Rodlike Polymers Research Articles

Orientational order and topological defects in a dilute solutions of rodlike polymers at low Reynolds number.

The relationship between the polymer orientation and the chaotic flow, in a dilute solution of rigid rodlike polymers at low Reynolds number, is investigated by means of direct numerical simulations. It is found that the rods tend to align with the velocity field in order to minimize the friction with the solvent fluid, while regions of rotational disorder are related to strong vorticity gradients, and therefore to the chaotic flow. The "turbulent-like" behavior of the system is therefore associated with the emergence and interaction of topological defects of the mean director field, similarly to active nematic turbulence. The analysis has been carried out in both two and three spatial dimensions.

Size- and Shape-controlled Biodegradable Polymer Brushes Based on l-Amino Acid for Intracellular Drug Delivery and Deep-Tissue Penetration.

We report size- and shape-controlled polymer brushes based on l-amino acid bioresource and study the role of polymer topology on the enzymatic biodegradation and deep-tissue penetration under in vitro and in vivo. For this purpose, l-tyrosine-based propargyl-functionalized monomer is tailor-made and polymerized via solvent-free melt polycondensation strategy to yield hydrophobic and clickable biodegradable poly(ester-urethane)s. Postpolymerization click chemistry strategy is applied to make well-defined amphiphilic one-dimensional rodlike and three-dimensional spherical polymer brushes by merely varying the lengths of PEG-azides in the reaction. These core-shell polymer brushes are found to be nontoxic and nonhemolytic and capable of loading clinical anticancer drug doxorubicin and deep-tissue penetrable near-infrared biomarker IR-780. In vitro enzymatic drug-release kinetics and lysotracker-assisted real-time live-cell confocal bioimaging revealed that the rodlike polymer brush is superior than its spherical counterparts for faster cellular uptake and enzymatic biodegradation at the endolysosomal compartments to release DOX at the nucleus. Further, in vivo live-animal bioimaging by IVIS technique established that the IR-780-loaded rodlike polymer brush exhibited efficient deep-tissue penetration ability and emphasized the importance of polymer brush topology control for biological activity. Polymer brushes exhibit good stability in the blood plasma for more than 72 h, they predominately accumulate in the digestive organs like liver and kidney, and they are less toxic to heart and brain tissues. IVIS imaging of cryotome tissue slices of organs confirmed the deep-penetrating ability of the polymer brushes. The present investigation opens opportunity for bioderived and biodegradable polymer brushes as next-generation smart drug-delivery scaffolds.

Molecular rotators anchored on a rod-like anionic coordination polymer adhered by charge-assisted hydrogen bonds.

On the basis of variable-temperature single-crystal X-ray diffraction, variable-temperature/frequency dielectric analysis, variable-temperature solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations, here we present a new model of crystalline supramolecular rotor (i-PrNHMe2)[CdBr3], where a conformationally flexible near-spherical (i-PrNHMe2)+ cation functions as a rotator and a rod-like anionic coordination polymer {[CdBr3]-}∞ acts as the stator, and the adhesion of them is realized by charge-assisted hydrogen bonds.

Alignment-Rheology Relationship of Biosourced Rod-Like Colloids and Polymers under Flow.

Fluids composed of biosourced rod-like colloids (RC) and rod-like polymers (RP) have been extensively studied due to various promising applications relying on their flow-induced orientation (e.g., fiber spinning). However, the relationship between RC and RP alignment and the resulting rheological properties is unclear due to experimental challenges. We investigate the alignment-rheology relationship for a variety of biosourced RC and RP, including cellulose-based particles, filamentous viruses, and xanthan gum, by simultaneous measurements of the shear viscosity and fluid anisotropy under rheometric shear flows. For each system, the RC and RP contribution to the fluid viscosity, captured by the specific viscosity ηsp, follows a universal trend with the extent of the RC and RP alignment independent of concentration. We further exploit this unique rheological-structural link to retrieve a dimensionless parameter (β) directly proportional to ηsp at zero shear rate (η0,sp), a parameter often difficult to access from experimental rheometry for RC and RP with relatively long contour lengths. Our results highlight the unique link between the flow-induced structural and rheological changes occurring in RC and RP fluids. We envision that our findings will be relevant in building and testing microstructural constitutive models to predict the flow-induced structural and rheological evolution of fluids containing RC and RP.

Nematic-isotopic phase separations induced by hydrogen bonding between a rodlike polymer and solvent molecules

ABSTRACT We theoretically study nematic-isotropic phase transitions and phase separations in aqueous rodlike polymer solutions, such as rigid DNA (or rodlike polymer) in water. By taking into the hydrogen bonding between a rodlike polymer and solvent molecules, we predict novel phase diagrams, such as overhang-type coexistence curves with isotropic-nematic ( I + N ) phase separations and re-entrant I + N separations. We demonstrate that the hydrogen bonding between molecules of different components stabilises the nematic phase at lower polymer concentrations and temperatures.

Lyotropic Nematic Phases of Isotropic Nanoparticles via Semiflexible Polymer Ligands.

Lyotropic liquid crystalline(LC) nanomaterials are normally achieved through particle shape anisotropy. Herein, it is shown that lyotropic nematic rather than cubic phases are produced from sphericalnanoparticles (NPs) with semi-flexible polymer ligands. ZrO2 nanocrystals (4nm dia.) are coated with a dense shell of poly(hexyl isocyanate) (PHIC), a helical rod-like polymer that forms lyotropic LC phases in a range of organic solvents. Solvent casted NPs with PHIC ligands above the persistence length form linear assemblies, separated by a characteristic distance related to the chain length while NPs with shorter, rigid rod PHIC ligands pack hexagonally. Concentrated NP-PHIC dispersions present nematic textures similar to the free PHIC nematic solutions but at lower critical concentrations, widening the isotropic-nematic biphasic region. 2 H NMR spectra of the NPs dispersed in a deuterated solvent display quadrupolar splittings that increase with NP concentration, showing that the PHIC ligands are magnetically aligned. The high degree of orientation order is evidence that splaying of the ligand shell transforms the spherical NPs to rod-like shapes that assemble to produce nematic lyotropic LC phases and linear NP arrays. This approach to creating anisotropic assemblies can be extended to other types of spherical NPs and semiflexible polymers.

Local and Global Order in Dense Packings of Semi-Flexible Polymers of Hard Spheres.

The local and global order in dense packings of linear, semi-flexible polymers of tangent hard spheres are studied by employing extensive Monte Carlo simulations at increasing volume fractions. The chain stiffness is controlled by a tunable harmonic potential for the bending angle, whose intensity dictates the rigidity of the polymer backbone as a function of the bending constant and equilibrium angle. The studied angles range between acute and obtuse ones, reaching the limit of rod-like polymers. We analyze how the packing density and chain stiffness affect the chains' ability to self-organize at the local and global levels. The former corresponds to crystallinity, as quantified by the Characteristic Crystallographic Element (CCE) norm descriptor, while the latter is computed through the scalar orientational order parameter. In all cases, we identify the critical volume fraction for the phase transition and gauge the established crystal morphologies, developing a complete phase diagram as a function of packing density and equilibrium bending angle. A plethora of structures are obtained, ranging between random hexagonal closed packed morphologies of mixed character and almost perfect face centered cubic (FCC) and hexagonal close-packed (HCP) crystals at the level of monomers, and nematic mesophases, with prolate and oblate mesogens at the level of chains. For rod-like chains, a delay is observed between the establishment of the long-range nematic order and crystallization as a function of the packing density, while for right-angle chains, both transitions are synchronized. A comparison is also provided against the analogous packings of monomeric and fully flexible chains of hard spheres.

Rheology of emulsions with polymer solutions as the continuous phase

We investigate the effect of the addition of polymers on the flow properties of emulsions. Surfactant-stabilised 80 v% oil-in-water emulsions, exhibiting a yield stress, with either xanthan gum (a stiff, rodlike polymer) or polyethylene oxide (PEO, a flexible, elastic polymer) in the continuous phase (concentrations between 0.005 wt% and 0.5 wt%) are prepared and investigated using shear rheology and confocal microscopy. The flow properties of the emulsions are very robust, and only at high concentrations of polymer (≥ 0.2 wt%), significant changes in the flow properties are observed. In the case of xanthan gum, higher shear stresses are measured. For high concentrations the yield stress is masked by the high zero shear viscosity and shear thinning behaviour of the xanthan gum giving rise to an apparent second power law regime. In the case of PEO, an increase in the shear thinning exponent is observed, together with a decrease in the yield stress. The interaction of PEO with the surfactant SDS (sodium dodecyl sulfate) at higher PEO concentrations strongly affects the emulsion rheology, perhaps by reducing the friction coefficient between the oil droplets.

Facile Fabrication of Starch-Based Microrods by Shear-Assisted Antisolvent-Induced Nanoprecipitation and Solidification.

Rod-like particles have attracted increasing attention because of their unique shape-dependent properties, which enable their superior performance compared to their isotropic counterparts. Thus, rod-like particles have potential applications in many fields, especially in biomedicine. However, the fabrication of uniform rod-like particles is challenging because of the principle of interfacial energy minimization. Herein, we present a facile, rapid, and cost-effective strategy for preparing starch-based microrods with tunable aspect ratios via shear-assisted antisolvent-induced nanoprecipitation and solidification. The preformed spherical particles swollen by the mixed solvent were elongated by the shear force and solidified in rod-like shape by antisolvent induction. The resulting starch-based microrods can encapsulate hydrophobic active substances and be modified with functional groups, indicating their potential applications as drug carriers and biologically active materials. The formation mechanism of the starch-based microrods discovered in this study provides a new perspective on the fabrication of rod-like polymer particles.

Enhancement of drag and mixing in a dilute solution of rodlike polymers at low Reynolds numbers

We study the dynamics of a dilute solution of rigid rodlike polymers in a viscous fluid at low Reynolds number by means of numerical simulations of a simple rheological model. We show that the rotational dynamics of polymers destabilizes the laminar flow and causes the emergence of a turbulent-like chaotic flow with a wide range of active scales. This regime displays an increased flow resistance, corresponding to a reduced mean flow at fixed external forcing, as well as an increased mixing efficiency. The latter effect is quantified by measuring the decay of the variance of a scalar field transported by the flow. By comparing the results of numerical simulations of the model in two- and three-dimensions, we show that the phenomena observed are qualitatively independent on the dimensionality of the space.

A Rationally Designed Building Block of the Putative Magnetoreceptor MagR.

The ability of animals to perceive guidance cues from Earth's magnetic field for orientation and navigation has been supported by a wealth of behavioral experiments, yet the nature of this sensory modality remains fascinatingly unresolved and wide open for discovery. MagR has been proposed as a putative magnetoreceptor based on its intrinsic magnetism and its complexation with a previously suggested key protein in magnetosensing, cryptochrome, to form a rod-like polymer structure. Here, we report a rationally designed single-chain tetramer of MagR (SctMagR), serving as the building block of the hierarchical assembly of MagR polymer. The magnetic trapping experiment and direct magnetic measurement of SctMagR demonstrated the possibility of magnetization of nonmagnetic cells via overexpressing a single protein, which has great potential in various applications. SctMagR, as reported in this study, serves as a prototype of designed magnetic biomaterials inspired by animal magnetoreception. The features of SctMagR provide insights into the unresolved origin of the intrinsic magnetic moment, which is of considerable interest in both biology and physics. © 2022 Bioelectromagnetics Society.

Effectiveness of Hydroxyurea in the Management of the Painful Crisis in Sickle Cell Anemia

Background: Sickle cell syndromes are inbred disorders distinguished by the presence of blade (Sickle) hemoglobin in red blood corpuscles. The sickling of red cells in patients with SCA is caused by the polymerization of molecules of non-oxygenated hemoglobin S (α2ß2s) into rigid rod-like polymers. In the open-label study of hydroxyurea therapy, the synthesis of embryo hemoglobin increased in most patients with SCA resulting in a humane myelotoxicity and rise in painful crises. By suppressing the sickling process, increased levels of embryo hemoglobin sinew the less frequency of painful crises.

Bayesian estimations of orientation distribution functions from small-angle scattering enable direct prediction of mechanical stress in anisotropic materials

Properties of soft materials are influenced by their anisotropic structuring under nonequilibrium fields. Although anisotropic structure-property relationships have been extensively explored theoretically, comparison to experiments requires determination of the microstructural orientation probability distribution function (OPDF) of microstructural elements. Small angle scattering (SAS) measurements encode information about the OPDF, but tools to navigate this connection are incomplete. Here, we develop and validate an explicit framework to link arbitrary OPDFs to SAS measurements. Specifically, we propose, validate, and apply a method, maximum a posteriori scattering inference (MAPSI), whereby the OPDF may be obtained from SAS measurements using a Bayesian estimation method. Using this method, we obtain estimates of the full 3D OPDF for two model semidilute fd-virus (rodlike) dispersions at concentrations that are approximately equal to and twice the overlap concentration. From the OPDF, we calculate its second and fourth moments and compare these to predictions for a dilute suspension of rigid rods and to a recent theory for semidilute suspensions. Finally, we use both the theoretical and measured moments to calculate the stress, both for dilute and semidilute suspensions. These predictions are not only compared to each other, but also to measured values of the shear stress, and point to new insights into the behavior of suspensions of highly elongated particles in the transition between dilute and semidilute behavior. We also use this new framework to provide perspective on the connection between scalar parameterizations of scattering and the OPDF that have frequently been used in the past. The new tools developed in this work provide an unprecedented path toward experimental validation of dynamical theories of rodlike colloids and polymers, and for measurement of nonequilibrium structures and stresses of other complex fluids and soft materials with SAS.

Nanofibers Produced by Electrospinning of Ultrarigid Polymer Rods Made from Designed Peptide Bundlemers.

Mimicking the hierarchical assembly of natural fiber materials is an important design challenge in the manufacturing of nanostructured materials with biomolecules such as peptides. Here, we produce nanofibers with control of structure over multiple length scales, ranging from peptide molecule assembly into supramolecular building blocks called "bundlemers," to rigid-rod formation through a covalent connection of bundlemer building blocks, and, ultimately, to uniaxially oriented fibers made with the rigid-rod polymers. The peptides are designed to physically assemble into coiled-coil bundles, or bundlemers, and to covalently interact in an end-to-end fashion to produce the rigid-rod polymer. The resultant rodlike polymer exhibits a rigid, cylindrical nanostructure confirmed by transmission electron microscopy (TEM) and, correspondingly, exhibits shear-thinning behavior at low shear rates observed in many nanoscopic rod systems. The rigid-rod chains are further organized into final fiber materials via electrospinning processing, all the while preserving their unique rodlike structural characteristics. Morphological and structural investigations of the nanofibers through scanning electron microscopy, transmission electron microscopy, and X-ray scattering, as well as molecular characterization via Fourier transform infrared (FTIR) and Raman spectroscopy, show that continuous nanofibers are composed of oriented rigid-rod chains constituted by α-helical peptides within bundle building blocks. Mechanical properties of electrospun fibers are also presented. The ability to produce nanofibers from the oriented rigid-rod polymer reveals bundlemer chains as a viable tool for the development of new fiber materials with targeted structure and properties.

Room Temperature to 150 °C Lithium Metal Batteries Enabled By a “Molecular Ionic Composite” Solid Electrolyte

Molecular ionic composites (MICs) are a new class of solid electrolyte materials developed recently in our group. These materials are constructed from various ionic liquids and a highly charged rigid rodlike polymer, poly(2,2′-disulfonyl-4,4′-benzideneterephthalamide) (PBDT). MICs demonstrate an unprecedented combination of thermal properties (stability up to 300 °C), mechanical properties (E′ up to ~ 1 GPa), and ion transport properties (ionic conductivity up to 8 mS/cm).[1-3] Here we present preparation and characterization of a MIC membrane based on the PBDT polymer, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI) and LiTFSI. This MIC membrane is robust and flexible, and exhibits ionic conductivity ~ 0.2 mS/cm at room temperature. Due to the electrochemical and mechanical stability of the MIC membrane at elevated temperature, Li/MIC/LiFePO4 coin cells demonstrate excellent cycling performance over a wide temperature range from 20 to 150 °C. This study demonstrates that MIC materials represent a promising electrolyte platform for safe and wide-temperature-range lithium batteries.

Polymer Stiffness Regulates Multivalent Binding and Liquid-Liquid Phase Separation

Multivalent binding is essential to many biological processes because it builds high-affinity bonds by using several weak binding interactions simultaneously. Multivalent polymers have shown promise as inhibitors of toxins and other pathogens, and they are important components in the formation of biocondensates. Explaining how structural features of these polymers change their binding and subsequent control of phase separation is critical to designing better pathogen inhibitors and also to understanding diseases associated with membraneless organelles. In this work, we will examine the binding of a multivalent polymer to a small target. This scenario could represent a polymeric inhibitor binding to a toxic protein or RNA binding to an RNA-binding protein in the case of liquid-liquid phase separation. We use simulation and theory to show that flexible random-coil polymers bind more strongly than stiff rod-like polymers and that flexible polymers nucleate condensed phases at lower binding energies than their rigid analogs. We hope these results will provide insight into the rational design of polymeric inhibitors and improve our understanding of phase separation in cells and membraneless organelles.

Interaction of Low Molecular Weight Poly(diallyldimethylammonium chloride) and Sodium Dodecyl Sulfate in Low Surfactant-Polyelectrolyte Ratio, Salt-Free Solutions.

Coacervation is widely used in formulations to induce a beneficial character to the formulation, but nonequilibrium effects are often manifest. Electrophoretic NMR (eNMR), pulsed-gradient spin-echo NMR (PGSE-NMR), and small-angle neutron scattering (SANS) have been used to quantify the interaction between low molecular cationic poly(diallyldimethylammonium chloride) (PDADMAC) and the anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution as a model for the precursor state to such nonequilibrium processes. The NMR data show that, within the low surfactant concentration one-phase region, an increasing surfactant concentration leads to a reduction in the charge on the polymer and a collapse of its solution conformation, attaining minimum values coincident with the macroscopic phase separation boundary. Interpretation of the scattering data reveals how the rodlike polymer changes over the same surfactant concentration window, with no discernible fingerprint of micellar type aggregates, but rather with the emergence of disklike and lamellar structures. At the highest surfactant concentration, the emergence of a weak Bragg peak in both the polymer and surfactant scattering suggests these precursor disk and lamellar structures evolve into paracrystalline stacks which ultimately phase separate. Addition of the nonionic surfactant hexa(ethylene glycol) monododecyl ether (C12E6) to the system seems to have little effect on the PDADMAC/SDS interaction as determined by NMR, merely displacing the observed behavior to lower SDS concentrations, commensurate with the total SDS present in the system. In other words, PDADMAC causes the disruption of the mixed SDS/C12E6 micelle, leading to SDS-rich PDADAMC/surfactant complexes coexisting with C12E6-rich micelles in solution.

Rhombellane-related Crystal Networks

Rhombellanes are mathematical structures existing in various environments, in crystal or quasicrystal networks, or even in their homeomorphs, further possible becoming real molecules. Rhombellanes originate in the K2.3 complete bipartite graph, a tile found in the linear polymeric staffanes. In close analogy, a rod-like polymer derived from hexahydroxy-cyclohexane, HHCH, was imagined. Further, the idea of linear polymer synthesized from dehydro-adamantane, DHAda, was extended in the design of a three-dimensional crystal network, called here Ada-Ada, of which tile is a hyper-adamantane (an adamantane of which vertices are just adamantanes). It was suggested that Ada-Ada would be synthesized starting from the real molecule tetrabromo-adamantane, by dehydrogenation and polymerization. The crystal structures herein proposed were characterized by connectivity and ring sequences and also by the Omega polynomial.

Mechanics of transiently cross-linked nematic networks

Polymeric networks are ubiquitous in biology and are vital components to some of the key functions of life. Composite networks of stiff and flexible polymers such as the actin-filamin network of the cytoskeleton posses novel mechanical properties that arise from physical interactions, geometry and topology of the network. Particularly, (a) the cross-linking chains in these networks dynamically break and reform in time that drive their rheological properties, and (b) stiff rod-like polymers have been found to show liquid crystalline phases including nematic alignment. Models of such transient nematic networks are either phenomenological or computational thereby lacking the simplicity of physics-based models in elucidating the key physical mechanisms. We present here a modelling framework using the statistically-based transient network theory to describe the rate-dependent mechanics of nematic networks. The model bridges continuum mechanics quantities to statistical measures of chain distribution in the network such as the conformation tensor. We show that the model degenerates to classical theories of anisotropic solids when the bonds are permanent and to anisotropic fluids when the bond exchange is rapid. The effect of the interplay between the bond dynamics and geometry of the network on its emergent mechanics is explored and illustrated using the example of a thin-walled tube under pressure. The generality of the framework and its potential to describe continuum level mechanics based on a variety of local physical interactions and network geometries is discussed.

Non-monotonic phase behaviour of a mixture containing non-adsorbing particles and polymerising rod-like molecules

Hypothesis: Previous works have shown that many-body interactions induced by dispersants with increasing correlation length will generate a diminishing two-phase region [Soft Matter 14, 6921 (2018)]. We conjecture that the attenuation of the depletion attraction due to many-body interactions is a ubiquitous phenomenon in medium-induced interactions. We propose mixtures of colloidal particles and rod-like polymers as a feasible experimental system for verifying these predictions, since the intra-molecular correlations are not screened in a good solvent for rod-like polymers as they are in flexible polymers. The length of the rods can grow and become the dominant length scale that determines the range of the depletion interactions for the imbedded non-adsorbing particles.Simulations: We study many-body depletion forces induced by polymerizing rod-like polymers on spherical non-adsorbing colloids, using Metropolis Monte Carlo simulations. We also employ a simple mean-field theory to further justify our numerical predictions.Findings: We demonstrate that the phase diagram displays the same qualitative features that have previously been predicted by many-body theory, for mixtures containing flexible polymers under theta solvent conditions. The contraction of the particle two-phase region that we observe, as the correlation length increases beyond some specific value, could be a signature of the weakening of the depletion caused by many-body effects.