Polymer Coil Dimensions Research Articles

Molecular Origin of Efficient Phonon Transfer in Modulated Polymer Blends: Effect of Hydrogen Bonding on Polymer Coil Size and Assembled Microstructure

Molecular level engineering of polymer or polymer blends has been recently demonstrated an effective strategy to regulate thermal conductivity. Such materials are of great interest to meet critical requirements of transparent, lightweight, flexible, and so on for thermal management in electronic applications. In this work, modulated polymer blends with poly(vinyl alcohol) (PVA) and biopolymers (lignin, gelatin) were designed and significantly enhanced thermal conductivity was achieved by tuning the intermolecular interaction among polymer components. The hydrogen bond interaction has been revealed as the major driving force that affects the polymer coil dimension in aqueous solution, the microstructure of coil–coil interaction in solid film, and thus, the thermal conduction. A solid relationship across molecular level interaction to macroscale thermal conduction is constructed via careful characterization of the coil size in liquid phase and assembled microstructure in solid phase. Appropriate integration...

Tumbling and Deformation of Isolated Polymer Chains in Shearing Flow

Using Brownian dynamics simulations of polymer chains over a wide range of resolution, we find universal scaling laws for polymer coil dimensions and tumbling time. At high shear rates γ̇, the coil thickness in the gradient direction becomes independent of chain length, scaling as NK0γ̇–1/4, where NK denotes the numbers of Kuhn steps, and the tumbling time scales as NKγ̇–3/4, correcting scaling laws presented in prior studies. We find this to be a consequence of the formation of loops whose length is limited by the time required to stretch them and derive scaling laws from a balance of convection and diffusion of monomers. We find that, in the absence of hydrodynamic interaction (HI) and excluded volume (EV), for wormlike chains, the shrinkage in chain stretch observed at ultrahigh shear rates is pushed out to arbitrarily high shear rates if the chain is resolved increasingly finely below the persistence length. Finally, scaling laws in the presence of excluded volume and hydrodynamic interactions are derived that are expected to be valid for long chains at high shear rates.

Study of action mechanisms and properties of Cr3+ cross-linked polymer solution with high salinity

Performance characteristics of partially hydrolyzed polyacrylamide (HPAM) and cross-linked polymer (CLP, Cr3+ as the cross linker) solutions have been investigated. A Brookheld viscometer, rheometer, dynamic light scattering system, and core flow device have been used to measure the viscosity, viscoelasticity, polymer coil dimensions, molecular configuration, flow characteristics, and profile modification. The results show that, under conditions of high salinity and low HPAM and Cr3+ concentrations, cross-linking mainly occurred between different chains of the same HPAM molecule in the presence of Cr3+, and a cross-linked polymer (CLP) system with a local network structure was formed. Compared with an HPAM solution of the same concentration, the apparent viscosity of the CLP solution increased slightly or remained almost unchanged, but its viscoelasticity (namely storage modulus, loss modulus, and first normal stress difference) increased, and the resistance coefficient and residual resistance coefficient increased significantly. This indicates that the CLP solution exhibits a strong capability to divert the sequentially injected polymer flood from high-permeability zones to low-permeability zones in a reservoir. Under the same HPAM concentration conditions, the dimensions of polymer coils in the CLP solution increased slightly compared with the dimensions of polymer coils in HPAM solution, which were smaller than the rock pores, indicating that the cross-linked polymer solution was well adapted to reservoir rocks. Core flood experiments show that at the same cost of reagent, the oil recovery by CLP injection (HPAM-1, Cr3+ as the cross linker) is 3.1% to 5.2% higher than that by HPAM-2 injection.

Rheology Behavior of Hydrophobically Modified Poly(acrylic acid) with Twin-Tailed Pendant in Water—Ethylene Glycol Mixture

A hydrophobically modified poly(acrylic acid) (HMPA) with twin-tailed hydrophobic pendant side groups was prepared by precipitation polymerization. The rheology behavior of HMPA was examined in mixtures of water and ethylene glycol (EG) of different proportions. It was shown that the solvent had a direct impact on both the steady and dynamic rheology behaviors of the HMPA solutions. The change of hydrophobic interactions in the EG-rich mixtures may be attributed to the observed decrease in polymer coil dimension together with a lower tendency of the hydrophobes to form junctions. As the temperature decreased, the viscosities and numbers of active junctions of HMPA in water–EG mixtures increased.

Effect of Non‐Ideal Mixed Solvents on Dimensions of Poly(N‐Vinylpyrrolidone) and Poly(Methyl Methacrylate) Coils

An addition of a small amount of non‐solvent tetrahydrofuran (THF) to good solvent water gave rise to a strong solvent power for poly(N‐vinylpyrrolidone) (PVP). It was found that PVP coils in mixtures of water and THF first swelled as the fraction of THF was increased, and then the coils contracted after a critical composition of the solvent mixture based on the measurement of dilute solution viscosities. It was reached that the power of the mixed solvents was not the simple average of the power of individual components. The influence of the non‐ideal mixing of water and THF on the power of these mixtures for PVP and the dimensions of PVP coils was taken into account. Especially the formation of pseudo‐clathrate hydrate structure with the composition φ THF ≈ 0.44 was found to be an important factor to change the solvation and dimensions of PVP coils. Some other solvent mixtures for PVP and poly(methyl methacrylate) (PMMA) were also found to be non‐ideal mixtures. The viscosities of these solvent mixtures could show positive or negative deviation from the values obtained from the addition rule. It was shown again that the influence of the non‐ideality of these solvent mixtures on the dimensions of polymer coils was great. The action of mixed solvents changed the dimension of polymer coils, not only because of excluded volume effects but also because of the different molecular interactions present in these mixed solvents.

Solvent effects on phototriggered conformational changes in an azobenzene-functionalized poly( p-phenylene vinylene)

Poly(2-hexyloxy-5-((10-(4-(phenylazo)phenoxy)decyl)oxy)-1,4-phenylene vinylene) (HPA-10-PPV) is an azobenzene-functionalized poly( p-phenylene vinylene) derivative that previously has been shown to undergo changes in the position and shape of its fluorescence spectrum in response to trans → cis-azobenzene photoisomerization. This effect was initially observed in a binary dichloromethane-methanol solution and was attributed to a phototriggered expansion of polymer coil dimensions. In this report we explore the mechanism by which azobenzene isomerization induces this conformational change and the solvent properties that govern the magnitude of the change. Phototriggered fluorescence shifts are observed in mixtures of dichloromethane and each of 12 cosolvents, 7 protic and 5 aprotic. The shifts are largest in protic solvents but do not correlate with any single solvent parameter or combination of parameters. Smaller shifts are observed in mixtures with aprotic cosolvents, and the magnitude of these shifts correlates with solvent polarity/polarizability. The conformational changes responsible for the fluorescence shifts are attributed to a change in polymer–solvent interactions induced by the difference between properties of the trans- and cis-azobenzene isomers. Isomerization to the more polar cis-azobenzene promotes an increase in polymer–solvent interactions. These results suggest a means by which the magnitude of phototriggered fluorescence changes could be increased in future derivatives.

Effect of charge density, molecular weight, and hydrophobicity on polycations adsorption and flocculation of polystyrene latices and silica

AbstractAdsorption and flocculation behavior of two series of synthetic polycations was investigated in dispersions of silica and polystyrene latices with various particle size and surface charge densities. Polycations of the first series (polydiallyldimethyl ammonium chloride‐PDADMAC) varied in molecular weight only, while polycations of the second series (derivatives of polymethacrylic acid) varied in both molecular weight and hydrophobicity. We have found that maximum adsorbed amount of high molecular weight PDADMAC on latex particles was nearly independent of the surface charge density when the particle size was comparable to the polymer coil dimensions in solution. Both low and high molecular weight PDADMACs were efficient flocculants, although significantly lower amounts of high molecular weight polyelectrolyte were required for the phase separation in the dispersions due to particles aggregation through “charge patch” mechanism. The increase of polymer hydrophobicity leads to higher adsorbed amounts and broadening of flocculation window by polycations of the second series on both substrates. However, no strong enhancement of segment–surface interactions on hydrophobic substrates was observed. Since formation of multilayers upon adsorption was also excluded, the difference in adsorption and flocculation behavior was related to the more compact conformation of hydrophobically associating derivatives in solution and at the interface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3422–3429, 2006

Phototriggered Fluorescence Color Changes in Azobenzene-Functionalized Conjugated Polymers

We report fluorescence studies of phototriggered changes in spectral position and shape for two azobenzene-functionalized poly(p-phenylenevinylene) derivatives, poly(2-methoxy-5-(4-phenylazophenyl-4'-(1,10-dioxydecyl))-1,4-phenylenevinylene) (MPA-10-PPV) and poly(2-hexyloxy-5-(4-phenylazophenyl-4'-(1,10-dioxydecyl))-1,4-phenylenevinylene) (HPA-10-PPV). Upon trans --> cis azobenzene photoisomerization, small (ca. 1 nm) blue shifts in spectral position are observed for MPA-10-PPV in 100% toluene, a good solvent for this polymer. These shifts are reversed upon visible irradiation and can be cycled many times. To probe the dependence of these shifts on initial polymer conformation, a dichloromethane-methanol cosolvent study was performed in which the solvent quality was decreased incrementally to induce a reduction in polymer coil dimensions. Unirradiated dichloromethane solutions of both MPA-10-PPV and HPA-10-PPV showed a red shift and reduction in quantum yield with increasing methanol concentration as expected based on literature results for other poly(p-phenylenevinylene) derivatives. These changes have been attributed to a dramatic conformational collapse by others and occur for these azo polymers over the 30-60% (v/v) methanol range. While little or no light-induced spectral shifting was observed at low (<or=20%) and high (>or=70%) methanol concentrations, significant spectral shifts were observed for both polymers upon azobenzene photoisomerization in solutions with 30-60% methanol, the same range over which the polymer undergoes collapse to a highly coiled state. The largest shifts are visible to the eye, with a 65:35 (v/v) dichloromethane-methanol solution of HPA-10-PPV showing yellow-orange fluorescence when the azobenzenes are trans, green fluorescence when they are cis, and yellow-orange again after the azobenzenes are returned to the trans state. We attribute these color changes to a reversible UV-phototriggered expansion of polymer coil dimensions that occurs as a result of trans --> cis azobenzene side chain isomerization and provide temperature data to support this conclusion.

Star‐like Fullerene Containing Poly(Vinylpyrrolydone) Derivatives: Chloroform Solution Properties

Star‐like fullerene C60 derivatives with different branch number, synthesized by the reaction of fullerene with poly(vinylpyrrolydone) (PVP) macromolecules bearing the terminal amino‐groups, were investigated in solution by the viscometry, dielectric, and electrooptical Kerr‐effect methods in comparison with the ordinary linear PVPs of the same molecular mass. It was shown that covalent linkage of branches to fullerene through amino‐groups leads to appearance of a polar and optically anisotropic nanoparticle (amine‐substituted C60) in the center of the coil of star‐like polymers that radically changes dielectric and electrooptical properties of the initial polymer. Effect of fullerene on the dimension of polymer coil had been detected also.

Solution rheology of hydrophobically modified associative polymers: Solvent quality and hydrophobic interactions

The rheological behavior of a model hydrophobically modified alkali soluble emulsion (HASE) polymer, comprised of a random copolymer backbone of methacrylic acid and ethylacrylate and pendant hydrophobic macromonomers, is examined in cosolvents of water and propylene glycol (PG) of different proportions. We find the solvent solubility parameter to have a direct impact on both the steady and dynamic behavior of the polymer solutions. In particular, scaling of the relative viscosity (ηrel) and the elastic modulus (G′) at a fixed frequency with the solvent solubility parameter (δs) reveals the presence of two distinct regimes with different dependences on δs. In “water-rich” solvents, both ηrel and G′ show a strong dependence on δs in contrast to “PG-rich” solvents, in which there is slight or no dependence on δs. The concentration dependences of both ηrel and G′ are also found to be different in water-rich solvents from that in PG-rich solvents. In water-rich solvents, ηrel and G′ reveal power-law dependences with exponents of 2.5 and 3.2, respectively, compared to exponents of 1.4 and 2.3 in PG-rich solvents. The different behavior in PG-rich solvents is ascribed to the presence of minimal hydrophobic associations, with the polymer behavior analogous to that of unmodified polymers without hydrophobes. This hypothesis is supported by the similarity in ηrel scaling with concentration observed for both the HASE polymer in PG-rich solvents and a similar polymer without the hydrophobes in both solvents. The lack of hydrophobic interactions in the PG-rich solvents may be attributed to the observed decrease in polymer coil dimension together with a lower tendency of the hydrophobes to form micelles in less polar media.

Polymeric Hydrate−Inhibitor Adsorption Measured by Neutron Scattering

We use small-angle neutron scattering to characterize a polymeric hydrate inhibitor, poly(N-vinyl-2-pyrrolidone), adsorbed onto hydrate crystal surfaces. Gas hydrates are crystals in which water molecules encage small molecules such as propane or methane. Their stability at temperatures above the freezing point of water presents a significant challenge to oil and gas transport. Hydrate formation can be kinetically suppressed by certain polymeric inhibitors, but little is known about the mechanism of this effect. We measure a polymer coverage of 5 ± 3 mg/m2, but on only a small (2%) fraction of the available surface. Unlike the expected self-similar structure seen in other systems, this layer has the unusual property of a thickness several times the polymer coil dimension. Therefore, most of the polymer is not bound directly to the surface, suggesting the formation of surface aggregates. We speculate on the role of these aggregates in the growth inhibition of hydrate crystals.

Viscometric properties of viscosity index improvers in lubricant base oil over a wide temperature range. Part I: Group II base oil

AbstractCapillary viscometry has been employed to measure the viscosities of dilute polymer solutions over the temperature range ‐10 to 150 °C. A Group II base oil containing 95% saturates was used as solvent for an olefin copolymer (OCP), a hydrogenated diene copolymer (HDP), and a polymethacrylate (PMA). These three polymers represent the three major families of viscosity index (VI) improvers used nowadays in lubricant formulations. Intrinsic viscosities and Huggins' constants were also determined. The thickening effects of the olefin copolymer and the hydrogenated diene copolymer were found to be higher at low temperatures (e.g., 40 °C) than at higher ones (e.g., 100 °C), which phenomenon was attributed to stronger intermolecular hydrodynamic interactions at low temperatures, as indicated by the Huggins constants. For the hydrogenated diene copolymer and the polymethacrylate polymer, the viscosity increased abruptly when the temperature went below 10 °C. This unusual observation was attributed to the crystallisation of a small fraction of the base oil. Based on the intrinsic viscosity data, it was concluded that at temperatures between 10 and 150 °C, the polymer coil dimension remains a constant for the olefin copolymer and the hydrogenated diene copolymer VI improvers, but increases with increasing temperature for the polymethacrylate VI improver.

Microscopic theory of polymer-mediated interactions between spherical particles

We develop an analytic integral equation theory for treating polymer-induced effects on the structure and thermodynamics of dilute suspensions of hard spheres. Results are presented for the potential of mean force, free energy of insertion per particle into a polymer solution, and the second virial coefficient between spheres. The theory makes predictions for all size ratios between the spheres and the polymer coil dimension. Based on the Percus–Yevick (PY) closure, the attractive polymer-induced depletion interaction is predicted to be too weak under athermal conditions to induce a negative value for the second virial coefficient, B2cc, between spheres in the colloidal limit when the spheres are much larger than the coil size. A nonmonotonic dependence of the second virial coefficient on polymer concentration occurs for small enough particles, with the largest polymer-mediated attractions and most negative B2cc occurring near the dilute–semidilute crossover concentration. Predictions for the polymer-mediated force between spheres are compared to the results of computer simulations and scaling theory.

Model of aggregation of colloidal fine particles in the presence of supersized polymer

A simple model of the process of stabilization and destabilization of fine colloidal suspensions induced by supersized linear polymers has been tested by the direct simulation method. In the model, a single polymer molecule may bind a number of colloidal particles and thus form an aggregate. It is assumed that a simultaneous attachment of a few fine particles to one macromolecule does not necessarily destabilize the suspension. The destabilization of the system (occurring if aggregate sedimentation dominates its diffusion ability) takes place only when the number of the attached particles per macromolecule exceeds the critical value which depends on the polymer coil dimension in the dispersion medium. The model permits interpretation of several experimental observations of the behavior of colloidal sols upon introduction of very high molecularweight polymers. The simulation results have been compared with the experimental data on the effect of polyacrylamide on the stability of AgI sol.

Photocrosslinking reaction of polydimethylsiloxane/benzophenone-containing polyimides in solution.

The intermolecular crosslinks and the changes in polymer coil dimension during the competitive intra-and intermolecular photocrosslinking reactions were studied for polyimides of benzophenoneteracarboxylic dianhydride with oligomers having various degrees of bis(aminopropyl) polydimethylsiloxane (BAPSX, n=8, 15, 61) in tetrahydrofuran under u.v.irradiation at 30°C. The magnitude of Mw, 1/2, and A2 was evaluated by a light-scattering measurement. The deviation of the intermolecular crosslinks from linearity during the reaction becomes more pronounced as the initial polymer concentration decreases or the number of BAPSX oligomers in a polyimides increases. The value of Φinter/[C]θ for a polyimide with a BAPSX oligomer (n=8) was determined to be 6.7×102 dm3 mol-1 in the early stage of crosslinks formation. The extent of the contraction of polymer coils due to intramolecular crosslinking increases as the number of BAPSX oligomers in a polyimide decreases.

Photocrosslinking of polyimide containing benzophenone unit: The effects of polymer compositions on reaction rates and polymer coil dimensions due to the reaction in solution.

The kinetic parameters and the changes in polymer coil dimensions during the competitive intra- and intermolecular photocrosslinking reactions in THF solution depend on the number of alkyl substituents in the diamine component and the amount of benzoph- enonetetracarboxylic dianhydride(BTDA) in polyimide. When a second orth-alkyl substituent is introduced, the quantum yield for intramolecular reaction, including some side reaction with solvent increases and oppositely the quantum yield for intermolecular reaction decreases. The magnitude of 1/2 and Mw is related to the degree of the competition between intra- and intermolecular crosslinking. The contraction ratio, g, of polymer coils decreases smaller as the amount of BTDA in the polyimide increases.

Synthetic pH sensitive polyampholyte hydrogels: A preliminary study

A combined capillary drop viscometer-pH cell has been constructed and used to study the solution properties of some polymeric weak acids, bases, and ampholytes containing methacrylic acid (MAA), dimethylaminoethyl methacrylate (DMAEMA), and 2-hydroxyethyl methacrylate (HEMA). The behavior of polyelectrolytes based on MAA or DMAEMA is consistent with established thinking, and is dominated by the chain expansions which accompany ionization of acidic (MAA) or protonation of basic (DMAEMA) functionality. The solution behavior of the polyampholytes is complex and was studied as a preliminary to investigations of crosslinked hydrogel analogues. Briefly, it was found that changes in polymer coil dimensions were dictated by the formation or “breakage” of intramolecular salt bridges by, for example, lowering the solution pH to protonate weakly acidic, or raising the pH to deprotonate weakly basic functionality. Similar effects were observed on adding counterions which preferentially complex with one of the bound ions. The pH “sensitivity” of polymer coil dimensions increased with the concentration of charged functionality in the polymer. Chemically crosslinked polyampholytes were prepared and equilibrium water contents were measured as a function of pH. In contrast, due to network constraints, the pH “sensitivity” of the hydrogels, as measured by changes in equilibrium water uptake, increased with a decrease in the level of charged functionality in the polymer.

The solution and solid-state thermochromism of unsymmetrically substituted polysilanes

The thermochromic behavior of a number of dialkyl-substituted polysilanes has been studied in some detail. The formation of a long wavelength-absorbing species in solution at low temperatures is dependent on the polymer structure. Evidence for polymer aggregation has been found in solutions as dilute as 10−5 M (based on the monomer unit). Fluorescence emission studies at very low concentrations (<10−6 M) suggest that single-molecule events can result in the observed thermochromic changes. We have obtained no evidence for the proposed coil-to-rod transition at low temperature by either light or neutron scattering; indeed the scattering studies seem to suggest that the polymer coil dimensions actually shrink slightly prior to the onset of aggregation. It is proposed that the thermochromism observed for many dialkyl polysilanes in solution is initiated by the formation of extended segments within a polymer chain which are long enough to stabilize intra- and intersegmental interactions. In extremely dilute solutions this interaction results in a shrinkage of a single polymer chain; at higher concentrations the interaction results in aggregation.

Photocrosslinking of polymers containing cinnamoyl groups: The effect of molecular weight of copolymers on the reaction in solutions

The rate and the change in polymer coil dimension during the competitive intra- and intermolecular photocrosslinking reactions were studied for copolymers of 2-cinnamoyl-oxyethyl methacrylate with methyl methacrylate having various degrees of polymerization ( N n = 650–5600 ) in tetrahydrofuran solution under u.v. irradiation at 30°. The rate parameter, K D inter, for intermolecular reaction is proportional to N n −0.46 and the quantum yield, Φ D intra, decreases linearly with a slope of 2 × 10 −7 per N n of copolymers. The number of cinnamoyl groups for intramolecular crosslinking increases with increasing the molecular weight. The magnitude of the contraction of polymer coils due to intramolecular crosslinking increases as the molecular weight decreases. The contraction ratio, g = 〈s 2〉 cr 〈s 2〉 1 , becomes 0.02–0.05 at the gel point in a dilute solution, showing that the volume of the crosslinked polymer coil shrinks up to 1 350 - 1 100 of the volume of the corresponding linear polymer with the same molecular weight. The gel formed contains many intramolecular cross-links.

Influence of base oil refining on the performance of viscosity index improvers

The effect of three viscosity index (VI) improvers of different chemical type on kinematic viscosity at 98.9°C was studied in lube base stocks from Darius crude oil. These base stocks differed in their degree of refining and finishing, i.e. whether they had been hydrofinished or clay treated. They covered a wide range of viscosities from spindle oil to heavy neutral with VI from Low VI stock to Extra High VI stock. The thickening effect at high temperature and the viscosity temperature relationship were evaluated. Differences observed in the performance of VI improvers have been explained on the basis of the variation in specific viscosity and of the changes in the polymer coil dimensions in terms of the reduced viscosity as a function of temperature following Muller's criteria based on the chemistry of lubricating oil base stocks.