Model Polymer Research Articles

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.

High‐Density Polyethylene with In‐Chain Photolyzable and Hydrolyzable Groups Enabling Recycling and Degradation

AbstractPolyethylenes endowed with low densities of in‐chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post‐polymerization Baeyer–Villiger oxidation of keto‐polyethylenes from non‐alternating catalytic ethylene‐CO chain growth copolymerization yield high molecular weight in‐chain keto‐ester polyethylenes (Mn≈50.000 g mol−1). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in‐chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups.

High-Density Polyethylene with In-Chain Photolyzable and Hydrolyzable Groups Enabling Recycling and Degradation.

Polyethylenes endowed with low densities of in-chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post-polymerization Baeyer-Villiger oxidation of keto-polyethylenes from non-alternating catalytic ethylene-CO chain growth copolymerization yield high molecular weight in-chain keto-ester polyethylenes (Mn ≈50.000 g mol-1 ). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in-chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups.

Numerical modelling and experimental study of a super-coiled polymer for dual actuator-sensor applications

Numerical modelling and experimental study of a super-coiled polymer for dual actuator-sensor applications

Coarse-grained molecular dynamics simulation on strain-hardening and fracture behaviors of polycarbonate: Effect of polydispersity and spatial distribution

Coarse-grained molecular dynamics simulation of polycarbonate is utilized to investigate the relationship between molecular structure (i.e., polydispersity and molecular spatial distribution) and strain-hardening and fracture behavior of polycarbonate. We find that strain-hardening modulus and chain extensibility, which are the constitutive parameters of the Eindhoven Glassy Polymer model are highly affected by spatial distribution but are insensitive to polydispersity. This is attributed to the higher rate of nonaffine deformation in the structure with a high radius of gyration. On the other hand, maximum stress at fracture is highly influenced by both spatial distribution and polydispersity due to the ability to sustain entanglements at larger strain. We suggest the phenomenological expression of maximum stress as a function of the radius of gyration, the number of entanglements, and polydispersity.

Computational design of nucleating agents of poly (methyl methacrylate) microcellular foams: “savanna‐like” surface structures and their effects on foaming

AbstractTo further the computational design of polymer foaming, this work investigated the interactions between polymer and nucleating agents by evaluating the removal forces needed to remove the polymer from the nucleating agent using molecular dynamics simulations. Silica nanoparticles modified with different organic groups and different surface modification ratios represented model nucleating agents and poly methyl methacrylate (PMMA), a model polymer. Modified organic groups with a certain length and flexibility grafted sparsely on the silica surface, creating a “savanna‐like” structure, increased the interaction between PMMA and the silica nanoparticle. The simulation results predicted the effects of the modified organic group and surface modification ratio R of the silica nanoparticle seen in actual batch foaming experiments using CO2 and PMMA with modified silica nanoparticles. Cell size shows a minimum and cell nucleation density a maximum in the foamed polymer under certain conditions, which correlate with the simulation results for the interactions between the polymer and nucleating agent. Based on the correspondence between the simulation and the experimental results, the effectiveness of such simulations for the design of nucleation agents appeared promising.Highlights Computational design of nucleating agents for microcellular foams. Evaluation of the interaction of polymers with various nucleating agents. Large interactions due to the “savanna‐like” structure of nucleating agents. Demonstration of polymer foaming with designed nucleating agents.

Synthesis, electrospinning, and molecular docking of poly(methyl methacrylate) Schiff bases and their applications as polymeric antimicrobial agents and for dye removal

The antibacterial activity of a variety of modified poly(methyl methacrylate) Schiff bases against common microbial infections and removal of methylene blue (MB) dye were screened. The Schiff bases were synthesized from the reaction of the modified (PMMA) with vanillin (PMMA)Van and cinnamaldehyde (PMMA)Cin. By using Fourier transformer infrared (FT-IR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), the structures of the nanofibers of the synthesized Schiff bases were confirmed. The modified Kirky–Bauer method was used to screen the antibacterial activities of all the obtained materials against various bacterial species, including gram-positive bacterial (Bacillus subtilis (4k1p), Staphylococcus aureus), Gram-negative bacteria (Escherichia coli (7ab3), Pseudomonas aeruginosa). Inhibition zones against gram-positive bacteria ranged in diameter from 7 to 14 mm, whereas for the Gram-negative bacteria, the inhibition zones found to be ranged between 6 and 13 mm. With a minimum bactericidal concentration (MBC) of 8 mg/mL and a minimum inhibitory concentration (MIC) of 2 mg/mL, (PMMA)Van shown the greatest antibacterial activity. Lastly, molecular docking research was done to better understand the interactions between this series' targets and inhibitors for (PMMA)Van and (PMMA)Cin (4k1p and 7ab3). Molecular modeling of these surface-adsorbed polymers indicated that (PMMA)Van binds more strongly with Nitrogen than does (PMMA)Cin through extra hydrogen-bonding interactions. All the developed materials were evaluated for the removal of 0.1 g/L methylene blue dye (MB) from an aqueous solution. The elimination percentage of MB dye ranged from 26.67% by using 0.05 g powder of (PMMA)Cin to 85.63% by employing 0.05 g nanofibers of (PMMA)Van.Graphical

Therapeutic potential of low-molecular weight lignin model polymer fractions for treating skin lesions in animals: a pilot study.

Bacterial infections and resistance to antibiotics are increasingly severe problems. In recent years, Staphylococcus species have emerged as important pathogens in animals and humans. Current therapeutic methods against these species have serious disadvantages; therefore new agents with antibacterial potential, such as plant-based substances, are very important in therapy. We report a pilot study with new method of fractioning the dehydrogenate polymer DHP obtained from coniferyl alcohol and application of the low-MW fractions of 200-3000 Da for antibacterial activity in healing animal lesions. In vivo experiments were conducted on the dogs having a skin lesion. Dogs were treated with the suspension containing the low-MW DHP fractions as the active ingredient, in combination with alginate for 7 days. Cytological smears and microbiological analyses of the affected area were performed. Staphylococcus spp. was isolated from lesions in all dogs from our research. The results show that the low-MW DHP suspension in alginate promotes skin healing and reduction of the infection of the lesions in the affected animals. Pharmaceutical composition containing the low-MW DHP fractions exerts a soothing effect on the subject in wound treatment. Reduction in the number of bacteria by 30% and more were noticed in 6 dogs, while in 4 dogs this percentage is above 50%. No side effects were noticed. Synthesized lignin oligomers may have a significant place as antimicrobial and skin healing agents, especially since an increasing number of multidrug-resistant staphylococci are found on the skin lesions in animals.

The influence of hydrogen bonding between different crystallization tendency drugs and PVPVA on the stability of amorphous solid dispersions

Amorphous solid dispersion (ASD) is one of the formulation strategies for drugs displaying low solubility and low oral bioavailability. In this study, high drug-loaded ASDs of drugs with different crystallization tendencies were prepared by spray drying. The aim was to investigate the influence of hydrogen bonding between the drug and the model polymer PVPVA on the physical stability of ASDs containing drugs with different crystallization tendencies. From the 60-day stability study results, the intermolecular hydrogen bonding has a considerable stabilizing effect on the ASDs of the drug with a moderate crystallization tendency. Nimesulide (hydrogen bond donor) can maintain the amorphous form for a longer time than Fenofibrate (no-hydrogen bond donor) during storage. In the ASDs with fast crystallization tendency drugs (naproxen and caffeine), intermolecular hydrogen bonds are not very effective in preventing drug crystallization, and the effect on the stability of ASD is relatively weak. However, for drugs with a slow tendency to crystallize (indomethacin and miconazole), the ASDs remained in an amorphous state during the monitored storage period, making it impossible to compare the effect of intermolecular hydrogen bonds on the stability of this type of ASDs. It also reveals that intermolecular hydrogen bonds can increase the drug loading capacity of ASDs. The relationship between drug loading and ASD stability was further analyzed by the state diagram. This study clearly pointed out that the physical stability of ASDs of drugs with different crystallization tendencies is affected to a different extent by intermolecular hydrogen bonds.

An atomistic-continuum concurrent statistical coupling technique for amorphous materials using anchor points

A generalized framework for anchor point based concurrent coupling of finite element method (FEM) and molecular dynamics (MD) domains, incorporating previous related methods, is presented. The framework is robust and is agnostic of material crystallinity and atomistic description. The method follows an iterative approach to minimize the total energy of the coupled FEM-MD system, while maintaining displacement constraints between the domains. Two distinct forms of the coupling method are discussed in detail, differing in the nature of the constraint, both of which are able to make use of specialized MD solvers such as LAMMPS with little or no modification. Both methods make use of springs that join groups of atoms in the MD to the FEM domain. Method 1, termed ‘Direct Coupling’, couples MD anchor points directly to the FEM domain in a force-based manner and has the added advantage of being able to couple to specialized FEM solvers such as ABAQUS. Method 2 couples the MD to the FEM domain in a more ‘soft’ manner using the method of Lagrange multipliers and least squares approximation. The relative performance of these two methods are tested against each other in a uniaxial tension test using a graphene monolayer at 300 K temperature and a block of thermosetting polymer EPON862 at low temperature, showing comparable results. Convergence behaviour of the two coupling methods are studied and presented. The methods are then applied to the fracture of a centre-cracked graphene monolayer and compared with results from an identical pure MD simulation. The results corroborate the effectiveness of the developed method and potential use as a plug-and-play tool to couple pre-existing specialized FEM and MD solvers. Future work will focus on applying these methods to simulate elevated-temperature amorphous polymer models and their brittle fracture.

Study of the topography and magnitude of occlusal contacts using various hardware methods

This work is devoted to a comparative study of the diagnostic capabilities of intraoral scanners for determining the topography of occlusion contacts and their size (area).
 In the Swiss smile clinic (Moscow) and at the Department of Orthopedic Dentistry of the RUDN Medical Institute, 5 patients aged from 20 to 40 years (4 men and 1 woman) were examined — infants with orthognathic bite, intact first permanent molars without signs of the above erasure and periodontal pathologies. Each patient was examined using 3 intraoral scanners for two parameters of occlusion on teeth 1.6 — the topography of occlusal contacts and their area (size). With the help of scanner software, color patterns of occlusiograms were obtained, teeth were isolated and the topography of contacts was analyzed. The total number of occlusal contacts on tooth 1.6, the presence and number of contacts on each tubercle and in the central fissure were determined. Occlusal contacts were marked using Baush articulation paper with a thickness of 200 microns and a dental photo was taken in an occlusal mirror with a Canon Mark4 device. To determine the contact value, the total area was measured in the Avantis 3D program (Russia). The results obtained are summarized in tables. Based on the data analysis, it is concluded that the results of studying the topography of occlusal contacts of teeth and their area depend significantly on the research methodology and the intraoral scanner used.
 In order to exclude the human factor (the variability of the nature of occlusal closure with each closing of the patient’s mouth), it is advisable to repeat the studies in laboratory conditions on polymer models reinforced in an occlusator or verticulator.

On the application of generalised Newtonian fluids in the modelling of drag-reducing rigid polymers

Drag-reducing polymers with rod-like molecular structure are known to exhibit significant shear-thinning yet only weak elastic properties, making them suited to modelling by generalised Newtonian fluids (GNFs) based on the second invariant of the rate of deformation tensor, D. However only qualitative agreement with experiments is obtained when such models are employed in the direct numerical simulation of turbulent flows. In this study, we investigate GNFs to obtain guidelines for their application in predicting turbulent drag reduction, and show that the appearance of flow-type sensitivity or elastic effects, however small, places a limit on their accuracy. By incorporating a dependence on the third invariant of D, to bring in sensitivity to flow type, we demonstrate that reasonably good quantitative agreement with experimental data can be obtained.

General theory for plane extensible elastica with arbitrary undeformed shape

A general expression for the strain energy of a homogeneous, isotropic, plane extensible elastica with an arbitrary undeformed configuration is derived. This expression appears to be suitable for one-dimensional models of polymers or vesicles, the natural configuration of which is characterized by locally changing curvature. In a linear setting, we derive the macroscopic stress–strain relations, providing an universal criterion for the neutral curve location. In this respect, we further demonstrate that the neutral curve existence constitutes the fundamental requirement for the conformational dynamics of any inextensbile biological filament.

Phase transitions in systems of particles with only hard-core interactions

This article contains our comments and views on the status of the current understanding of phase transitions in systems in thermodynamic equilibrium with only hard-core interactions, based on our work in this area. The equation of state for the hard sphere gas in d-dimensions is discussed. The universal repulsive Lee-Yang singularity in the complex activity plane, and its relation to the directed and undirected polymer models are outlined. We also discuss orientationally disordered crystalline mesophases, and some of their models.

Adsorption of Random Copolymer on a Chemically Heterogeneous Periodic Stripe-Patterned Surface

The adsorption of a single random copolymer chain containing correlations in a sequence on the chemically heterogeneous periodic surface with the alternating striped texture is studied theoretically. The problem is solved within the framework of a partially directed walk polymer model in three dimensions using the generating functions approach and the annealed disorder approximation for averaging over the ensemble of random sequences of units in the copolymer. Dependences of the adsorption transition point on the composition of the random copolymer and the degree of correlation in the random sequence of units for various periodic surfaces are presented. It is shown that for compositionally symmetric and weakly symmetric surfaces there is the optimal composition of the random copolymer and the degree of correlation in the sequence of units, at which the inverse temperature corresponding to the adsorption transition point has a local minimum. In the case of the compositionally symmetric surface, the “optimal” random copolymer is also symmetric in composition. For surfaces with a pronounced composition asymmetry the best adsorbent is a homopolymer complementary to sites that prevail on the surface. The degree of asymmetry range, in which the dependence of the inverse transition temperature on the copolymer composition and the correlation parameter exhibits the local minimum, is fairly narrow.

Investigation of Corrosion Mechanisms of Copper Microstructures Underneath Polymer Coatings: Experiment and Simulation

BACKGROUND Reliability and stability of electronic components are crucial for both consumer and producer. External influences (e.g. bias, humidity) can enable corrosion processes and lead to accelerated failure. For example, field-driven electrochemical migration (ECM) of copper (Cu), a material that is widely used for electrical connections, can drive corrosion processes and ultimately lead to component failure. METHODOLOGY In this work, a miniaturized test chip, manufactured with techniques used in the semiconductor industry, is employed to investigate ECM and corrosion mechanisms of copper electrodes covered by an organic coating. Combinations of applied bias and aqueous electrolytes atop the organic layers are used to drive ions into and inside the coating. The distribution of ions in the polymer layer and at the interface Cu/coating is investigated by optical, electrochemical and analytical methods (e.g. EIS, LA-ICP-MS). The experimental work is complemented with a dynamic multi-ion finite element simulation model created with COMSOL Multiphysics®. The simulation model of polymer coated copper structures is developed starting from a previous electrochemical model of Cu electrodes in aqueous electrolytes, which was validated experimentally. Refinement and validation is achieved by comparison with literature and experimental data acquired through test chip measurements. RESULTS The course of current and solution resistance transients determined by EIS show the slow progression of corrosion processes until a fast breakdown is observed. Experimental results and the comparison with simulation enable insights into electrochemical migration of Cu and corrosion mechanisms. The combination of the two helps elucidate corrosion processes and thereby allows the identification of on-going electrochemical processes in electronic components at different stages.

Modeling the viscoelastic-viscoplastic behavior of glassy polymer membrane with consideration of non-uniform sub-chains in entangled networks

Glassy polymers are common engineering materials and usually work in a linear elastic stage. However, some functional glassy polymers, such as perfluorinated sulfonic acid (PFSA) membranes, face more complicated working conditions: varied temperature, humidity, and long-term loading, where the viscoelastic behavior has a huge impact on their durability. The early studies on the constitutive model of glassy polymers focus on the elastic–plastic behavior, especially yielding and strain hardening, while showing limitations in predicting the time-dependent viscoelastic response of the PFSA membrane at complex conditions. This paper establishes a viscoelastic-viscoplastic (VE-VP) constitutive model of glassy polymers based on the non-uniform length distribution of entangled molecular chains. During loading, heating and hydration, the prior activation of short entangled chains is the precondition of the viscoelastic response of the material in the small deformation stage. To distinguish activated molecular chains from others, a calculation method of chain activation is established based on the energy conservation criterion and applied to monitor the activation state of the entangled chain network. For the verification of the model, uniaxial tensile, stress relaxation, and dynamic thermomechanical tests are conducted. The present model shows great accuracy in predicting the VE-VP behavior of the PFSA membrane, with the error less than 8% in the stress relaxation tests, providing a new perspective of constitutive modeling for glassy polymers.

Determining glass transition in all-atom acrylic polymeric melt simulations using machine learning.

The functionality of many polymeric materials depends on their glass transition temperatures (Tg). In computer simulations, Tg is often calculated from the gradual change in macroscopic properties. Precise determination of this change depends on the fitting protocols. We previously proposed a robust data-driven approach to determine Tg from the molecular dynamics simulation data of a coarse-grained semiflexible polymer model. In contrast to the global macroscopic properties, our method relies on high-resolution microscopic details. Here, we demonstrate the generality of our approach by using various dimensionality reduction and clustering methods and apply it to an atomistic model of acrylic polymers. Our study reveals the explicit contribution of the side chain and backbone residues in influencing the determination of the glass transition temperature.

Comparison and review of classical and machine learning-based constitutive models for polymers used in aeronautical thermoplastic composites

Abstract Most of the stress–strain relationships of thermoplastic polymers for aeronautical composites tend to be nonlinear and sensitive to strain rate and temperature, so accurate constitutive models are urgently required. Classical and machine learning-based constitutive models for thermoplastic polymers are compared and discussed. In addition, some typical models have been recovered and compared by authors to evaluate the performance of classical and machine learning-based constitutive models, so that the advantages and shortcomings of these models can be demonstrated. By reviewing constitutive models, it was found that the equations of physical constitutive models are derived according to thermodynamical principles, so the physical constitutive models can describe the deformation mechanism at the microscopic level. The phenomenological constitutive models may combine the macroscopic phenomena and theories of physical models, and good performance and wide range of applications can be realized. In addition, phenomenological constitutive models combined with machine learning algorithms have attracted attentions of investigators, and these models perform well in predicting the stress–strain relationships. In the future, the constitutive models combining the theories of physical constitutive models, phenomenological constitutive models, and machine learning algorithms will be increasingly attractive as some challenging issues are effectively addressed.

Micromechanism-based chemo-mechanical cohesive model for polymer interface under transient chemical mass diffusion

This paper presents a fully coupled thermodynamically consistent chemo-mechanical cohesive zone model for polymer interfaces subjected to a chemo-mechanical environment. A bond-chain-interface method is exploited to describe the macroscopically interfacial performances controlled by the chemical reaction extent and the microscopic properties of interface. The energetics of bond stretching and the coupling between reactive-diffusive mechanisms and mechanics at the polymer interface are taken into account. The cohesive zone model is implemented using finite element method software ABAQUS through UEL subroutines. The numerical simulation with the cohesive element is directly compared to a single lap shear experiment for chemo-mechanical fracture of a bio-inspired polymer interface. Besides, a particularly numerical example including the chemical diffusion and compression case is conducted, it clearly shows the proposed model can capture the features of shear flux and stress-driven diffusion, which verifies the completeness of the chemo-mechanical interface theory. Finally, a parametric analysis is conducted to assess the influences of critical bond stretch, areal chain density and chemical reaction rate on the evolution of interfacial damage and rate of chemical diffusion. The model also accounts for the phenomenon where a strong polymer interface effectively restricts chemical diffusion across an interface. This research provides a novel investigative tool to study chemo-mechanical fracture of polymer interfaces, with potential applications in materials science and engineering.