Polymer Coil In Solution Research Articles

Initial stage dynamics of bridging flocculation of polystyrene latex particles with low charge density polycation in a mixing flow near the isoelectric point

Dynamics of ortho-kintetic flocculation of PSL particles with long-chain polycation of low charge density was studied together with the adsorption process of polyelectrolyte near isoelectric point as a function of ionic strength. Within the range of investigation, the initial rate of flocculation was found to take the maximum value immediately after the onset of mixing, but the flocculation gradually slows down with the progress of adsorption. The initial rate of flocculation goes through the minimum as ionic strength increases. Without salt addition, the rate of flocculation is about three times faster than that of salt-induced rapid coagulation. With slightly increasing ionic strength the rate of flocculation slows down because of the reductions of the stiffness and the size of polymer coil in solution and also of the smooth rearrangement of adsorbed chains. The adsorption process monitored by the electrophoresis demonstrates that the zero mobility appears much earlier than the time predicted by collision process in the presence of salt (KCl 100 mM). This trend can be explained by the concept of electrokinetically stagnant layer and by smooth spreading of polyelectrolyte on the colloidal surface. The kinetics of adsorption is in good accordance with the change in the flocculation rate.

Branched polymers characterized by comprehensive two-dimensional separations with fully orthogonal mechanisms: Molecular-topology fractionation × size-exclusion chromatography

Polymer separations under non-conventional conditions have been explored to obtain a separation of long-chain branched polymers from linear polymers with identical hydrodynamic size. In separation media with flow-through channels of the same order as the size of the analyte molecules in solution, the separation and the elution order of polymers are strongly affected by the flow rate. At low flow rates, the largest polymers are eluted last. At high flow rates, they are eluted first. By tuning the channel size and flow rate, conditions can be found where separation becomes independent of molar mass or size of linear polymers. Long-chain branched polymers did experience lower migration rates under these conditions and can be separated from linear polymers. This type of separation is referred to as molecular-topology fractionation (MTF) at critical conditions. Separation by comprehensive two-dimensional molecular-topology fractionation and size-exclusion chromatography (MTF×SEC) was used to study the retention characteristics of MTF. Branching selectivity was demonstrated for three- and four-arm “star” polystyrenes of 3–5×106g/mol molar mass. Baseline separation could be obtained between linear polymer, Y-shaped molecules, and X-shaped molecules in a single experiment at constant flow rate. For randomly branched polymers, the branching selectivity inevitably results in an envelope of peaks, because it is not possible to fully resolve the huge numbers of different branched and linear polymers of varying molar mass. It was concluded that MTF involves partial deformation of polymer coils in solution. The increased coil density and resistance to deformation can explain the different retention behavior of branched molecules.

Interactions between microgel particles

The behaviour of microgel dispersions falls between near-hard-sphere colloids and ultra-soft colloidal systems (e.g., polymer coils in solution and star polymers), and depending on the conditions they can exhibit physical properties of both types of particle. Microgels are the ultimate in ‘designer’ particles as the effective interaction between them can be modified reversibly from being essentially repulsive (the solvent-swollen state) to weakly attractive (the collapsed state) through readily achievable in situ chemical means. A brief summary of the directions in which microgel research is moving is given, with particular focus on current understanding and representations of the effective interactions between these particles.

Computer simulations and theory of polymer tethered nanorods: the role of flexible chains in influencing mesophase stability

The mesophase behaviour of a polymer tethered nanorod is assessed by means of statistical mechanical theory and molecular dynamics simulation. A model system is considered in which a colloidal nanorod is tethered to a flexible polymer chain, which is able to form an “ideal” polymer coil in solution. As chain length increases, it is shown that the stability of the nematic phase first increases and then decreases, while smectic stability is continually enhanced. For a sufficiently long chain, the nematic phase is suppressed altogether and an isotropic-smectic phase transition is seen. It is shown by statistical mechanical theory that the major influence of the chain can be understood in terms of the radius of the polymer coil relative to the width of the nanorod. This provides the possibility of using good or poor solvent conditions to tune the mesophase stability of a colloidal system of nanorods, simply by changing the influence of a tethered polymer chain.

Dragging a Polymer Chain into a Nanotube and Subsequent Release

We present a scaling theory and Monte Carlo (MC) simulation results for a flexible polymer chain slowly dragged by one end into a nanotube. We also describe the situation when the completely confined chain is released and gradually leaves the tube. MC simulations were performed for a self-avoiding lattice model with a biased chain growth algorithm, the pruned-enriched Rosenbluth method (PERM). The nanotube is a long channel opened at one end and its diameter D is much smaller than the size of the polymer coil in solution. We analyze the following characteristics as functions of the chain end position x inside the tube: the free energy of confinement, the average end-to-end distance, the average number of segments imprisoned in the tube, and the average stretching of the confined part of the chain for various values of D and for the number of repeat units in the chain, N. We show that when the chain end is dragged by a certain critical distance x* into the tube, the polymer undergoes a first-order phase tr...

Rheology of Olefinic Copolymer Layers Adsorbed on Solid Surfaces

The rheology of two adsorbed layers of olefinic copolymers (OCPs) between two cobalt surfaces was investigated using a surface force apparatus (SFA). Each polymer layer is obtained by adsorption in a dilute solution of OCP and dispersant OCP (DOCP) in a 175 neutral solvent basestock at 24°C. The aim of these experiments is the mechanical characterization of the compressed polymer films. The hydrodynamic thickness RH detected is compared with the thickness of the polymer layers L and the hydrodynamic radius RH of the polymer coil in solution. All these distances, strongly related to the chemical structure of the polymer, indicate that the layers are not always homogeneous. For OCP, 0.55L ≈ LH ≈ 2RH, and for DOCP L ≈ LH ≈ 2.7RH. Finally the two layers present different inelastic behaviors. The DOCP layer presents a mesh more compact and more uniform than the OCP layer as indicated by the thickness measurements. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology...

Synthesis and characterization of model associative polymers

AbstractModel linear associative polymers with number average molecular weights in the range of 16,600 to 100,400 were prepared by connecting blocks of commercially available poly(oxyethylene) with isophorone diisocyanate, followed by capping with either hydroxyl, dodecyl, or hexadecyl linear alkyl end groups. The molecular weight distributions measured by gel permeation chromatography are somewhat broad, as expected from the synthetic method. In a 40/60 by weight solvent mixture of diethylene glycol monobutyl ether (Butyl Carbitol) and water, the relative viscosities of model associative polymers and poly(oxyethylene) standards collapsed to a single master curve; viscosity average molecular weights obtained from the intrinsic viscosities measured in this solvent mixture compare favorably to those obtained by size exclusion chromatography. In water, the model polymers with alkyl end groups interact at extremely dilute concentrations to produce a pronounced increase in reduced viscosity that increases as concentration and alkyl end group length increase. The Huggins parameters for solutions of model associative polymers with the hexadecyl and dodecyl end groups vary between 1 and 16, and decrease as molecular weight increases, as hydrophobe length decreases, and as temperature increases. The concentration at which the viscosity data deviate from the Huggins equation is less than the polymer coil overlap concentration, which is on the order of 1–3 g/dL, as estimated from the reciprocal of the intrinsic viscosity data. This suggests that we can define a critical network concentration c*h as the concentration at which the associative polymers hydrophobic end groups first interact to form a rheologically significant network. However, the transition occurs over a concentration range, rather than at a particular critical micellar concentration, as is the case of ordinary surfactants or hydrophobically modified hydroxyethylcellulose. The dimensions of the associative polymer coils in solution, and the signs and relative magnitudes of heat and entropy of dilution as estimated from classical molecular theories, are similar to those obtained by other authors for poly(oxyethylene) homopolymers. A physical model based on equilibrium kinetics for the association process correctly mimics the dependence of viscosity on molecular weight and concentration, and indicates that the free energy of association must become larger as the length of the alkyl end groups becomes larger relative to the hydrophilic backbone. © 1995 John Wiley & Sons, Inc.

Quenching of the triplet state of poly(2-vinylnaphthalene) in solution: Effect of molecular weight

The rate of decay of triplet-triplet absorption of excited poly(2-vinylnaphthalene) (P2VN) and 2-ethylnaphthalene (2EN) in room temperature benzene solutions was studied as a function of an added triplet quencher, piperylene. It was found that the efficiency of triplet quenching decreases as the molecular weight of the polymer increases, which is interpreted as arising from the density of the polymer coil in solution. If triplet energy migration occurs along the polymer chain the exciton diffusion constant is not significantly larger than the physical diffusion of the monomer model compound, 2EN. The triplet state was produced in solution by a 4 MeV electron beam, because the S 1 → T 1 process was found to be very inefficient for P2VN under optical excitation conditions.

Molecular dimensions of polystyrene in solution near the theta point

Hydrodynamic dimensions of polymer coils in solution were investigated around the theta point for the polystyrenecyclohexane system by quasielastic light scattering. Below the theta point, the hydrodynamic radius decreases very slightly and does not exhibit the collapse of the coil near the critical solution temperature in contrast with the radius of gyration.

A comparison of the volume occupied by macromolecules in the adsorbed state and in bulk solution: Adsorption of narrow molecular weight fractions of poly(vinyl alcohol) at the polystyrene/water interface

A commercial sample of poly(vinyl alcohol) ( M w of 45,000) has been fractionated on a preparative scale by gel permeation chromatography. Several fractions were obtained and these were characterized by ultracentrifugation, acetate analysis, and viscometry. The M w of the fractions ranged from 4,000 to 70,000. The acetate content and values for the Huggins/Martin constant, calculated from the viscosity data, showed no variation with molecular weight. The following Mark-Houwink equation was established: [η] 25°C = 2.7 × 10 −4M w 0.71 . By use of the Stockmayer-Fixman equation the polymer-solvent interaction parameter, χ 1, was found to be 0.465. The effective hydrodynamic dimensions and the rms dimensions of the polymer coils in solution were calculated from the ultracentrifugation and viscosity data, respectively, for each fraction. These fractions were used for a study of the dependence of adsorption on molecular weight. The amount adsorbed at the plateau of the isotherm, Λ, and the adsorbed layer thickness, δ, calculated from ultracentrifugation, both increased linearly with M w 1 2 . The volume occupied by each polymer molecule in the adsorbed state was found to be approximately the same as that occupied by the effective hydrodynamic sphere in bulk solution. However, the adsorbed layer thickness was found to be greater than the effective hydrodynamic diameter of the polymer coils in solution. Thus the adsorption was interpreted in terms of a possible deformation of the random coil but with no interpenetration with or compression of adjacent adsorbed molecules.

Study of the concentration dependence of the viscosity of dilute polymer solutions. Compression of polymer chains

STUDY of the hydrodynamic and thermodynamic properties of polymer solutions is an important task for practical reasons and is also of considerable theoretical value. The properties of infinitely dilute polymer solutions have been studied fairly thoroughly, both theoretically and experimentally. The derived theories of viscosity, light scattering, diffusion and sedimentation, and flow birefringence at c-+0 satisfactorily fit the existing experimental material and permit determination of the molecular weight, dimensions, shape and other molecular parameters of individual polymer chains [1]. The situation is different with regard to the concentration dependence of the hydrodynamic and optical properties of polymer solutions. Theories of the dependence of these properties on the concentration of polymer solutions have been derived only for the low concentration region, or more correctly for low values of c[t/], and these fit the experimental data only qualitatively. The properties of polymer solutions are dependent to some extent on the dimensions of the polymer chains, therefore for construction of the concentration dependence of their hydrodynamic and optical properties it is necessary to take account also of the dependence of the dimensions of the polymer chain on the concentration of the solution. The dimensions of polymer coils in solution are determined not only by entropic factors, but also by the energetics of polymer-solvent and polymerpolymer interaction. In good solvents these interactions result in effective mutual repulsion of polymer chain segments. The result of this is both increase in the size of the coils in comparison with the size in an ideal solvent, and also compression of the coils as a consequence of intermolecular interaction [2-4]. One of the methods of estimating the compression of polymer coils is by study of the viscosity of dilute polymer solutions. The first a t tempt at estimating the comression of polymer coils was made in reference [5]. The present work is devoted to development of a method of estimating the compression of