Polymer Conformation Research Articles

Chain-Kinked Design: Improving Stretchability of Polymer Semiconductors through Nonlinear Conjugated Linkers.

The manipulation of the polymer backbone structure has a profound influence on the crystalline behavior and charge transport characteristics of polymers. These strategies are commonly employed to optimize the performance of stretchable polymer semiconductors. However, a universal method that can be applied to conjugated polymers with different donor-acceptor combinations is still lacking. In this study, we propose a universal strategy to boost the stretchability of polymers by incorporating the nonlinear conjugated linker (NCL) into the main chain. Specifically, we incorporate meta-dibromobenzene (MB), characterized by its asymmetric linkage sites, as the NCL into the backbone of diketopyrrolopyrrole-thiophene-based (DPP-based) polymers. Our research demonstrates that the introduction of MB prompts chain-kinking, thereby disrupting the linearity and central symmetry of the DPP conjugated backbone. This modification reshapes the polymer conformation, decreasing the radius of gyration and broadening the free volume, which consequently adjusts the level of crystallinity, leading to a considerable increase in the stretchability of the polymer. Importantly, this method increases stretchability without compromising mobility and exhibits broad applicability across a wide range of donor-acceptor pair polymers. Leveraging this strategy, fully stretchable transistors were fabricated using a DPP polymer that incorporates 10 mol % of MB. These transistors display a mobility of approximately 0.5 cm2 V-1 s-1 and prove remarkably durable, maintaining 90% of this mobility even after enduring 1000 cycles at 25% strain. Overall, we propose a method to systematically control the main-chain conformation, thereby enhancing the stretchability of conjugated polymers in a widely applicable manner.

Directional and Reconfigurable Assembly of Active Colloidal Motors Triggered by Chemical Communications

AbstractAnisotropic colloidal particles can directionally self‐assemble, but the resulting assemblies cannot reconfigure unless the surface properties of colloidal particles change. Although external fields with adjustable inputs can guide the reconstruction of active structures after stimulating the dynamic assembly of active colloidal motors, the interaction between colloidal motors is unclear. Here, the study reports a bioinspired communication and directed assembly of peanut‐shaped colloidal motors with the emergence of ordered ribbon structures triggered by self‐generated chemical fields. The colloidal motors photocatalytically decompose the fuel to create the chemical concentration gradient fields and exert long‐range attractions on the colloidal scale, which enable colloidal motors to communicate by sensing each other, synchronizing orientation, and assembling side‐by‐side after the collision between their local flow fields. The inter‐individual communication occurs at a critical distance of ≈4.4 µm, resulting from the interplay between hydrodynamic effects, long‐ranged phoretic attraction, and short‐ranged magnetic interaction. The linear ribbons are still active owing to the symmetry breaking of the local fluid field and can be switched between rigid and flexible states according to light conditions to simulate the polymer conformation. The complexity of colloidal motors can be combined with external manipulations to manufacture active soft materials with precise and adaptive functions.

Conformational Properties of Polymers at Droplet Interfaces as Model Systems for Disordered Proteins.

Polymer models serve as useful tools for studying the formation and physical properties of biomolecular condensates. In recent years, the interface dividing the dense and dilute phases of condensates has been discovered to be closely related to their functionality, but the conformational preferences of the constituent proteins remain unclear. To elucidate this, we perform molecular simulations of a droplet formed by phase separation of homopolymers as a surrogate model for the prion-like low-complexity domains. By systematically analyzing the polymer conformations at different locations in the droplet, we find that the chains become compact at the droplet interface compared with the droplet interior. Further, segmental analysis revealed that the end sections of the chains are enriched at the interface to maximize conformational entropy and are more expanded than the middle sections of the chains. We find that the majority of chain segments lie tangential to the droplet surface, and only the chain ends tend to align perpendicular to the interface. These trends also hold for the natural proteins FUS LC and LAF-1 RGG, which exhibit more compact chain conformations at the interface compared to the droplet interior. Our findings provide important insights into the interfacial properties of biomolecular condensates and highlight the value of using simple polymer physics models to understand the underlying mechanisms.

Stochastic Electrical Detection of Single Ion-Gated Semiconducting Polymers.

Semiconducting polymer chains constitute the building blocks for a wide range of electronic materials and devices. However, most of their electrical characteristics at the single-molecule level have received little attention. Elucidating these properties can help understanding performance limits and enable new applications. Here, coupled ionic-electronic charge transport is exploited to measure the quasi-1D electrical current through long single conjugated polymer chains as they form transient contacts with electrodes separated by ≈10nm. Fluctuations between internal conformations of the individual polymers are resolved as abrupt, multilevel switches in the electrical current. This behavior is consistent with the theoretical simulations based on the worm-like-chain (WLC) model for semiflexible polymers. In addition to probing the intrinsic properties of single semiconducting polymer chains, the results provide an unprecedented window into the dynamics of random-coil polymers and enable the use of semiconducting polymers as electrical labels for single-molecule (bio)sensing assays.

Understanding the Impacts of Molecular and Macromolecular Crowding Agents on Protein-Polymer Complex Coacervates.

Complex coacervation refers to the liquid-liquid phase separation (LLPS) process occurring between charged macromolecules. The study of complex coacervation is of great interest due to its implications in the formation of membraneless organelles (MLOs) in living cells. However, the impacts of the crowded intracellular environment on the behavior and interactions of biomolecules involved in MLO formation are not fully understood. To address this knowledge gap, we investigated the effects of crowding on a model protein-polymer complex coacervate system. Specifically, we examined the influence of sucrose as a molecular crowder and polyethylene glycol (PEG) as a macromolecular crowder. Our results reveal that the presence of crowders led to the formation of larger coacervate droplets that remained stable over a 25-day period. While sucrose had a minimal effect on the physical properties of the coacervates, PEG led to the formation of coacervates with distinct characteristics, including higher density, increased protein and polymer content, and a more compact internal structure. These differences in coacervate properties can be attributed to the effects of crowders on individual macromolecules, such as the conformation of model polymers, and nonspecific interactions among model protein molecules. Moreover, our results show that sucrose and PEG have different partition behaviors: sucrose was present in both the coacervate and dilute phases, while PEG was observed to be excluded from the coacervate phase. Collectively, our findings provide insights into the understanding of crowding effects on complex coacervation, shedding light on the formation and properties of coacervates in the context of MLOs.

Microscopy and modelling investigations on the morphology of the biofilm exopolysaccharide produced by Burkholderia multivorans strain C1576

Bacteria form very often biofilms where they embed in a self-synthesized matrix exhibiting a gel-like appearance. Matrices offer several advantages, including defence against external threats and the easiness of intercellular communication. In infections, biofilm formation enhances bacteria resistance against antimicrobials, causing serious clinical problems for patients' treatments. Biofilm matrices are composed of proteins, extracellular DNA, and polysaccharides, the latter being the major responsible for matrix architecture. The repeating unit of the biofilm polysaccharide synthesized by Burkholderia multivorans strain C1576 contains two mannoses and two sequentially linked rhamnoses, one of them 50 % methylated on C-3. Rhamnose, a 6-deoxysugar, has lower polarity than other common monosaccharides and its methylation further reduces polarity. This suggests a possible role of this polysaccharide in the biofilm matrix; in fact, computer modelling and atomic force microscopy studies evidenced intra- and inter-molecular non-polar interactions both within polysaccharides and with aliphatic molecules. In this paper, the polysaccharide three-dimensional morphology was investigated using atomic force microscopy in both solid and solution states. Independent evidence of the polymer conformation was obtained by transmission electron microscopy which confirmed the formation of globular compact structures. Finally, data from computer dynamic simulations were used to model the three-dimensional structure.

Persistence Length of PEGMA Bottle Brushes Determined by Pyrene Excimer Fluorescence.

Seven pyrene-labeled poly(oligo(ethylene glycol) methyl ether methacrylate)s (PyEG5-PEGnMAs) were prepared with n = 0, 3, 4, 5, 7, 9, and 19 ethylene glycol units by copolymerizing a small amount of penta(ethylene glycol) 1-pyrenemethyl ether methacrylate with an EGnMA monomer. The conformation of the PyEG5-PEGnMA polymers evolved from a random coil for PyEG5-PEG0MA or poly(methyl methacrylate) to a polymeric bottle brush (PBB) architecture with increasing side chain length. The fluorescence decays of the PyEG5-PEGnMA samples were fitted according to the fluorescence blob model (FBM) whose parameters were used, in combination with the Kratky-Porod equation, to calculate the persistence length of these polymers. The persistence lengths obtained from the PEF experiments were found to increase with the square of the number (NS) of non-hydrogen atoms in the side chain as expected theoretically. The persistence lengths found with the PyEG5-PEGnMA samples in DMF also matched those found earlier for another series of PEGnMA samples labeled with 1-pyrenebutanol. The good agreement found between the persistence lengths obtained with the PEGnMA samples labeled with two different pyrene derivatives illustrates the robustness of the method and its applicability for measuring the unknown persistence length of polydisperse polymer samples.

Hydraulic conductivity and multi-scale pore structure of polymer-enhanced geosynthetic clay liners permeated with bauxite liquors

A study was conducted to investigate the multi-scale pore structure-based mechanism controlling the hydraulic conductivity of polymer-enhanced geosynthetic clay liners (GCLs) prepared by the wet-mixed method to bauxite liquors (BLS and BLA). The multi-scale pore structures were evaluated using MIP and N2GA tests quantitatively. Conventional GCL permeated with BLS had a larger flow path volume than with DI water (0.194 > 0.119 cm³/g), attributed to the bentonite swelling inhibition and the montmorillonite dissolution, leading to the higher hydraulic conductivity (3.0 × 10−7 > 2.7 × 10−11 m/s). Polymer-enhanced GCLs developed more micropores and had a smaller quantity proportion and volume of flow paths since polymer formed more micropores to clog pores, contributing to a lower hydraulic conductivity than conventional GCL to BLS. The hydraulic conductivity of polymer-enhanced GCL to BLS (ionic strength: 622.5 mM) was higher than that to BLA (156.9 mM) (2.6 × 10−9 > 6.0 × 10−12 m/s), given that the coiled or contracted polymer conformation left a smaller quantity proportion (5.54% < 6.71%) and volume (0.0002 cm3/g < 0.0035 cm3/g) of micropores.

The translocation of a polymer through a nanopore with sandglass‐like geometry

AbstractIn recent years, non‐uniformly geometrical nanopores, such as conical nanopores, have gained significant attention in nanopore sensing technology due to their advantages in analyte manipulation and clear output signals. This paper focuses on the polymer translocation through a sandglass‐like nanopore, characterized by a double‐conical geometry with a tip at the middle. We systematically investigate the effects of pore geometry on the translocation dynamics through computational simulations and theoretical analyses. The polymer translocation process is divided into three stages: approaching, threading, escaping, corresponding to the movement from the entry to the tip, through the tip, and from the tip to the exit, respectively. Our findings reveal that the duration of the approaching stage highly depends on the polymer conformations, while the durations of the threading and escaping stages are primarily influenced by the driving force associated with the pore geometry and the accompanying free energy change. Additionally, we report a relationship between the threading speed of the polymer at the tip and the combination of the driving force there and the free energy change during the threading stage.

Exploring conformations of comb-like polymers with varying grafting density in dilute solutions.

Comb-like polymers have shown potential as advanced materials for a diverse palette of applications due to the tunability of their polymer architecture. To date, however, it still remains a challenge to understand how the conformational properties of these polymers arise from the interplay of their architectural parameters. In this work, extensive simulations were performed using dissipative particle dynamics to investigate the effect of grafting density, backbone length, and sidechain length on the conformations of comb-like polymers immersed in a good solvent. To quantify the effect of these architectural parameters on polymer conformations, we computed the asphericity, radius of gyration, and backbone and sidechain end-to-end distances. Bond-bond correlation functions and effective Kuhn lengths were computed to quantify the topological stiffness induced by sidechain-sidechain interactions. Simulation results reveal that the effective Kuhn length increases as grafting density and sidechain length increase, in agreement with previous experimental and theoretical studies. This increase in stiffness results in comb-like polymers adopting extended conformations as grafting density and sidechain length increase. Simulation results regarding the radius of gyration of comb-like polymers as a function of grafting density are compared with scaling theory predictions based on a free energy proposed by Morozova and Lodge [ACS Macro Lett. 6, 1274-1279 (2017)] and scaling arguments by Tang et al. [Macromolecules 55, 8668-8675 (2022)].

Dynamic transformation of bio-inspired single-chain nanoparticles at interfaces.

The interfacial behavior of macromolecules dictates their intermolecular interactions, which can impact the processing and application of polymers for pharmaceutical and synthetic use. Using molecular dynamics simulations, we observe the evolution of a random heteropolymer in the presence of liquid-liquid interfaces. The system of interest forms single-chain nanoparticles through hydrophobic collapse in water, lacking permanent crosslinks and making their morphology mutable in new environments. Complex amphiphilic polymers are shown to be capable of stabilizing high interfacial tension water-hexane interfaces, often unfolding to maximize surface coverage. Despite drastic changes to polymer conformation, monomer presence in the water phase is generally maintained and most changes are due to increased hydrophobic solvent exposure toward the oil phase. These results are then compared to the behavior at the water-graphene interface, where the macromolecules adsorb but do not remodel. The polymer's behavior is shown to depend significantly on both its own amphiphilic character and the deformability of the interface.

A Perspective on the Prospect of Pickering Emulsion in Reservoir Conformance Control with Insight into the Influential Parameters and Characterization Techniques

In reservoir conformance control, polymer gels and foams are majorly used; however, they have drawbacks such as inducing formation damage, having weaker shear resistance, requiring a higher pumping rate, and limited penetration depth. Emulsions are a potential alternative that can address these issues, but they are not widely used. Current surfactant-based emulsions require high emulsifier concentrations for stability and often rely on multiple additives to address various factors, which makes the surfactant synthesis and utilization of emulsions quite challenging. However, Pickering emulsions, which utilize solid particles for emulsion stabilization, have emerged as a promising solution for reservoir conformance control. Compared to conventional polymer gels and foams, Pickering emulsions offer superior shear resistance, deeper penetration, and reduced formation damage. This review provides an overview of recent developments in the utilization of Pickering emulsions for conformance control, highlighting important parameters and characteristics that must be considered during the design and deployment of a Pickering emulsion for water shut-off operation. This review also sheds light on current challenges and provides recommendations for future development of the particle-stabilized colloid system.

Molecular conformations of dumbbell-shaped polymers in good solvent.

We study conformational properties of diluted dumbbell polymers composed of two rings attached to both ends of a linear spacer segment. Our investigation involves analytical methods of field theory and bead-spring coarse-grained molecular dynamics simulations. We focus on the influence of the relative length of the spacer segment to the length of side rings on the shape and the relative size of dumbbells as compared to linear polymers of equal mass. We find that dumbbells with short spacers exhibit a significantly more compact structure than linear polymers. Conversely, as the spacer length increases, the influence of the side rings on the size of the dumbbells becomes negligible. Consequently, dumbbell molecules with long spacers attain a size comparable to corresponding linear chains. Our analytical theory accurately predicts a quantitative conformational crossover between the behaviors of short-spacer and long-spacer dumbbells, which is further confirmed by our numerical simulations.

Entropic stress of grafted polymer chains in shear flow.

We analyze the shear response of grafted polymer chains in shear flow via coarse-grained molecular dynamics simulations with an explicit solvent. We find that the solvent flow penetrates into almost the whole brush for "mushroom"-type brushes but only a few bond distances for dense brushes. In all cases, the external stress on the wall equals the entropic stress associated with the distorted polymer conformations. We find that the external stress increases linearly with shear rate at low rates and sublinearly at high rates. The transition from linear to sublinear scaling occurs where chains react to flow by reorienting. Sublinear scaling with shear rate disappears if the shear rate is nondimensionalized with the effective relaxation time of chain subsegments located in the outer part of the brush that experiences flow.

Mold-Free Manufacturing of Highly Sensitive And Fast Response Pressure Sensors Through High-Resolution 3d Printing And Conformal Oxidative Chemical Vapor Deposition Polymers.

In this work, w e showcase a new manufacturing paradigm to exclude conventional mold-dependent manufacturing of pressure sensors, which typically requires a series of complex and expensive patterning processes. Our mold-free manufacturing leverages high-resolution 3D printed multiscale microstructures as substrate and a gas-phase conformal polymer coating technique to complete the mold-free sensing platform. The array of dome and spike structures with a controlled spike density of a 3D-printed substrate ensures a large contact surface with pressures applied and extended linearity in a wider pressure range. For uniform coating of sensing elements on the microstructured surface, oxidative chemical vapor deposition is employed to deposit a highly conformal and conductive sensing element, poly(3,4-ethylenedioxythiophene) at low temperatures (< 60 °C). The fabricated pressure sensor reacts sensitively to various ranges of pressures (up to 185 kPa-1 ) depending on the density of the multiscale features and shows an ultra-fast response time (∼36 μs). The mechanism investigations through the finite element analysis identify the effect of the multiscale structure on the figure-of-merit sensing performance. Our unique findings are expected to be of significant relevance to the technology that requires higher sensing capability, scalability, and facile adjustment of a sensor geometry in a cost-effective manufacturing manner. This article is protected by copyright. All rights reserved.

Effect of stereo-chemistry and hydrophilic nature of synthetic carboxylic acid polymers on conformation, intermolecular structure and hydration at air-water interface

Conformation, intermolecular structure and hydration of different stereo-isomers of poly(methacrylic acid) and poly(acrylic acid), specifically isotactic-poly(methacrylic acid) (i-PMA), syndiotactic-poly(methacrylic acid) (s-PMA) and syndiotactic-poly(acrylic acid) (s-PAA) at vacuum-water interface were studied using molecular dynamics simulations. The adsorbed chain conformation was analyzed by radius-of-gyration components parallel and perpendicular to the interface, relative shape anisotropy parameter, distribution and autocorrelation function of dihedral angles, and orientation distribution of different groups relative to interface plane. i-PMA and s-PAA adsorb in planar conformation (i-PMA is curved compared to s-PAA) whereas s-PMA adsorbs in random coil conformation. Different chemical groups of s-PAA and i-PMA show preferential orientation whereas it is absent in the case of s-PMA. The random coil conformation of s-PMA exhibits greater intra-chain hydrogen bonding whereas extended chain of s-PAA exhibits greater polymer-water hydrogen bonding. The overall contribution to polymer-water hydrogen bonds by carbonyl oxygen atoms is greater than that by hydroxyl hydrogen atom. Water molecules hydrogen bonded to s-PAA show faster dynamics compared to those bonded to i-PMA and s-PMA. The slower dynamics of polymer-water hydrogen bonds is correlated to the slower dynamics of polymer conformations. Knowledge of orientation of chemical groups is useful for understanding binding of adsorbed polymer with other polymers and ligands.

Structure of Cellulose Ether Affected by Ionic Surfactant and Solvent: A Small-Angle Neutron Scattering Investigation.

Polysaccharides and their derivatives are commonly used in pharmaceutical and agricultural formulations as rheology modifiers. Their performance is related to their conformation in solution, which in turn is affected by other ingredients present in the formulation. This study focuses on modulating the conformation of relatively rigid cellulose chains in aqueous solutions. In particular, we have investigated the nonionic cellulose derivative ethyl(hydroxyethyl)cellulose (EHEC) in water in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) and/or ethanol acting as modulating agents. We have used small angle neutron scattering (SANS) with contrast variation to determine the EHEC chain conformation in the presence of (but not masked by) ethanol and SDS. In dilute and semidilute aqueous solutions, EHEC exhibits worm-like chain conformation due to the rigid cellulose backbone. Addition of ethanol does not impact the polymer conformation to a great extent. Addition of SDS alters the EHEC chain conformation, resulting in polyelectrolyte-like scattering behavior due to repulsive interactions between bound charged micelles which show similar structure as the free SDS micelles in solution (in the absence of polymers). Ethanol affects the polymer + surfactant system primarily by acting on the surfactant (bound on polymer) which, in turn, affects the polymer conformation. At higher ethanol concentrations (20 wt %), EHEC regains the worm-like chain conformation because of the detachment of the bound SDS micelles. To the best of our knowledge, this is the only study providing details on chain conformation of the rigid polymer EHEC in dilute or semidilute aqueous solutions in the presence of surfactant and alcohol and one of very few papers utilizing SANS for the characterization of polymer + surfactant + water + alcohol interactions. Such fundamental understanding of interactions and structure in multicomponent mixtures supports the design of industrial formulations.

Unraveling the Phase Behavior, Mechanical Stability, and Protein Reconstitution Properties of Polymer-Lipid Hybrid Vesicles.

Hybrid vesicles consisting of natural phospholipids and synthetic amphiphilic copolymers have shown remarkable material properties and potential for biotechnology, combining the robustness of polymers with the biocompatibility of phospholipid membranes. To predict and optimize the mixing behavior of lipids and copolymers, as well as understand the interaction between the hybrid membrane and macromolecules like membrane proteins, a comprehensive understanding at the molecular level is essential. This can be achieved by a combination of molecular dynamics simulations and experiments. Here, simulations of POPC and PBD22-b-PEO14 hybrid membranes are shown, uncovering different copolymer configurations depending on the polymer-to-lipid ratio. High polymer concentrations created thicker membranes with an extended polymer conformation, while high lipid content led to the collapse of the polymer chain. High concentrations of polymer were further correlated with a decreased area compression modulus and altered lateral pressure profiles, hypothesized to result in the experimentally observed improvement in membrane protein reconstitution and resistance toward destabilization by detergents. Finally, simulations of a WALP peptide embedded in the bilayer showed that only membranes with up to 50% polymer content favored a transmembrane configuration. These simulations correlate with previous and new experimental results and provide a deeper understanding of the properties of lipid-copolymer hybrid membranes.

A sulfur cathode design strategy for polysulfide restrictions and kinetic enhancements in Li-S batteries through oxidative chemical vapor deposition

Lithium-sulfur (Li-S) batteries offer a promising solution for achieving high-density and low-cost energy storage devices. However, the practical utilization of Li-S batteries is hindered by the main bottleneck of polysulfides transport from the cathode to the electrolyte and anode, which leads to the detrimental degradation of the electrolyte and non-uniform microstructure evolution on the anode, ultimately resulting in rapid capacity fading. To overcome this limitation, we propose a groundbreaking mitigation strategy that leverages the oxidative chemical vapor deposition (oCVD) technique to limit the shuttling of polysulfides in the cathode. This gas-phase approach is unique in that highly conducting and conformal polymer coating entirely eliminates the use of traditional binders in the cathode while enhancing the kinetic conditions of the sulfur conversion and inhibiting the shuttling of polysulfides during battery operation. Complementary experimental and theoretical investigations identify that polysulfides are physically and chemically confined in the cathode region. The sulfur cathode manufactured using this approach demonstrates high active material loading (90 wt%), a high sulfur utilization ratio of 84.4% (∼1413 mAh g−1 at 0.1 C), and capacity retention of 85% after 300 cycles (∼810 mAh g−1) at 0.5 C. The pouch cell also showcases a high specific energy of up to 202 Wh kg−1 with a low electrolyte/sulfur ratio of 4.55, proving the immense potential for practical applications.

Early stages of X-ray induced molecular unit modifications in poly(lactic acid)

Exposure of polymers to ionizing radiation and high-energy particle beams is involved in many processes – from food sterilization to radiotherapy protocols. The resulting effects, at the final stages, determine the functional, structural, and morphological alteration of the material. However, the processes responsible for cumulative chain scission, crosslinking, and reactions with the environment are often difficult to disentangle as a sequence of elementary events. Here we report a spectroscopic study – by attenuated-total reflection Fourier transform infrared spectroscopy and powder x-ray diffraction measurements, together with differential scanning calorimetry and thermogravimetric analyses – that sheds light on the very initial stages of the mechanisms involved in radiation-induced modifications of poly(lactic acid) (PLA). The results, collected on samples from biobased processes and exposed to low x-ray doses in the range of 100–103Gy after different thermal treatments, show spectroscopic evidence of the emergence of molecular unit perturbations – mainly related to methyl and carbonyl groups with the formation of C=C double bonds – with a clear-cut dependence on the polymer conformation. Understanding the mechanisms involved and the role of crystallinity provides information potentially useful for the development of PLA with a suitable radiation hardness for applications in radiotherapy.