Current Research Projects

  • image

    Defects on Relaxing Emulsion Droplets

    Synopsis

    Arrested relaxation occurs when an emulsion droplet is prevented from relaxing to an equilibrium spherical shape due to the jamming of colloidal particles adsorbed on its surface. We generated simulated packings of spheres on ellipsoidal surfaces in order to understand the influence of curvature on the jammed structures that form. A nontrivial coupling between dislocation density and Gaussian curvature is observed. For systems with few particles (n<200), we characterize the symmetries of the resulting configurations.

  • image

    Defects on Relaxing Emulsion Droplets

    Synopsis

    Arrested relaxation occurs when an emulsion droplet is prevented from relaxing to an equilibrium spherical shape due to the jamming of colloidal particles adsorbed on its surface. We generated simulated packings of spheres on ellipsoidal surfaces in order to understand the influence of curvature on the jammed structures that form. A nontrivial coupling between dislocation density and Gaussian curvature is observed. For systems with few particles (n<200), we characterize the symmetries of the resulting configurations.

  • image

    Nematic Elastomers Origamis

    Synopsis

    Nematic liquid crystal elastomers are synergetic materials that show a strong coupling between orientational order and the elasticity of the polymer matrix; thus they are viewed as excellent candidates for soft actuators and artificial muscles. We report on recent analytical and numerical studies of thin sheets of nematic liquid crystal elastomers undergoing prescribed macroscopic shape change.

  • image

    Arrested Coalescence

    Synopsis

    With applications ranging from food products to cosmetics via targeted drug delivery systems, structured anisotropic colloids provide an efficient way to control the structure, properties and functions of emulsions. When two fluid emulsion droplets are brought in contact, a reduction of the interfacial tension drives their coalescence into a larger droplet of the same total volume and reduced exposed area. This coalescence can be partially or totally hindered by the presence of nano or micron-size particles that coat the interface as in Pickering emulsions. We investigate numerically the dependance of the mechanical stability of these arrested shapes on the particles size, their shape anisotropy, their polydispersity, their interaction with the solvent, and the particle-particle interactions. We discuss structural shape changes that can be induced by tuning the particles interactions after arrest occurs, and provide design parameters for the relevant experiments.

  • image

    Thermomechanical History of Nematic Elastomers

    Synopsis

    Deformation of an initially polydomain nematic elastomer film induces a transition to the monodomain configuration. We model the resulting microstructural evolution and stress-strain response using a recently introduced hybrid particle-finite element elastodynamics simulation approach. We explore how the thermomechanical history of the sample, e.g. its crosslink density and phase at time of network formation, affects the width of the poly-monodomain transition and the associated stress-strain behavior. We find that when the sample is cross-linked in the isotropic phase, the material shows a semi-soft response with a well-defined plateau in the stress-strain curve. By contrast when the sample is cross-linked in the nematic phase, the resulting strong local disorder broadens the transition and the plateau is much less pronounced. This simulation approach allows us to explore the fundamental physics governing dynamic mechanical response of nematic elastomers and also provides a potentially useful computational tool for engineering device applications.

  • image

    Fast GPU Elastodynamics Modeling

    Synopsis

    We are developing a novel fast computational technique for modeling the shape evolution of elastomeric materials at the continuum-level. Our algorithm, a hybrid Particle{Finite Element approach, allows for modeling shape change of samples with complex geometry subject to nonuniform external stimuli. It also captures the dynamics of internal degrees of freedom that can be modulated independently from the polymer matrix such as in liquid crystal elastomers. A dramatic performance improvement is observed when ported onto graphics processing units (GPU).

  • image

    Coloring and Recoloring

    Synopsis

    The graph recoloring problem is a fascinating mathematical challenge that falls in the category of np-complete problems; for planar graphs, it is known that this can be achieved using only four colors. Recoloring a four-colored graph however is a deterministic problem for which an upper bound of the computational cost is trivially found to be of order N (Number of vertices). We explore, and attempt to optimize the computational cost of recoloring a four-colored graph.