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Structure, Properties, And Dynamics Of Nanoparticle-Tethered Polymers

2015
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Release : 2015
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Book Synopsis Structure, Properties, And Dynamics Of Nanoparticle-Tethered Polymers by : Sung A. Kim

Download or read book Structure, Properties, And Dynamics Of Nanoparticle-Tethered Polymers written by Sung A. Kim. This book was released on 2015. Available in PDF, EPUB and Kindle. Book excerpt: Understanding how polymer [-] nanoparticle interactions influences structure, dynamics, and properties of composites is of fundamental importance for both the science and technology applications of organic [-] inorganic hybrid materials. Great attention has been given to changes organic polymer species undergo in forming polymer nanoparticle composites. This thesis focuses on a specific type of hybrid systems created by densely grafting polymer chains onto inorganic nanoparticles to form self-suspended nanoparticle suspensions in which every polymer chain is both anchored to and confined between the surfaces of neighboring particles. We have studied the hierarchical structure and relaxation dynamics of polymer chains in these self-suspended nanoparticle suspensions. We have investigated the conformations and thermo-physical properties of self-suspended suspensions based on polyethylene glycol (PEG) chains tethered to silica nanoparticles. It is found that the structure and crystallization of confined PEG could be very different depending on the length scale on which the structure is observed. Below the size of one hybrid unit, particle-tethered PEG chains form more stable conformations, whereas tethered PEG is more amorphous than free chains on length scales above one hybrid unit. We also report how tethering, crowding, and confinement by nanoparticles change the viscoelastic and dielectric relaxation dynamics of nanoparticle-tethered polymer chains. In this study, diverse molecular weights of cis-1,4-Polyisoprene (PI), a type A dielectric polymer, is synthesized in the spectrum from unentangled to wellentangled regime with amine end group functionality. By tethering this polymer to nanoparticles at varying grafting densities it is possible to study dynamics of polymer chains under confinement using bulk measurements. Global chain relaxation is conveniently explored since the net dipole moment of an entire chain of cis-1,4-PI is parallel to the end-to-end vector of the tethered molecules. We have found that tethered PI chains exhibit slower relaxation dynamics and are stretched compared to free polymers. We have studied that nanoparticles could impose topological constraints to the tubes of tethered chains when short molecular weight chains are sparsely tethered. In addition, jamming of soft glasses with increasing temperature and decreasing grafting density have been observed from dielectric spectroscopy and rheology experiments.

Tethered Nanoparticle - Polymer Composites

2014
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Release : 2014
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Book Synopsis Tethered Nanoparticle - Polymer Composites by : Samanvaya Srivastava

Download or read book Tethered Nanoparticle - Polymer Composites written by Samanvaya Srivastava. This book was released on 2014. Available in PDF, EPUB and Kindle. Book excerpt: Nanoparticle - polymer composites, or polymer nanocomposites, are ubiquitous in the modern world. Controlled dispersion of nanoparticles in nanocomposites is often a critical requirement and has lead to evolution of a variety of strategies for regulating nanoparticle interactions and assembly. This work focuses on one such technique wherein the nanoparticle surfaces are densely tethered with polymer chains. Complete screening of the interparticle interactions and steric repulsion among the tethered chains thus results in repulsive and stable nanoparticles across a range of polymer molecular weights and chemistries and nanoparticle volume fraction. These nanoparticles are found to be ideal for studying polymer nanocomposites, and a phase diagram constructed on the basis of nanoparticle arrangements is presented. Tethered nanoparticles, in the limit small tethered polymer chains, also serve as model systems for studying the properties of soft nanoparticles. Well-dispersed suspensions of these soft nanoparticles in oligomers exhibit unique properties across the jamming transition, including anomalous structural and dynamic trends typically associated with complex molecular fluids. In the jammed regime, these suspensions behave as typical soft glasses and allow for quantitative comparisons with the existing models for soft glasses. At the same time, the tethered chains facilitate relaxations even in the deeply jammed regime and thus lead to novel features including Newtonian behavior and terminal relaxations in the jammed suspensions. On the other end of the spectrum, studies of suspensions of these nanoparticles in extremely large polymer chains provide insights on the physical processes responsible for the atypical, negative non-Einsteinian deviations in the viscosity typically observed in blends of nanoparticles in large polymer hosts. We also explore the origins of atypical faster - than - diffusion relaxation mechanisms in soft materials through studying the relaxation mechanisms in these jammed suspensions as well as single-component tethered nanoparticle fluids. A simple theoretical framework is presented to account for the genesis of driving mechanisms in our systems, and comparisons between theoretical and experimental results provide strong support to the existing theory that hyperdiffusion in soft materials arises from the system's response to internal stresses; however, the origin of these internal stresses might vary considerably from one material to another.

The Structure and Dynamics of Nanoparticle Polymer Composites

2016
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Release : 2016
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Book Synopsis The Structure and Dynamics of Nanoparticle Polymer Composites by : Rahul Mangal

Download or read book The Structure and Dynamics of Nanoparticle Polymer Composites written by Rahul Mangal. This book was released on 2016. Available in PDF, EPUB and Kindle. Book excerpt: This work undertakes the fundamental study of the structure and dynamics of polymer nanocomposites (PNCs), with a specific focus on composites where the size of dispersed nanoparticles is comparable to host polymer dimensions. Using small angle X-ray scattering (SAXS) as a major tool we discuss a strategy for creating model PNCs in which spherical nanoparticles are uniformly dispersed in high molecular weight entangled polymers. In particular, by carefully harnessing favorable enthalpic interactions between particle-tethered and host polymers we show that particle-particle aggregation can be completely avoided. Based on the interaction between polymer tethered nanoparticles and the host polymer melts a new phase diagram is also constructed to define boundaries where particle aggregation in any PNC can be avoided. Investigation of the mechanical properties of these model PNCs through oscillatory shear rheology measurements reveal that nanoparticles have profound effects on their host polymer's physical properties and dynamics on essentially all timescales. At low particle content, nanoparticles appear to promote an early onset of terminal relaxation of the polymer chains for high molecular weight hosts and vice versa for low molecular weight hosts. We also show, that progressive addition of NPs to polymers induce additional constraints for the polymer chain motion than typically observed in entangled melts, leading to an earlier discovery of the confinement tube. This apparent confinement of high molecular weight polymers in PNCs at high particle loading manifests as a profound slow-down in terminal chain relaxation and glassy rheological behavior analogous to what has been reported in thin polymer films. Investigation of nanoparticle dynamics through X-ray Photon Correlation Spectroscopy (XPCS) reveals that as the nanoparticle size, is progressively increased above the tube diameter of the host polymer, particles undergo a transition from normal diffusion to hyperdiffusive relaxation dynamics. In contrast, for unentangled hosts, diffusive particle relaxations are observed. Remarkably, in entangled polymer hosts particle motion was found to be weakly dependent on host polymer molecular weight. A local viscosity model capable of explaining these observations is discussed and the results compared with findings from a recently proposed scaling/theoretical model for hopping of nanoparticles in polymers.

Structure and Dynamics of Nanoparticle-polymer Composites

2021 Nanoparticles
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Release : 2021
Genre : Nanoparticles
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Book Synopsis Structure and Dynamics of Nanoparticle-polymer Composites by : Ari Yun Liu

Download or read book Structure and Dynamics of Nanoparticle-polymer Composites written by Ari Yun Liu. This book was released on 2021. Available in PDF, EPUB and Kindle. Book excerpt:

Rheology, Structure and Dynamics of Polymer-tethered Nanoparticles and Their Suspensions

2020
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Release : 2020
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Book Synopsis Rheology, Structure and Dynamics of Polymer-tethered Nanoparticles and Their Suspensions by : Xiaotun Liu

Download or read book Rheology, Structure and Dynamics of Polymer-tethered Nanoparticles and Their Suspensions written by Xiaotun Liu. This book was released on 2020. Available in PDF, EPUB and Kindle. Book excerpt: Well-dispersed, solvent-free silica nanoparticles tethered with polymers exhibit soft glassy rheology and jamming behavior due to "cages" induced by interpenetrated chains. In this study, we use small-angle X-ray scattering (SAXS) and rheology to investigate slow structural and mechanical evolution of a soft glassy material composed of silica nanoparticles densely grafted with poly(ethylene glycol) methyl ether (mPEG) chains. The measurements reveal significant equilibration processes in the materials that have not been reported previously, but appear characteristic of caging and of the soft-but-jammed state of matter in which the materials fall. Equilibration dynamics are found to be thermally activated and associated with local rearrangements of tethered chains to their equilibrium conformations. At fixed temperature, the strength of the equilibrated cages is inferred from the shear modulus at intermediate frequency and are observed to be substantially larger than the unequilibrated values, but to decrease in a predictable manner as temperature rises. We identify geometric confinement due to packing of spherical nanoparticles as the driving force for chain interpenetration, and propose a simple geometric model to rationalize equilibration processes in the materials in terms of corona interpenetration, cage dynamics, and yielding of self-suspended hairy nanoparticles. We further explore the effects of geometric confinement on caging behavior by dispersing the SiO2-PEG hairy nanoparticles in PEG oligomers. Jamming behavior analogous to the solvent-free systems is observed down to a critical core volume fraction of 0.065, substantially below where the glass-to-liquid transition is reported in suspensions of non-Brownian spheres. At particle concentrations above this value, the oligomer-suspended hairy nanoparticle systems exhibit a non-monotonic flow curve indicative of permanent shear banding below a critical shear rate. The stress decomposition shows a significant unrelaxable stress upon flow cessation, which likely corresponds to the chain orientations due to interpenetration. Spectroscopic analysis suggests that tethered chains adopt more trans conformations compared to untethered counterparts, providing molecular evidence of geometric confinement-induced chain interpenetration in hairy nanoparticle soft glasses.

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