Chiral colloidal clusters

Abstract

Chirality is an important element of biology, chemistry and physics. Once symmetry is broken and a handedness is established, biochemical pathways are set. In DNA, the double helix arises from the existence of two competing length scales, one set by the distance between monomers in the sugar backbone, and the other set by the stacking of the base pairs. Here we use a colloidal system to explore a simple forcing route to chiral structures. To do so we have designed magnetic colloids that, depending on both their shape and induced magnetization, self-assemble with controlled helicity. We model the two length scales with asymmetric colloidal dumbbells linked by a magnetic belt at their waist. In the presence of a magnetic field the belts assemble into a chain and the steric constraints imposed by the asymmetric spheres force the chain to coil. We show that if the size ratio between the spheres is large enough, a single helicity is adopted, right or left. The realization of chiral colloidal clusters opens up a new link between colloidal science and chemistry. These colloidal clusters may also find use as mesopolymers, as optical and light-activated structures, and as models for enantiomeric separation.

Crystal nucleation of colloidal hard dumbbells

“…[10][11][12][13] The surface tension for the fluid-CP1 interface of hard dumbbells with L * = 0.4 is βγ σ 2 1.8. 28 The height of free energy barrier is given by G * = 16πγ 3 /3(ρ s | μ|) 2 in CNT. If we assume that the interfacial tension does not change significantly with increasing pressure, we can estimate the free energy barrier height as a function of pressure by integrating the Gibbs-Duhem equation to obtain | μ|.…”

Directing Assembly of DNA-Coated Colloids with Magnetic Fields To Generate Rigid, Semiflexible, and Flexible Chains

“…[4][5][6] Recently, the development of colloidal polymers (long chains of linked nano or micron-sized particles that are analogous to linear polymer molecules) has generated interest. [7][8][9][10] Colloidal polymer systems have multiple advantages, including being small enough to be influenced by Brownian forces yet large enough to enable studies with 'single molecules' using ordinary light microscopy. Various methods have been used to assemble colloidal polymer chains, including methods that produce anisotropic patches that act as binding sites [11][12][13][14] and the use of anisotropic dipolar interactions in a directed assembly of colloids using either magnetic [15][16][17][18][19] or electric fields.…”

Polarization-dependent optomechanics mediated by chiral microresonators

“…For rotating particles, the fit of ACFs with equation 3 gives a direct measurement of the particle rotational frequency, O, which is used to evaluate the averaged optical torque transferred to the trapped particle. As O is set by the equilibrium between optical and rotational drag torques 43 , the optical torque modulus, G þ rad , is equal to the rotational drag torque on a sphere rotating in a fluid at low Reynolds number 10 , G drag ¼ 8pZR 3 0 O. Note that we also monitor the particle dynamics in the trap by video microscopy (Supplementary Movies 1 and 2) so that we can verify the absence of tumbling and the uniform rotation about the light propagation (z À ) axis.…”

“…It is a key feature in nature and has a fundamental role in several phenomena 2 . Molecules that cannot be superimposed upon their mirror images are chiral, and life has a preference for these configurations 3,4 . Chirality distinguishes between left-and right-handed materials, and often advances in materials science, including nanostructured materials and metamaterials, make evidence of the added value introduced by the presence of this property [5][6][7] .…”