Self-assembly of amphiphilic peanut-shaped nanoparticles

Abstract

We use computer simulation to investigate the self-assembly of Janus-like amphiphilic peanut-shaped nanoparticles, finding phases of clusters, bilayers and micelles in accord with ideas of packing familiar from the study of molecular surfactants.However, packing arguments do not explain the hierarchical self-assembly dynamics that we observe, nor the coexistence of bilayers and faceted polyhedra. This coexistence suggests that experimental realizations of our model can achieve multipotent assembly of either of two competing ordered structures.Components are said to 'self-assemble' when they organize to form stable patterns or aggregates without external direction. Self-assembly is driven by interactions as different as weak covalent bonds and capillary forces, involves components ranging in size from Angströms to centimeters, and occurs both in inorganic settings and in living organisms [1][2][3][4][5][6][7][8][9]. Mimicry of the self-assembly seen in the natural world promises the development of new, functional materials patterned on the nanometer scale [10,11]. In pursuit of this goal, we take inspiration from the self-assembly of molecular surfactants to investigate using computer simulation the behavior of a simple model of their colloidal counterparts. Molecular surfactants, comprising chemically linked hydrophobic and hydrophilic groups, are of central importance in biology and industry, able to form a plethora of phases in water or mixtures of water and oily liquids. These phases include micelles [12], bilayers and vesicles, as well as numerous bicontinous phases [13] that serve as internal cellular packaging [14] and are the bane of many a plumber.Here we ask: What might self-assemble in aqueous solution from amphiphilic, peanutshaped colloidal nanoparticles? Such particles can now be prepared in large quantities, starting from spherical, crosslinked polystyrene 'seed' particles of radius ∼ 50 nm. Mixing these seeds with styrene initiates monomer-polymer phase separation and creates particles with a peanut-like shape characterized by two fused spherical lobes of controllable relative size. Additional treatment of the seed particle renders peanuts amphiphilic, with one lobe hydrophobic and the other hydrophilic [15][16][17]; the resulting body can be regarded as a generalized Janus particle [18]. (We note that colloidal silica dumbbells can be synthesized by other routes [19], and that micrometer-scale peanuts show potential as Pickering stabilizers of * swhitelam@lbl.gov arXiv:0907.3227v2 [cond-mat.soft] 19 Feb 2010 2 oil-in-water emulsions [20].) In an attempt to answer our posed question we have constructed a model of interacting peanuts whose minimal character is motivated by the insight into self-assembly afforded by similarly simple model systems [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Our model can be evolved with computational efficiency sufficient to allow observation of collective, thermally-driven dynamics on timescales of seconds. Its construction rests up...

Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

“…They found that, as well as spherical micellar-type structures and wormlike strings, also bilayers and faceted polyhedra were possible as supracolloidal structures. Whitelam and Bon [47] used computer simulations to investigate the self-assembly of Janus-like peanut-shaped nanoparticles and found phases of clusters, bilayers, and nonspherical and spherical micelles, in accordance with a packing parameter that is used conventionally and in analogy to predict the assembled structures for molecular surfactants. They also found faceted polyhedra, a structure not predicted by the packing parameter (see Fig.…”

Vesicular gold assemblies based on host–guest inclusion and its controllable release of doxorubicin

“…In our case, the weight fraction of hydrophilic PEG in PEG and PNIPAM was 30%, and the ratio of the number of PEG to the number of nanoparticles was three, so we hypothesized that the amphiphilic HIC would lead to vesicles above the LCST of PNIPAM. Figure 1 shows the morphology of HIC at 37 • C. In the transmission electron microscopy (TEM) image ( figure 1(a)), one can see an obvious contrast between the interior and the shell of the particles, which was a characteristic image of hollow spheres as reported [16][17][18][19][20][21]. At a higher magnification, closely attached individual nanoparticles on the shell were visible, demonstrating that the vesicles were actually composed of individual AuNPs.…”

“…So far, most applications have used colloidal AuNPs made of ligandstabilized water-soluble gold crystallites [13][14][15]. Vesicular gold aggregates, although they have advantages as a vector of drug delivery and a prototype of living cells, have been reported only very recently [16][17][18][19][20][21]. More significantly, applications of gold vesicles have seldom been explored.…”

“…It has been reported that amphiphilic nanoparticles could self-assemble into vesicles [16][17][18][19][20][21]. A major strategy for the fabrication of amphiphilic AuNP is to covalently attach a copolymer or polymer mixture on the surface of gold nanocrystals [18-20, 22-24, 15, 25, 26].…”

Assembly of open clusters of colloidal dumbbells via droplet evaporation

“…Corresponding dumbbells consist of two colloidal spheres with different sizes or dissimilar materials [2]. Many studies have investigated the self-assembly of colloidal dumbbells into more complex structures, including micelles, vesicles [3,4], bilayers [5][6][7] and dumbbell crystals [8][9][10]. Particularly, open clusters of colloidal dumbbells with syndiotactic, chiral [11,12] and stringlike structures [13] are significant because they can be regarded as colloidal molecules [14,15] that exhibit unique magnetic, optical and rheological properties [16].…”