morphology and the crystallization of P3HT. Figure 10 shows the characteristic
bright fields and GIXD 2D patterns recorded for two M w fractions of P3HT
(M w ¼ 7.9 kDa and M w ¼ 50 kDa). Oriented films prepared by slow-DEC show
different structural and morphological features when the molecular weight of P3HT
changes (see Fig. 10). The observed differences in morphology and structure as a
function of M w reflect different crystallization modes that are attributed to the
presence or absence of chain folding and tie-chains.
All M w fractions of P3HT give rise to oriented and periodic lamellar structures in
films grown by epitaxy on TCB [43, 44]. In the TEM bright field (TEM-BF) images,
a characteristic contrast is observed between crystalline domains and amorphous
interlamellar zones (see Figs. 10 and 11). Therefore, one can observe the periodic
alternation of crystalline (dark) and bright (amorphous) domains, i.e., the semicrystalline structure of the polymer. Additional differences between films of different
M w s are obtained by GIXD and ED. The effect of M w on nanocrystal orientation is
particularly well observed in the GIXD patterns when the incident X-ray beam is
oriented parallel to the P3HT chain direction (see Fig. 10). For low-M w P3HT, the
GIXD 2D pattern reflects the coexistence of three populations of nanocrystals with
(0 1 0), (0 0 1), and (0 1 1) contact planes. These three types of lamellae share the
same in-plane orientation of their a P3HT axis (direction of alkyl side chains), i.e.,
a P3HT ⊥c TCB . For P3HT samples with a high M w of 50 kDa that crystallize with
folded chains, the GIXD pattern is very different and shows a sequence of (h 0 0)
Scherrer rings. Such a pattern indicates that the epitaxied films for M w ¼ 50 kDa
have a fiber-like symmetry, i.e., films consist of a variety of nanocrystals with
different contact planes and a well-defined in-plane orientation of the P3HT chains
enforced by 1D epitaxy on TCB.
Beside orientation of nanocrystals, M w impacts strongly on the nanomorphology
and in particular the semicrystalline structure of P3HT. In the original work by
Brinkmann and Rannou on P3HT films grown by DEC [44], the total lamellar
periodicity measured in the BF images is close to the length of the ‘fully extended’
chain for M w ~6–8 kDa and it saturates to a value of ca. 27 Æ 2 nm for M w ! 17 kDa.
This behavior is due to a transition from an oligomeric-like system with fully
extended chains in all-trans conformation to a semicrystalline system with a
periodic alternation of crystalline lamellae separated by extended amorphous
interlamellar zones harboring chain folds, chain ends, and tie molecules [43–45].
Incidentally, the total lamellar period L lam in epitaxied P3HT films can exceed
the value of 28 nm in films obtained by DEC if the growth of the films is performed
at a ‘slow’ rate of 20 μm/s (slow-DEC) versus 1 mm/s for the original DEC method
used by Brinkmann and Rannou [44]. Figure 12 shows the M n -dependence of the
total lamellar period (crystalline plus amorphous) L lam measured in epitaxied films
grown at 1 mm/s (DEC) and 20 μm/s (slow-DEC). In the regime of folded chain
crystallization (M w > 10 kDa), the slower growth rates result in longer lamellar
periods for films of high-M w P3HT. For instance, for M w ¼ 50 kDa (M n ¼ 26 kDa),
L lam ~ 45 nm can be observed versus 28 nm for films grown rapidly on a Koeffler
bench [44]. Similar large lamellar periods were only observed in the case of
spherullitic growth by swelling/deswelling of thin films by Crossland et al. [69]
(see Tremel and Ludwigs [20]).
98
M. Brinkmann et al.
bright fields and GIXD 2D patterns recorded for two M w fractions of P3HT
(M w ¼ 7.9 kDa and M w ¼ 50 kDa). Oriented films prepared by slow-DEC show
different structural and morphological features when the molecular weight of P3HT
changes (see Fig. 10). The observed differences in morphology and structure as a
function of M w reflect different crystallization modes that are attributed to the
presence or absence of chain folding and tie-chains.
All M w fractions of P3HT give rise to oriented and periodic lamellar structures in
films grown by epitaxy on TCB [43, 44]. In the TEM bright field (TEM-BF) images,
a characteristic contrast is observed between crystalline domains and amorphous
interlamellar zones (see Figs. 10 and 11). Therefore, one can observe the periodic
alternation of crystalline (dark) and bright (amorphous) domains, i.e., the semicrystalline structure of the polymer. Additional differences between films of different
M w s are obtained by GIXD and ED. The effect of M w on nanocrystal orientation is
particularly well observed in the GIXD patterns when the incident X-ray beam is
oriented parallel to the P3HT chain direction (see Fig. 10). For low-M w P3HT, the
GIXD 2D pattern reflects the coexistence of three populations of nanocrystals with
(0 1 0), (0 0 1), and (0 1 1) contact planes. These three types of lamellae share the
same in-plane orientation of their a P3HT axis (direction of alkyl side chains), i.e.,
a P3HT ⊥c TCB . For P3HT samples with a high M w of 50 kDa that crystallize with
folded chains, the GIXD pattern is very different and shows a sequence of (h 0 0)
Scherrer rings. Such a pattern indicates that the epitaxied films for M w ¼ 50 kDa
have a fiber-like symmetry, i.e., films consist of a variety of nanocrystals with
different contact planes and a well-defined in-plane orientation of the P3HT chains
enforced by 1D epitaxy on TCB.
Beside orientation of nanocrystals, M w impacts strongly on the nanomorphology
and in particular the semicrystalline structure of P3HT. In the original work by
Brinkmann and Rannou on P3HT films grown by DEC [44], the total lamellar
periodicity measured in the BF images is close to the length of the ‘fully extended’
chain for M w ~6–8 kDa and it saturates to a value of ca. 27 Æ 2 nm for M w ! 17 kDa.
This behavior is due to a transition from an oligomeric-like system with fully
extended chains in all-trans conformation to a semicrystalline system with a
periodic alternation of crystalline lamellae separated by extended amorphous
interlamellar zones harboring chain folds, chain ends, and tie molecules [43–45].
Incidentally, the total lamellar period L lam in epitaxied P3HT films can exceed
the value of 28 nm in films obtained by DEC if the growth of the films is performed
at a ‘slow’ rate of 20 μm/s (slow-DEC) versus 1 mm/s for the original DEC method
used by Brinkmann and Rannou [44]. Figure 12 shows the M n -dependence of the
total lamellar period (crystalline plus amorphous) L lam measured in epitaxied films
grown at 1 mm/s (DEC) and 20 μm/s (slow-DEC). In the regime of folded chain
crystallization (M w > 10 kDa), the slower growth rates result in longer lamellar
periods for films of high-M w P3HT. For instance, for M w ¼ 50 kDa (M n ¼ 26 kDa),
L lam ~ 45 nm can be observed versus 28 nm for films grown rapidly on a Koeffler
bench [44]. Similar large lamellar periods were only observed in the case of
spherullitic growth by swelling/deswelling of thin films by Crossland et al. [69]
(see Tremel and Ludwigs [20]).
98
M. Brinkmann et al.