3D confinement effect: Block copolymers form novel phase separation structures in the nanoparticles owing to frustration of the nanosized confinement effect. Whereas films of the block copolymers form lamellar structures, the nanoparticles formed unique structures (Janus‐type, tennis‐ball‐, mushroom‐, wheel‐, and screwlike structures) depending on the ratio between particle diameter and molecular weight.

Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion-like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder-order phase transition and order-order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.

Divide and conquer: Polymer nanoparticles with phase-separation structures prepared with block copolymers and homopolymer blends were used to fabricate unique suprapolymer structures by cross-linking one polymer moiety and dissolving the other (see scheme; PI = polyisoprene, PSt = polystyrene).

This paper reports static and dynamic control of the phase separation structures of polymer blended nanoparticles. The phase separated nanoparticles were prepared from various combinations of polymers by evaporating good solvents from the polymer blended solutions after adding poor solvents into the solutions. Transmission electron microscope observation of the nanoparticles shows that two types of phase separation structures were formed in them. One is Janus type structure and another is core-shell type structure. When the difference of the Flory-Huggins solubility parameter (d) between two blended polymers is large, one polymer having a higher d value encapsulated another polymer. As a result, a core-shell type structure is formed. On the other hand, when the difference of d value is small, both moieties of polymer are exposed to the poor solvent, and then, a Janus structure is formed. Moreover, when the thermoresponsive polymer was blended with a hydrophobic polymer, a Janus type or core-shell structure was formed by changing the preparation temperature. The core-shell type structure was transformed to a Janus type structure by heating the nanoparticles. This control and transformation of structures of nanoparticles can be applied to nano-sensing devices, switching devices and drug delivery systems.

The effect of confinement on microphase-separated structures of a diblock copolymer is investigated in nanoparticles serving as a three-dimensional (3D) confinement system. We succeeded in preparing nanoparticles having various types of complex structures from hydrophobic diblock copolymers by a simple solvent evaporation method. The detailed 3D structural analysis of the nanoparticles by transmission electron microtomography (TEMT) revealed that complex structures were found only to form in the nanoparticle surface region, the thickness of which corresponded to the single-molecule length of the block copolymer in the bulk state. These results indicate that 3D confinement fundamentally affects block copolymer self-assemblies most strongly in the surface region of nanoparticles but only weakly in the central region.