Dynamics of Unentangled <i>cis</i>-1,4-Polyisoprene Confined to Nanoporous Alumina

Alexandris, Stelios; Σακελλαρίου, Γεώργιος; Steinhart, Martin; Floudas, George

doi:10.1021/ma5006638

Cited by 67 publications

(127 citation statements)

References 46 publications

Supporting

Mentioning

116

Contrasting

Unclassified

Order By: Relevance

“…All these effects are similar to results reported for PNCs. [17][18][19][20][21] The inset of Fig.3 shows the temperature dependence of the alpha relaxation time estimated from the peak position of the loss spectra ω peak (τ α = 1/(ω peak )). Good agreement between our measurements and literature data 55 indicate our samples are free of solvent from sample preparations.…”

Section: Resultsmentioning

confidence: 99%

Revealing spatially heterogeneous relaxation in a model nanocomposite

Cheng

Mirigian

Carrillo

et al. 2015

The Journal of Chemical Physics

View full text Add to dashboard Cite

The detailed nature of spatially heterogeneous dynamics of glycerol-silica nanocomposites is unraveled by combining dielectric spectroscopy with atomistic simulation and statistical mechanical theory. Analysis of the spatial mobility gradient shows no 'glassy' layer, but the α-relaxation time near the nanoparticle grows with cooling faster than the relaxation time in the bulk, and is ~20 times longer at low temperatures. The interfacial layer thickness increases from ~1.8 nm at higher temperatures to ~3.5 nm upon cooling to near T g . A real space microscopic description of the mobility gradient is constructed by synergistically combining high temperature atomistic simulation with theory. Our analysis suggests that the interfacial slowing down arises mainly due to an increase of the local cage scale barrier for activated hopping induced by enhanced packing and densification near the nanoparticle surface. The theory is employed to predict how local surface densification can be manipulated to control layer dynamics and shear rigidity over a wide temperature range.

show abstract

Section: Resultsmentioning

confidence: 99%

Revealing spatially heterogeneous relaxation in a model nanocomposite

Cheng

Mirigian

Carrillo

et al. 2015

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…The characteristic time τ for the slow process was found to exhibit a very strong dependence on molecular weight, τ ∼ M w 5.7 , which could be eliminated by coating the CPG (controlled porous glass) with a silane that prevented adsorption. Floudas et al 44 also reported broadened normal and segmental mode spectra from dielectric loss data of unentangled PI confined in nanoporous alumina. On the basis of these observations, the authors argued that confinement of even unentangled chains produces a broader distribution of relaxation events than in their unconfined and unentangled analogues.…”

Section: ■ Introductionmentioning

confidence: 94%

Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains

2015

View full text Add to dashboard Cite

Relaxation dynamics of nanoparticle-tethered cis-1,4-polyisoprene (PI) are investigated using dielectric spectroscopy and rheometry. A model system composed of polymer chains densely grafted to spherical SiO 2 nanoparticles to form self-suspended suspensions facilitates detailed studies of slow global chain and fast segmental mode dynamics under surface and geometrical confinementfrom experiments performed in bulk materials. We report that unentangled polymer molecules tethered to nanoparticles relax far more slowly than their tethered entangled counterparts. Specifically, at fixed grafting density we find, counterintuitively, that increasing the tethered polymer molecular weight up to values close to the entanglement molecular weight speeds up chain relaxation dynamics. Decreasing the polymer grafting density for a fixed molecular weight has the opposite effect: it dramatically slows down chain relaxation, increases interchain coupling, and leads to a transition in rheological response from simple fluid behavior to viscoelastic fluid behavior for tethered PI chains that are unentangled by conventional measures. Increasing the measurement temperature produces an even stronger elastic response and speeds up molecular relaxation at a rate that decreases with grafting density and molecular weight. These observations are discussed in terms of chain confinement driven by crowding between particles and by the existence of an entropic attractive force produced by the space-filling constraint on individual chains in a self-suspended material. Our results indicate that the entropic force between densely grafted polymer molecules couples motions of individual chains in an analogous manner to reversible cross-links in associating polymers. ■ INTRODUCTIONUnderstanding the behaviors of macromolecules tethered to rigid supports/fillers is a longstanding challenge in soft matter science. Movement of short, unentangled linear polymer chains tethered to a support can normally be described using models for Brownian motion of beads linked by harmonic springs, such as that proposed by Rouse, 1−3 with the added constraint that the bead tethered to the support cannot move. When the molecular weights of the tethered chains become long enough to allow individual molecules to entangle, reptation and armretraction dynamics 4−10 are expected to be overlaid with those associated with surface attachment. 11 Model polymers with long-chain branches, such as stars, H-polymers, combs, and pompoms, exhibit aspects of these dynamics, and the concepts of arm retraction, hierarchical relaxation, and branch point diffusion play crucial roles in understanding their overall rheological properties. 12−15 Dynamics of entangled polymers in a variety of branched architectures have been studied with diverse approaches, including NMR, 16−18 neutron scattering, 19−21 rheology, 16,18−22 dielectric spectroscopy, 18−21 and others. Among these techniques, dielectric spectroscopy is advantageous because a material can be interrogated in an undeformed state wi...

show abstract

“…For polymeric fluids, the polymer chains near the inner wall can be strongly adsorbed. There exist experimental evidences for that from dielectric spectroscopy measurements for polymers confined to nanoporous alumina . These immobile chains create a “dead zone” of thickness Δ R .…”

Section: Theoretical Considerationsmentioning

confidence: 99%

Theory on Capillary Filling of Polymer Melts in Nanopores

Yao

Butt

Floudas

et al. 2018

Macromol. Rapid Commun.

Self Cite

View full text Add to dashboard Cite

A unified theory for the imbibition dynamics of entangled polymer melting into nanopores is presented. Experiments demonstrate the validity of t dependence but contradict the predictions of the classical Lucas-Washburn equation because of the prefactor. A reversal in dynamics of capillary filling is reported with increasing polymer molecular weight. Polymer imbibition under nanometer confinement can be discussed by two mechanisms: one is the standard hydrodynamic flow, resulting in a parabolic flow profile. When the inner wall has a strong attraction to the polymer, a layer of immobile chains is created, resulting in an increase of the effective viscosity and to slower imbibition. The other is the reptation model proposed by Johner et al., leading to a plug flow profile and to the reduction in the effective viscosity (faster imbibition). The reversal in dynamics of polymer imbibition can be explained by the competition between these two mechanisms.

show abstract

Dynamics of Unentangled cis-1,4-Polyisoprene Confined to Nanoporous Alumina

Cited by 67 publications

References 46 publications

Revealing spatially heterogeneous relaxation in a model nanocomposite

Revealing spatially heterogeneous relaxation in a model nanocomposite

Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains

Theory on Capillary Filling of Polymer Melts in Nanopores

Contact Info

Product

Resources

About