Supporting Information
I. Materials
TABLE I: Examples of typical materials possessing negative surface charge which are applicable for LbL
deposition
Material
Comment
CdTe Nanocrystals1
Synthesis in aqueous media, stabilized with thiol ligands like
mercaptopropionic acid (MPA) or thioglycolic acid (TGA), zeta
potential (MPA stabilized, pH =12 ): -37.5 mV (measurement)
CdSe/CdS Nanorods2
Synthesis in organic media, transferred into water by ligand exchange
with MPA, typical dimensions 5 x 30 nm,
zeta potential (pH = 12): -70.27 mV (measurement)
Au Nanocrystals3
Synthesis in aqueous media, citrate stabilized,
zeta potential (pH = 7): -33.87 mV (measurement)
Silver Nanowires
PVP stabilized, particles form no stable colloid so the suspension has
to be sonicated during deposition,
zeta potential (pH = 7): -37.69 mV (measurement)
Titania nanosheets4
N-doped semiconductor with photocatalytic properties
Hematite4
Ferromagnetic and biocompatible nanomaterial ,
Zeta potential: -15.6 mV (literature)
Carbon nanotubes5
Suitable for LbL after functionalisation, e.g. as sulphonate
Clay particles6
Inorganic sheet like structures
PEDOT-PSS7
Conductive Polymer blend
Dendrimers8
Carboy terminated shaped polyelectolyte
TABLE 2: Examples of typical materials possessing positive surface charge which are applicable for LbL
deposition
Material
Comment
Polydiallyldimethylammine
Commercially available, can be substituted with a variety of other
chloride (PDDA)9
polyelectrolytes, zeta potential(pH = 7): +27.71 mV(measurement)
Aluminium oxide10
Synthesis in aqueous media by a sol-gel process,
zeta potential(pH = 3): +62.59 mV (measurement)
Poly ethylene imine11
Positively charged linear polyelecrolyte
Poly allylamine12
Positively charged linear polyelecrolyte
Dendrimers8
Amine group terminated star shaped polyelectolyte
Polyaniline Nanofibers13
Conductive Polymer Fibers
Measurement of zeta potentials was carried out using the electrophretic light scattering method with a
Beckman Coulter Delsa Nano
TABLE III: Essential Parts of the spraying set-up
II. Parts List
Part
Description
Spraying nozzle
SU1A from Spraying Systems Deutschland GmbH
Step-motor
Qmot (1.8°, 0-40V, max 1 A) from Trinamic
Magnetic valves
0201 from Christian Bürkert GmbH & Co. KG
Microcontroller Board
Arduino Duemillenova, refer to arduino.cc
Magnetic Valves Controller
PC relay card (kit) from pollin.de(No. 710 722)
Motor Controller
Step-motor controller (kit) from pollin.de(No. 810
027)
III. Control Program
A description of the files contained in the control program package. For more information please refer
to the comments inside the source code files.
TABLE IV: Description of the different control program files and folders
File/Folder
Description
./lib
C programs that operate the stepper and nozzle controller
./arduino
Contains the firmware for the arduino microcontroller board
main.py
Main program providing the user interface and handles the command list
ispray.py
Provides a function for time controlled spraying
beam.py
Provides the subroutine that reads and interprets the output of the arduino
board
parser.py
Function that translates the user input
arduino.py
Provides an interface for the communication with the arduino board
stepper.py
Provides a class to control the stepper motor
IV. Syntheses of CdSe/CdS Nanocrystals and Phase Transfer
For the preparation of CdSe/CdS nanorods a hot injection synthesis approach was adapted from Manna
et. al2. 67 mg Se dispersed in 414 mg trioctylphosphine (TOP) were injected into a mixture of 60 mg
CdO 280 mg octadecylphosphonic acid(ODPA) and 3 g of trioctylphosphine oxide (TOPO) at 355 °C.
After 45 seconds the temperature was quenched by the injection of 4 ml toluene. From this solution
CdSe nanocrystals were precipitated with methanol and further redispersed in pure toluen. Their
concentration in toluene can be estimated from UV-Vis absorption spectra as reported in ref14.
To obtain core-shell particles 80 nmol CdSe-nanocrystals were coinjected with 120 mg sulfur and 1.5 g
of TOP into a mixture of 60 mg CdO, 280 mg ODPA, 80 mg hexylphosphonic acid(ODPA) and 3 g of
TOPO at 360 °C. After 360 s of reaction time the resulting CdSe/CdS particles were obtained in the
same way as mentioned above, except the particles were redispersed in m-hexane.
To be processed by electrostatic assembly methods, the nanocrystals have to be soluble in a polar
solvent, for example, water. The phase transfer was achieved by vigorously stirring the n-hexane
dispersed particles together with solution of 1.2 ml mercaptopropionic acid and 1 g of KOH in 100 ml
methanol for 1 h. By this the particles were transferred into the methanol phase. From the methanol
phase the particles can now be precipitated by centrifugation and redispersed in diluted aqueous KOH
solution (pH = 10).
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