Most colloidal interactions can be tuned by changing properties of the medium. Here we show that activating the colloidal particles with random self-propulsion can induce giant effective interactions between large objects immersed in such a suspension. By performing Brownian dynamics simulations, we systematically study the effective force between two hard walls in a 2D suspension of self-propelled (active)colloidal hard spheres. We find that at relatively high densities, the active colloidal hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing the density of active colloids, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction starts dominating the effective interaction between the two walls. The two long range forces oppose each other, and the effective interaction can be tuned from a long range repulsion into a long range attraction by reducing the density of active particles. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.

.

A defining mechanical property of amorphous materials is the existence
of a yield stress. In the case of soft materials, flow occurs only
when the applied stress exceeds a threshold value. Understanding the
mechanisms of yielding and subsequent flow is important for a variety
of rheological applications. In this context, it has been recently
proposed that spatially correlated plastic events drive the flow,
implying that spatial confinement would impact the nature of dynamical
properties. We explore these issues by using numerical simulations to
study the response of a confined quiescent glass to different stress
fields, viz. Couette (spatially homogeneous) and Poiseuille (spatially
inhomogeneous). We demonstrate how the dynamics at the local scale is
linked to observed macroscopic rheology. Further, using complementary
experimental studies, we try to build up the scenario for the onset of
flow in such materials.

The normal modes of a continuum solid endowed with a random distribution of line defects that behave like elastic strings are described. These strings interact with elastic waves in the bulk, generating wave dispersion and attenuation. As in amorphous materials, the attenuation as a function of frequency $\omega$ behaves as $\omega^4$ for low frequencies, and, as frequency increases, crosses over to $\omega^2$ and then to linear in $\omega$. Dispersion is negative in the frequency range where attenuation is quartic and quadratic in frequency. Explicit formulae are provided that relate these properties to the density of string states. The possibility of linking this model with the microstructure of amorphous materials is discussed.

I introduce the basic (Starobinsky and Linde) models of chaotic inflation, and discuss their status in light of the recent observational data from the PLANCK satellite mission (March 2013) and the BICEP2 telescope (March 2014). Reheating (after inflation) is briefly reviewed too.

The reshaping of cell membranes is deeply rooted in many biological processes. We combine theoretical modeling with experimental biophysics to study the driving force underlying the remodeling of biological membranes induced by BAR proteins. In particular, we employ a combination of coarse-grained simulations with field-theoretical and continuum methods to model the large-scale behavior of proteins on the membrane at molecular resolution. In addition, we use quantitative fluorescence and atomic force microscopy to elucidate the underlying mechanics and morphological changes of the membrane induced by BAR proteins at much larger time and length scales. We study how the molecular interactions couple to the long-wavelength membrane restructuring phenomena. Our research also sheds light on the complex and unknown role of the protein’s subdomains, namely the amphipathic helices, in interacting with the membrane and generating its curvature. Finally, it gives vital clues how protein self-assembly and crowding affect the mechanical properties of membranes to regulate their shape and dynamics in living cells.

I will start by showing how a seemingly small change in the
definition of a quantity measuring dynamic heterogeneity
(the so-called four-point structure factor) can result in a
huge increase of dynamic correlations. I will argue that
these additional correlations are the signature of a transient
viscoelasticity. Next, I will turn to a simpler quantity, a
correlation function of time-dependent transverse particle
displacements. I will show that in a glass, the shear modulus
can be easily obtained from this function. In a glassy fluid,
the same function provides information about transient viscoelastic
response.

Nanoclays e.g. natural Na-montmorillonite and synthetic Laponite are colloids of layered minerals. When dispersed in water, these powdered minerals swell on absorption of water and exfoliate into smaller entities, known as tactoids, with charge double layers on their surfaces. The aqueous suspensions can exhibit a spontaneous ergodicity breaking phase transition from free flowing liquids to nonequilibrium, kinetically arrested states such as gels and glasses at low particle concentrations [1]. These classes of materials are being used extensively in polymer nanocomposite, as rheological modifiers, gas absorbents and recently in drug delivery researches. The understanding of the physicochemical properties of clay dispersions under different conditions can therefore help to predict and control their final macroscopic behavior. In this talk, I shall demonstrate the use of ultrasound attenuation spectroscopy to estimate the degree of exfoliation (the dispersibility) of tactoids in samples of different ages and of different concentrations of clay and added electrolytes. Our analysis shows that a substantial fraction of the aggregates in glassy suspensions are actually tactoids that are composed of more than one platelet [2]. We further evaluate the influence of clay dispersibility on the suspension stability and the mechanical properties of arrested phases at different ionic conditions by using electroacoustics and rheometry.