Depolarized Scattering from Block Copolymer Grains Using Circularly Polarized Light

Abstract

The grain structure of ordered block copolymer materials affects their viscoelastic, adhesive, optical, and electrical properties. Depolarized light scattering has proven to be an important method for characterizing this grain structure. In this paper, we use both theory and experiments to demonstrate the relationship between grain structure and depolarized light scattering from ordered block copolymer samples performed with crossed circular polarizers. We model the sample assuming it comprises randomly oriented ellipsoidal grains with optic axes coincident with the ellipsoid axes. We show that the scattering pattern obtained using circularly polarized (CP) light is azimuthally symmetric, in contrast to that obtained using linearly polarized (LP) light which exhibits 4-fold angular modulation. The integrated scattered power in the CP case is twice as large as that in the LP case. By simultaneously fitting CP and LP light scattering data, we obtain robust measures of parameters that characterize grain structures. In addition, CP light scattering can, in principle, be used to characterize nonrandom grain orientation distributions.

Phase Behavior of Mixtures of Block Copolymers and a Lithium Salt

“…The sample was placed between crossed polarizers in a heating block that was electrically heated by two heating elements, and the temperature of the sample was controlled by an Omega Engineering temperature controller (CN9111A). 40 In order to determine the order-disorder transition temperature (T odt ) of the sample, the birefringence method was employed. 41 In the orderto-disorder experiments, the total depolarized transmitted laser power was obtained as the sample was heated in approximately 10 °C increments from 80 °C to 110 °C.…”

Confined versus Unconfined Crystallization in Block Copolymer/Salt Mixtures Studied by Depolarized Light Scattering

“…The samples used in the DPLS experiments were prepared by melting The schematic of a custom-made apparatus used in the DPLS measurement was described in ref 34 . The light source in this study was a Coherent continuous-wave diode laser with wavelength of 633nm and an output power adjustable from 0 to 40 mW.…”

“…At each temperature step for the shallow quench and deep quench, linear and circular scattering patterns (LP and CP) were captured, one without and the other with the two quarter-wave plates in the beam path as described in ref 34 . The analysis of both sets of scattering patterns led to similar conclusions.…”

“…where I 0 is the intensity in the forward direction, and C 0 and C 4 are functions that can be determined from measurements of I LP (q , μ ) and I CP (q , μ) as shown in ref 34 . These equations show that the CP scattering pattern is always azimuthally symmetric, while the LP pattern can exhibit a 4-fold symmetry.…”

Propagation of Elliptically Polarized Light through Ordered Block Copolymers

“…This grain structure can affect the mechanical, electrical, and optical properties of the material. When the ordered morphology is lamellar or cylindrical, the grains are optically uniaxial and exhibit form birefringence, and the grain structure can be characterized using depolarized light scattering (DPLS). − DPLS complements other BCP characterization methods such as small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), and electron microscopy (EM). − Although recent studies have shown the potential usefulness of these techniques to determine micron-scale structural features of block copolymers, they are primarily used to determine the ordered morphology on the length scale of the unit cell rather than grain structure. In contrast, all of the DPLS signals from ordered block copolymers arise from the grain structure, as typical unit cell sizes in block copolymers are much smaller than the wavelength of light.…”