The interactions between different types of colloidal particles are measured and analyzed. We use these interactions to
build different self-assembled microstructures, such as dimers, chains, wires, crystals and superstructures. In the
experiments we have used different size, different symmetry of colloids (elastic dipoles and quadrupoles) and different
way of colloidal binding (via localized defects and via entangled defects). We use optical tweezers for directed selfassembly
of colloidal particles. Special attention is devoted to the hierarchical superstructures of large and small
particles. We show that smaller, submicron colloidal particles are trapped into the topological defect rings or loops,
twisting around larger colloidal particles, which are sources of strong nematic deformations. Various possible
applications are discussed, especially in photonics and metamaterials.
We describe and analyze experiments, where optical manipulation of small colloidal particles in the nematic liquid
crystal (NLC) was used to create artificial colloidal structures, such as 1D chains and 2D colloidal crystals, and
superstructures of different types of colloids. In all cases, the colloidal particles are strongly bound to each other, with a
typical pair interaction energy of several 1000 k<sub>B</sub>T per 1μm size particle. There are two distinct mechanisms of colloidal
binding in a spatially homogeneous NLC: (i) binding via spatially localized topological (point) defects, and (ii) binding
via entangled topological defects, where the defect line winds around and wraps several colloidal particles.
Colloidal structures assembled in confined nematic liquid crystals are examined. Theoretical predictions based on
Landau-type approaches are complemented with the latest studies of laser assisted colloidal assembling. Effective
colloidal interactions are particularly sensitive to the confinement and external fields. Their complexity leads to
numerous stable or metastable colloidal superstructures not present in isotropic solvents. Particularly important are
colloidal structures coupled by entangled disclinations. Such a string-like coupling is very robust and opens new routes
to assemble new photonic materials.
The ability to generate regular spatial arrangements of particles on different length scales is one of the central issues of
the "bottom-up" approach in nanotechnology. Current techniques rely on single atom or molecule manipulation by the
STM, colloidal particle manipulation by laser or optoelectronic tweezers, microfluidics, optofluidics, micromanipulation
and classical lithography. Of particular interest is self-assembly, where the pre-determined spatial arrangements of
particles, such as 3D photonic crystals, could be realized spontaneously. Dispersions of particles in liquid crystals show
several novel classes of anisotropic forces between inclusions, which result in an amazing diversity of self-assembled
patterns, such as linear chains and 2D photonic crystals of microspheres. The forces between the particles in nematic
colloids are extremely strong and long-range, resulting in several thousand times stronger binding compared to the
binding in water based colloids. The mechanisms of self-assembly in nematic colloids are discussed, showing this is a
novel paradigm in colloidal science, which can lead to new approaches in colloidal self-assembly for photonic devices.