Threshold Strain Value for Perpendicular Orientation in Dynamically Sheared Diblock Copolymers

Maring, Daniel; Wiesner, Ulrich

doi:10.1021/ma961234z

Cited by 63 publications

(88 citation statements)

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“…At this high deformation, the macromolecular response of the copolymer dominates, causing integrated motion of PS blocks towards a parallel alignment. [11][12][13][14] However, as suggested by Daniel et al [21] and Pakula et al, [23] necking and rupture of domain structures takes place at very high elongational flows. Hence, with a combination of all these effects, we obtained very small and broken PS/PI domains, with some evidence of parallel alignment in as-spun coaxial fibers.…”

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confidence: 93%

“…[8,9] The phenomenon of flow-induced alignment of lamellar BCPs is very well studied in bulk systems. [10][11][12] Three different orientations of lamellar morphology, namely, parallel, [13] perpendicular, and transverse [14][15][16] have been obtained as a function of shear rate, shear frequency, and temperature. We refer the reader to a review paper [7] that elaborates on the various methods to control BCP microdomains and the potential applications of these domains as nanometersized membranes, templates for fabrication of a variety of nano-objects, and templates for fabrication of high-density information-storage media.…”

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Confined Assembly in Coaxially Electrospun Block Copolymer Fibers

et al. 2006

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Electrospinning has received a lot of attention in recent years as a simple process to produce sub-micrometer-scale fibers. The process involves continuous stretching of polymer solution or melt in the presence of a strong electric field, which forms ultrathin fibers. A large amount of research is being carried out to achieve control of the diameter, morphology, and spatial alignment of electrospun nanofibers. [1,2] Unlike other 1D nanostructures, such as nanowires and nanotubes, nanofibers exhibit a wide range of unique properties, making them far more attractive for many applications, such as filtration, catalysis, sensing, protective clothing, and tissueengineering scaffolds.[3] Being a continuous process, electrospinning can produce extremely long fibers comparable to those formed via conventional mechanical drawing and spinning techniques. Nanofiber mats exhibit extremely high surface-to-mass ratios, greatly improving their efficiency for catalysis and filtration. [2] Another fascinating feature of this process is that it can be applied to a wide variety of nanostructured materials. Bognitzki et al. [4] fabricated sub-micrometerscale fibers by electrospinning ternary solutions of polylactide and poly(vinylpyrrolidone). They found that the fibers displayed an internal phase morphology, and, by selectively removing one phase, they obtained highly porous fibers. However, these morphologies were largely controlled by rapid phase separation and rapid solidification of the polymer jet, and no method for controlling these morphologies was demonstrated. In the present study, we utilize this simple process to fabricate block copolymer (BCP) nanofibers. BCP solutions and melts are known to self-assemble into a variety of nanoscale morphologies including spheres, rods, micelles, lamellae, vesicles, tubules, and cylinders, [5,6] depending on the volume fraction and interaction parameter between different blocks. We have been able to produce macroscale-length fibers with diameters of a few hundred nanometers that exhibit internal structures of only tens of nanometers in size. Such materials, we believe, can combine the unique properties of continuous nanofibers and BCP self-assembly for use in a variety of applications of nanostructured materials. BCP self-assembly has attracted increasing interest in recent years for applications in nanotechnology.[7] Precise control over the size, shape, and periodicity of these nanoscale microdomains is the key factor needed to realize nanoscale systems. Various methods, including shear and elongational deformation, compressional deformation, electric fields, and temperature gradients, have been utilized to induce orientation of the microdomains. To our knowledge, shear flow has been most extensively studied as a simple means to induce phase transitions and orient self-assembled structures in block copolymers. [8,9] The phenomenon of flow-induced alignment of lamellar BCPs is very well studied in bulk systems. [10][11][12] Three different orientations of lamellar morphology, namely, p...

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Confined Assembly in Coaxially Electrospun Block Copolymer Fibers

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“…To our knowledge, the only experimental determination in γ-ω space of the regions in which parallel or perpendicular lamellae are selected has been carried out for PS-PI block copolymers [Maring and Wiesner (1997); Leist et al (1999)]. It has been found that the line separating regions of perpendicular and parallel orientations was approximately given by γω = const.…”

Section: Discussionmentioning

confidence: 99%

“…10 indicate that the perpendicular orientation would be observed for large enough ω and γ. Otherwise, both parallel and perpendicular lamellae would coexist, and the selection between them would depend on experimental details such as quenched or annealed history of the sample and the starting time of the shear, as found in PS-PI copolymer samples [Patel et al (1995); Maring and Wiesner (1997); Larson (1999)] and cannot be addressed by the stability analysis here.…”

Section: Discussionmentioning

confidence: 99%

“…Of particular interest, and the least understood, is the selection between parallel and perpendicular orientations and the dependence on shear frequency ω and strain amplitude γ [Koppi et al (1992); Maring and Wiesner (1997)] as well as temperature [Koppi et al (1992); Pinheiro and Winey (1998)]. Near the order-disorder transition temperature T ODT and at low shear frequencies, parallel alignment has been found in poly(ethylene-propylene)-poly-(ethylethylene) (PEP-PEE) samples [Koppi et al (1992)], while for poly(styrene)-poly-(isoprene) (PS-PI) copolymers, the observed ultimate orientation is parallel [Maring and Wiesner (1997); Leist et al (1999)] or perpendicular [Patel et al (1995)], depending on sample processing details such as thermal history and shear starting time [Larson (1999)]. At higher but still intermediate frequencies (where ω < ω c , with ω c the characteristic frequency of polymer chain relaxation dynamics), the preferred orientation is perpendicular for both PEP-PEE and PS-PI copolymers under high enough shear strain [Koppi et al (1992); Patel et al (1995); Maring and Wiesner (1997); Leist et al (1999)].…”

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Stability of parallel/perpendicular domain boundaries in lamellar block copolymers under oscillatory shear

Huang

Viñals

2007

Journal of Rheology

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SynopsisWe introduce a model constitutive law for the dissipative stress tensor of lamellar phases to account for low frequency and long wavelength flows. Given the uniaxial symmetry of these phases, we argue that the stress tensor must be the same as that of a nematic but with the local order parameter being the slowly varying lamellar wavevector. This assumption leads to a dependence of the effective dynamic viscosity on orientation of the lamellar phase. We then consider a model configuration comprising a domain boundary separating laterally unbounded domains of so called parallel and perpendicularly oriented lamellae in a uniform, oscillatory, shear flow, and show that the configuration can be hydrodynamically unstable for the constitutive law chosen. It is argued that this instability and the secondary flows it creates can be used to infer a possible mechanism for orientation selection in shear experiments.1

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Block Copolymers in External Fields: Rheology, Flow‐Induced Phenomena, and Applications

Cloître

Vlassopoulos

2011

Applied Polymer Rheology

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Threshold Strain Value for Perpendicular Orientation in Dynamically Sheared Diblock Copolymers

Cited by 63 publications

References 24 publications

Confined Assembly in Coaxially Electrospun Block Copolymer Fibers

Confined Assembly in Coaxially Electrospun Block Copolymer Fibers

Stability of parallel/perpendicular domain boundaries in lamellar block copolymers under oscillatory shear

Block Copolymers in External Fields: Rheology, Flow‐Induced Phenomena, and Applications

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