Dynamics Of Polymer Chains Research Articles

Study on the coil–globule transition and dynamics of polymer chain confined in slit

ABSTRACTThe coil–globule transition and dynamics of a lattice self‐avoiding bond fluctuation polymer chain confined in slit are studied by Monte Carlo simulations. The coil–globule transition temperature of polymer chain is increased at intermediate slit height H (H ∼ RG0 with RG0 the radius of gyration of polymer in dilute solution) due to the squeeze of the polymer in the repulsive slit, but it is decreased by surface attraction as the polymer is extended along the surface. We have compared the difference between the rotational relaxation time τR for the reorientation of end‐to‐end vector and the relaxation time τ for the polymer diffusing over a distance of the size of polymer. We find that τR is clearly distinct from τ as they have different scaling exponents in their slit height‐dependent behaviors and for the polymer in the extended coil state, that is, αR > α. And both exponents increase with an increase in the intrapolymer attraction and surface attraction. However, these scaling relations are destroyed by strong surface attraction when the polymer is adsorbed on surfaces. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1053–1062

Effects of solvent quality on contact formation dynamics of polymer chain

We investigate the interplay effects of internal friction and solvent quality on the contact formation dynamics based on non-Markovian diffusion equation supplemented with an exponential sink term accounting for the electron transfer quenching. The mean contact formation time has been derived under Wilemski-Fixman approximation. We show that internal friction induces fractional viscosity dependence of looping time, which will be affected remarkably by solvent quality condition. Besides, internal friction promotes a diffusion-limited mechanism by slowing chain relaxation, while solvent quality being another key factor shifts the critical internal friction for the crossover of the transition from reaction to diffusion-limited regimes.

Structure and Dynamics of Solvated Polymers near a Silica Surface: On the Different Roles Played by Solvent.

Whereas it is experimentally known that the inclusion of nanoparticles in hydrogels can lead to a mechanical reinforcement, a detailed molecular understanding of the adhesion mechanism is still lacking. Here we use coarse-grained molecular dynamics simulations to investigate the nature of the interface between silica surfaces and solvated polymers. We show how differences in the nature of the polymer and the polymer-solvent interactions can lead to drastically different behavior of the polymer-surface adhesion. Comparing explicit and implicit solvent models, we conclude that this effect cannot be fully described in an implicit solvent. We highlight the crucial role of polymer solvation for the adsorption of the polymer chain on the silica surface, the significant dynamics of polymer chains on the surface, and details of the modifications in the structure solvated polymer close to the interface.

Long Range Polymer Chain Dynamics of Highly Flexible Polysiloxane in Solution Probed by Pyrene Excimer Fluorescence.

A poly(dimethylsiloxane-co-(3-aminopropyl)methylsiloxane) polymer (PDMS with 20.3 mol % of (3-aminopropyl)methyl siloxane monomer) has been labeled randomly with 1-pyreneacetyl groups to generate a series of polysiloxanes (Py-PDMS) with pyrenyl contents ranging from 0.7 mol % to 5.2 mol % of the total number of structural units. The remainder of the amino groups were acetylated to avoid intra-chain quenching of the excited singlet states of pyrene via exciplex formation with free amino groups while allowing the formation of excimers to proceed. The fluorescence spectra and temporal decays of the Py-PDMS samples were acquired in tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and dioxane. <kMF>blob, the average rate constant for intra-chain pyrene excimer formation, was determined from the analysis of the fluorescence decays. <kMF>blob was found to equal 1.16 (±0.13) × 109, 1.14 (±0.12) × 109, and 0.99 (±0.10) × 109 s−1 in THF, DMF, and dioxane, respectively, at room temperature. They are the largest values found to date for any polymeric backbone in these solvents. The qualitative relationship found here between <kMF>blob and the chemical structures of the polymers indicates that the luminescence characteristics of randomly labeled polymers is a very useful method to probe the long range dynamics of chains of almost any polymer that is amenable to substitution by a lumophore.

Cooperative rearranging region and dynamical heterogeneity of nanocomposites in poly(l-lactide) and functionalized carbon nanotubes systems

The study of the cooperative rearranging region and the rheological behavior was undertaken to evaluate the dynamics of nanocomposites constituted by chain extended poly(L-lactide) (PLLA) and multiwalled carbon nanotubes (MWCNTs). Temperature modulated differential scanning calorimetry (TMDSC) and melt rheology were specifically employed to study the dynamics of polymer chains in amorphous solid state and liquid state, respectively. Results indicated that addition of functionalized MWCNTs increased chain rigidity leading to an increase of the size of cooperativity, although glass transition temperature could remain constant. Rheological measurements demonstrate significant variation of the modulus and viscosity of nanocomposites. Similar to Cole-Cole plot and semi-circle equation in dielectric measurements, an equation is presented to recognize the amount of heterogeneity in nanocomposite systems according to rheological data. Overall results indicate that the dynamical heterogeneity of PLLA was clearly changed by both factors: polymer chain extension and MWCNT functionalization.

Active learning of constitutive relation from mesoscopic dynamics for macroscopic modeling of non-Newtonian flows

We simulate complex fluids by means of an on-the-fly coupling of the bulk rheology to the underlying microstructure dynamics. In particular, a continuum model of polymeric fluids is constructed without a pre-specified constitutive relation, but instead it is actively learned from mesoscopic simulations where the dynamics of polymer chains is explicitly computed. To couple the bulk rheology of polymeric fluids and the microscale dynamics of polymer chains, the continuum approach (based on the finite volume method) provides the transient flow field as inputs for the (mesoscopic) dissipative particle dynamics (DPD), and in turn DPD returns an effective constitutive relation to close the continuum equations. In this multiscale modeling procedure, we employ an active learning strategy based on Gaussian process regression (GPR) to minimize the number of expensive DPD simulations, where adaptively selected DPD simulations are performed only as necessary. Numerical experiments are carried out for flow past a circular cylinder of a non-Newtonian fluid, modeled at the mesoscopic level by bead-spring chains. The results show that only five DPD simulations are required to achieve an effective closure of the continuum equations at Reynolds number Re=10. Furthermore, when Re is increased to 100, only one additional DPD simulation is required for constructing an extended GPR-informed model closure. Compared to traditional message-passing multiscale approaches, applying an active learning scheme to multiscale modeling of non-Newtonian fluids can significantly increase the computational efficiency. Although the method demonstrated here obtains only a local viscosity from the polymer dynamics, it can be extended to other multiscale models of complex fluids whose macro-rheology is unknown.

Dynamics, Aggregation, and Interfacial Properties of the Partially Hydrolyzed Polyacrylamide Polymer for Enhanced Oil Recovery Applications: Insights from Molecular Dynamics Simulations

We hereby employ molecular dynamics (MD) simulations (∼6 μs in total) to investigate the chain dynamics, aggregation, and interfacial properties of the partially hydrolyzed polyacrylamide (HPAM) polymer. HPAM is widely used in chemical enhanced oil recovery (cEOR) applications. The conformational changes and aggregation properties are examined in different conditions simulating cEOR activities. Also, we examined the degree of polymerization (20-, 50-, and 100 -mers) effect on the polymer chain dynamics and aggregation. MD simulations showed that HPAM has a high conformational diversity ranging from coiled to compact conformations. The former is abundantly found in fresh water. In brine solutions, HPAM is found to be very sensitive to ions and adopts a more compact conformation. HPAM-ion interactions drive the conformational thermodynamic equilibrium between the compact and coiled conformations toward the compact conformation. Furthermore, ion interactions are largely impcating its aggregation. HPAM has a ...

Poly(lactic acid) phase transitions in the presence of nano calcium carbonate: Opposing effect of nanofiller on static and dynamic measurements

The effect of stearic acid-coated nano calcium carbonate (NCC) on transitions and chain mobility of poly(lactic acid) (PLA) was investigated. Dispersion state of NCC in polymeric matrix was explored using scanning electron microscopy and surface tension component measurements. Trends of PLA transitional phenomena were investigated using the results of dynamical mechanical analysis (DMA) and differential scanning calorimetry (DSC) in the nanocomposite systems based on PLA and NCC. In addition, two types of crystal structures and decreasing the glass transition temperature were distinguished using temperature-modulated DSC (TMDSC). Higher melting points of polymer crystals were found in TMDSC experiments due to low and dynamic heating rate compared to the conventional DSC. Dynamics of polymer chains, affected by NCC, were quantified using cooperativity length, ξ α, and the number of relaxing structural units, Nα, in the glass transition region. NCC particles hindered the cooperative motion of polymer chains at glass transitions and crystallization in TMDSC measurements, whereas the DMA results indicated that NCC particles may act as lubricant and simplified chain mobility.

Aggregation States and Dynamics of Polymer Chains at Model Interfaces with Inorganic Fillers

Aggregation States and Dynamics of Polymer Chains at Model Interfaces with Inorganic Fillers

Interaction of spin-labeled HPMA-based nanoparticles with human blood plasma proteins - the introduction of protein-corona-free polymer nanomedicine.

In this paper, we revised the current understanding of the protein corona that is created on the surface of nanoparticles in blood plasma after an intravenous injection. We have focused on nanoparticles that have a proven therapeutic outcome. These nanoparticles are based on two types of biocompatible amphiphilic copolymers based on N-(2-hydroxypropyl)methacrylamide (HPMA): a block copolymer, poly(ε-caprolactone) (PCL)-b-poly(HPMA), and a statistical HPMA copolymer bearing cholesterol moieties, which have been tested both in vitro and in vivo. We studied the interaction of nanoparticles with blood plasma and selected blood plasma proteins by electron paramagnetic resonance (EPR), isothermal titration calorimetry, dynamic light scattering, and cryo-transmission electron microscopy. The copolymers were labeled with TEMPO radicals at the end of hydrophobic PCL or along the hydrophilic HPMA chains to monitor changes in polymer chain dynamics caused by protein adsorption. By EPR and other methods, we were able to probe specific interactions between nanoparticles and blood proteins, specifically low- and high-density lipoproteins, immunoglobulin G, human serum albumin (HSA), and human plasma. It was found that individual proteins and plasma have very low binding affinity to nanoparticles. We observed no hard corona around HPMA-based nanoparticles; with the exception of HSA the proteins showed no detectable binding to the nanoparticles. Our study confirms that a classical "hard corona-soft corona" paradigm is not valid for all types of nanoparticles and each system has a unique protein corona that is determined by the nature of the NP material.

Monte Carlo simulation on the dynamics of a semi-flexible polymer in the presence of nanoparticles.

The dynamics of a semi-flexible polymer chain in the presence of periodically distributed nanoparticles is simulated by using off-lattice Monte Carlo simulations. For repulsive or weak attractive nanoparticles, the dynamics are slowed down monotonically by increasing the chain stiffness kθ or decreasing the inter-particle distance d. For strong attractive nanoparticles, however, the dynamics show nonmonotonic behaviors with kθ and d. An interesting result is that a stiff polymer may move faster than a flexible one. The underlying mechanism is that the nanoparticle's attraction is weakened by the chain stiffness. The nonmonotonic behavior of the polymer's dynamics with kθ is explained by the competition between the weakening effect of the chain stiffness on the nanoparticle's attraction and the intrinsic effect of chain stiffness which reduces the dynamics of the polymer. In addition, the nonmonotonic behavior of the polymer's dynamics with d is explained by the competition between the nanoparticle-exchange motion of the polymer dominated at small d and the desorption-and-adsorption motion at large d. The excluded volume effect of the nanoparticles plays a more important role for stiffer polymers as the attraction of the nanoparticles is weakened by the chain stiffness.

Inelastic and quasi-elastic neutron scattering. Application to soft-matter

Microscopic dynamical events control many of the physical processes at play in condensed matter: transport, magnetism, catalysis and even function of biological assemblies. Inelastic (INS) and Quasi-Elastic Neutron Scattering (QENS) are irreplaceable probes of these phenomena. These experimental techniques reveal the displacements of atoms and molecules over distances spanning from angstroms to a few tens of nanometers, on time scales ranging from a fraction of picoseconds to microseconds. In this context, the different INS and QENS machines (Time-of-Flight (ToF), Backscattering (BS) and Neutron spin-echo (NSE)) stand at a central position. After introducing an underlying basic theoretical toolbox for neutron scattering, the principles and key elements of a ToF measurement are described. While, here, we mainly focus on disk choppers spectrometers, all the INS/QENS instruments share a common ground: they directly and simultaneously probe correlation functions in both time and space, so that the scattering vector (Q) dependence of the systems characteristic time(s) can be measured. To illustrate, the potentialities of the technique in the field of soft-matter, we show a multiscale approach of the dynamics of a polymer melt. The system is probed from the molecular to the mesoscopic scale (1 ps to 0.6 μs and 0.1 to 40 nm), in bulk and under nanometric confinement. We address the different dynamical modes of a high mass entangled polymer chain: local monomer dynamics, Rouse modes up to the reptation process. This study exemplifies that, used in conjunction with hydrogen/deuterium isotopic effects, high resolution QENS can be bridged to the Zero Average Contrast (ZAC) method to probe, in a non destructive way, the dynamics of a single polymer chain in bulk but also under severe nanometric confinement. Connection and complementarity of the neutron derived analysis with Pulsed-Field Gradient and Relaxation NMR techniques are discussed.

Investigation of dielectric properties of free standing electrospun nonwoven mat

ABSTRACTFlexible materials with balanced dielectric as well as conductive characteristics have elucidated considerable demand in field of research where conventional dielectric or insulators can be replaced by recent advances in various electronics appliances. Our work describes the detailed analyses of dielectric properties like dielectric constant, losses, and electric modulus by means of broadband dielectric spectroscopy over frequency ranging from 0.1 Hz to 10 MHz and temperature ranging from 0 to 60 °C for poly(vinyl alcohol)‐polyaniline (PVA‐PANI) free standing electrospinning nonwoven mat. It has been contemplated that the dielectric constant was enhanced by increasing PANI concentration for complete range of frequency at room temperature. The enhanced dielectric constant value (5.14 at 0.1 Hz, 2.66 at 1 KHz, 2.58 at 10 KHz, and 2.19 at 10 MHz) was anticipated for 7 wt % loading of PANI which was attributed to the presence of dipoles and interfacial polarization enclosed by the polymers. The increased dielectric constant with PANI dosing as well as with temperature attributed to favorable interfacial polarization. Shifting of peak is noticed in the spectra of imaginary electric modulus with increase in temperature which indicates increased chain dynamics of polymers in the mat. Three‐dimensional analysis of the field emission scanning electron microscopy images was carried out by SPIP analytical software. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46121.

Reorientation Kinetics of Local Conformation of Polyisoprene at Substrate Interface.

The performance of a polymer composite material, in which inorganic fillers are dispersed, is closely related to the aggregation states and dynamics of polymer chains at the interface with the filler. In this study, the local conformation of polyisoprene (PI) at a quartz substrate interface was studied as a model system for the rubber/filler composite material. PI films were prepared from a toluene solution onto quartz substrates by a spin-coating method. Sum-frequency generation spectroscopy revealed that the local conformation of PI chains at the quartz interface depended on the spinning rate. The tilt angle of methyl groups increased with the rotational speed, probably due to the centrifugal force applied to chains and probably also the evaporation rate of the solvent during the solidification process. This result indicates that the interfacial orientation of PI chains can remain even at room temperature, which is 87 K higher than the bulk glass transition temperature (Tgb). The interfacial orientation disappeared at a temperature approximately 120 K higher than Tgb.

Effects of internal friction on contact formation dynamics of polymer chain

ABSTRACTA theoretical framework is presented to study the contact formation dynamics of polymer chains, in accompany with an electron-transfer quenching. Based on a non-Markovian Smoluchowski equation supplemented with an exponential sink term, we derive the mean time of contact formation under Wilemski–Fixman approximation. Our particular attentions are paid to the effect of internal friction. We find out that internal friction induces a novel fractional viscosity dependence, which will become more remarkable as internal friction increases. Furthermore, we clarify that internal friction inevitably promotes a diffusion-controlled mechanism by slowing the chain relaxation. Finally, we apply our theory to rationalise the experimental investigation for contact formation of a single-stranded DNA. The theoretical results can reproduce the experimental data very well with quite reasonable estimation for the intrinsic parameters. Such good agreements clearly demonstrate the validity of our theory which has appropriately addressed the very role of internal friction to the relevant dynamics.

Spectroscopic Techniques for the Characterization of Polymer Nanocomposites: A Review.

Due to the growing interest in nanocomposites, a molecular characterization of these materials is essential for the understanding of their properties and for the development of new materials. Spectroscopic techniques that bring information at a molecular level are unavoidable when characterizing polymers, fillers and composites. Selected examples of the application of fluorescence, solid-state nuclear magnetic resonance (NMR), infrared and Raman spectroscopies, illustrate the potential of these techniques for the analysis of the filler surface, the evaluation of the state of filler dispersion in the host matrix, the extent of interaction between the polymer and the filler particles or the dynamics of polymer chains at the polymer–filler interface.

Modeling the dynamics of polymer chains in water solution. Application to sensor design

This paper is devoted to a mathematical model of a chaotic dynamics of a polymer chain in water. The model consists of a parabolic equation that is derived according to the self-consistent field approach. This model is employed for the numerical simulation of a biological sensor that detects the presence of a specific protein in the fluid. The sensor is absolutely simple and seems to be new. Besides that, the suggested equation is interesting from the mathematical point of view. It includes a non-local operator of integration not only over the past time interval as in the problems with memory but also over the future time interval. It is unusual for parabolic problems.

Possible Dynamics of Polymer Chains by Means of a Ricatti s Procedure - an Exploitation for Drug Release at Large Time Intervals

In this paper, we propose an analyzis method for the dynamics of polymer chains, based on a Ricatti procedure induced by possible correlations through the compatibility of the thermal radiation-classical damped oscillator dynamics. Then, the quantification (radiation frecquency is directly proportional to the color temperature) and the erasure of one bit of information becomes a natural processes induced by the system structure itself. The theory has implications in the dynamics of biological structures (arhitecture of tumors, information on tumor growth and angiogenesis, etc.) in the form of Resonant Recognition Model.

The influence of temperature and density on the microscopic structure and dynamics of long polymer chains: Molecular dynamics and dissipative particle dynamics modeling

Long polymer chains that mainly exhibit thermoplastic properties are recognized to demonstrate excellent thermal and mechanical features at the molecular level. For the purpose of facilitating its study, we present the results of a coarse-grained Molecular Dynamics (MD) and Dissipative Particle Dynamics (DPD) simulations under the Canonical ensemble (NVT) conditions. For each simulation method, the structure, static and dynamic properties were analyzed, with particular emphasis on the influence of density and temperature on the equilibrium of the polymer. We find, after correcting the Soft Repulsive Potential (SRP) parameters used in DPD method, that both simulation methods describe the polymer physics with the same accuracy. This proves that the DPD method can simplify the polymer simulation and can reproduce with the same precision the equilibrium obtained in the MD simulation.

Matrix tacticity controlled tuning of microstructure, constitutive behavior and rheological percolation effect of melt‐mixed amino‐functionalized MWCNT/PP nanocomposites

Amino‐functionalized multi walled nanotube (MWCNT‐NH2) filled isotactic PP and isotactic‐syndiotactic (70:30) mixed PP based melt‐mixed nanocomposites have been comparatively evaluated with regard to morphological, rheological and thermo‐mechanical properties. The ratio of mean free space lengths (Lf) to infiltrated mean free space lengths (Linf) between nanotubes in isotactic‐syndiotactic (70:30) blended matrix based nanocomposites increased relatively indicating a dispersed‐morphology. The rheological percolation threshold increased up to a higher extent of MWCNT‐NH2 loading (from øc ∼ 2.3 × 10−4 in isotactic to øc ∼ 11 × 10−4 in iso‐syndio blend) accompanied with the formation of a mechanically responsive network structure. van‐GurpPalmen plot showed a transition in the rheological response as a consequence of network morphology getting shifted to higher concentration of MWCNT‐NH2 in the isotactic‐syndiotactic mixed PP based nanocomposites than in the isotactic based one. Constitutive modeling of complex viscosity response of the nanocomposites led to functional correlation between the percolation and relaxation dynamics of polymer chains. POLYM. ENG. SCI., 58:1115–1126, 2018. © 2017 Society of Plastics Engineers