Morphogenesis of microshapes

Introduction:
Increasing interest in nanotechnologies and biocomplexity has created the need in understanding the morphogenesis of complex self-assembled shapes, which  either exist in nature or can be synthesized for a specific purpose. These shapes can be the parts for micro electrical/optical machines, microtubules in the cell skeletons, seashells, etc. Liquid crystal templating  of hexagonal mesostructured silica (known, for example, as MCM-41) brings a unique example of a material due to the following reason. This is already of great interest to industry because of its nanosize highly  uniform porosity, and consequently, can be functionalized by putting various substances inside the pores. Secondly, the material has a relatively simple molecular structure; hence, the chemistry is well  understood. And finally, it is a good test system to study the morphogenesis due to the complex micron size shape of the mesoporous silicas.

A zoo of shapes is shown below (SEM images, colors are artificial):

particles

Main goal:
To develop quantitative theory of morphogenesis of mesoporous silica shapes, to create experimental recipes of synthesis of specific shapes in a  controlled way, to predict and synthesize new shapes.

Present Status and Preliminary Results:
If the mesoscale synthesis is relatively well elaborated, the basic  mechanism responsible for the overall morphogenesis of silica mesoporous shapes is not understood. The basic hypothesis is that the complex  morphology of the shapes is a result of relaxation of mechanical stresses which appeared due to differential polymerization of silica precursor. Such a difference in the polymerization is expected to occur, e.g.,  due to the change of the environment during the synthesis, or because of the older inner parts of the shapes vs. the younger outer layers. Now we are showing that the shape formation is at least partially described by the equilibrium thermodynamics.
         Some experimentally observed  shapes and corresponding computer 3D similations are shown below:

Experiment:

Simulations:

Self-assembly of  meso(nano)porous shapes, fibers  is shown to be described by the Boltzmann distribution of free energy predicted by the equilibrium thermodynamics.

TOC_figure

Recent selected publications:

Volkov, D., J. Benson, Y. Kievsky, I. Sokolov “Towards understanding of shape formation mechanism of mesoporous silica particles”, Phys.Chem. Chem. Phys., in press, DOI: 10.1039/b917424a (front page)

S. Naik, I.Sokolov, Mesoporous “Silica Fibers and Discoids Endowed with Circular Pore Architecture using Disodium Trioxosilicate as Silica Source”, Microporous and Mesoporous Materials, 116 (2008) 581–585

S.P. Naik , Igor Sokolov, “Room Temperature Synthesis of Nanoporous Silica Spheres and their Formation Mechanism” Solid State Communications, 2007 Volume 144, Issues 10-11, December 2007, Pages 437-440S.

P. Naik , S. P. Elangovan , T. Okubo, and Igor Sokolov “Morphology Control of Mesoporous Silica Particles”. Journal of Physical Chemistry (C), v. 111, n. 30, pp. 11168 - 11173, 2007.

Igor Sokolov, Yaroslav Y. Kievsky, Jason M Kaszpurenko “Self-assembly of ultra-bright fluorescent silica particles”, Small, (2007) , v.3, (3), pp. 419-423.

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