Transient gels in colloid–polymer mixtures studied with fluorescence confocal scanning laser microscopy

Verhaegh, N.A.M.; Asnaghi, D.; Lekkerkerker, H. N. W.

doi:10.1016/s0378-4371(98)00420-8

Cited by 66 publications

(63 citation statements)

References 33 publications

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“…0 1, and it equals Fq 9sinqR ÿ qR cosqR 2 =qR 6 [24] for a sphere of radius R with a uniform distribution of the electron density. Under the conditions of our experiment (specific weight [19] of silica particles and the solvent cyclohexane are 1.7 and 0:77 g=ml, respectively, corresponding to a refractive index contrast of n 2:1 10 ÿ6 for 10 keV x rays), the total small-angle scattering cross section R d=dd of one sphere is about Fig. 1(b).…”

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“…In brief, samples were prepared by filling flat glass capillaries with dilute colloid/polymer suspensions with 5% volume fraction of sterically stabilized silica hard spheres [19] of radius R 112 nm; effectively about 10%-15% of the volume was filled by penetrable random polymer coils of 14 nm radius of gyration. The polymer induces a weak depletion attraction between the silica spheres promoting spontaneous formation of large single crystals [13] (up to about 1 mm along the capillary walls and usually filling the 0.2 mm space between the flat walls of the capillary allowing for single-crystal diffraction measurements).…”

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Bragg Rods and Multiple X-Ray Scattering in Random-Stacking Colloidal Crystals

et al. 2003

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Synchrotron small-angle x-ray diffraction images of random-stacking-induced Bragg scattering rods are obtained in a wide range of wave vectors from a single colloidal crystal. The results reveal a strong multiple scattering effect, which leads to new features in the diffraction pattern -secondary Bragg rods. We argue that dynamic x-ray diffraction is rather common for high-quality colloidal photonic crystals and should be taken into account. DOI: 10.1103/PhysRevLett.90.028304 PACS numbers: 82.70.Dd, 42.70.Qs, 61.10.-i The spontaneous formation of crystals in dispersions of colloidal spheres [1,2] remains an intriguing phenomenon, which has aroused renewed interest because of its photonic applications [3]. Modern microscopy [4 -7] allows 3D imaging of colloidal crystals giving mainly information on local structure and ordering. Scattering techniques are more appropriate for the study of longrange order in colloidal crystals. Until recently this involved primarily light scattering [2,[8][9][10][11], which limits the range of scattering vectors severely and is known to be extremely prone to multiple scattering. In the x-ray field a new era has spawned by the advent of synchrotron radiation, which offers high-quality x-ray beams and has led to the development of 2D x-ray detectors. These now permit small-angle x-ray diffraction (SAXD) on colloidal single crystals [12] and allow us to achieve a resolution sufficient to determine long-range order parameters in high-quality crystals [13]. So far, the so-called kinematic theory, where it is assumed that diffraction is weak, has been used [12 -15] to describe x-ray diffraction patterns from colloidal crystals. However, already long ago it was realized that in perfect crystals with long-range periodic positional order, the kinematic approach fails and one has to use the more complicated dynamic theory [16], which accounts for mutual interactions between the incident and all the diffracted waves. While for SAXD in colloidal crystals the applicability of the kinematic approach is hardly ever questioned, our results indicate a significant effect of dynamic x-ray diffraction, which reveals itself in our crystals in an unusual way as novel features in the diffraction pattern.Calculations [17] indicate that colloidal hard spheres should favor a face centered cubic crystal as a closepacked structure, but in practice a random hexagonal close-packing (rhcp) structure is rather more common [5,[9][10][11]13,14] either as a transient state or possibly even permanently (factors such as polydispersity may readily influence the very small free energy differences involved). Because of the irregular stacking of hexagonal layers in three possible lateral positions, some features in the reciprocal lattice of rhcp are smeared out into Bragg scattering rods [10,13,14,18] in the direction perpendicular to the hexagonal layers [ Fig. 1(a)]. Periodicities common to all layers lead to sharp Bragg spots.We have been able to image Bragg scattering rods directly in a single diffraction patter...

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Bragg Rods and Multiple X-Ray Scattering in Random-Stacking Colloidal Crystals

et al. 2003

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“…Initially, the gel behaves as a solid but after a finite lag time τ d , the gel yields and catastrophically collapses. Sudden or 'delayed' network collapse is observed in a wide variety of materials [7][8][9][10][11][12][13][14][15][16] and seems to be ubiquitous at small U c /k B T . However, while sudden collapse * Corresponding author:P.Bartlett@bristol.ac.uk has been attributed to channel formation within the gel [12,13], the microscopic processes operating have never been fully established.…”

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Sudden collapse of a colloidal gel

Bartlett¹,

Teece²,

Faers³

2012

Phys. Rev. E

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Metastable gels formed by weakly attractive colloidal particles display a distinctive two-stage time-dependent settling behavior under their own weight. Initially a space-spanning network is formed that for a characteristic time, which we define as the lag time τ d , resists compaction. This solid-like behavior persists only for a limited time. Gels whose age tw is greater than τ d yield and suddenly collapse. We use a combination of confocal microscopy, rheology and time-lapse video imaging to investigate both the process of sudden collapse and its microscopic origin in an refractiveindex matched emulsion-polymer system. We show that the height h of the gel in the early stages of collapse is well described by the surprisingly simple expression, h(τ ) = h0 − Aτ 3 2 , with h0 the initial height and τ = tw − τ d the time counted from the instant where the gel first yields. We propose that this unexpected result arises because the colloidal network progressively builds up internal stress as a consequence of localized rearrangement events which leads ultimately to collapse as thermal equilibrium is re-established.

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“…The interparticle attraction is then generally weak (of the order of kT) and the formed structure is therefore time dependent ("transient" gel). This feature combined with the effect of the gravitational force leads to specific sedimentation/creaming behaviours that have been the object of several recent studies [3][4][5][6]. On the contrary, when the attractive forces are strong enough, the particles form irreversible bonds and thermal motion does not induce restructuration of the so-called "permanent" a e-mail: talini@fast.u-psud.fr gel [7].…”

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Systematic study of the settling kinetics in an aggregating colloidal suspension

2001

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We present a study of the settling of a strongly-aggregating colloidal suspension. Using wellcontrolled samples, the different settling behaviours have been systematically investigated according to the values of the volume fraction Φ of the suspension and of the inclination angle of the cell. In a vertical cell, three velocity regimes are observed. To describe the first and final regimes, we propose a simple 1D model that takes into account the microscopic structure of the gel constituted by a packing of fractal aggregates. The second regime coincides with the opening of fractures within the gel and its description would require a more complex model. When the cell is inclined at an angle α to the vertical, new settling regimes can emerge and an enhancement of the settling velocity can be observed as in usual macroscopic suspensions. Using both our 1D model and arguments similar to the ones used for macroscopic suspensions (PNK model), we propose a description of the influence of inclination that is in good agreement with the experimental data. We also present the various experimental settling behaviours we have observed in a Φ vs. α diagram that covers the whole range of experimental conditions. PACS. 82.70.Dd Colloids -47.20.Bp Buoyancy-driven instability -61.43.Hv Fractals; macroscopic aggregates (including diffusion-limited aggregates)In the past years, increasing attention has been paid to aggregation phenomena in colloidal suspensions [1,2]. Beside their fundamental interest, colloids are involved in many practical applications (drilling muds, paints, concrete, food industry. . .) for which their ability to remain in a well-dispersed state, or, on the contrary, to flocculate is of great importance. Moreover, it is essential to predict their stability under the action of an external field and in particular when submitted to gravity.Colloidal aggregation is encountered in several different systems that can be more or less complex (e.g., containing anisotropic particles, added polymer. . .) in which aggregation results from different natures of attractive interparticle interactions. For instance, attraction can be depletion induced: a depletant such as a non-adsorbing polymer is added to the colloidal suspension that can form a gel [1]. The interparticle attraction is then generally weak (of the order of kT) and the formed structure is therefore time dependent ("transient" gel). This feature combined with the effect of the gravitational force leads to specific sedimentation/creaming behaviours that have been the object of several recent studies [3][4][5][6]. On the contrary, when the attractive forces are strong enough, the particles form irreversible bonds and thermal motion does not induce restructuration of the so-called "permanent" a e-mail: talini@fast.u-psud.fr gel [7]. These gels can however be very loose and compact under the action of their own weight [8][9][10].In this paper, we will focus on colloidal suspensions in which aggregation is induced by van der Waals attractive forces and which form such "...

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Transient gels in colloid–polymer mixtures studied with fluorescence confocal scanning laser microscopy

Cited by 66 publications

References 33 publications

Bragg Rods and Multiple X-Ray Scattering in Random-Stacking Colloidal Crystals

Bragg Rods and Multiple X-Ray Scattering in Random-Stacking Colloidal Crystals

Sudden collapse of a colloidal gel

Systematic study of the settling kinetics in an aggregating colloidal suspension

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