“Dense diffusion” in colloidal glasses: short-ranged long-time self-diffusion as a mechanistic model for relaxation dynamics

Wang, J. Galen; Li, Qi; Peng, Xiaoguang; McKenna, Gregory B.; Zia, Roseanna N.

doi:10.1039/d0sm00999g

Cited by 10 publications

(7 citation statements)

References 147 publications

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“…The dynamics of the packed particles near the interface was further analyzed using the self-intermediate scattering function (SISF), F S ( q ,Δ t̄ ), to clarify the behavior of densely packed particles. 71,72 The SISF near the interface is defined aswhere N SISF is the number of small particles present within 20 a S from the air–solvent interface. Additionally, q is the wave vector of magnitude q = 2π/ L , where L is the specific length of the observation.…”

Section: Resultsmentioning

confidence: 99%

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Mild stratification in drying films of colloidal mixtures

et al. 2022

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Section: Resultsmentioning

confidence: 99%

“…The dynamics of the packed particles near the interface was further analyzed using the self-intermediate scattering function (SISF), F S (q, D% t), to clarify the behavior of densely packed particles. 71,72 The SISF near the interface is defined as…”

Section: Diffusion Of Particles In the Packed Region (Zone I)mentioning

confidence: 99%

Mild stratification in drying films of colloidal mixtures

et al. 2022

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“…The difficulty of achieving the metastable line evinces a qualitative shift in dynamics, for which we have already found evidence in our prior work: a qualitative change of particle dynamics in quenches deeper than the liquid [24]. This leads to our primary objection to the use of equilibrium liquid-state dynamics in glass theories to predict the behavior of the solid state.…”

Section: Introductionmentioning

confidence: 92%

“…For example, both MCT and ABHT employ a dense form of the Percus-Yevick closure for the radial distribution function (which is formally correct only for the liquid) with no change in the partition function. A discussion of these theories can be found in [24], among others. The glassy phase can thus appear as a metastable line that ostensibly can be followed via a presumably infinitely slow quench, where equilibrium is achieved upon each sequentially small increase in volume fraction.…”

Section: Introductionmentioning

confidence: 99%

Vitrification is a spontaneous non-equilibrium transition driven by osmotic pressure

Wang

Zia

2021

J. Phys.: Condens. Matter

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Persistent dynamics in colloidal glasses suggest the existence of a non-equilibrium driving force for structural relaxation during glassy aging. But the implicit assumption in the literature that colloidal glasses form within the metastable state bypasses the search for a driving force for vitrification and glassy aging and its connection with a metastable state. The natural relation of osmotic pressure to number-density gradients motivates us to investigate the osmotic pressure as this driving force. We use dynamic simulation to quench a polydipserse hard-sphere colloidal liquid into the putative glass region while monitoring structural relaxation and osmotic pressure. Following quenches to various depths in volume fraction φ (where φ RCP ≈ 0.678 for 7% polydispersity), the osmotic pressure overshoots its metastable value, then decreases with age toward the metastable pressure, driving redistribution of coordination number and interparticle voids that smooths structural heterogeneity with age. For quenches to 0.56 ≤ φ ≤ 0.58, accessible post-quench volume redistributes with age, allowing the glass to relax into a strong supercooled liquid and easily reach a metastable state. At higher volume fractions, 0.59 ≤ φ < 0.64, this redistribution encounters a barrier that is subsequently overcome by osmotic pressure, allowing the system to relax toward the metastable state. But for φ ≥ 0.64, the overshoot is small compared to the high metastable pressure; redistribution of volume stops as particles acquire contacts and get stuck, freezing the system far from the metastable state. Overall, the osmotic pressure drives structural rearrangements responsible for both vitrification and glassy age-relaxation. We leverage the connection of osmotic pressure to energy density to put forth the mechanistic view that relaxation of structural heterogeneity in colloidal glasses occurs via individual particle motion driven by osmotic pressure, and is a spontaneous energy minimization process that drives the glass off and back to the metastable state. This connection of energy, pressure, and structure identify the glass transition, 0.63 < φ g ≤ 0.64.

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“…The observed dependence of τ′ β on Σ is consistent with the cage effect widely reported in colloidal glasses in the bulk 75 and at liquid−liquid/(air) interfaces, 29 as well as the cage effect of nanoparticles observed in polymer nanocomposite systems. 76 To test this in a quantitative manner, the phenomenological VFT model that is commonly used to describe the divergent growth of the relaxation time with nanoparticles volume fraction in colloids 77,78 is also applied for our system. The VFT model has an expression as follows i k j j j j j y…”

Section: Interfacial Relaxation Behavior In Jnp-sandwiched Multilayer...mentioning

confidence: 99%

Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

et al. 2023

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Interfacial rheology is crucial in dictating morphology and ultimate properties of particle-stabilized polymer blends, but is challenging to be determined. In this study, a fully polymeric dumbbell-shaped Janus nanoparticle (JNP) of polymethyl methacrylate (PMMA) and polystyrene (PS) spheres with equal sizes (∼80 nm) was prepared and used as an efficient compatibilizer for PMMA/PS blends. The JNPs were preferentially localized at the PMMA/PS interface, thereby reducing the interfacial tension and refining the morphology in both droplet-matrix and co-continuous type blends, whereby a JNP concentration ∼2.5 wt % is sufficient to reach a saturation in droplet size reduction due to compatibilization. Based on the linear viscoelastic moduli and corresponding relaxation spectra (H(τ)*τ) of JNP-compatibilized droplet-matrix blends, besides the droplet shape relaxation time (τF), a longer relaxation time (τβ), typically related to interfacial viscoelasticity, was readily identified. The dependence of τβ on the JNP concentration (W JNPs) was significantly dominated by the droplet size reduction induced by the JNP compatibilization, with τβ decreasing with increasing W JNPs. The viscoelastic properties extracted from τβ typically originate from a combination of gradients in interfacial tension due to the particle redistribution at the droplet interface (Marangoni stresses) and the deviatoric stresses of intrinsic rheological origin. The latter originate from the intrinsic viscoelasticity of the particle-laden interface, which is enhanced by particle jamming and particle–polymer interactions, such as entanglements between chains from the polymeric spheres and those penetrating from the bulk into the spheres. To address the challenge of isolating these contributions, a JNP-sandwiched PMMA/PS multilayer structure was designed to exclude the effect of Marangoni stresses and droplet curvature, thus having no τF but a new relaxation (τ′β), which characterizes the contribution of intrinsic interfacial viscoelasticity. The τ′β was observed to increase with JNP coverage (Σ) following the Vogel–Fulcher–Tammann model that is typically used to describe the divergent behavior of the “cage” effect in classical colloidal glasses. Moreover, a multimode Maxwell model fitting allows to split the interfacial relaxation into the confined diffusion of JNPs within their cage and the entanglements between the JNPs and the bulk.

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“Dense diffusion” in colloidal glasses: short-ranged long-time self-diffusion as a mechanistic model for relaxation dynamics

Abstract:
Despite decades of exploration of the colloidal glass transition, mechanistic explanation of glassy relaxation processes has remained murky. State-of-the-art theoretical models of the colloidal glass transition such as Random First...

Cited by 10 publications

References 147 publications

Mild stratification in drying films of colloidal mixtures

Mild stratification in drying films of colloidal mixtures

Vitrification is a spontaneous non-equilibrium transition driven by osmotic pressure

Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

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“Dense diffusion” in colloidal glasses: short-ranged long-time self-diffusion as a mechanistic model for relaxation dynamics

Abstract: Despite decades of exploration of the colloidal glass transition, mechanistic explanation of glassy relaxation processes has remained murky. State-of-the-art theoretical models of the colloidal glass transition such as Random First...

Cited by 10 publications

References 147 publications

Mild stratification in drying films of colloidal mixtures

Mild stratification in drying films of colloidal mixtures

Vitrification is a spontaneous non-equilibrium transition driven by osmotic pressure

Understanding the Rheology of Polymer–Polymer Interfaces Covered with Janus Nanoparticles: Polymer Blends versus Particle Sandwiched Multilayers

Contact Info

Product

Resources

About

Abstract:
Despite decades of exploration of the colloidal glass transition, mechanistic explanation of glassy relaxation processes has remained murky. State-of-the-art theoretical models of the colloidal glass transition such as Random First...