Effects of nanoscopic-confinement on polymer dynamics (original) (raw)
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Polymer chain dynamics under nanoscopic confinements
Magnetic Resonance Imaging, 2005
It is shown that the confinement of polymer melts in nanopores leads to chain dynamics dramatically different from bulk behavior. This so-called corset effect occurs both above and below the critical molecular mass and induces the dynamic features predicted for reptation. A spinodal demixing technique was employed for the preparation of linear poly(ethylene oxide) (PEO) confined to nanoscopic strands that are in turn embedded in a quasi-solid and impenetrable methacrylate matrix. Both the molecular weight of the PEO and the mean diameter of the strands were varied to a certain degree. The chain dynamics of the PEO in the molten state was examined with the aid of field-gradient NMR diffusometry (time scale, 10 À2-10 0 s) and field-cycling NMR relaxometry (time scale, 10 À9-10 À4 s). The dominating mechanism for translational displacements probed in the nanoscopic strands by either technique is shown to be reptation. On the time scale of spin-lattice relaxation time measurements, the frequency dependence signature of reptation (i.e., T 1~m 3/4) showed up in all samples. A btubeQ diameter of only 0.6 nm was concluded to be effective on this time scale even when the strand diameter was larger than the radius of gyration of the PEO random coils. This corset effect is traced back to the lack of the local fluctuation capacity of the free volume in nanoscopic confinements. The confinement dimension is estimated at which the crossover from confined to bulk chain dynamics is expected.
Entropic attraction: Polymer compaction and expansion induced by nano-particles in confinement
The Journal of chemical physics, 2015
We investigated nanoparticle (NP)-induced coil-to-globule transition of a semi-flexible polymer in a confined suspension of ideal NP using Langevin dynamics. DNA molecules are often found to be highly compact, bound with oppositely charged proteins in a crowded environment within cells and viruses. Recent studies found that high concentration of electrostatically neutral NP also condenses DNA due to entropically induced depletion attraction between DNA segments. Langevin dynamics simulations with a semi-flexible chain under strong confinement were performed to investigate the competition between NP-induced monomer-monomer and monomer-wall attraction under different confinement heights and NP volume fractions. We found that whether NP induce polymer segments to adsorb to the walls and swell or to attract one another and compact strongly depends on the relative strength of the monomer-wall and the NP-wall interactions.
Nanoscopic-Confinement Effects on Local Dynamics
Physical Review Letters, 2000
The segmental dynamics of 1.5-2.0 nm polymer films confined between parallel solid surfaces is investigated with dielectric spectroscopy in polymer͞silicate intercalated nanocomposites. The confinement effect is evident by the observation of a mode, much faster than the bulk-polymer a relaxation and exhibiting much weaker temperature dependence. This is discussed in relation to either the interlayer spacing restricting the cooperative volume of the a relaxation or to the dominance of the more mobile interphase regions as predicted by simulations; the data qualitatively support the former.
Large-scale dynamics of a single polymer chain under severe confinement
Physical Review E, 2010
We address the dynamical behavior of a single polymer chain under nanometric confinement. We show how neutron spin-echo, combined with contrast matching and zero average contrast, makes it possible to, all at once, ͑i͒ match the intense porous detrimental elastic small angle neutron scattering contribution to the total intermediate scattering function I͑Q , t͒ and ͑ii͒ measure the Q dependence of the dynamical modes of a single chain under confinement. The method presented here has a general relevance when probing the large scale dynamics of a system of large molecular mass under confinement.
Single polymer confinement in a tube: Correlation between structure and dynamics
The Journal of Chemical Physics, 2009
In this paper, we construct an effective model for the dynamics of an excluded-volume chain under confinement by extending the formalism of Rouse modes. We make specific predictions about the behavior of the modes for a single polymer confined to a tube. The results are tested against Monte Carlo simulations using the bond-fluctuation algorithm which uses a lattice representation of the polymer chain with excluded-volume effects.
Transport of Flexible Molecules in Narrow Confinements
International Journal of Micro-Nano Scale Transport, 2010
Dynamical characteristics of flexible polymer molecules in nanoscopic confinements are primarily dictated by the relative values of the confinement length scales with respect to the polymer persistence length. Depending on whether the channel height is larger [1] or smaller [2] than the polymer persistence length, altogether different polymer dynamics is ensued, as illustrated in the pioneering theoretical studies by de Gennes [1] and Odijk [2]. Rapid advances of nanofabrication and polymer handling, over the last few years, have been able to provide experimental validation to these studies and at the same time have been able to unravel different intriguing physical issues unique to nanoconfinement induced dynamics of polymer molecules. These studies have led to a plethora of new applications ranging from the estimation of structural and mechanical properties of polymer to fabrication of novel, portable diagnostic tool kits. In this review article, we shall revisit different physical and technological issues involved in polymer dynamics in nanoconfinements. First, we shall identify the effect of varying degrees of confinement (de Gennes and Odijk regime [1,2]) on the stretching dynamics and the overall representation of the polymer molecule. Next, we shall discuss the possible physical interaction forces on the polymer molecule introduced by the presence of the confining walls and the resulting effects like formation of wall adjacent depletion layers, asymmetric distribution of polymer mass density from the wall to the channel center line etc. Thirdly, we will highlight the possible effects of a background field (flow field or electric field or a combination of both and they may bear signatures of the involved nanoscopic length scales) on the overall nanoscale polymer dynamics. We will also briefly discuss the technological intricacies involved in the relevant nanofabrication and polymer handling schemes and also the issues governing the polymer dynamics modeling involving such scales. Finally, we shall conclude by indicating the possible directions, anticipated outcomes, and significances of future research in polymer transport and dynamics in nanoscopic confinements.
Hydrodynamic effects on confined polymers
2013
We consider the statics and dynamics of a exible polymer conned between parallel plates both in the presence and absence of hydrodynamic interactions. The hydrodynamic interactions are described at the level of the uctuating, compressible Navier-Stokes equation. We consider two cases: (i) connement for both the solvent and the polymer, and (ii) connement for the polymer only (in a 3D solvent), which is experimentally feasible, for instance, by (optical) trapping. We nd a continuous transition from 2D to 3D dynamic scaling as a function of decreasing degree of connement within the de Gennes and the weak-connement regimes. We demonstrate that, in the presence of hydrodynamics, the polymer's center-of-mass diusion coecient in the direction parallel to the walls scales dierently as a function of the level of connement in cases (i) and (ii). We also nd that in the commonly used Langevin dynamics description, the polymer swells more parallel to the walls than in the presence of hydrodynamics, and the planar diusion coecient shows scaling behavior similar to case (ii) rather than case (i). In addition, we quantify the dierences in the static structure factor of the polymer between cases (i) and (ii), and between case (i) and Langevin dynamics.
Effect of Nanoconfinement on Polymer Chain Dynamics
Macromolecules, 2020
reported a set of interesting results for the viscosity of unentangled polystyrene of two different molecular weights determined from capillary infiltration into a confining matrix of silica nanoparticles. They found that the viscosity and glass transition temperature (T g) increase as the pore size of the matrix decreases, that is, the confinement effect becomes stronger. They attributed the change in viscosity to a change in segmental relaxation, that is, an increase in T g. However, their interpretation did not consider that a changing T g leads to a change in the monomeric friction coefficient and viscosity-molecular weight relations should be compared at constant friction factor, that is, at a constant distance from the glass transition temperature. We reanalyzed the results at constant friction factor under a framework of changing chain dynamics as confinement strength increases rather than being due only to the changing glass transition temperature. Our reanalysis of the data from Hor et al. as well as data from other literature shows that as unentangled polymers become increasingly confined, the chain dynamics change from Rouse-like to those of an entropic barrier regime. For entangled polymers, the chain dynamics change from those of a reptation-like regime to those of an entropic barrier regime.
Equilibrium organization, conformation, and dynamics of two polymers under box-like confinement
2021
Motivated by recent nanofluidics experiments, we use Brownian dynamics and Monte Carlo simulations to study the conformation, organization and dynamics of two polymer chains confined to a single box-like cavity. The polymers are modeled as flexible bead-spring chains, and the box has a square cross-section of side length L and a height that is small enough to compress the polymers in that dimension. For sufficiently large L, the system behaviour approaches that of an isolated polymer in a slit. However, the combined effects of crowding and confinement on the polymer organization, conformation and equilibrium dynamics become significant when where is the transverse radius of gyration for a slit geometry. In this regime, the centre-of-mass probability distribution in the transverse plane exhibits a depletion zone near the centre of the cavity (except at very small L) and a 4-fold symmetry with quasi-discrete positions. Reduction in polymer size with decreasing L arises principally fro...
Model polymer nanocomposites provide an understanding of confinement effects in real nanocomposites
Nature Materials, 2007
Owing to the improvement of properties including conductivity, toughness and permeability, polymer nanocomposites are slated for applications ranging from membranes to fuel cells 1,2. The enhancement of polymer properties by the addition of inorganic nanoparticles is a complex function of interfacial interactions, interfacial area and the distribution of inter-nanofiller distances. The latter two factors depend on nanofiller dispersion, making it difficult to develop a fundamental understanding of their effects on nanocomposite properties. Here, we design model poly(methyl methacrylate)-silica and poly(2-vinyl pyridine)silica nanocomposites consisting of polymer films confined between silica slides. We compare the dependence of the glasstransition temperature (T g) and physical ageing on the interlayer distance in model nanocomposites with the dependence of silica nanoparticle content in real nanocomposites. We show that model nanocomposites provide a simple way to gain insight into the effect of interparticle spacing on T g and to predict the approximate ageing response of real nanocomposites. The effect of nanoscale confinement on T g has been studied in polymers since the mid 1990s 3-15. With ultrathin films, deviations from bulk T g (T g,bulk) as large as 45-50 K in supported films 4,11 and 70 K in free-standing films 5 have been reported. In supported films, the thickness dependence of T g is affected by polymer-substrate interactions 3,4,6-8,12 and the free surface 3,5,10,11,13 , the impact of which increases as the ratio of interfacial area to volume increases. At the free surface, T g is reduced compared with T g,bulk , as revealed by fluorescence measurements 10. This effect propagates into the film 10 , reducing the T g of ultrathin free-standing films and supported films lacking attractive polymer-substrate interactions. Thus, the T g reduction originates with the free-surface effect; as shown recently 10 , nanoconfinement itself only affects the magnitude of the T g gradient within the film. With moderate-to-strong attractive polymer-substrate interactions, for example, hydrogen bonds between oxygen atoms in poly(methyl methacrylate) (PMMA) or nitrogen atoms in poly(2-vinyl pyridine) (P2VP) and hydroxyl groups on silica surfaces, T g increases with decreasing thickness 4,6-9,12. In nanocomposites with well-dispersed nanofiller, T g can exhibit substantial deviations relative to the bulk polymer 16-21 , decreasing when polymer-nanofiller interfaces yield free surfaces 16,21 and increasing when wetted interfaces with attractive interactions result 21. These outcomes in nanocomposites were predicted through simulation 22 before their experimental demonstration 16,21 .