Supporting Information
Aspect Ratio Effect of Nanorod Surfactants on the Shape and
Internal Morphology of Block Copolymer Particles
Kang Hee Ku1, Hyunseung Yang1, Jae Man Shin1, Bumjoon J. Kim1, *
1Department
of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science
and Technology, Daejeon 305-701, Republic of Korea
Correspondence to Bumjoon J. Kim (E-mail: bumjoonkim@kaist.ac.kr)
Keywords: nanorod, block copolymer, aspect ratio, nanoparticle surfactant, emulsion particle
Experimental Procedure
Synthesis of Aspect Ratio(AR)-Controlled CuPt NRs. CuPt NRs were synthesized by the
thermal degradation method with the standard air-free technique, as described in the
previous work. 1,2 Cu(acac)2 (24 mg) and Pt(acac)2 (43 mg) were dissolved in 1-octadecene (5
mL). Then, 1,2-hexadecanediol (105 mg) and calculated amounts of oleic acid (OA) and
oleylamine (OLA) were added to the reaction mixture, with 1.5, 0.6, 0.6, 0.8, and 0.8 mL of
OA and 0, 0.7, 0.8, 1.2, and 1.5 mL of OLA being used to synthesize NR-1, NR-3, NR-6, NR-10,
and NR-15, respectively. The solution was heated and stirred at 120 °C under a nitrogen
atmosphere for 20 min, and then the temperature was increased to 225 °C and maintained
for 30 min to prepare the product. The solution was cooled down to room temperature, and
the product was precipitated in ethanol by centrifugation at 3600 rpm for 10 min. To purify
the CuPt NRs, they were dispersed in a 50:50 mixture of hexane and acetone, and the
desired product was separated by precipitation at 3600 rpm. Thermal gravimetric analysis
(TGA) was used to calculate the weight fractions of the CuPt core and the organic ligands of
CuPt NRs, and their volumes were calculated by using the densities of oleylamine (0.813
g/cm3), oleic acid (0.895g/cm3), Cu (8.96 g/cm3), and Pt (21.45 g/cm3). Also the volume
fractions of PS-b-P4VP(PDP) polymers in the BCP particles were calculated from their feed
masses by considering the densities of PS-b-P4VP (1.05 g/cm3) and PDP (0.908 g/cm3).
Fabrication of BCP Particles. The PS-b-P4VP block copolymers (the molecular weight
(Mn)= 34 kg/mol, PS block fraction (fPS)= 0.79, polydispersity index (PDI)= 1.15, from Polymer
Sources Inc.) was dissolved in chloroform to produce a 1 wt% polymer solution. Then, the
PDP molecules in chloroform were added to the PS-b-P4VP solution with 0.5 feed ratio of
4VP to PDP units. After adding the CuPt NRs (фCuPt = 0.037) with various ARs (1 to 15), the
total solution (0.2 mL) were stirred for 24 h and emulsified in deionized water (DI water, 2.5
mL) containing 0.5 wt% of cetyl trimethylammonium bromide (CTAB) using a homogenizer
for 1 min at 20,000 rpm. The organic solvent was slowly evaporated at room temperature for
24 h. The sample was washed with DI water to remove the large excess of remaining
surfactants by repeated centrifugations performed at 13,000 rpm for 10 min, and it was
redispersed in DI water for further characterization.
Characterization. Field-emission SEM (Hitachi S-4800), and TEM (JEOL 2000FX) were
used to observe the surfaces and the internal structures of the particles. To investigate the
internal structures of the microspheres by cross-sectional TEM, the samples were prepared
by drop-casting suspensions of the BCP particles onto an epoxy film and allowing the solvent
to evaporate. Then, the epoxy-supported films were cured in an oven at 60 °C for 24 h. The
epoxy-supported films were microtomed into 50-nm slices with a diamond knife at room
temperature. The prepared samples were exposed to I2 vapor to selectively stain the P4VP
domains of the PS-b-P4VP.
NR-1
NR-3
NR-6
NR-10
NR-15
Organic
ligand (wt%)
13.05
12.54
12.56
12.64
12.67
Inorganic
core (wt%)
86.95
87.46
87.44
87.36
87.33
Figure S1. TGA data of the oleic acid/oleylamine capped CuPt NRs; (a) NR-1, (b) NR-3, (c) NR6, (d) NR-10, and (e) NR-15.
References
(1)
Liu, Q.; Yan, Z.; Henderson, N. L.; Bauer, J. C.; Goodman, D. W.; Batteas, J. D.; Schaak,
R. E. J. Am. Chem. Soc. 2009, 131, 5720.
(2)
Kwon, T.; Min, M.; Lee, H.; Kim, B. J. J Mater. Chem. 2011, 21, 11956.