Pathways to Macroscale Order in Nanostructured Block Copolymers

Abstract

Polymeric materials undergo dramatic changes in orientational order in response to dynamic processes, such as flow. Their rich cascade of dynamics presents opportunities to create and combine distinct alignments of polymeric nanostructures through processing. In situ rheo-optical measurements complemented by ex situ x-ray scattering reveal the physics of three different trajectories to macroscopic alignment of lamellar diblock copolymers during oscillatory shearing. At the highest frequencies, symmetry arguments explain the transient development of a bimodal texture en route to the alignment of layers parallel to the planes of shear. At lower frequencies, larger-scale relaxations introduce rearrangements out of the deformation plane that permit the formation of lamellae perpendicular to the shear plane. These explain the change in the character of the pathway to parallel alignment and the emergence of perpendicular alignment as the frequency decreases.

Orientation behaviour of AB and ABC block copolymers under large amplitude oscillatory shear flow in bulk and in concentrated solution

“…The x-y plane is formed by the flow direction (x-axis, 1) and the vorticity axis (y-axis, 3). So the 1,3-birefringence ∆n ≡ ∆n 13 (subscript refers to the axis definition) is measured in this geometry with ∆n 13 = n 11 -n 33 . Due to the dominating form contribution [68,69] of the microphase separated IS diblock copolymer to the birefringence, this is a good tool for measuring the alignment process of the microdomains.…”

“…Most of the later works on the alignment kinetics of lamellar diblock copolymers in the bulk state were done by the groups of Kornfield [11][12][13][14][15][16][17] and Wiesner [5,7,8,10]. They examined the same block copolymer, namely a symmetrical polystyrene-blockpoly(1,4-isoprene) diblock copolymer with an overall molecular weight of 20 kg/mol in a LAOS field.…”

Nanopatterns Produced by Directed Self-Assembly in Block Copolymer Thin Films

“…In bulk systems, shear induced alignment has proven the most successful, and has focused large research efforts, both experimentally [76,77], and theoretically [78], which go beyond the scope of this chapter and are reviewed elsewhere [79]. Shear alignment of thin films was shown to be very efficient on spherical and cylindrical block copolymer phases, if it is performed at a temperature between the highest of the two glass transition temperature and the order-disorder transition temperature of the diblock [80]: T g < T < T ODT .…”

Real science at the petascale

“…The non-equilibrium dynamics of these liquid crystalline phases can provide insight into the pathways and kinetics of self-assembly in non-cubic4cubic as well as cubic4cubic phase transitions that are also being actively studied experimentally (Seddon et al 2006). Shear flow fields as well as other fields such as roll casting and extensional flow are used in the processing of functional materials for switchable optical, transport and electronic properties as well as ordered nanostructures (Chen et al 1997).…”