Colloidal crystals [Elektronische Ressource] : preparation, characterization, and applications / vorgelegt von Jianjun Wang

Wangj

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2007
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Colloidal Crystals:
Preparation, Characterization, and Applications




Dissertation zur Erlangung des Grades
„Doktor der Naturwissenschaften“
am Fachbereich Chemie, Pharmazie und Geowissenschaften
der Johannes-Gutenberg-Universität in Mainz




vorgelegt von


Jianjun Wang
geboren in Zhejiang / P. R. China

Mainz, 2006
Content
1 General Introduction

1.1 Colloidal System………………………………………………………………1
1.2 Colloidal Crystals………………………………………………………………2
1.3 Colloidal Crystals and Photonic Crystals………………………………………3

1.4 Colloidal Crystals and Phononic Crystals……………………………………4
1.5 Colloidal Crystals, 2D and 3D Patterned Structures……………………………7
1.6 Objective and Scope of Thesis…………………………………………………8

References……………………………………………………………………………11
2 Synthesis of Nano- and Microspheres
2.1 General…………………………………………………………………………13

2.2 Surfactant Free Emulsion Polymerization……………………………………17
2.3 Seeded Emulsion Polymerization………………………………………………20
2.4 Miniemulsion Polymerization…………………………………………………23

2.5 Characterization of Particles……………………………………………………24
2.5.1 Dynamic Light Scattering25

2.5.2 Scanning Electron Microscopy……………………………………………27
References……………………………………………………………………………29
3 Fabrication of Colloidal Crystals and Inverse Opals

3.1 Background……………………………………………………………………30
3.2 Experimental……………………………………………………………………33
3.3 Fabrication of Monomodal Colloidal Crystals (mCC)

3.3.1 Effect of Process Parameters on Formation of mCCs……………………34
3.3.2 Optical Properties of mCCs………………………………………………36 3.4 Fabrication of Binary Colloidal Crystals
3.4.1 Introduction………………………………………………………………37

3.4.2 Relative Particle Concentration……………………………………………40
3.4.3 Size Ratio Variation………………………………………………………43
3.4.4 Direct Replica Formation…………………………………………………45

3.4.5 Spectra……………………………………………………………………46
3.5 Preparation of Multilayered Trimodal Colloidal Structures and Binary Inverse
Opals………………………………………………………………………………47

3.6 Fabrication of Colloidal Crystals with Other Methods
3.6.1 Automated Preparation Method for Colloidal Arrays of Monomodal and
Binary Colloidal Mixtures by Contact Printing with Pintool
Plotter……………………………………………………………………53
3.6.2 Vertical Cell Lifting Method for Colloidal Crystal Preparation……………57

3.7 Conclusions……………………………………………………………………58
References……………………………………………………………………………61
4 Characterization of Colloidal Crystals with Brillouin Light Scattering

4.1 Introduction63
4.2 Brillouin Light Scattering (BLS) ………………………………………………64
4.3 Experimental……………………………………………………………………67

4.4 Characterization of Dry Colloidal Crystals……………………………………68
4.5 Characterization of Wet Opals…………………………………………………73
4.6 Conclusions……………………………………………………………………82

References……………………………………………………………………………83
5 Application of colloidal crystals
5.1 Inverse Opals of Polyaniline and Its Copolymers Prepared by Electrochemical
Techniques……………………………………………………………………85
5.1.1 Introduction………………………………………………………………85 5.1.2 Polyaniline (PANI) ………………………………………………………87
5.1.3 Synthesis of PANI by Electropolymerization with mCC Templates………88

5.1.3.1 Fabrication of Pure PANI Inverse Opals………………………………92
5.1.3.2 Fabrication of PANI Composite Inverse Opals…………………95
5.1.4 Application for Electrocatalysis…………………………………………98
5.2 Preparation of 3D Monodisperse Carbon Particle Arrays with Hierarchic Structures
by Silica Inverse Opal Templates………………………………………………100

5.2.1 Experimental……………………………………………………………100
5.2.2 Results……………………………………………………………………101
5.3 Fabrication of Gold/Silica Composite Inverse Opals……………………………106

5.4 Conclusions…………………………110
References……………………………………………………………………………111
6 Summary…………………………………………………………………………115
Acknowledgment…………………………………………………………………………………118
CV







Chapter 1 General Introduction
1.1 Colloidal System
Colloids are small objects dispersed in a medium having at least one dimension
in the range of 1nm to 1µm and often the upper limit can be extended to hundreds of
microns. Brownian motion - resulting from the random bombardment of solvent
molecules, is the characteristic feature of the colloidal particles. Colloidal particles are
important in a broad range of technologies and in the processing of various materials
including foods, inks, paints, coatings, cosmetics and photographic films, and thus are
intensely studied in materials science, chemistry, and biology. Figure 1.1 shows a
partial list of these colloidal systems, together with their typical range of critical
1 dimensions.


Fig. 1.1: A list of some of representitive colloidal systems, together with their typical
ranges of dimensions. In this chart the upper limit of the critical dimension for
1 colloids has been extended from 1µm to 100µm.
- 1 - Chapter 1 General Introduction
1.2 Colloidal Crystals

Colloidal crystals are three-dimensional periodic lattices assembled from
monodispersed spherical colloidal particles. For example, the natural opals, which
show attractive iridescence, are polycrystalline colloidal crystals composed of the
silica colloids and surrounding medium, and the iridescence is due to the diffraction
of visible or near infrared light as a consequence of the periodic modulation of the
refractive index between the silica particles and the surrounding medium as
demonstrated in Figure 1.2.

Fig. 1.2: a) Photographic image of a natural opal , and b) SEM image of the shadowed
2replica of the opal.

Colloidal crystals have gained continuous interest mainly because of two
reasons: Firstly, from the fundamental standpoint, colloidal crystals provide the best
experimental realization of a hard sphere model, whose phase behaviour is completely
dominated by entropy, thus the rich variety of the self assembly phenomena provide a
fascinating test bed for the basic physical processes such as melting, freezing, and
3-7glass transitions. Secondly, from materials standpoint, bottom up assembly - the
8 9 10assembly process present in bacteria, macromolecules, and submicron particles,
generates ordered structures with a precision that challenges current lithographic
techniques. Most importantly, in recent years colloidal crystals have fully
demonstrated the potential to obtain interesting and useful functionality not only from
- 2 - Chapter 1 General Introduction
the constituent materials of the colloidal particles but also from the long-range order
of the crystalline lattice (metamaterials).

1.3 Colloidal Crystals and Photonic Crystals

Photonic crystals (PC) are an artificial crystalline solid built from building blocks
that are approximately a thousand times larger than the atoms in traditional molecular
11-13crystals. Because the length scale of the lattice is in the Vis or near IR range, the
photonic crystal can influence the propagation of the electromagnetic waves in a
similar way as a semiconductor does for electrons, that is, there exists a band gap that
excludes the passage of the photons of some specific frequencies. This property can
be utilized to control and manipulate photons, as depicted in Figure 1.3 where a point
defect or line defect is introduced in the PC in order to suppress the spontaneous
emission of light which determines fundamentally the maximum available output of
the solar cell or to fabricate the wave-guide without any energy loss even at sharp
14bends. Joannopoulus’s photonic crystals micropolis, shown in Figure 1.4 is believed
11to represent the all-optical chip of the future, where signals are transmitted with light
rather than electrons. With the all-optical chips, it would be possible to build a
12personal computer that operates at hundreds of terahertz (10 Hz), which is a great
step forward in comparison with the semiconductor technology based on which
9producing a 10GHz (10 Hz) personal computer is difficult.

Fig. 1.3: Scheme of the point defect in PC to trap light (left) and line defect in PC to
14 guide light without any energy loss even at sharp bends (right).


- 3 - Chapter 1 General Introduction
Face centered cubic (fcc) colloidal crystals made of dielectric spheres do not
possess a complete 3D photonic band gap - one that extends throughout the entire
Brillouin zone in the photonic band structure, but a pseudo gap (so called stop gap) - it
only shows up in the transition spectrum along a certain propagation direction,
because of a symmetry-induced degeneracy of the polarization modes at the W point
15of the Brillouin zone. But this degeneracy can be broken by using shape-anisotropic
16or dielectrically anisotropic objects as building blocks. Photonic crystals can also be
realized if the dielectric contrast of these systems is increased by using colloidal
crystals as removable templates to structure high-index solids. The resulting
macroporous samples, called inverse opals, possess arrays of air voids embedded with
high-index solids such as ceramics or metals. In the