Observation of a microcrystalline gel in colloids with competing interactions

Zhang, Tian Hui; Groenewold, Jan; Kegel, Willem K.

doi:10.1039/b917254h

Cited by 22 publications

(35 citation statements)

References 23 publications

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“…The fast and often abrupt decay of these peaks suggests that the local correlations have a well-defined and rather short range, beyond which the system becomes homogeneous; the correlation range can thus be considered as a measure of the average size of the aggregates. 30 In order to extract this range from the g ( r ), we defined a threshold value, h , and we calculated the maximum interparticle distance, r h max , at which the oscillations of | g ( r ) −1| reach that chosen value, 31 | g ( r h max ) – 1| ≡ h .…”

Section: Resultsmentioning

confidence: 99%

Self-Assembly of Heterogeneously Charged Particles under Confinement

2013

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Self-assembly—the spontaneous organization of microscopic units into well-defined mesoscopic structures—is a fundamental mechanism for a broad variety of nanotechnology applications in material science. The central role played by the anisotropy resulting from asymmetric shapes of the units and/or well-defined bonding sites on the particle surface has been widely investigated, highlighting the importance of properly designing the constituent entities in order to control the resulting mesoscopic structures. Anisotropy driven self-assembly can also result from the multipolar interactions characterizing many naturally occurring systems, such as proteins and viral capsids, as well as experimentally synthesized colloidal particles. Heterogeneously charged particles represent a class of multipolar units that are characterized by a competitive interplay between anisotropic attractive and repulsive interactions, due to the repulsion/attraction between charged-like/oppositely charged regions on the particle surface. In the present work, axially symmetric quadrupolar colloids are considered in a confined planar geometry; the role of both the overall particle charge and the patch extension as well as the effect of the substrate charge are studied in thermodynamic conditions such that the formation of extended structures is favored. A general tendency to form quasi-two-dimensional aggregates where particles align their symmetry axes within the plane is observed; among these planar self-assembled scenarios, a clear distinction between the formation of microcrystalline gels—branched networks consisting of purely crystalline domains—as opposed to disordered aggregates can be observed based on the specific features of the particle–particle interaction. Additionally, the possible competition of interparticle and particle–substrate interactions affects the size and the internal structure of the aggregates and can possibly inhibit the aggregation process.

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Section: Resultsmentioning

confidence: 99%

Self-Assembly of Heterogeneously Charged Particles under Confinement

2013

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“…1a), as in our previous studies. 21 In order to systematically explore the effect of attraction on the properties of the clusters, observations are conducted at a similar volume fraction of 0.06 in solutions with increasing attraction strength, as set by the polymer volume fraction. In dispersions with U ¼ À8.8 k B T (Fig.…”

Section: Resultsmentioning

confidence: 99%

Non-equilibrium cluster states in colloids with competing interactions

et al. 2012

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Cluster formation and gelation are studied in a colloidal model system with competing short-range attractions and long-range repulsions. In contrast to predictions by equilibrium theory, the size of clusters spontaneously formed at low colloidal volume fractions decreases with increasing strength of the short-range attraction. Moreover, the microstructure and shape of the clusters sensitively depend on the strength of the short-range attraction: from compact and crystalline clusters at relatively weak attractions to disordered and quasi-linear clusters at strong attractions. By systematically varying attraction strength and colloidal volume fraction, we observe gelation at relatively high volume fraction. The structure of the gel depends on attraction strength: in systems with the lowest attraction strength, crowding of crystalline clusters leads to microcrystalline gels. In contrast, in systems with relatively strong attraction strength, percolation of quasi-linear clusters leads to low-density gels. In analyzing the results we show that nucleation and rearrangement processes play a key role in determining the properties of clusters and the mechanism of gelation. This study implies that by tuning the strength of short-range attractions, the growth mechanism as well as the structure of clusters can be controlled, and thereby the route to a gel state.

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“…Once degassed in a dessicator connected to a vacuum pump, the elastomer was poured into the Petri dish, and the lid with the glass slide assembly was placed over it. (3) The whole assembly was placed in an oven at 80 C for 24 h to cure the elastomer. (4) Once at ambient temperature, the sample holder was separated from the mold with the help of a few drops of ethanol, and screwed to the rotor of an inexpensive peristaltic pump (variable-flow peristaltic pump, Fisher Scientific), installed on a support in such a way that the sample holder rotated exactly in a vertical plane parallel to gravity.…”

Section: Rotational Averaging-out Of Gravitational Sedimentationmentioning

confidence: 99%

A qualitative confocal microscopy study on a range of colloidal processes by simulating microgravity conditions through slow rotations

et al. 2012

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We report qualitatively on the differences between colloidal systems left to evolve in the Earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsion above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsion, an unusual sequence of dilute-fluid-dilute-crystal-dense-fluid-dense-crystal phases was observed throughout the suspension under the effect of gravity. This was related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out of gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes.

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Observation of a microcrystalline gel in colloids with competing interactions

Abstract: A stable short-range crystalline structure is observed in colloidal systems with competing short-range attractions and long-range repulsions. We term these structures ''microcrystalline gels'' as the microcrystals are embedded in a dense disordered network.

Cited by 22 publications

References 23 publications

Self-Assembly of Heterogeneously Charged Particles under Confinement

Self-Assembly of Heterogeneously Charged Particles under Confinement

Non-equilibrium cluster states in colloids with competing interactions

A qualitative confocal microscopy study on a range of colloidal processes by simulating microgravity conditions through slow rotations

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