Supporting Information for All-Nanoparticle Thin Film Coatings

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1 Supportig Iformatio for All-Naoparticle Thi Film Coatigs Daeyeo Lee, Michael F. Ruber ad Robert E. Cohe Experimetal Details Materials. Aatase titaium oxide aoparticles STS-100 (18 wt. % TiO 2 suspesio i water, average particle size of 7 m, ad specific surface area of 320 m 2 /g) were geerously provided by Ishihara Sagyo Kaisha, Ltd (Japa). Silica aoparticles, Ludox SM-30 (30 wt. % SiO 2 suspesio i water, average particle size of 7 m, ad specific surface area of 345 m 2 /g), ad Ludox TM-40 (40 wt. % SiO 2 suspesio i water, average particle size of 22 m, ad specific surface area of 140 m 2 /g) were purchased from Sigma-Aldrich (St. Louis, MO). The average size of aoparticles was provided by the suppliers. Glass slides were purchased from VWR Iteratioal. The zeta-potetial of each aoparticle at ph 3.0 was measured usig a ZetaPals (Brookhave Istrumet Corp.). Fabricatio of TiO 2 /SiO 2 aoparticle-based multilayer coatigs. Sequetial adsorptio of TiO 2 ad SiO 2 aoparticles oto glass substrates was performed by usig a automated dippig machie. The cocetratio ad solutio ph of each aoparticle suspesio were adjusted to 0.03 wt. % ad ph 3.0 (usig 1.0 M HCl), respectively. Glass substrates were degreased with deterget ad the cleaed with 1.0 M NaOH solutios uder soicatio for 15 mi. Deioized water (> 18 MΩ m, Millipore Milli-Q (MQ)) was used to make the aoparticle suspesios. The dippig time i each aoparticle solutio was 10 mi followed by three rise steps (2, 1, ad 1 mi) i deioized water. A Barstead Thermolye furace was used to calciate the films at 550 C for 3 h. S1

2 Characterizatio. Thickesses of the TiO 2 /SiO 2 aoparticle-based multilayers assembled o glass substrates were determied by usig a Woolham Co. VASE spectroscopic ellipsometer; the data aalysis was doe usig the WVASE32 software package. A ucoated glass slide was first scaed i the ellipsometer. Measuremets were performed from 300 to 900 m at a agle of icidece of 70. The data obtaied were fitted to a Cauchy model which assumes that the real part of the refractive idex ( f ) ca be described by: B C f ( λ) = A + + (S1) 2 4 λ λ where, A, B ad C are costats, ad λ is the wavelegth of the light. The values of refractive idex reported i this study were determied at 633 m. As the differece i the refractive idices of the porous films ad the glass substrates was sigificat (typically larger tha 0.2), the measuremets of thickess ad refractive idex of the films were possible usig the ellipsometer. We have previously reported the successful use of ellipsometry to measure the thickess of polymeric multilayers o trasparet rubbery substrates made of poly(dimethylsiloxae). 1 I that case, the mismatch i the refractive idex betwee the substrates ad the films was less tha 0.2. Film thickess of the multilayers was also measured usig a Tecor P10 surface profilometer. Differeces i the thickesses measured usig the two methods (ellipsometry ad profilometry) were less tha 10 %. Root-mea-squared (RMS) surface roughess of the multilayers was determied by usig a Naoscope IIIa i a Dimesio 3000 AFM microscope (Digital Istrumets, Sata Barbara, CA) i the tappig mode i the air. RMS roughess was obtaied from AFM images with a sca size of S2

3 µm 2. Trasmissio measuremets were performed usig a Varia Cary 6000 spectrophotometer. Sessile drop cotact agle measuremets utilizig deioized water were performed with a VCA-2000 cotact agle system (AST Products, Ic., MA). A water drop of approximately 0.5 L was placed o the multilayer coated surfaces usig a syrige. Advacig cotact agle values were determied from dyamic video files that captured at 15.6 frames/s usig the software provided (VCA Optima XE Versio 1.90) by the maufacturer. Determiatio of porosity ad refractive idex of the aoparticle framework of thi films usig ellipsometry. Figure S1. Measuremet of thickess ad refractive idex of all-aoparticle thi films i medium 1 (i.e., air). Step 1. The effective refractive idex ( f,1 ) of the aoporous thi film is measured i air ( f,air = 1.00) iside a ellipsometric cell made of quartz (Hellma) as show i Figure S1. f,1 ca be represeted usig a first priciple mixig rule for the effective refractive idex as: f,1 = p f,air + (1-p) f,framework. Thickess of multilayer thi films i the dry state was measured iside as well as outside the quartz cell. S3

4 The differece betwee the two measuremets was egligible (typically less tha 0.5 m) idicatig that the use of the quartz cell does ot alter the measuremets. Previous studies have show that these types of cells ca be used reliably to measure the thickesses of thi films i various solvets. 2-4 Figure S2. Measuremet of thickess ad refractive idex of a all-aoparticle thi film i medium 2 (i.e., water). Step 2. The effective refractive idex ( f,2 ) of the aoporous thi films is measured i water ( water = 1.33) o the same spot where the previous measuremet i air was made as show i Figure S2. f,2 ca be represeted usig the first priciple mixig rule for the effective refractive idex as: f,2 = p f,water + (1-p) f, framework. Step 3. After cofirmig that the values of thickess from steps 1 ad 2 do ot differ (differece was typically less tha 2 m), the porosity (p) ad the refractive idex of the aoparticle framework ( f,,framework ) was calculated usig the two equatios above. These values ca be expressed as: f, 2 f,1 f,2 f,1 p = = (S2) 0.33 f, water f, air f,1 f, air p f, framework = (S3) 1 p S4

5 Step 4. To determie the chemical compositio of the TiO 2 /SiO 2 aoparticle-based multilayers, the refractive idex of each aoparticle was first measured usig the method described above. Multilayers comprisig TiO 2 /poly(viyl sulfoate) (PVS) ad poly(diallyldimethylammoium chloride) (PDAC)/SiO 2 were assembled o Si substrates ad the calciated at 550 C for 3 h to create aoporous films of TiO 2 ad SiO 2 aoparticles, respectively. The calciatio process removes the orgaic polymers ad also fuses the aoparticles together; therefore, the aoparticle thi films do ot udergo swellig i water. The solutio ph of the TiO 2 aoparticles, PVS, SiO 2 aoparticles, ad PDAC solutios for LbL assembly was adjusted to 2.0, 4.0, 9.0, ad 4.0, respectively, usig 1.0 M HCl or 1.0 M NaOH solutio. The cocetratio of polymer solutios ad aoparticle suspesios was adjusted to 10 mm (based o repeat uit) ad 0.03 wt. %, respectively. Figure S3, for example, shows the chages i the thickess ad refractive idex of calciated (PDAC/7 m SiO 2 aoparticle) multilayers as a fuctio of the umber of deposited bilayers. The thickess of calciated (PDAC/7 m SiO 2 ) multilayers i air ad water does ot differ sigificatly. O the other had, the refractive idex of the films icreases i water as the air i the pores of the films is replaced by water which has the higher refractive idex. By pluggig i the values of refractive idex of the calciated films ito Equatios (S2) ad (S3), the porosity of the calciated films ad the refractive idex of 7 m SiO 2 aoparticles ( f,sio ) could be calculated. Followig this procedure, the refractive idex of each 2 aoparticle was determied. The refractive idex of 7 m TiO 2, 22 m SiO 2 ad 7 m SiO 2 aoparticles was determied to be 2.21 ± 0.05, 1.47 ± 0.01 ad 1.47 ± 0.004, respectively. These S5

6 values are i good agreemet with the values of refractive idex reported for bulk materials, i.e., aatase TiO 2 = 2.0 ~ 2.7 ad SiO 2 = 1.4 ~ 1.5. (a) Thickess (m) Air water (b) Refractive idex Air water Number of bilayers Number of bilayers Figure S3. (a) Thickess ad (b) refractive idex of calciated (PDAC/7 m SiO 2 ) multilayers as a fuctio of deposited bilayers measured i air ad i water via ellipsometry. The porosity (p) ad the composite refractive idex of the aoparticle framework ( f,framework ) of the TiO 2 /SiO 2 aoparticle-based thi films were the determied by measurig the effective refractive idex of these films i air ad i water ad usig equatios S2 ad S3. The first priciple mixig rule for a composite refractive idex was the used to calculate the volume fractio of TiO 2 ( v TiO ) ad SiO 2 2 aoparticles ( v SiO2 ) i the TiO 2 /SiO 2 aoparticle-based multilayers usig the followig equatios: v f, framework f, SiO2 = 1 f, f, SiO2 ( p) (S4) v = ( p + v ) (S5) 1 2 SiO2 TiO We used the simplest form of effective medium formulas to calculate the effective refractive idex S6

7 of porous thi films as our goal was to demostrate the validity of this method based o ellipsometry.. The method described above, however, ca readily be exteded to other effective medium theories icludig Looyega, Maxwell-Garett, ad Bruggema equatios. 5 Determiatio of chemical compositio of TiO 2 /SiO 2 aoparticle multilayer thi films via quartz crystal microbalace (QCM) ad X-ray photoelectro spectroscopy (XPS). To moitor the mass uptake durig the layer-by-layer assembly, quartz crystal microbalace (QCM) crystals with gold electrodes were used. The gold electrodes were cleaed with hot water ad ethaol ad dried with N 2 gas. The gold electrode was the treated with 16-mercaptodecaoic acid before the LbL assembly was performed. A mass cotrol QCM system20 comprised of a HP 53131A/ 225 MHz uiversal couter ad computer was coected to a automated dipper. The frequecy shift caused by material adsorptio oto the QCM crystal was moitored every secod by a computer. The weight fractio ( w ) of TiO 2 aoparticles was estimated from the followig relatio o the assumptio that the frequecy shift ( f ) is proportioal to the mass icrease at each adsorptio step: w f = (S6) f + f SiO2 The weight fractios of TiO 2 aoparticles were measured ad averaged over at least 6 bilayers of depositio for each TiO 2 ad SiO 2 aoparticle multilayer system. Due to the presece of aopores which would be filled with water durig the QCM measuremets, the iterpretatio of QCM data (i.e., the assumptio o the relatio betwee the mass uptake ad the frequecy shift), however, is ot straightforward. S7

8 The mass fractio of the TiO 2 /SiO 2 aoparticle based multilayers was also measured usig X-ray photoelectro spectroscopy (XPS). A Kratos AXIS Ultra Imagig XPS with a Al K source was used at ormal agle of detectio relative to the surface plae. As this characterizatio techique probes the chemical compositio of surface (to depths of less tha 10 m) rather tha the bulk film, multilayers with TiO 2 or SiO 2 aoparticles as outermost layer were fabricated for XPS measuremets. For multilayers comprisig 7 m TiO 2 ad 22 m SiO 2 aoparticles, 6 ad 6.5 bilayer samples were aalyzed. For multilayers comprisig 7 m TiO 2 ad 7 m SiO 2 aoparticles, 12 ad 12.5 bilayer samples were aalyzed. Half a bilayer represets a multilayer with a TiO 2 aoparticle layer as the outermost layer. While it is difficult to estimate the chemical compositio of the bulk films from these data, the two values obtaied with TiO 2 ad SiO 2 aoparticles as outermost layers for each system provides a plausible rage (as preseted i Table 2 of the paper) for the chemical compositio of the etire films. Photocatalytic Activities of TiO 2 /SiO 2 aoparticle-based Multilayers. Methylee blue (MB) was used as the model cotamiat. Multilayer coated glass substrates were cotamiated by immersig them ito a 30 µm MB solutio for 5 mi. Cotamiated samples were irradiated with ultraviolet light (UVM-57, UVP) cetered at 302 m with a itesity of 1.5 mw/cm 2. The amout of MB remaiig i the multilayer coatigs was moitored by measurig the UV-Vis spectra ad comparig the absorbace measured at 660 m. The cotact agles after UV irradiatio of MB cotamiated samples were measured without risig the samples. S8

9 Water Spreadig Movie. A movie demostratig the superhydrophilicity of (7 m TiO 2 /22 m SiO 2 ) 6 coatigs is also provided. A water droplet (0.5 µl) was placed oto the multilayer modified glass ad the movie was captured by takig sapshots at 16 frames/sec rate. The movie shows the spreadig of a water droplet at 50 % of the actual speed. Referece (1) Nolte, A. J.; Ruber, M. F.; Cohe, R. E. Macromolecules 2005, 38, (2) Lee, D.; Nolte, A. J.; Kuz, A. L.; Ruber, M. F.; Cohe, R. E. J. Am. Chem. Soc. 2006, 128, (3) Itao, K.; Choi, J. Y.; Ruber, M. F. Macromolecules 2005, 38, (4) Bruer, H.; Vallat, T.; Mayer, U.; Hoffma, H. J. Colloid ad Iterface Sci. 1999, 212, (5) Theiß, W. Surf. Sci. Rep. 1997, 29, S9

577. Estimation of surface roughness using high frequency vibrations

577. Estimation of surface roughness using high frequency vibrations 577. Estimatio of surface roughess usig high frequecy vibratios V. Augutis, M. Sauoris, Kauas Uiversity of Techology Electroics ad Measuremets Systems Departmet Studetu str. 5-443, LT-5368 Kauas, Lithuaia