Solvents Of Different Quality Research Articles

Amphiphilic polymer Co-networks based on cross-linked tetra-PEG-b-PCL star block copolymers

A new class of AB4-type amphiphilic polymer co-networks (ACN) was prepared by hetero-complementary 2-(4-nitrophenyl)-benzoxazinone/amine end group cross-linking chemistry in dimethyl sulfoxide (DMSO). For this purpose, a well-defined star block copolymer (tetra-PEG-b-PCL) consisting of a hydrophilic tetra-arm PEG core (Mn ∼ 5 kg mol−1) and hydrophobic PCL wings with a total molar mass of Mn ∼ 10 kg mol−1 was synthesized by ring-opening polymerization (ROP). This tetra-PEG-b-PCL star block copolymer was functionalized either with 2-(4-nitrophenyl)-benzoxazinone or with amino terminal groups. The ACN synthesis was carried out by conversion of these two star block copolymers. The overlap concentration of c* ∼76 g L−1 determined by viscosity measurements of both stars showed no significant temperature dependence. The network syntheses carried out at different concentrations (0.5 c* to 2.5 c*) resulted in conversion degrees in the range of p ≈ 95 % or higher as detected by HR MAS NMR spectroscopy. As in previous work on the synthesis of A4B4 networks using the same cross-linking chemistry, deviations from the expected network structure (increased proportion of double links between two stars) were detected also here by multi quantum NMR spectroscopy. The expected environmentally sensitive behavior of the ACNs was confirmed in terms of their equilibrium swelling in solvents of different quality to PEG and PCL. The scaling of the swelling and viscoelasticity data as a function of preparation concentration showed deviations from the expectations of a perfectly cross-linked star polymer network. Finally, a two-step gelation process was observed by rheology at 30 °C in DMSO, which is related to associations between the 2-(4-nitrophenyl)-benzoxazinone groups surrounded by PCL blocks that become apparent on the time scale of rheology when the molar mass is increased as a result of cross-linking.

Effect of increasing the number of amino groups in the solubility of Copolysiloxanes using dissipative particle dynamics

ABSTRACT In this work, the effect of increasing the number of amino groups in a copolysiloxane poly dimethyl-A-1,1′, dimethylpropylnaminemethylsiloxane is studied by numerical simulations. The goal is the prediction of the impact made by these groups in their solubility properties as functions of the type of solvent so that the choice of polymer/solvent can be optimised for various applications. Two polysiloxanes that are relevant: polydimethylsiloxane and polymethyilhydrogenosiloxane are studied as well. The simulations of these systems are performed using the dissipative particle dynamics model. The information on the properties is derived from density profiles, radii of gyration, second virial coefficients, and radial distribution functions for each system. The interactions of polymers in solvents of different quality (ethanol, toluene, water) are analysed in detail. An increase in the polymer’s solubility is observed as the number of amino groups is increased in toluene. Similar behaviour is found in good solvents for PDMS and PMHiS.

Direct Nanoscopic Measurement of Laminar Slip Flow Penetration of Deformable Polymer Brush Surfaces: Synergistic Effect of Grafting Density and Solvent Quality.

A detailed quantitative nanoscopic description of soft surfaces under dynamic flow is lacking, despite its importance. To better understand the role of surface texture in nanoscopic mass transport in complex media, we used Förster resonance energy transfer in combination with total internal reflectance fluorescence microscopy (FRET-TIRFM) to directly measure laminar slip flow penetration depth (slip length) on poly(N-isopropylacrylamide) (pNIPAM) thin films (50-110 nm) of different grafting densities (0.60, 0.38, and 0.27 chain/nm2) in solvents of different qualities created via cononsolvency in situ. Nontrivial synergistic interplay of grafting density and solvent quality on slip length was observed. Slip lengths are typically tens of nm (40-100 nm), increasing and then reaching a plateau with applied linear flow velocity (192-2,952 μm/s) regardless of experimental system. Slip length was systematically larger for lower density films, but the effect of grafting density was more significant in a good solvent than a poor solvent. Interestingly, however, the stagnant film thickness (polymer swollen thickness minus the slip length) collapsed to almost a singular value for a given grafting density regardless of solvent quality, likely suggesting a large gradient of segmental mobility at nonequilibrium. Moreover, we found that slip flow penetrates into soft pNIPAM surfaces more deeply in a good solvent than in a poor solvent and that this behavior was general and independent of grafting density. This behavior is counter to the notion that less interaction between a fluid (probe) and a solid surface promotes slip.

Effect of solvents on the microstructure aggregation of a heavy crude oil

We study the asphaltene microstructure in a heavy crude oil in response to the addition of solvents of different qualities by measuring the intrinsic viscosity and the Huggins coefficient. Dilution with good solvents (xylene and cyclohexanone) causes the native asphaltene clusters swelling, while that with poor solvents (a diesel oil and a C11-C14 alkanes mixture) may induce different microstructural rearrangements. The mixture of C11-C14 alkanes induces the aggregation of clusters, while the diesel oil their shrinkage. Moreover, if the diesel is added in small quantities instead of cluster shrinkage it may induce cluster aggregation thus forming larger “macro-clusters”. These structures survive after further dilution in both poor and good solvents and their formation is always accompanied by a reduction of the Huggins coefficient that implies the better solubility of these self-aggregated structures in the used solvent. Finally, an unusual negative Huggins coefficient is measured, when the macro-clusters are formed and the solution is diluted in a good solvent. This might be due to a prevalence of the intra-macro-cluster interactions on the inter-macro-cluster ones.

Scaling Laws for Polymer Chains Grafted onto Nanoparticles

AbstractAn experimental approach is presented for identifying the scaling laws for polymer chains grafted onto gold nanoparticles. Poly(ethylene oxide) of various molecular weights are grafted onto gold nanoparticles via thiol end‐functional groups. The polymer‐grafted nanoparticles are self‐assembled into monolayers from solvents of different quality. Over a significant range of graft densities, nanoparticle monolayers deposited from good (athermal) solvent exhibit particle spacing that scales according to theoretical predictions for chains in dilute solution. This unexpected result for ordered nanoparticle monolayers is discussed in the context of the deposition process. In monolayers deposited from theta solvent, molecular weight scaling of particle spacing breaks down, possibly due to chain length dependence of solvent quality. In poor solvent, the structure of nanoparticle assemblies is not sufficiently ordered to obtain reliable measurements, possibly due to loss of nanoparticle dispersion. This approach opens up the possibility for accurate measurement of the effect of solvent on grafted chain scaling in nanoparticle assemblies.

Size of Elastic Single-Chain Nanoparticles in Solution and on Surfaces

We introduce herein a simple model of covalent-bonded single-chain nanoparticles (SCNPs) by considering these intrachain cross-linked nano-objects as elastic unimolecular networks. According to this model, each SCNP is regarded as a network of elastic strands connected by cross-links. The free energy of the SCNP is decomposed in two contributions: (i) an elastic free energy due to the presence of these strands and (ii) an excluded volume contribution arising from the balance of monomer–monomer and monomer–solvent interactions. We provide scaling law expressions for the size (R), diffusion coefficient (D), apparent molar mass (Mapp), and shrinking factor (⟨G⟩) of elastic SCNPs in good, theta, and bad solvents. Also, we derive scaling laws for the height (H) of elastic SCNPs deposited on both low- and high-surface free energy substrates. A comparison of experimental results to model predictions for covalent-bonded polystyrene SCNPs in solution of narrow molecular weight distribution (1.09 ≤ Đ ≤ 1.26), different amount of reactive groups (0.025 ≤ x ≤ 0.3), and varying precursor molar mass (44 ≤ M ≤ 235 kDa) is performed based on literature data. For the same system, a similar comparison of experimental and theoretical H data corresponding to the case of SCNPs deposited on low- and high-energy substrates is also carried out. This simple elastic model provides a useful framework for connecting the amount of reactive groups and precursor molar mass with the size upon intrachain cross-linking for a variety of covalent-bonded SCNPs both in solvents of different quality and on substrates of different surface free energy.

Conformation of ionizable poly Para phenylene ethynylene in dilute solutions

The conformation of dinonyl poly para phenylene ethynylenes (PPEs) with carboxylate side chains, equilibrated in solvents of different quality have been studied using molecular dynamics simulations. PPEs are of interest because of their tunable electro-optical properties, chemical diversity, and functionality which are essential in wide range of applications. The polymer conformation determines the conjugation length and their assembly mode and affects electro-optical properties which are critical in current and potential uses. This study investigates the effect of carboxylate fraction on PPEs side chains on the conformation of chains in the dilute limit, in solvents of different quality. The dinonyl PPE chains are modeled atomistically, where the solvents are modeled both implicitly and explicitly. Dinonyl PPEs maintained a stretched out conformation up to a carboxylate fraction f of 0.7 in all solvents studied. The nonyl side chains are extended and oriented away from the PPE backbone in toluene and in implicit good solvent, whereas in water and implicit poor solvent, the nonyl side chains are collapsed toward the PPE backbone. Rotation around the aromatic ring is fast and no long range correlations are seen within the backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 582–588

Structure and swelling of polymer networks: insights from NMR

This review addresses the relationship between the structure of elastomers and gels, i.e., polymer networks far above the glass transition, and their macroscopic properties. The network structure is characterized by the density of crosslinks, the chain length distribution, topological defects, and entanglement effects, and can be tuned by varying the preparation conditions. These quantities ultimately determine the functional (mostly mechanical) properties, and sensitively affect the swelling behavior. Here, we review current efforts using different NMR spectroscopy methods to unravel structural details of various networks made from poly(dimethylsiloxane), and correlate these with their swelling behavior in solvents of different quality. It was found that a specific NMR observable based upon segmental orientation correlations reflects not only the network chain structure, but also the thermodynamic state. This allowed us to draw relevant conclusions on the validity of the Flory–Rehner theory for network swelling, and on the applicability of simple models to describe network elasticity.

Chain Degradation during Dissolution of Polymer-Fullerene Nanocomposites as a Result of Interaction of Entangled Polymer Matrix with the Filler

Chain degradation of poly(α-methylstyrene) and polystyrene during dissolution of their nanocomposites with fullerene C60 in solvents of different quality with respect to fullerene was studied in detail by size exclusion chromatography and UV spectroscopy. Chain ruptures have been shown to arise during swelling of composites but only for samples with entangled polymer matrix. The data obtained confirm that the hindered mobility of chains because of interaction of the entangled matrix with fullerene is the only cause of degradation. Chain rupture leads to radical depolymerization accompanied by covalent binding of fullerene with the chain fragments, which results in changing of the polymer matrix structure. Chain degradation indicates deterioration of the mechanical properties of the polymers in the presence of C60. The possibility of chain degradation in polymer-filler nanocomposites under deformation with the simultaneous observation of an apparent reinforcement effect because of the addition of filler in the polymer matrix is discussed.

Memory Effects of Diblock Copolymer Brushes and Mixed Brushes

Memory effects of microphase segregation in diblock copolymer brushes and binary mixed homopolymer brushes exposed to solvents of different quality and selectivity are studied using Single-Chain-in-Mean-Field (SCMF) simulations. We gauge these memory effects by a fluctuation memory measure, reflecting the correlation between the quenched fluctuations of grafting points and the microphase-separated morphology, and a domain memory measure, quantifying the correlation between surface morphologies during cyclic exposure to different solvents. The fluctuation and domain memory measures are closely correlated, and both of them have their root in the broken translational symmetry of the distribution of grafting points. They become stronger upon increasing the fluctuations of the grafting points. The effects of solvent quality and selectivity, grafting density, and composition of brushes on the memory measures are discussed.

Micromechanical Cantilever Technique: A Tool for Investigating the Swelling of Polymer Brushes

Polymer brush coatings are well-known for their ability to tailor surface properties in a wide range of applications from colloid stabilization to medicine. In most cases, the brushes are used in solution. Consequently, efforts were expended to experimentally investigate or theoretically predict the swelling behavior of the brushes in solvents of different qualities. Here, we show that the micromechanical cantilever (MC) sensor technique is a tool to perform time-resolved physicochemical investigations of thin layers such as polymer brushes. Complementary to scattering techniques, which measure the thickness, the MC sensor technique provides information about changes in the internal pressure of the brushes during a swelling and deswelling process. We show that the kinetics of both swelling and deswelling are dependent on solvent quality. Comparing the measured data with its thickness evolution, which was calculated based on the Flory-Huggins theory, we found that only the first 10% of the thickness increase of the polymer brush results in a significant pressure increase inside the polymer brush layer.

Computer simulation of aqueous block copolymer assemblies: Length scales and methods

AbstractAtomistic, coarse‐grain, and mesoscopic computer simulation methods applied recently to the study of block copolymer assemblies in solution are reviewed. At the atomic level, particle‐based simulations have provided insight into specific interactions such as hydrogen bonding between polymer and water. Coarse‐grain models have given a generalized view of the conformations of polymer chains in solvents of different qualities by grouping clusters of atoms into effective interaction sites. Mesoscopic self‐consistent field theory allows for the study of the phase diagram of block copolymers in water using a mean‐field continuum description. Advances in and results with these methodologies are presented along with present challenges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1907–1918, 2006

Monte Carlo simulation of solvent effects on the threading of poly(ethylene oxide)

Recently, we described a coarse-grained model of poly(ethylene oxide) (PEO) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt (Helfer et al Macromolecules at press). We now use that coarse-grained model to determine how the amount of threading is affected by dilution of the PEO melt with good, Θ, or poor solvents. We employ two distinctly different methods for incorporating the solvent. One method employs explicit coarse-grained solvent molecules, which have the same size as a coarse-grained bead of the polymer. Solvents of different quality are produced by changes in the values of the interaction energies between solvent and polymer beads. The other method does not employ explicit solvent particles but simply modifies the attractive part of the discretized Lennard-Jones potential that describes the pair-wise long-range interaction of coarse-grained PEO while leaving unchanged the rotational isomeric state model that describes the short-range intramolecular interactions. The thermodynamic quality of this implicit solvent is inferred from its effect on the mean square radius of gyration of PEO. The intermolecular pair correlation functions show that cyclic and linear molecules aggregate together in a poor solvent, which contributes to the increase in the amount of threading, relative to the situation found at the same concentration in a good solvent. However, the magnitude of this effect of the poor solvent is insufficient to overcome the decrease in threading upon increasing dilution expected from simple application of the law of mass action. Although the qualitative effects are similar for the two different methods of treating the solvent, quantitative comparison suggests that the use of explicit solvent particles gives a stronger connection with the anticipated behaviour of real systems. The present results for equilibrium structures in a Monte Carlo simulation are not as sensitive to the details of the treatment of the solvent as were earlier results (Chang and Yethiraj 2001 J. Chem. Phys. 114 7688) for the dynamics of the collapse of a single chain in a poor solvent.

Dissipative particle dynamics simulation of grafted polymer brushes under shear

The dissipative particle dynamics technique has been used to study grafted polymer chains under shear in solvents of different quality. We show that width of the grafted polymer chains decreases with increasing shear rate for an adsorbed monolayer and bilayer in an athermal solvent but that the layer shrinks in a poor solvent and there is no further decrease in the width on shearing. The polymer chains are preferentially aligned along the direction of the shear and tilted away from the surface normal with even the smallest shear rates. The orientational ordering with respect to the layer director increases with increasing shear. Reducing the quality of the solvent dramatically reduces the width of the grafted layers and the friction between them.

The influence of solvent quality on the mechanical properties of thin cast isotactic poly(methyl methacrylate) coatings

Thin coatings of isotactic poly(methyl methacrylate) were cast on glass from solvents of different quality, which was expected to result in different molecular morphologies. The elastic moduli and hardness of the coatings were measured using a nanoindenter. The aim was to examine the viability of this technique for assessing the influence of the morphology on the mechanical properties. The interpretation of the data was complicated by both the influence of the hard substrate and possibly by the plasticising effect of retained solvent in the bulk. Nevertheless, it was reasonable to conclude that a coating cast from a good solvent was stiffer and harder than that from a poor solvent. This is consistent with previous frictional and spectroscopic studies.

Trees at an Interface

A lattice tree at an interface between two solvents of different quality is examined as a model of a branched polymer at an interface. Existence of the free energy is shown, and the existence of critical lines in its phase diagram is proven. In particular, there is a line of first order transitions separating a positive phase from a negative phase (the tree being predominantly on either side of the interface in these phases), and a curve of localization–delocalization transitions which separate the delocalized positive and negative phases from a phase where the tree is localized at the interface. This model is generalized to a branched copolymer which is examined in a certain averaged quenched ensemble. Existence of a thermodynamic limit is shown for this model, and it is also shown that the model is self-averaging. Lastly, a model of branched polymers interacting with one another through a membrane is considered. The existence of a limiting free energy is shown, and it is demonstrated that if the interaction is strong enough, then the two branched polymers will adsorb on one another.

Dynamics of Hairy-Rod Polymers: Semidilute Regime

Photon correlation spectroscopy was employed in both the polarized (VV) and depolarized (VH) geometries in order to investigate the dynamics of concentration and orientation fluctuations of model hairy-rod poly(p-phenylenes) in semidilute solution. These materials possess a large inherent optical anisotropy, which allowed the unambiguous detection of orientation relaxation. By probing the dynamics in two solvents of different qualities, chloroform, a good solvent, and toluene, it was possible to distinguish nearly molecular from aggregate processes. Two modes were detected in the VV correlation function: the fast cooperative diffusion, Dc, which increased nearly linearly with concentration (Dc/D0 − 1 ∼ c0.9), and a slow mode, Dslow, which slowed with concentration (Dslow ∼ c-1). The latter process was assigned to the self-diffusion of small aggregates, as confirmed by independent pulsed field gradient NMR measurements. Broad VH correlation functions were obtained at high concentrations and revealed the presence of a dominant mode exhibiting a decay rate, ΓVH, which decreased with increasing q and concentration (ΓVH ∼ c-0.25). This mode was assigned to orientational correlations in space, due to some local ordering of parts of the molecules. These findings cannot be accounted for by the existing theories.

On the possible role of nonelectrostatic interactions in the mechanism of the slow polyelectrolyte mode observed by dynamic light scattering

The effect of a poor solvation of a polyelectrolyte chain backbone in a polar solvent was investigated as a possible origin of large multichain domains in polyelectrolyte solutions giving rise to the slow polyelectrolyte mode observed by dynamic light scattering. It was investigated if these domains could be interpreted as polymeric aggregates formed due to the poor backbone solvation. Static and dynamic light scattering experiments on polyions in solvents of different quality with respect to the polyelectrolyte chain backbone, and the temperature dependence of the slow mode, showed that this hypothesis is not realistic. Poor solvation of the polyelectrolyte chain backbone in polar solvents is therefore not the origin of domain formation in solutions of strongly charged polyelectrolytes. This conclusion was confirmed also by analysis of literature data in view of the investigated issue.

Self-entanglement in ring polymers

We represent ring polymers with the off-lattice rod-bead model. We produce perfect unbiased model instances that have between 32 and 2048 beads. These rings are produced at several different values of bead radius, to represent polymers in solvents of different quality. These instances are subject to a novel smoothing operation that facilitates the determination of their topological state, which is represented with the Alexander polynomial. We observe that the probability of observing a trivial knot (P) has a decreasing exponential dependence on the contour length (N) of the polymer, or that P=exp(−N/N0). The characteristic length (N0) varies by many orders of magnitude depending on chain flexibility and solvent quality. For Gaussian rings in a theta solvent, the characteristic length (N0) is 2.6×102. For a good solvent, N0∼8×105. We also explore the expectation value of the minimum number of crossings and suggest that it probably cannot be represented as a power law or exponential function of N. We also suggest that sufficiently large rings will always be composite, and not prime.

Liquefaction of Australian brown coal with mixed solvents of different qualities and reactivities of transferable hydrogens

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLiquefaction of Australian brown coal with mixed solvents of different qualities and reactivities of transferable hydrogensIsao Mochida, Akihisa Takayama, Ryuji Sakata, and Kinya SakanishiCite this: Energy Fuels 1990, 4, 4, 398–401Publication Date (Print):July 1, 1990Publication History Published online1 May 2002Published inissue 1 July 1990https://doi.org/10.1021/ef00022a011RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (500 KB) Get e-Alerts Get e-Alerts