ORDERING IN LANGMUIRBLODGETT FILMS OF STOEBER SILICA PARTICLES

1
ORDERING IN LANGMUIR-BLODGETT FILMS OF STOEBER
SILICA PARTICLES   Márta Szekeresa,b, Olexiy
Kamalina, Robert A. Schoonheydta, Kurt Wostync,
Koen Claysc, André Persoonsc and Imre
Dékányb   aCentrum voor Oppervlaktechemie en
Katalyse, Katholieke Universiteit Leuven,
Kasteelpark Arenberg 23, 3001 Leuven,
Belgium bDepartment of Colloid Chemistry,
University of Szeged, Aradi vt. 1, 6720 Szeged,
Hungary cAfdeling Chemische en Biologische
Dynamica, Katholieke Universiteit Leuven,
Celestijnenlaan 200D, 3001 Leuven, Belgium
2D
3D
INTRODUCTION
MATERIALS and METHODS
ARTIFICIAL OPAL
Preparation of the particle monolayers and
multilayers Hydrophilic silica particles of
different particle diameters were prepared by the
Stoeber method 1. Hydrophobic and positively
chargel silica particles were prepared by
silylation using trimethoxy-silyl-propyl-trimethyl
-ammonium cation. Surface methoxilated silica was
prepared by extensive washing with methanol. For
LB-deposition, spreading suspensions were
prepared in chloroform, ethanol/chloroform,
methanol/chloroform and methanol medium, with or
without surfactant addition Particle monolayers
spread on MilliQ water surface were transferred
onto microscopic glass plates cleaned with
chromic acid or onto previously deposited
particle layers Characterization of the silica
particles, particle monolayers and
multilayers Particles BET surface area (Coulter
Omnisorp 100), SEM particle size and morphology
(Philips SEM 515), MICROELECTROPHORESIS zeta
potential (Zetamaster II), IM index matching for
refractive index determination, FT-IR surface
chemical analysis (Nicolet Omnic FT-IR
spectrometer). Films p - A isotherms (NIMA 611
Langmuir trough), SEM film morphology (Philips
SEM 515), surfactant concentration in the films
(DTABr mass spectrometry ANCA 20-20 GSL
spectrometer, SDS Stains-all method 2),
VIS-NIR transmission spectra (Cary 5 UV-VIS-NIR
spectrometer)
Photonic bandgap materials (PBG) are periodic
structures on an optical wavelength scale PBG
materials are transparent for optical wavelengths
except for the energy coupled into the PBG
structure Inexpensive way of fabricating PBGs
mass-production of all-optical chips and optical
integrated circuits The "bottom up"
construction strategy based on self-assembly of
colloidal size particles into fcc crystals Mimic
the natural process of the formation of gemstone
opals from spherical silica particles Bulk
crystal formation sedimentation, solvent
evaporation, electrophoretic and filtration
techniques Layer-by-layer construction
Langmuir-Blodgett deposition of hcp crystalline
layers on top of each other Layer-by-layer
construction allows to incorporate designed
crystal defects for wide range of applications
l 0.12 nm
Silica particle layer hexagonal close
packing PHOTONIC APPLICATIONS
PARTICLE FILM PREPARATION
SILICA PARTICLES
Molar concentration of reactants for the
preparation of Stoeber silica particles of
different sizes
Composition of spreading suspensions for the LB
particle film preparation
Typical p A isotherm I - gaseous phase
state, II - solid condensed state, III -
collapsed film Steep pressure rise rigid
films The density of the silica particles can be
calculated from the A0 values considering hcp
packing (unit cell area 2r2 sqrt3) 1.8 g/cm3
Deposition of the particle monolayers in the
LB trough Spreading Hydrophilic particles and
hydrophobic positively charged particles can be
spread by using surfactant Methoxilated
particles spread without surfactant Compression
symmetrical, rate 20 cm2/min Deposition p 10
mN/m, speed 1 mm/ min, possible only in
upstroke
Characterization of the silica particles
SURFACE MODIFICATION WITH METHANOL
ORDERING IN MONOLAYERS
 
SEM picture of the DTABr-methanol-chloroform
(82)-BS2 monolayer, cDTABr 1.8 mM, d 450
nm - poor ordering
SEM picture of the methanol modified silica
monolayer, cDTABr 1.8 mM, d 700 nm -
large crystalline domains
FT-IR spectra of hydrophilic silica sample
measured in He flow at 25 and 550 oC Si-OH
streching 3723 cm-1 water, hydrogen bonded OH
around 3500 cm-1 Si-O overtone,combination
bands 1989 cm-1, 1875 cm-1 OH-bending
1629 cm-1 With increasing temperature the
adsorbed water disappears the OH streching band
shifts to free silanol OH, the water band at 3500
cm-1 disappears, the intensity of OH band at
1629 decreases. Free surface silanol groups are
stable at 550 oC.
FT-IR spectra of methanol treated silica sample
measured in He flow at 25 and 550 oC
Si-OH streching 3701 cm-1 methanol OH
streching 3653 cm-1 CH3 streching
bands 2948 cm-1, 2852 cm-1 Si-O
overtone,combination bands 1923 cm-1, 1860 cm-1
OH bending 1620 cm-1 CH3 bending 1460
cm-1 The methanol OH peak at 3653 cm-1 disappears
during heating. The intensity of CH3 peaks
decreases but the peaks do not disappear. The OH
bending peak is unchanged. The remaining carbon
content without methanol OH reveals surface
methoxylation.
Effect of the solvent in chloroform containing
medium poor ordering can be seen. Changing the
medium from pure chloroform to pure methanol
improves the ordering. Effect of the surfactant
the type, the chain length or the concentration
of the surfactant dose not change the ordering
properites significantly
MULTILAYERS
PHOTONIC BANDGAP PROPERTIES
?max 2 D ? (neff2 cos2 ?)
Diffraction from a 3D photonic crystal 4
First order
Second order
SEM picture of the 6-layer silica film
The layered structure is kept in the
subsequent depositions, the ordering in the
crystalline domains improves and the domain size
increases
Angular dispersion of the photonic bandgap
Transmission spectra of ordered Stoeber silica
multilayers
Photonic bandgap attenuation of light
transmission at the Bragg diffraction maxima
First order
REFERENCES
Second order
With increasing number of layers the first order
attenuation peak Intensity increases and the with
of the peak decrseases. This behavior is
characteristic of photonic bandgap materials 3.
lmax d neff
lmax 2 d neff
d lattice constant, neff effectice refractive
index of the silica slab
1 W. Stoeber, A. Fink, E. Bohn, J. Colloid
Interface Sci., 1968, 26, 62. 2 F. Rusconi, E.
Valton, R. Nguyen, E. Dufourick, Anal. Biochem.,
2001, 295, 31.. 3 P. Jang, J. F. Bertone, K. S.
Hwang, V. L. Colvin, Chem. Mater., 1999, 11,
2123. R. Rengarajan, P. Jiang, V. Colvin, D.
Mittelmann, Appl. Phys. Lett., 2000, 77,
3517. 4 Yu. A. Vlasov, X. Z. Bo, J. C. Sturm,
and D. J. Norris Nature, 2001, 414, 289..
The positions of the first order and second order
Bragg diffraction minima correspond with the
calculated values based on the lattice parameter
d and the optical parameter neff