Effect of lithium trifluoromethanesulfonate on the phase diagram of a liquid-crystalline amphiphilic diblock copolymer

Yamada, T.; Li, J.; Koyanagi, C.; Iyoda, T.; Yoshida, H.

doi:10.1107/S0021889807013453

conference papers

JOURNAL OF
APPLIED
CRYSTALLOGRAPHY

ISSN: 1600-5767

Volume 40| Part s1| April 2007| Pages s585-s589

doi:10.1107/S0021889807013453

Effect of lithium trifluoromethanesulfonate on the phase diagram of a liquid-crystalline amphiphilic diblock copolymer

Takeshi Yamada,^a Jingze Li,^b,^c Chinami Koyanagi,^c Tomokazu Iyoda ^b,^c and Hirohisa Yoshida ^d,^c ^*

^aGraduate School of Engineering, Tokyo Metropolitan University, Japan, ^bChemical Resources Laboratory, Tokyo Institute of Technology, Japan, ^cCREST-JST, Japan, and ^dFaculty of Urban Environmental Science, Tokyo Metropolitan University, Japan
^*Correspondence e-mail: yoshida-hirohisa@c.metro-u.ac.jp

(Received 14 August 2006; accepted 21 March 2007; online 14 April 2007)

Phase transitions and nanometre-scale ordered structures of a binary system of a liquid-crystalline amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate} [PEO_m-b-PMA(Az)_n, where m and n are the degrees of polymerization of the PEO and PMA(Az) domains, respectively], and lithium trifluoromethanesulfonate (LiCF₃SO₃) were investigated by differential scanning calorimetry and small-angle X-ray scattering (SAXS). PEO₁₁₄-b-PMA(Az)₅₁ formed a highly ordered hexagonally packed PEO cylinder structure in the temperature range below 393 K and transformed to a body-centred-cubic structure in the isotropic state above 393 K. The PEO₁₁₄-b-PMA(Az)₅₁/LiCF₃SO₃ systems with various LiCF₃SO₃ concentrations (molar ratio 0 < LiCF₃SO₃/EO = f_Li < 1) formed the hexagonally packed cylinder structure at room temperature. From the effects of LiCF₃SO₃ concentration on the phase transitions, the size and the order of the hexagonally packed cylinder structure, it was found that PEO₁₁₄-b-PMA(Az)₅₁ and LiCF₃SO₃ formed a complex efficiently at a molar equivalent of three ethylene oxide repeating units per LiCF₃SO₃ unit. The ordering of the hexagonally packed cylinder structure decreased with increasing LiCF₃SO₃ concentration and the radius of the PEO cylinder evaluated by SAXS profile fitting increased from 2.7 to 8.3 nm. For the PEO₁₁₄-b-PMA(Az)₅₁/LiCF₃SO₃ system with f_Li = 1, the hexagonally packed cylinder structure remained even in the isotropic state because the PEO volume fraction (ϕ_PEO) increased from ϕ_PEO = 0.06 (f_Li = 0) to ϕ_PEO = 0.23 (f_Li = 1) on the formation of the LiCF₃SO₃/PEO complex.

Keywords: amphiphilic diblock copolymers; small-angle X-ray scattering; lithium trifluoromethanesulfonate; nanocomposites.

1. Introduction

Nanometre-scale electron-conducting materials have been paid much attention because they are expected to provide a breakthrough in lithography limits. These materials are also interesting in terms of special physical properties like quantum size effects. Block copolymers are used as templates for making nanoscale objects in many studies (Lazzari & López-Quintela, 2003 ) because they can provide various nanoscale ordered structures which are easily modified by changing their fractions, degree of polymerization and chemical structures (Hamley, 1998 ).

There are various methods for analyzing nanostructures, e.g. atom-force microscopy (AFM), transmission and scanning electron microscopies (TEM and SEM) and small-angle scattering (SAS), which have different advantages. SAS is a powerful tool for analyzing average structures of materials because the irradiated volume is much larger than the measurement area for AFM or TEM (Hamley & Castelletto, 2004 ). Other advantages of SAS are that it can be used for various samples such as liquids, solutions, films, powders or supercritical fluids (Arai et al., 2003 ) and can be coupled with various fields, for instance, temperature (Yoshida et al., 1995 ), pressure (Kawabata et al., 2004), magnetic, mechanical and shear fields (Kato et al., 2004 ). Many numerical analysis methods for analyzing SAS data for micelle solutions (Lemmich et al., 1996 ) and block copolymers (Hashimoto et al., 1994 ) have also been reported. The combination of the use of brilliant synchrotron X-radiation with thermal analysis makes it possible to analyze the dynamics of phase transitions for organic and polymeric materials (Yamada et al., 2005 ).

Recently we reported the syntheses of liquid-crystalline amphiphilic diblock copolymers, poly(ethylene oxide)-b-poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate} [PEO_m-b-PMA(Az)_n, where m and n are the degrees of polymerization of the PEO and PMA(Az) domains, respectively] (Tian et al., 2002 ). PEO_m-b-PMA(Az)_n copolymers (Fig. 1) form a highly ordered hexagonally packed PEO cylinder structure selectively over a wide range of volume fraction because the liquid crystallinity of the PMA(Az) domains stabilizes a cylinder structure rather than a sphere structure (Yoshida et al., 2004 ). We also reported the nanometre-size control of the hexagonally packed cylinder structure of PEO_m-b-PMA(Az)_n by blending a PEO homopolymer (Jung et al., 2005 ) and PEO_m-b-PMA(Az)_n (Jung & Yoshida, 2006 ).

Figure 1
Chemical structure of the PEO_m-b-PMA(Az)_n copolymer.

PEO has potential as an electron-conducting material because it forms complexes with alkali metal ions (Rhodes & Frech, 2001 ). Since PEO–metal ion complexes have ionic conductivity in the solid state, they have been investigated as polymer electrodes in rechargeable batteries (Tominaga et al., 2003 ). The combination of an anisotropic nanometre-scale structure of block copolymers and PEO–metal ion complexes is expected to produce new ionic conductive materials. We have reported the anisotropic ionic conductivity of the PEO_m-b-PMA(Az)_n complex with lithium trifluoromethanesulfonate (LiCF₃SO₃) (Li et al., 2005 ). The structure and the phase transitions of the PEO_m-b-PMA(Az)_n complex with LiCF₃SO₃ are also important in considering the anisotropic conductivity. In this study, the effects of LiCF₃SO₃ on the phase diagram of PEO₁₁₄-b-PMA(Az)₅₁ were investigated by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS).

2. Samples and experiments

2.1. Samples

PEO₁₁₄-b-PMA(Az)₅₁ copolymer was synthesized by atomic transfer radical polymerization as reported elsewhere (Tian et al., 2002). The molecular weight dispersion was 1.23 determined by gel permeation chromatography. LiCF₃SO₃ supplied from Aldrich was used without further purification. LiCF₃SO₃ and PEO₁₁₄-b-PMA(Az)₅₁ were dissolved in distilled tetrahydrofuran separately. Then an appropriate amount of LiCF₃SO₃ solution was added to the PEO₁₁₄-b-PMA(Az)₅₁ solution. The mixed solution was stirred at room temperature for 6 h. After removing the solvent, the complex samples were annealed at 413 K for 16 h and cooled down to room temperature. The LiCF₃SO₃ concentration is indicated by the molar ratio of LiCF₃SO₃ to one repeating unit of PEO, LiCF₃SO₃/EO = f_Li. The f_Li range in this study was from 0 to 1 (Table 1).

Table 1
Characteristics of the samples studied

f_Li is the molar ratio of LiCF₃SO₃ to a repeating unit of PEO. a, Δa/a, R, C and ϕ_PEO are the hexagonal lattice constant, the paracrystal distortion, the radius of a PEO cylinder, the coefficient including electron density difference and the relative PEO volume fraction estimated by SAXS profile fitting.

f_Li	f_Li⁻¹	a (nm)	Δa/a	R (nm)	C	ϕ_PEO
0	—	21.3	0.134	2.7	169	0.06
8.3 × 10⁻³	120	21.7	0.194	2.8	44	0.06
2.5 × 10⁻²	40	23.4	0.149	3.6	76	0.09
5.0 × 10⁻²	20	23.6	0.179	3.8	81	0.09
1.3 × 10⁻¹	8	26.6	0.246	6.2	346	0.19
2.5 × 10⁻¹	4	28.9	0.216	7.0	1151	0.21
1.0	1	31.1	0.174	8.3	1250	0.26

2.2. Experiments

2.2.1. Differential scanning calorimetry

DSC measurements were performed using a DSC 6200 calorimeter (Seiko Instruments Inc.) equipped with an electric cooling control apparatus (Haake EK90/MT) over the temperature range between 223 and 473 K. The scanning rate was 10 K min⁻¹ in a nitrogen flow atmosphere (40 ml min⁻¹) and the sample weight used for the DSC was about 3 mg.

2.2.2. Small-angle X-ray scattering

SAXS measurements were performed using the synchrotron X-radiation facility of the 2.5 GeV storage ring at BL-10C at the Photon Factory, High Energy Accelerator Research Organization (Tsukuba, Japan). Monochromatic X-rays with a wavelength λ of 0.1488 nm selected by double Si crystals were used for SAXS measurements. Two kinds of optics which covered 0.1 < q < 3 nm⁻¹ and 0.06 < q < 1.5 nm⁻¹ were used, where q = (4π/λ)sin θ and θ is half of the diffraction angle. SAXS profiles at various temperatures were obtained using the simultaneous DSC instrument (Yoshida et al., 1995). Powder samples were covered with thin aluminium foil and put in an aluminium vessel. The exposure time was 60–300 s.

3. Results and discussion

3.1. Phase transitions

Fig. 2 shows DSC heating curves for the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with various f_Li. In the case of PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0), four endothermic phase transitions were observed around 313, 333, 373 and 393 K. These phase transitions correspond to melting of the PEO domain (~313 K), melting of the azobenzene moieties (~333 K), the liquid-crystalline transition from smectic C to smectic A (~373 K, indicated by an arrow in the inset) and the isotropic transition (~393 K) (Yoshida et al., 2004; Watanabe et al., 2006 ). With increasing LiCF₃SO₃ concentration the endothermic peak of the PEO melting decreased and disappeared above f_Li = 1.3 × 10⁻¹. LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ above f_Li = 2.5 × 10⁻¹ had a new endothermic peak around 433 K. This temperature is similar to the melting temperature of complexes of PEO with LiCF₃SO₃ (Rhodes & Frech, 2001). According to their report, one LiCF₃SO₃ forms a complex with three ethylene oxide (EO) units in the PEO/LiCF₃SO₃ complex. LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ with f_Li = 2.5 × 10⁻¹, in which the number of PEO repeating units per LiCF₃SO₃ was four, gave the largest fusion enthalpy of all the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ complexes, therefore the endothermic peak of LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ with f_Li = 2.5 × 10⁻¹ and 1.0 observed around 433 K was assigned as melting of the LiCF₃SO₃/PEO complex in the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ system. The melting peak of the LiCF₃SO₃/PEO complex in LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ with f_Li = 1 was broad and small. This fact suggested that the excess amount of LiCF₃SO₃ disturbed the crystallization of the PEO/LiCF₃SO₃ complex. Below f_Li = 1.3 × 10⁻¹, in which the number of PEO repeating units per LiCF₃SO₃ was more than 20, the melting peak of PEO in the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems became broad and small with increasing LiCF₃SO₃ concentration. The existence of a small amount of LiCF₃SO₃ relative to the PEO repeating unit inhibited the crystallization of the PEO domain in PEO₁₁₄-b-PMA(Az)₅₁. The molar equivalent was important for forming crystals of PEO/LiCF₃SO₃ complex.

Figure 2
DSC heating curves of PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0, bottom) and LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with f_Li = 8.3 × 10⁻³, 2.5 × 10⁻², 5.0 × 10⁻², 1.3 × 10⁻¹, 2.5 × 10⁻¹ and 1.0 from bottom to top.

On the other hand, phase transitions concerning the hydrophobic PMA(Az) domain in PEO₁₁₄-b-PMA(Az)₅₁ showed different tendencies with LiCF₃SO₃ concentration. Both the melting of azobenzene moieties and the isotropic transition were scarcely influenced by the addition of LiCF₃SO₃ for the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems below f_Li = 5.0 × 10⁻². However, in the case of f_Li = 1.3 and 2.5 × 10⁻¹, the isotropic transition temperature (T_Iso) and enthalpy (ΔH_Iso) shifted slightly to higher temperatures and decreased compared with the isotropic transition of PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0). The solid PEO/LiCF₃SO₃ complex in the PEO domain, having a higher melting temperature than T_Iso, reduced the molecular mobility of the PMA(Az) domain in the isotropic state, therefore T_Iso increased. The decrease of ΔH_Iso indicated the restricted molecular motion of the liquid-crystalline parts by the solid PE/LiCF₃SO₃ complex and disorder in the smectic layer of the PMA(Az) domain.

3.2. Nanostructures

3.2.1. PEO₁₁₄-b-PMA(Az)₅₁

Fig. 3 shows SAXS profiles of PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0) at room temperature and 423 K (isotropic state). The nanostructure at room temperature was assigned as the hexagonally packed PEO cylinder structure, because the ratio of each diffraction peak to the first-order peak (q*) was q*: (3q*)^0.5: (4q*)^0.5: (7q*)^0.5. At q = 2.0 nm⁻¹, another peak corresponding to smectic layers of PMA(Az) domains was observed at room temperature. At 423 K, where the PMA(Az) domain was in the isotropic state, the peak coming from the smectic layers disappeared. On the other hand, three peaks, shown by arrows in Fig. 3, were observed, although these peak intensities were much weaker than those at room temperature. Since the ratios of the diffraction peaks were q*: (2q*)^0.5: (3q*)^0.5, the nanostructure at 423 K was assigned as having a body-centered-cubic (b.c.c.) structure. The hexagonally packed PEO cylinder structure of PEO₁₁₄-b-PMA(Az)₅₁ changed to the b.c.c. structure at the isotropic transition.

Figure 3
SAXS profiles of PEO₁₁₄-b-PMA(Az)₅₁ obtained at room temperature (R.T., triangles) and 423 K (filled circles). Arrows: peak positions at 423 K. Solid line: best-fit result from equation (1)

The radius of the PEO cylinder (R) was estimated by the paracrystal model (Hashimoto et al., 1994). In this model, the observed scattering intensity from a hexagonally packed cylinder structure having a random orientation [I(q)] is given by

$[I(q) = q^{-1} I_{\bot}(q), \eqno (1)]$

where $[I_ \bot (q)]$ is a scattering function having uniaxial orientation. $[I_ \bot (q)]$ is given by

$[I_{\bot} (q, \phi) = {1 \over {2\pi }}\int\limits_0^{2\pi} {\left\langle {f^2 } \right\rangle } - \left| {\left\langle f \right\rangle } \right|^2 + \left| {\left\langle f \right\rangle } \right|^2 Z\ {\rm d}\phi, \eqno (2)]$

where f and Z indicate the form factor and the structure factor, respectively. The form factor f(q) is given by

$[f(q) = C{{J_1 (qR)}\over{qR}}\exp \biggl (-{{q^2 \sigma _{\rm s}^2}\over 2} \biggr), \eqno (3)]$

$[\left\langle {f^n } \right\rangle = {{\int_0^\infty {P(R)\,f^n (q, R)\ {\rm d}R} }\over{\int_0^\infty {P(R)\ {\rm d}R}}}, \eqno (4)]$

$[P(R) \simeq \exp \biggl [- {{(R - \overline R)^2 } \over {2\sigma _{\rm R}^2 }} \biggr], \eqno (5)]$

where C is a constant including the electron density difference and scattering volume, J₁ is the first-order Bessel function, R is the radius of the cylinder, $[\overline R]$ is the mean radius, σ_R is the standard deviation of R and σ_s is the characteristic thickness of a interface. σ_s is related to the thickness of the interface between each domain (t) by t/(2π)^0.5 (Shibayama & Hashimoto, 1986 ). The structure factor Z is given by

$[Z = Z_1 Z_2, \eqno (6)]$

$[\eqalignno{Z_1 &= \{q - \exp [- (\Delta ^2 a)q^2 P]\}\big(1 - 2\exp [- (1/2)(\Delta ^2 a)q^2 P]&\cr &\quad\times\cos \{aq\cos [\phi - (\pi/ 6)]\} + \exp [- (\Delta ^2 a)q^2 P]\big)^{-1}, &(7)}]$

$[\eqalignno{Z_2 &= \{q - \exp [- (\Delta ^2 a)q^2 P]\}\big\{1 - 2\exp [- (1/2)(\Delta ^2 a)q^2 P]&\cr &\quad\times\cos [aq\sin (\phi)] + \exp [- (\Delta ^2 a)q^2 P]\big\}^{-1} &(8)}]$

$[P = \cos ^2 [\phi - (\pi/ 6)] + \sin ^2 \phi, \eqno (9)]$

where a and Δa are the lattice constant of the hexagonal structure and the paracrystal distortion factor, respectively. For the profile-fitting calculation, t was fixed to 0.5 nm because the interface thickness was estimated as two or three repeating units of PMA(Az) from the thermodynamic relationship between the isotropic transition entropy and the degree of polymerization of PMA(Az) (Yamada et al., 2004 ). Since the effect of σ_R on the profile-fitting calculation was small, σ_R/R was also fixed to 0.05. Four fitting parameters, a, Δa, R and C, were used for the profile -fitting calculation. The best-fit results for PEO₁₁₄-b-PMA(Az)₅₁ are superimposed on the SAXS profile observed at room temperature in Fig. 3. The fitting results are listed in Table 1. The calculated result did not match the experimental data because the scattering from large grains overlapped in the low-q region and the intensity was not high enough in the high-q region. The PEO volume fraction (ϕ_PEO) was estimated using

$[\phi _{\rm PEO} = {{2\pi}\over{3^{1/2}}}\left({R\over{a_{}}}\right)^2. \eqno (10)]$

ϕ_PEO of PEO₁₁₄-b-PMA(Az)₅₁ was 0.06. In the case of a linear diblock copolymer having a step-function-type electron density profile, the border between the hexagonally packed cylinder structure and the b.c.c. structure is ϕ_A = 0.12, where ϕ_A is the minor component (Lodge & Muthukumar, 1996 ). Although the ϕ_PEO value of PEO₁₁₄-b-PMA(Az)₅₁ (0.06) was lower than the border ϕ_PEO value between the hexagonally packed cylinder structure and the b.c.c. structure (0.12) (Lodge & Muthukumar, 1996), the hexagonally packed cylinder structure was stable at room temperature for PEO₁₁₄-b-PMA(Az)₅₁. For PEO₁₁₄-b-PMA(Az)_n, the hexagonally packed cylinder structure is stable when the PMA(Az) domain is in the smectic phase to compensate for the conformational entropy loss of the smectic phase formation by the increase of freedom in the interface between the hydrophilic and hydrophobic domains (Yoshida et al., 2004). This assumption conformed to the observation of the transformation from the hexagonally packed cylinder structure to the b.c.c. structure at the isotropic transition. Anthamatten & Hammond determined phase diagrams of side-chain liquid-crystalline copolymers by theoretical calculation. When the side-chain liquid crystal took a planar anchoring on the interface between each block, the side-chain liquid-crystal copolymer preferred to form the cylinder structure over a wide range of volume fractions compared with linear block copolymers (Anthamatten & Hammond, 2001 ).

3.2.2. LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems

Fig. 4 shows SAXS profiles of LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems having various f_Li values at room temperature. In the q range between 0.1 and 1 nm⁻¹, the diffraction peaks corresponding to the hexagonally packed cylinder structure were observed for all systems. The diffraction peak of the smectic layers also appeared at q = 2 nm⁻¹. Although the peak position of the smectic layers scarcely changed below f_Li = 2.5 × 10⁻¹, the half bandwidth increased with increasing LiCF₃SO₃ concentration. In particular, above f_Li = 1.3 × 10⁻¹ the smectic layer peak became broad and the position of the peak shifted to lower q for the system with f_Li = 1.0. When the LiCF₃SO₃ concentration was close to the molar equivalent value, the formation of the complex between three EO units and one LiCF₃SO₃ occurred efficiently. The complex of PEO/LiCF₃SO₃ acted as a cross linkage between the PEO chains and decreased the molecular mobility of the PEO. Then the hydrophilic PEO cylinder changed to a viscous cylinder and induced disordering of the smectic layers in the hydrophobic PMA(Az) domain. The SAXS experiment results showed a good agreement with the DSC results shown in Fig. 2.

Figure 4
SAXS profiles of PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0, bottom) and LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with f_Li = 8.3 × 10⁻³, 2.5 × 10⁻², 5.0 × 10⁻², 1.3 × 10⁻¹, 2.5 × 10⁻¹ and 1.0 from bottom at room temperature.

The nanostructures of LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ were evaluated by SAXS profile fitting using equation (1). The fitted results for LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with f_Li = 2.5 × 10⁻¹ and 1.0 are shown in Fig. 5, and the values obtained are listed in Table 1. These fitted results also did not match the experimental results in the low-q region for the same reason as for PEO₁₁₄-b-PMA(Az)₅₁ (f_Li = 0). Since the PEO complexes with LiCF₃SO₃ had a larger volume than PEO, the radius of the PEO cylinder (R) increased with increasing LiCF₃SO₃ concentration. Concurrently, LiCF₃SO₃ acted as a cross-linker between the PEO chains and restricted the molecular motion of the PEO, therefore the disorder (Δa/a) also increased with increasing LiCF₃SO₃ concentration.

Figure 5
Typical fitting results for LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with f_Li = 2.5 × 10⁻¹ (top) and 1.0 (bottom) at room temperature.

Fig. 6 shows SAXS profiles for the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems with f_Li = 2.5 × 10⁻² (ϕ_PEO = 0.09) and f_Li = 1 (ϕ_PEO = 0.23) at 423 and 473 K, respectively, where both systems are in the isotropic state. The nanostructure of the system with f_Li = 2.5 × 10⁻² in the isotropic state was the b.c.c. structure, the same as that of PEO₁₁₄-b-PMA(Az)₅₁ at 423 K (Fig. 2). The ϕ_PEO values of the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems used in this study, from 0.06 to 0.23 as shown in Table 1, covered the border ϕ_PEO value (0.12) between the hexagonally packed cylinder structure and the b.c.c. structure expected by theoretical calculations for linear block copolymers (Lodge & Muthukumar, 1996). Therefore, the nanostructure of the system with f_Li = 1.0 was the hexagonally packed cylinder structure in the isotropic state, because ϕ_PEO = 0.23 was larger than the border value. These results also indicated that LiCF₃SO₃ increased ϕ_PEO of the LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems by the formation of an LiCF₃SO₃/PEO complex.

Figure 6
SAXS profiles of LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems in the isotropic state. Open circles: f_Li = 1 at 473 K; open squares: f_Li = 2.5 × 10⁻² at 423 K.

4. Conclusion

Phase transitions and nanostructures of LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems were investigated by DSC and SAXS. The LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems above f_Li = 2.5 × 10⁻¹, which corresponds to four PEO repeating units per LiCF₃SO₃ molecule, formed a complex of LiCF₃SO₃/(EO)₃. The complex of LiCF₃SO₃/PEO melted at 433 K, which was higher than the isotropic transition of the PMA(Az) domain. The addition of LiCF₃SO₃ induced disordering in the PEO₁₁₄-b-PMA(Az)₅₁ nanostructure and the liquid-crystal structure due to the molecular motion of the PEO domains being restricted by the complex formation. On the other hand, the addition of LiCF₃SO₃ increased the radius of the PEO cylinder and the volume fraction of the PEO domain. The structure transition from the hexagonally packed cylinder to the b.c.c. structure occurred for LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ with f_Li = 2.5 × 10⁻² (ϕ_PEO = 0.09) in the isotropic state, but not for LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ with f_Li = 1.0 (ϕ_PEO = 0.23).

Acknowledgements

The authors are grateful to the Japan Science and Technology Agency for support of this research through the CREST project.

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ISSN: 1600-5767

Volume 40| Part s1| April 2007| Pages s585-s589

doi:10.1107/S0021889807013453

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conference papers\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Effect of lithium tri­fluoro­methane­sulfonate on the phase diagram of a liquid-crystalline amphiphilic diblock copolymer

1. Introduction

2. Samples and experiments

2.1. Samples

2.2. Experiments

2.2.1. Differential scanning calorimetry

2.2.2. Small-angle X-ray scattering

3. Results and discussion

3.1. Phase transitions

3.2. Nanostructures

3.2.1. PEO114-b-PMA(Az)51

3.2.2. LiCF3SO3/PEO114-b-PMA(Az)51 systems

4. Conclusion

Acknowledgements

References

conference papers

Effect of lithium trifluoromethanesulfonate on the phase diagram of a liquid-crystalline amphiphilic diblock copolymer

3.2.1. PEO₁₁₄-b-PMA(Az)₅₁

3.2.2. LiCF₃SO₃/PEO₁₁₄-b-PMA(Az)₅₁ systems