Symmetric-to-asymmetric transition in triblock copolymer-homopolymer blends

Nanoparticle surfactants as a route to bicontinuous block copolymer morphologies

The surface chemistry of nanoparticles can be modified so that these particles behave like surfactants and localize at interfaces between two fluids. We demonstrate that small volume fractions phi(P) of such surfactant nanoparticles added to lamellar diblock copolymers lead initially to a decrease in lamellar thickness with phi(P), a consequence of decreasing interfacial tension, up to a critical value of phi(P), beyond which the block copolymer adopts a bicontinuous morphology. These bicontinuous morphologies have stable domain spacings below 100 nm that further decrease with increasing phi(P) and offer new routes to nanoscopically engineered polymer films with potential photovoltaic, fuel cell, and battery applications.

Crossover from stretched to compressed exponential relaxations in a polymer-based sponge phase

X-ray photon correlation spectroscopy was used to characterize the wave vector- and temperature-dependent dynamics of spontaneous thermal fluctuations in a sponge (L3) phase that occurs in a blend of a symmetric poly(styrene-ethylene/butylene-styrene) triblock copolymer with a polystyrene homopolymer. Measurements of the intermediate scattering function reveal a crossover from stretched- to compressed-exponential relaxations as the temperature is lowered from 180 to 120 degrees C.

Fluctuation dynamics of block copolymer vesicles

X-ray photon correlation spectroscopy was used to characterize the wave-vector- and temperature-dependent dynamics of spontaneous thermal fluctuations in a vesicle (L4) phase that occurs in a blend of a symmetric poly(styrene-ethylene/butylene-styrene) triblock copolymer with a polystyrene homopolymer. Measurements of the intermediate scattering function reveal stretched-exponential behavior versus time, with a stretching exponent slightly larger than 2/3. The corresponding relaxation rates show an approximate q(3) dependence versus wave vector. Overall, the experimental measurements are well described by theories that treat the dynamics of independent membrane plaquettes.

Block copolymers in tomorrow's plastics

In this era of portability and rapid technological advances, polymers are more than ever under pressure to be cheap and offer tailored property profiles. Often, the key lies in designing blends and alloys carefully structured at the appropriate scale (preferably less than a micrometre) from existing polymers. Block copolymers - two or more different polymer chains linked together - have long been thought to offer the solution. Local segregation of the different polymer blocks yields molecular-scale aggregates of nanometre size. Recent progress in synthetic chemistry has unveiled unprecedented opportunities to prepare tailored block copolymers at reasonable cost. Over twenty years of intense academic research and the advent of powerful statistical theories and computational methods should help predict the equilibrium and even non-equilibrium behaviour of copolymers and their blends with other polymers. The gap between block copolymer self-assembly and affordable nanostructured plastics endowed with still-unexplored combinations of properties is getting narrower.