Ordering Phenomena in ABA Triblock Copolymer Gels

Abstract

Temperature and concentration dependencies of the degree of order in ABA triblock copolymer gels are discussed. Two factors can influence the ordering phenomena: the conformation of the midblocks (links of the network) and the polydispersity of the endblock domains (nodes of the network). The latter is defined by the scattering density profile (polymer chain packing) at the domain boundary: a sharp boundary corresponds to less polydisperse domains and to increased order in the arrangement of the network nodes. The structure of the network can be described in terms of a highly distorted crystalline lattice with close-packed spheres or with cubic (presumably BCC) equilibrium morphology. The appearance of the latter is never detected in the gels with a stretched conformation of the midblock.

Temperature-dependent self-assembly and rheological behavior of a thermoreversible pmma-PnBA-PMMA triblock copolymer gel

“…Structure formation of ABA triblock copolymers in mid‐block selective solvents and their mechanical properties have been studied extensively . Structure and mechanical properties of these systems depend on the absolute and relative copolymer block lengths, the copolymer concentration in solution, pH, and temperature, which may strongly affect the polymer–solvent interactions .…”

“…Since the gel formation is a result of relative change in interactions between the solvent and the blocks, temperature plays an important role on block solvency, hence the gel structure. For example, for [PS–PEB–PS] and [PS–PEP–PS] triblock polymers in mineral oil, annealing above the glass transition temperature of PS end‐blocks resulted in formation of a long‐range ordered structure, such as body‐centered‐cubic (bcc) aggregate structures . The ordered structure has been considered to be the equilibrium structure, which evolves from the kinetically‐trapped structure during annealing.…”

Silica reinforced triblock copolymer gels

“…1 (curve A) shows a typical SAXS diffraction pattern for a neat PS-PEB-PS triblock copolymer gel. As extensively discussed elsewhere [21][22][23], the plot of I(q) as a function of q is dominated by the polystyrene micellar cores, and contains information on the corresponding structure factor and the form factor, respectively. The polystyrene form factor peaks, which result from intradomain interferences contain information on the size and shape of the polystyrene domains, whereas the structure factor peaks, which originate from the interdomain interference, provide information on the mutual arrangement of the polystyrene domains within the rubbery matrix.…”

“…The midblocks form either loops or bridges between micelles, depending on whether the polymer endblocks are located in the same nanophase or not. Two models were found to be useful to describe the scattering patterns of the triblock copolymer gels: a hard sphere liquid model (Percus-Yevick model) or a local co-ordination model [22][23]. The first model represents a liquid of effective hard-sphere cores surrounded by a (fictitious) hard-sphere shell.…”

Anomalous rheology in a nanostructured diblock copolymer/hydrocarbon system and its kinetic origin

“…Annealing between the PS glass‐transition temperature ( T g ) and the order–disorder transition temperature allowed an equilibrium BCC morphology to develop. Reynders et al25, 26 showed a similar quenched‐in disordered morphology at room temperature in triblock copolymer solutions and its rearrangement into equilibrium cubic structures at high temperatures. Lodge et al7 designated a glass window for the concentrated solutions of a polystyrene‐ b ‐polyisoprene at low temperatures; the solvated PS domains were below T g , and this inhibited structural equilibration.…”