Block Copolymers—Designer Soft Materials

Bates, Frank S.; Fredrickson, Glenn H.

doi:10.1063/1.882522

Cited by 2,977 publications

(2,994 citation statements)

References 28 publications

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“…The interdigitated structure used is similar to the cylindrical phase, which can also form in such materials. 30 These structures are illustrated in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

Bicontinuous minimal surface nanostructures for polymer blend solar cells

Kimber

Walker

Schröder‐Turk

et al. 2010

Phys. Chem. Chem. Phys.

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This paper presents the first examination of the potential for bicontinuous structures such as the gyroid structure to produce high efficiency solar cells based on conjugated polymers. The solar cell characteristics are predicted by a simulation model that shows how the morphology influences device performance through integration of all the processes occurring in organic photocells in a specified morphology. In bicontinuous phases, the surface defining the interface between the electron and hole transporting phases divides the volume into two disjoint subvolumes. Exciton loss is reduced because the interface at which charge separation occurs permeates the device so excitons have only a short distance to reach the interface. As each of the component phases is connected, charges will be able to reach the electrodes more easily. In simulations of the current-voltage characteristics of organic cells with gyroid, disordered blend and vertical rod (rods normal to the electrodes) morphologies, we find that gyroids have a lower than anticipated performance advantage over disordered blends, and that vertical rods are superior. These results are explored thoroughly, with geminate recombination, i.e. recombination of charges originating from the same exciton, identified as the primary source of loss. Thus, if an appropriate materials choice could reduce geminate recombination, gyroids show great promise for future research and applications.

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“…The interdigitated structure used is similar to the cylindrical phase, which can also form in such materials. 30 These structures are illustrated in Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

Bicontinuous minimal surface nanostructures for polymer blend solar cells

Kimber

Walker

Schröder‐Turk

et al. 2010

Phys. Chem. Chem. Phys.

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“…The measurement temperature is denoted by T and the reference temperature by T ref [71]. Using a least-squares fit, the material parameters c 1 Table 3. The WLF fit parameters of the ISI triblock copolymers do not differ much from typical values that are observed for homopolystyrene [72].…”

Section: Rheological Analysismentioning

confidence: 99%

“…A huge variety of block copolymers exists due to many possible combinations of different blocks, accessible by an increasing number of different synthetic methods [1][2][3][4]. They exhibit particular properties which are caused by the combination of different blocks most often leading to self-assembled periodic microphase separated structures.…”

Section: Introductionmentioning

confidence: 99%

Influence of block sequence and molecular weight on morphological, rheological and dielectric properties of weakly and strongly segregated styrene-isoprene triblock copolymers

Georgopanos

Handge

Abetz

et al. 2016

Polymer

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In this work, morphological, thermal, viscoelastic and dielectric properties of triblock copolymers consisting of styrene (S) and isoprene (I) blocks are discussed. SIS and ISI triblock copolymers were synthesized by sequential anionic polymerization, three of them exhibiting molecular weights below the entanglement molecular weight M e , three of them exhibiting molecular weights in the order of M e and two of them exhibiting molecular weights above M e . The objective of this work is the investigation of the influence of molecular weight and block sequence on relaxation of the block copolymer chains. Morphological investigations using small angle X-ray scattering and transmission electron microscopy studies reveal that a larger molecular weight is associated with a more pronounced microphase separation. The presence of two glass transition temperatures reveals microphase separation of the PI and PS blocks. The Fox-Flory equation was applied in order to describe the molecular weight dependence of the glass transition temperature of the polyisoprene and the polystyrene blocks. The analysis of rheological data reveals a Maxwell fluid behaviour for the weakly segregated block copolymers, whereas for the strongly segregated block copolymers a pronounced elastic behaviour at low frequencies of small amplitude shear oscillations was observed.In the intermediate regime of molecular weight, a complex viscoelastic behaviour appears. The plateau modulus G N o is influenced by the sequence of the PS and the PI blocks (SIS or ISI). Our analysis of segmental and normal mode relaxation in dielectric spectroscopy experiments show that the relaxation processes are strongly influenced by the block sequence (PI blocks tethered at one or 1 both ends) and the molecular weight. As a result, the block sequence in triblock copolymers influences dynamical properties in the glassy state and in the melt.

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“…In contrast, reports of scaling behavior for block polymers with bottlebrush (z = 1) and other complex, non-linear architectures are limited due to the synthetic challenges associated with (1) precisely controlling the architecture, molecular weight, and composition and (2) efficiently preparing multiple samples to study trends.…”

mentioning

confidence: 99%

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

et al. 2017

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Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z). The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

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Block Copolymers—Designer Soft Materials

Cited by 2,977 publications

References 28 publications

Bicontinuous minimal surface nanostructures for polymer blend solar cells

Bicontinuous minimal surface nanostructures for polymer blend solar cells

Influence of block sequence and molecular weight on morphological, rheological and dielectric properties of weakly and strongly segregated styrene-isoprene triblock copolymers

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

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