Supporting Information for. Controlling the Interaction and Non-Close-Packed

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1 Supporting Information for Controlling the Interaction and Non-Close-Packed Arrangement of Nanoparticles on Large Areas Madlen Schmudde, Christian Grunewald, Christian Goroncy, Christelle N. Noufele, Benjamin Stein, Thomas Risse,* Christina Graf* Institut für Chemie und Biochemie, Physikalische und Theoretische Chemie, Freie Universität Berlin, Takustraße 3, D Berlin, Germany, Synthesis of the Nanoparticles Materials. Tetraethyl orthosilicate (TEOS, Fluka, 99%), L-arginine (Fluka, 99.5%), cyclohexane (Carl Roth, 99.5%), ethanol (EtOH, Berkel AHK, 100%), ethanol (EtOH, Fisher Scientific, 96%), ammonia solution (Carl Roth, 25-27%), N-(6-aminohexyl)-aminopropyltrimethoxysilane (AHAPS, ABCR, 92%), sodium dodecyl sulfate (SDS, Merck, 85%), sodium dodecyl sulfate (SDS, Fisher Scientific, electrophoretic grade), 11-mercaptoundecanoic acid (Aldrich, 95%), N- 1

2 (3-(dimethylamino)propyl)-N -ethylcarbodiimide hydrochloride (EDC, Fluka, 98%) and N- hydroxysuccinimide (NHS, Aldrich, 98%), potassium persulfate (Aldrich, 99%), styrene containing 4-tert-butylcatechol as stabilizer (Aldrich, 99%) were used as received. QCM-D sensor chips coated with a gold layer (4.95±0.02 MHz, Q-Sense, Västra Frölunda, Sweden) were used as substrates during the self-assembling experiments. Prior to the experiments the sensor chips were cleaned by 10 min of UV/ozone treatment (Bioforce, Ames, IA) and immersion in a 2 % aqueous SDS solution for 30 min. Subsequently, they were rinsed with ultrapure water (18.2 MΩ, 25 C) and dried under nitrogen before storage. Right before usage the sensor chips were treated again for 10 min with UV/ozone. The reaction vessels utilized in all reaction steps with silica nanoparticles were cleaned before use with hydrofluoric acid (8 vol %) to remove insoluble deposits on the glass surface. After that they were copiously rinsed with water. All redispersion steps of the nanoparticles were carried out in an ultrasonic bath (Bandelin Sonorex RK512H (215 W, 35 khz)). Synthesis of Monodisperse SiO 2 Particles with a Rough Surface (rsinp). 1 In a 25 ml flask L-arginine (0.05 mmol) was diluted in water (6.9 ml) and a layer of cyclohexane (0.55 ml) was added. The solution was heated to 60 C and TEOS (3 mmol) was dropped quickly to the cyclohexane layer. After stirring for 20 h at 60 C at 300 rpm particles of 20±2 nm diameter were formed. The particles were used as seeds and were grown in five steps to a final diameter of 130±4 nm. In each growth step, the seed dispersion was used without purification and was diluted with water to a final concentration of 5 g/l. 2 mm L-arginine were used in each step. The volumes of TEOS and cyclohexane used in each growth step are given in 2

3 Table S1. The particles were separated by centrifugation at 240 g and were redispersed in ethanol. The nanoparticles were purified by two further centrifugation (240 g) and redispersion steps. The particles were stored in ethanol for further applications. Table S1. Amounts of chemicals used for the seeded growth steps of rough SiO 2 nanoparticles Growth step Diameter seed particles Volume of dispersion from the step before TEOS [mmol] Cyclohexane 1 20± ± ±2 80 a ±3 67 b ±4 193 c a Volume contains 54.1 mmol of non-reacted TEOS and 17 ml cyclohexane. b Volume contains 74.9 mmol of non-reacted TEOS and 22 ml cyclohexane. c Volume contains 96.5 mmol of non-reacted TEOS and 27 ml cyclohexane. Synthesis of Monodisperse SiO 2 Particles with a Smooth Surface (ssinp) by a Modified Synthesis according to Reculusa. 2 Seed particles were synthesized according to the method of Hartlen et al. 1 described above and further used without cleaning. 1 ml of this dispersion was diluted with 10 ml of ethanol and 2.2 ml of ammonia were added. A solution of 4.5 mmol of TEOS diluted with 4 ml of ethanol was added via a peristaltic pump with a pump rate of 1.8 ml/h. The particles were separated by centrifugation at 240 g and were redispersed in ethanol. The nanoparticles were purified by two 3

4 further centrifugation (240 g) and redispersion steps. The particles were stored in ethanol for further applications. Synthesis of Monodisperse SiO 2 Particles with a Smooth Surface (ssinp2, ssinp3) by Growing Stöber Shells on Hartlen Seed Particles. 3,4 The seed particles were used from the Hartlen synthesis without cleaning. The dispersion was diluted to a concentration of 0.2 g/l with ethanol and ammonia was added to result in a final concentration of 2 mm. TEOS was diluted with ethanol in a ratio of 1:4 and was added to the reaction mixture in 0.5 ml steps every 10 min (see Table S2). For further growth steps the obtained dispersions were also used without cleaning and the particle and ammonia concentrations were adjusted as described above. The amount of TEOS, which was added in each growth step, was calculated so that in each case the volume of the nanoparticles was doubled. The amounts of the chemicals used for the synthesis are given in Table S2 and S3. The particles were separated from the reaction mixture by centrifugation at 240 g and redispersed in ethanol. The nanoparticles were purified by two further centrifugation (240 g) and redispersion steps. The particles were stored in ethanol for further applications. TEM images of smooth silica particles with 118±3 nm and 162±4 nm diameter are shown in Figure S1. 4

5 Table S2. Amounts of chemicals used for the seeded growth steps of smooth SiO 2 nanoparticles with a final diameter of 118±4 nm Growth step Diameter seed particle Volume of seed dispersion Concentration of the seed solution [g/l] Ethanol Ammonia TEOS b [mmol] 1 53± ± ± a Volume of TEOS was diluted 1:4 with ethanol Table S3. Amounts of chemicals used for the seeded growth steps of smooth SiO 2 nanoparticles with a final diameter of 162±4 nm Growth step Diameter seed particle Volume of seed dispersion Concentration of the seed solution [g/l] Ethanol Ammonia TEOS b [mmol] 1 94±3 a ± a Same particles as used in the third growth step in Table S2 b Volume of ethanol in [ml] 5

6 Figure S1: SEM images of the surface morphology of smooth silica nanoparticles of (A) 118±3 nm and (B) 162±4 nm diameter. Functionalization of SiO 2 Particles with AHAPS. In an argon atmosphere, a dispersion of silica nanoparticles was diluted with ethanol to a final concentration of 1 g/l, mixed with ammonia and N-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) (see Table S4) and stirred at 500 rpm for 9 h. The reaction mixture was refluxed for 2 h at 80 C. The particles were purified by three centrifugation (960 g) and redispersion steps in ethanol. Subsequently, the functionalized particles were stored in ethanol under argon atmosphere at 8 C. 6

7 Table S4. Amounts of chemicals used for the functionalization of SiO 2 nanoparticles NP Volume of the Dispersion in EtOH Mass Concentration of NP [mg/ml] Volume of Ammonia AHAPS [mmol] rsinp ssinp ssinp ssinp Transfer of AHAPS Functionalized Silica Nanoparticles to Water For binding the nanoparticles on an 11-mercaptoundecanoic acid functionalized gold surface a transfer to water is necessary. Therefore, the ethanolic nanoparticle dispersion was diluted with ultrapure water to 0.1 g/l in an argon atmosphere. The percentage of ethanol in the solution was between 0.6% and 2.1%. The particle dispersion was ultrasonificated for 5 20 min and directly used. Synthesis of Polystyrene Nanoparticles 5 The emulsion polymerization for preparing polystyrene nanoparticles was performed according to the method of Zhang et al. 5 In a 250 ml three neck round bottom flask 8.2 µmol potassium persulfate and 8.5 µmol sodium dodecyl sulfate were dissolved in 50 ml ethanol and 20 ml ultrapure water. After the reaction was placed under an argon atmosphere, 8.7 mmol styrene were added and the reaction mixture was heated to 70 C und stirred for 9 h at this temperature. The polystyrene nanoparticles were purified by three centrifugation (941 g) and redispersion steps in ultrapure water. 7

8 2. QCM-D and SEM Measurements on a Non-Functionalized Gold Surface Figure S2: QCM-D measurements of the binding process of amino-functionalized silica nanoparticles with 118±3 nm (dotted curve) and 162±4 nm (dashed-dotted curve) diameter on a gold surface. Table S5. Summarized data obtained for the QCM-D measurements of smooth aminofunctionalized silica colloids on a gold surface NP Diameter (SEM) R q Diameter (DLS) Zetapotential [mv] Δf [Hz] ΔD [ppm] NNdistance a ρ A [particles per µm 2 ] ssinp2 118±3 1.2± ±2 50±4-345±5 41±1 268± ±0.4 ssinp3 162±4 1.3± ±3 53±2-473±5 40±1 340±32 6.2±0.8 a Nearest neighbor distance between the particles. 8

9 Figure S3: SEM images of the two-dimensional arrangement of (A) 118±3 nm and (C) 162±4 nm diameter amino-functionalized silica nanoparticles on a gold surface typical for 50% of the whole surface. The corresponding histograms show the distribution of nearest neighbor distances of (B) 118±3 nm and (D) 162±4 nm particles. 9

10 3. SEM Measurements on an 11-Mercaptoundecanoic Acid Functionalized Gold Surface Figure S4: SEM images and corresponding histograms of the two-dimensional arrangement of (A, B) 118±3 nm, (C, D) 136±4 nm, and (E, F) 162±4 nm amino-functionalized silica nanoparticles on an 11-mercaptoundecanoic acid functionalized gold surface. 10

11 Table S6. Summarized data obtained for the arrangement of smooth amino-functionalized silica colloids on an 11-mercaptoundecanoic acid functionalized gold surface NP Diameter Diameter (DLS) Zetapotential [mv] NNdistance a rsinp1 137±4 163±7 41±2 368±38 ssinp1 136±4 187±5 38±15 317±35 ssinp2 118±3 165±7 26±3 274±27 ssinp3 162±4 201±13 24±2 335±40 a Nearest neighbor distance between the particles 4. Geometric Considerations Regarding the Position of Polystyrene Nanospheres between Silica Nanoparticles In Figure S6A (top view) the limiting case 1 for the position of a polystyrene nanoparticle in the silica array is shown, where the particle is placed on the center connecting axis of two silica nanoparticles. The parameters needed for the calculation of half of the minimal center-to-center distance between two silica nanoparticles d PS-Si where a polystyrene nanoparticle placed inbetween them touches the gold surface are shown in Figure S6B (side view). d PS-Si is calculated according to Eq. S1: (S1) In Figure S6C (top view) limiting case 2 is shown, where the polystyrene nanoparticle is located in the center of an equilateral triangle formed by three silica nanoparticles. By using the 11

12 d PS-Si the center-to-center distance between the silica nanoparticles is calculated applying the height in an equilateral triangle (see Eq. S2 S4): S2 3 2 S3 By converting Eq. S2 to d Si-Si and using Eq. S3 for h one obtains Eq. S4: 3 3 S4 Figure S5: Geometric considerations regarding the packing of polystyrene spheres (blue spheres) on top of an ordered array of ordered silica spheres (red spheres): (A) top view of a polystyrene particle in the middle of the center connecting axis between two silica spheres, (B) side view of the same situation, and (C) top view of a polystyrene particle which is located in the center of an equilateral triangle formed by three silica nanoparticles 12

13 REFERENCES (1) Hartlen, K. D., Athanasopoulos, Aristidis P. T., Kitaev, V. Facile Preparation of Highly Monodisperse Small Silica Spheres (15 to >200 nm) Suitable for Colloidal Templating and Formation of Ordered Arrays. Langmuir 2008, 24, (2) Reculusa, S., Poncet-Legrand, C., Ravaine, S., Mingotaud, C., Duguet, E., Bourgeat-Lami, E. Syntheses of Raspberrylike Silica/Polystyrene Materials. Chem. Mater. 2002, 14, (3) Bogush, G., Zukoski, C. Uniform Silica Particle Precipitation: An Aggregative Growth Model. J. Colloid Interface Sci. 1991, 142, (4) Philipse, A. P. Quantitative Aspects of the Growth of (Charged) Silica Spheres. J. Colloid Interface Sci. 1988, 266, (5) Zhang, J., Chen, Z., Wang, Z., Zhang, W., Ming, N. Preparation of Monodisperse Polystyrene Spheres in Aqueous Alcohol System. Mater. Lett. 2003, 57,