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Abstract

In the past few years , the growing need for renewable energy sources has driven a rapid
development of new hierarchic materials, focusing on the production of complex 3D
inorganic mesomaterials. Among numerous approaches proposed in the literature, self
assembly has recently become a very powerful method to create versatile nanostructured
inorganic mesomaterials that challenge our conventional views of crystal growth by the
attachment of fully grown nanocrystal units. Looking from an application point of view,
recently published review pointed out “What is needed are fast and easily controllable self assembly mechanisms , which ideally work at room temperature (E. Sturm and H. Cölfen, 2017)
While diverse mesomaterials with promising properties have been synthesized with great
success, proper understanding of the driving force of the mesocrystal assembly has not
yet evolved . One of the main reasons is the lack of experimental evidence that would lead
to a theoretical consensus on its nature.
In my thesis I address the problem of the self assembly mechanism which was
exploited to the extent of full control over final rutile’s TiO 2 3D branched morphology.
The first part of the thesis deals with multilevel branched struct ures produced by the
self assembly of primary rutile precipitates and uncovers the key processes controlling
this non classical crystallization path. I have shown that the formation of complex
mesocrystals of rutile is accomplished by the oriented attachment of nanocrystalline
precipitates along low energy planes, resulting in lateral attachment and twinning.
Moreover, the first experimental evidence that indicates the presence of electromagnetic
force fields being active during oriented attachment of nanocrystals is provided In the
second part the two identified self assembling mode s of rutile, together with variation in
supersaturation were exploited in order to get the control over oriented attachment and
twinning. The results showed the dependence of t win incidents on aspect ratio of
precipitated rutile nanocrystals, which is linearly increasing with medium acidity, i.e. the
lower it is, the higher the affinity for twin oriented attachment. To quantify the degree of
branching of rutile mesocrystals, we proposed a new generally applicable criterion, the so
called morphology factor. It provides a quantitative measure of nanoparticle morphology
and can be used to evaluate the increase of specific surface area for any material,
independently of their size. Finally, in the last part, all the knowledge on the self
assembly mechanism was used and focused on the production of applicable, i.e.
homogeneous and reproducible twin based rutile mesocrystals. We achieved homogeneous
branched products by the low temperature synthesis strategy that is based on continuous
homogenization of the reactive solution. The results showed the importance and impact
of homogeneity on the specific surface area of the mesocrystals, expressed in terms of
morphology factor, and approaches the above target.