Reaction kinetics and mechanical models of liposome adhesion at charged interface.

Dynamics of adhesion of single liposome at the charged mercury interface is analyzed through its amperometric signal using a reaction kinetics model and a mechanical model. We present analytical solutions of the reaction kinetics model for decoupling and identifying temporal evolution of three distinct states: i) the initial state corresponding to an intact liposome, ii) the intermediate state where the liposome is partly deformed, and iii) the final state of a lipid monolayer. The results obtained with this model indicate that all three states simultaneously evolve from the onset of the adhesion process. The new mechanical model provides a physical interpretation of the three states and emphasizes the role of the forces involved in liposome adhesion process. The main conclusion is that the water content of the liposome is released through the pores formed in the membrane rather than through the channels parallel to the electrode. Both models reproduce the measurements well in the wide potential range and offer a complementary insight into the dynamics of single adhesion event, which can find application in studies of cell adhesion and in drug delivery.

Phase behaviour of colloidal assemblies on 2D corrugated substrates.

We investigate--using Monte Carlo computer simulations--the phase behaviour of dimeric colloidal molecules on periodic substrates with square symmetry. The molecules are formed in a two-dimensional suspension of like charged colloids subject to periodic external confinement, which can be experimentally realized by optical methods. We study the evolution of positional and orientational order by varying the temperature across the melting transition. We propose and evaluate appropriate order parameters as well as the specific heat capacity and show that the decay of positional correlations belongs to a class of crossover transitions while the orientational melting is a second-order phase transition.

Colloidal ionic complexes on periodic substrates: ground-state configurations and pattern switching.

We theoretically and numerically studied ordering of "colloidal ionic clusters" on periodic substrate potentials such as those generated by optical trapping. Each cluster consists of three charged spherical colloids: two negatively and one positively charged. The substrate is a square or rectangular array of traps, each confining one such cluster. By varying the lattice constant from large to small, the observed clusters are first rodlike and form ferro- and antiferrolike phases, then they bend into a bananalike shape, and finally they condense into a percolated structure. Remarkably, in a broad parameter range between single-cluster and percolated structures, we have found stable supercomplexes composed of six colloids forming grapelike or rocketlike structures. We investigated the possibility of macroscopic pattern switching by applying external electrical fields.

Dimeric and dipolar ground state orders in colloidal molecular crystals.

A two-dimensional colloidal suspension subject to a periodic substrate evolves into a colloidal molecular crystal under situations of strong confinement. We focus on the long-range orientational order thereby emerging, in the ground state. We study by simulations the situations where in each trap lies a pair of identical colloids, or alternatively a pair of oppositely charged macroions. We consider square or triangular geometries for the periodic confinement, together with less symmetric distorted lattices.

Dimeric and dipolar ground state orders in colloidal molecular crystals

A two dimensional colloidal suspension subject to a periodic substrate evolves into a colloidal molecular crystal under situationsofstrongconfinement. Wefocusonthelongrangeorientationalordertherebyemerging, inthegroundstate. We study by simulations the situations where in each trap lies a pair of identical colloids, or alternatively a pair of oppositelychargedmacroions. We consider square or triangular geometries for the periodic confinement, together with less symmetric distorted lattices.

Uma suspensão bidimensional coloidal sujeita a um substrato periódico evolui para um cristal coloidal molecular em situações de forte confinamento. Nós focamos na ordem de orientação emergindo a partir do estado fundamental. Fazendo uso de simulações, estudamos as situações onde em cada armadilha reside um par de colóides idênticos ou, alternativamente, um par de macro-íons de cargas opostas. Consideramos geometrias quadradas ou triangulares para o confinamento periódico com arranjos simétricos com menor distorção.

Ground states of colloidal molecular crystals on periodic substrates.

Two-dimensional suspensions of spherical colloids subject to periodic external fields exhibit a rich variety of molecular crystalline phases. We study in simulations the ground state configurations of dimeric and trimeric systems, that are realized on square and triangular lattices, when either two or three macroions are trapped in each external potential minimum. Bipartite orders of the checkerboard or stripe types are reported together with more complex quadripartite orderings, and the shortcomings of envisioning the colloids gathered in a single potential minimum as a composite rigid object are discussed. This work also sheds light on simplifying assumptions underlying previous theoretical treatments and that made possible the mapping onto spin models.