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Fluorescence resonance energy transfer (FRET) is a non-invasive characterization method for studying molecular structures and dynamics, providing high spatial resolution at nanometer scale. Over the past decades, FRET-based measurements are developed and widely implemented in synthetic polymer systems for understanding and detecting a variety of nanoscale phenomena, enabling significant advances in polymer science. In this review, the basic principles of fluorescence and FRET are briefly discussed. Several representative research areas are highlighted, where FRET spectroscopy and imaging can be employed to reveal polymer morphology and kinetics. These examples include understanding polymer micelle formation and stability, detecting guest molecule release from polymer host, characterizing supramolecular assembly, imaging composite interfaces, and determining polymer chain conformations and their diffusion kinetics. Finally, a perspective on the opportunities of FRET-based measurements is provided for further allowing their greater contributions in this exciting area., (© 2022 Wiley-VCH GmbH.)

This study investigates the effect of adding oligomers on the rheological properties of polymer nanocomposite melts with the goal of enhancing the processability of nanocomposites. The scaling analysis of plateau modulus (G N ) is used in understanding the complex mechanical behavior of entangled poly(methyl acrylate) (PMA) melts upon oligomer addition. Increasing the oligomer amount led to a decrease in G N and an apparent degree of entanglement (Z) in the neat polymer melt. The particle dispersion states at two particle loadings with oligomer addition are examined in transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The dilution exponent is found unchanged at 7 and 17 vol% particle loadings for the well-dispersed PMA-SiO 2 nanocomposites compared to the neat PMA solution. These findings suggest that attractive particles with strong interfacial layers do not influence the tube dilution scaling of the polymer with the oligomer. To the contrary, composites with weak polymer-particle interfaces demonstrate phase separation of particles when oligomers are introduced and its exponent for tube dilution scaling reaches 4 at a particle loading of 17 vol%, potentially indicating that network-forming clusters influence chain entanglements in this scenario., (© 2023 Wiley-VCH GmbH.)

In this study, a series of ladder-like polysiloxanes are synthesized by introducing double-chain Si-O-Si polymer as the backbone and the carbazole and triphenylphosphine oxide with high triplet energy as side groups. The ladder-like structures of polysiloxanes are achieved through a controlled polymerization method that involves the monomer self-assembly and subsequent surface-restricted solid-phase in situ condensation through freeze-drying. The introduction of siloxane improves thermal stability of the polymers and inhibits the conjugation of the polymers between the side groups, leading to an increase in the triplet energy level. Therefore, all these polymers perform higher triplet energy levels than phosphorescent emitter (FIrpic). The cyclic voltammetry measurements demonstrate that the bipolar polymer exhibits a high highest occupied molecular orbital (HOMO) value of -5.32 eV, which is consistent with the work function of ITO/PEDOT:PSS, consequently facilitating hole injection. Furthermore, the incorporation of triphenylphosphine oxide promotes electron injection. Molecular simulations reveal that the frontier orbital distributions of the bipolar polymer are located on the carbazole and triphenylphosphine groups, respectively, which facilitate the transport of electrons and holes., (© 2023 Wiley-VCH GmbH.)

Hybrid vesicles consisting of phospholipids and block-copolymers are increasingly finding applications in science and technology. Herein, small angle X-ray scattering (SAXS) and cryo-electron tomography (cryo-ET) are used to obtain detailed structural information about hybrid vesicles with different ratios of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and poly(1,2-butadiene-block-ethylene oxide) (PBd 22 -PEO 14 , M s  = 1800 g mol -1 ). Using single particle analysis (SPA) the authors are able to further interpret the information gained from SAXS and cryo-ET experiments, showing that increasing PBd 22 -PEO 14 mole fraction increases the membrane thickness from 52 Å for a pure lipid system to 97 Å for pure PBd 22 -PEO 14 vesicles. Two vesicle populations with different membrane thicknesses in hybrid vesicle samples are found. As these lipids and polymers are reported to homogeneously mix, bistability is inferred between weak and strong interdigitation regimes of PBd 22 -PEO 14 within the hybrid membranes. It is hypothesized that membranes of intermediate structure are not energetically favorable. Therefore, each vesicle exists in one of these two membrane structures, which are assumed to have comparable free energies. The authors conclude that, by combining biophysical methods, accurate determination of the influence of composition on the structural properties of hybrid membranes is achieved, revealing that two distinct membranes structures can coexist in homogeneously mixed lipid-polymer hybrid vesicles., (© 2023 The Authors. Small published by Wiley-VCH GmbH.)

We compute by molecular simulation the energy/entropic partition of the force in a stretched double-stranded (ds)DNA molecule that is not yet available from the single-molecule measurements. Simulation using the coarse-grained wormlike chain (WLC) model predicts a gradual decrease in the internal (bending) energy of DNA at stretching. The ensuing negative energy contribution to force f U is outweighed by the positive entropy contribution f S . The ratio f U /f, used to assess the polymer elasticity, is about -1 at the moderate extension of DNA. At the high extension, the extra energy expenses due to the contour length elongation make the ratio f U /f less negative. The simulation findings of the hybrid energy/entropy nature of DNA elasticity at weak and moderate forces are supported by computations using the thermoelastic method mimicking the polymer experiments in bulk. It is contended that the observation of the negative energy elasticity in DNA can be generalized to other semiflexible polymers described by the WLC model., (© 2022 Wiley Periodicals LLC.)

A one-pot approach for the preparation of diblock copolymers consisting of polystyrene and polymyrcene blocks is described via a temperature-induced block copolymer (BCP) formation strategy. A monomer mixture of styrene and myrcene is employed. The unreactive nature of myrcene in a polar solvent (tetrahydrofuran) at -78 °C enables the sole formation of active polystyrene macroinitiators, while an increase of the temperature (-38 °C to room temperature) leads to poly(styrene-block-myrcene) formation due to polymerization of myrcene. Well-defined BCPs featuring molar masses in the range of 44-117.2 kg mol -1 with dispersities, Ð, of 1.09-1.21, and polymyrcene volume fractions of 30-64% are accessible. Matrix assisted laser desorption ionization-time of flight mass spectrometry measurements reveal the temperature-controlled polymyrcene block formation, while both transmission electron microscopy and small-angle X-ray scattering measurements prove the presence of clearly microphase-separated, long range-ordered domains in the block copolymers. The temperature-controlled one-pot anionic block copolymerization approach may be general for other terpene-diene monomers., (© 2020 Wiley-VCH GmbH.)

Partially deuterated polymers, made by saturating the double bonds of polydienes with deuterium, have been found to produce weak but significant coherent patterns in small-angle neutron scattering (SANS) experiments. The results suggest the presence of slight differences in deuteration levels among the chains. The scattering profiles for such materials and for blends containing them were calculated with the multicomponent random phase approximation (RPA). The coherent intensity for the deuterated component alone is predicted to be proportional to the variance of its scattering length distribution and to have a q dependence corresponding to the pure component structure factor. The SANS data for a variety of partially deuterated polyolefins are shown to be consistent with these predictions. The theory also predicts that the scattering from their blends with an hydrogenous component is enhanced by this scattering length inhomogeneity, that the enhancement is additive, and that the conventional two component RPA may be used to analyze the data after this contribution is subtracted. Experimentally, we find that uncorrected scattering from blends rich in such deuterated components lead to anomalous estimates of chain dimensions and thermodynamic interactions. The anomalies disappear when the proposed correction is applied. [ABSTRACT FROM AUTHOR]

Dynamic moduli G* and zero‐shear viscosity ηo,ring data in both melt and solution states were reported for putative cyclic poly(3,6‐dioxa‐1,8‐octanedithiol) (RDODT) with molecular weights ranging from 43 to 556 kg/mol. Measurements over wide temperature ranges provide up to 18 decades of reduced frequency to characterize RDODT melts and solutions with Zw = Mw/Me,lin from 23 to 300, where Mw is the weight average molecular weight and Me,lin ≈ 1850 g/mol is the entanglement molecular weight of the linear counterparts (LDODT). The G* of all the seven RDODT melts and eight of their solutions with Zw > 15 all have a rubbery plateau with the plateau moduli about same as GNo of the corresponding LDODT. The value Zw ≈ 15 marks the threshold for the change in scaling of ηo,ring from the Rouse‐like ηo,ring ∼ Zw1.0 to a much stronger dependence of ηo,ring ∼ Zw5.8 for Zw up to 300. Such a Zw5.8‐dependence has not been seen before in cyclic polymers and cannot be accounted for by current theoretical models for cyclic polymers. The Coupling Model had been used before to explain the Mw3.4 ‐dependence of linear entangled polymers and the stronger Mw ‐dependence of multi‐arm star branched polymers. It is applied to cyclic RDODT melts and solutions and the results provide an explanation of the observed Zw5.8‐dependence of ηo,ring. [ABSTRACT FROM AUTHOR]

Lateral migration and focusing of particles in viscoelastic fluids have recently been widely exploited in various microfluidic applications, such as particle counting and separation. However, there are still many unresolved problems regarding the underlying mechanisms that induce lateral migration in polymer solutions. In particular, as the sizes of particles and polymers (e.g., radius of gyration) become comparable, continuum mechanics (constitutive modeling)-based analyses are expected to fail, which has not yet been investigated. If lateral particle migration occurs only due to conventional bulk viscoelastic effects, the equilibrium particle positions are expected to remain constant when the aspect ratio ( r p c ) of the particle to channel dimensions is nearly fixed. In this study, we found that as the channel dimension of the cross section decreases, a transition occurs in which individual polymers (λ -deoxyribonucleic acid) behave as deformable particles, and consequently, the equilibrium positions change. This study contributes to clarifying the lateral particle migration in polymer solutions and can be applied to various applications, such as deformability-selective particle separation. [ABSTRACT FROM AUTHOR]

This work presents a unified polymer reaction engineering methodology for the catalytic olefin polymerization process. The proposed modelling approach offers a modelling pathway from the polymerization recipe to production rate and polymer microstructure, and finally to rheological properties. Furthermore, this work introduces for the first time the constraint of the actual reaction performance of the polymerization catalyst in the inverse rheology and microstructural deconvolution problem, limiting the solution only to the most realistic potential molecular weight distributions (MWDs) that a specific catalyst can produce. This approach can be applied for both single‐ and multi‐site catalysts, providing not a potential MWD but the unique one that the selected catalyst can offer under given polymerization conditions. Depending on the available catalyst reaction performance insight, the constraint can vary and include from the number of active sites in use to the exact kinetic parameters of each site type. The potential of the proposed methodology is highlighted within a series of indicative examples, including forward, reverse engineering and deconvolution applications. [ABSTRACT FROM AUTHOR]

The current work qualitatively surveys the phenomenon of polymer drag reduction from the standpoint of the salient coherent motions in the near-wall region of wall-bounded turbulent flows. In an attempt to make the work self-containing, turbulence is introduced phenomenologically in terms of the scale separation concept. In concert with this theme, the idea of drag crisis is then developed in terms of reduction in this scale separation. Leveraging such a perspective, it is explained how the polymer chain dynamics spatiotemporally modulate the near-wall structure of turbulent boundary layers to affect drag reduction. To this end, a sea of literature pertaining to coherent motions in Newtonian wall-bounded flows is juxtaposed with the turbulence-inhibiting characteristics of polymer chains to develop a polymer-modified version for the near-wall cycle of turbulence generation and its sustenance. The future of polymer drag reduction, in light of the current state of knowledge and contemporary challenges, is also discussed. [ABSTRACT FROM AUTHOR]

We present an algorithm to predict the linear relaxation spectra for linear polymers of fully general and arbitrary polydispersity. As is common in the tube theory descriptions of linear polymers, we assume that the stress relaxation is affected by both the constraint release and tube escape modes, but unlike most existing descriptions we consider how these two modes of relaxation affect each other. We argue that the proper description for relaxation in an arbitrary blend of linear polymers requires consideration of multiple embedded tubes affecting the different relaxation pathways; we propose a novel but minimal description involving five embedded tubes. Building on prior work for binary blends, we derive the scaling level descriptions of the relaxation pathways. We use a large number of existing experimental results on the stress and dielectric relaxations to validate our model, ensuring we explore a very broad range of parameter space. [ABSTRACT FROM AUTHOR]

Stress overshoot is one of the most important nonlinear rheological phenomena exhibited by polymeric liquids undergoing start-up shear at sufficient flow strengths. Despite considerable previous research, the fundamental molecular characteristics underlying stress overshoot remain unknown. Here, we analyze the intrinsic molecular mechanisms behind the overshoot phenomenon using atomistic nonequilibrium molecular dynamics simulations of entangled linear polyethylene melts under shear flow. Through a detailed analysis of the transient rotational chain dynamics, we identify an intermolecular collision angular regime in the vicinity of the chain orientation angle 73952; ≈ 20° with respect to the flow direction. The shear stress overshoot occurs via strong intermolecular collisions between chains in the collision regime at 73952; = 15°-25°, corresponding to a peak strain of 2-4, which is an experimentally well-known value. The normal stress overshoot appears at approximately 73952; = 10°, at a corresponding peak strain roughly equivalent to twice that for the shear stress. We provide plausible answers to several basic questions regarding the stress overshoot, which may further help understand other nonlinear phenomena of polymeric systems. [ABSTRACT FROM AUTHOR]

Many studies have established a major effect of nanoscale confinement on the glass transition temperature (Tg) of polystyrene (PS), most commonly in thin films with one or two free surfaces. Here, we characterize smaller yet significant intrinsic size effects (in the absence of free surfaces or significant attractive polymer-substrate interactions) on the Tg and fragility of PS. Melt infiltration of various molecular weights (MWs) of PS into anodic aluminum oxide (AAO) templates is used to create nanorods supported on AAO with rod diameter (d) ranging from 24 to 210 nm. The Tg (both as Tg,onset and fictive temperature) and fragility values are characterized by differential scanning calorimetry. No intrinsic size effect is observed for 30 kg/mol PS in template-supported nanorods with d = 24 nm. However, effects on Tg are present for PS nanorods with Mn and Mw = 175 kg/mol, with effects increasing in magnitude with increasing MW. For example, in 24-nm-diameter template-supported nanorods, Tg,rod - Tg,bulk = -2.0 to -2.5 °C for PS with Mn = 175 kg/mol and Mw = 182 kg/mol, and Tg,rod Tg,bulk = ~-8 °C for PS with Mn = 929 kg/mol and Mw = 1420 kg/mol. In general, reductions in Tg occur when d ≤ ; -2Rg, where Rg is the bulk polymer radius of gyration. Thus, intrinsic size effects are significant when the rod diameter is smaller than the diameter (2Rg) associated with the spherical volume pervaded by coils in bulk. We hypothesize that the Tg reduction occurs when chain segment packing frustration is sufficiently perturbed by confinement in the nanorods. This explanation is supported by observed reductions in fragility with the increasing extent of confinement. We also explain why these small intrinsic size effects do not contradict reports that the Tg-confinement effect in supported PS films with one free surface exhibits little or no MW dependence. [ABSTRACT FROM AUTHOR]

Due to their unique topology of having no chain ends, dilute solutions of ring polymers exhibit behavior distinct from their linear chain counterparts. The universality of their static and dynamic properties, as a function of solvent quality z in the thermal crossover regime between θ and athermal solvents, is studied here using Brownian dynamics simulations. The universal ratio U RD of the radius of gyration R g to the hydrodynamic radius R H is determined, and a comparative study of the swelling ratio α g of the radius of gyration, the swelling ratio α H of the hydrodynamic radius, and the swelling ratio α X of the mean polymer stretch X along the x -axis, for linear and ring polymers, is carried out. The ratio U RD for dilute ring polymer solutions is found to converge asymptotically to a constant value as z → ∞ , which is a major difference from the behavior of solutions of linear chains, where no such asymptotic limit exists. Additionally, the ratio of the mean stretch along the x -axis to the hydrodynamic radius, (X / R H) , is found to be independent of z for polymeric rings, unlike in the case for linear polymers. These results indicate a fundamental difference in the scaling of static and dynamic properties of rings and linear chains in the thermal crossover regime. [ABSTRACT FROM AUTHOR]

Cyclodextrins are a class of biocompatible and highly water‐soluble oligosaccharide polymers, with vast applications in industries ranging from drug delivery to agriculture. Currently, most fiber production relies on using environmentally unfriendly organic solvents and polymeric additions. Cyclodextrins are seldom used on their own without a carrier polymer, however in this work, (2‐hydroxypropyl)‐β‐cyclodextrin) fibers are successfully produced with water, as the "green" solvent with pressurized gyration and electrospinning, without using a carrier polymer. The average fiber diameter of the pressurized gyration produces fibers ranged between 5.5 and 5.8 µm, while the average fiber diameter of the electrospun fibers ranged between only 183 and 305 nm. These findings show the thinnest diameter of pure cyclodextrin fibers achieved in current literature. Both techniques have specific advantages, such as electrospinning being able to produce nanofibers, while pressurized gyration has productivity of over 1.5 g min−1. Here, a pioneering study into the production of cyclodextrin‐only fibers with two different fiber production techniques and the creation of a cyclodextrin‐super‐mat that combines both types of fibers is presented. [ABSTRACT FROM AUTHOR]

Three subjects in polymer and soft matter physics are outlined in the present article. The first relates to concepts of an ideal glass transition. We describe work on ultra‐stable glass, either a 20‐million‐year‐old amber or a vapor deposited amorphous fluoropolymer, which examines the temperature dependence of the dynamics in a window between a low fictive temperature and the glass transition temperature. From this "finesse" of the problem of the geological time scales in sub‐glass temperature systems strong evidence that the divergence of the relaxation times at finite temperature from WLF‐types of extrapolation is not correct. The second topic is polymer nonlinear viscoelasticity as it relates to dynamic heterogeneity. We show results from mechanical hole burning experiments that suggest that dynamic heterogeneity arises from the nature of specific relaxation mechanisms rather than heterogeneous changes in, for example, the fictive temperature. Included is a discussion of large amplitude oscillatory shear testing and how it relates to characterization of nonlinear viscoelastic materials. The last topic addressed is the rheology of circular macromolecules. Here, we take a historical perspective and describe important new results from several laboratories that seem inconsistent. New works from our own studies on circular DNA are also discussed. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear behavior of carbon black-filled polybutadiene solutions under large-amplitude oscillatory shear is investigated. The results show that in the nonlinear regime, the third harmonic intensity, as measured by the ratio of the third to the first harmonics I3/I1, decreases significantly above a critical concentration ϕc of the polymer in the matrix, which results in the amplitude stress deviating strongly from the linear dependence of strain, while the time dependence of stress remains sinusoidal. Increasing the filler particle size significantly decreases the critical ϕc. However, increasing the filler loading basically has no effect on the transition to linear-nonlinear dichotomy. This transition happens when the mesh size ξ of the entangled polymer network in the matrix becomes smaller than the primary filler particle size. Above ϕc, the topological hindrance of the entangled polymer chains apparently considerably slows down the recovery speed of the broken filler network in the material. Hence, the quasisinusoidal response in the system that has a strain-dependent modulus is probably due to the restoration of the broken filler network requiring longer than the time scale of a typical dynamic perturbation. [ABSTRACT FROM AUTHOR]

Both entangled and unentangled polymer melts exhibit stress overshoots when subject to shearing flow. The size of the overshoot depends on the applied shear rate and is related to relaxation mechanisms such as reptation, chain stretch, and convective constraint release. Previous experimental work shows that melts subjected to interrupted shear flows exhibit a smaller overshoot when sheared after partial relaxation. This has been shown to be consistent with predictions by constitutive models. Here, we report molecular dynamics simulations of interrupted shear of polymer melts where the shear flow after the relaxation stage is orthogonal to the originally applied flow. We observe that, for a given relaxation time, the size of the stress overshoot under orthogonal interrupted shear is larger than observed during parallel interrupted shear, which is not captured by constitutive models. Differences in maxima are also observed for overshoots in the first normal stress and chain end-to-end distance. We also show that measurements of the average number of entanglements per chain and average orientation at different scales along the chain are affected by the change in shear direction, leading to nonmonotonic relaxation of the off-diagonal components of orientation and an appearance of a "double peak" in the average number of entanglements during the transient. We propose that such complex behavior of entanglements is responsible for the increase in the overshoots of stress components and that models of the dynamics of entanglements might be improved upon by considering a tensorial measurement of entanglements that can be coupled to orientation. [ABSTRACT FROM AUTHOR]

Chain entanglement, either cohesional or topological, distinguishes polymers from other engineering materials. It impedes the movement of molecular segments and influences the polymer rheology, morphology, and mechanical properties. Although a high level of entanglement can increase the polymer toughness, excessive entanglement should be avoided because it causes a high melt viscosity making the processing difficult. This review tended to elucidate the influence of entanglement on the polymer structure, determining the material properties and processability. A wide range of methods used to fine control the degrees of chain entanglement are summarized. The methods are applicable to polymers in solutions, melts, and condensed states with advantages and limitations discussed in detail. The authors also examined the effect of the entanglement on polymer crystallization—the mechanism remains a controversial issue. This review will provide general guidance to designing and processing polymer materials with desired properties via a rational route of controlling the chain entanglement. [ABSTRACT FROM AUTHOR]

The packing length p figures prominently in scaling predictions of the entanglement length and bulk modulus for polymer melts and solutions. p has been argued to scale as the ratio of chain displaced volume V and mean square end-to-end distance R 2. This scaling works for several cases; however, it is not obvious how to apply it to chains with side groups, and the scaling must fail for sufficiently thin, stiff chains. In this work, we measure the packing length in simulations, without making any scaling assumptions, as the typical distance of closest approach of two polymer strands in a simulated bead-spring melt. We use the intermolecular correlation function to measure the distance up to which a given polymer strand dominates the local volume fraction. Using our measured packing length, we find good agreement of entanglement properties with Lin–Noolandi scaling for flexible polymers of different architectures. [ABSTRACT FROM AUTHOR]

A semi-empirical constitutive equation is suggested for the model comb polymer with the purpose to simultaneously describe the intrinsic medium amplitude oscillatory shear (MAOS) behaviors and transient behaviors in start-up elongational experiments. The molecular stress and hierarchical relaxation of comb polymers are discussed on the basis of the orientation-stretch coupled conformation tensor of both backbone and arm, which are governed by the same evolution equation with different relaxation times. The discrete Baumgaertel–Schausberger–Winter spectrum is adopted for the backbone relaxation. The model has four parameters that are fully determined from the linear spectrum. The equation set is solved analytically by the perturbation method under MAOS and solved numerically under start-up extensional flows. The predictions on the nonlinear rheological behaviors are well consistent with the experiments. [ABSTRACT FROM AUTHOR]

Semiflexible polymers and their assemblies are important in biology as cross‐linked networks of semiflexible polymers form a major structural component of tissue and living cells. This research used shear rheology to demonstrate the tuning from worm‐like to rod‐like conformation in semiflexible polymers by polymer‐solvent interactions. The conformation was assessed by the persistence length lp, and its influence, in the semidilute regime, was assessed by the scaling of zero‐shear viscosity ηo with concentration c and molecular weight M¯. The polymers were poly n‐butyl and poly n‐octyl isocyanate (PBIC and POIC, respectively). PBIC exhibited the largest lp in chlorinated solvents, and the solutions obeyed the scaling law ηo∝c3.0M¯6.6. However, when PBIC was dissolved in benzene the lp was greatly reduced and the scaling law now was ηo∝M¯4.2, consistent with a worm‐like conformation. On the other hand, POIC dissolved in chlorinated and benzenic solvents exhibited a worm‐like conformation and the scaling was ηo∝c2.5M¯3.5. These results were contrasted with those of hydroxypropyl cellulose (HPC) aqueous solutions, which exhibit worm‐like conformation, the solutions obeyed the scaling ηo ∝ c2.5. Finally, the shear viscosity of the polyisocyanates and HPC obeyed the Saito scaling, valid for anisotropic particles in solution. [ABSTRACT FROM AUTHOR]

We develop a method for efficient prediction of linear and nonlinear rheology of polydisperse polymers by judicious selection of a small number of representative polymer molecules from the large ensemble of chains comprising the molecular weight and branching distribution. Specifically, we use a numerical inversion of the double reptation model to select five or six representative molecular species to optimally fit the linear rheology of commercial polymers and then use the regressed parameters to compute the nonlinear rheology via the Rolie-double-poly (RDP) model. The method is tested for several model systems, namely, two polydisperse linear polystyrene (PS) samples described in Shivokhin et al. [Polym. Eng. Sci. 56, 1012–1020 (2016)] and Münstedt [J. Rheol. 24, 847–867 (1980)], a commercial linear low density polyethylene (LLDPE), and a low density polyethylene (LDPE) whose rheological properties are measured in the current study. For the linear polymers including the PS samples and the LLDPE, the predictions of the "representative" RDP model of the start-up extensional rheology are comparable to those of the "full" RDP model based on all the species drawn from the gas permeation chromatography characterization. The method then successfully predicts the linear rheology of blends of LLDPE and LDPE using the same representative molecules found by fitting each of the pure polymers. Further fitting the extensional rheology of the LDPE requires using the "priorities" q i and stretch relaxation times τ s , i of the representative molecules as adjustable parameters, whose values are then held fixed when predicting the extensional rheology of blends of the LDPE with the LLDPE roughly as successfully as does branch-on-branch model. The reduction in the number of representative polymer species offers new opportunities for faster simulations of flowing polymers, as well as for the prediction of segmental orientation to be used in the modeling of flow-induced crystallization. [ABSTRACT FROM AUTHOR]

A series of biaryl Group 4 complexes with a bidentate and a tridentate pincer ligand have been synthesized and characterized. The complexes have been applied as metallocene analogues for the controlled polymerization of ethylene and the copolymerization of ethylene and 1‐hexene, with a particular focus on the control of the degree of long chain branching in these polymers. [ABSTRACT FROM AUTHOR]

We present a new strategy for introducing population balances into full-chain constitutive models of living polymers with linear chain architectures. We provide equations to describe a range of stress relaxation processes covering both unentangled systems (Rouse-like motion) and well-entangled systems (reptation, contour length fluctuations, chain retraction, and constraint release). Special attention is given to the solutions that emerge when the "breaking time" of the chain becomes fast compared to various stress relaxation processes. In these "fast breaking" limits, we reproduce previously known results (with some corrections) and also present new results for nonlinear stress relaxation dynamics. Our analysis culminates with a fully developed constitutive model for the fast breaking regime in which stress relaxation is dominated by contour length fluctuations. Linear and nonlinear rheology predictions of the model are presented and discussed. [ABSTRACT FROM AUTHOR]

The linear viscoelasticity of polydisperse samples and their discretization into a blend of nf monodisperse fractions is compared. The molecular weight distribution of the polydisperse sample is described using a lognormal distribution, which has two parameters that are related to the weight‐averaged molecular weight, Zw, and the polydispersity index, ρ. Due to its success on similar systems, a variant of the double reptation model is used to describe the linear rheology. Given Zw and ρ, the optimal number of monodisperse fractions nf∗ is obtained using the Bayesian information criterion. It quantifies and negotiates the tradeoff between accuracy (discrepancy with the response of the polydisperse sample) and complexity (number of fractions). The optimal number of fractions was found to be somewhat insensitive to Zw; however, it increased with ρ from about 6 for ρ = 1.01 to about 20 for ρ = 2.0. Changing the underlying viscoelastic model had only a weak effect on the conclusions. Furthermore, using a blend of monodisperse fractions was found to be preferable to direct sampling even when an ensemble of chains was requested. [ABSTRACT FROM AUTHOR]

Obtaining a rigorous and reliable method for linking computer simulations of polymer blends and composites at different length scales of interest is a highly desirable goal in soft matter physics. In this paper a multiscale modeling procedure is presented for the efficient calculation of the static structural properties of binary homopolymer blends. The procedure combines computer simulations of polymer chains on two different length scales, using a united atom representation for the finer structure and a highly coarse-grained approach on the mesoscale, where chains are represented as soft colloidal particles interacting through an effective potential. A method for combining the structural information by inverse mapping is discussed, allowing for the efficient calculation of partial correlation functions, which are compared with results from full united atom simulations. The structure of several polymer mixtures is obtained in an efficient manner for several mixtures in the homogeneous region of the phase diagram. The method is then extended to incorporate thermal fluctuations through an effective χ parameter. Since the approach is analytical, it is fully transferable to numerous systems. [ABSTRACT FROM AUTHOR]

We apply the self-consistent polymer reference interaction site model (SC/PRISM) to liquid state calculations of the chain dimensions in polymer melts with added nanoparticle fillers. The nanoparticles are assumed to be smaller than the polymer radius of gyration and are attracted to the polymer so that they are miscible. We find that the nanoparticles perturb the chain dimensions, causing an increase in the radius of gyration with increasing nanoparticle volume fractions, assuming reasonable interaction energies between the various components. The magnitude of the expansion is in qualitative agreement with recent neutron scattering results and suggests that the SC/PRISM approach is reasonable when dealing with these apparent nonlinear phenomena present in nanocomposites in the protein limit. [ABSTRACT FROM AUTHOR]

Polymer fluids are modeled with dissipative particle dynamics (DPD) as undiluted bead-spring chains and their solutions. The models are assessed by investigating their steady shear-rate properties. Non-Newtonian viscosity and normal stress coefficients, for shear rates from the lower to the upper Newtonian regimes, are calculated from both plane Couette and plane Poiseuille flows. The latter is realized as reverse Poiseuille flow (RPF) generated from two Poiseuille flows driven by uniform body forces in opposite directions along two-halves of a computational domain. Periodic boundary conditions ensure the RPF wall velocity to be zero without density fluctuations. In overlapping shear-rate regimes the RPF properties are confirmed to be in good agreement with those calculated from plane Couette flow with Lees–Edwards periodic boundary conditions (LECs), the standard virtual rheometer for steady shear-rate properties. The concentration and the temperature dependence of the properties of the model fluids are shown to satisfy the principles of concentration and temperature superposition commonly employed in the empirical correlation of real polymer-fluid properties. The thermodynamic validity of the equation of state is found to be a crucial factor for the achievement of time-temperature superposition. With these models, RPF is demonstrated to be an accurate and convenient virtual rheometer for the acquisition of steady shear-rate rheological properties. It complements, confirms, and extends the results obtained with the standard LEC configuration, and it can be used with the output from other particle-based methods, including molecular dynamics, Brownian dynamics, smooth particle hydrodynamics, and the lattice Boltzmann method. [ABSTRACT FROM AUTHOR]

Molecular theories for polymer rheology are based on conformational dynamics of the polymeric chain. Hence, measurements directly related to molecular conformations appear more appealing than indirect ones obtained from rheology. In this study, primitive chain network simulations are compared to experimental data of entangled DNA solutions [Teixeira et al., Macromolecules 40, 2461 (2007)]. In addition to rheological comparisons of both linear and nonlinear viscoelasticities, a molecular extension measure obtained by Teixeira et al. through fluorescent microscopy is compared to simulations, in terms of both averages and distributions. The influence of flow on conformational distributions has never been simulated for the case of entangled polymers, and how DNA molecular individualism extends to the entangled regime is not known. The linear viscoelastic response and the viscosity growth curve in the nonlinear regime are found in good agreement with data for various DNA concentrations. Conversely, the molecular extension measure shows significant departures, even under equilibrium conditions. The reason for such discrepancies remains unknown. [ABSTRACT FROM AUTHOR]

We investigated the dynamics of single chains diffusing in cross-linked polymer networks using the three-dimensional bond fluctuation method. We considered single chain dynamics in dry polymer networks, at monomer density of 0.51, and similarly, in networks swollen up to the maximum degree of swelling. In order to compare time scales at different degrees of network swelling we calculated the single monomer relaxation time τ0, which showed a strong decrease with swelling. The scaling laws of terminal relaxation times τd and the diffusion coefficients D as function of renormalized chain length covered both the Rouse and the entangled regime. We found that the entanglement length Ne as function of monomer density of the network has similar values to those calculated for polymer melts, at the same concentration. The effect of fixed topological constraints in polymer networks on the concentration dependence of the entanglement length is discussed. [ABSTRACT FROM AUTHOR]

We investigate the structural, dynamical, and viscoelastic properties of colloid-polymer mixtures at intermediate colloid volume fraction and varying polymer concentrations, thereby tuning the attractive interactions. Within the examined range of polymer concentrations, the samples varied from fluids to gels. In the liquid phase, an increasing correlation length of the density fluctuations when approaching the gelation boundary was observed by static light scattering and microscopy, indicating clustering and formation of space-spanning networks. Simultaneously, the correlation function determined by dynamic light scattering decays completely, indicating the absence of dynamical arrest. Clustering and formation of transient networks when approaching the gelation boundary is supported by significant changes in the viscoelastic properties of the samples. Upon increasing the polymer concentration beyond the gelation boundary, the rheological properties changed qualitatively again, now they are consistent with the formation of colloidal gels. Our experimental results, namely, the location of the gelation boundary as well as the elastic (storage) and viscous (loss) moduli, are compared to different theoretical models. These include consideration of the escape time as well as predictions for the viscoelastic moduli based on scaling relations and mode coupling theories. [ABSTRACT FROM AUTHOR]

A matrix method is used to determine fluctuations of junctions and points along the polymer chains making up a phantom Gaussian network that has the topology of an infinite, symmetrically grown tree. The functionalities of the junctions alternates between [lowercase_phi_synonym]1 and [lowercase_phi_synonym]2, such that one end of each network chain has functionality [lowercase_phi_synonym]1, while the opposite end has functionality [lowercase_phi_synonym]2. Quantities calculated include fluctuations of [lowercase_phi_synonym]1-functional and [lowercase_phi_synonym]2-functional junctions, and fluctuations of points along network chains, as well as correlations of these fluctuations. This was done for points and junctions along any path in the network, where these points and junctions were separated by no junctions or several junctions, Fluctuations have also been calculated for the distances between points and junctions. The present results represent significant generalizations of earlier work in this area [Kloczkowski et al., Macromolecules 22, 1423 (1989)]. These generalizations and extensions should be very useful in a number of contexts, such as interpreting small-angle neutron scattering results on labeled paths in polymer networks, or fluctuations of loops in the Gaussian network model of proteins. [ABSTRACT FROM AUTHOR]

We investigate the ability of Monte-Carlo algorithms to describe the single-chain dynamics in a dense homogeneous melt and a lamellar phase of a symmetric diblock copolymer. A minimal, coarse-grained model is employed that describes connectivity of effective segments by harmonic springs and where segments interact via soft potentials, which do not enforce noncrossability of the chain molecules. Studying the mean-square displacements, the dynamic structure factor, and the stress relaxation, we show that local, unconstraint displacements of segments via a Smart Monte Carlo algorithm give rise to Rouse dynamics for all but the first Monte Carlo steps. Using the slithering-snake algorithm, we observe a dynamics that is compatible with the predictions of the tube model of entangled melts for long times, but the dynamics inside the tube cannot be resolved. Using a slip-link model, we can describe the effect of entanglements and follow the different regimes of the single-chain dynamics over seven decades in time. Applications of this simulation scheme to spatially inhomogeneous systems are illustrated by studying the lamellar phase of a symmetric diblock copolymer. For the local, unconstraint dynamics, the single-chain motions parallel and perpendicular to the interfaces decouples; the perpendicular dynamics is slowed down but the parallel dynamics is identical to that in a homogeneous melt. Both the slithering-snake dynamics and the slip-link dynamics give rise to a coupling of parallel and perpendicular directions and a significant slowing down of the dynamics in the lamellar phase. [ABSTRACT FROM AUTHOR]

We present a new framework for the description of macromolecules subject to confining geometries. The two main ingredients are a new computational method and the definition of a new molecular size parameter. The computational method, hereafter referred to the confinement analysis from bulk structures (CABS), allows the computation of equilibrium partition coefficients as a function of confinement size solely based on a single sampling of the configuration space of a macromolecule in bulk. Superior in computational speed to previous computational methods, CABS is capable of handling slits, channels, and box confining geometries for all molecular architectures. The new molecular size parameter, hereafter referred to the steric exclusion radius Rs, is explicitly defined and computed for a number of rigid objects and flexible polymers. We suggest that Rs is the relevant molecular size parameter for characterization of spatial confinement effects on macromolecules. Results for the equilibrium partition coefficient in the weak confinement regime depend only on the ratio of Rs to the confinement size regardless of molecular details. [ABSTRACT FROM AUTHOR]

We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide range of reduced polymer densities: (i) semidilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semiflexible (bio)polymers such as F-actin or suspensions of rodlike viruses. Together, these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts. [ABSTRACT FROM AUTHOR]

Chain diffusion is studied in mixtures of bidisperse linear polymers of same chemical identity by means of simulations. The two subpopulations are moderately to highly entangled, with the shorter chain length NS, fulfilling NS/Ne>=5. To this end, a coarse grained model calibrated to reproduce both the structure and dynamics of chains in monodisperse entangled melts is used [A. Rakshit and R. C. Picu, J. Chem. Phys. 125, 164907 (2006)]. Its performance in reproducing chain dynamics in a polydisperse melt is tested by extensively comparing the results with those obtained from an equivalent fine scale representation of the same system (a bead-spring model). The coarse grained model is used further to investigate the scaling of the diffusion coefficient with the length of the two types of chains and its dependence on the respective fractions. The model reproduces many features observed experimentally. For example, the diffusion coefficient of one of the chain types decreases with increasing the length of the other type chains. It is shown that, in this model, this effect is not linked to constraint release. When the matrix chains become sufficiently long, their length does not influence the diffusion coefficient of the short chains anymore. The diffusion coefficient of the short chains scales with their weight fraction in a manner consistent with experimental observations. In mixtures, the dynamics of the short chains is slower and that of the long chains is marginally faster than in their respective monodisperse melts. [ABSTRACT FROM AUTHOR]

The polymer properties of canine mucus were investigated through the method of rotating magnetic particle microrheometry. Mucus is visualized as a physically entangled biopolymer of low polydispersity in a water-based solution. Mucus was modeled according to the constitutive law of a Doi-Edwards fluid. The magnetic-particle equation of rotational motion is analytically solved in the linear viscoelastic limit rendering theoretical flow profiles which are used to fit the experimental trace signals of the particle remanent-magnetic-field decay. The zero-shear-rate viscosity was found to be 18 000 P and the relaxation time at about 42 s. The molecular weight between entanglements for mucins was estimated at 1.7 MDa rendering an estimation of about seven physical cross-links per molecule. Rheological investigations were extended also to diluted and concentrated rations of the normal mucus simulating the conditions found in more physiological extremes. [ABSTRACT FROM AUTHOR]

Recent experimental evidence has motivated us to present a set of new theoretical considerations and to provide a rationale for interpreting the intriguing flow phenomena observed in entangled polymer solutions and melts [P. Tapadia and S. Q. Wang, Phys. Rev. Lett. 96, 016001 (2006); 96, 196001 (2006); S. Q. Wang et al., ibid. 97, 187801 (2006)]. Three forces have been recognized to play important roles in controlling the response of a strained entanglement network. During flow, an intermolecular locking force fiml arises and causes conformational deformation in each load-bearing strand between entanglements. The chain deformation builds up a retractive force fretract within each strand. Chain entanglement prevails in quiescence because a given chain prefers to stay interpenetrating into other chains within its pervaded volume so as to enjoy maximum conformational entropy. Since each strand of length lent has entropy equal to kBT, the disentanglement criterion is given by fretract>fent∼kBT/lent in the case of interrupted deformation. This condition identifies fent as a cohesive force. Imbalance among these forces causes elastic breakdown of the entanglement network. For example, an entangled polymer yields during continuous deformation when the declining fiml cannot sustain the elevated fretract. This opposite trend of the two forces is at the core of the physics governing a “cohesive” breakdown at the yield point (i.e., the stress overshoot) in startup flow. Identifying the yield point as the point of force imbalance, we can also rationalize the recently observed striking scaling behavior associated with the yield point in continuous deformation of both shear and extension. [ABSTRACT FROM AUTHOR]

Thin polystyrene films supported by oxidized silicon (SiOx/Si) substrates may be unstable or metastable, depending on the film thickness, h, and can ultimately dewet the substrate when heated above their glass transition. In the metastable regime, holes nucleate throughout the film and subsequently grow due to capillary driving forces. Recent studies have shown that the addition of a second component, such as a copolymer or miscible polymer, can suppress the dewetting process and stabilize the film. We examined the hole growth dynamics and the hole morphology in thin film mixtures composed of polystyrene and tetramethyl bisphenol-A polycarbonate (TMPC) supported by SiOx/Si substrates. The hole growth velocity decreased with increasing TMPC content beyond that expected from changes in the bulk viscosity. The authors show that the suppression of the dewetting velocity is primarily due to reductions in the capillary driving force for dewetting and to increased friction at the substrate-polymer interface. The viscosity, as determined from the hole growth dynamics, decreases with decreasing film thickness, and is connected to a depression of the glass transition of the film. [ABSTRACT FROM AUTHOR]

Grand canonical Monte Carlo simulation and simple statistical thermodynamic theory are used to model the aggregation and phase separation of systems of reversibly polymerizing monomers, capable of forming chains with or without the ability to cyclize into rings, with isotropic square-well attractions between nonbonded pairs of monomers. The general trend observed in simulation of chain-only systems, as predicted in a number of published theoretical works, is that the critical temperature for phase separation increases and the critical monomer density decreases with rising polymer bond strength. Introduction of the equilibrium between chains and rings into the theory lowers the predicted critical temperature and increases the predicted critical density. While the chain-only theories predict a vanishing critical density in the limit of complete polymerization, when ring formation is taken into account the predicted critical density in the same limit approaches the density of the onset of the ring-chain transition. The theoretically predicted effect of cyclization on chemical potential is in good qualitative agreement with a subset of simulation results in which chain-only systems were compared with equilibrium mixtures of rings and chains. The influence of attractions on the aggregation number and radius of gyration of chains and rings observed in simulations is also discussed. [ABSTRACT FROM AUTHOR]

The effects of dynamic contact angle (θd), between a substrate and the melt of a dewetting polymer thin film, on the evolution of rim instabilities of dewetting holes were reported. Various θd’s were achieved by covering SiOx surfaces with different coverage of octadecyltrichlorosilane. On each surface, the morphology of the dewetting holes was examined in detail as the hole grew to a certain size. Rim instabilities, in terms of undulations in both r and z directions, became more pronounced as θd increased, under which condition, narrower and higher rims were also observed. Experimentally, atomic force microscopic scans of the rim were used to obtain the rim profile, which was predicted using θd. The predicted rim profile was used, in combination with the analysis of Rayleigh instability of a cylindrical fluid, to interpret the rim instability. The model captures the basic trend of the rim instability dependency on θd. The study demonstrates the importance of the substrate properties on the rim instability and the destabilization of polymer thin films during hole growth. [ABSTRACT FROM AUTHOR]

The volumetric properties of highly-charged defect-free polyelectrolyte networks with tetrafunctional crosslinks are studied through molecular dynamics simulations in the canonical ensemble. The network backbone monomers, which are monovalent, and the counterions, which are mono-, di-, or trivalent, are modeled explicitly in the simulations, but the solvent is treated implicitly as a dielectric medium of good solvation quality. The osmotic pressure of the network-solvent system is found to depend greatly on the strength of electrostatic interactions. Discontinuous volume phase transitions are observed when the electrostatic interactions are strong, and the onset of these transitions shifts to higher solvent dielectricity as the counterion valency increases. The roles of the various virial contributions to the osmotic pressure are examined. The network elasticity entropy is found to behave nearly classically. As the network contracts and collapses with increasing strength of electrostatic interactions, the loss of counterion entropy leads to increased counterion osmotic pressure contributions via two mechanisms. The reduction in available configurational space increases the counterion translational entropy contribution to the ideal part of the osmotic pressure, and the greater number of counterion-monomer contacts formed due to counterion condensation and confinement increases the counterion excluded-volume entropy contribution to the excess part of the osmotic pressure. These observations contrast the decrease in the single ideal-gas-like counterion translational entropy contribution to the osmotic pressure predicted by the counterion condensation–charge renormalization theory. An accompanying decrease in the total electrostatic energy balances the loss of counterion excluded-volume entropy as the polyelectrolyte networks collapse in low-dielectric solvents. This interplay between the electrostatic energy and the counterion excluded-volume entropy appears to be responsible for the discontinuous volume phase transitions that are observed in polyelectrolyte networks. The structure of the polyelectrolyte network is also found to be affine in the swollen state, with constituent chains nearly fully extended, and nonaffine in the collapsed state, with the chains adopting a Gaussian conformation. [ABSTRACT FROM AUTHOR]

Extensive molecular-dynamics simulations have been performed to study the effect of chain conformational rigidity, controlled by bending and torsion potentials, on self-diffusion in polymer melts. The polymer model employs a novel torsion potential that avoids computational singularities without the need to impose rigid constraints on the bending angles. Two power laws are traditionally used to characterize the dependence of the self-diffusion coefficient on polymer length: D∝N-ν with ν=1 for Ne (Rouse regime) and with ν=2 for N>Ne (reptation regime), Ne being the entanglement length. Our simulations, at constant temperature and density, up to N=250 reveal that, as the chain rigidity increases, the exponent ν gradually increases towards ν=2.0 for Ne and ν=2.2 for N>Ne. The value of Ne is slightly increased from 70 for flexible chains, up to the point where the crossover becomes undefined. This behavior is confirmed also by an analysis of the bead mean-square displacement. Subsequent investigations of the Rouse modes, dynamical structure factor, and chain trajectories indicate that the pre-reptation regime, for short stiff chains, is a modified Rouse regime rather than reptation. [ABSTRACT FROM AUTHOR]

Coarse-grained models that preserve atomistic detail display faster dynamics than atomistic systems alone. We show that this “ indirect speed up” is robust: coarse-grained dynamic observables computed with time scaled by a constant factor are in excellent agreement with their underlying atomistic counterparts. Borrowing from accelerated dynamics methods used in the field of rare events, we predict the scaling factor within 7%, based on reduced intermolecular attraction yielding faster neighbor cage escapes. [ABSTRACT FROM AUTHOR]

In this work we focus on the dynamics of macromolecular networks formed by end-linking identical polymer stars. The resulting macromolecular network can then be viewed as consisting of spacers which connect branching points (the cores of the stars). We succeed in analyzing exactly, in the framework of the generalized Gaussian model, the eigenvalue spectrum of such networks. As applications we focus on several topologies, such as regular networks and dendrimers; furthermore, we compare the results to those found for regular hyperbranched structures. In so doing, we also consider situations in which the beads of the cores differ from the beads of the spacers. The analytical procedure which we use involves an exact real-space renormalization, which allows to relate the star network to a (much simpler) network, in which each star is reduced to its core. It turns out that the eigenvalue spectrum of the star-polymer structure consists of two parts: one follows in terms of polynomial equations from the relaxation spectrum of the corresponding renormalized structure, while the second part involves the motion of the spacer chains themselves. Finally, we show exemplarily the situation for copolymeric dendrimers, calculate their spectra, and from them their storage and the loss moduli. [ABSTRACT FROM AUTHOR]

Processes on different length scales affect the dynamics of chain molecules. The friction experienced by a short chain segment depends on both small-scale chain properties and on the local environment of the segment. As a consequence, the (monomeric) friction coefficients of the two components of a binary polymer blend will, in general, differ from each other and from the friction coefficients of the corresponding melts. In this work, we investigate local friction in polyolefin blends with the aid of a small-scale simulation approach. The polymer chains, in united atom representation, are assumed to occupy the sites of a partially filled simple cubic lattice. The simulation focuses on short chain sections with straight backbones and enumerates all possible binary contacts and relative movements of such sections. By evaluating the exact enumeration results in conjunction with equations of state for the blends, we are able to make predictions about the variation of the friction coefficients with local chain architecture and thermodynamic state (temperature, pressure, and composition). We calculate relative values of friction coefficients at temperatures well above the glass transition for blends of PEP, an alternating copolymer of polyethylene and polypropylene, with polyethylene and polyisobutylene and for blends of polyethylene and atactic polypropylene. We also investigate a blend of PEP with head-to-head polypropylene and compare our results with experimental data. [ABSTRACT FROM AUTHOR]

We present a theoretical approach which maps polymer blends onto mixtures of soft-colloidal particles. The analytical mesoscale pair correlation functions reproduce well data from united atom molecular dynamics simulations of polyolefin mixtures without fitting parameters. The theory exactly recovers the analytical expressions for density and concentration fluctuation structure factors of soft-colloidal mixtures (liquid alloys). © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An integral equation model is developed for athermal solutions of flexible linear polymers with particular reference to good solvent conditions. Results from scaling theory are used in formulating form factors for describing the single chain structure, and the impact of solvent quality on the chain fractal dimension is accounted for. Calculations are performed within the stringlike implementation of the polymer reference interaction site model with blobs (as opposed to complete chains) treated as the constituent structural units for semidilute solutions. Results are presented for the second virial coefficient between polymer coils and the osmotic compressibility as functions of the chain length and polymer volume fraction, respectively. Findings from this model agree with results from scaling theory and experimental measurements, as well as with an earlier investigation in which self-avoiding chains were described using Gaussian form factors with a chain length and concentration-dependent effective statistical segment length. The volume fractions at the threshold for connectedness percolation are evaluated within a coarse-grained closure relation for the connectedness Ornstein-Zernike equation. Results from these calculations are consistent with the usual interpretation of the semidilute crossover concentration for model solutions of both ideal and swollen polymer coils. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]