Chain Stretch Research Articles

The effect of dynamic tube dilation on chain stretch in nonlinear polymer melt rheology

The pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic (Doi and Edwards [10]). At deformation rates larger than the inverse Rouse time of the polymer chain, chains are stretched and their confining tubes become increasingly anisotropic. In a tube model with variable tube diameter, this leads to an interchain tube pressure term in the lateral direction of the tube (Marrucci and Ianniruberto [15]), which limits chain stretch. Here we assume that chain stretch is balanced by two restoring tensions with weights of 1/3 in the longitudinal direction of the tube, due to a linear entropic spring force, and 2/3 in the lateral direction, due to a nonlinear interchain tube pressure, both of which are characterized by the Rouse stretch relaxation time τ R . This approach is in quantitative agreement with the time-dependent and steady-state elongational viscosity of two monodisperse polystyrene melts with molar masses of 390,000 and 200,000 kg/mol as investigated by Bach et al. [2] and Hassager [12]. In bidisperse polymer blends, the interchain pressure is reduced in accordance with dynamic dilation of the tube. Implementation of the dilation effect into the evolution equation of the stretch leads to a quantitative description of the elongational behavior of bidisperse polystyrene blends consisting of a long and a short chain component as investigated by Nielsen et al. [22]. Due to the effect of chain ends, dynamic tube dilation is also of importance for monodisperse polymer melts with low molar masses having few entanglements, as demonstrated for two polystyrene melts with molar masses of M w = 102,800 and 51,700 g/mol. If dynamic tube dilation is taken into account, quantitative agreement between highly nonlinear viscoelastic experiments and predictions can be obtained based exclusively on the linear-viscoelastic characterization of polymer melts.

Spectroscopic study on interaction between bisphenol A or its degraded solution under microwave irradiation in the presence of activated carbon and human serum albumin

In this study, the interaction between bisphenol A (BPA) or its degraded solution under microwave irradiation after their adsorption on activated carbon (AC/MW) and human serum albumin (HSA) was investigated by UV–vis and fluorescence spectroscopy techniques. The results showed that BPA could bind to HSA molecule, which could cause the stretch of peptide chains. Also, the degraded BPA solution with a few residues could still interact with HSA. Otherwise, the influences of pH and ionic strength on the interaction were estimated. The fluorescence quenching modes of HSA initiated by BPA at three temperatures (298, 310 and 315 K) were all obtained using Stern–Volmer and Lineweaver–Burk equations. The number of binding sites ( n), binding constants ( K D) and energy transfer efficiency ( E) were all calculated. The thermodynamic parameters (Δ H, Δ G and Δ S) and binding distances ( r) were all measured at the three temperatures, respectively. Synchronous fluorescence spectroscopy was also carried out.

A Model for Flow‐enhanced Nucleation Based on Fibrillar Dormant Precursors

AbstractA model for flow‐enhanced nucleation is presented based on the concept of a polymer melt containing a fixed number of nucleation precursors with a fixed size distribution. Depending on the size, precursors can either be active (i.e. susceptible to nucleation, the characteristic time scale of which is governed by the deformation rate) and grow into a spherulite or remain dormant. The size distribution of precursors is derived by combining nucleation theory and experimentally determined quiescent spherulite number densities. Longitudinal precursor growth, causing activation of dormant precursors, is a function of molecular deformation: the stretch of high molecular weight chains. Both the eXtended Pom‐Pom and the Rolie‐Poly model are tested to calculate the molecular deformation. A quantitative agreement is found between simulations and experimental results. magnified image

Crystal structure of a 117 kDa glucansucrase fragment provides insight into evolution and product specificity of GH70 enzymes

Glucansucrases are large enzymes belonging to glycoside hydrolase family 70, which catalyze the cleavage of sucrose into fructose and glucose, with the concomitant transfer of the glucose residue to a growing α-glucan polymer. Among others, plaque-forming oral bacteria secrete these enzymes to produce α-glucans, which facilitate the adhesion of the bacteria to the tooth enamel. We determined the crystal structure of a fully active, 1,031-residue fragment encompassing the catalytic and C-terminal domains of GTF180 from Lactobacillus reuteri 180, both in the native state, and in complexes with sucrose and maltose. These structures show that the enzyme has an α-amylase-like (β/α)(8)-barrel catalytic domain that is circularly permuted compared to the catalytic domains of members of glycoside hydrolase families 13 and 77, which belong to the same GH-H superfamily. In contrast to previous suggestions, the enzyme has only one active site and one nucleophilic residue. Surprisingly, in GTF180 the peptide chain follows a "U"-path, such that four of the five domains are made up from discontiguous N- and C-terminal stretches of the peptide chain. Finally, the structures give insight into the factors that determine the different linkage types in the polymeric product.

Effect of epoxy oligomer on viscoelasticity of acrylic polymer

Linear and nonlinear viscoelasticity of an adhesion material for integrated circuit chips were investigated to control the processability. The material consists of acrylic polymer (AP) and epoxy oligomer (EP). EP content in AP/EP blend is 70 vol %. From the linear viscoelasticity, it was found that the iso-free volume state of AP/EP blend was 20°C lower than that of AP and the entanglement molecular weight Me of AP/EP was three times higher than that of AP. Nonlinear stress relaxation modulus G(t,γ) showed that the time-strain separability, G(t,γ) = G(t)h(γ), was applicable at long time above a characteristic time τk, where G(t) is linear relaxation modulus and h(γ) is the damping function. The τk value was estimated to be 10 s for AP/EP and below 0.1 s for AP at an iso-free volume state. (h(γ) for AP and AP/EP behaved like a usual linear homopolymer.) The time evolution of the elongational viscosity ηE(t) of each sample showed that AP/EP system exhibited strong strain hardening at , although AP did not show strain hardening at strain rate measured, when the data were compared at an iso-free volume state. These results strongly suggest that the strain hardening behavior of AP/EP is attributable to enhancement of the stretch of AP polymer chains by diluting EP oligomer chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Stretching of polymer chains by fluctuating flow fields

We investigate polymer stretching by fluctuating flow fields via numerical solutions of the Brownian dynamics of multibead polymer chains taking into account nonlinear elasticity, hydrodynamic interactions and good solvent, excluded volume interaction effects. By varying the scaling exponent of the energy spectrum whilst keeping the same Reynolds and Deborah numbers, as well as microscale length and turnover times, we show that steeper spectra are associated with stronger stretching. We compute the probability density functions of chain length, and explain their main features by examining explicit molecular histories. We quantify the interaction between strain rate tensor structure and chain geometry as a means of understanding better the different stretching mechanisms in mild, moderate and strong polymer stretching regimes.

Ln(binolam)3]⋅(OTf)3, a New Class of Propeller‐Shaped Lanthanide(III) Salt Complexes as Enantioselective Catalysts: Structure, Dynamics and Mechanistic Insight

The ligand 3,3'-bis(diethylaminomethyl)-1,1'-bi-2-naphthol (binolam) contains an arrayed Brønsted acid-Brønsted base (BABB) system, which is responsible for the original shape of its lanthanide compounds. The solution structure of Pr, Nd and Yb compounds is solved by means of paramagnetic NMR spectroscopy and it is demonstrated that they are substantially isostructural, but with a completely new fold compared to the apparently similar heterobimetallic systems based on 1,1'-bis(2-naphthol) (binol) and alkali cations. The aromatic nuclei lie in a region equatorial with respect to the C(3) symmetry axis, whereas the alkylamine chain stretches almost parallel to C(3), above (and below) Ln(3+). This is also found in the crystal structure of the binolamo-scandium complex. A detailed study of the proton-exchange processes within the network of BABBs present in the complex is reported, which provides insight into the mechanism of the enantioselective Henry reaction promoted by these systems.

Establishment of immortalized human periodontal ligament cells derived from deciduous teeth

Although periodontal ligament (PDL) cells have previously been isolated from permanent teeth, they have not been isolated from deciduous teeth. Here, we used human telomerase reverse transcriptase (hTERT) induction to establish the first immortalized PDL cell lines derived from deciduous teeth. Cells were transfected with plasmids containing hTERT. Single-cell cloning was then performed using the limited dilution method. Reverse transcriptase polymerase chain reaction and stretch PCR were used to detect hTERT expression in the clones. In order to determine whether the clones could differentiate into osteoblasts, we stimulated the cells with ascorbic acid and β-glycerophosphate. We success-fully obtained 3 single-cell clones, and named them single cell derived from human deciduous PDL (SH) 9, 10 and 11. All the SH cells showed hTERT expression and stable proliferation after >80 population doublings and expressed the marker genes of PDL cells, including scleraxis, periostin, cementum-derived protein 23, and tenomodulin. Although all the clones expressed osteoblastic markers, only the clones from the SH 9 cell line differentiated into osteoblastic cells. This is the first report of the immortalization of PDL cells derived from deciduous teeth. These cells could be useful in studies investigating the cellular mechanisms and regenerative processes of human PDL cells.

A Study on the Chain−Particle Interaction and Aspect Ratio of Nanoparticles on Structure Development of a Linear Polymer

The stability of metastable flow-induced precursor (FIPs) in the polymer melts in presence of nanoparticles, viz. single-walled carbon nanotube (SWCNT) and zirconia nanoparticles, is studied at, 142 °C, close to the equilibrium melting point of unconstrained extended chain crystals of linear polyethylene (PE). The results conclusively demonstrate the influence of chain−particle interactions, between PE and the nanoparticles, on the stretch of the long chains. With the applied flow, SWCNTs together with PE chains are observed to align along the flow direction, giving rise a strong streak like pattern along the equator. At the initial stages, intensity of the observed streak in the presence of SWCNTs is stronger than that for the neat polyethylene. The streak intensity stabilizes with time, where the time required for the stabilization depends on the amount of the dispersed nanotubes in the polymer matrix. On the contrary, in the presence of zirconia nanoparticles, where the chain−particle interactions between PE and the nanoparticles are weak the initially observed streak tends to disappear with time, where the time required is strongly dependent on the concentration of the nanoparticles in the polymer matrix. Thus, compared to the neat polymer, the presence of zirconia nanoparticles destabilizes the shish formation. The chain orientation along the flow direction is determined using Herman’s orientation function and the length of the oriented chains (shish) by Ruland’s streak analysis. On cooling, with the crystallization of the polymer, scattering develops along the meridian, indicating the development of folded chain crystals, where the oriented chains present along the flow direction provide the epitaxy matching thus suppressing the nucleation barrier. The meridional intensity (arising with the formation of crystals, called kebabs) at room temperature, shows strong dependence on the stable streak intensity (chain orientation along the flow direction, called shish) along the equator prior to cooling.

Molecular modeling of responsive polymer films

Fil: Tagliazucchi, Mario Eugenio. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Quimica, Fisica de los Materiales, Medioambiente y Energia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Quimica, Fisica de los Materiales, Medioambiente y Energia; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Quimica Inorganica, Analitica y Quimica Fisica; Argentina

Analytic calculation of nucleation rates from a kinetic Monte Carlo simulation of flow induced crystallization in polymers

We present an analytically derived model for flow induced crystallization (FIC), based upon the recent Graham–Olmsted simulation. We use combinatorial techniques to calculate nucleation energy landscapes, which correctly predict simulation data. Applying both the analytic calculation and the simulation, we put forward a simple expression relating nucleation rate to polymer chain stretch. We also investigate bimodal blends, an important step to understanding polydisperse systems and eventually modeling industrial polymer melts.

Protein β-Sheet Nucleation Is Driven by Local Modular Formation

Despite its central role in the protein folding process, the specific mechanism(s) behind beta-sheet formation has yet to be determined. For example, whether the nucleation of beta-sheets, often containing strands separated in sequence by many residues, is local or not remains hotly debated. Here, we investigate the initial nucleation step of beta-sheet formation by performing an analysis of the smallest beta-sheets in a non-redundant dataset on the grounds that the smallest sheets, having undergone little growth after nucleation, will be enriched for nucleating characteristics. We find that the residue propensities are similar for small and large beta-sheets as are their interstrand pairing preferences, suggesting that nucleation is not primarily driven by specific residues or interacting pairs. Instead, an examination of the structural environments of the two-stranded sheets shows that virtually all of them are contained in single, compact structural modules, or when multiple modules are present, one or both of the chain termini are involved. We, therefore, find that beta-nucleation is a local phenomenon resulting either from sequential or topological proximity. We propose that beta-nucleation is a result of two opposite factors; that is, the relative rigidity of an associated folding module that holds two stretches of coil close together in topology coupled with sufficient chain flexibility that enables the stretches of coil to bring their backbones in close proximity. Our findings lend support to the hydrophobic zipper model of protein folding (Dill, K. A., Fiebig, K. M., and Chan, H. S. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 1942-1946). Implications for protein folding are discussed.

Constitutive equations for the Doi–Edwards model without independent alignment

We present two representations of the Doi–Edwards model without Independent Alignment explicitly expressed in terms of the Finger strain tensor, its inverse and its invariants. The two representations provide explicit expressions for the stress prior to and after Rouse relaxation of chain stretch, respectively. The maximum deviations from the exact representations in simple shear, biaxial extension and uniaxial extension are of order 2%. Based on these two representations, we propose a framework for Doi–Edwards models including chain stretch in the memory integral form.

Polymeric liquids in extension: fluid mechanics or rheometry?

We use a transient 3D free surface finite element method to simulate flow of entangled polymer fluids in the dual cylinder wind-up extensional rheometer. The constitutive equations are K-BKZ integral representations of the Doi–Edwards models with and without the independent alignment approximation (IA). It is demonstrated that the actual kinematics in this rheometer is a mixture of planar and uniaxial extension. Moreover, the ratio of planar to uniaxial deformation is highly dependent upon whether IA is invoked. Without IA, the flow has a tendency toward planar extension, while it tends to be more uniaxial with IA invoked. As a second illustration of the techniques, we simulate the phenomenon of delayed rupture after rapid extension of entangled polymer systems. It is demonstrated that this phenomenon can be explained on the basis of the Doi–Edwards model in terms of a Considere-type instability after chain stretch relaxation.

Magnetism-induced ballistic conductance changes in palladium nanocontacts

We present first-principles calculations of the effects of magnetism on the ballistic conductance of a model Pd nanocontact, made of a short Pd monatomic stretched chain placed between two Pd leads, simulated by semi-infinite (100) slabs. The stretching makes the suspended Pd chain generally ferromagnetic. The spin-resolved ballistic conductance, calculated according to the Landauer-Buttiker formula is found to be 0.85G0 for the spin-up and 1.15G0 for the spin-down electrons (G0 = 2e2/h is the conductance quantum). The total conductance ~2G0 is lower, but still relatively close to that of the nonmagnetic Pd nanocontact with the same geometry, calculated to be 2.3G0. To illustrate how magnetism and conductance depend on structural details, we change the three atom chain docking from the top to a hollow surface site, where at the same stress the Pd contact is nonmagnetic and the conductance decreases to 1.8G0. Overall we find these calculated ballistic conductance values of very similar magnitude to the first histogram peak in the experimental data obtained for Pd at low temperature in mechanically controllable break junctions. We conclude that the 15% conductance changes caused by the onset or the demise of local magnetism, similar in magnitude to geometry-related conductance changes, are probably too small to be used as a diagnostic for the presence or absence of nanocontact magnetism.

Nonlinear Rouse-chain relaxations in obstacle media

The entropic interplay of a nonlinearly deformed chain in obstacle media provides elementary knowledge into single-chain dynamics and nonlinear viscoelasticity of polymer liquids flowing in porous or entangled media. This work scrutinized, using Brownian dynamics simulation, the relaxation dynamics of nonlinearly deformed Rouse chains suspended in 2D array of point obstacles. The simulation disclosed a highly confined, anisotropic path of chain retraction that forces a hierarchy of Rouse retraction propagating from the outer segments toward the central ones. Such a constrained Rouse retraction was generally more retarded than free Rouse retraction in dilute system. The classical Doi theory on a 1D Rouse chain captures a similar feature, yet it generally underpredicts the degree of chain retraction as observed in the simulation and seemingly predicts an incorrect dependence on the strain magnitude. For sufficiently long chains, the simulation revealed, in addition, a long-persisting tail of chain stretch well beyond the Rouse regime. This long-time anomaly has further been noted to be closely correlated with another previously unnoticed, dominantly diffusive coil-size relaxation taking place on time scales between the Rouse time and the reptation time. The last feature has been attributed to a general coupling between terminal chain retraction and early-stage chain reptation for relatively long chains. In light of the present findings for obstacle media, we discuss recent experimental trends noted for entangled polymer solutions.

The interchain pressure effect in shear rheology

Recently, the tube diameter relaxation time in the evolution equation of the molecular stress function (MSF) model (Wagner et al., J Rheol 49: 1317–1327, 2005) with the interchain pressure effect (Marrucci and Ianniruberto, Macromolecules 37:3934–3942, 2004) included was shown to be equal to three times the Rouse time in the limit of small chain stretch. From this result, an advanced version of the MSF model was proposed, allowing modeling of the transient and steady-state elongational viscosity data of monodisperse polystyrene melts without using any nonlinear parameter, i.e., solely based on the linear viscoelastic characterization of the melts (Wagner and Rolon-Garrido 2009a, b). In this work, the same approach is extended to model experimental data in shear flow. The shear viscosity of two polybutadiene solutions (Ravindranath and Wang, J Rheol 52(3):681–695, 2008), of four styrene-butadiene random copolymer melts (Boukany et al., J Rheol 53(3):617–629, 2009), and of four polyisoprene melts (Auhl et al., J Rheol 52(3):801–835, 2008) as well as the shear viscosity and the first and second normal stress differences of a polystyrene melt (Schweizer et al., J Rheol 48(6):1345–1363, 2004), are analyzed. The capability of the MSF model with the interchain pressure effect included in the evolution equation of the chain stretch to model shear rheology on the basis of linear viscoelastic data alone is confirmed.

Dynamics of monodisperse linear entangled polymer melts in extensional flow: The effect of excluded-volume interactions

We present an extension of the Rouse-CCR tube model for linear entangled polymers, by incorporating interchain repulsive excluded-volume interactions, to interpret extensional viscosity data of narrow molecular weight distribution polystyrene melts in strong extensional flows. The expression for the stress tensor is also adapted to account for modifications of the effective tube diameter due to flow-induced chain stretch. Despite its simplicity, the resulting model correctly captures the extensional rheological behavior of linear entangled monodisperse polystyrene melts already published in the literature.

Elongational Flow of Blends of Long and Short Polymers: Effective Stretch Relaxation Time

We study the onset of chain stretch and emergent extension hardening in the nonlinear rheological response of molten binary blends of long and short polymers. We predict that, upon dilution with short chains, the effective stretch relaxation time of the long chains initially increases in proportion to varphi_{L};{-alpha} (where varphi_{L} is the volume fraction of long chains and alpha is the dilution exponent for entanglements). We confirm this behavior experimentally, in a set of experiments that measure both the dilution exponent from linear rheology and the effective stretch relaxation time under extensional flow.

Saturation of Pointlike Nuclei and the Transition to Oriented Structures in Flow-Induced Crystallization of Isotactic Polypropylene

The influence of molecular weight and processing conditions on the crystallization kinetics of isotactic polypropylene is studied using rheometry. Flow-induced crystallization experiments are performed with shear rates at which molecular stretch of the longest chains is expected. Depending on the molecular weight, a saturation of pointlike nuclei is observed with increasing shear time. In most cases, the process accelerates after sufficient flow time, and this change in kinetics is due to the occurrence of fibrillar nucleation resulting in the formation of row structures and/or shishes. The number of pointlike nuclei is derived from the rheometry experiments by modeling the system as a suspension. This method has some important advantages, i.e., (1) it is applicable to systems where optical microscopy does not work (i.e., colored systems) and (2) it is much easier, faster, and more accurate than optical methods.