Polymer Molecules In Solution Research Articles

Unraveling the Molecular Weight Dependence of High Magnetic Field to Manipulate the Semiconducting Polymer Molecular Orientation.

The magnetic alignment of molecules, which exploits the anisotropy of diamagnetic susceptibility, provides a clean and versatile approach to the structural manipulation of semiconducting polymers. Here, the magnetic-alignment dynamics of two molecular-weight (MW) batches of a diketopyrrolopyrrole (DPP)-based copolymer (PDVT-8) were investigated. Microstructural characterizations revealed that the magnetically aligned, high-MW (Mn = 53.7 kDa) PDVT-8 film exhibited a higher degree of backbone chain alignment and film crystallinity compared with the low-MW (Mn = 17.6 kDa) PDVT-8 film grown via the same magnetic alignment method. We found that as the MW increases, the degree of preaggregation of the polymer molecules in solution significantly increases and the aggregation mode changes from H-aggregation to J-aggregation through a cooperative assembly mechanism. These events improved the responsiveness of high-MW polymer molecules to magnetic fields. Field-effect transistors based on the magnetic aligned high-MW PDVT-8 films exhibited a 6.8-fold increase in hole mobility compared to the spin-coated films, along with a mobility anisotropy ratio of 12.6. This work establishes a significant correlation among chain aggregation behavior in solution, polymer film microstructures, magnetic responsiveness, and carrier transport performance in donor-acceptor polymer systems.

Determination of the Shape and Dimensions of the Polymer Molecules in Solutions Using Diffusional NMR Relaxation

Determination of the Shape and Dimensions of the Polymer Molecules in Solutions Using Diffusional NMR Relaxation

Soluble Unimolecular Polymer Nanoparticles by Crosslinking of Polyethylenimine with Isophthalaldehyde

Polyethylenimine (PEI) is a cationic polymer widely used in non-viral gene delivery systems and other polymer technologies. PEI with a MW of 25 kD was cross-linked in aqueous solution by the aromatic di-aldehyde isophthalaldehyde. This di-aldehyde cross-links PEI by forming stable imines with the primary amine groups in branched PEI. Cross-linking was evaluated at different concentrations of PEI using NMR, dynamic light scattering (DLS or QELS) and solvent extraction. It is demonstrated that isophthalaldehyde was able to cross-link PEI intramolecularly in solution near physiological pH resulting in the formation of unimolecular cross-linked nanoparticles. Proton NMR was used to examine the cross-linking reaction <i>in-situ</i>. The aldehyde resonance of isophthalaldehyde became broadened as cross-linking occurred. Organic-aqueous liquid-liquid extraction studies supported both that the cross-linking was intramolecular and that the cross-linked structures were stable to hydrolysis in water at neutral pH. As cross-linking occurred, the percentage of isophthalaldehyde that could be extracted from the solution was reduced. The molecular radii and aggregation behavior was monitored by QELS. The particle size of the polymer molecules in solution decreased with increased cross-linking, indicating the intra-molecular cross-linking between the PEI branches. These results clearly show that cross-linking of PEI with isophthalaldehyde creates soluble unimolecular polymer nanoparticles. These materials hold promise for a variety of applications in biotechnology.

The two-state reversible kinetics of a long polymer molecule in solution with a delocalized coupling term. An exact analytical model

We develop a mathematical recipe for calculating the exact delocalized rate constant, for the end loop motion of a long polymer. It undergoes reversible reaction between two disjunct states, the open and the closed state, due to the effect of the surrounding solvent. The Smoluchowski-like equation mathematically represents the diffusion of the end monomers of the open polymer chain and the closed chain in terms of a free particle performing random motion under different harmonic potentials. The coupling term between the two potentials is assumed to be represented by a delocalized coupling term. For a favorable disposition towards the more realistic experimental behavior, the rate constant have effect incorporated from all the bond making and bond breaking phenomenon of the chemical reactions different from the end loop formation. It not only involves the end looping but can evaluate for reactions where only one of the ends of the open-chain is involved.

Interpreting the looping rates of a polymer molecule in solution: Exact solution using a simple analytical method

Simple analytical method for intramolecular looping of long chain polymer has been formulated using Smoluchowski-like equation flanked by Dirac delta function sink term of finite strength. Solution for loop closure probability has been defined in terms of Laplace Transform of the Green’s function for different end motion of the polymer, in absence of sink. Two different rate constants, the average term and the long term rate constant which vary with several parameters has been derived. Our results are in agreement with that produced by detailed operator algebra method.

Understanding the reversible looping kinetics of a long chain polymer molecule in solution with Dirac Delta coupling. An exact analytical perspective.

In this article, we present an exact analytically solvable two state model for calculating the rate of reversible looping of a long chain polymer molecule in solution. In our two state model, one of the two states represent an open chain polymer molecule and the other state represents a closed chain.. One can quantitatively measure the kinetic parameters such as the rate constants, the long term rate constant and the average term rate constant of the reaction from macroscopic measurements like the length of the polymer, the bond length and the relaxation time. The dynamics of the end-to-end distance of both open chain and the closed chain polymer are represented by a Smoluchowski-like equation for a single particle doing random walk under the realm of two different harmonic potentials. The coupling between these two potentials are assumed to be a Dirac Delta function in our model. We have also incorporated the effect of all other chemical reactions involving at least one end of the open chain polymer molecule on the rate of end-to-end loop formation. The closed chain polymer molecule can be converted to an open-chain molecule by breaking any bond - the effect of these reactions on the rate of end-to-end loop formation as well as the rate involving one of the ends are also considered in our model.

Tuning the Viscoelasticity of Hydrogen-Bonded Polymeric Materials through Solvent Composition

The interactions between polymer molecules in solution are strongly affected by the way that the constituent polymers interact with the solvent. In this work, we use a mixed solvent system (dimethyl sulfoxide and ethylene glycol) to tailor the strength of the hydrogen-bonding interactions between partially quaternized poly(4-vinylpyridine) [QVP] and poly(methacrylic acid) [PMAA]. The charge introduced by the quaternization reaction enables homogeneous solutions to be formed over a large concentration range, even in the presence of attractive hydrogen-bonding interactions between the proton-donating PMAA and the proton-accepting QVP. The viscoelastic properties of equimolar QVP/PMAA solutions are superposed onto master curves that are well-described by a fractional Maxwell liquid model. This model provides a means for quantifying the dependence of the relaxation times on the solvent composition. These relaxation times increase by a factor of 1000 as the hydrogen-bonding interactions are strengthened by a d...

Dynamics of Nanoparticles in Entangled Polymer Solutions.

The mean square displacement ⟨r2⟩ of nanoparticle probes dispersed in simple isotropic liquids and in polymer solutions is interrogated using fluorescence correlation spectroscopy and single-particle tracking (SPT) experiments. Probe dynamics in different regimes of particle diameter (d), relative to characteristic polymer length scales, including the correlation length (ξ), the entanglement mesh size (a), and the radius of gyration (Rg), are investigated. In simple fluids and for polymer solutions in which d ≫ Rg, long-time particle dynamics obey random-walk statistics ⟨r2⟩:t, with the bulk zero-shear viscosity of the polymer solution determining the frictional resistance to particle motion. In contrast, in polymer solutions with d < Rg, polymer molecules in solution exert noncontinuum resistances to particle motion and nanoparticle probes appear to interact hydrodynamically only with a local fluid medium with effective drag comparable to that of a solution of polymer chain segments with sizes similar to those of the nanoparticle probes. Under these conditions, the nanoparticles exhibit orders of magnitude faster dynamics than those expected from continuum predictions based on the Stokes-Einstein relation. SPT measurements further show that when d > a, nanoparticle dynamics transition from diffusive to subdiffusive on long timescales, reminiscent of particle transport in a field with obstructions. This last finding is in stark contrast to the nanoparticle dynamics observed in entangled polymer melts, where X-ray photon correlation spectroscopy measurements reveal faster but hyperdiffusive dynamics. We analyze these results with the help of the hopping model for particle dynamics in polymers proposed by Cai et al. and, on that basis, discuss the physical origins of the local drag experienced by the nanoparticles in entangled polymer solutions.

Understanding looping kinetics of a long polymer molecule in solution. Exact solution for delta function sink model

A diffusion theory for intramolecular reactions of polymer chain in dilute solution is formulated. We give a detailed analytical expression for calculation of rate of polymer looping in solution. The physical problem of looping can be modeled mathematically with the use of a Smoluchowski-like equation with a Dirac delta function sink of finite strength. The solution of this equation is expressed in terms of Laplace Transform of the Green’s function for end-to-end motion of the polymer in absence of the sink. We have defined two different rate constants, the long term rate constant and the average rate constant. The average rate constant and long term rate constant varies with several parameters such as length of the polymer (N), bond length (b) and the relaxation time τR. The long term rate constant is independent of the initial probability distribution.

Simulation of Individual Polymer Chains and Polymer Solutions with Smoothed Dissipative Particle Dynamics

In an earlier work (Litvinov et al., Phys.Rev.E 77, 066703 (2008)), a model for a polymer molecule in solution based on the smoothed dissipative particle dynamics method (SDPD) has been presented. In the present paper, we show that the model can be extended to three-dimensional situations and simulate effectively diluted and concentrated polymer solutions. For an isolated suspended polymer, calculated static and dynamic properties agree well with previous numerical studies and theoretical predictions based on the Zimm model. This implies that hydrodynamic interactions are fully developed and correctly reproduced under the current simulated conditions. Simulations of polymer solutions and melts are also performed using a reverse Poiseuille flow setup. The resulting steady rheological properties (viscosity, normal stress coefficients) are extracted from the simulations and the results are compared with the previous numerical studies, showing good results.

Watching two conjugated polymer chains breaking each other when colliding in solution

While collision theory successfully describes the kinetics of chemical reactions, very little is known about the processes at the molecular level, especially if the reacting molecules are large. In this study, using single-molecule spectroscopy, we visually observed that collision between two conjugated polymer (CP) molecules in solution leads to simultaneous rupture of both chains. In addition to opening up the possibility of monitoring chemical processes in solution at the single-molecule level, these results demonstrate that mechanical bending of two stiff conjugated backbones against each other (the effect of leverage) by Brownian motion can weaken the chemical bond and markedly accelerate photochemical oxygen-induced chain scission by at least 20 times. The catalytic effect of the chain bending is also enhanced by a prolonged interaction between the chains owing to their entanglement. These findings are important for the solution processing of CPs in their application in organic electronics, for understanding the degradation mechanisms in CPs and for the development of new catalysts based on mechanical interactions with target molecules. Mechanical forces that result from collisions between molecules play a central role in chemical reactions. The finer details of their involvement remain poorly understood, however, especially for larger molecules possessing an enormous number of degrees of freedom. Now, a team led by Ivan Scheblykin from Lund University, Sweden, has developed a fluorescence microscopy approach that enables a direct visualization of collisions between two individual polymer molecules in solution. The researchers found that the randomly moving molecules, which exhibit a rigid, double-bonded carbon backbone, broke into smaller fragments upon impact. This disintegration stems from molecular entanglement and bending stress where the stiff polymer chains touch each other. The team's single-molecule chemistry approach provides a deeper knowledge of reaction mechanisms at the molecular level and opens the door to new synthetic routes in materials chemistry. By applying single-molecule imaging technique in free solution, we visually observed polymer chains break apart when they collide with each other just because of their Brownian motion. The oxidation scission reaction is catalyzed by the leverage effect, analogous to breaking a stiff wooden stick over the knee. Our surprising results suggest that new catalysts could be designed with the idea of stiff molecules working as ‘knives’ and ‘leverages’ breaking chemical bonds. We believe that our work opens up the possibility of monitoring chemical processes in solution at the single-molecule level.

Novel strategies for fabricating reduced fat foods: Heteroaggregation of lipid droplets with polysaccharides

This study describes the formation of emulsion-based materials with novel textural characteristics by controlled heteroaggregation of food-grade colloidal particles and polymers. Heteroaggregation was induced by mixing a suspension of colloidal particles (β-lactoglobulin-coated lipid droplets) with a solution of polymer molecules (pectin) under conditions where the particles and polymers had similar charges (pH 7) or opposite charges (pH 4). The mean particle size, microstructure, flow behavior, and shear modulus of the mixtures formed depended on particle-to-polymer ratio and solution pH. At pH 4, negatively charged pectin molecules were attracted to the surfaces of positively charged protein-coated droplets leading to particle aggregation, increased viscosity, and gel formation, which were attributed to bridging flocculation. At pH 7, pectin molecules were not attracted to the droplet surfaces, but there was still an increase in emulsion viscosity and gel strength above a critical pectin concentration due to depletion flocculation. Bridging flocculation (pH 4) led to more extensive particle aggregation, higher viscosities, and stronger gels than depletion flocculation (pH 7). The presence of pectin in the emulsions had little impact on their microstructure or lipid digestion rate in a simulated gastrointestinal model. This study has important implications for the creation of reduced fat foods, and the development of foods, cosmetics, personal care, and other products with novel properties.

Using atomic force microscopy to probe the adsorption kinetics of poly(ethylene oxide) on glass surfaces from aqueous solutions

This paper presents force–distance measurements using the AFM in order to study the adsorption kinetics of high molecular weight polyethylene oxide (4 million Da) with a broad molecular weight distribution onto glass surfaces. The measurements were conducted at different incubation times in the polymer solution. In 0.01 M NaCl the PEO was found to take a relatively long time (>2 days) to attain full surface coverage, during the period from the first contact of the polymer solution with the surface to full surface coverage, the range of the interaction between the two surfaces increases from around 20 nm to 130 nm, indicating slow adsorption kinetics, which can be attributed to the exchange between the adsorbed layer with the polymer molecules in solution as well as a change that might occur in the conformation of the adsorbed chains. During this period, the adhesion observed on separation of the surfaces was found to be dependant with incubation time in the PEO solution reaching its maximum value in the time frame of 29–47 h of incubation. These results seem to be different from earlier data obtained from adsorption of the PEO on the glass surface from the KNO 3 solutions on lower molecular weight polymers. Therefore experiments were also conducted in the presence of KNO 3 where it was found that the adsorption was faster and resulted in thicker layers compared to the adsorption from the NaCl solution. This is attributed mainly to the high concentration of K + ions, which are effective binders of the lone pair electrons of the ether groups (–O–) of the PEO and the negatively charged silica on the glass surface.

Adsorption of linear polymers on polyethersulfone membranes: Contribution of divalent counterions on modifying of hydrophilic–lipophilic balance of polyelectrolyte chain

The effect of divalent metal ions on conformational changes, size and hydrophilicity of poly(acrylic acid), PAA, in solution as well as its relation with characteristics of adsorbed polymer layers on polyethersulfone membrane, PESm, were studied and analyzed by several techniques. PAA adsorption on PESm in the presence of divalent metal ions was established to be occurring by an adsorption mechanism promoted by interchain polymer–metal bonds between polymer molecules in solution and pre-adsorbed polymer layers on the surface. Results suggest that changes of hydrophilic–lipophilic balance of polymer chains can be related to adsorption mechanisms of PAA; these changes are consequence of decrease of negative charges on carboxylate groups by coordination of added metal ions and by increase of ionic strength. Besides, the surface and permeability characteristics of adsorbed polymer layers were related to the changes of size, aggregation and conformations of polymer chains in solution as metal ion concentration was increased.

溶液中の高分子に対するrandom coil modelについて

溶液中の高分子に対するrandom coil modelについて

Numerical Study of Extension Rheological Properties of Polymer Solutions using FENE Model

Dilute polymer solutions represent a complex rheological response. A finitely extensible nonlinear elastic (FENE) bead-spring chain model for dilute solutions of polymer molecules in a Newtonian solvent is employed to describe the bead-bead interaction within a molecule. Brownian dynamics simulation is used to capture the most important rheological properties of dilute polymer solutions. A program based on this model is developed to simulate the steady elongational flow and inception of elongational flow, and the flow situations and the rheological material functions are investigated. Semi-implicit predictor-corrector methods are introduced and the results qualitatively agree with rheological theory.

Smoothed dissipative particle dynamics model for polymer molecules in suspension

We present a model for a polymer molecule in solution based on smoothed dissipative particle dynamics (SDPD) [Español and Revenga, Phys. Rev. E 67, 026705 (2003)]. This method is a thermodynamically consistent version of smoothed particle hydrodynamics able to discretize the Navier-Stokes equations and, at the same time, to incorporate thermal fluctuations according to the fluctuation-dissipation theorem. Within the framework of the method developed for mesoscopic multiphase flows by Hu and Adams [J. Comput. Phys. 213, 844 (2006)], we introduce additional finitely extendable nonlinear elastic interactions between particles that represent the beads of a polymer chain. In order to assess the accuracy of the technique, we analyze the static and dynamic conformational properties of the modeled polymer molecule in solution. Extensive tests of the method for the two-dimensional (2D) case are performed, showing good agreement with the analytical theory. Finally, the effect of confinement on the conformational properties of the polymer molecule is investigated by considering a 2D microchannel with gap H varying between 1 and 10 microm , of the same order as the polymer gyration radius. Several SDPD simulations are performed for different chain lengths corresponding to N=20-100 beads, giving a universal behavior of the gyration radius R_{G} and polymer stretch X as functions of the channel gap when normalized properly.

Conformational and dynamo-optical properties of fluorinated poly(p-phenylene-1,3,4-oxadiazole-imide-amide) molecules in solutions

Abstract Conformational parameters of the fluorinated poly( p -phenylene-1,3,4-oxadiazole-imide-amide) molecules in dilute solutions in N , N ′-dimethylacetamide, N , N ′-dimethylformamide and 96% sulphuric acid were evaluated by using the data of hydrodynamic and dynamo-optical investigations. Optical anisotropy of the statistical Kuhn segment was found to be about half of that for poly(amide-benzimidazole) and close to that previously obtained for poly( p -phenylene-1,3,4-oxadiazole) molecules. The observed effect is referred to the higher equilibrium flexibility of the polymer chain attributed to the hexafluoroisopropylidene units incorporated into the molecule backbone. Noticeable degradation of the polymer molecules in solution in 96% H 2 SO 4 at ambient temperature was detected and characterised.

Computer simulations of stretching and collapse of polymer molecules in solution

AbstractComputer simulations are reported for system of linear polymer molecules, diblock copolymer and dendrimer in dilute solution without and with elongational flow. The effect of fluctuating hydrodynamics interactions (HI) on the coil‐stretch transition of linear polymers and dendrimers in elongational flow is studied. The process of coiling of homo‐ and blockcopolymer from completely extended state is also simulated.

Matrix-assisted pulsed laser evaporation of polymeric materials: a molecular dynamics study

Matrix-assisted pulsed laser evaporation (MAPLE) has been recently developed to deposit high-quality thin films for a wide range of polymeric materials. To analyze the evaporation of polymer molecules in MAPLE, we present a molecular dynamics (MD) simulation of laser ablation where the target material is modeled as a solution of polymer molecules in a molecular matrix. The breathing sphere model is used for MD simulations of laser ablation of the molecular matrix. Polymer molecules are described using a bead-spring model, where each bead represents one or several polymer groups. The initial stage of polymer ejection is investigated at different laser fluences and pulse durations. The influence of polymer molecules on the stability of clusters formed in the plume and the processes that can lead to polymer decomposition are discussed.