The Different Size Structures of Phase Separation on Blend Polymer Thin Films
Hai-Ning. Cui
Haiwon Lee#
Vasco Teixeira
GRF-Functional Coatings Group, Physics Department, University of Minho, Campus de
Gualtar, P-4710-057 Braga, Portugal, fax: 351-253-678981. E-mail address:
Cui@fisica.uminho.pt.
#
Department of Chemistry, Hanyang University, Seoul 133-791, South Korea
The thin blend films with perfectly flat surface and maze-like structure have been developed
for widespread application, such as antireflection, protective, lithographic coating and new
plasticized polymer electrolyte
1, 3
. The polymer blends normally tend to phase separation,
which was tried to avoid in molten polymer blends, because it decrease the physical properties
of the blend system 10. On the contrary we proposed to apply phase separation and obtained
ultra thin phase separation (UTPS) or micro (nano)-meter phase/thickness structure in a thin
blend film. Until now one of the best interesting candidate polymer for LED is polythiophene
derivative
13
. Some kinds of blend films of functional polymer, ploy 3-(2-(5-
Chlorobenzotriazole) ethyl) thiophene (PCBET), with polyvinylcarzole (PVK)
17
or poly
18
(methyl methacrylate) (PMMA) have been done.
In order to obtain the UTPS film of blend polymer (schematic cross section of film in Figure
2), we approach it in a physical method that is suitable for many kind polymers or other
materials. As we know, the dispersion modes of different phases in a mixture of molten
polymers depend on the blend compositions, molecular weight, temperature, miscibility, chain
mobility and interfacial tension 23. But the importance and effect of these factors will become
weak in making process of an ultra thin blend film. It becomes a little easy to generate thin films
of polymer mixtures with homogeneous surface in macro scale and with nano phase in micro
scale, because we can use spin cast method by a diluted or very diluted solution. First we
prepare two solutions through ultrasonic method to make micro emulsion. During solvent
volatilizing of the spin cast, micro emulsion phase become stable micro phase separation in the
thin solid film states. The size of dispersion solid phase is equal or larger than that of dispersion
liquid phase of the micro emulsion, because it is possible that more than two micro-emulsion
phases aggregating one solid phase during volatilizing process. The size of dispersion phases of
film could depend mainly on different blend ratio of two polymers in UTPS. For two polymers
mixture system, we choose a solvent that suits the two polymers to make a solution. The
required thickness of the film is determined by concentration of solution, volatility of solvent
and spin speed of the cast process. To obtain the useful UTPS film that is similar to one inside
Fig. 2, the thickness of the film (t) should be equal or smaller than the even size (L) of the micro
phase of the function polymer. Before fabricating the casting film the solution is treated by
ultrasonic wave for 15 min. for better mixing of two polymers.
We show here that size controlled nanometer phase structure and nanometer thickness film of
blend polymers (Fig. 1). The tip of a modified AFM (atomic force microscopy) investigates the
electrical characterization of UTPS in which there are the mono micro/nano phases of
semiconductor polymer and insulating matrix. It can directly provide both morphology and
electrical properties of micro domain of a blend film of conducting and insulating materials. The
lateral force microscopy (LFM) confirmed the results of AFM. Photo-luminescences (PL)
results suggest that the suitable blend leads to the enhancement of PL emission of PCBET.
Photodiode
Piezo
Å.
Cantilever
Film
L
t
A
Feedback &
x,y,z Scan
Control
ITO Glass
Holder
x,y,z
Scanner
0
2 m
b
0
2 m
e
Å.
Å.
0
2 m
d
Figure 1. Electrical measurement of micro-domains with modified AFM. The sample is the
cross section of the ultra thin phase separation (UTPS) film.
Figure 2. AFM images of films at different mixing ratios of PCBET/PVK: (b) 6:4, (d) 4:6, (e)
2:8, Scale: 8x8 μm2.
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