Modeling of Biomineralization and Structural Color Biomimetics by Controlled Colloidal Assembly - Bioinspiration: From Nano to Micro Scales - page 219

7.1 Introduction

Crystallization plays a crucial role in biomineralization, the preparation of func-
tional materials [ 1 - 4 ], the structural characterization of natural and synthetic
molecules [ 5 , 6 ], and the development of advanced technologies [ 7 , 8 ]. Nowadays,
many nanomaterials are crystalline phases, and the essential structures and utmost
important properties of the systems are determined by nucleation and the correlation
between the nucleating nanophase and the substrate, etc. The control of crystalliza-
tion is directly related to some soft materials and nanophase formation [ 9 ].
Up to now, crystallization is still considered as art other than science, mainly
because there is not sufficient knowledge on its critical early stages and the atomic
processes. In this regard, the kinetics of the transition from the metastable structure
to the stable structure has so far been open to question. The key challenge is the
in situ imaging of the atomic/molecular dynamic process, which is limited by both
the spatial and the temporal definitions of current technologies and the absence of
the direct observation on the transition process in real space, except for some local
events of crystallization/quasicrystallization of large species, namely proteins [ 10 ]
and colloidal particles [ 11 ]. Notice that computer simulations have been applied
to acquire the information [ 12 ]. Nevertheless, due to the constraint of computation
power and the methodologies, the knowledge obtained is still limited. It is therefore
of critical importance to develop a new methodology to “simulate” or “monitor” the
atomic/molecular dynamic process of the nucleation and growth of crystals [ 13 ].
Colloids, the dispersions of nano/microsized particles in a fluid background
solvent, range from ink, milk, mayonnaise, paint, and smoke and have many
practical applications [ 14 - 16 ]. Nowadays, colloids have been employed as a model
system to study phase transitions [ 17 - 22 ]. In this regard, these nano/microsized
colloids provide an important platform for sampling the aggregation and assembly
at the single particle level because of its visible size, tractable dynamics, and
tunable interparticle interactions [ 12 - 16 , 23 - 25 ]. In addition, colloidal particles in
solutions behave like big “atoms” [ 19 , 20 ], and the phase behavior of colloidal
suspensions is similar to that of atomic and molecular systems [ 21 ]. Therefore,
from the point of view of crystallization modeling, the growth units are colloidal
particles, and thus the crystallization process can be observed directly by a normal
optical microscope. Furthermore, the interaction among colloidal particles can be
turned by the adjustment of the ionic strength, pH of solutions/suspensions, and
the applied electric field strength and frequency; therefore, the thermodynamic
driving force for the crystallization can be controlled precisely in such a system.
This allows the quantitative measurement and the data interpretation similar to
computer experiments [ 20 , 21 ]. Besides, proteins and viruses are in the colloidal
domain. Any advantage in the understanding of colloidal crystallization will exert a
direct impact on the control of proteins and biomacromolecule crystallization. Apart
from modeling, from the technological point of view, the knowledge of nucleation,
growth, and defect generation is very important in identifying robust technologies
in electronic, photonic, and life sciences and technologies.