Melting of Colloidal Crystal Films

Peng, Yi; Wang, Ziren; Alsayed, Ahmed; Yodh, Arjun G.; Han, Yilong

doi:10.1103/physrevlett.104.205703

Cited by 105 publications

(76 citation statements)

References 33 publications

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“…Suspensions of particles with nearly hard-sphere interactions exhibit equilibrium fluid and crystal phases, in agreement with the behavior expected for hard spheres, and form a non-equilibrium glass when rapidly concentrated [6]. Microscopic imaging experiments on hard-sphere colloidal suspensions have therefore been used to explore processes involved in transitions to or from crystals [7][8][9][10][11][12], and to test theoretical predictions for the glass transition [13][14][15][16][17][18]. Inducing an attraction between particles, for example by adding a non-adsorbing depletant [19], shifts the equilibrium phase boundaries [20].…”

Section: Introductionmentioning

confidence: 99%

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

2018

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We developed a model depletion system with colloidal particles that were refractive index-and density-matched to 80 (w/w)% glycerol in water, and characterized the effect of interparticle interactions on the structure and dynamics of non-equilibrium phases. 2,2,2-trifluoroethyl methacrylate-co-tert-butyl methacrylate copolymer particles were synthesized following [1]. Particles were dispersed in glycerol/water solutions to generate colloidal suspensions with good control over electrostatic interactions and a moderately high background viscosity of 55 mPa·s. To probe the effects of charge screening and depletion attractions on the suspension phase behavior, we added NaCl and polyacrylamide (M w = 186 kDa) at various concentrations to particle suspensions formulated at volume fractions of φ = 0.05 and 0.3 and imaged the suspensions using confocal microscopy. The particles were nearly hard spheres at a NaCl concentration of 20 mM, but aggregated when the concentration of NaCl was further increased. Changes in the particle structure and dynamics with increasing concentration of the depletant polyacrylamide followed the trends expected from earlier experiments on depletion-driven gelation. Additionally, we measured the viscosity and corrected first normal stress difference of suspensions formulated at φ = 0.4 with and without added polymer. The solvent viscosity was suitable for rheology measurements without the onset of instabilities such as secondary flows or edge fracture. These results validate this system as an alternative to one common model system, suspensions of poly(methyl methacrylate) particles and polystyrene depletants in organic solvents, for investigating phase behavior and flow properties in attractive colloidal suspensions.

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Section: Introductionmentioning

confidence: 99%

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

2018

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“…How do grain boundaries and other defects affect thin-film melting, and where does melting start in single crystal films without grain boundaries? We began exploring some of these questions in a recent paper [5], and in this contribution we describe further experimentation that supports claims of Ref. [5] and introduces some different melting mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…In our NIPA colloidal crystals, square lattices vanish at about seven layers and spheres only self-assemble into n᭝ when n > 7. Previous experimental work has focused on the static structures of the thin films [22,23,26]; very recently we began investigation of the melting behaviors of these thin-film structures [5].…”

Section: Introductionmentioning

confidence: 99%

“…A critical development in this regard has been the fabrication of temperature-sensitive micrometer-sized Nisopropylacrylamide (NIPA) microgel spheres [15,16]. With these colloidal spheres, melting [5,10,15,17], freezing [18], glass transitions [19], and jamming transitions [20] can be driven by moderate temperature changes in a single sample which tune particle diameter and thus colloid volume fraction. NIPA colloidal crystals have been observed to melt from grain boundaries via a first-order transition in 3D [15], and exhibit a two-step melting process with a middle hexatic phase in 2D [10].…”

Section: Introductionmentioning

confidence: 99%

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Melting of multilayer colloidal crystals confined between two walls

et al. 2011

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Video microscopy is employed to study the melting behaviors of multilayer colloidal crystals composed of diameter-tunable microgel spheres confined between two walls. We systematically explore film thickness effects on the melting process and on the phase behaviors of single crystal and polycrystalline films. Thick films (>4 layers) are observed to melt heterogeneously, while thin films (≤4 layers) melt homogeneously, even for polycrystalline films. Grain-boundary melting dominates other types of melting processes in polycrystalline films thicker than 12 layers. The heterogeneous melting from dislocations is found to coexist with grain-boundary melting in films between 5- and 12-layers. In dislocation melting, liquid nucleates at dislocations and forms lakelike domains embedded in the larger crystalline matrix; the "lakes" are observed to diffuse, interact, merge with each other, and eventually merge with large strips of liquid melted from grain boundaries. Thin film melting is qualitatively different: thin films homogeneously melt by generating many small defects which need not nucleate at grain boundaries or dislocations. For three- and four-layer thin films, different layers are observed to have the same melting point, but surface layers melt faster than bulk layers. Within our resolution, two- to four-layer films appear to melt in one step, while monolayers melt in two steps with an intermediate hexatic phase.

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“…Above it, hydrophobic interactions dominate; most of the water is expelled and the particle shrinks [13]. This property has enabled studies of annealing and controlled melting [14,15] of colloidal crystals through control over the particle volume fraction. The added acrylic acid monomer adds pH-dependent size behavior to the spheres, as well as additional charge stabilization at high temperature and pH [16].…”

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Variable Dislocation Widths in Colloidal Crystals of Soft Thermosensitive Spheres

Hilhorst

Petukhov

2011

Phys. Rev. Lett.

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We report on detailed measurements of the core structure of Shockley partial dislocations in colloidal crystals. In crystalline arrays of micrometer sized thermosensitive particles, the interactions between the colloidal building blocks were tuned by changing the temperature. Individual dislocation cores were observed in a confocal microscope and their behavior as a function of temperature was studied. The obtained results qualitatively agree with the Peierls theory and are promising for further studies in which both Peierls stress and dislocation core width are measured simultaneously. DOI: 10.1103/PhysRevLett.107.095501 PACS numbers: 61.72.Ff, 07.60.Pb, 61.72.Lk, 82.70.Dd For over a century, since the early experiments on colloids by Perrin [1], colloidal particles have been employed as a model system for atoms. The merits of using colloids as model atoms are reflected in a process such as crystal nucleation. Nucleation of an atomic crystal occurs very quickly and on a length scale of angstroms or nanometers, precluding a real space study of crystal nucleation. The same process in a colloidal system takes minutes and can be observed directly with a microscope [2], while the physics behind the process remains essentially the same. In this way, homogeneous nucleation [2], as well as nucleation at impurity dopants [3], has been studied in great detail. In many ways, this example illustrates one of the key aspects of colloid science: to generate slow and seeable model systems.Another area of research that could benefit from the colloidal approach is dislocation theory. The historic Peierls theory for dislocations was put forward shortly before the outbreak of World War II [4]. Over a decade later, the core structure of dislocations was observed experimentally for the first time, as a result of the advent of high resolution electron microscopy [5][6][7]. Despite these advances a direct comparison between core structure and macroscopic material properties has not been made. Here, we will discuss a system of colloidal thermosensitive spheres that readily crystallize into a random hexagonal close packed lattice. Through analysis of confocal microscopic images, Shockley partial dislocations can be identified and characterized. The width of the dislocations is shown to be strongly dependent on temperature, which is discussed within the light of the generalized Peierls theory [8] and the properties of the thermosensitive colloids. The results hold promise for experiments in which dislocation width and crystal shear strength are measured simultaneously.Colloidal crystals form an ideal system to study dislocations. Because of the weak interactions between the particles, the formation of dislocations costs relatively little energy. In addition, because of the extremely low stacking fault energy, Shockley partial dislocations can exist in unpaired form, i.e., without the presence of a second Shockley partial with Burgers vectors adding up to a full dislocation [9]. Other peculiar dislocations have been observed, such as ...

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Melting of Colloidal Crystal Films

Cited by 105 publications

References 33 publications

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

Melting of multilayer colloidal crystals confined between two walls

Variable Dislocation Widths in Colloidal Crystals of Soft Thermosensitive Spheres

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