Fluctuation Effects in Symmetric Diblock Copolymer–Homopolymer Ternary Mixtures near the Lamellar–Disorder Transition

Abstract

We have systematically mapped the phase behavior of a series of symmetric CE/C/E ternary copolymer/homopolymer mixtures, where C is poly(cyclohexylethylene) and E is poly(ethylene), identifying the location in composition of the technologically important bicontinuous microemulsion (BμE) channel as a function of diblock molecular weight. The lamellar-to-disorder transition, characterized by dynamic mechanical spectroscopy, small-angle X-ray scattering, and optical transmission measurements, exhibits increasingly second-order behavior as the BμE state is approached with increasing homopolymer content. Real-space transmission electron microscopy images obtained from rapidly frozen specimens evidence the development of large-scale fluctuating smectic correlations in the disordered state as the order–disorder transition is approached. This discovery provides fresh insights into the unexplained role of fluctuations in the formation of the BμE in ternary mixtures formed from binary blends of homopolymers that display an Ising-like critical point and a symmetric diblock copolymer governed by a weak, fluctuation-induced, first-order phase transition.

Structure, viscoelasticity, and interfacial dynamics of a model polymeric bicontinuous microemulsion

“…32 Briefly, polyethylene (PE, M n = 2.1 kg mol À1 ) and polycylohexylethylene (PCHE, M n = 2.6 kg mol À1 ) homopolymers and a symmetric poly(cylohexylethylene-b-ethylene) (PCHE-PE-14, M n = 13.6 kg mol À1 , volume fraction of the PCHE block f PCHE = 0.52 AE 0.01) diblock copolymer were prepared by catalytic hydrogenation of the corresponding unsaturated precursors (poly-(1,4-butadiene), poly(styrene), and poly(styrene-b-1,4-butadiene), respectively) synthesized by anionic polymerization. 32 Briefly, polyethylene (PE, M n = 2.1 kg mol À1 ) and polycylohexylethylene (PCHE, M n = 2.6 kg mol À1 ) homopolymers and a symmetric poly(cylohexylethylene-b-ethylene) (PCHE-PE-14, M n = 13.6 kg mol À1 , volume fraction of the PCHE block f PCHE = 0.52 AE 0.01) diblock copolymer were prepared by catalytic hydrogenation of the corresponding unsaturated precursors (poly-(1,4-butadiene), poly(styrene), and poly(styrene-b-1,4-butadiene), respectively) synthesized by anionic polymerization.…”

“…2D data were collected with Rayonix area CCD detectors; for brevity we will refer to all such experiments simply as SAXS. We estimate that the specimens are cooled below the solidification temperature in roughly 5 s. 32 All samples were stained with ruthenium tetroxide vapor for 4 h to enhance contrast between microphases. The BmE (f H = 0.86) sample was contained in a 1.5 mm nominal diameter quartz capillary (Charles Supper Company) and the temperature was controlled during scattering experiments with a modified Linkam HFS91 heating stage.…”

“…12,20,22 In contrast, coarsening of a two-phase morphology generated by spinodal decomposition of polymer/solvent blends can lead to bicontinuous structures with micrometer, and even millimeter size domains. [25][26][27][28][29][30][31][32][33] Under appropriate conditions such three-component mixtures will selfassemble into a thermodynamically stable bicontinuous microemulsion (BmE) with structural dimensions ranging from 10 to 500 nm. 3,25 Ternary systems composed of two immiscible liquids and a corresponding amphiphile (e.g., blends of either oil/water/ surfactant or A-and B-type homopolymers stabilized with the corresponding AB diblock copolymer) are characterized by rich phase diagrams containing numerous morphologies and exhibiting an extraordinary range of structural dynamics.…”

“…34 The domain spacing (d), correlation length (x), and amphiphilicity factor ( f a ) of the BmE can be extracted by fitting the T-S model to experimental scattering data. 32 This report describes an in-depth investigation of the structure and dynamics of the BmE created by mixing these three materials. Although a variety of theoretical descriptions have been advanced, a complete theory that fully captures the thermodynamic and dynamic features of the BmE remains elusive.…”

Controllable multicompartment morphologies from cooperative self-assembly of copolymer–copolymer blends

“…Multifunctional hybrid micelles can be achieved by controlling the intermolecular selfassembly strategies including monomer selection, architecture design, solution conditions (pH, temperature, ionic strength), etc 8,[41][42][43][44][45][46] . This approach represents a powerful and straightforward way to systematically tune the resulting micellar structures without having to synthesize even more complex multiblock copolymers 18 .…”