Annealing of Cocontinuous Polymer Blends: Effect of Block Copolymer Molecular Weight and Architecture

Abstract

Cocontinuous morphologies of polymer blends are thermodynamically unstable: they will coarsen when held above their glass or melting transition temperature. We have found that properly chosen diblock copolymers (bcp) can arrest coarsening during quiescent annealing. The effects of bcp on the cocontinuous morphologies of polystyrene (PS)/polyethylene (PE), PS/poly(methyl methacrylate) (PMMA) and PS/styrene-ran-acrylonitrile copolymer (SAN) blends were studied using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) with image analysis. Bcp effectiveness was dependent on copolymer molecular weight, concentration, and asymmetry. Our interpretation emphasizes the role of bcp micelle creation and destruction as potential bottlenecks in the kinetics of interfacial adsorption of copolymer during mixing and of interfacial desorption during coarsening. In cases where adsorption and desorption appear to be facile, our results for the rate of coarsening are consistent with equilibrium predictions from self-consistent field theory for the dependence of interfacial tension upon copolymer asymmetry. We show that the coarsening of cocontinuous blends can provide a method to quantify the reduction in interfacial tension due to block copolymer addition, which is difficult to measure by conventional methods.

Preparation of Porous Organogels Using Water Soluble Polymer Templates

“…After annealing, cubic shaped and cryomicrotomed samples were plunged in toluene to selectively extract the PCL phase. Subsequent μCT and SEM observations (Figure ) and gravimetric analysis (Equation ) confirm the formation of a cocontinuous microstructure . The PCL phase remains fully continuous for all annealing times, since it is almost fully extracted (96–104%).…”

“…Quiescent annealing over the melting temperature results in coarsening of the cocontinuous microstructure. The phenomenon is driven by the interfacial tension that exists between the PVOH and PCL phases, and is slowed down by polymer viscosity . The complete extraction of the PCL phase yields porous PVOH materials comprising networks of interconnected pores increasing in size with annealing time.…”

Role of block copolymer on the coarsening of morphology in polymer blend: Effect of micelles

“…The stability of micelles during quiescent annealing becomes important. In our case, large molecular weight of copolymer generates , which is large enough (>>20) that spontaneous micelle dissolution and reformation can be negligible at the equilibrium critical micelle concentration . Actually, in theories concerning the coarsening of droplets, the contact probability is a statistical value depending only on the volume fraction and the droplet size, where the process of getting touched is regarded to be faster than the drainage and merging process.…”

“…Adding diblock copolymer with two segments miscible or partially miscible with two respective polymers is a convenient approach to compatibilize the blend, although nanoparticles with suitable surface treatment are also a choice . A lot of efforts have been paid on how to choose the molecular structure, molecular weight, concentration of copolymer, and processing conditions . In contrast to the fast transportation of surfactant in water/oil emulsion, the mobility of high molecular weight block copolymer is much lower and cannot necessarily move to the interface between two bulk polymers during finite mixing time.…”

“…In contrast to the fast transportation of surfactant in water/oil emulsion, the mobility of high molecular weight block copolymer is much lower and cannot necessarily move to the interface between two bulk polymers during finite mixing time. Moreover, the critical micelles concentration (CMC) of high molecular weight of copolymer is very low, which makes it easier to form micelles and decreases the interfacial coverage. To solve the transportation problem of block copolymer from bulk to the interface, the so‐called reactive blending technique that can produce block copolymer in situ during mixing is often adopted in industry .…”