Supporting Information
Ordered Patterns Formed on Polymer Film through Trapping and Locking
Ligang Lin*, Yuanyuan Wang, Hui Sun, Chao Zhang, Yonghui Zhong, Yuzhong Zhang
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Table of Contents
1. Experimental and measurements details
2. CSM images of four kinds of designed polyimide polymers with typical ring structure.
3. The influence of volatile solvent on pattern formation
4. Optical micrographs of PES film with dimethylacetamide as solvent
5. The influence of polymer concentration on pattern formation
6. The influence of evaporation temperature on pattern formation
7. References
8. Other Supplementary Material
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1. Experimental and measurements details
1.1 Materials and reagents
Polyethersulfone (PES) with the average weight molecular mass (Mw) of 58 000 was from
BASF Corporation. Polyvinylidene fluoride (PVDF), Mw=322 000, was from Solvay
Corporation. Ethylene-vinyl alcohol copolymer (EVAL) with 38% of vinyl group content was
from Kuraray Chemicals Manufacturer. Polyimide (PI) was prepared based on various
diamines and dianhydrides. And the preparation method of PI will be given later. The
monomers including pyromellitic dianhydride (PMDA), 3,3’,4,4’-Biphenyltetracarboxylic
dianhydride (BPDA), 4,4’-Oxydianiline(ODA), p-phenylenediamine (PDA), 2,2-Bis[4-(4aminophenoxy)phenyl]propan (BAPP) were purchased from TCI Shanghai Development Co.,
Ltd. The monomers of 3, 3’, 4, 4’-benzophenonetetracarboxylic dianhydride (BTDA) and
4,4’-Diamino-3,3’-dimethyldiphenylmethane
(DMMDA)
were
from
Beijing
Multi
Technology Corporation and Shanghai EMST Corporation, respectively. All the monomers
were purified by recrystallization. The solvents such as N-methyl-pyrrolidone (NMP),
Dimethylformamide (DMF), Dimethylacetamide (DMAc) and tetrahydrofuran (THF) were
from
Sinopharm
Chemical
Reagent
Corporation.
Other
reagents
were
from
Aladdin Industrial Corporation. All chemicals used were of analytical reagent (A.R.) grade.
1.2 Film preparation method
Four kinds of polymer films (PI, PVDF, PES and EVAL) were prepared with the following
process, respectively. If no special declaration, the mixed solvent of NMP and THF with
a volume ratio of 4:1 was used in this experiment. THF, which boiling point is 66℃, was used
as volatile solvent. Dimethylacetamide and dichloromethane are also used during some
comparative experiments, which will be discussed later. The polymers, which have been dried
in a vacuum oven at 80℃ for 24h, were gradually added to the mixed solvent mixture,
respectively, and stirred for 24h to ensure complete dissolution of polymers. The polymer
concentrations were from 9.5 wt.% to 25.4 wt.%. The influence of polymer concentrations
will be discussed later. Before casting, the solutions were degassed. The homogeneous
solutions were cast on the glass plates on heating panel, and then the solvents evaporation
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began. During the solvent evaporation process, surface morphology can be preliminary
observed by video camera. The influence of evaporation time and temperature on film surface
will be discussed later. After certain evaporation time, the glass plates with films were
immersed into water coagulation bath. The solid films can be obtained by the phase inversion
process, which is a well-known method for membrane industry
[S1-S5]
. During this process,
solvent exchange occurred and the solidified films formed because water is the non-solvent
for those polymers. To ensure that all of the solvents were removed, the films were immersed
in the water bath for 24h at room temperature. Before morphology investigation, the film
samples were dried to remove the water. If no special declaration, the polymer concentration
and evaporation time were controlled at 13.9% and 40 s, respectively.
In addition, the polyimide materials used in this work were prepared by a two-step solutionimidization route. The diamine monomer was dissolved in DMF, and then the diamine
monomer was gradually added into the solution. The mole ratio and solid content of
diamine/dianhydride mixture were 1:1 and 13 wt%, respectively. The mixture reacted for 10 h
at room temperature producing a viscous polyamic acid solution. The chemical imidization
was carried out with acetic anhydride and pyridine at room temperature for 14h. The reaction
mixture was then added to ethanol solution. The precipitate was collected by filtration,
washed with water, and dried in vacuo at 150 ℃ to obtain the solid of polyimide materials. It
should be noted that the polyimide film discussed in Figure. 1 was prepared with BTDA and
DMMDA monomers. Other diamines (ODA, PDA, BAPP) and dianhydrides (PMDA, BPDA)
were used for the polyimide films discussed in Figure.S1.
1.3 Morphology Characterizations and Measurement
The surface structures of films were studied by confocal scan microscope, CSM 700, from
ZEISS, German. By this true color confocal microscope, 3D topographies with high
resolution can be obtained. With more than 100 frames per second, the surfaces of film
samples remain untouched while topographical measurements were taken. By the easy-to-use
software, the measurement of layer thickness evaluation can be obtained. The light source is
from a xenon lamp with wavelength range from 400 to 700 nm.
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2. CSM images of four kinds of designed polyimide polymers with typical
ring structure
Figure S1. The CSM images of four kinds of designed polyimide polymers with typical ring
structure. (A) Surface pattern of PMDA/ODA polyimide film. (B) Surface pattern of
BPDA/ODA polyimide film. (C) Surface pattern of BPDA/PDA polyimide film. (D) Surface
pattern of PMDA/BAPP polyimide film. To verify the role of ring structure of polymer on
pattern formation, four kinds of typical polyimide material with various ring sequences have
been prepared by a two-step solution-imidization route based on a series of diamines and
dianhydrides. The experimental details were provided in Materials and Methods section.
During the film preparation, the evaporation time, temperature and polymer concentration
were fixed at 40 s, 20 °C and 13.9 wt.% , respectively. From Figure.S1, all the films involved
showed ordered arrays, which provides additional evidence for our analysis on the necessary
conditions for pattern emergence.
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3. The influence of volatile solvent on pattern formation
Figure S2. The influence of volatile solvent on pattern formation. (A) In the absence of
volatile solvent, no ordered patterns were observed. (B) Observed ordered patterns in the
presence of volatile solvent (tetrahydrofuran). (C) Observed ordered patterns in the
presence of volatile solvent (dichloromethane). The influence of polymer structure on pattern
formation have been investigated and discussed in other sections. We now address another
question: Do those ordered structures form in the absence of volatile solvent? In this
experiment, three kinds of recipe were used for the polymer solution. For case A mentioned
above, polyethersulfone polymer was dissolved into a solvent (N-methyl-pyrrolidone), while
no volatile solvent used. For case B, polyethersulfone was dissolved into a mixed solvent (Nmethyl-pyrrolidone/tetrahydrofuran). Here, the tetrahydrofuran was used as volatile solvent.
For case C, polyethersulfone was dissolved into a mixed solvent (N-methylpyrrolidone/dichloromethane). The dichloromethane was also a well-known volatile solvent.
Based on the contrastive analysis on the images in Figure S2, it can be concluded that the
solvent evaporation is necessary for the formation of the ordered array. The hexagonal
arrangement of patterns formed on the surfaces of polymer films due to the convection
induced by the solvent evaporation. This is consistent with Bénard-Marangoni phenomenon
[S6-S8]
where a temperature gradient induces an increase in the Marangoni number (9-10) and
consequently an increase in instabilities. Further experiments results for the solvents will be
presented later.
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4. Optical micrographs of PES film with dimethylacetamide as solvent
Figure S3. Optical micrographs of PES film with dimethylacetamide as solvent. (A) PES
film with ordered patterns. (B) 3D view of the PES ordered patterns. In this experiment,
polyethersulfone was dissolved into a mixed solvent composed of dimethylacetamide and
tetrahydrofuran. The results show that, similar with the case of N-methyl-pyrrolidone solvent,
the ordered patterns can be obtained with dimethylacetamide as solvent. From what we have
mentioned above, it is thus clear that the solvent such as N-methyl-pyrrolidone and
dimethylacetamide play an important role for the homogeneous polymer solution, while the
volatile solvent such as tetrahydrofuran and dichloromethane play a decisive role for the
ordered patterns.
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5. The influence of polymer concentration on pattern formation
Figure S4. The influence of polymer concentration on pattern formation. (A) CSM image of
film under the preparation condition of 9.5 wt.% of polyethersulfone concentration. (B) CSM
image of film under 11.5 wt.% of polymer concentration. (C) CSM image of film under 13.9
wt.% of polymer concentration. (D) CSM image of film under 16.8 wt.% of polymer
concentration. (E) CSM image of film under 19.6 wt.% of polymer concentration. (F) CSM
image of film under 22.6 wt.% of polymer concentration. (G) CSM image of film under 23.5
wt.% of polymer concentration. (H) CSM image of film under 25.4 wt.% of polymer
concentration. In this experiment, the polyethersulfone films were prepared under various
polymer concentrations. Other factors such as evaporation time and temperature were fixed at
40 s and 20 °C, respectively. The results show that too high or too low polymer concentration
is not conducive to the pattern formation. As explained for the trapping and locking process,
the tangled polymer chains have hindrance influence for the upward solvent molecules, which
has significant influence on the convection and expected patterns. At low polymer
concentration, the volatile solvents can diffuse easily in the solution due to low viscosity, and
the chains may be bypassed. With the increasing polymer concentration, as mentioned as
cases B to G above, the evaporating solvents drive the ordering or packing of the polymers
into packed arrays. However, excessive polymer concentration means higher viscosity. For
the case H, the diffusion resistance of volatile solvent in solution is larger due to higher
viscosity and more entanglement of chains. The pulling or drawing role of evaporating
solvents to the polymer chains is not enough to support the pattern growth on the surface. The
patterns cannot be trapped onto the surface. Above results give further evidence for the
proposed formation mechanism of patterns on polymer film.
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6. The influence of evaporation temperature on pattern formation
Figure S5. The influence of evaporation temperature on pattern formation under 25.4 wt.% of
polymer concentration. (A) CSM image of polyethersulfone film under 20 °C of evaporation
temperature. (B) CSM image of polyethersulfone film under 60 °C of evaporation
temperature. In this experiment, the polyethersulfone films were prepared under different
evaporation temperatures. Other factors such as evaporation time and polymer concentration
were fixed at 40 s and 25.4 wt.%, respectively. For case A mentioned above, the pattern
cannot be observed under polymer concentration (25.4 wt.%) due to higher transport
resistance of volatile solvent in solution. It is well-known that heating can promote the
evaporation. It is interesting to investigate whether the ordered patterns would occur when
evaporation temperature increases while other conditions are fixed. From case B, when
evaporation temperature was increased from 20 °C to 60 °C, the ordered patterns occur as
expected. Above results give further evidence for the proposed pattern formation mechanism.
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7. References
[S1]
P. van deWitte, P.J. Dijkstra, J.W.A. van den Berg, J. Membr. Sci. 1996, 117, 1.
[S2] J. Ren, Z. Li, Desalination. 2012,285, 336.
[S3]
Črtomir Stropnik, Vladimir Kaiser, Desalination , 2002,145, 1.
[S4]
G.R. Guillen, Y. Pan, M. Li, Ind. Eng. Chem. Res. 2011, 50, 3798.
[S5]
H. J. Lee, B. Jung, Y. S. Kang, J. Membr. Sci. 2004, 245, 103.
[S6]
M. Bestehorn, Phys. Rev. E , 1993, 48, 3622.
[S7] J. Margerit, P. Colinet, G. Lebon, Phys. Rev. E. 2003, 68, 041601.
[S8]
B.Cheid, C. Ruyer-Quil, U.Thiele, Fluid Mech. 2005, 527, 303.
[S9]
E. L. Koschmieder, S. A. Prahl, J. Fluid Mech. 1990, 215, 571.
[S10] T. Boeck, N.K. Vitanov, Phys. Rev. E. 2002, 65, 037203.
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8. Other Supplementary Material
Snapshots of film appearance. A video shows the surface patterns observed during
experiments was prepared. Since the video is not allowed to be submitted, some snapshots are
provided in Figure S6. A large area of periodic ordered patterns can be seen on the film. The
polyimide film was prepared with 13.9 wt.% of polymer concentration under 20 °C. A mixed
solvent composed of dimethylacetamide and tetrahydrofuran was used.
Figure S6. The snapshots of film appearance in laboratory.
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