Highly birefringent colloidal particles for tracer studies

Abstract

We report on the preparation and characterization of highly birefringent, monodisperse colloidal particles with sizes between 100 nm and some micrometres made by emulsification of a reactive acrylate monomer in aqueous solution. Photopolymerization of the emulsion droplets in the liquid crystalline state results in particles with frozen orientational order. Particles that had not been polymerized have a higher effective birefringence than the polymerized particles at room temperature, as shown by measurements of the depolarized scattering intensity using quasi-elastic light scattering (QELS). We also present preliminary results showing that larger particles can be made to rotate with optical tweezers with circular polarization.The presence of hydrodynamic interactions (HI) in colloidal suspensions and polymer solutions leads to qualitatively new phenomena that are not found in simple liquids. Examples are the equilibrium dynamics and the flow behaviour of dense colloidal suspensions [1-3]. When a colloidal particle moves due to the random forces imparted by the surrounding fluid molecules, it excites a flow field that transfers linear momentum to surrounding particles. The flow field due to a translating particle is inhomogeneous, which results in neighbouring particles experiencing a torque. Similarly to this coupling of rotation and translation, the flow field excited by the Brownian rotation of a colloidal particle can transfer angular momentum to neighbouring particles, leading to rotation-rotation coupling.While detailed insight on the influence of HI on the translational degrees of freedom in colloidal suspensions has been obtained from quasi-elastic light scattering (QELS) and real-space imaging experiments, much less is known about the effect of HI on the rotational motion. Rotational motion can be observed in depolarized quasi-elastic light scattering experiments on optically anisotropic particles [4,5], using time-resolved phosphorescence anisotropy measurements on specially labelled particles [6], or nuclear magnetic resonance [7]. Measured autocorrelation functions of the scattered electric field measured by depolarized QELS now contain information not only on the particle displacements but also on their

Kinesin rotates unidirectionally and generates torque while walking on microtubules

“…1A). Via anti-GFP antibodies, we bound the motors to microspheres composed of an ordered liquid crystal RM257 (18)(19)(20) with a birefringence of 0.18, 20 times larger compared with that of quartz cylinders commonly used in optical torque wrenches (21)(22)(23). This high birefringence enables high contrast in polarization microscopy and a fast response time in angular trapping applications (19).…”

Chemical and biological sensing using liquid crystals

“…Emulsion droplets can be prepared by various techniques, such as photopolymerization [91], ultrasonication [92], shearing of droplets and subsequent crystallization fractionation [93, 94], droplet break-off in a co-flowing stream (microfluidics) [95], and dispersion polymerization [91, 96, 97]. However, the majority of these methods do not permit control over LC droplet size in the range that is optimal for LC sensing (1-10 μm, see below).…”

Design of Functional Materials Based on Liquid Crystalline Droplets

“…46–48 These methods, while generally effective for the preparation of LC droplets larger than 10 μm, do not work well at the 1 μm-scale. Recently, however, a new technique, which involves the templated synthesis of polyelectrolyte multilayer (PEM) capsules using sacrificial silica micro- or nano-particles and subsequent filling of the capsules with LC, has provided the necessary level of control to explore size-dependent ordering of LC droplets with sizes around 1 μm (Figure 3).…”