Electronic Supplementary Material (ESI) for Soft Matter. This journal is The Royal Society of Chemistry 014 Supplementary Material Effect of local chain deformability on the temperature-induced morphological transitions of polystyrene-b-poly(n-isopropylacrylamide) micelles in aqueous solution Xi-Xian Ke 1, Lian Wang, Jun-Ting Xu 1,* Bin-Yang Du 1, Ying-Feng Tu 3, Zhi-Qiang Fan 1 1 MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science & Engineering, Zhejiang University, Hangzhou 31007, China College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China 3 Department of Polymer Science and Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 1513, P. R. China. 1
Synthesis and characterization of PS-b-PNIPAM block copolymers RAFT-terminated PS (PS-containing macro-raft agent) was first synthesized. Styrene (30 ml, 0.613 mol), DDAT (0.385 g, 0.6533 mmol) and AIBN (0.0107 g, 0.0653 mmol) were added into a Schlenk flask. The mixture was degassed by thrice freeze-pump-thaw cycles and sealed in vacuum. The sealed flask was immersed into an oil bath preheated to 80 C. After a desired reaction time, the reaction flask was quenched into liquid nitrogen, then the reactant was diluted with small amount of tetrahydrofuran (THF), and precipitated in excess methanol. This dissolution and precipitation cycle was repeated for three times. The precipitates was collected by filtration and dried under vacuum at 40 C for 48 h. The chemical shifts of the H- NMR peaks are following: 0.90 (m, 3H, -CH 3 ), 1.17-.30 (m, -CH -CH-), 3.5 (t, H, -CH S), 6.8-7.38 (m, C 6 H 5 of styrene). A typical PS-b-PNIPAM diblock copolymer was synthesized as follows. PScontaining macro-raft agent, AIBN and NIPAM were introduced into a 10 ml Schlenk flask. The mixture was degassed by three freeze-pump-thaw cycles, and finally filled with N, then the reaction flask was sealed and immersed into an oil bath pre-heated to 70 C. After a preset time, the reaction was quenched into liquid nitrogen, then the mixture was diluted with dioxane and precipitated in cold Et O, the product was collected by filtration and dried under vacuum at 40 C for 48 h. 1 H- NMR (500 MHz, CDCl 3 ), (TMS, ppm): 0.88 (m, 3H, -CH 3 ), 1.16-.64 (m, - CH(CH 3 ) and -CH -CH- on the polymer s main chain ), 4.0 (s, -NHCH(CH 3 ) ), 5.67-7.35 (m, C 6 H 5 of styrene and -NHCH(CH 3 ) ). Molecular weights of the PS-b-
PNIPAM diblock copolymers were calculated from the intensities of the characteristic peaks in the 1 H-NMR spectra based on the molecular weight of PS block measured by 1 H-NMR. For PS 65 -b-pnipam 108 containing 65 styrene units and 108 NIPAM units, M w /M n = 1.16. For PS 65 -b-pnipam 360 with a longer PNIPAM block, M w /M n = 1.6. PS-containing macro-raft agent and the PS-b-PNIPAM diblock copolymers were characterized with 1 H-NMR and GPC. 1 H-NMR spectra were measured on a Bruker DMX-500 NMR spectrometer using chloroform-d (CDCl 3 ) as the solvent and tetramethylsilane (TMS) as the internal standard. Gel permeation chromatography (GPC) was conducted at 5 C in DMF containing 0.5 wt% potassium bromide with a flow rate of 1 ml/min, using a Waters 510 HPLC pump, Waters Styragel columns, and a Waters 410 differential refractometer (Millipore Corp., Bedford, MA). PMMA was used as a calibration standard. The polymerization conditions and characterization results of the PS-b-PNIPAM diblock copolymers are summarized in Table S1. Table S1. Polymerization conditions and results of the PS-b-PNIPAM diblock copolymers. a Sample 1 Time (h) 4 1 M n b PDI c Chemical composition d ƒ PS e 19330 47800 1.16 1.6 PS 65 -b-pnipam 108 36% PS 65 -b-pnipam 360 15% a Polymerization was carried out at 70 C with 1,4-dioxane as the solvent. [1] :[PScontaining macro-raft agent]:[aibn]=3000:10:. b M n was determined by 1 H-NMR based on the equation: M n = (M n of PS) + (M n of PNIPAM) {I 4.0 /[(I 5.67-7.35 -I 4.0 )/5]} + 364, where I 5.67-7.35 and I 4.0 represents the intensities of the characteristic resonances in range of 5.67-7.35 ppm and at 4.0 ppm, respectively. c PDI = M w /M n, determined by GPC. d Calculated from the 1 H-NMR. e Volume fraction of the PS block in the block copolymers. [] 3
PS B-1 B-.8 3. 3.6 4.0 4.4 4.8 5. 5.6 LogM W Figure S1. GPC curves of PS-containing macro-raft agent and PS-b-PNIPAM block copolymers. B-1: PS 65 -b-pnipam 108 ; B-: PS 65 -b-pnipam 360. a b c S d e CH 3 CH 3 C 10 H 0 CH S C S CH CH C COOH n CH 3 h g+i g h c f i b+d e f a S CH a b d e d' e' 3 CH 3 C 10 H 0 CH S C S CH CH CH CH CH COOH n m C O CH 3 g,i h g' h g i h' g' h' NH CH CH 3 CH 3 i' b,d,d' e,e' i' a 8 7 6 5 4 3 1 0 (ppm) 8 7 6 5 4 3 1 0 (ppm) Figure S. 1 H-NMR spectra of PS-containing macro-raft agent (left) and PS 65 -b- PNIPAM 108 block copolymer (right). (a) 460 PS 65 -b-pnipam 108 (b) 600 PS 65 -b-pnipam 360 Intensity (kcps) 440 40 400 380 360 heating cooling 0 30 40 50 60 70 T ( C ) Intensity (kcps) 500 400 300 00 100 heating cooling 0 0 5 30 35 40 45 50 55 60 T ( C ) Figure S3. Variation of the scattering light intensity of the PS-b-PNIPAM micellar solutions with temperature. (a) PS 65 -b-pnipam 108 ; (b) PS 65 -b-pnipam 360 4
Figure S4. TEM images of PS 65 -b-pnipam 108 micelles at 40 C (a) and PS 65 -b- PNIPAM 360 at 50 C (b). Figure S5. TEM images of PS 65 -b-pnipam 108 micelles (a) and PS 65 -b-pnipam 360 micelles (b) after being cooled back to 5 C from elevated temperature. 5
g () ( )-1 1. 1.0 0.8 0.6 0.4 0. PS 65 -b-pnipam 108 (5 C) 45 60 75 90 105 10 135 g () ( )-1 1. 1.0 0.8 0.6 0.4 0. PS 65 -b-pnipam 108 (60 C) 45 60 75 90 105 10 135 0.0 0.0 0.01 0.1 t(ms) 1 10 100 0.01 0.1 1 10 100 t(ms) g () ( )-1 1. 1.0 0.8 0.6 0.4 0. PS 65 -b-pnipam 360 (5 C) 45 60 75 90 105 10 135 g () ( )-1 1. 1.0 0.8 0.6 0.4 0. PS 65 -b-pnipam 360 (40 C) 45 60 75 90 105 10 135 0.0 0.0 0.01 0.1 1 10 100 t(ms) 0.01 0.1 1 10 100 t(ms) Figure S6. Electric-field autocorrelation function g (1) (t) of PS-b-PNIPAM micelles in aqueous solution measured by DLS at different scattering angles. The symbols represent the experimental data and the solid lines are the best fits with Eq. 1 (in the main manuscript) with fit quality of R = 0.999. Figure S7. TEM images of PS 65 -b-pnipam 108 micelles prepared by slow addition of water into DMF solution followed by dialysis. (a) at 5 C; (b) at 60 C. (c) cooling back to 5 C. 6
Calculations of micellar free energy at 5 C. The driving force for micelle formation and morphological transformations is the tendency to minimize the overall micelle free energy under a specific set of experimental conditions. The overall micelle free energy can be expressed as [3] F F core F interface F corona (1) Where the term F core is the free energy of the core that involves deformation of the core block conformations such as stretching or compressing, leading to deviation from its random coil conformation. In this case, this corresponds to the PS block. The term F interface is determined by the surface tension between the core and solvent at the interface. The term F corona relates to the steric and electrostatic (if ionic block exists, however that is not the case here) interactions between corona blocks and solvent. Here, it is the PNIPAM block. F core can be correlated to the degree of stretching or compression (Sc) of the PS blocks in the core and calculated as [4] S c R core / R 0 () Where R core is the radius of the PS core in the spherical and cylindrical micelles. In the case of vesicles, half of the wall thickness was utilized as R core. The quantity R 0 is the unperturbed end-to-end distance of the PS chain which can be calculated from the equation [5] R0 0. 067M 0.5 (3) Where M is the number-average molecular weight of the PS blocks. The value of R 0 is calculated to be 5.55 nm when the PS block s molecular weight is 6.76 kg/mol. 7
Therefore, the free energy of PS blocks in the micellar core can be calculated based on the following equation: [6] core / kt k jsc F ( 1) S c (4) Here, k j is the numerical coefficients of a dense PS core: j =1for lamella, k 1 = π /8; j = for cylinder, k = π /16; and j = 3 for sphere, k 3 = 3π /80. The second term, F interface, relates to the interfacial free energy between the core (PS) blocks at the interface and the solvents. Therefore Finterface s (5) Where s is the interfacial area per chain, and γ is surface tension, which is related to core solvent by the following expression: [7] ( kt / a PS )( PS solvent / 6) 0.5 (6) Where a is the PS monomer length. The term in this study is the PS-water PS solvent interaction parameter. Quantitatively, these parameters can be estimated using the van Laar-Hildebrand equation if we neglect the entropic contribution: [6] P S [ VS P S /( RT )]( ) (7) Where V S is the molar volume of the solvent and δ P and δ S are solubility parameters of the polymer and selective solvent, respectively. Since the solubility parameter of PS is 9.04 (cal/cm 3 ) 0.5, while that of water is 3.4 (cal/cm 3 ) 0.5, the P S can be calculated as ps water 6.7. [6] The third term, F corona, is based on the expression proposed by Zhulina et al. in their theory of diblock copolymer micelles. The corona could be treated as chains tethered on a planar substrate when the corona is much shorter than the core block. 8
This free energy is expressed by: F corona / kt Cˆ H Cˆ F N PNIPAM ( sa 1/ PNIPAM ) (8) Where Ĉ H and Ĉ F are numerical coefficients, N is the polymerization degree of the PNIPAM block, s is the area occupied by per PNIPAM chain at the interface between the corona and core of the micelles, a PNIPAM is the length of a NIPAM unit, and is the scaling exponent with a value of 3/5 in the good solvent or 1/ in the solvent. In the good solvent, Ĉ H and Ĉ F can be expressed as: Cˆ C Cˆ H H F C F ( l PNIPAM / a PNIPAM ) 1/3 1/3 (9) (10) Where C H and C F are constants with values of 0.68 and 1.83, respectively, l PNIPAM is the Kuhn length of PNIPAM and is the excluded volume of PNIPAM in a specific solvent. The values of l PNIPAM and a PNIPAM are 0.68 nm and 0.5 nm, [7] respectively. The excluded volume parameter υ is related to the second virial coefficient A : [8] 3 0 /( a N PNIPAM A A M ) (11) Where M 0 is the molecular weight of the PNIPAM monomer and N A is Avogadro s number. The values of A in the literature for our specific molecular weight and/or scaling laws have enabled us to determine the values of A for different length of PNIPAM in water. [9] 9
Table S. Physical parameters for PS-b-PNIPAM micelles at 5 C Sample A a (cm 3 mol/g ) υ b (nm 3 ) ĈH morphology R c core (nm) S c d s e (nm ) PS 65 -b- 5.61 1.5 1.09 PNIPAM 108 Vesicle 10.1 1.84 1.3 Sphere 0.6 4.74 1.80 PS 65 -b- 4.15 1.13 0.99 PNIPAM 360 Cylinder 16.0.91 1.54 Sphere 19.7 3.57 1.90 a A is related to molecular weight: [9] A =5.9 10-3 M -0.5. b υ is the excluded volume parameter of PNIPAM in water. c R core is the radius of spherical and cylindrical micelles and half of wall thickness for vesicles. d S c is the degree of stretching of PS blocks in the micellar core. e s is the interfacial area per chain. Table S3. Free energy calculations for PS-b-PNIPAM micelles at 5 C Sample morphology F core /kt F interface /kt F corona /kt F total /kt PS 65 -b-pnipam 108 Vesicle 4.15 0.1 18.0 4.9 Sphere 5.19 9.44 13.1 47.75 PS 65 -b-pnipam 360 Cylinder 5.1 5.19 45.07 75.47 Sphere 4.70 31.08 37.83 73.61 References [1] J. Adelsberger, A. Meier-Koll, A. M. Bivigou-Koumba, P. Busch, O. Holderer, T. Hellweg, A. Laschewsky, P. Müller-Buschbaum, C. M. Papadakis, The collapse transition and the segmental dynamics in concentrated micellar solutions of P(Sb-NIPAM) diblock copolymers, Colloid and Polymer Science, 011, 89(5-6), 711-70. [] F. Cheng, E. M. Bonder, A. Doshi, F. Jäkle, Organoboron star polymers via armfirst RAFT polymerization: synthesis, luminescent behavior, and aqueous selfassembly, Polymer Chemistry, 01, 3(3), 596. [3] Zhang. L, Eisenberg. A, Formation of crew-cut aggregates of various morphologies from amphiphilic block copolymers in solution.polymers for Advanced Technologies, 1998. 9(10-11), 677-699. 10
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