Supplementary Information Self-assembly of Metal-Polymer Analogues of Amphiphilic Triblock Copolymers 1 Zhihong Nie, 1 Daniele Fava, 1, 2, 3 Eugenia Kumacheva 1 Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada 2 Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario M5S 3E5, Canada 3 Institute of Biomaterials & Biomedical Engineering University of Toronto, 4 Taddle Creek Road, Toronto, Ontario M5S 3G9, Canada Shan Zou, Gilbert C. Walker Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada Michael Rubinstein Department of Chemistry, University of North Carolina,Chapel Hill, North Carolina 27599-3290 1. Synthesis of thiol-terminated polystyrene Thiol-terminated polystyrene was synthesized using living anionic polymerization. 1 A 50-mL Schlenk tube containing a magnetic stirring bar was purged with nitrogen, and 30 ml of benzene was added via cannula. Styrene (2.0 ml) was added via a syringe followed by the addition of the n-butyllithium as initiator. After the styrene was consumed, the polystyryl anions were titrated in stoichiometric ratio with propylene sulfide. The polymer was protonated with acidic methanol and precipitated in methanol. Polymer number-average molecular weight (M n ) and polydispersity index (M v /M n ) were 12000 and 1.09, respectively, as determined by gel permeation chromatography.
2. Dynamic light scattering experiments Dynamic light scattering (DLS) was used to monitor aggregation of triblocks in the THF-water mixture. We note that the measured values of hydrodynamic diameters of the self-assembled structures were not expected to reflect the exact dimensions of the aggregates2. Figure S1a and b shows the TEM image and the distribution of hydrodynamic diameters (Dh) of the individual triblocks in THF, respectively. In Fig. S1c we show a representative TEM image of the nanospheres that were formed upon the addition of water to the solution of triblocks in THF and the distribution in hydrodynamic diameters of the nanospheres (Fig. S1d). a b c d Figure S1. Self-assembly of triblocks in the THF-water mixture. a,b, The TEM image (a)
and the distribution of hydrodynamic diameters of the individual triblocks in THF. c,d, A typical TEM image (c) and the distribution of hydrodynamic diameters (d) of the nanospheres self-assembled in the THF-water mixture at water content of 15%. 3. Dissolution of PS-terminated NRs in organic solvents Following the purification of polystyrene-tethered NRs by four cycles of centrifugation, the nanoparticles were dried at room temperature and redispersed in various organic solvents. Figure 2a (from left to right) shows photographs of the solutions of the NRs in toluene, dichloromethane, THF, and DMF. a b Toluene CH 2 Cl 2 THF DMF c 0.4 Absorbance 0.3 0.2 0.1 0.0 400 600 800 1000 1200 Wavelength (nm) Figure S2. Solution of triblocks in organic solvents. a, Photographs of triblocks in (from left to right) toluene, dichloromethane, THF and DMF. b, Typical TEM image of triblocks deposited on the solid substrate from their solution in THF. The scale bar is 100 nm. c, Absorption spectrum of triblocks dispersed in water prior to PS grafting (dashed line) and in DMF after PS attachment (solid line). 4. Monitoring the growth and dissociation of triblock nanochains
We monitored the evolution of nanochains in the DMF-water mixture by measuring absorption spectra of the triblocks at different time intervals, as shown in Fig. S3. 1 2 3 4 5 6 Figure S3. Absorption spectra of triblocks in the DMF-water mixture (C W =10 wt%) measured at various time intervals after the addition of water: 4 min (1), 8 min (2), 12 min (3), 20 min (4), 30 min (5), 240 min (6). The dashed line shows the absorption spectrum of the same triblocks in DMF solution. We monitored the dissociation of triblock nanochains following the addition of organic solvents. The chains were self-assembled in the DMF-water mixture (C W =10 wt%) and dialyzed against deionized water to remove DMF. THF was added in different amounts to the solution of nanochains, and the system was equilibrated for at least 30 min. 5. Phase separation experiments
Phase separation experiments were conducted to find the globules of polystyrene localized between the metal blocks assembled in a chain. We assumed that local monomer-monomer and monomer-solvent interactions are the same in free polymer chains and in the PS chains grafted to the nanorods. Water was added drop-wise into a 2.0 wt% polystyrene (MW 13,000 g/mol) solution in DMF. After the addition of one droplet of water, the solution was stirred for at least 30 min in a sealed vial. After adding water in a particular amount, the phase separated system was incubated for 2 days and the supernatant solution was carefully removed. The sediment was dried for three days in the vacuum oven at 40 o C. The concentrations of PS in the sediment were determined as a function of the concentration of water in the system. Polymer concentration in the globule, C glob, leveled off at 5 wt% water content in the system, as shown in Fig. S4. This result indicated that the density of PS in the gap between the metal blocks in the nanochains did not change at water content above 5 wt %. 0.36 C glob (g/ml) 0.32 0.28 2 4 6 8 C w (wt%) Figure S4. Variation in polystyrene concentration in the sediment, C glob, plotted as a function of
water content, C w, in the DMF-water mixture. Using the results of phase separation experiments we estimated the number of PS chains attached to the NR end in the following way. We assumed that local monomer-monomer and monomer-solvent interactions are the same in free polymer chains and in the PS chains grafted to the nanorods 3. From the TEM images (e. g, for CW = 20 wt %) we calculated the volume of the PS linker localized between the NRs to be ca. 1430 nm 3 and the volume of the PS cap attached to the nanorods end of nanorod to be ca. 715 nm 3. The concentration of polystyrene in sediment is ca. 0.35 g/ml (see Fig. S4). Thus the mass of PS in the sediment with volume 715 nm 3 is 0.35 g/cm3 * 715*10-21 cm 3 = 250 *10-21 g The mass of a single PS chain is 12000 g/mol / N av 2*10-20 g. The number of PS chains attached to the NR end was found as 250 *10-21 g/2*10-20 g 13 chains/nr end 6. Measurements of contour and persistence lengths of nanochains The contour path of the nanochains in TEM images was digitized to give corresponding two dimensional coordinates 3. The contour length of chains, L, was derived using the coordinates of the chains of triblocks. The persistence length of the nanochains, L p, was obtained by analyzing chains as follows. 4 The segmented length along the contour of chain, l, and the mean cosine, <cosθ>, of two tangential vectors separated by the segmented length, l, were extracted from the coordinates of chains. The values of persistence length, L p, were obtained by plotting the
correlation functions <cosθ> ~ l, and fitting them to the exponential decay function <cosθ>=exp(-l/l p ). Each contour length and persistence length of nanochains was obtained by analyzing approximately 100 chains. 7. Nanochains self-assembled in the DMF-water mixtures a b c Figure S5. Different magnification SEM images of triblock chains grown in the DMF-water mixture at C W =20 wt%. Image in c clearly shows alternating polymer and metal phases. The scale bar in a, b, and c is 1000 nm, 300 nm, and 50 nm, respectively. References 1. Stouffer, J. M. & McCarthy, T. J. Polymer Monolayers Prepared by the Spontaneous Adsorption of Sulfur-Functionalized Polystyrene on Gold Surfaces. Macromolecules 21, 1204-1208 (1988). 2. Orendorff, C. J., Hankins, P. L. & Murphy, C. J. ph-triggered assembly of gold nanorods. Langmuir 21, 2022-2026 (2005). 3. M. Rubinstein, R. Colby, R.H. Polymer Physics (Oxford University Press, Oxford, 2003, 454 pp. 4. Rivetti, C., Guthold, M. & Bustamante, C. Scanning force microscopy of DNA deposited onto mica: Equilibration versus kinetic trapping studied by statistical polymer chain analysis. J. Mol. Biol. 264, 919-932 (1996).