Thin colloidal crystals : a series of structural transitions (original) (raw)

Particle Excursions in Colloidal Crystals

Physical Review Letters, 2001

We have performed synchrotron small-angle x-ray diffraction experiments on charge-stabilized colloidal crystals. The mean squared displacements, obtained from Debye-Waller factors, decrease with increasing density beyond freezing. Irrespective of the range of the repulsion, our data and previous results lie on a common curve, linearly scaled between the melting and close-packed densities. Surprisingly, the excursions are smaller than predicted by theory.

Direct observation of a buckling transition during the formation of thin colloidal crystals

Progress in Colloid & Polymer Science, 1997

We have investigated a S Newr ( E i ) C. I4cchlngcr 1' Lcldcrcr Fakultnt fur Phyqik colloidal suspension in a thin wedge LTt~txcrsitht K o n s t n~i z formcd by two glass plates in thc 75434 Konstanz. Gcrrnnr~?: prcscncc ofn lateral pressure. Starring T. Palhcrg with a single hexagonal layer. with [nstitul fur Physik increasing separation between the L,Tn~\~rsitit MBIIIZ glass plates additional layers are 55099 Mainr. German)

Liquid-like behavior in colloidal crystals

Physica B: Condensed Matter, 1996

The van der Waals approach to predict liquid vapor coexistence, becomes exact in the limit of weak, long-ranged attractive forces. However, for shorter-ranged attractions, the liquid range shrinks and eventually disappears altogether. When the width of the attractive well becomes very small (less than 7% of the diameter of particles), an iso-structural solid-solid transition, reminiscent of the liquid-vapor transition, appears in the crystalline phase. This transition, that should be experimentally observable in certain colloidal suspensions, ends in a critical point. In quasi-two-dimensional systems (e.g. confined colloids), this critical point induces the formation of a stable hexatic phase.

Layering transitions in confined colloidal crystals: The hcp-like phase

Physical Review E, 2007

This paper investigates the sequence of morphological transitions in a nearly hard sphere arrangement confined in a wedge cell. A model that shows smooth transitions between the different particle orderings for a small number of layers is proposed. In this model, both the buckling and the ͑100͒ hexagonal close packed ͑hcp͒ phases are particular cases of a much more general particle arrangement tendency that we call hcp-like ordering. This phase, which does not correspond to any known close packed ordering, is able to adopt packing arrangements commensurate with the cell thickness. More striking, the hcp-like phase adapts itself to the progressive changes of the cell thickness by a smooth change in the interlayer spacing. We present hcp-like orderings up to six layers and a complete sequence of transformations between two and four layers. Finally, a packing model of the transition from two to three layers is also presented.

Amorphous and crystalline states of ultrasoft colloids: a molecular dynamics study

Rheologica Acta, 2007

In this work, we study the temperature-induced development of "dynamically arrested" states in dense suspensions of "soft colloids" (multi-arm star polymers and/or block-copolymers micelles) by means of molecular dynamics (MD) simulations. Temperature increase in marginal solvents results in "soft sphere" swelling, dynamical arrest, and eventually crystallization. However, two distinct "dynamically arrested" states were found, one almost amorphous ("glassy") and one with a considerable degree of crystallinity, yet lower than that of the fully equilibrated crystal. It is remarkable that even that latter state permitted self-diffusion in the timescale of the simulations, an effect that underlies the importance of the "ultra-soft" nature of inter-particle potential. The "number of connections" criterion for crystallinity proved to be very successful in identifying the ultimate thermodynamic trend from the very early stages of the α-relaxation.

Video microscopy of colloidal suspensions and colloidal crystals

2002

Colloidal suspensions are simple model systems for the study of phase transitions. Video microscopy is capable of directly imaging the structure and dynamics of colloidal suspensions in different phases. Recent results related to crystallization, glasses, and 2D systems complement and extend previous theoretical and experimental studies. Moreover, new techniques allow the details of interactions between individual colloidal particles to be carefully measured.

Correlation between crystalline order and vitrification in colloidal monolayers

Journal of Physics: Condensed Matter, 2015

We investigate experimentally the relationship between local structure and dynamical arrest in a quasi-2d colloidal model system which approximates hard discs. We introduce polydispersity to the system to suppress crystallisation. Upon compression, the increase in structural relaxation time is accompanied by the emergence of local hexagonal symmetry. Examining the dynamical heterogeneity of the system, we identify three types of motion : "zero-dimensional" corresponding to β-relaxation, "one-dimensional" or stringlike motion and "two-dimensional" motion. The dynamic heterogeneity is correlated with the local order, that is to say locally hexagonal regions are more likely to be dynamically slow. However we find that lengthscales corresponding to dynamic heterogeneity and local structure do not appear to scale together approaching the glass transition.

Formation of two-dimensional colloid crystals in liquid films under the action of capillary forces

Journal of Physics: Condensed Matter, 1994

When two similar small particles are attached to a liquid interface they attract each other due to a lateral capillay force. This force appears because the gravitational potential energy of the floating particles decreases when they are approaching each other. This force is proportional to R6 ( R is the particle radius), so it decreaxs very fast with panicle size and becomes negligible for R c 10 Km. We found that the situation is quite different when ihe particles (instead of being freely floating) are panidly immersed in a liquid layer on a substrate. In this case the energy of capillary attraction is propaltional to R2 and "s out to be much larger than kT even with particles of diameter about 10 nm. The effect is related to the particle three-phme contact angle, i.e. to the intermolecular forces, rather than to gravity. The experiments show that the lateral capillary forces can bring about the formation of a twodimensional anay (20-crystal) h m both micrometre-size and submicrometre particles: latex spheres. protein globules. etc.

Observation of solid–solid transitions in 3D crystals of colloidal superballs

Nature Communications, 2017

Self-organization in anisotropic colloidal suspensions leads to a fascinating range of crystal and liquid crystal phases induced by shape alone. Simulations predict the phase behaviour of a plethora of shapes while experimental realization often lags behind. Here, we present the experimental phase behaviour of superball particles with a shape in between that of a sphere and a cube. In particular, we observe the formation of a plastic crystal phase with translational order and orientational disorder, and the subsequent transformation into rhombohedral crystals. Moreover, we uncover that the phase behaviour is richer than predicted, as we find two distinct rhombohedral crystals with different stacking variants, namely hollow-site and bridge-site stacking. In addition, for slightly softer interactions we observe a solid-solid transition between the two. Our investigation brings us one step closer to ultimately controlling the experimental self-assembly of superballs into functional materials, such as photonic crystals.