements, we quantified the interactions between PDMS-grafted silica nanoparticles (PDMS-g-silica) in pure solvents and a concentrated polymer solution with a focus on detecting the impact of solvent quality on graft layer stretching. This work is an extension of our previous work where we showed that interfacial wetting of the grafted polymer leads to depletion restabilization in semidilute and concentrated polymer solutions in good solvents (Dutta, N.; Green, D. Langmuir 2008, 24, 5260-5269). Subsequently, we showed that the criterion for depletion restabilization holds for both good and marginally poor solvents (Dutta, N.; Green, D. Langmuir 2010, 26, 16737-16744). In this work, we quantified nanoparticle interactions in terms of the second virial coefficient (B2), which captures the stretching of the brush in a good solvent in comparison to compression in a poor solvent. The transition from stretching to compression of the graft layer as a function of solvent quality was also supported by self-consistent mean-field (SCF) calculations. The PDMS-g-silica nanoparticles in a concentrated polymer solution in a good solvent within the complete wetting region behaved as though they were in a good solvent rather than in a polymer melt where on the basis of the SCF calculations the graft layers were expected to behave ideally. Overall, our results indicate that turbidity measurements can be used to determine the second virial coefficients for polymer-grafted nanoparticles in solvents and concentrated polymer solutions, and the relative values of the coefficients correspond well to those from theoretical calculations.

Formation of parallel aligned nano-fibrils of a donor–acceptor conjugated copolymer via controlling J-aggregates and post treatment

We increased the content of J-aggregates in poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2′ : 5′,2′′ : 5′′,2′′′-quaterthiophene](PDQT) solution by choosing appropriate solvents. It was found that the higher content of J-aggregates in solution in good solvents (i.e. CF) led to the formation of parallel aligned nano-fibrils. This morphological transition from the disordered domains to ordered ones could also occur after thermal treatment or solvent vapor annealing. Parallel aligned fibrils of PDQT formed in films via annealing at 200 °C for 20 min or solvent vapor annealing in a CF atmosphere with a relatively low vapor pressure for 24 hours. In the films filled with parallel aligned fibrils, the PDQT molecules adopted an edge-on orientation and the π–π stacking direction of molecules was perpendicular to the growth direction of fibrils. PDQT chains preferred to adopt the extended conformations without chain-folding due to the extremely rigid backbones. The intact conjugation planes of rigid PDQT chains with extended conformations allow the further growth of parallel aligned fibrils, which enhanced the connectivity between crystalline domains. The results in this work are thought to be helpful to improve the charge-carrier transport in PDQT films.

A theoretical study on the inverted phase formation in diblock copolymer solutions

The inverted phase, in which the swollen minority block plus solvent forms the continuous microdomain, has been frequently observed in block copolymer (BCP)∕preferential good solvent solutions in our previous experimental works. In this paper, self-consistent field theory is employed to study the formation of inverted phase in A-B BCP solutions. The parameters of both the BCP and solvent are studied. The results show that the characteristics of both the BCP and the solvent are responsible for the inverted phase formation. With the value of χ(AB)N (χ(AB) is the Flory interaction parameter between A and B blocks and N is the degree of the polymerization), the preferential affinity of the solvent for the minority block, or the solvent monomer size increasing, the existence window of the inverted phases enlarges. Meanwhile, we analyze and discuss the formation of the inverted phase in terms of the enthalpy interaction and entropy contribution of the solvent and the results suggest that both of them play important roles in the formation of inverted phase and the comparative importance of the two items depends on the solvent molecular size.

Consistent and transferable coarse-grained model for semidilute polymer solutions in good solvent

We present a coarse-grained model for linear polymers with a tunable number of effective atoms (blobs) per chain interacting by intra- and intermolecular potentials obtained at zero density. We show how this model is able to accurately reproduce the universal properties of the underlying solution of athermal linear chains at various levels of coarse-graining and in a range of chain densities which can be widened by increasing the spatial resolution of the multiblob representation, i.e., the number of blobs per chain. The present model is unique in its ability to quantitatively predict thermodynamic and large scale structural properties of polymer solutions deep in the semidilute regime with a very limited computational effort, overcoming most of the problems related to the simulations of semidilute polymer solutions in good solvent conditions.

Dynamics of Competitive Polymer Adsorption onto Planar Surfaces in Good Solvent

Adsorption of mixed polymer solutions in good solvent containing polymers of different chain length has been studied by applying simulation techniques on a coarse-grained bead-spring polymer model. Fully flexible polymers at varying bead-surface interaction strength and different combinations of flexible, semiflexible, and stiff polymers at a single bead-surface interaction strength have been examined. Monte Carlo simulation techniques have been employed to investigate static equilibrium properties and Brownian dynamic simulations to follow the dynamics of the adsorption process. The properties examined comprise the adsorbed number of polymers, adsorbed number of beads, bead density profiles, components of the polymer radius of gyration, tail, loop, and train configurations, and nematic bond order of adsorbed beads. The adsorption involves an initially independent adsorption of the two polymer types followed by competitive adsorption. The competitive adsorption is characterized by a maximum of the adsorbed amount and a desorption of the polymer with the smallest surface affinity and a continued, but reduced, growth of the adsorbed amount of the polymer with the largest surface affinity. The surface affinity difference between the two polymer types of different length increased with increasing bead-surface interaction. Furthermore, the surface affinity of a polymer initially decreased but then largely increased at increasing stiffness. As a consequence, a stiff short polymer was found to displace a 4-fold longer flexible polymer. The spatial extension of adsorbed polymers as characterized by the radius of gyration parallel and perpendicular to the surface of a polymer of a given flexibility was independent of the flexibility of the other polymer type. The fraction of beads in tails was increased and in trains reduced as the surface affinity of the dissimilar polymer type was raised. Finally, the adsorption layer of a stiff polymer possesses a nematic bond order. In mixed polymer systems, the nematic bond order of a given polymer type manifests a dependence on the flexibility of the other type.

Synthesis and Optical Properties of Chiral Polydiacetylenes

Chiral diacetylenes featuring ester and urethane groups are readily prepared from amino acids and diynediols. The ability of the butadiyne moiety to undergo topotactic polymerization is dependent on both the length of the chain to the urethane group and the size of the amino acid. In some cases, the polymerization proceeds as well as the well-studied achiral parent compound, 4BCMU. The polymers form yellow solutions in good solvents where the chains adopt a random-coil configuration. Addition of a nonsolvent changes the solution color to red as the chains adopt a helical conformation.

A Hole-Transporting Material with Controllable Morphology Containing Binaphthyl and Triphenylamine Chromophores

An organic compound with two triphenylamine moieties linked with binaphthyl at the 3,3'-positions (2,2'-dimethoxyl-3,3'-di(phenyl-4-yl-diphenyl-amine)-[1,1']-binaphthyl, TPA-BN-TPA) can be synthesized by Suzuki coupling. Amorphous and homogeneous films are obtained by either vacuum deposition or spin-coating from solution in good solvents, while single crystals are grown in an appropriate polar solvent. X-ray crystallography showed that a TPA-BN-TPA crystal is a multichannel structure containing solvent molecules in the channels. The intramolecular charge-transfer state resulting from amino conjugation effects is observed by solvatochromic experiments. The high glass-transition temperature (130 °C) and decomposition temperature (439 °C) of this material, in combination with its reversible oxidation property, make it a promising candidate as a hole-transport material for light-emitting diodes. With TPA-BN-TPA as the hole-transporting layer in an indium tin oxide/ TPA-BN-TPA/aluminum tris(8-hydroxyquinoline)/Mg:Ag device, a brightness of about 10100 cd m -2 at 15.6 V with a maximum efficiency of 3.85 cd A -1 is achieved, which is superior to a device with N,N'-di(1-naphthyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine as the hole-transporting layer under the same conditions. Other devices with TPA-BN-TPA as the blue-light-emitting layer or host for a blue dye emitter are also studied.

On the Supermolecular Structure of Fullerene C60 Solutions

Small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) techniques were used for investigation of fullerene C60 solutions in toluene and p‐xylene. On all SAXS curves, intensity decreases to some constant value of IC with increase of scattering angle. The value of IC depends on concentration non‐monotonically: it first slightly increases, then drops sharply to some minimal value, and then increases again. A qualitative explanation of such dependence is offered. It is supposed that the presence of fullerene C60 in solution suppresses thermal fluctuations of density in the solvent. In combination with the X‐ray data the results obtained for solutions of fullerene C60 by various others techniques (calorimetry, densimetry, etc.) are discussed. Possible models of a supermolecular structure of fullerene C60 solutions in good solvents are considered.

Interaction parameter (chi); expansion factor (epsilon); steric hindrance factor (sigma); and shielding function F(xi); for the system PEA-organic solvents by intrinsic viscosity measurements

In this work we present experimental data of the Flory binary interaction parameter, chi, of poly (ethylene adipate) PEA, a plasticizer material. We have used the viscometric method for measuring dilute PEA solutions in good solvents: benzene, chloroform and acetone. A procedure based on the Stockmayer-Fixman, (SF), hydrodynamic solutions theory, allows us to evaluate some thermodynamic parameters via the intrinsic viscosity [eta], measured in several good solvents. This method also estimates the unperturbed parameter, ktheta, and the steric hindrance parameter, (sigma), by viscosity measurements at constant temperature of 30ºC. By correlation of the molecular weight (M) and intrinsic viscosity data, according to the Stockmayer-Fixman (SF) solution theory model, values of Flory binary interaction parameter chi, equal to chi1,2 =0.1544 ± 0.01; chi1,2 =0.1631 ± 0.01; and chi1,2 =0.1922 ± 0.01, for PEA in benzene, chloroform and acetone, respectively, were obtained. In addition we applied the Debye-Bueche theory, in order to estimate values of: expansion factor (epsilon), shielding factor (xi) and depth of shielding (L) for the system PEA-organic solvents, by [eta] and (M) experimental data correlation. The results confirm that values obtained, correspond to "good solvents" for the PEA polymer.

Brownian Motion of Colloidal Spheres in Aqueous PEO Solutions

The Brownian motion of colloidal spheres in aqueous poly(ethylene oxide) (PEO) solutions ranging in concentration from 0.2 to 15 wt % is measured with diffusing wave spectroscopy over more than 6 decades of time. The measured colloidal sphere mean-squared displacements are shown to satisfy the generalized Stokes−Einstein relation that relates the particle mean-squared displacement to the polymer solution shear modulus as the microrheological creep compliance calculated from the colloidal sphere Brownian motion was found to agree with that measured by mechanical rheometry. The microrheological zero shear viscosity concentration dependence for the entangled solution regime, η ∼ c4.7, is in agreement with that reported by others from mechanical rheometry measurements on polymer−good solvent solutions and is stronger than the tube model prediction, η ∼ c3.9. Essentially the entire deviation between the predicted and measured entangled solution regime zero shear viscosity concentration dependence is accounted ...

Conformations and solution structure of polyelectrolytes in poor solvent

AbstractUsing extensive Molecular Dynamics (MD) simulations we study the behavior of polyelectrolytes in poor solvents, where we take explicitely care of the counterions. The resulting pearl‐necklace structures are subject to strong conformational fluctuations, only leading to small signatures in the form factor, which is a severe obstacle for experimental observations. In addition we study how the necklace collapses as a function of Bjerrum length. At last we demonstrate that the position of the first peak in the inter‐chain structure factor varies with the monomer density close to $ρ^{1/3}_{m}$ for all densities. This is in strong contrast to polyelectrolyte solutions in good solvent.

Viscosity of Polyelectrolyte Solutions with Oppositely Charged Surfactant

The rheological properties of aqueous solutions of poly(acrylic acid) and an oppositely charged surfactant, dodecyltrimethylammonium bromide (C12TAB), are reported. The solution viscosity decreases rapidly as surfactant is added. The effects of polymer molecular weight, polymer concentration, and polymer charge have been studied with no added salt. The results are compared with the predictions of a simple model based on the scaling theory for the viscosity of unentangled semidilute polyelectrolyte solutions in good solvent.1 This model takes into account two effects of added surfactant. The effective chain length of the polyelectrolyte is shortened when a significant fraction of the length wraps around micelles, and an effective addition of salt arises from the polyelectrolyte and surfactant counterions, further lowering the viscosity. The only parameter used in this model is independently determined using an ion-selective electrode, allowing the model to make a quantitative prediction of solution viscosity for strongly charged polyelectrolytes with no adjustable parameters. Comparison with literature data for weakly charged polyelectrolytes suggests only partial binding of polymer to the micelle surface in this case.