Extended Polymer Chains Research Articles

Self-interacting polymer chains terminally anchored to adsorbing surfaces of three-dimensional fractal lattices

We have studied the adsorption problem of self-attracting linear polymers, modeled by self-avoiding walks (SAWs), situated on three-dimensional fractal structures, exemplified by 3d Sierpinski gasket (SG) family of fractals as containers of a poor solvent. Members of SG family are enumerated by an integer b (b≥2), and it is assumed that one side of each SG fractal is an impenetrable adsorbing surface. We calculate the critical exponents γ1,γ11, and γs, which are related to the numbers of all possible SAWs with one, both, and no ends anchored to the adsorbing boundary, respectively. By applying the exact renormalization group (RG) method (for the first three members of the SG fractal family, b=2,3, and 4), we have obtained specific values of these exponents, for θ-chain and globular polymer phase. We discuss their mutual relations and relations with corresponding values pertinent to extended polymer chain phase.

High performance of electrochemical sensors based on LbL films of gold nanoparticles, polyaniline and sodium montmorillonite clay mineral for simultaneous detection of metal ions

We report the effects of the incorporation of gold nanoparticles (AuNPs) into LbL films of emeraldine salt polyaniline (PAni-ES) and sodium montmorillonite clay mineral (Na+-MMT). We observed the higher performance of electrochemical sensors was induced by AuNPs towards trace level detection of cadmium (Cd2+), lead (Pb2+) and copper (Cu2+) ions. The detection was performed by square wave anodic stripping voltammetry (SWASV) using ITO electrodes modified with LbL films composed of three supramolecular architectures: PAni-ES/AuNPs, AuNPs/Na+-MMT and PAni-ES/AuNPs/Na+-MMT, which were compared to the LbL films without AuNPs. The results are consistent with the AFM dates indicating that the increase of roughness favors at low limit of detection for the sensors. The incorporation of AuNPs and PAni-ES leads to an interaction via ion-dipole, as characterized by FTIR and Raman spectra. This interaction, consequently, causes a more extended polymer chain, which intercalate into Na+-MMT galleries, according to X-ray diffraction data. The results demonstrate the possible control of film properties by exploiting molecular-level interactions in multicomponent nanostructured films favoring directly in electrochemical sensors response.

Interaction Mechanisms between Air Bubble and Molybdenite Surface: Impact of Solution Salinity and Polymer Adsorption.

The surface characteristics of molybdenite (MoS2) such as wettability and surface interactions have attracted much research interest in a wide range of engineering applications, such as froth flotation. In this work, a bubble probe atomic force microscope (AFM) technique was employed to directly measure the interaction forces between an air bubble and molybdenite mineral surface before/after polymer (i.e., guar gum) adsorption treatment. The AFM imaging showed that the polymer coverage on the surface of molybdenite could achieve ∼5.6, ∼44.5, and ∼100% after conditioning in 1, 5, and 10 ppm polymer solution, respectively, which coincided with the polymer coverage results based on contact angle measurements. The electrolyte concentration and surface treatment by polymer adsorption were found to significantly affect bubble-mineral interaction and attachment. The experimental force results on bubble-molybdenite (without polymer treatment) agreed well with the calculations using a theoretical model based on the Reynolds lubrication theory and augmented Young-Laplace equation including the effect of disjoining pressure. The overall surface repulsion was enhanced when the NaCl concentration decreased from 100 to 1 mM, which inhibited the bubble-molybdenite attachment. After conditioning the molybdenite surface in 1 ppm polymer solution, it was more difficult for air bubbles to attach to the molybdenite surface due to the weakened hydrophobic interaction with a shorter decay length. Increasing the polymer concentration to 5 ppm effectively inhibited bubble attachment on mineral surface, which was mainly due to the much reduced hydrophobic interaction as well as the additional steric repulsion between the extended polymer chains and bubble surface. The results provide quantitative information on the interaction mechanism between air bubbles and molybdenite mineral surfaces on the nanoscale, with useful implications for the development of effective polymer depressants and fundamental understanding of bubble-solid interactions in mineral flotation. The methodologies used in this work can be readily extended to studying similar interfacial interactions in many other engineering applications such as froth flotation deinking and bitumen extraction in oil sands industry.

Translocation and Binding in the Recognition of Short Oligonucleotides by a Biological Nanopore

Polymer interactions with pore-forming membrane proteins, as evidenced by the resulting block of ionic current, may be classified into two types: (1) the threading of an extended polymer chain of which only a small length contributes to the block and (2) a binding reaction, where the polymer enters the pore entirely and interacts as a particle. The former phenomenon typically occurs in dilute aqueous electrolyte solutions (e.g. KCl <1 M) and requires long and charged molecules and can allow sequencing (e.g. of DNA). In contrast, the binding reaction typically occurs with short, neutral polymer molecules, requires high salinity (e.g. KCl 3-4 M) and enables the high-resolution discrimination of polymer masses1. The aerolysin nanopore has recently been shown to strongly interact with short adenine oligonucleotides (A3-A10) and this interaction allows mass discrimination on the basis of the depth of block of ionic current induced by the binding of the analyte,2 suggesting a binding-type interaction. Using low-noise current recording, we have indentified strong dynamics of this interaction between DC and 50 kHz and indentified short visits to deeper blocked states preceding and following the principal, mass-dependent state (pre- and post-blocks). Statistical analysis indicates that the probability of post- but not pre-blocks decreases with (1) oligomer length and (2) transmembrane voltage. We interpret this finding in terms of a combined translocation and binding interaction, probably involving several binding sites for DNA in the pore. In line with this hypothesis, longer polynucleotides (A30) showed stable and long-lasting interactions with near-complete block of current.(1) Robertson et al. Proc. Natl. Acad. Sci. U S A 2007, 104, 8207-8211.(2) Cao et al. Nature Nanotechnology 2016, 1-7.

Control of electro‐osmotic flow by mixed polymer brushes: Molecular dynamics simulations

Molecular dynamics simulations of electro‐osmotic flow through a channel coated by a mixed polymer brush reveal the modulation of electro‐osmotic flow. The mixed polymer brush consists of two types of neutral chains, denoted as PA and PB chains, respectively. The effect of the interaction strength between PA and PB monomers on fluid transport is studied. It was found that the PA‐PB interaction plays an important role in controlling the flow. The mixed polymer brush adopts a layered structure owing to the difference in solvent‐polymer interactions. Stronger shear force from the solvent flow leads to larger extension of polymer chains on the top layer (or PA chains). Such layering structure also causes different coupling between polymer conformational dynamics and fluid dynamics. At high grafting densities, there are remarkable differences in the velocity profiles for different PA‐PB interactions. For repulsive and attractive interactions, the increase of grafting density leads to reduced fluid transport. However, when the attraction between PA and PB interactions becomes stronger, the flow behavior is more complicated depending on the grafting density. Our simulation results indicate the change of ionic distribution induced by the conformational transition due to the PA‐PB interaction has significant contributions to the flow controlling. POLYM. ENG. SCI., 57:1293–1300, 2017. © 2017 Society of Plastics Engineers

Nanocellulose-PE-b-PEG copolymer nanohybrid shish-kebab structure via interfacial crystallization

We report a novel nanohybrid shish-kebab (NHSK) architecture of cellulose nanofibers (CNFs) and a block copolymer, (polyethylene-b-polyethylene glycol) (PE-b-PEG). Cellulose microfibers were ultrasonically dispersed to generate cellulose nanofibers in the size range of 50±10nm in diameter, while the block copolymer was crystallized using a solution crystallization approach to prepare NHSK. This unique approach allows the flocculated NHSK product to transfer quickly from toluene to ethanol, in order to shorten the preparation time. Morphological analysis reveals, for the first time, that nanocellulose can be used to induce crystallization of a block copolymer to generate NHSK and trans-crystalline structure. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results reveals the crystal morphology and crystallinity changes by virtue of crystallization. The ordered periodic growth and alignment of polymer crystals is recognized as the virtue of molecular origin of extended polymer chains. The proposed hypothesis affords elucidation of NHSK architecture and promotes the designing of novel nanohybrids with controllable functionality.

Polyelectrolyte brushes as supportive substrate for bacterial S-layer recrystallization: Polymer charge and chain extension factors

Polymer brushes of different structure (full extension vs collapsed) and charge (+, 0 −) have been employed as supporting “smart” interface for investigating the recrystallization pathways of isolated SbpA bacterial surface proteins. Such study has been done by means of Quartz Crystal Microbalance with Dissipation monitoring (QCMD), which allowed following the real-time evolution of frequency (related to the adsorbed mass per area) and dissipation (elastic properties) factors, either individually or combined as the so-called Df plots. Results showed higher affinity of SbpA for positively charged brushes with poly{[2-(methacryloyloxy)ethyl] trimethylammonium chloride} (PMETAC) in their composition as well as for negative poly(sulfo propyl methacrylate) (PSPM) brushes which were grown in limited chain extension conditions. The crystal structure of the formed layer could be elucidated by complementary Atomic Force Microscopy (AFM).

Modeling of rheological behavior for polymer nanocomposites via Brownian dynamic simulation

Reptation dynamics of the coarse-grained polymer molecular chain is investigated to predict rheological behavior of polymeric nanocomposites by applying Brownian dynamics simulation to the proposed full chain reptation model. Extensibility of polymer chain and constraint release from chain stretch or retraction are of main concern in describing the nanocomposite systems. Rheological results are well predicted by applying the improved simulation algorithm using stepwise Wiener processes. Strong shear thinning and elongational strain hardening are predicted and compared with the experimental results of polyamide 6/organoclay nanocomposites. The full chain reptation model enables us to predict dynamic motion of the polymer chain segments and understand mechanisms for characteristic rheological behaviors.

Influence of some inorganic salts on the intrinsic viscosity of poly(acrylic acid) in aqueous solutions

In this work, the effect of temperature, concentration of sodium sulfate and potassium sulfate on the intrinsic viscosity of poly(acrylic acid) were investigated. Our data shows excellent conformance with the Wolf equation. The addition of salt screens the electrostatic repulsions between charges along the backbone of the polyelectrolyte chain. Consequently the intrinsic viscosity of PAA was decreased by increasing concentration of salt. Also the results reveal that the reduction of intrinsic viscosity of PAA in the presence of sodium sulfate is more than those of potassium sulfate. Potassium cation shows a screen effect less than sodium cation. Therefore the intrinsic viscosity of PAA in the presence of potassium sulfate is more than those of sodium sulfate. The flow activation energy was evaluated by Arrhenius equation. The flow activation energy data was correlated to polymer concentration with a meaningful equation. The UV–Vis spectra of poly(acrylic acid) shows that the absorption intensity of PAA was decreased with addition of sodium sulfate or potassium sulfate. The structure of the extended polymer chains reformed to random-coil conformation in the presence of salt, thus the value of electric multipole moment decreased. Consequently the absorption intensity of PAA was decreased with addition of sodium sulfate or potassium sulfate.

Stiffness, Strength, and Toughness of Electrospun Nanofibers: Effect of Flow-Induced Molecular Orientation

The simultaneous sharp rise in stiffness, strength, and toughness of electrospun nanofibers at small diameters is explained here as the result of the molecular orientation induced by the strong stretching of the electrospinning extensional flow. Differing from the common view that this phenomenon is related to the nanofibers size scale, we show by theoretical analysis that it is likely the result of an abrupt transition in polymer chain extension that occurs at high flow strain rates. Consequently, the molecular orientation and mechanical properties experience a matching transition, followed by a linear rise with the strain rate. The model compares well with published experimental data, supporting the assertion that the observed phenomena can be explained as the consequence of electrospinning conditions instead of size dependence. We show how the mechanical properties can be tuned by controlling the process as well as set the goal for future improvement in these properties.

Impact of adsorption of poly(aspartic acid) and its copolymers with polyethylene glycol on thermal characteristic of Cr2O3

The polymer structure impact on the adsorption layer conformation formed on the chromium (III) oxide surface was investigated. As adsorbates, three macromolecular compounds were tested: poly(l-aspartic acid) homopolymer and two block copolymers containing the poly(amino acid) segments as well as the poly(ethylene glycol) ones in the chain structure. Due to the ionic nature of the poly(amino acid), all measurements were carried out as a function of solution pH value. The most probable polymer chain binding mechanism was determined on the basis of the values obtained from the adsorption, potentiometric titration, turbidimetry and thermogravimetry experiments. The acquired results indicate that the solution pH has a great influence on the adsorbed macromolecule conformation. Additionally, in the case of the block copolymers, the individual structural unit affinity for the solid particles can be modified by the pH changes. Therefore, a significant difference in the mass decrement measured for the systems at pH 3 and 10 can be explained by the contribution of electrostatic forces and hydrogen bond formation to the polymer adsorption mechanism. Structure of the adsorbed polymer layer determines also the suspension stability. The solid surface charge neutralization by the macromolecules bound to the Cr2O3 surface at pH 3 impairs the sample stability, whereas the presence of the extended polymer chains in the basic solution leads to the durability improvement.

Rheological response of methylcellulose toward alkanediyl-α,ω-bis(dimethylcetylammonium bromide) surfactants with varying spacer length

The modulation of properties of methylcellulose (MC) by cationic gemini surfactants with varying spacer lengths was studied employing tensiometry, rheometry and turbidimetry. Surface tension measurements anticipate that the gemini surfactant with longer spacer chain length saturates MC at lower concentrations owing to its greater hydrophobicity compared to shorter spacer analogues. Rheometric and turbidimetric measurements suggest that at very low concentrations of gemini surfactants, ion-dipole type of interactions between MC and gemini surfactants promote the extension of polymer chains which is manifested by an initial increase in the low shear viscosity and gelation temperature of MC–gemini surfactant systems, and lowering of turbidity. Such interactions were found to be stronger in case of 16-4-16 than 16-5-16, and almost absent in case of 16-6-16 surfactant system. However at concentrations above CAC, hydrophobic forces operative between MC and gemini surfactants were found to be more for 16-6-16 than that of 16-5-16 and 16-4-16. The final levelling of MC viscosity in presence of all the three gemini surfactants and the variation of gelation temperature suggests the solubilization of network junctions in the surfactant micelles. Moreover, the presence of gemini surfactant strongly affects the interaction of MC with a model hydrophobic drug rifampicin.The results highlight the importance of gemini surfactants and their spacer length in controlling the structural dynamics of MC and its effective use in pharmaceutical and food industry.

Extensional rheometry of cellulose ether solutions: flow instability

Capillary breakup extensional rheometry of semi-dilute hydroxyethyl cellulose (HEC) solutions was performed under several step-stretch conditions. The resulting parameters, i.e. terminal steady state extensional viscosity (η E ) and the timescale for viscoelastic stress growth, commonly referred to as the extensional relaxation time (λ E ) were found to be sensitive to the step-stretch conditions. The λ E decreased with increasing step-strain as opposed to the η E . Prior to the filament break-up, a ‘bead-on-string’ instability was observed close to the mid-plane. It is believed that this instability originated from the accumulation of viscoelastic stresses near the filament neck leading to the ‘elastic recoil’ of the extended polymer chains. The reasons for this belief are discussed in detail with the perspective of the past literature. Such type of flow instability has been reported for the first time for a cellulosic system. Various dimensionless numbers were plotted for the HEC solutions and compared with those obtained from past studies for various biopolymers as well as synthetic polymers.

Fructan synthesis, accumulation and polymer traits. II. Fructan pools in populations of perennial ryegrass (Lolium perenne L.) with variation for water-soluble carbohydrate and candidate genes were not correlated with biosynthetic activity and demonstrated constraints to polymer chain extension.

Differences have been shown between ryegrass and fescue within the Festulolium subline introgression family for fructan synthesis, metabolism, and polymer-size traits. It is well-established that there is considerable variation for water-soluble carbohydrate and fructan content within perennial ryegrass. However there is much still to be discovered about the fructan polymer pool in this species, especially in regard to its composition and regulation. It is postulated that similar considerable variation for polymer traits may exist, providing useful polymers for biorefining applications. Seasonal effects on fructan content together with fructan synthesis and polymer-size traits have been examined in diverse perennial ryegrass material comprising contrasting plants from a perennial ryegrass F2 mapping family and from populations produced by three rounds of phenotypic selection. Relationships with copy number variation in candidate genes have been investigated. There was little evidence of any variation in fructan metabolism across this diverse germplasm under these conditions that resulted in substantial differences in the complement of fructan polymers present in leaf tissue at high water-soluble carbohydrate concentrations. The importance of fructan synthesis during fructan accumulation was unclear as fructan content and polymer characteristics in intact plants during the growing season did not reflect the capacity for de novo synthesis. However, the retention of fructan in environmental conditions favoring high sink/low source demand may be an important component of the high sugar trait and the roles of breakdown and turnover are discussed.

Influence of the counter ion on the properties of organic and inorganic acid doped polyaniline and their Schottky diodes

Pure and doped Polyaniline (PANI) was prepared by chemical oxidative polymerization of aniline. The FT-IR spectrum confirms the presence of dopants in PANI functional groups of SO32− groups in PANI. SEM morphology reveals the various shapes and size of the PANI. UV–Vis spectra confirm the absorption peaks at 270 and 340nm is due to the π–π∗ transition of the benzenoid rings. The strong absorption peak around 603nm showed extension of polymer chains. PL studies of PANI reveal the emission peaks around 325nm and 510nm of PANI. The conductivity measurements are carried out for the prepared PANI’s pellets.The heterojunction device structure In/PANI-DBSA/Al and In/PANI-HCl/Al was made to fabricate by thermal evaporation method. The current voltage (I–V) characteristics of these devices are weak rectifying behavior with the non-linear nature. The diode parameters such as ideality factor, barrier height and saturation current densities were calculated using the modified Shockley equation.

Thermochromism, Franck–Condon Analysis and Interfacial Dynamics of a Donor–Acceptor Copolymer with a Low Band Gap

The electronic properties of the donor–acceptor (DA) polymer poly{5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c]-1,2,5-thiadiazole} (PTBT) have been investigated using spectroscopic and computational techniques. Electronic absorption and emission spectra reveal the presence of an ordered and a disordered phase in solution. Franck–Condon modeling of the ordered phase yields Huang–Rhys factors of 0.55 (20 °C) and 0.51 (−180 °C), indicating little structural distortion between ground and excited state. DFT calculations with resonance Raman spectroscopy are consistent with a lowest energy excited state that is electronically delocalized and has little charge-transfer character, unexpected for a copolymer with a low bandgap (∼1.8 eV). Transient absorption spectroscopy of PTBT:fullerene blends reveals near-unity internal charge-transfer yields in both ordered and disordered film morphologies. In the disordered blend, charge transfer is complete within the laser pulse (100 fs), whereas the ordered blend also features a slower phase due to exciton diffusion in the phase separated morphology. In the ordered blend, the spectra and dynamics of charge transfer reveal that excitons and charges promptly occupy delocalized states on extended polymer chains. The pervasive use of donor–acceptor structures in polymer devices makes understanding the interplay of morphology and electronic structure of these polymers essential and here a spectroscopic and computational investigation gives an extensive picture of the electronic properties and their effect on charge dynamics in a DA polymer.

Photoinduced atom transfer radical polymerization in a polar solvent to synthesize a water-soluble poly(2-methacryloyloxyethyl phosphorylcholine) and its block-type copolymers

Photoinduced atom transfer radical polymerization (ATRP) has promising applications because it requires small amounts of transition metal catalysts and low temperatures, and can be extended to numerous monomers. We investigated the photoinduced ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC) in a polar medium and prepared block-type copolymers with a poly(MPC) segment. Polymerizations in methanol at room temperature were rapid and well-controlled under photoirradiation, with a linear relationship between monomer conversion and actual exposure time. Extension of polymer chains to prepare ABA triblock-type copolymers composed of poly(MPC) and poly(glycidyl methacrylate (GMA)), which possesses a reactive epoxy group in the side chain, was achieved by one-pot photoinduced ATRP in a shorter time and under milder reaction conditions than those in conventional ATRP. The synthesized poly(MPC) and its ABA triblock-type copolymers had sufficiently narrow molecular weight distributions. These results endorse photoinduced ATRP as an attractive technique to obtain water-soluble polymers with a poly(MPC) segment.

Gel Mechanics: A Thermo-mechanically Coupled Theory for Fluid Permeation in Elastomeric Materials

An elastomeric gel is a cross-linked polymer network swollen with a solvent, and certain gels can undergo large reversible volume changes as they are cycled about a critical temperature. We have developed a continuum-level theory to describe the coupled mechanical deformation, fluid permeation, and heat transfer of such thermally-responsive gels. In discussing special constitutive equations we limit our attention to isotropic materials, and consider a model based on a Flory-Huggins model for the free energy change due to mixing of the fluid with the polymer network, coupled with a non-Gaussian statistical-mechanical model for the change in configurational entropy — a model which accounts for the limited extensibility of polymer chains. We have numerically implemented our theory in a finite element program. We have shown that our theory is capable of simulating swelling, squeezing of fluid by applied mechanical forces, and thermally-responsive swelling/deswelling of such materials.

Molecular structure of self-healing polyampholyte hydrogels analyzed from tensile behaviors.

Recently, charge balanced polyampholytes (PA) have been found to form tough and self-healing hydrogels. This class of physical hydrogels have a very high equilibrated polymer concentration in water (ca. 40-50 wt%), and are strongly viscoelastic. They are synthesized by random copolymerization of equal amounts of oppositely charged monomers at a high concentration, followed by a dialysis process of the small counter-ions and co-ions in water. The randomly distributed, opposite charges of the polymer form multiple ionic bonds of intra- and inter-chains with strength distribution. The strong inter-chain bonds, stabilized by topological entanglement, serve as quasi-permanent crosslinks, imparting the elasticity, while the weak bonds, both inter- and intra-chains, reversibly break and re-form to dissipate energy to toughen the materials. In this work, we intend to clarify the structure of the physical PA hydrogels from the tensile behaviors of the PA hydrogels. To clarify the structure and its formation mechanism, we analysed the tensile behaviors of the samples before and after the dialysis. We separated the quasi-permanent crosslinking of strong inter-chain bonds and the dynamic crosslinking of weak inter-chain bonds by using a combined model that consists of the Upper Convected Maxwell model and the Gent strain hardening model. The model fitting of the tensile behaviors extracts quantitative structural parameters, including the densities of weak and strong inter-chain bonds and the theoretical finite extensibility of polymer chains. Based on the fitting results of the combined model, the structural parameters of partial chains at a fixed observation time, including the Kuhn number, Kuhn length, and chain conformation, are determined using the scaling theory. The effects of monomer concentration at preparation, the effect of dialysis and the initial strain rate on the dynamic structure of PA gels, are discussed based on these analyses.

Why do some immobilized N-alkylated polyethylenimines far surpass others in inactivating influenza viruses?

A number of N-alkylated polyethylenimines (PEIs) were covalently attached to glass-slide surfaces, and their virucidal efficacies against three different strains of influenza viruses were examined quantitatively. The anti-influenza activities of the modified surfaces varied widely, with the most potent, immobilized N,N-hexyl,methyl-PEI and N,N-dodecyl,methyl-PEI, reducing the viral titer by over three logs (i.e., >99.9%). While the virucidal activities of the glass surfaces derivatized with N-alkylated PEIs displayed no discernible correlation with such surface properties as hydrophobicity, charge, protein affinity, roughness, adhesive interactions, and polymer-chain extension lengths, they exhibited a marginal correlation with the surface density of the quaternary ammonium group, as titrated by means of fluorescein binding. However, this correlation markedly improved (to the correlation coefficient of 0.97 with a two-tailed p value of 0.044) when the titration was instead carried out using a macromolecular conjugate, the dye coupled to the protein lysozyme, suggesting that the critical determinant of the virucidal activity is the density of the immobilized quaternary ammonium groups accessible to influenza virions.