Solutions Of Linear Polymers Research Articles

Fluidification of entangled polymers by loop extrusion

Loop extrusion is one of the main processes shaping chromosome organization across the cell cycle, yet its role in regulating deoxyribonucleic acid (DNA) entanglement and nucleoplasm viscoelasticity remains overlooked. We simulate entangled solutions of linear polymers under the action of generic loop extruding factors (LEFs) with a model that fully accounts for topological constraints and LEF-DNA uncrossability. We discover that extrusion drives the formation of bottlebrushlike structures which significantly lower the entanglement and effective viscosity of the system through an active fluidification mechanism. Interestingly, this fluidification displays an optimum at one LEF every 300–3000 base pairs. In marked contrast with entangled linear chains, the viscosity of extruded chains scales linearly with polymer length, yielding up to 1000-fold fluidification in our system. Our results illuminate how intrachain loop extrusion contributes to actively modulate genome entanglement and viscoelasticity . Published by the American Physical Society 2024

Soft glassy materials with tunable extensibility.

Extensibility is beyond the paradigm of classical soft glassy materials, and more broadly, yield-stress fluids. Recently, model yield-stress fluids with significant extensibility have been designed by adding polymeric phases to classically viscoplastic dispersions [Nelson et al., J. Rheol., 2018, 62, 357; Nelson et al., Curr. Opin. Solid State Mater. Sci., 2019, 23, 100758; Dekker et al., J. Non-Newtonian Fluid Mech., 2022, 310, 104938]. However, fundamental questions remain about the design of and coupling between the shear and extensional rheology of such systems. In this work, we propose a model material, a mixture of soft glassy microgels and solutions of high molecular weight linear polymers. We establish systematic criteria for the design and thorough rheological characterization of such systems, in both shear and extension. Using our material, we show that it is possible to dramatically change the behavior in extension with minimal change in the shear yield stress and elastic modulus, thus enabling applications that exploit orthogonal modulation of shear and extensional material properties.

Universal scaling of the diffusivity of dendrimers in a semidilute solution of linear polymers.

The static and dynamic properties of dendrimers in semidilute solutions of linear chains of comparable size are investigated using Brownian dynamics simulations. The radius of gyration and diffusivity of a wide variety of low generation dendrimers and linear chains in solution follow universal scaling laws independent of their topology. Analysis of the shape functions and internal density of dendrimers shows that they are more spherical than linear chains and have a dense core. At intermediate times, dendrimers become subdiffusive, with an exponent higher than that previously reported for nanoparticles in semidilute polymer solutions. The long-time diffusivity of dendrimers does not follow theoretical predictions for nanoparticles. We propose a new scaling law for the long-time diffusion coefficients of dendrimers which accounts for the fact that, unlike nanoparticles, dendrimers shrink with an increase in background solution concentration. Analysis of the properties of a special case of a higher functionality dendrimer shows a transition from polymer-like to nanoparticle-like behaviour.

EFFECT OF POLYMER MODIFIER ON THE MOR­PHO­LOGICAL AND SEPARATION PROPERTIES OF ASYMMETRIC MICROFILTRATION MEMBRANES

Modifying membranes is a common approach to improve their separation ability. In this work, a series of the membranes, which reject colloidal particles of a wide diapason of their size, was obtained by modifying acetylcellulose microfiltration membranes with such rigid polymer as polymetylmetacrilate. Modifying was carried out by precipitation of the polymer in the membrane pores, the depo­sition occurred from the solutions of different concentrations. Other way was multistage modifying membranes with a solution of the same concentration. Depending on the modifying conditions, the content of polymetylmetacrilate in the membrane was 12–44 %. Morphology of the composite membranes was investigated by optical and scanning electron microscopy. Water test was also performed at 0.5–2 bar. The membranes obey Darcy law in this pressure diapason: thus, the pore radius can be approximately estimated from the Hagen – Poiseuille equation (18–63 nm). Moreover, the modifier minimizes the membrane compression: a decrease of the permeate flux is 19 % (pristine membrane) and 8% for membranes containing high amount of the modifier. Colloidal solutions of water-soluble linear polymer, vegetable protein and sol of hydrated iron oxide were also used for the membrane testing. The selectivity of composite membranes enhances in the row: polyvinylpyrollidone < iron oxide < albumin. In the case of vegetable protein, the membrane selectivity is 30–91% depending on the modifier content. The membrane with highest separation ability was used for clarification of goiaba juice: the selectivity towards total solids was found to reach 33–73%. The permeate can be used for the production of beverages, the concentrate is recommended for confectionery industry. Polymethylmetacrylate can be recommended for the membrane modifying as a binding component in the composite containing also hydrophilic agent.

Construction of fracturing fluid with excellent proppant transport capacity using low molecular weight hydrophobic association polymer and surfactant

Slick water fracturing fluid is widely used for fracturing unconventional reservoirs such as shale and tight gas, and it has aided in developing unconventional oil and gas reservoirs. However, the problem of slick water in terms of its weak proppant transport capacity has not been effectively solved. Conventional methods of increasing the proppant transport capacity of a fracturing fluid by increasing viscosity and pumping rate have resulted in serious reservoir damage and increased costs, showing more and more limitations. To address this issue, a low molecular weight polymer/surfactant (LMPS) fracturing fluid system was developed. LMPS increased the fluid elasticity through the interaction between the hydrophobic groups on the polymer and the surfactant while maintaining low viscosity, thus obtaining excellent proppant transport capacity. The low molecular weight polymer is a type of hydrophobic association water-soluble polymer (HAWSP) prepared by photoinitiation. Its viscosity-average molecular weight was determined to be 1.24 × 106 g/mol, much more than that of a typical drag reducer of traditional slick water (about 1 × 107 g/mol). The low molecular weight of HAWSP is conducive to preparation, dissolution, pumping, and reducing the damage of polymer to the reservoir. When 300 mg/L of sodium dodecyl benzene sulfonate (SDBS) surfactant was added to a 0.2 wt% HAWSP solution, it formed a robust self-assembled network that significantly enhanced the elasticity and raised the storage modulus G' from 0.11 to 5.95 Pa. The 20/40 mesh ceramsite proppant remained suspended in the LMPS solution (36 mPa·s) for 30 min, whereas ceramsite completely settled within 30 s in an ordinary linear polymer solution with similar viscosity. Simultaneously, despite having a lower molecular weight, the drag reduction rate test shows that the drag reduction performance of the LMPS fracturing fluid was similar to the tested conventional commercial linear polymer. The self-assembled network of HAWSP/surfactant can increase the viscoelasticity of the fracturing fluid, which is expected to overcome the weakness of insufficient proppant transport capacity of slick water, thus improving development efficiency of unconventional gas reservoirs.

Validity of Effective Potentials in Crowded Solutions of Linear and Ring Polymers with Reversible Bonds.

We perform simulations to compute the effective potential between the centers-of-mass of two polymers with reversible bonds. We investigate the influence of the topology on the potential by employing linear and ring backbones for the precursor (unbonded) polymer, finding that it leads to qualitatively different effective potentials. In the linear and ring cases the potentials can be described by Gaussians and generalized exponentials, respectively. The interactions are more repulsive for the ring topology, in analogy with known results in the absence of bonding. We also investigate the effect of the specific sequence of the reactive groups along the backbone (periodic or with different degrees of randomness), establishing that it has a significant impact on the effective potentials. When the reactive sites of both polymers are chemically orthogonal so that only intramolecular bonds are possible, the interactions become more repulsive the closer to periodic the sequence is. The opposite effect is found if both polymers have the same types of reactive sites and intermolecular bonds can be formed. We test the validity of the effective potentials in solution, in a broad range of concentrations from high dilution to far above the overlap concentration. For this purpose, we compare simulations of the effective fluid and test particle route calculations with simulations of the real all-monomer system. Very good agreement is found for the reversible linear polymers, indicating that unlike in their nonbonding counterparts many-body effects are minor even far above the overlap concentration. The agreement for the reversible rings is less satisfactory, and at high concentration the real system does not show the clustering behavior predicted by the effective potential. Results similar to the former ones are found for the partial self-correlations in ring/linear mixtures. Finally, we investigate the possibility of creating, at high concentrations, a gel of two interpenetrated reversible networks. For this purpose we simulate a 50/50 two-component mixture of reversible polymers with orthogonal chemistry for the reactive sites, so that intermolecular bonds are only formed between polymers of the same component. As predicted by both the theoretical phase diagram and the simulations of the effective fluid, the two networks in the all-monomer mixture do not interpenetrate, and phase separation (demixing) is observed instead.

New Progress of Rheology in Industrial Field, Contribution to Development and Enlightenment in Psychorheology

We have tried to measure purely mechanical sensory feelings of cosmetics with using commercial rheometers. To obtain mechanical parameters relating to the score of sensory feeling, we have to measure under the same condition during the evaluation of sensory feeling, that is, the movement of finger and the structure of cosmetics. Sensory feelings of madeup skin can also be measured using stress-controled rotaional rheometers if we fix a measuring part of human body without stress. Understanding the rheological properties of cosmetic emulsions is helpful to design a new product with a desired sensory feeling. Emulsions with high dispersoid concentration have yield point, but high concentration linear polymer solution dose not. This was qualitatively explained with the difference in mobility at the contact point between dispersoids.

DNA Conformation Dictates Strength and Flocculation in DNA-Microtubule Composites.

Polymer topology has been shown to play a key role in tuning the dynamics of complex fluids and gels. At the same time, polymer composites, ubiquitous in everyday life, have been shown to exhibit emergent desirable mechanical properties not attainable in single-species systems. Yet, how topology impacts the dynamics and structure of polymer composites remains poorly understood. Here, we create composites of rigid rods (microtubules) polymerized within entangled solutions of flexible linear and ring polymers (DNA) of equal length. We couple optical tweezers microrheology with confocal microscopy and scaled particle theory to show that composites with linear DNA exhibit a strongly nonmonotonic dependence of elasticity and stiffness on microtubule concentration due to depletion-driven polymerization and flocculation of microtubules. In contrast, composites containing ring DNA show a much more modest monotonic increase in elastic strength with microtubule concentration, which we demonstrate arises from the decreased conformational size and increased miscibility of rings.

Flows of Linear Polymer Solutions and Other Suspensions of Rod-like Particles: Anisotropic Micropolar-Fluid Theory Approach.

We formulate equations governing flows of suspensions of rod-like particles. Such suspensions include linear polymer solutions, FD-virus, and worm-like micelles. To take into account the particles that form and their rotation, we treat the suspension as a Cosserat continuum and apply the theory of micropolar fluids. Anisotropy of suspensions is determined through the inclusion of the microinertia tensor in the rheological constitutive equations. We check that the model is consistent with the basic principles of thermodynamics. In addition to anisotropy, the theory also captures gradient banding instability, coexistence of isotropic and nematic phases, sustained temporal oscillations of macroscopic viscosity, shear thinning and hysteresis. For the flow between two planes, we also establish that the total flow rate depends not only on the pressure gradient, but on the history of its variation as well.

Effects of polymers on the cavitating flow around a cylinder: A large-scale molecular dynamics analysis.

The cavitation flow of linear-polymer solutions around a cylinder is studied by performing a large-scale molecular dynamics simulation. The addition of polymer chains remarkably suppresses cavitation. The polymers are stretched into a linear shape near the cylinder and entrained in the vortex behind the cylinder. As the polymers stretch, the elongational viscosity increases, which suppresses the vortex formation. Furthermore, the polymers exhibit an entropic elasticity owing to stretching. This elastic energy increases the local temperature, which inhibits the cavitation inception. These effects of polymers result in the dramatic suppression of cavitation.

Nanoparticle dynamics in semidilute polymer solutions: Rings versus linear chains

We study the dynamics of nanoparticles in semidilute solutions of ring and linear polymers using hybrid molecular dynamics–multiparticle collision dynamics simulations. The dynamics of the monomers, the polymer centers-of-mass, and the nanoparticles coincide for these two architectures for solutions of the same monomer concentration. The long time diffusivities of the nanoparticles follow the predictions of a polymer coupling theory [Cai et al., Macromolecules 44, 7853–7863 (2011)], suggesting that nanoparticle dynamics are coupled to segmental relaxations for both polymer architectures examined here. At intermediate time scales, the nanoparticle dynamics are characterized by subdiffusive exponents, which markedly deviate from coupling theory and closely follow those of the polymers. Instead, the nanoparticle dynamics are strongly coupled to the polymer center-of-mass motions for both architectures, rather than to their segmental dynamics. The presence of ring concatenations does not affect the long-time diffusivity of the nanoparticles but leads to a slight decrease in the subdiffusive exponents of the nanoparticles and the polymer center-of-mass.

Nonlinear rheometry of entangled polymeric rings and ring-linear blends

We present a comprehensive experimental rheological dataset for purified entangled ring polystyrenes and their blends with linear chains in nonlinear shear and elongation. In particular, data for shear stress growth coefficient, steady-state shear viscosity, and first and second normal stress differences are obtained and discussed as functions of shear rate as well as molecular parameters (molar mass, blend composition and decreasing molar mass of linear component in blend). Over the extended parameter range investigated, rings do not exhibit clear transient undershoot in shear, in contrast to their linear counterparts and ring-linear blends. For the latter, the size of the undershoot and respective strain appear to increase with shear rate. Universal scaling of strain at overshoot and fractional overshoot (ratio of maximum to steady-state shear stress growth coefficient) indicates subtle differences in the shear-rate dependence between rings and linear polymers or their blends. The shear thinning behaviour of pure rings yields a slope nearly identical to predictions (-4/7) of a recent shear slit model and molecular dynamics simulations. Data for the second normal stress difference are reported for rings and ring-linear blends. While N 2 is negative and its absolute value stays below that of N 1 , as for linear polymers, the ratio -N 2 /N 1 is unambiguously larger for rings compared to linear polymer solutions with the same number of entanglements (almost by factor of two), in agreement with recent non-equilibrium molecular dynamics simulations. Further, -N 2 exhibits slightly weaker shear rate dependence compared to N 1 at high rates, and the respective power-law exponents can be rationalized in view of the slit model (3/7) and simulations (0.6), although further work is needed to unravel the molecular original of the observed behaviour. The comparison of shear and elongational stress growth coefficients for blends reflects the effect of ring-linear threading which leads to significant viscosity enhancement in elongation. Along the same lines, the elongational stress is much larger than the first normal stress in shear, and their ratio is much larger for rings and ring-linear blends compared to linear polymers. This conforms the interlocking scenario of rings and their important role in mechanically reinforcing linear matrices.

Dynamics and rheology of ring-linear blend semidilute solutions in extensional flow. Part I: Modeling and molecular simulations

We use Brownian dynamics (BD) simulations and single molecule experiments to investigate the influence of topological constraints and hydrodynamic interactions on the dynamics and rheology of solutions of ring-linear polymer blends at the overlap concentration. We find agreement between simulation and experiment in which rings in solution blends exhibit large conformational fluctuations. A subpopulation of rings shows extension overshoots in the startup of the flow, and other populations display tumbling and tank-treading at the steady state. Ring polymer fluctuations increase with the blend fraction of linear polymers and are peaked at a ring Weissenberg number WiR≈1.5. On the contrary, linear and ring polymers in pure solutions show a peak in fluctuations at the critical coil-stretch Weissenberg number Wi=0.5. BD simulations show that extension overshoots on the startup of the flow are due to flow-induced intermolecular ring-linear polymer hooks, whereas fluctuations at the steady state are dominated by intermolecular hydrodynamic interactions (HIs). This is supported by simulations of bidisperse linear polymer solution blends, which show similar trends in conformational dynamics between rings and linear polymers with a matched contour length. Compared to BD simulations, single molecule experiments show quantitatively larger fluctuations, which could arise because experiments are performed on higher molecular weight polymers with stronger topological constraints. To this end, we have advanced the understanding of the effects of topological interactions and intermolecular HIs on the dynamics of semidilute ring-linear polymer blend solutions.

Multiscale Approaches for Confined Ring Polymer Solutions.

We apply a hierarchy of multiscale modeling approaches to investigate the structure of ring polymer solutions under planar confinement. In particular, we employ both monomer-resolved (MR-DFT) and a coarse-grained (CG-DFT) density functional theories for fully flexible ring polymers, with the former based on a flexible tangent hard-sphere model and the latter based on an effective soft-colloid representation, to elucidate the ring polymer organization within slits of variable width in different concentration regimes. The predicted monomer and polymer center-of-mass densities in confinement, as well as the surface tension at the solution-wall interface, are compared to explicit molecular dynamics (MD) simulations. The approaches yield quantitative (MR-DFT) or semiquantitative (CG-DFT) agreement with MD. In addition, we provide a systematic comparison between confined linear and ring polymer solutions. When compared to their linear counterparts, the rings are found to feature a higher propensity to structure in confinement that translates into a distinct shape of the depletion potentials between two walls immersed into a polymer solution. The depletion potentials that we extract from CG-DFT and MR-DFT are in semiquantitative agreement with each other. Overall, we find consistency among all approaches as regards the shapes, trends, and qualitative characteristics of density profiles and depletion potentials induced on hard walls by linear and cyclic polymers.

Investigation of Ring and Star Polymers in Confined Geometries: Theory and Simulations.

The calculations of the dimensionless layer monomer density profiles for a dilute solution of phantom ideal ring polymer chains and star polymers with arms in a -solvent confined in a slit geometry of two parallel walls with repulsive surfaces and for the mixed case of one repulsive and the other inert surface were performed. Furthermore, taking into account the Derjaguin approximation, the dimensionless layer monomer density profiles for phantom ideal ring polymer chains and star polymers immersed in a solution of big colloidal particles with different adsorbing or repelling properties with respect to polymers were calculated. The density-force relation for the above-mentioned cases was analyzed, and the universal amplitude ratio B was obtained. Taking into account the small sphere expansion allowed obtaining the monomer density profiles for a dilute solution of phantom ideal ring polymers immersed in a solution of small spherical particles, or nano-particles of finite size, which are much smaller than the polymer size and the other characteristic mesoscopic length of the system. We performed molecular dynamics simulations of a dilute solution of linear, ring, and star-shaped polymers with , 300 (360), and 1201 (4 × 300 + 1-star polymer with four arms) beads accordingly. The obtained analytical and numerical results for phantom ring and star polymers are compared with the results for linear polymer chains in confined geometries.

Dynamical Entanglement and Cooperative Dynamics in Entangled Solutions of Ring and Linear Polymers.

Understanding how entanglements affect the behavior of polymeric complex fluids is an open challenge in many fields. To elucidate the nature and consequence of entanglements in dense polymer solutions, we propose a novel method: a "dynamical entanglement analysis" (DEA) to extract spatiotemporal entanglement structures from the pairwise displacement correlation of entangled chains. By applying this method to large-scale molecular dynamics simulations of linear and unknotted, nonconcatenated ring polymers, we find a strong and unexpected cooperative dynamics: the footprint of mutual entrainment between entangled chains. We show that DEA is a powerful and sensitive probe that reveals previously unnoticed and architecture-dependent spatiotemporal structures of dynamical entanglement in polymeric solutions. We also propose a mean-field approximation of our analysis that provides previously under-appreciated physical insights into the dynamics of generic entangled polymers. We envisage DEA will be useful to analyze the dynamical evolution of entanglements in generic polymeric systems such as blends and composites.

Universal Equation of State Describes Osmotic Pressure throughout Gelation Process.

The equation of state of the osmotic pressure for linear-polymer solutions in good solvents is universally described by a scaling function. We experimentally measure the osmotic pressure of the gelation process via osmotic deswelling. We find that the same scaling function for linear-polymer solutions also describes the osmotic pressure throughout the gelation process involving both the sol and gel states. Furthermore, we reveal that the osmotic pressure of polymer gels is universally governed by the semidilute scaling law of linear-polymer solutions.

Nonmonotonic dependence of comb polymer relaxation on branch density in semidilute solutions of linear polymers

The relaxation of comb polymers in semidilute solutions is studied using single-molecule fluorescence microscopy and Brownian dynamics simulations with long-range hydrodynamic interactions (HI). Unexpectedly, comb polymer relaxation is found to depend nonmonotonically on branching density, such that lightly branched chains relax faster than linear chains in semidilute solutions. These results challenge commonly held notions in the field and show that the dynamics of branched polymers in nondilute solutions is governed by a coupling between polymer architecture, long-range HI, and excluded volume interactions.

Thermodynamic framework for switching the lower critical solution temperature of thermo-sensitive particle gels in aqueous solvent

Switching the lower critical solution temperatures (LCSTs) of thermo-sensitive particle gels including poly(N-isopropylacrylamide) (PNIPAM), poly(N-diethylacrylamide) (PNDEAM), and poly(N-vinylcaprolactam) (PNVCL) was investigated in various aqueous solvents. Three prepared particle gels represented a single LCST in a pure water solution near human body temperature. By adding a chaotropic co-solvent, such as dimethylformamide (DMF) or dimethyl sulfoxide (DMSO), to given gels in aqueous solution, the degree of influence on change of LCST was significantly different due to the difference in chemical structures. LCSTs of polymer solutions were affected by changing solvent conditions from pure water to mixed solvents. The LCST behaviors of linear PNIPAM, PNDEAM, and PNVCL in water/DMF or DMSO were determined by thermo-optical analysis (TOA), which supported the switchability of LCSTs in hydrogel systems. We used the photon correlation spectroscopy (PCS) technique to measure the switched LCSTs of hydrogel particles in mixed solvent systems. The switched LCSTs of the investigated systems exhibited a non-linear trend by varying co-solvent contents. A molecular thermodynamic framework, a combination of the modified double lattice with chain length dependence (MDL-CL) model and the Flory-Rehner (F-R) model, was utilized to describe and correlate the liquid-liquid equilibrium (LLE) and thermosensitive swelling behaviors between linear and cross-linked polymer solutions. With the addition of chaotropic co-solvents, a non-linear trend for phase behaviors of the three polymers was described after taking into account temperature and composition dependence on the association fraction (ηij) between the species. We assumed the donor-acceptor concept and competitive hydrogen bonding between polymer/water and water/co-solvent. The association fraction for the secondary lattice model was modified from an arbitrarily determined value to a physically meaningful value. Accordingly, the phase equilibrium of the amphiphilic polymers influenced by the structure-breaker characteristics of the co-solute was properly implemented in both experimental and modeling aspects.

Scaling Exponent and Effective Interactions in Linear and Cyclic Polymer Solutions: Theory, Simulations, and Experiments

Cyclic polymers have garnered increasing attention in the materials community as lack of free-chain ends in cyclic polymers results in significant differences in structure, thermodynamics, and dyna...