Self Assembly of Anisotropic Particles

Top PDF Self Assembly of Anisotropic Particles:

Directed Assembly and Manipulation of Anisotropic Colloidal Particles by External Fields

Directed Assembly and Manipulation of Anisotropic Colloidal Particles by External Fields

We have investigated the fundamental principles for the assembly and manipulation of anisotropic particles by external electric and magnetic fields. The interest in the effects driven by external and particle-localized electric fields has surged in the last few years. Much of this interest is a result of the new applications that such effects can find in microfluidics, lab-on-a-chip devices, microelectromechanical systems, biosensors, biomedical microdevices and other high-technology products. Exciting new developments in these areas could be anticipated as new types of particles interfacing microchips are fabricated and developed. This research, however, is likely to result in numerous fundamental investigations as well. The anisotropic particle manipulation and assembly effects described in this dissertation are diverse and numerous; not all of them have been understood in complete theoretical detail. This is particularly true for strongly nonlinear processes such as the polarization of counterionic layers at high electrolyte concentrations and high field intensities, the electrophoretic behavior of particles of anisotropic conductivity, and response to AC fields of high frequency. The simulation methodology developed here can be used to predict the directed self-assembly of other types of anisotropic Janus and patchy particles. This dissertation covers only a small fraction of an emerging large and stimulating research area that is likely to develop rapidly in the near future.
Show more

164 Read more

Field-Driven Reconfigurable Assemblies and Self-Propelling Microbots Engineered from Anisotropic Particles.

Field-Driven Reconfigurable Assemblies and Self-Propelling Microbots Engineered from Anisotropic Particles.

The reversible, sequence-dependent, reconfiguration described above is actuated by a uniform magnetic field. A further level of control over the dynamics of these assemblies can be achieved by superimposing a non-uniform gradient magnetic field (∇𝐻 ⃗⃗⃗ ) that can remotely translocate the assemblies. We illustrate how, by combining the uniform field-triggered reversible actuation with field gradient-driven spatial navigation, a microcube assembly with a BABBAB sequence can form a prototype of a microbot that can manipulate single live cells. Snapshots of this microbot grabbing, transporting and releasing a target yeast cell are shown in Figure 2.13a-e. The microbot cluster is transported to the target location in its open configuration (Fig. 2.13a) by the application of a transversal uniform magnetic field with an imposed additional longitudinal gradient (by turning on all three coils 1, 2, 3 in Fig. 2.1). In the subsequent step, the transverse magnetic field is removed, resulting into chain self-folding into the closed state. Thus, the cluster acts as a “micro- tweezer” and captures the target yeast cell. The cell is then transported in two-dimensional space by tuning the magnitude and direction of the applied magnetic field gradient (Fig. 2.13c-d). Upon reaching a target location, the yeast cell is released by activating the uniform magnetic field (Fig. 2.13e).
Show more

153 Read more

Engineering a Library of Anisotropic Building Blocks for DNA-Programmed Colloidal Self-Assembly

Engineering a Library of Anisotropic Building Blocks for DNA-Programmed Colloidal Self-Assembly

A simple and effective method of circumventing the segregation issue is to com- pletely eliminate all DNA interactions during crystallization, and to drive crystal formation by other means, such as sedimentation. In this experiment, a mixture of P and P 0 particles, with the ratio used above, is first prepared in a buffer with no added salt, which effectively turns off all attractive DNA interactions at room temperature. Due to the small size of our particles, sedimentation is performed in a low-speed benchtop centrifuge overnight, forming a dense pellet of particles. The salt concentration in the supernatant is then increased from 0mM to 150mM NaCl in multiple addition steps consisting of gentle pipette mixing and further centrifuga- tion, turning on all attractive interactions and stabilizing the assembled structure at room temperature. The resultant pellet has large crystalline domains having a close packed structure, which can be broken apart manually and visualized by microscopy, Figure 3.4c,d. As expected, the impurity particles are well dispersed.
Show more

144 Read more

Strong Magnetic Field Induced Segregation and Self-Assembly of Micrometer Sized Non-Magnetic Particles

Strong Magnetic Field Induced Segregation and Self-Assembly of Micrometer Sized Non-Magnetic Particles

technology which makes strong magnetic fields of 10 T or higher easily attainable [2]. A lot of interesting phenomena have been observed and attracted considerable attention in the field of materials processing. Aspects that have been investigated include magnetic orientation [3], magneto-thermodynamics [4], magneto- hydrodynamics [5] and magnetic effect on chemical reactions [6]. More particularly, the treatment of materials containing particles is a favoured topic. The controllable behavior of small non-magnetic particles using strong magnetic fields — e.g., anisotropic materials preparation [1, 7] and millimeter sized particles assembly [8] — has been of great interest. Although such materials normally show little response to ordinary magnetic fields, e.g., < 1 Tesla, strong magnetic fields, e.g., 10 Tesla can induce efficient magnetic responses from non- magnetic materials [9]. In this case, strong magnetic fields provide an opportunity to control small non-magnetic particle behavior during material preparation.
Show more

16 Read more

Anisotropic structural color particles from colloidal phase separation

Anisotropic structural color particles from colloidal phase separation

Structural colors, generating from periodic arranged nanostructures composed of media with different reflective indices have been widely observed and investigated in natural gems and many living beings, such as feathers or skins of some kinds of birds, fishes, and insects (1–5). Inspired by these natural examples, a variety of artificial struc- tural color materials with film, fiber, or particle morphologies have been developed for different applications by using various methods, including etching, printing, self-assembling, etc. (6–15). In particular, since droplet microfluidics was used as microreactors, the develop- ment of spherical structural color materials has found exciting avenues (16–19). This new strategy not only ensures the mono- dispersity but also increases the componential and morphological diversity of the structural color particles (SCPs). Besides benefiting from their spherical symmetry, the photonic bandgaps (PBGs) of the resultant microfluidic SCPs are usually independent of rotation under illumination at a fixed incident angle, which broadens the perspective values of the structural color materials for displaying, coding, sensing, and so on (20–26). However, despite the substantial progress that has been made in SCPs, their main applications are still limited to the isotropic morphologies and photonic nanostructures, since most of the self-assembly approaches in droplet microreactors can only achieve spherical particles, which are difficult for controllable fixation, location, and orientation. In addition, because of the relatively low refractive index contrast among their components, which causes apparent light transmission and reduced reflection, most of the SCPs are suffering from dim and undistinguishable structural colors in practical applications. Thus, the creation of novel SCPs with dis- tinctive functions is still anticipated.
Show more

10 Read more

Large Eddy Simulation of Deposition of Anisotropic Particles in a Turbulent Channel Flow

Large Eddy Simulation of Deposition of Anisotropic Particles in a Turbulent Channel Flow

concentration of large particles close to the walls in regime 3 (Sun et al, 2011). Higher lev- els of accuracy when predicting particle deposi- tion are expected when the flow field is ob- tained from direct numerical simulation (DNS) (Ounis et al, 1993; Zhang and Ahmadi, 2000; Zhang et al, 2001) or large eddy simulation (LES), together with sub-grid scale (SGS) ve- locity fluctuation contributions (Njobuenwu and Fairweather, 2014b; Salmanzadeh et al, 2010; Uijttewaal and Oliemans, 1996; Wang and Squires, 1996). Salmanzadeh et al (2010) and Njobuenwu and Fairweather (2014b) observed that the inclusion of the SGS turbulence fluctu- ations improves the model predictions for parti- cle deposition rate, especially for small parti- cles. In (Njobuenwu and Fairweather, 2014b), the shear lift force was applied for spherical particles, whilst profile lift due to particle orien- tation was accounted for when considering non-spherical particles. The authors obtained good agreement in regime 3 for spherical par- ticles against the benchmark experimental da- ta, but reported an under-prediction of the ex- perimental deposition rate for non-spherical particles in the same regime. The non-inclusion of the shear lift force whose magnitude is of the order of the square of the particle diameter for disk and needle-like particles, and whose mag- nitude is higher than the drag force in the sub- viscous layer, as will be shown later in the force balance analysis, was responsible for the under-prediction.
Show more

9 Read more

Non Equilibrium Dynamics of DNA Nanotubes

Non Equilibrium Dynamics of DNA Nanotubes

From the experimental point of view, engineering artificial systems for understanding bi- ological systems offers three advantages. First, building simple nanoscale systems that are easy to modify provides a platform for rigorous testing, refining, and confirming mathemat- ical models of biomolecular processes. In the case of microtubules, a detailed understanding of the molecular machinery of α,β-tubulin is difficult to attain because the activity of the monomer and polymer are affected by complex systems of exogenous and endogenous cel- lular factors. Claiming that studying artificial system will help understanding biology is still controversial. Not all insights obtained from artificial systems are guaranteed to have biological relevance, as will be discussed in section 1.5. Second, the similar length scales of the biological molecules and their technological analogs permits engineering of a more advanced artificial system that can alter or even improve the performance of the biolog- ical system of interest. Third, for non-equilibrium self-assembly, collective behavior may arise from simple local rules which might yield insights into the principles of self-organized system. This set of principles could be essential for engineering materials that exhibit novel behaviors, such as adaptive assembly [BR09, SY10], self-healing [Win06, SCW08], and self-replication [SW05].
Show more

218 Read more

Capillary Assembly of Anisotropic Particles

Capillary Assembly of Anisotropic Particles

Particles at interfaces induce a deformation field, determined by the particle shape and its wetting conditions. A rough or chemically heterogeneous microparticle can create an undulated contact line where fluid, vapor and particle meet [9, 44] A non-spherically shaped particle also creates an undulated contact line, even in the absence of chemical heterogeneities or contact line pinning. [11, 14, 18, 45] The deformation induced by an isolated microparticle can be described in various ways depending on the distance from the contact line. Far from the particle, the interface deformation is typically a quadrupole in polar coordinates [9]. Closer to the particle, the deformation field is eccentric if the particle shape is elongated [28]. Very close to the particle surface, the interface deformation is dominated by fine details of the particle shape and the boundary conditions at the three phase contact line. [6, 7, 9, 11, 14, 18] These particle-induced distortions create excess area, which corresponds to an increase in interfacial energy. When deformation fields from neighboring particles overlap, far field capillary interactions occur, causing particles to orient and attract to minimize the overall free energy of the system. These interactions can also be understood as a function of the distance between interacting particles. Far from contact, the energy of interaction between pairs of microparticles can be described as pairs of interacting quadrupoles in polar coordinates [9]. This energy enforces mirror symmetric orientations as the particles attract. At moderate separation distances, the eccentricity in the deformation field induces a torque that enforces a particular alignment as particles approach [28]. Finally, in the very near field, where separation distances are comparable to the characteristic lengths of the particles, the finer details of the geometry and wetting conditions of the particle surface dominate the interaction [11, 18].
Show more

130 Read more

Self-Assembly and Stimuli-Responsive Properties of Amphiphilic Self-Immolative Block Co-Polymers

Self-Assembly and Stimuli-Responsive Properties of Amphiphilic Self-Immolative Block Co-Polymers

responsive dendrimers. These are molecules which contain a focal point on one end and branch outwards in the other direction in a series of generations. Self-immolative dendrimers were independently developed in 2003 by three groups to degrade under unique environmental triggers 38-40 . The trigger can be incorporated as the focal point which, upon the specific stimulus, leads to the downstream generations becoming unstable and being released in an exponential manner. This is important because the single stimulus leads to an amplification of released reporter molecules. Additionally, the dispersity of these large dendrimers are low (<1.1), which makes the behaviour of these molecules very consistent and predictable 41-45 . Unfortunately self-immolative dendrimers are limited in their use due to their complicated multi-step synthesis, and the increasing steric bulk that each successive generation gains, rendering high-generation
Show more

120 Read more

Design and Fabrication of Hierarchical Three-Dimensional Porous Nanostructures using Template-Directed Self-Assembly of Colloidal Particles.

Design and Fabrication of Hierarchical Three-Dimensional Porous Nanostructures using Template-Directed Self-Assembly of Colloidal Particles.

In this section, photoresist with a phase mask array of 350 nm particles was exposed to un- polarized light with a wavelength of 365 nm which was generated by a mercury arc lamp. To ensure that the wavelength was constant across the sample, the sample was fabricated using a 365 nm optical filter in the same configuration as described in the previous section. As described in Section 4.1, the combination of a longer wavelength with a smaller particle size is expected to result in a shorter intensity period within the photoresist, however the lattice structure will be more susceptible to failure. The sample was sonicated to remove the spheres and then developed. The results of this exposure are seen in Figure 4-20. Again, the weakness of the structure can be observed, as well as the presence of defects in the interstitial regions. Though collapsed, the nature of the interior lattice can be observed in these samples. The circled section in Figure 4-20 in particular shows a region in which the periodic intensity effect is observed.
Show more

81 Read more

Self assembly of virus like particles of porcine circovirus type 2 capsid protein expressed from Escherichia coli

Self assembly of virus like particles of porcine circovirus type 2 capsid protein expressed from Escherichia coli

PCV2-infected pigs. Therefore, it is a good candidate antigen for the design of new recombinant vaccines against PCV2 infection and for the development of sero- logic tests. There are several PCV2 vaccines currently on the market. The CIRCOVAC® (Merial Com, lyon, France), which is an inactivated PCV2 vaccine. The vac- cine of Suvaxyn PCV2 One Dose (Fort Dodge Animal Health, Fort Dodge, IA) was the first PCV2 vaccine approved for commercial use in the United States by the United States Department of Agticulture. This vac- cine is a chimeric virus that was developed to have the PCV2 capsid and the PCV1genome. Another available two vaccines are subunit vaccine, Ingelvac® CIRCOFLX™ (Boehringer Ingelheim Vermdedica Inc, St. joseph, MO) and Circumvent PCV (Intervet Inc, Millsboro, DE), which are the capsid-based subunit vaccine expressed in inactivated baculovirus. In recent years, two main expression systems, including prokaryocytes and eukar- yocytes, have been applied to express Cap protein as an antigen for animal immunization against PCV2. The prominent characteristic of the recombinant Cap protein is its ability to independently self-assemble to form virus-like particles (VLPs) in eukaryocytes, such as insect-baculovirus and yeast expression systems [5,6]. However, few papers have reported on the production of successful Cap protein VLPs in Escherichia coli (E. coli) [7].
Show more

5 Read more

Polymersome modification and functionalisation via particle bilayer interactions

Polymersome modification and functionalisation via particle bilayer interactions

Amphiphiles are often described as molecules that possess a dual hydrophobic-hydrophilic character. The hydrophobic tail is often one or two long alkyl chains, while the hydrophilic part is known to be ionic and commonly referred to as head group of the molecular structure. Amphiphiles come in a variety of forms, both naturally occurring phospholipids, such as phosphatidyl choline, which is the major component of biological membranes and can be obtained from a variety of readily available source, e.g. Soybeans or egg yolk, and the fully synthetic such as sodium dodecyl sulphate (SDS) or cetyltrimethylammonium bromide (CTAB), which has been widely used in commercial products, such as hair conditioner and facial cleanser. Amphiphilic molecules have gained considerable interest among scientists for not only its use as surfactants but also the potential applications and their microscopic morphologies in bulk and in aqueous solutions, which motivates the studies including those on self-assembly principles, theories, structures and functionalisation of the amphiphilic molecules. In aqueous solution amphiphiles undergo self-assembly in order to minimise energetically unfavourable hydrophobe/water interactions, which results in various morphologies. The factors that determine the nanostructures of these assemblies are influenced by the packing parameter, which is dependent on the dimensions of amphiphilic molecules.
Show more

127 Read more

Immersive 3D Visualization of the Collective Behavior of Particles and  Crystal Dislocations Using Virtual Reality Technology

Immersive 3D Visualization of the Collective Behavior of Particles and Crystal Dislocations Using Virtual Reality Technology

Using computational methods we first obtain the transient locations and orientation information for the grain particles and crystal dislocations. We save these information in various data files. We render the models by reading the data files in text format and updating the data files in each frame for the purpose of simulation. The data files are created by solving for the differential equations of the displacement and rotations in MATLAB. These data files consist of the location information for Dislocations and the location, orientation, velocity, ace- leration, angular velocity, and angular acceleration information of individual particles in the granular assembly for each time step. Here time step is a small increment in time that we consider to get the particle location and orientation information as the assembly is going through the strain and pressure to obtain transient information. The data files in case of the Delaunay network consist of the connected grain numbers or indices of a tetrahe- dral.
Show more

16 Read more

Self-Replication and Self-Assembly for Manufacturing

Self-Replication and Self-Assembly for Manufacturing

This paper introduces JohnnyVon 2.0, which builds on its predecessor by adding phenotypes to the simulation. The design of JohnnyVon 2.0 was partly inspired by the work of Seeman on building nanometer-scale structures with DNA [14], [15]. In living organisms, replication is based on DNA (the genotype) and the information encoded in DNA is used to build proteins (the major structural material of the phenotype). Seeman has shown that DNA can serve both as a device for self-replication (genotype) and (surprisingly) as a building material for nanoscopic structures and tools (phenotype). By choosing the appropriate sequence of codons, DNA can be programmed to self- assemble into a wide variety of structures, such as cubes, octahedra, one-dimensional strands, two-dimensional meshes, and three-dimensional arrays. Seeman discusses a variety of potential nanotechnological applications for these structures. For example, a three-dimensional DNA array could facilitate x-ray crystallography, by serving as a scaffolding for holding molecular samples in a regular lattice [15].
Show more

45 Read more

Asphaltene Self-Assembly

Asphaltene Self-Assembly

This unique behavior may seem counterintuitive because in many colloidal systems, including proteins and nano- or microparticle suspensions, repulsive electrostatics often dominate due to the high degree of self-similarity and subsequently similar surface charge distributions of the colloidal materials. The addition of an electrolyte screens such repulsion, and can reduce the interparticle spacing. Asphaltenic aggregates, however, are amphoteric and consist of a broad range of molecules with varying size and functional moieties. When asphaltenic aggregates adsorb at the oil/water interface they can have dissimilar surface charges, depending on the pH and the asphaltene chemistry. It is feasible then that, at pH 7, some adsorbed aggregates have a net negative surface charge due to deprotonation of acidic groups while other aggregates exhibit a positive net surface charge from basic moieties. This would lead to attractive electrostatic interactions that act over a long range in the absence of electrolyte, but are significantly shielded in the presence of added salt (cf. Figure 5.6). In such a case, the attractive electrostatics may act as a significant driving force for asphaltenic interfacial consolidation, facilitating rapid formation of a physically crosslinked network. Adding electrolyte would weaken the primary driving force for interfacial consolidation, resulting in the longer time to form the interfacial network.
Show more

285 Read more

Bottom Up Fabrication of Protein Nanowires via Controlled Self Assembly of Recombinant Geobacter Pilins

Bottom Up Fabrication of Protein Nanowires via Controlled Self Assembly of Recombinant Geobacter Pilins

Design, recombinant production, and structural characterization of pilin build- ing blocks. Computational analyses of the PilA sequence via AGGRESCAN (14) identi- fied two regions in the mature pilin peptide (residues 1 to 22 and 25 to 31) as having the highest aggregation propensity (Fig. 1B). Aggregation scores were particularly high for the first 10 amino acids, which were also among the most hydrophobic residues identified in a Kyte-Doolittle plot (15) (Fig. 1B). The aggregation and hydrophobicity analyses therefore predict truncations of the first 21 or 22 amino acids as those having the highest impact on solubility. As this extended truncation preserves the aromatic and charged residues required for fiber formation and conductivity (Fig. 1B), we targeted this N-t region to engineer pilin derivatives suitable for recombinant expres- sion with a self-splicing intein linker and a solubility and affinity tag (chitin binding domain [CBD]). The recombinant approach reproducibly recovered in the soluble fraction of culture lysates fusion proteins containing pilins engineered with truncations of 10, 19, 20, and 22 amino acids (Fig. 1B and C). Affinity chromatography in a chitin column retained the fusion proteins bound to the chitin matrix and permitted the elution of the pilin peptide after inducing the self-splicing of the intein linker with dithiothreitol (DTT) (see Fig. S1 in the supplemental material). Figure 2A shows, as an example, the enrichment of the CBD-PilA 19 fusion protein in soluble fractions collected
Show more

15 Read more

Self-Assembly of Brush Polymers

Self-Assembly of Brush Polymers

These results indicate that under thermal equilibrium, brush BCPs with similarly sized side chains undergo a morphology transition when the volume fraction of one of the blocks exceeds 70%. Asymmetric brush BCPs can also be kinetically trapped into a (undulating) lamellar morphology where the order of the sample decreases with increased asymmetry. In order to make more conclusive statements about the morphology transitions of asymmetric brush BCPs, it will be important to obtain SAXS data from samples that have achieved thermal equilibrium. Furthermore, it may prove valuable to explore the effect of the backbone length on the self-assembly of these macromolecules, as lower molecular weight brush BCPs have been shown to achieve thermal equilibrium more rapidly than those with higher molecular weights. 11
Show more

109 Read more

Algorithmic self-assembly of DNA

Algorithmic self-assembly of DNA

We can use the biochemistry of whiplash PCR to compute the -formula, and use the bio- chemistry of hybridization to generate a combinatorial library of DNA representing all possible inputs which obey the equality constraints. Following Adleman (1994), the combinatorial library consists of DNA representing paths through a graph. We use bipartite assembly graphs, in which nodes are either black or white and are labelled by distinct single symbols, and directed edges are labelled by symbol strings (possibly length zero) whose symbols are disjoint from those used at nodes. Each symbol represents a unique sequence of DNA. An oligo is generated for each edge in the graph, using the sequences for the symbols of the origin node, the edge, and the destination node: since the graph is bipartite, edges are either from white nodes to black nodes (in which case “sense” oligos are synthesized), or from black nodes to white nodes (in which case the Watson- Crick complementary “anti-sense” oligos are synthesized). These oligos may be mixed in a single test tube and full-length product may be generated using assembly PCR 22 (Stemmer et al. 1995). This reaction creates long “repetitive” DNA, which may then be cut at a restriction site to yield defined-length product, and then made single-stranded. For each path through the graph, the se- quence of node and edge symbols on that path will be generated in DNA by assembly PCR; the complementary DNA will also be generated 23 . Figure 2.10 gives an assembly graph for generating all DNA representing inputs where x 11 = x 12 .
Show more

109 Read more

The Scd6/Lsm14 protein xRAPB has properties different from RAP55 in selecting mRNA for early translation or intracellular distribution in Xenopus oocytes

The Scd6/Lsm14 protein xRAPB has properties different from RAP55 in selecting mRNA for early translation or intracellular distribution in Xenopus oocytes

Oocytes accumulate mRNAs in the form of maternal ribonucleoprotein (RNP) particles, the protein components of which determine the location and stability of individual mRNAs prior to translation. Scd6/Lsm14 proteins, typified by RAP55, function in a wide range of eukaryotes in repressing translation and relocating mRNPs to processing bodies and stress granules. In Xenopus laevis, the RAP55 orthologue xRAPA fulfills these functions. Here we describe the properties of a variant of xRAPA, xRAPB, which is a member of the Lsm14B group. xRAPB differs from xRAPA in various respects: it is expressed at high concentration earlier in oogenesis; it interacts specifically with the DDX6 helicase Xp54; it is detected in polysomes and stalled translation initiation complexes; its over-expression leads to selective binding to translatable mRNA species without evidence of translation repression or mRNA degradation. Since both Xp54 and xRAPA are repressors of translation, activation appears to be effected through targeting of xRAPB/Xp54.
Show more

37 Read more

Self assembly of cyclic polymers

Self assembly of cyclic polymers

As a consequence of improved synthetic methods, enabling the preparation of well-defined, high purity cyclic polymers, the self-assembly of amphiphilic cyclic polymers has received increasing attention in recent years. By comparing the aggrega- tion of cyclic polymers with equivalent linear polymers, we can determine the effect of cyclization on self-assembly and increase our understanding of structure – property relation- ships. Indeed, the examples discussed in this review have high- lighted the profound effect cyclization can have on particle dimensions, stability, and morphology, as well as the packing of polymer chains within the assembly. In general, cyclic diblock copolymers form smaller, entropically disfavoured aggregates in comparison to linear diblock copolymers, as a consequence of the confined and looped nature of cyclic poly- mers, resulting in a greater number of unfavourable core- solvent junctions. The self-assembly of cyclic diblock copoly- mers is however similar to that of linear triblock copolymers, which are also required to loop upon aggregation. For the self- assembly of more complex cyclic topologies, assemblies of cyclic polymers are often larger than the equivalent linear polymer assembly as a consequence of poor polymer packing. Furthermore, the cyclization of amphiphilic polymers can lead to unique self-assembly behaviour that cannot be achieved through the self-assembly of linear polymers or can impart improved properties to the resulting nanostructures, for example, greater thermal stability and robustness towards salt additives.
Show more

12 Read more

Show all 10000 documents...