Flexibility Of Polymer Chains Research Articles

Thermoplastic polyimide with good comprehensive performance based on carbazole groups and short flexible linkages

AbstractThermoplastic polyimides (TPIs) can meet the requirements of advanced electronic packaging such as flexible copper clad laminate (FCCL) applied under extreme conditions, attributed to their excellent thermal stability, mechanical properties, electrical insulation and chemical resistance. With the increasing demands for electronic devices, such as applications in high‐frequency communication, it is highly desirable to develop high‐performance TPI with good thermoplasticity, thermal stability, mechanical properties and dielectric properties. However, there is a trade‐off between thermoplasticity and other properties. Herein, we introduce an effective strategy to afford TPIs with good performance by copolymerization of a diamine monomer consisted of a coplanar aromatic carbazole group and a short flexible linkage methylene group. On the one hand, short flexible linkages help improve the flexibility of polymer chains and are not too much to enable small‐scale molecular motions below Tg. On the other hand, coplanar aromatic donor groups benefit to strong charge transfer complex (CTC) interaction and π‐π stacking interaction. Based on this strategy, the resultant TPI possesses good thermoplasticity with a proper Tg of 348 °C. Meanwhile, it preserves a low coefficient thermal expansion of 48 ppm K−1, low dielectric constant/dielectric loss factor of 3.27/0.0073 at 10 GHz, and tensile strength of ca. 78 MPa.

Establishing superfine nanofibrils for robust polyelectrolyte artificial spider silk and powerful artificial muscles

Spider silk exhibits an excellent combination of high strength and toughness, which originates from the hierarchical self-assembled structure of spidroin during fiber spinning. In this work, superfine nanofibrils are established in polyelectrolyte artificial spider silk by optimizing the flexibility of polymer chains, which exhibits combination of breaking strength and toughness ranging from 1.83 GPa and 238 MJ m−3 to 0.53 GPa and 700 MJ m−3, respectively. This is achieved by introducing ions to control the dissociation of polymer chains and evaporation-induced self-assembly under external stress. In addition, the artificial spider silk possesses thermally-driven supercontraction ability. This work provides inspiration for the design of high-performance fiber materials.

Role of crosslinkers on the properties of bio‐based wood adhesives

AbstractAs people became more conscious of the risks associated with pollution in the early 21st century, eco‐friendly adhesives made from plant oil began to be used. Bio‐based adhesives are widely used due to their low price, easy accessibility, and high biodegradability; however, their low adhesive strength is an issue. This work incorporates three natural crosslinkers: tannic acid (TA), sorbitol (SR), and cellulose (CL) to address the drawbacks of bio‐based adhesives, such as low adhesive strength, inferior output in humidity and longer curing time that result from excess water. Methylene diphenyl diisocyanate (MDI) was used to react with soybean oil‐based polyol (SOP) plus the crosslinkers to make bio‐based polyurethane adhesives. The maximum bonding strength of the soybean‐based adhesive containing 10 wt.% of SR (SR‐10%) was measured at 6.19 MPa which is about 44% higher than the sample without SR. The higher strength is due to the crosslinking ability of SR. The effect of crosslinking is also observed in the study of polar protic and polar aprotic solvents used to dissolve the adhesive. As compared with the polar aprotic solvent tetrahydrofuran, TA‐containing adhesive samples showed a maximum tensile strength of 3.69 MPa in methanol; a polar protic solvent that can participate in further hydrogen bonding to form a higher crosslinked complex. The glass transition temperature (Tg) increases with the increase in crosslinker amount. The observed increase in Tg may be attributable to an increase in crosslinking density, which reduces polymer chain flexibility and causes a stronger material.Highlights Bio‐adhesives based on soybean oil and diisocyanate were synthesized. Natural crosslinking agents such as tannic acid, sorbitol, and cellulose were used. The effect of crosslinking using polar protic and aprotic solvents was studied. The glass transition temperature increases with the increase in crosslinker amount.

Correlation between Ionic Conductivity and Mechanical Properties of Solid-like PEO-based Polymer Electrolyte.

Poly(ethylene glycol) methyl ether methacrylate polymer networks (PEO-based networks), with or without anionic bis(trifluoromethanesulfonyl)imide (TFSI)-grafted groups, are promising electrolytes for Li-metal all solid-state batteries. Nevertheless, there is a need to enhance our current understanding of the physicochemical characteristics of these polymer networks to meet the mechanical and ionic conductivity property requirements for Li battery electrolyte materials. To address this challenge, our goal is to investigate the impact of the cross-linking density of the PEO-based network and the ethylene oxide/lithium ratio on mechanical properties (such as glass transition temperature and storage modulus) and ionic conductivity. We have synthesized a series of cross-linked PEO-based polymers (si-SPE for single ion solid polymer electrolyte) via solvent-free radical copolymerization. These polymers are synthesized by using commercially available lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate (LiMTFSI), poly(ethylene glycol)methyl ether methacrylate (PEGM), and [poly(ethylene glycol) dimethacrylate] (PEGDM). In addition, we have synthesized a series of cross-linked PEO-based polymers (SPE for solid polymer electrolyte) using LiTFSI as the ionic species. Most of the resulting polymer films are amorphous, self-standing, flexible, homogeneous, and thermally stable. Interestingly, our research has revealed a correlation between ionic conductivity and mechanical properties in both the SPE and si-SPE series. Ionic conductivity increases as glass transition temperature, α relaxation temperature, and storage modulus decrease, suggesting that Li+ transport is influenced by polymer chain flexibility and Li+/EO interaction.

Rational Design of F-Modified Polyester Electrolytes for Sustainable All-Solid-State Lithium Metal Batteries.

Solid polymer electrolytes (SPEs) are one of the most practical candidates for solid-state batteries owing to their high flexibility and low production cost, but their application is limited by low Li+ conductivity and a narrow electrochemical window. To improve performance, it is necessary to reveal the structure-property relationship of SPEs. Here, 23 fluorinated linear polyesters were prepared by editing the coordination units, flexible linkage segments, and interface passivating groups. Besides the traditionally demonstrated coordinating capability and flexibility of polymer chains, the molecular asymmetry and resulting interchain aggregation are observed critical for Li+ conductivity. By tailoring the molecular asymmetry and coordination ability of polyesters, the Li+ conductivity can be raised by 10 times. Among these polyesters, solvent-free poly(pentanediol adipate) delivers the highest room-temperature Li+ conductivity of 0.59 × 10-4 S cm-1. The chelating coordination of oxalate and Li+ leads to an electron delocalization of alkoxy oxygen, enhancing the antioxidation capability of SPEs. To lower the cost, high-value LiTFSI in SPEs is recycled at 90%, and polyesters can be regenerated at 86%. This work elucidates the structure-property relationship of polyester-based SPEs, displays the design principles of SPEs, and provides a way for the development of sustainable solid-state batteries.

Synthesis of a Conceptual New Single-Ion Conducting Polymer Electrolyte for All-Solid-State Batteries

The increasing global population and the rapid change in climatic conditions strengthens the demand for a more efficient handling of energy consumption and energy storage technologies. In this context, all-solid-state batteries (ASSBs) as next-generation rechargeable lithium-ion batteries offer an improved energy and power density based on the integration of novel separators and electrode materials. In comparison to their liquid representatives, ASSBs provide a higher intrinsic safety via non-flammable components and in addition greater long-term durability. In relation to common electrolyte classes, solid polymers stand out due to their good mechanical flexibility, easy film-formation ability, good contact supply between cell components, and lower production costs, favoring the application as electrolytes, protective coatings, as well as additives in cathode composites. Among a variety of polymers, poly(ethylene oxide) (PEO) is a well-studied and established host polymer due to its great ability to dissolve lithium salts like LiBH4, LiPF6 or LiTFSI. Based on a low glass transition temperature (Tg) of about - 60 to - 50 °C, PEO shows a high degree of polymer chain flexibility which facilitates the migration of the lithium cations through the solid electrolyte. Nevertheless, its semi-crystalline character often leads to low conductivities below its melting point (Tm) of around 60 °C, making pure PEO unattractive as solid electrolyte. Copolymerization, the addition of a small amount of solvent to produce so called gel polymer electrolytes, the addition of some plasticizers, or the interplay of polymer and inorganic fillers try to counteract this trend. The synthetical concept behind this work is aiming to benefit from the flexible nature of PEO, and at the same time to improve the ionic conductivities and especially the lithium migration by structural realignment away from a dual-ion towards a single-ion conducting polymer electrolyte (SICPE). The polar PEO-backbone ensures polymer chain mobility, whereas a rigid aromatic structure unit as side chain bears the fixed anionic group. The immobilization of the anionic charges on the polyether backbone tends to guide the electrolyte to higher lithium transference numbers, fewer polarization effects, and the suppression of dendrite growth, resulting in an overall improved cell performance. Synthesis steps via the novel SICPE are characterized with the help of nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Thermal analyses of the homopolymer already show the positive influence of the flexible PEO-backbone by lowering the Tg from 100 to 150 °C for related aliphatic derivatives down to 60 to 80 °C in our case. On the basis of electrochemical impedance spectroscopy (EIS) measurements, the interplay of chemical, thermal, and electrochemical key properties is investigated. The gained results tend to open a discussion panel concerning occurring challenges for solid-state polymer electrolytes and the interdependencies between electrolyte constitution and polymer characteristics.

Branched Copolymers with Tunable Clusteroluminescence in High Quantum Yield.

A novel type of fluorescence without large conjugated structures called clusteroluminescence (CL) has attracted a great deal of attention in recent years. Despite its many advantages, the emerging CL still encounters difficulties of low quantum yield (QY) and preliminary mechanisms. In this work, the branched structure was introduced into poly(maleic anhydride-alt-vinyl acetate) by chain transfer monomer. The emission wavelength of the branched copolymers is red-shifted with the increase of branching degree, and the absolute QY of solids can reach up to 29.87%. Further characterizations reveal that the branched structure can improve the flexibility of polymer chains, thereby promoting the intrachain interactions of subgroups. Furthermore, in the case of branched anhydride copolymers, the equilibrium between intrachain interactions and nonradiative transitions holds a crucial significance in determining the QY. This endeavor not only offers new insights into the mechanism of CL but also presents a novel approach to surmount the low QY of anhydride copolymers, thus broadening the horizons of CLgens to unexplored domains.

Adsorption of Low Density Lipoproteins on an Azobenzene-Containing Polymer Brush: Modelling by Coarse-Grained Molecular Dynamics

One of the strategies to reduce the contents of low density lipoproteins (LDLs) in blood is a hemoperfusion, when they are selectively retracted from plasma by an adsorber located outside the patient’s body. Recently, a photo-controllable smart surface was developed experimentally, that is characterized by high selectivity and reusability. It comprises a nanocarrier functionalised by a brush of azobenzene-containing polymer chains. We present a mesoscopic model that mimics principal features of this setup and focus our study on the role played by the length and flexibility of the chains and grafting density of a brush. The model for LDL comprises a spherical core covered by a shell of model phospholipids. The model is studied via coarse-grained molecular dynamics simulation, performed with the aid of the GMBOLDD package modified for the case of soft-core beads. We examined the dependencies of the binding energy on both the length of polymer chains and the grafting density of a brush and established optimal conditions for adsorption. These are explained by competition between the concentration of azobenzenes and phospholipids in the same spatial region, flexibility of polymer chains, and excluded volume effects.

Synthesis of the Ultem series polyetherimides

Polyetherimides (PEIs) are a class of structural polymers with the most successful combination of such essential properties for practical applications as high heat resistance, thermal stability, ultimate tensile strength, elastic modulus, good dielectric properties, and high chemical and radiation resistance. However, along with these advantages, PEIs are compounds with high softening and melting points, which complicates their processing into products. In recent decades, specialists have found numerous ways to decrease the glass transition temperature by increasing the flexibility of the main polymer chain. To this end, functional groups with a higher degree of rotation, such as isopropylidene, hexafluoroisopropylidene, 1,2-dichloroethylene, and other substituents, are introduced into the main polymer chain. Polyetherimide, whose precursors are 3(4)-nitrophthalic anhydride, m-phenylenediamine, and bisphenol A, was first produced by General Electric under the Ultem brand name and is currently believed to be one of the best-known engineering thermoplastics. In particular, two synthetic methods can be used to obtain such polyetherimides. The first technique uses a cyclization of poly(amidocarboxylic acid), which is obtained by the polycondensation of dianhydride of 2,2-bis-[4-(3,4-dicarboxyphenoxy)phenyl]propane and m-phenylenediamine. The second technique uses the polynitro substitution of 1,3-bis[N-(3-nitrophthalimido)]benzene and the dynatrium salt of bisphenol A. To date, the Russian scientific literature lacks reviews with detailed descriptions of known methods for the preparation of Ultem series polyetherimides. The present review generalizes and systematizes the available literature data regarding the synthesis of the Ultem series PEIs. In addition, this study describes preparation methods of soluble thermoplastic polyetherimides of this series, available synthesis methods of initial monomers with reaction yields, and physical characteristics of such polymers.

Fabrication of advanced positively charged polyamide nanofiltration membrane for effective removal of heavy metal ions via surfactant-plasticizer-synergy assisted interfacial polymerization

Positively charged nanofiltration (NF) membrane has shown great potential for the removal of heavy metal ions from contaminated water. In order to fabricate positively charged membranes, polyethyleneimine (PEI) is widely used considering the existence of abundant amine groups in this branched macromolecule. However, the PEI-based NF membranes often suffer from low permeance due to the highly dense polyamide film. In this study, a surfactant-plasticizer-synergy (SPS) assisted fabrication strategy is proposed to fabricate PEI-based NF membrane with high performance. The surfactant sodium dodecyl sulfate (SDS) and nontoxic plasticizer acetyl tributyl citrate (ATBC) are added into the aqueous phase and organic phase respectively to regulate the interfacial polymerization (IP) reaction between PEI and terephthaloyl chloride (TPC). As a result of the enhanced miscibility of the two phases at the presence of SDS, the diffusion of PEI monomer is promoted and this contributes to a positively charged membrane surface, which effectively improves the rejections of NF membrane towards positive ions. On the other hand, the plasticizer ATBC softens the polyamide film as confirmed by the reduced Young’s modulus. This could enhance the flexibility of polymer chains and promote the transportation of water molecule. Compared with the nascent PEI-TPC membrane, the permeance of PEI/SDS + TPC/ATBC experiences a dramatic promotion from 2.5 L∙m−2∙h−1∙bar−1 to 9.7 L∙m−2∙h−1∙bar−1 and the MgCl2 rejection also increases from 95.9% to 97.8%. More importantly, the rejections of PEI/SDS + TPC/ATBC towards various heavy metal ions are all above 90.0% and they also follow the order: Mn2+(97.6%) > Ni2+(96.8%) > Cu2+(95.7%) > Cd2+(91.0%). This SPS assisted IP reaction may provide a simple and low-cost strategy for the fabrication of high-performance TFC membranes for diverse applications in the future.

Biocidal Potency of Polymers with Bulky Cations.

The performance of antimicrobial polymers depends sensitively on the type of cationic species, charge density, and spatial arrangement of cations. Here we report antimicrobial polymers bearing unusually bulky tetraaminophosphonium groups as the source of highly delocalized cationic charge. The bulky cations drastically enhanced the biocidal activity of amphiphilic polymers, leading to remarkably potent activity in the submicromolar range. The cationic polynorbornenes with pendent tetraaminophosphonium groups killed over 98% E. coli at a concentration of 0.1 μg/mL and caused a 4-log reduction of E. coli within 2 h at a concentration of 2 μg/mL, showing very rapid and potent bactericidal activity. The polymers are also highly hemolytic at similar concentrations, indicating a biocidal activity profile. Polymers of a similar chemical structure but with more flexible backbones were made to examine the effects of the flexibility of polymer chains on their activity, which turned out to be marginal. We also explore variants with different spacer arm groups separating the cations from the backbone main chain. The antibacterial activity was comparably potent in all cases, but the polymers with shorter spacer arm groups showed more rapid bactericidal kinetics. Interestingly, pronounced counterion effects were observed. Tightly bound PF6- counteranions showed poor activity at high concentrations due to gross aggregate formation and precipitation from the assay media, whereas loosely bound Cl- counterions resulted in very potent activity that monotonically increased with increasing concentration. In this paper, we reveal that bulky phosphonium cations are associated with markedly enhanced biocidal activity, which provides an innovative strategy to develop more effective self-disinfecting materials.

REVIEW ON MUCOADHESIVE DRUG DELIVERY SYSTEMS

This review considers the basic mechanisms by which mucoadhesive can adhere to a mucous membrane in terms of the nature of the adhering surfaces and the forces that may be generated to secure them together.it also include contact stage and consolidation stage. Mucosal adhesion is backed by several theories. Much attention has been focused in the field of mucoadhesive formulation developments compared to other delivery systems. Mucoadhesion while considering drug delivery is having several merits, because of the ideal physiochemical characters of the mucosal membrane. Ideally a mucoadhesive dosage form interacts with the mucosal membrane by ionic bonds, covalent bonds, Van-der-Waal bonds and hydrogen bonds. Various sites for mucoadhesive drug delivery system are ocular, nasal, buccal cavity; GIT, vaginal, rectal and several specific dosage forms have been reported. Factors affecting mucoadhesion are molecular weight, flexibility of polymer chain, pH, presence of carboxylate group and density. Several synthetic and natural polymers are identified as suitable candidates for mucoadhesive formulation. Ex-vivo/in-vitro studies utilizing gut sac of rats provides in-depth knowledge about the adhesive property of the dosage form as well as polymers. AFM can be used as a part of imaging methods. Mucoadhesive drug delivery system shows promising future in enhancing the bioavailability and specific needs by utilizing the physiochemical characters of both the dosage form and the mucosal lining. It has to be noted that only a moist surface can bring the mucoadhesive nature of the dosage form.

Ultrasound-mediated delivery of flexibility-tunable polymer drug conjugates for treating glioblastoma.

Effective chemotherapy delivery for glioblastoma multiforme (GBM) is limited by drug transport across the blood-brain barrier and poor efficacy of single agents. Polymer-drug conjugates can be used to deliver drug combinations with a ratiometric dosing. However, the behaviors and effectiveness of this system have never been well investigated in GBM models. Here, we report flexible conjugates of hyaluronic acid (HA) with camptothecin (CPT) and doxorubicin (DOX) delivered into the brain using focused ultrasound (FUS). In vitro toxicity assays reveal that DOX-CPT exhibited synergistic action against GBM in a ratio-dependent manner when delivered as HA conjugates. FUS is employed to improve penetration of DOX-HA-CPT conjugates into the brain in vivo in a murine GBM model. Small-angle x-ray scattering characterizations of the conjugates show that the DOX:CPT ratio affects the polymer chain flexibility. Conjugates with the highest flexibility yield the highest efficacy in treating mouse GBM in vivo. Our results demonstrate the association of FUS-enhanced delivery of combination chemotherapy and the drug-ratio-dependent flexibility of the HA conjugates. Drug ratio in the polymer nanocomplex may thus be employed as a key factor to modulate FUS drug delivery efficiency via controlling the polymer flexibility. Our characterizations also highlight the significance of understanding the flexibility of drug carriers in ultrasound-mediated drug delivery systems.

The Effect of Crosslinking Degree of Hydrogels on Hydrogel Adhesion.

The development of adhesive hydrogel materials has brought numerous advances to biomedical engineering. Hydrogel adhesion has drawn much attention in research and applications. In this paper, the study of hydrogel adhesion is no longer limited to the surface of hydrogels. Here, the effect of the internal crosslinking degree of hydrogels prepared by different methods on hydrogel adhesion was explored to find the generality. The results show that with the increase in crosslinking degree, the hydrogel adhesion decreased significantly due to the limitation of segment mobility. Moreover, two simple strategies to improve hydrogel adhesion generated by hydrogen bonding were proposed. One was to keep the functional groups used for hydrogel adhesion and the other was to enhance the flexibility of polymer chains that make up hydrogels. We hope this study can provide another approach for improving the hydrogel adhesion generated by hydrogen bonding.

Water‐Triggered Stiffening of Shape‐Memory Polyurethanes Composed of Hard Backbone Dangling PEG Soft Segments

Shape-memory polymers (SMPs) induced by heat or water are commonly used candidates for biomedical applications. Shape recovery inevitably leads to a dramatic decrease of Young's modulus due to the enhanced flexibility of polymer chains at the transition temperature. Herein, the principle of phase-transition-induced stiffening of shape-memory metallic alloys (SMAs) is introduced to the design of molecular structures for shape-memory polyurethane (SMPUs), featuring all-hard segments composed of main chains that are attached with poly(ethylene glycol) (PEG) dangling side chains. Different from conventional SMPs, they achieve a soft-to-stiff transition when shape recovers. The stiffening process is driven by water-triggered segmental rearrangement due to the incompatibility between the hard segments and the soft PEG segments. Upon hydration, the extent of microphase separation is enhanced and the hard domains are transformed to a more continuous morphology to realize more effective stress transfer. Meanwhile, such segmental rearrangement facilitates the shape-recovery process in the hydrated state despite the final increased glass transition temperature (Tg ). This work represents a novel paradigm of simultaneously integrating balanced mechanics, shape-memory property, and biocompatibility for SMPUs as materials for minimally invasive surgery such as endoluminal stents.

Selective Plasticization of Poly (ethylene oxide) (PEO) Block in Nanostructured Polystyrene− PEO− Polystyrene Triblock Copolymer Electrolytes

The plasticization of a polymer electrolyte usually promotes its ionic conductivity but decreases its storage modulus due to the increased polymer chain flexibility. Herein, we show that such a tradeoff between the ionic conductivity and the mechanical robustness of the polymer electrolyte can be alleviated by selective plasticization of the ion-conductive block, such as poly(ethylene oxide) (PEO) in a polystyrene (PS)− PEO−PS block copolymer (SEO) electrolyte using an ether type plasticizer, tetraethylene glycol dimethyl ether (TEGDME). At maximum plasticizer loading, the room temperature ionic conductivity increases by up to 3 orders, whereas the storage modulus, G′ reduces to half, is still on the order of 102 MPa. At above the melting temperature of the PEO block, the dynamic storage modulus, G′ of the plasticized membrane surpasses its dry PS-PEO-PS counterpart. Such a phenomenon results from that, a) TEGDME co-crystallizes with PEO to promote its crystallinity and hence the storage modulus, b) TEGDME swells the amorphous PEO phase to enhance the polymer chain segmental mobility and hence ionic conductivity, and c) the PS phase remains intact from TEGDME to keep the SEO elastic.

Unveiling the reinforcement effects in cottonseed protein/polycaprolactone blend biocomposites

Cottonseed protein (CP) was compounded with polycaprolactone (PCL) in different concentrations by melt blending, and then hot-pressed to prepare CP/PCL blend films. A co-continuous phase is formed when the CP/PCL content is 50/50, and the tensile strength, modulus and toughness are 9, 10, and 63 times greater than that of neat CP film. This remarkable improvement is mainly due to the intrinsic flexibility of long PCL polymer chains, whilst the polymeric crystalline structure can still be formed. Furthermore, 1 wt% of compatibilizing agent — glycidyl methacrylate (GMA) or maleic anhydride (MA), is added to the blends. Measurements from scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) showed the presence of chemically reactive compatibilization between the compatibilizer and CP or PCL phase, and the two phases with strong binding forces are well dispersed. Meanwhile, the compatibilizer can induce the protein secondary structure to unfold, further increasing the physical compatibilization between the protein and polymer chains, which has a noticeable contribution to the blend's mechanical, hydrophobic properties and thermal stability. This work adds new element to the knowledge of compatibilization in terms of optimised interfaces of polymer blends, and provide new insights into fabricating high performance protein derived bioplastics and biocomposites.

Relative Chain Flexibility Determines the Spatial Arrangement and the Diffusion of a Single Ring Chain in Linear Chain Films

The flexibility of a single polymer chain, characterized by its persistence length, is considered to be an intrinsic property of the polymer chain, which determines its conformation and transport p...

Influence of lactide vs glycolide composition of poly (lactic-co-glycolic acid) polymers on encapsulation of hydrophobic molecules: molecular dynamics and formulation studies

The work demonstrates the preparation of PLGA (PLGA 50:50, PLGA 75:25) nanoparticles, to encapsulate a hydrophobic molecule (coumarin-6), using the microreactor-based continuous process. The formulations were characterized using dynamic light scattering and transmission electron microscopy to determine their size, homogeneity, zeta potential, and surface morphology. The resulting nanoparticles were safe to the CHO cells (≈80% cell survival), at the concentration of ≤600 µg/mL and were successfully taken up by the cells, as demonstrated using confocal microscopy. Moreover, imaging flow cytometry confirmed that the nanoparticles were internalized in 73.96% of the cells. Furthermore, molecular dynamics simulation and docking studies were carried out to explore the effect of polymer chain length of PLGA and lactide vs glycolide (LA:GA) ratio on their compatibility with the coumarin-6 molecules and to study the coiling and flexibility of PLGA in the presence of coumarin-6 molecules. Flory–Huggins interaction parameter (χ) was calculated for polymer chains of varying lengths and LA:GA ratio, with respect to coumarin-6. χ parameter increased with increase in polymer chain length, which indicated superior interaction of coumarin-6 with the smaller chains. Amongst all the polymeric systems, PLGA55 exhibited the strongest interaction with coumarin-6, for all the chain lengths, possibly because of their homogeneous spatial arrangements and superior binding energy. PLGA27 showed better compatibility compared to PLGA72 and PGA, whereas PLA-based polymers exhibited the least compatibility. Analysis of the radius of gyration of the polymer chains in the polymer–coumarin-6 complexes, at the end of molecular dynamics run, exhibited that the polymer chains displayed varying coiling behavior and flexibility, depending upon the relative concentrations of the polymer and coumarin-6. Factors like intra-chain interactions, spatial arrangement, inter-chain binding energies, and polymer–coumarin-6 compatibility also influenced the coiling and flexibility of polymer chains.

Polyelectrolyte solutions in Taylor-Couette flows

Taylor-Couette (TC) flow is ideal for studying the flow behavior of complex solutions due to the wide variety of available hydrodynamic flow states. For non-Newtonian solutions, the presence of polymers in solution changes the solution rheology, which in turn modifies accessible flow states. While significant prior work exists on the effects of elasticity and shear thinning of polymer solutions on TC flow, the effects of changes in polymer chain conformation on these properties and the resultant changes in the TC flow states have not been extensively studied. Here, we have explored the effects of changing polymer chain conformation of polyelectrolyte solutions on laminar and turbulent TC flow by using a quasi-static ramp protocol to vary the inner cylinder rotation rates. The ionic strength of the cationic polyacrylamide (CPAM) solution was varied to modify the equilibrium polymer equilibrium conformation and solution rheological properties. In general, as the increasing solution ionic strength increases polymer chain flexibility and decreases elasticity and degree of shear thinning, there is a shift toward more Newtonian-like flow behavior. Additionally, the effects of co- and counter-rotation of the cylinders on the stability of flow states were observed as a function of solution ionic strength, and phase diagrams of the resulting flow states were mapped as a function of the inner and outer cylinder Reynolds numbers. It was found that co-rotation of the cylinders stabilizes some of the polymer-influenced flow states, while counter-rotation de-stabilizes flow states.