Adsorption-desorption kinetics in nanoscopically confined oligomer films under shear

Manias, Evangelos; Субботин, А. А.; Hadziioannou, Georges; Brinke, G. ten

doi:10.1080/00268979500101621

Cited by 33 publications

(49 citation statements)

References 30 publications

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“…In these more recent studies, it was found that the effective diffusion coefficient depends markedly on the surfactant used, for the same polymer and annealing temperature. Because the surfactant can only affect the polymer motion inside the galleries, one concludes that this motion of the intercalated polymer is the process which dictates the intercalation kinetics [33]. Furthermore, for some systems the intercalating polymers were found to possess a mobility that was much faster than the self-diffusion coefficient of the corresponding polymer in the bulk [31], or in a thin film [34].…”

Section: Kinetics Of Polymer Melt Intercalationmentioning

confidence: 98%

Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes

Giannelis

Krishnamoorti

Manias

1999

Advances in Polymer Science

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1,123

789

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The static and dynamic properties of polymer-layered silicate nanocomposites are discussed, in the context of polymers in confined spaces and polymer brushes. A wide range of experimental techniques as applied to these systems are reviewed, and the salient results from these are compared with a mean field thermodynamic model and non-equilibrium molecular dynamics simulations. Despite the topological constraints imposed by the host lattice, mass transport of the polymer, when entering the galleries defined by adjacent silicate layers, is quite rapid and the polymer chains exhibit mobilities similar to or faster than polymer self-diffusion. However, both the local and global dynamics of the polymer in these nanoscopically confined galleries are dramatically different from those in the bulk. On a local scale, intercalated polymers exhibit simultaneously a fast and a slow mode of relaxation for a wide range of temperatures, with a marked suppression (or even absence) of cooperative dynamics typically associated with the glass transition. On a global scale, relaxation of polymer chains either tethered to or in close proximity (<1nm as in intercalated hybrids) to the host surface are also dramatically altered. In the case of the tethered polymer nanocomposites, similarities are drawn to the dynamics of other intrinsically anisotropic fluids such as ordered block copolymers and smectic liquid crystals. Further, new non-linear viscoelastic phenomena associated with melt-brushes are reported and provide complementary information to those obtained for solution-brushes studied using the Surface Forces Apparatus.

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Section: Kinetics Of Polymer Melt Intercalationmentioning

confidence: 98%

Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes

Giannelis

Krishnamoorti

Manias

1999

Advances in Polymer Science

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1,123

789

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“…Moreover, they exhibit shear thinning for very moderate shear rates and the onset of this non-Newtonian behaviour shifts to lower shear rates in narrower confinements [6], [7]. Molecular-Dynamics (MD) computer simulations have proven to be effective in interpreting this counter-intuitive behaviour of nanoscopically confined films [11]- [15] and unvealed the origin of the "glassy" dynamics in ultra-thin confinements [11], [12].…”

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confidence: 99%

“…Our previous studies [12]- [14] revealed a strong tendency of the adsorbed chains to align and stretch against the confining surface for the shear rates employed. This behaviour clearly is a major contribution to the shear thinning observed [22].…”

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confidence: 99%

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On the nature of shear thinning in nanoscopically confined films

Manias¹,

Bitsanis²,

Hadziioannou³

et al. 1996

Europhys. Lett.

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PACS. 68.15+e -Liquid thin films. PACS. 66.20+d -Diffusive momentum transport (including viscosity of liquids). PACS. 83.10Ji -Fluid dynamics (nonlinear fluids).Abstract. -Non-Equilibrium Molecular Dynamics (NEMD) computer simulations were employed to study films in nanometer confinements under shear. Focusing on the response of the viscosity, we found that nearly all the shear thinning takes place inside the solid-oligomer interface and that the adsorbed layers are more viscous than the middle part of the films. Moreover, the shear thinning inside the interfacial area is determined by the wall affinity and is largely insensitive to changes of the film thickness and the molecular architecture. The rheological response of the whole film is the weighted average of these two regions -"viscous" interfacial layer and bulk-like middle part-resulting in an absence of a universal response in the shear thinning regime, in agreement with recent SFA experiments of fluid lubricants.

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“…23 In addition, molecular dynamics simulations of oligomers in confined geometries under shear also show enhanced desorption/adsorption kinetics from attractive surfaces. 25,26 The large shear stresses at the silicon surface can account for the enhanced desorption/adsorption kinetics, but several details of the observed enhancement in the kinetics are not fully resolvable. For example, the enhanced desorption/adsorption kinetics do not clearly indicate that wall slip is occurring in this system.…”

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confidence: 99%

Enhanced Polymer Segment Exchange Kinetics Due to an Applied Shear Field

et al. 1999

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Introduction. Fundamental knowledge about the behavior of polymer melts near solid surfaces is important to many technologies such as electronics packaging, adhesion, coatings, and polymer processing. When polymers are placed under flow, surface effects can be critical in widely used polymer processing methods such as die extrusion and injection molding. Changes in the extrusion die material can suppress or induce instabilities that lead to unsatisfactory products. 1 These results show that the short-ranged interactions between the polymer and the substrate (coupled with the general viscoelastic properties of polymers) have macroscopic impacts. These processing instabilities have been correlated with "wall slip" at the polymer/solid interface where the apparent fluid velocity near the solid surface is no longer zero. Much work has been performed to determine the important physical parameters for wall slip and to understand the underlying mechanisms of the behavior of polymers at solid boundaries with the goal of better designing processing routes. [2][3][4][5][6][7][8][9][10][11][12] However, the effect of flow on the microscopic behavior of polymer chains directly at a solid surface is not well understood. Few experimental data are available for the behavior of polymer melt chains at the solid interface because of the inherent difficulty of distinguishing between surfacebound chains and the melt matrix. [13][14][15] In this communication, neutron reflectometry was used to study the effect of a shear deformation on the adsorption/desorption kinetics of an entangled polymer melt at an attractive solid substrate. The high spatial resolution of neutron reflectivity, O (Å), provides information directly at the polymer/solid interface. A labeled (deuterated) polymer layer was formed at the surface of a silicon wafer and was welded with a hydrogenated polymer matrix. The fraction of deuterated polymer segments at the silicon surface was monitored with different annealing times with no applied shear and with varying shear rates after a set annealing time. Increases in the shear rate resulted in an increased rate of desorption of the surface-bound polymer chains (or adsorption of the matrix polymers). To the best of our knowledge, this shear-induced adsorption/desorption of an entangled polymer melt at an attractive solid surface was directly observed for the first time. These results provide important experimental evidence of molecular mechanisms which should be incorporated into future models of flow effects on polymer dynamics at surfaces.

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Adsorption-desorption kinetics in nanoscopically confined oligomer films under shear

Cited by 33 publications

References 30 publications

Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes

Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes

On the nature of shear thinning in nanoscopically confined films

Enhanced Polymer Segment Exchange Kinetics Due to an Applied Shear Field

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