Extended Polymer Chains Research Articles

Free energy and extension of stiff polymer chains confined in nanotubes with diverse cross-sectional shapes

The statistical mechanics of stiff polymer chains confined within narrow tubes is a foundational topic in polymer physics, extensively analyzed in prior research. For cylindrical, rectangular, and slit-like confinements, the chains’ free energy and extension adhere to a scaling law consistent with the Odijk theory. While this scaling law may not apply to tubes with different cross-sectional geometries, there is a lack of research examining the behavior of stiff chains in tubes with intricate cross-sectional shapes. In this study, we investigate the partition function of a stiff chain confined within an elliptic tube using the path integral approach, deriving a deflection length in a concise closed form through dimensional analysis. This length scale facilitates straightforward expressions for the chain's free energy and extension. Notably, we discover a shape-independent property of these expressions applicable to tubes with a wide variety of cross-sectional geometries. Extensive numerical simulations are conducted using a biased chain-growth Monte Carlo method, incorporating the Pruned and Enriched Rosenbluth algorithm, to validate the theoretical predictions on the confinement free energy and extension of chains in tubes with differing shapes.

Toward Synthetic Intrinsically Disordered Polypeptides (IDPs): Controlled Incorporation of Glycine in the Ring-Opening Polymerization of N-Carboxyanhydrides.

Intrinsically disordered proteins (IDPs) do not have a well-defined folded structure but instead behave as extended polymer chains in solution. Many IDPs are rich in glycine residues, which create steric barriers to secondary structuring and protein folding. Inspired by this feature, we have studied how the introduction of glycine residues influences the secondary structure of a model polypeptide, poly(l-glutamic acid), a helical polymer. For this purpose, we carried out ring-opening copolymerization with γ-benzyl-l-glutamate and glycine N-carboxyanhydride (NCA) monomers. We aimed to control the glycine distribution within PBLG by adjusting the reactivity ratios of the two NCAs using different reaction conditions (temperature, solvent). The relationship between those conditions, the monomer distributions, and the secondary structure enabled the design of intrinsically disordered polypeptides when a highly gradient microstructure was achieved in DMSO.

Dynamics of a viscoelastic droplet migrating in a ratchet microchannel under AC electric field

Droplet-based microfluidic devices can be powered or manipulated by applying an external electric field, and the ability to precisely control the flow in such devices is essential for various engineering and biomedical applications. In this numerical study, we investigate the deformation dynamics of a viscoelastic droplet in a ratchet microchannel under the influence of an AC electric field. We employ the leaky-dielectric electrohydrodynamic model for both the immiscible fluid phases coupled with the Oldroyd-B model for the droplet fluid. The effect of geometrical parameters such as the type of ratchet and the wavenumber of the ratchets along with the flow parameters such as the electrocapillary number, Weissenberg number and the capillary number significantly affect the droplet shape dynamics and the polymer chain extension. For the parameters considered in this work, the electric force tends to stretch the droplet in the streamwise direction and enhances the droplet deformation and polymer extension. Several interesting effects arise as a result of the coupling of the periodic hydrodynamic forcing of the ratchet walls and the electric field. Specifically, an exponential rise in the polymer chain extension for higher ratchet wavenumbers is observed, along with the cross-stream migration of the droplet for higher electrocapillary numbers when it reaches the outlet of the ratchet constriction.

Low-entropy amorphous dielectric polymers for high-temperature capacitive energy storage

A short-range ordered, long-range disordered structure in a low-entropy amorphous polymer, with locally extended polymer chains, inhibits electron transport in dielectric polymers, enhancing capacitive performance at elevated temperatures.

Thermoresponsive membrane based on UCST-type organoboron polymer for smart gating and self-cleaning

Thermoresponsive polymers can endow membranes with tunable separation and self-cleaning performance. However, up to now, there have been only very limited choices of thermoresponsive polymers for the fabrication of smart membranes. Herein, thermoresponsive membranes based on UCST-type organoboron polymer (Poly(CPBA)) were fabricated for the first time. Poly(CPBA) synthesized via a nucleophilic ring-opening reaction with Poly(GMA) and 3-carboxyphenylboronic acid has shown typical thermoresponsive behavior in water and water/ethanol mixture. Under vacuum conditions, Poly(CPBA) formed the cross-linked boroxine network on the membrane surface via a dehydration-induced condensation reaction. The reversible conformational change of Poly(CPBA) near UCST acted as a smart “gating” to regulate both pore size and surface properties of the membrane. When the temperature exceeded UCST, the fully extended polymer chains provided a strong washing force to remove contaminants, resulting in effective self-cleaning performance (FRR up to 99.2 %). In particular, due to the presence of the boroxine network, the polymer chains were firmly “stuck” on the membrane surface, providing stable performance and superior repeatability of the composite membrane.

Mechanical Behavior of Hybrid Thin Films Fabricated by Sequential Infiltration Synthesis in Water-Rich Environment.

Sequential infiltration synthesis (SIS) is an emerging technique for fabricating hybrid organic-inorganic materials with nanoscale precision and controlled properties. Central to SIS implementation in applications such as membranes, sensors, and functional coatings is the mechanical properties of hybrid materials in water-rich environments. This work studies the nanocomposite morphology and its effect on the mechanical behavior of SIS-based hybrid thin films of AlOx-PMMA under aqueous environments. Water-supported tensile measurements reveal an unfamiliar behavior dependent on the AlOx content, where the modulus decreases after a single SIS cycle and increases with additional cycles. In contrast, the yield stress constantly decreases as the AlOx content increases. A comparison between water uptake measurements indicates that AlOx induces water uptake from the aqueous environment, implying a "nanoeffect" stemming from AlOx-water interactions. We discuss the two mechanisms that govern the modulus of the hybrid films: softening due to increased water absorption and stiffening as the AlOx volume fraction increases. The decrease in the yield stress with SIS cycles is associated with the limited mobility and extensibility of polymer chains caused by the growth of AlOx clusters. Our study highlights the significance of developing hybrid materials to withstand aqueous or humid conditions which are crucial to their performance and durability.

Dynamic modeling of hard-magnetic soft actuators: Unraveling the role of polymer chain entanglements, crosslinks, and finite extensibility

In recent years, there has been increasing interest in hard-magnetic soft materials (HMSMs) due to their ability to retain high residual magnetization and undergo large deformations under external magnetic loading. The performance of these materials in the dynamic mode of actuation is significantly influenced by internal properties, such as entanglements, crosslinks, and the finite extensibility of polymer chains. This article presents a theoretical framework for modeling the dynamic behavior of a hard-magnetic soft material-based planar actuator. A physics-based nonaffine material model is utilized to consider the inherent properties of polymer chain networks. The governing equation for dynamic motion is derived using Euler–Lagrange’s equation of motion for conservative systems. The devised dynamic model is utilized to examine the dynamic response, stability, periodicity, and resonance properties of a planar hard-magnetic soft actuator for different values of polymer chain entanglements, crosslinks, and finite extensibility parameters. The Poincaré maps and phase-plane plots are presented to analyze the stability and periodicity of the nonlinear vibrations of the actuator. The results reveal that transitions between aperiodic and quasi-periodic oscillations occur when the density of polymer chain entanglements and cross-linking changes. The findings from the present investigation can serve as an initial step towards the design and manufacturing of remotely controlled actuators for various futuristic applications.

Highly Conductive Inkjet-Printed PEDOT:PSS Film under Cyclic Stretching.

Inkjet-printed conductive polymer PEDOT:PSS films have provided a new developing direction for realizing the stretchable transparent electrodes in optoelectronic devices. However, their conductivity and stretchability are limited as the presence of insulating PSS chains, rigid PEDOT conjugated backbone, and stronger inter-chain interactions in the pristine polymer, respectively. Here, we report a PEDOT:PSS film with preferable electrical and mechanical performances by inkjet-printing the formulated printable ink containing PEDOT:PSS, formamide (FA), d-sorbitol (SOR), sodium dodecyl benzene sulfonate (DBSS), and ethylene glycol (EG). The inkjet-printed uniform PEDOT:PSS film exhibits a high conductivity of 1050 S/cm and sheet resistance of less than 145 Ω/sq on both rigid and flexible substrates. Moreover, the resistance can remain stable after 200 cycles of stretching at 55% strain. The film also presents good stability during repetitive stretching-releasing cycles. The significantly enhanced conductivity of the film lies on the conformational transition of the backbone by secondary doping and post-treatment with FA as well as removing the excess PSS components after phase separation between PEDOT and PSS. Meanwhile, SOR serves as a plasticizer to break the original hydrogen bonds between PSSH chains and provides larger free volume for polymer chain extension, which gives the PEDOT:PSS film the ability to tolerant cyclic tension. This is one of the optimal performances currently reported for inkjet-printed stretchable PEDOT:PSS films. The inkjet-printed PEDOT:PSS film with high conductivity, stretching properties, as well as good biocompatibility exhibits promising prospects as anodes on optoelectronic devices.

Multi-size optimization of macroporous cellulose beads as protein anion exchangers: Effects of macropore size, protein size, and ligand length

Multi-size optimization of ion exchangers based on protein characteristics and understanding of underlying mechanism is crucial to achieve maximum separation performance in terms of adsorption capacity and uptake kinetic. Herein, we characterize the effects of three different sizes, macropore size, protein size, and ligand length, on the protein adsorption capacity and uptake kinetic of macroporous cellulose beads, and provide insights into the underlying mechanism. In detail, (1) for smaller bovine serum albumin, macropore size has a negligible effect on the adsorption capacity, while for larger γ-globulin, larger macropores improve the adsorption capacity due to the high accessibility of binding sites; (2) there is a critical pore size (CPZ), at which the adsorption uptake kinetic is minimum. When pore sizes are higher than the CPZ, uptake kinetics are enhanced by pore diffusion. When pore sizes are lower than CPZ, uptake kinetics are enhanced by surface diffusion; (3) increasing ligand length improves the adsorption capacity by three-dimensionally extended polymer chains in pores and enhances uptake kinetic by improved surface diffusion. This study offers an integrated perspective to qualitatively assess the effects of multiple sizes, providing guidance for designing advanced ion exchangers for protein chromatography.

Modeling fracture in polymeric material using phase field method based on critical stretch criterion

In this work, the phase field method (PFM) is applied for modeling fracture in the polymeric type of materials. Considering the large extensibility of polymer chains before fracture, a crack initiation criteria based on a critical stretch value is proposed. The tensile stretches in the material contribute to the active strain energy, which is responsible for driving fracture. Additive decomposition of strain energy into active and passive parts is adopted based on the critical stretch value of polymer chains in a phase-field setting. This critical value is determined by assuming an equivalent uniaxial tensile state of stress in front of the crack tip at the onset of fracture. The stretch of individual polymeric chains is determined by using a polymer network model. The critical fracture toughness of the polymer is kept constant up to the onset of fracture and a gradually reducing value of it is adopted in front of the crack tip beyond the critical stretch. A hybrid phase-field formulation with a staggered solver is used owing to its numerical efficiency and robustness. The effectiveness and applicability of the present model are demonstrated through various numerical examples.

Non-toxic CuInS2 quantum dot sensitized solar cell with functionalized thermoplast polyurethane gel electrolytes

Functionalization of multi-walled carbon nanotubes (CNTs) was carried out through ultrasonication in acidic medium followed by chemical attachment of thermoplastic polyurethane and subsequent chain extension using butane-diol to obtain CNT-tagged polyurethane (PU-CNT). PU-CNT was functionalized by using propane sultone as a sulfonating agent to attach the pendent sulfonate moiety on urethane linkage. The functionalization of CNTs, tagging of CNTs with polymer chain, chain extension and subsequent functionalization of polymer have been confirmed though through spectroscopic techniques such as NMR, FTIR, UV–vis, and Raman spectroscopy. Thermal stability and the nature of interaction is explored through thermal measurements to understand the effect of CNT functionalization. Electrical conduction has been improved by the chemical attachment of CNTs with polymer (1.61 × 10−6 S/cm) which further increases through functionalization (1.37 × 10−4 S/cm) and thereby make them suitable for gel electrolyte. Quantum dot of CuInS2 has been synthesized using DDT as capping agent and its characteristic properties and the dimension are worked out for their suitability as active materials in solar cell. Optical band gap of quantum dots and HOMO/LUMO band structure of functionalized polyurethanes have been measured through UV–vis and cyclic voltametry, and thereby, draw the overall energy diagrams of possible combination of materials. Solar cell devices have been fabricated using the appropriate materials and found improved power conversion efficiency of 0.81% with Au (gold) as counter electrode. The reason behind the better efficiency is understood from the lesser energy gap between HOMO energy level of prepared gel electrolyte (SPU-CNT) and Au (gold) counter electrode, better conductivity and higher rate of hole transportation, to reduce the electron-hole pair recombination.

Swelling-induced Mechanochromism in Multinetwork Polymers.

We report a novel and versatile approach to achieving swelling-induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical-based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling-force-induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture.

Swelling‐induced Mechanochromism in Multinetwork Polymers

AbstractWe report a novel and versatile approach to achieving swelling‐induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical‐based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling‐force‐induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture.

Effects of electrostriction on the bifurcated electro-mechanical performance of conical dielectric elastomer actuators and sensors

AbstractDielectric elastomers (DEs) find applications in many areas, particularly in the field of soft robotics. When modeling and simulating DE-based actuators and sensors, a substantial portion of the literature assumes the selected DE material to behave in some perfectly hyperelastic manner, and the vast majority have assumed invariant permittivity. However, studies on simple planar DEs have revealed instabilities and hastened breakdowns when a variable permittivity is allowed. This is partly due to the intertwined electromechanical properties of DEs rooted on their labyrinthine polymeric microstructures. This work focuses on studying the effects of a varying (with stretch) permittivity on the out-of-plane deformation of a circular DE, using a model derived from principles of strain-induced polymer birefringence. In addition, we utilize the Edward–Vilgis model, which attempts to account for effects related to crosslinking, and length extension, slippage, and entanglement of polymer chains. Our approach reveals the presence of “stagnation” regions in the electromechanical behavior of the DE actuator material. These stagnation regions are characterized by both electrical and mechanical critical electrostrictive coefficient ratios. Mechanically, certain values of the electrostrictive coefficient ratio predict cases where deformation does not occur in response to a change in voltage. Electrically, certain cases are predicted where changes in capacitance cannot be measured in response to changes in deformation. Thus, some combined conditions of loading and material properties could limit the effectiveness of DE membranes in either actuation or sensing. Therefore, our results reveal mechanisms that could be useful to designers of actuators and sensors and unveil an opportunity for exploring new theoretical materials with potential novel applications. Furthermore, since there are known analogous formulations between electrical and optical properties, criticality principles studied in this article could be extended to optomechanical coupling.

Turbulent planar wakes of viscoelastic fluids analysed by direct numerical simulations

Direct numerical simulations employing the finitely extensible nonlinear elastic constitutive model closed with Peterlin's approximation (FENE-P) are used to investigate the far-field region of turbulent planar wakes of viscoelastic fluids and to develop the theory describing these flows. The theoretical results display excellent agreement with the simulations and provide new scaling laws for the evolution of the shear layer thickness $\delta (x) \sim x^{1/2}$ , mean velocity deficit ${\rm \Delta} U(x) \sim x^{-1/2}$ and, for very high Deborah numbers, of the maximum polymer shear stresses $\sigma ^{[p]}_c(x) \sim x^{-2}$ and averaged polymer chain extension $\textrm {tr}(\bar {C}(x) - \boldsymbol{\mathsf{I}}) \sim x^{-2}$ , where $x$ is the streamwise distance from the solid body generating the wake. The theory is able to show the existence of self-similarity for the profiles of mean velocity, mean polymer shear stress, averaged polymer chain extension and the conditions for similarity of the turbulent shear stress, and is very well supported by the numerical simulations. Similarly to the case of viscoelastic turbulent planar jets (Guimarães et al., J. Fluid Mech., vol. 899, 2020, p. A11), when the inlet Weissenberg and Deborah numbers are sufficiently large, turbulent viscoelastic wakes exhibit a considerable reduction of the spreading rate and of the normalised Reynolds stresses. However, for very large downstream locations the turbulent viscoelastic wake recovers the classical evolution laws observed for Newtonian turbulent planar wakes.

Grafting diethylaminoethyl dextran to macroporous cellulose microspheres: A protein anion exchanger of high capacity and fast uptake rate

Ion exchangers with high adsorption capacity and fast mass transfer synchronously are highly desired for protein separation and purification. For this purpose, here, we develop a high-performance anion exchanger by grafting diethylaminoethyl dextran (DEAE-dextran) on macroporous cellulose microspheres (MCMs). Static adsorption experiments for bovine serum albumin (BSA) show that the DEAE-dextran grafted MCMs have a higher adsorption capacity of 192.6 mg/mL than traditional non-grafted DEAE modified anion exchangers at a similar ionic capacity. The high adsorption capacity is due to the three-dimensionally extended polymer chains in pores that provide more and easily accessible ligands. Uptake kinetic results reveal that the DEAE-dextran grafted MCMs have a fast mass transfer rate and the maximum ratio (De/D0) of effective pore diffusivity (De) to free solution diffusivity (D0) reach 0.96, which is over three times higher than traditional non-grafted DEAE modified MCMs (0.29) and over nine times higher than commercial DEAE Sepharose FF (<0.10). It is attributed to the synergistic effect of the macropores and grafting ligands. The macropores provide wide channels for intraparticle pore diffusion, and the grafting ligands facilitate the surface transport of BSA by chain delivery occurred between adjacent DEAE-dextran chains. All these results demonstrate the DEAE-dextran grafted MCMs are promising as high-performance ion exchangers.

4D printing of PET-G via FDM including tailormade excess third shape

In this paper, for the first time, the 4D printing capability and shape memory effect of PETG as a novel shape memory thermoplastic has been investigated with an option of emerging tailormade excess curved third shape during the shape recovery step. A self-bending through the primary printed layers was observed due to entropic force relief caused by functionally-graded polymer chain extension in each layer. Implementation of printing temperature and speed of 200◦C and 70 mm/s, respectively, results in an opaque appearance and a more curved third shape. On the other hand, a transparent appearance with a gentle curved permanent shape was achieved by the parameters of 240◦C and 10 mm/s. The observations are attributed to the effect of printing parameters on the degree of polymer chains’ extension and its difference for each layer. Both samples show an exemplary shape memory effect behavior with higher than 96 % total shape recovery.

Understanding Gas Transport in Polymer-Grafted Nanoparticle Assemblies.

We rationalize the unusual gas transport behavior of polymer-grafted nanoparticle (GNP) membranes. While gas permeabilities depend specifically on the chemistry of the polymers considered, we focus here on permeabilities relative to the corresponding pure polymer which show interesting, "universal" behavior. For a given NP radius, Rc, and for large enough areal grafting densities, σ, to be in the dense brush regime we find that gas permeability enhancements display a maximum as a function of the graft chain molecular weight, Mn. Based on a recently proposed theory for the structure of a spherical brush in a melt of GNPs, we conjecture that this peak permeability occurs when the densely grafted polymer brush has the highest, packing-induced extension free energy per chain. The corresponding brush thickness is predicted to be , independent of chain chemistry and σ, i.e., at an apparently universal value of the NP volume fraction (or loading), ϕNP, ϕNP,max = [Rc/(Rc + hmax)]3 ≈ 0.049. Motivated by this conclusion, we measured CO-2 and CH4 permeability enhancements across a variety of Rc, Mn and σ, and find that they behave in a similar manner when considered as a function of ϕNP, with a peak in the near vicinity of the predicted ϕNP,max. Thus, the chain length dependent extension free energy appears to be the critical variable in determining the gas permeability for these hybrid materials. The emerging picture is that these curved polymer brushes, at high enough σ behave akin to a two-layer transport medium - the region in the near vicinity of the NP surface is comprised of extended polymer chains which speed-up gas transport relative to the unperturbed melt. The chain extension free energy increases with increasing chain length, up to a maximum, and apparently leads to an increasing gas permeability. For long enough grafts, there is an outer region of chain segments that is akin to an unperturbed melt with slow gas transport. The permeability maximum and decreasing permeability with increasing chain length then follow naturally.

Biocompatible mechano-bactericidal nanopatterned surfaces with salt-responsive bacterial release

Bio-inspired nanostructures have demonstrated highly efficient mechano-bactericidal performances with no risk of bacterial resistance; however, they are prone to become contaminated with the killed bacterial debris. Herein, a biocompatible mechano-bactericidal nanopatterned surface with salt-responsive bacterial releasing behavior is developed by grafting salt-responsive polyzwitterionic (polyDVBAPS) brushes on a bio-inspired nanopattern surface. Benefiting from the salt-triggered configuration change of the grafted polymer brushes, this dual-functional surface shows high mechano-bactericidal efficiency in water (low ionic strength condition), while the dead bacterial residuals can be easily lifted by the extended polymer chains and removed from the surface in 1 M NaCl solution (high ionic strength conditions). Notably, this functionalized nanopatterned surface shows selective biocidal activity between bacterial cells sand eukaryotic cells. The biocompatibility with red blood cells (RBCs) and mammalian cells was tested in vitro. The histocompatibility and prevention of perioperative contamination activity were verified by in vivo evaluation in a rat subcutaneous implant model. This nanopatterned surface with bacterial killing and releasing activities may open new avenues for designing bio-inspired mechano-bactericidal platforms with long-term efficacy, thus presenting a facile alternative in combating perioperative-related bacterial infection. Statement of significanceBioinspired nanostructured surfaces with noticeable mechano-bactericidal activity showed great potential in moderating drug-resistance. However, the nanopatterned surfaces are prone to be contaminated by the killed bacterial debris and compromised the bactericidal performance. In this study, we provide a dual-functional antibacterial conception with both mechano-bactericidal and bacterial releasing performances not requiring external chemical bactericidal agents. Additionally, this functionalized antibacterial surface also shows selective biocidal activity between bacteria and eukaryotic cells, and the excellent biocompatibility was tested in vitro and in vivo. The new concept for the functionalized mechano-bactericidal surface here illustrated presents a facile antibiotic-free alternative in combating perioperative related bacterial infection in practical application.

Epitaxially crystallized polyethylene exhibiting near‐equilibrium melting temperatures*

AbstractThe morphology and orientation of polymer crystals are important factors which determine the performance of thin‐film, polymer‐based technologies such as organic electronic devices and gas separation membranes. Here, we utilize polymer‐substrate epitaxy to achieve a highly oriented crystalline morphology during thin‐film processing. To accomplish this, we employ matrix‐assisted pulsed laser evaporation (MAPLE), a slow physical vapor deposition process, to deposit linear polyethylene epitaxially atop a graphene substrate. Via MAPLE, we demonstrate the ability to achieve a film morphology comprised of well‐aligned, edge‐on crystalline lamellae. Furthermore, we show that MAPLE can be exploited to grow crystalline lamellae composed entirely of extended polymer chains which exhibit a near‐equilibrium melting temperature. Our study demonstrates that MAPLE, as a bottom‐up approach, can deposit polymer thin films with improved control over crystalline morphology.