Observation of Inverted Phases in Poly(styrene-b-butadiene-b-styrene) Triblock Copolymer by Solvent-Induced Order−Disorder Phase Transition

Abstract

We report observation of inverted phases consisting of spheres and/or cylinders of the majority fraction block in a poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer by solventinduced order-disorder phase transition (ODT). The SBS sample has a molecular weight of 140K Da and a polystyrene (PS) weight fraction of 30%. Tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM) were utilized to study the copolymer microstructure of a set of solution-cast SBS films dried with different solvent evaporation rates, R. The control with different R leads to kinetic frozen-in of microstructures corresponding to a different combination parameter χ effZ of the drying films (where χeff is the effective interaction parameter of the polymer solution in the cast film and Z the number of "blobs" of size equal to the correlation length one block copolymer chain contains), for which faster evaporation rates result in microstructures of smaller χeffZ. As R was decreased from rapid evaporations (∼0.1 mL/h), the microstructure evolved from a totally disordered one sequentially to inverted phases consisting of spheres and then cylinders of polybutadiene (PB) in a PS matrix and finally reached the equilibrium phase, namely cylinders of PS in a PB matrix. We interpret the formation of inverted phases as due to the increased relative importance of entropy as χ effZ is decreased, which may dominate the energy penalty for having a bigger interfacial area between the immiscible blocks in the inverted phases.

Temporary networks in polymer‐modified asphalts

“…Since the inter-block repulsion decreases with increasing temperature, it is often possible to identify an order- disorder transition temperature (ODT). An order-disorder transition can also be induced by applying a stress-in this case a shear-thinning is observed (25Ϫ27, 29Ϫ32)-or in solutions, by varying the solvent concentration (33,34). In PMA for roofing membranes containing high percentages of SBS (up to 15 wt%), Fawcett and co-workers (35) observed an extensive network created by the polystyrene domains, which is effective even above their glass transition temperature.…”

High-speed atomic force microscopy for nano-visualization of dynamic biomolecular processes

“…It is known that several types of phase separation patterns are formed using SBS films depending on the evaporation speed of the solvent [199]. Figure 65 shows typical (a) topographic and (b) phase images obtained simultaneously at a rate of 84 ms/frame in distilled water.…”

Morphological Transitions of Symmetric Polystyrene-block-Poly(1,4-butadiene) Copolymers in Thin Films upon Solvent-Annealing

“…[21][22][23]30 Thus, from the calculation of interaction parameters, it is seen that CHX used in this study is a θ-solvent for PS blocks and a good solvent for PBD blocks while HX is a selective solvent for only PBD blocks. Hence, CHX can provide a higher degree of swelling for PBD blocks than for PS blocks.…”

“…They showed that slightly different affinities of solvents for blocks could dramatically affect their morphologies. 21,22,30 Moreover, the affinity of solvents for polymers is changeable in a given system. Therefore, it is essential to consider the relative affinity of solvents for BCPs systematically.…”