Communication: Unusual dynamics of hybrid nanoparticles and their binary mixtures

Srivastava, Sunita; Chandran, Sivasurender; Kandar, A. K.; Sarika, C.; Basu, J. K.; Narayanan, Suresh; Sandy, Alec

doi:10.1063/1.3495480

Cited by 10 publications

(13 citation statements)

References 31 publications

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“…These singularities, in star polymers is observed due to the low size asymmetry (size ratios of the two components is closer to 1) as is the case for our mixtures with x ¼ 0.14 (lz1 refer Table 2). It is interesting to note that the behavior of PGNPs, especially in solution and for such large grafting density and grafted chain molecular weight, is likely to be very close to that of star polymers as has been suggested earlier [19,21,37,60,61]. In the binary mixtures of star polymers for lz2, a transition from asymmetric to double glass type is observed (in simulations) through logarithmically decaying correlators.…”

Section: Discussionsupporting

confidence: 55%

“…We have recently [21] observed intriguingly similar phase behavior for systems with different x values in the suspensions through the combination of small angle x-ray scattering, coarse grained molecular dynamic simulations and integral equation theory. In addition, we have also observed anomalous dynamic behaviors for PGNP polymer mixtures in both melt and solutions [19,20,37,39].…”

Section: Introductionmentioning

confidence: 73%

“…In XPCS experiments, we observe the speckle pattern (spatiotemporal intensity fluctuations) of the x-rays scattered from the sample, more specifically from the gold core of the PGNPs [19,20,37]. The temporal fluctuations will be used to measure the auto correlation function (g 2 (q,t)) and for stationary dynamics g 2 (q,t) can be related to the intermediate scattering function (F(q,t)) as follows…”

Section: Saxs and Xpcs Measurementsmentioning

confidence: 99%

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Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

Chandran

Begam

Sprung

et al. 2016

Polymer

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a b s t r a c tWe report the microrheological behavior and dynamics of the suspensions of polystyrene-grafted gold nanoparticles (PGNPs) mixed with linear polystyrene (PS) as a function of the PS concentration and size asymmetry parameter, x (¼M g /M m , with M g and M m being the grafted and free chain molecular weights, respectively) ¼ 2.76 and 0.14. Diffusive wave spectroscopy (DWS) is used for measuring the frequency dependent micro-rheology parameter, the loss modulus G 00 (u)(~u a ). For suspensions with x ¼ 0.14 a transition of a, from~1 to~1.6, is observed at a critical fraction of added polymers. On the other hand, a is always~1 for the suspensions with x ¼ 2.76. Corresponding x-ray photon correlation spectroscopy (XPCS) data on the same samples reveals a sharp transition in the nature of dynamics of PGNPs, from exponential to logarithmic, in suspensions with x ¼ 0.14, while for suspensions with x ¼ 2.76 this dynamical transition is not observed. Interestingly, the dynamical transition in x ¼ 0.14 based samples occurs at the same fraction of added polymers, where the transition of a from~1 to~1.6 was observed, thus providing a clear correlation between microscopic dynamics and micro-rheology. The conformational transitions of the grafted polymers is found to be the reason behind the observed differences in the dynamic behavior of the two systems. The important role of advanced x-ray scattering techniques in unravelling subtle aspects of nanoscale complex polymer and soft colloidal dynamics is thus revealed.

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Section: Discussionsupporting

confidence: 55%

Section: Introductionmentioning

confidence: 73%

Section: Saxs and Xpcs Measurementsmentioning

confidence: 99%

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Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

Chandran

Begam

Sprung

et al. 2016

Polymer

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“…Anomalous properties could include dynamical heterogeneity, which is associated with transient spatial fluctuations in the local dynamical behavior [13][14][15][16]. The dynamical behavior of polymer-grafted NPs in polymer melts has already been studied in various systems, such as correlated NP systems [17][18][19][20] and a dispersed NP system in PS with toluene [11]. However, our system is far simpler because (i) the NPs are dilute and the particle-particle interactions are negligible, and (ii) the matrix consists of a single-component amorphous polymer with no solvent.…”

Section: Introductionmentioning

confidence: 99%

Dynamical crossover between hyperdiffusion and subdiffusion of polymer-grafted nanoparticles in a polymer matrix

et al. 2013

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The dynamical behavior of polystyrene-grafted silica nanoparticles dispersed in an atactic polystyrene matrix was studied using x-ray photon correlation spectroscopy. The time-autocorrelation functions were subjected to fitting analyses based on continuous-time random walk models. The nanoparticles exhibited non-Brownian behavior, and as the temperature increased, the crossover from hyperdiffusion to subdiffusion occurred at 1.25T_{g}, where T_{g} is the glass transition temperature of the matrix polystyrene. Hyperdiffusive behavior is caused by the dynamical heterogeneity of the polymer matrix associated with the glass transition. When the temperature was higher than 1.25T_{g}, the interaction of the grafted polymers with the polymer matrix became relatively significant, and caused a dramatic change in the dynamical behavior of the nanoparticles.

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“…[1][2][3][4][5] Their structural and dynamical phase behavior has been shown to be significantly more diverse and richer than that of corresponding hard sphere colloids. [5][6][7][8][9][10] Star polymers and polymer grafted nanoparticles (PGNPs) constitute an important class of such soft nanocolloidal particles, for which some work has emerged recently where the structure and dynamics of either the pristine colloids or their binary mixtures have been investigated. 3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18] Extensive research on star polymers over the last decade has led to the emergence of a reasonably good understanding of the microscopic origins of their observed phase behavior, including prediction and verification of an effective interaction potential between these entities.…”

Section: Introductionmentioning

confidence: 99%

Suspensions of polymer-grafted nanoparticles with added polymers—Structure and effective pair-interactions

Chandran

Saw

Kandar

et al. 2015

The Journal of Chemical Physics

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We present the results of combined experimental and theoretical (molecular dynamics simulations and integral equation theory) studies of the structure and effective interactions of suspensions of polymer grafted nanoparticles (PGNPs) in the presence of linear polymers. Due to the absence of systematic experimental and theoretical studies of PGNPs, it is widely believed that the structure and effective interactions in such binary mixtures would be very similar to those of an analogous soft colloidal material-star polymers. In our study, polystyrene-grafted gold nanoparticles with functionality f = 70 were mixed with linear polystyrene (PS) of two different molecular weights for obtaining two PGNP:PS size ratios, ξ = 0.14 and 2.76 (where, ξ = Mg/Mm, Mg and Mm being the molecular weights of grafting and matrix polymers, respectively). The experimental structure factor of PGNPs could be modeled with an effective potential (Model-X), which has been found to be widely applicable for star polymers. Similarly, the structure factor of the blends with ξ = 0.14 could be modeled reasonably well, while the structure of blends with ξ = 2.76 could not be captured, especially for high density of added polymers. A model (Model-Y) for effective interactions between PGNPs in a melt of matrix polymers also failed to provide good agreement with the experimental data for samples with ξ = 2.76 and high density of added polymers. We tentatively attribute this anomaly in modeling the structure factor of blends with ξ = 2.76 to the questionable assumption of Model-X in describing the added polymers as star polymers with functionality 2, which gets manifested in both polymer-polymer and polymer-PGNP interactions especially at higher fractions of added polymers. The failure of Model-Y may be due to the neglect of possible many-body interactions among PGNPs mediated by matrix polymers when the fraction of added polymers is high. These observations point to the need for a new framework to understand not only the structural behavior of PGNPs but also possibly their dynamics and thermo-mechanical properties as well.

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Communication: Unusual dynamics of hybrid nanoparticles and their binary mixtures

Cited by 10 publications

References 31 publications

Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

Dynamical crossover between hyperdiffusion and subdiffusion of polymer-grafted nanoparticles in a polymer matrix

Suspensions of polymer-grafted nanoparticles with added polymers—Structure and effective pair-interactions

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