Dissipative Particle Dynamics Simulations On Transformation Dynamics Of Amphiphilic Aggregates

Aggregates self-assembled from scattered amphiphiles do not only exhibit various equilibrium morphologies in different conditions,but also undertake dynamic processes that are equally fascinating if the external conditions are changed.The morphological diversity of amphiphilic aggregates makes them extensively applicable in the fields of drug delivering,nanotechnologies, etc.We concentrate on the morphology transformation dynamics of two types of amphiphilic aggregates,budding dynamics of lipid bilayer membranes and inversion dynamics of polymeric micelles,respectively.Both have been simulated by either normal or modified dissipative particle dynamics(DPD).The achievements are listed as follows:1.We construct N-varied DPD simulation,in which addition and deletion of beads based on their density at the membrane boundary are introduced.The modification at the boundary provides sufficient excess areas that are indispensable to the budding of domains in planar membranes, whose morphology facilitates the observation of budding intermediates and the calculation of the elastic properties.2.The tubular bud intermediate has been featured in the simulations.Its formation plays an important role in the acceleration of neck constriction and the surface-area increase in the late stage of budding.The simulation shows that budding duration is shortened with increasing line tension and depends on the initial domain size quadratically.At low line tension, increasing bending modulus accelerates budding at first,but suppresses the process as it increases further.In addition,the budding process is determined by the surface tension.3.Normal DPD technique is used to simulate the inversion dynamics of a spherical micelle composed of symmetric diblock copolymers.The evolutions of the micelles morphology and constituent polymer configuration reveal that the inversion is a two-stage process.The rapid agglomeration of outer lyophobic blocks and the slow penetration of inner lyophilic blocks through the porous lyphobic layer dominate the two stages,respectively.Calculation of the radius of gyration and hydrodynamic radius indicates an intermediate with dilute core and a dense shell emerges in the inversion.We also find the characteristic time of inversion scales with the block copolymer chain length,which can be described by a simplified chemical-potential-driven flow model.4.In comparison with the experimental results,further simulations incorporating different denaturation times are conducted.They indicate the inversions do not experience molecularly scattered states,but form either collapsed intermediates or loosely associated clusters of small sizes.Light scattering techniques may be used to provide evidences of the intermediate formations,and further to judge the relative denaturation rates of the two blocks.