Tuning the Relaxation of Nanopatterned Polymer Films with Polymer-Grafted Nanoparticles: Observation of Entropy–Enthalpy Compensation

Bhadauriya, Sonal; Wang, Xiaoteng; Pitliya, Praveen; Zhang, Jianan; Raghavan, Dharmaraj; Stafford, Christopher M.; Douglas, Jack F.; Karim, Alamgir

doi:10.1021/acs.nanolett.8b02514

Cited by 25 publications

(60 citation statements)

References 53 publications

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“…The activation energy (E a ) increases for networks with larger R, while the entropy of activation (ln(τ 0 )) decreases for larger R. This behavior may be related to differences in the free volume fraction of the BTT and TCDDA moieties and the relative contributions of each to the network free volume with changing R compositions. Similar trends in E a and τ 0 have been observed for the polymer relaxation in nano-patterned polymer films [ 50 ] and polymer thin films [ 51 ]. From the Arrhenius behavior of τ eff , a compensation or isokinetic temperature (T comp ) was determined ( Figure 11 b) to be ~333 K (60 °C), which is below the T g for all R compositions but falls near the cure temperature (25 °C).…”

Section: Resultssupporting

confidence: 77%

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Alam

Allers

Jones

2020

IJMS

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NMR spectroscopy continues to provide important molecular level details of dynamics in different polymer materials, ranging from rubbers to highly crosslinked composites. It has been argued that thermoset polymers containing dynamic and chemical heterogeneities can be fully cured at temperatures well below the final glass transition temperature (Tg). In this paper, we described the use of static solid-state 1H NMR spectroscopy to measure the activation of different chain dynamics as a function of temperature. Near Tg, increasing polymer segmental chain fluctuations lead to dynamic averaging of the local homonuclear proton-proton (1H-1H) dipolar couplings, as reflected in the reduction of the NMR line shape second moment (M2) when motions are faster than the magnitude of the dipolar coupling. In general, for polymer systems, distributions in the dynamic correlation times are commonly expected. To help identify the limitations and pitfalls of M2 analyses, the impact of activation energy or, equivalently, correlation time distributions, on the analysis of 1H NMR M2 temperature variations is explored. It is shown by using normalized reference curves that the distributions in dynamic activation energies can be measured from the M2 temperature behavior. An example of the M2 analysis for a series of thermosetting polymers with systematically varied dynamic heterogeneity is presented and discussed.

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Section: Resultssupporting

confidence: 77%

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Alam

Allers

Jones

2020

IJMS

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“…Such a phenomenology, whose origin is discussed below in Section 3.8, is widely observed in diverse crystalline and glass materials. [110][111][112][113][114][115][116][117][118][119][120][121] In particular, it seems suitable to choose α P T g = 0.16 based on the empirical rule of Boyer and Bondi for polymers, which indicates that α P T g lies in the range 0.016 to 0.19, 122 which implies ∆S A ≈ ∆H A /T g if we take γ M to have a representative value of about 6, a value roughly consistent with our results from the GET and MD simulations below for coarse-grained models of polymer fluids. The product α P T g is also nearly constant in metallic GF materials 123 and α P T m is well-known to be fairly constant in metallic crystalline materials.…”

Section: Thermodynamic Scaling In the Arrhenius Relaxation Regimementioning

confidence: 99%

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Douglas,

2021

Preprint

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Numerous experimental and computational studies have established that most liquids seem to exhibit a remarkable, yet poorly understood, property termed 'thermodynamic scaling' in which the structural relaxation time τ α , and many other dynamic properties, can be expressed in terms of a 'universal' reduced variable, T V γ , where T is the temperature, V is the material volume, and γ is a scaling exponent describing how T and V are linked to each other when either quantity is varied. Here, we show that this scaling relation can be derived by combining the Murnaghan equation of state (EOS) with the generalized entropy theory (GET) of glass formation. In our theory, thermodynamic scaling arises in the non-Arrhenius relaxation regime as a scaling property of the fluid configurational entropy density s c , normalized by its value s * c at the onset temperature T A of glass formation, s c /s * c , so that a constant value of T V γ corresponds to a reduced isoentropic fluid condition. Molecular dynamics simulations on a coarse-grained polymer melt are utilized to confirm that the predicted thermodynamic scaling of τ α by the GET holds both above and below T A and to test whether the extent L of stringlike collective motion, normalized its value L A at T A , also obeys thermodynamic scaling, as required for consistency with thermodynamic scaling. While the predicted thermodynamic scaling of both τ α and L/L A is confirmed by simulation, we find that the isothermal compressibility κ T and the long wavelength limit S(0) of the static structure factor do not exhibit thermodynamic scaling, an observation that would appear to eliminate some proposed models of glass formation emphasizing fluid 'structure' over configurational entropy. It is found, however, that by defining a low temperature hyperuniform reference state, we may define a compressibility relative to this condition, δκ T , a transformed dimensionless variable that exhibits thermodynamic scaling and which can be directly related to s c /s * c . Further, the Murnaghan EOS allows us to interpret γ as a measure of intrinsic anharmonicity of intermolecular interactions that may be directly determined from the pressure derivative of the material bulk modulus. Finally, we show that many phenomenological relationships related to the glass formation and melting of materials can be understood based on the Murnaghan EOS

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“…We have observed the EEC effect to be a significant factor in simulations of polymer systems 107,108,[117][118][119][120][121][122] and experiments of polymer nanocomposites and thin films. 117,123,124 Notably, the magnitude of the EEC effect on relaxation and diffusion can be rather significant, even meriting the term 'astounding'. For example, the prefactor of eq 2 can change by a factor of about 10 47 as the activation energy grows upon approaching the melting temperature from below.…”

Section: Transition State Theorymentioning

confidence: 99%

Polymer Glass Formation: Role of Activation Free Energy, Configurational Entropy, and Collective Motion

Xu,

Douglas,

Sun

2021

Preprint

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We provide a perspective on polymer glass formation, with an emphasis on models in which the fluid entropy and collective particle motion dominate the theoretical description and data analysis. The entropy theory of glass formation has its origins in experimental observations relating to correlations between the fluid entropy and liquid dynamics going back nearly a century ago, and it has entered a new phase in recent years. We first discuss the dynamics of liquids in the high temperature Arrhenius regime, where transition state theory is formally applicable. We then summarize the evolution of the entropy theory from a qualitative framework for organizing and interpreting temperature-dependent viscosity data by Kauzmann to the formulation of a hypothetical 'ideal thermodynamic glass transition' by Gibbs and DiMarzio, followed by seminal measurements linking entropy and relaxation by Bestul and Chang and the Adam-Gibbs (AG) model of glass formation rationalizing the observations of Bestul and Chang. These developments laid the groundwork for the generalized entropy theory (GET), which merges an improved lattice model of polymer thermodynamics accounting for molecular structural details and enabling the analytic calculation of the configurational entropy with the AG model, giving rise to a highly predictive model of the segmental structural relaxation time of polymeric glass-forming liquids. The development of the GET has occurred in parallel with the string model of glass formation in which concrete realizations of the cooperatively rearranging regions are identified and quantified for a wide range of polymeric and other glass-forming materials. The string model has shown that many of the assumptions of AG are well supported by simulations, while others are certainly not, giving rise to an entropy theory of glass formation that is largely in accord with the GET. As the GET and string models continue to be refined, these models progressively grow into a more unified framework, and this Perspective reviews the present status of development of this promising approach to the dynamics of polymeric glass-forming liquids.

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Tuning the Relaxation of Nanopatterned Polymer Films with Polymer-Grafted Nanoparticles: Observation of Entropy–Enthalpy Compensation

Cited by 25 publications

References 53 publications

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Heterogeneous Polymer Dynamics Explored Using Static 1H NMR Spectra

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Polymer Glass Formation: Role of Activation Free Energy, Configurational Entropy, and Collective Motion

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