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Supporting Information
A new approach to produce polystyrene monoliths by gelation and capillary shrinkage
Dewang Li1, Yaq i an Den g2, J i n g yi Xi a1, Zh i t an W u1, To ngxi n S h an g1, P ei Li1, J unwei Ha n1, Yi n g T ao1*, an d Qu an- Hon g Yan g1 , 3
1 Nanoyang Group, State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300350, China.
2 Shenzhen Key Laboratory for Graphene-Based Materials, Engineering Laboratory for Functionalized Carbon Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China.
3 Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, China.
* Correspondence: yingtao@tju.edu.cn
2 η
η π η
π d
T d
N RT r
N D RT
A A
∝
=
= 6 3
(1)
Equation S1. Einstein-Stocks equation, where D (m2 s-1), R (8.314 J mol-1 K-1), NA (6.02×1023 mol-1), η (Pa s), r (m) and d (m), represent diffusion coefficient, molar gas constant, Avogadro constant, viscosity of the medium, the radius and the diameter of aggregate particles, respectively.
3 3 3
6 3
4 r d d
m = rπ = rπ ∝ (2)
Equation S2. Equation for the mass of aggregate particles, where ρ (g cm-3) represents the bulk density of PS.
Table S1. Recipes for the preparation of PS emulsions with different latex particle sizes.
Samples
Monomer St (mL)
SDS Surfactant (g)
Initiator KPS (aq, mL) a)
1 2.5 0.6 3.0
2 5.5 1.3 6.8
3 5.5 0.6 6.8
4 5.5 0.13 6.8
5 10 0 20
a) The concentration of the K2S2O8 aqueous solution is 0.01 g mL-1.
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Figure S1. Particle size distributions of the five as-polymerized PS emulsions (a) before and (b) after demulsification by EtOH.
Figure S2. TEM images of the microemulsion samples (a) 1, (b) 2, (c) 3, (d) 4, and (e) 5, insets are the corresponding enlarged views. These five samples have average particle sizes of 30 nm, 38 nm, 46 nm, 60 nm and 420 nm respectively. The particle sizes shown in the TEM images were usually smaller than those measured by DLS equipment, because no solvation layer of adsorbing water existed in them.
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Figure S3. (a) Optical photographs of the five PS emulsions with different latex particle sizes after demulsification by acetone. (b) Rheological storage modulus (G’) and loss modulus (G’’) as a function of oscillation frequency for the gel obtained from the sample 1 as shown in (a). An unchanged modulus under increasing oscillation frequency implies the stability of the formed gel structure.
Figure S4. Effect of EtOH volume on PS gelation. (a) Particle size distributions of secondary particles prepared with different EtOH volumes. (b) Gelling phenomenon with increasing EtOH volume ratio at 80 °C, where the demulsified sample from the 50 vol.% EtOH-H2O mixture failed to form a bulk material, while a PS gel was obtained as the amount of EtOH was increased to 67 vol.% and the size of the resulting bulk materials decreased with increasing volume ratio of EtOH.
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Figure S5. Particle size distribution curves of the PS dispersions after demulsification by adding different water-miscible organic solvents.
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Table S2. Three-dimensional Hansen Solubility Parameter (HSP, δt) contributions from nonpolar interactions (δd), polar interactions (δp) and hydrogen-bonding (δh) of PS and the solvents used here, and the peak size of secondary particles and the corresponding phenomena after adding various solvents at 25 °C.
Materials δd (MPa1/2) δp (MPa1/2) δh (MPa1/2)
PS 19.7 0.9 0.9 2 2.0
Acetone 15.5 10.4 7.0
1,4-dioxane 19.0 1.8 7.4
NMP 18.0 12.3 7.2
AA 18.0 7.5 13.4
ACN 15.3 18.0 6.1
DMF 17.4 13.7 11.3
EtOH 15.8 8.8 19.4
DMSO 18.4 16.4 10.2
MeOH 15.1 12.3 22.3
EG 17.0 11.0 26.0
TG 17.4 12.1 29.3
Solvents δt (MPa1/2)a) Peak size (nm) Phenomenon
Acetone 19.9 1280 Gelation
1,4-dioxane 20.4 1730 Gelation
NMP 22.9 142/981b) Only demulsification
AA 23.6 553 Only demulsification
ACN 24.4 575 Gelation
DMF 24.9 388 Only demulsification
EtOH 26.5 307 Only demulsification
DMSO 26.7 44.3/200 b) Only demulsification
MeOH 29.6 141 Only demulsification
EG 33.0 61.3 No demulsification
TG 36.2 42.6 No demulsification
a) The total HSP value is calculated according to: δt = (δd2
+ δp2 + δh2
)1/2. The δt value of PS is calculated to be 19.8 MPa1/2.
b) Two distribution peaks could be observed in NMP and DMSO, perhaps because the high
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viscosity of these two solvents at room temperature (see Table S2) hindered diffusion and aggregation to some extent. The larger peak sizes were used to calculate the d2T/η value because the smaller distribution peak would not lead to effective gelation.
Figure S6. Plot of secondary particle size after demulsification by water-soluble solvents as a function of the HSP value of the conressponding solvent (δt).
Table S3. Viscosity values of 20 vol% water mixed with following 80 vol% organic solvents η (mPa·s) Acetone Dioxane ACN NMP AA EtOH DMF DMSO
At 25 °C 1.26 2.65 0.927 7.13 4.01 2.90 3.14 5.15
At Tc － － － 2.32 1.56 1.06 1.58 1.85
η (mPa·s) MeOH EG TG
At 25 °C 1.88 11.3 68.0
At detected temperature a) 0.807 3.04 8.95
a) The detected temperatures of MeOH, EG, and TG are 70 °C, 80 °C, 80 °C respectively.
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Figure S7. DSC curves for (a) the demulsified and filtrated powder in a DMF solution (PS-P), and (b) the PS monolith (PS-M) from the DMF solution. The first cycle showed obviously different thermal behavior. PS powder (PS-P) showed two exothermic peaks at 107 °C, that overlapped the glass transition, and at 155 °C. The results were in agreement with previous reports on this unique phenomenon for PS “pauci-chain glass” from microemulsion latexes, and could be assigned to the sintering of microspheres and conformational change into slightly ordered regions respectively [1]. In contrast, monolithic sample (PS-P) had no exothermic peaks, which implies that the morphology was no longer mciro-PS particles but it became large pieces after gelation. Moreover, the endothermic peak at the glass transition temperature was ascribed to the thermal history induced by the fast cooling rate during washing [2]. All the above thermal behavior was erased in next cycle, and only the glass transition was observed.
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Figure S8. (a) TG curves of PS, PS-MgCl2, PS-P and PS-M samples under Ar. The obvious weight loss from 150 °C to 250 °C was ascribed to the decomposition of SDS species. It was observed that demulsification by MgCl2 did not result in the entire desorption of SDS as was the case with an organic solvent (DMF). (b) Optical photographs showing what happens when the same volume of water or organic solvent (DMF) added to the same samples demulsified by MgCl2 (aq), followed by heat treatment of 70 °C. As shown in the left image, gelation occurred after DMF addition, while only a sediment was obtained when the same volume of water was added.
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Figure S9. SEM images of the PS monoliths in Figure 4a. PS foams prepared by gelation in (a) acetone, (b) EtOH, (c) DMF solutions; and (d) the compact monolith obtained after capillary drying following gelation in DMF.
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Figure S10. Viscosity of gel samples formed in DMSO for 5 h (DMSO-5 h) and 10 h (DMSO-10 h) as a function of shear rate. The linear decreasing relationship of lgη vs. lgω indicates the stability of the gel under a shear force.
Figure S11. Optical and SEM images of gel samples formed in DMSO for 5 h or 10 h, and subsequent solvent exchanges for one (1st) or two (2nd) cycles. The 5h-1st, 5h-2nd and 10h-1st samples were condensed with a compact and continuous network, while the 10h-2nd sample had a highly porous network as a result of loosely connected domains.
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Figure S12. SEM images of PS monoliths with different degrees of shrinkage produced by changing the capillary drying period (a) 0 h, (b) 12 h, (c) 18 h, (d) 24 h, (e) 36 h and (f) 48 h.
Insets are their corresponding optical photographs. These samples were obtained from the PS gel which was produced using DMSO followed by two water exchange cycles. The combination of capillary drying and freeze drying was used for solvent removal.
REFERENCES
[1] Qian, R.; Wu, L.; Shen, D.; Napper, D. H.; Mann, R. A.; Sangster, D. F. Single-chain polystyrene glasses. Macromolecules 1993, 26 (11), 2950-2953.
[2] Langhe, D. S.; Murphy, T. M.; Shaver, A.; Laporte, C.; Freeman, B. D.; Paul, D. R.; Baer, E..
Structural relaxation of polystyrene in nanolayer confinement. Polymer 2012, 53 (9), 1925-1931.
