Diblock Copolymer Micelles in Solvent Binary Mixtures. 2. Selective Solvent/Good Solvent

Villacampa, Manuel; Apodaca, Elena Díaz de; Quintana, José R.; Katime, Issa

doi:10.1021/ma00116a014

Cited by 31 publications

(34 citation statements)

References 5 publications

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“…This has also been observed in similar organic micellar solution systems upon varying the solvent selectivity near the cmt. 21,41 However, it was also found that the aggregation number (and thus radius) increases with increasing selectivity for the coronal block. It is possible that R h remains independent of selectivity due to competing changes in the micelle structure; the increase in aggregation number with decreasing temperature (indicated by the progressive increase in scattered intensity in Figure 4b) may be offset by a decrease in the core radius as solvent is excluded from the core and the micelle becomes more dense.…”

Section: Resultsmentioning

confidence: 98%

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

2000

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The effect of the thermodynamic selectivity of a solvent on the self-assembly of a styreneisoprene (SI) diblock copolymer with block molecular weights of 1.1 × 10 4 and 2.1 × 10 4 g/mol is investigated. We explore the phase behavior from the melt state to dilute solution in solvents that are of varying selectivities for the two blocks. Bis(2-ethylhexyl) phthalate (DOP) is a neutral good solvent for SI. Di-n-butyl phthalate (DBP) and diethyl phthalate (DEP) are good solvents for PS but marginal and poor, respectively, for PI. Tetradecane (C14) is utilized as a complementary solvent that is good for PI but poor for PS. Small-angle X-ray scattering (SAXS) and static birefringence are used to locate and identify order-order (OOT) and order-disorder transitions (ODT). Dynamic and static light scattering were used to characterize the dilute solution micellar behavior. The neat polymer forms the gyroid (G 1) morphology at low temperature, an OOT to hexagonal-packed cylinders (C1) occurs at 185°C, and the ODT is located at 238°C. Dilution with DOP decreases the OOT temperature in agreement with the dilution approximation, i.e., OOT ∼ φ -1 , but the ODT follows a stronger dependence of ODT ∼ φ -1.4 . The slightly selective solvent DBP stabilizes the ordered state relative to DOP. Rich lyotropic and thermotropic behavior is observed among regions of lamellae (L), inverted gyroid (G2), inverted hexagonal-packed cylinders (C2), and inverted body-centered-cubic spheres (S2 bcc ). Solutions in DEP display similar morphological behavior, along with significantly increased ODT temperatures. Because of the asymmetric block copolymer composition, the phase behavior in the isoprene-selective solvent C14 is markedly different, as only G1, C1, and S1 bcc phases are observed. The overall sequence of phases with dilution and/or heating is rationalized on the basis of diagonal trajectories across the phase map (temperature vs composition) for undiluted block copolymers: addition of a neutral solvent corresponds to increasing the temperature and thus a "vertical" trajectory, whereas the partitioning between microdomains of a selective solvent amounts to a "horizontal" trajectory to a renormalized block volume composition. However, a variety of novel features are observed in DEP: the formation of face-centered-cubic packed micelles, a reentrant thermotropic ODT, and a large window of L + C 2 coexistence. The dependence of the principal length scale, d*, on φ, T, and structure is also considered. The strongly temperature-dependent selectivity produces a crossover in the scaling of d* vs φ for the lamellar phase: the addition of a selective solvent increases d*, but as the solvent becomes neutral, d* decreases. This phenomenon is captured by selfconsistent mean-field calculations.

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Section: Resultsmentioning

confidence: 98%

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

2000

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“…Although controlled synthesis of block copolymers provides access to various micelle structures, an alternative and facile approach to tune the state of self‐assembly is addition of selective solvents. Differences between the core block–solvent and corona block–solvent interactions can be adjusted by choice of the solvent, blends of solvents, or temperature . In the case of spherical micelles, physical properties such as overall micelle size ( R M ), core radius ( R c ), average aggregation number ( N agg ), and critical micelle temperature ( T CMT ) can be controlled by the solvent selectivity for a given polymer system …”

Section: Introductionmentioning

confidence: 99%

“…Theoretical scaling relationships predict that R M , R c , N agg , and T CMT tend to decrease as the solvent selectivity is reduced, in good agreement with recent experimental results. For example, Villacampa et al studied spherical micelles formed by poly(styrene‐ b ‐ethylene‐ alt ‐propylene) (PS‐PEP) in mixtures of 4‐methyl‐2‐pentanone (selective to PS) and 2‐chlorobutane (neutral solvent) using light scattering . They observed that T CMT and micelle molar mass (corresponding to N agg ) decrease with increasing fraction of 2‐chlorobutane in the solvent mixture, yet R M is nearly constant.…”

Section: Introductionmentioning

confidence: 99%

Structure of poly(styrene‐b‐ethylene‐alt‐propylene) diblock copolymer micelles in binary solvent mixtures

Choi

Lee

Lodge

et al. 2015

J Polym Sci B Polym Phys

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The effect of solvent selectivity on the micelle structure formed by a poly(styrene‐b‐ethylene‐alt‐propylene) diblock copolymer (PS‐PEP, MPS = 42,000 g/mol and MPEP = 62,000 g/mol) in solutions of squalane, a highly selective solvent for the PEP block, and 1‐phenyldodecane, a neutral solvent, is investigated using dynamic light scattering (DLS) and small‐angle X‐ray scattering (SAXS). The results reveal that addition of 1‐phenyldodecane systematically reduces solvent selectivity, leading to decreases in the critical micelle temperature (TCMT) and the average number of chains in a micelle (Nagg), and an increase in the solvent fraction in the core. However, the core blocks have essentially unperturbed dimensions (i.e., Rc ≈ 2 × ⟨Rg⟩o, where ⟨Rg⟩o is unperturbed radius of gyration of the core block), and therefore the micelle core radius (Rc) is nearly independent of solvent selectivity, which has not been anticipated by previous theoretical descriptions. These results demonstrate that under such conditions, excluded volume effects in the corona blocks play the dominant role in determining micelle structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 22–31

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“…This finding suggested that the amphiphilic diblock copolymer with long hydrophobic PChM block showed smaller A 2 value, thus indicating that the solubility in water for PMPC 82 -b-PChM 6 is lower than that for PMPC 82 -bPChM 3 . 24,25 The R g /R h value is largely related to the shape and polydispersity of aggregates. For example, the R g /R h values for rigid hard spheres and spherical shape aggregates are theoretically 0.78 and 1.0, respectively, but these values for random coil and ellipsoidal aggregates are 1.3-1.5.…”

Section: Aggregation Of Pmpc 82 -B-pchm N In Watermentioning

confidence: 99%

Aggregation behavior in water of amphiphilic diblock copolymers bearing biocompatible phosphorylcholine and cholesteryl groups

Ohno

Hasegawa

Liu

et al. 2014

Polym J

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Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-block-poly(cholesteryl 6-methacryloyloxyhexanoate) (PMPC 82 -b-PChM n ) copolymers with different PChM block lengths were prepared via reversible addition-fragmentation chain transfer controlled/living radical polymerization using a PMPC-based macro-chain transfer agent. The subscript number and n ( = 3 and 6) refer to the degree of polymerization of the PMPC and PChM blocks, respectively. PMPC 82 -b-PChM n cannot dissolve in water directly due to the strong hydrophobic nature of the PChM block. To prepare the aqueous solution, the diblock copolymer was dissolved in an organic solvent and then dialyzed against pure water. These diblock copolymers formed spherical and rod-like micelles in water, depending on the composition of cholesteryl (Chol) group in the polymer. The prepared aggregates were characterized using static light scattering, dynamic light scattering, transmission electron microscopy and fluorescence probe techniques. The characterization results suggest that the morphology of the polymer aggregates can be controlled from spherical to rod-like micelles by increasing the number of Chol groups in the polymer.

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Diblock Copolymer Micelles in Solvent Binary Mixtures. 2. Selective Solvent/Good Solvent

Cited by 31 publications

References 5 publications

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

Phase Behavior of a Block Copolymer in Solvents of Varying Selectivity

Structure of poly(styrene‐b‐ethylene‐alt‐propylene) diblock copolymer micelles in binary solvent mixtures

Aggregation behavior in water of amphiphilic diblock copolymers bearing biocompatible phosphorylcholine and cholesteryl groups

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