The relationship between dynamic and pseudo-thermodynamic measures of the glass transition temperature in nanostructured materials

Mangalara, Jayachandra Hari; Mackura, Mark E.; Marvin, Michael D.; Simmons, David

doi:10.1063/1.4977520

Cited by 44 publications

(41 citation statements)

References 90 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The nanoconfinement effect has a strong influence on the T g . Inspired by the pioneering work of Jackson and McKenna on the T g depression for the organic liquids confined in nanopores, the T g of polymers in the nanometer scales has received significant interest . The T g of thin films, defined by a simple nanoconfined physical model, has been characterized by different types of measurements, including dynamic, thermodynamic, and pseudothermodynamic (see subsequently for the definitions).…”

Section: Glass Transition For Polymersmentioning

confidence: 99%

Glass Transition Phenomenon for Conjugated Polymers

Qian

Cao

Galuska

et al. 2019

Macro Chemistry & Physics

View full text Add to dashboard Cite

Conjugated polymers are emerging as promising building blocks for a broad range of modern applications including skin‐like electronics, wearable optoelectronics, and sensory technologies. In the past three decades, the optical and electronic properties of conjugated polymers have been extensively studied, while their thermomechanical properties, especially the glass transition phenomenon which fundamentally represents the polymer chain dynamics, have received much less attention. Currently, there is a lack of design rules that underpin the glass transition temperature of these semirigid conjugated polymers, putting a constraint on the rational polymer design for flexible stretchable devices and stable polymer glass that is needed for the devices’ long‐term morphology stability. In this review article, the glass transition phenomenon for polymers, glass transition theories, and characterization techniques are first discussed. Then previous studies on the glass transition phenomenon of conjugated polymers are reviewed and a few empirical design rules are proposed to fine‐tune the glass transition temperature for conjugated polymers. The review paper is finished with perspectives on future directions on studying the glass transition phenomena of conjugated polymers. The goal of this perspective is to draw attention to challenges and opportunities of controlling, predicting, and designing polymeric semiconductors, specifically to accommodate their end use.

show abstract

Section: Glass Transition For Polymersmentioning

confidence: 99%

Glass Transition Phenomenon for Conjugated Polymers

Qian

Cao

Galuska

et al. 2019

Macro Chemistry & Physics

View full text Add to dashboard Cite

show abstract

“…Such behavior might seem counterintuitive. It is partially a consequence of the ensemble averaging in the time [56] or frequency domain being generically weighted towards the slower relaxing regions of the film. But, even more crucially, our above mathematical analysis shows this result is intimately connected with the double exponential form of the alpha time gradient.…”

Section: Practical Layer-averaged Time Scalementioning

confidence: 99%

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Phan

Schweizer

2019

Macromolecules

View full text Add to dashboard Cite

Based on the Elastically Collective Nonlinear Langevin Equation (ECNLE) theory of bulk relaxation in glass-forming liquids, and our recent ideas of how interface-nucleated modification of caging constraints are spatially transferred into the interior of a thick film, we present a force-based theory for dynamical gradients in thick films with one vapor interface that includes collective elasticity effects. Quantitative applications to the foundational hard sphere fluid and polymer melts of diverse fragilities are presented. We predict a roughly exponential spatial variation of the total activation barrier which is non-perturbatively modified to ∼ 10 particle diameters into the film. This leads, to leading order, to the prediction of a reduced alpha relaxation time gradient of a double exponential form characterized by a nearly constant spatial decay length, in qualitative accord with simulations. The relaxation acceleration at the surface grows exponentially with increasing packing fraction or decreasing temperature. The rate of increase with cooling of the alpha time strongly weakens upon approaching the vapor interface, with the top two layers remaining liquid-like down to ∼ 80 − 85% of the bulk glass transition temperature. These spatially heterogeneous changes of the temperature variation of the alpha time result in a large and long range gradient of the local glass transition temperature. An average interfacial layer thickness relevant to ensemble-averaged dielectric and other experiments is also computed. It is predicted to be rather large at the bulk glass transition temperature, decreasing roughly linearly with heating. Remarkably, to leading order the ratio of this layer-averaged interfacial relaxation time to its bulk analog is, to leading order, invariant to chemistry, volume fraction and temperature and of modest absolute magnitude. Spatially inhomogeneous power law decoupling of the alpha relaxation time from its bulk value is predicted, with an effective exponent that decays to zero with distance from the free surface in a nearly exponential manner, trends which are in qualitative accord with recent simulations. This behavior and the double exponential alpha time gradient are related, and can be viewed as consequences of an effective quasi-universal factorization of the total barrier in films into the product of its bulk temperature dependent value times a function solely of location in the film.

show abstract

“…Experimentally from dielectric spectroscopy, there is an overall broadening of the relaxation times, which leads to some longer and shorter relaxation times in comparison to the bulk polymer . This broadening of the distribution increases the sensitivity of the reported values from a measurement to how this distribution is averaged and has been demonstrated used simulations to dramatically impact conclusions if the averaging is not well understood . Recently, we have reported on the strong weighting of slow motions with incoherent neutron scattering (INS) that can explain the commonly reported reduced dynamics from INS .…”

Section: Discussionmentioning

confidence: 99%

“…A majority of the work examining confined polymers has focused on glasses of homopolymers, but copolymers and semi‐crystalline polymers are commonly more technologically relevant. The thin film behavior of glassy polymers is strongly influenced by the increased heterogeneity in comparison to the bulk polymer . Heterogeneity is an important component to the mechanical performance of a wide range of polymers including urethanes and semi‐crystalline polymers like polyethylene.…”

Section: Discussionmentioning

confidence: 99%

“…Three key concepts from the wealth of literature examining thin polymer films are (1) free surfaces tend to lead to a decrease in the T g with a greater decrease in T g for free standing than supported films, (2) strong interactions between the polymer and substrate can lead to increases in T g , and (3) the extent of the change in T g in the thin films reported depends on the measurement used . To explain the latter, one must consider that the thin film properties are heterogeneous with gradients in T g from the interfaces; how each measurement technique averages this distribution will change the reported T g . With the complex heterogeneity in the dynamics as determined from T g , the impact of confinement on mechanical properties is challenging to predict and thus direct measurements are necessary.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanical and viscoelastic properties of confined amorphous polymers

Vogt

2017

J Polym Sci B Polym Phys

View full text Add to dashboard Cite

Confinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (T g ) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. 1,2 These concerns persist for polymeric nanostructures, where mechanical properties are critical to feature stability. 3 The mechanical properties of many polymers are dependent on their processing history,

show abstract

The relationship between dynamic and pseudo-thermodynamic measures of the glass transition temperature in nanostructured materials

Cited by 44 publications

References 90 publications

Glass Transition Phenomenon for Conjugated Polymers

Glass Transition Phenomenon for Conjugated Polymers

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Mechanical and viscoelastic properties of confined amorphous polymers

Contact Info

Product

Resources

About