The hydrophilic−hydrophobic diblock copolymer (2-hydroxyethyl methacrylate, HEMA)41-block-(isoprene)84 was synthesized by anionic living polymerization using a protection technique for the hydroxyl
group of HEMA. The surface structures of the block copolymer film under dry and wet conditions were
analyzed by transmission electron microscopic observation and contact angle and angle-dependent X-ray
photoelectron spectroscopic measurements. The top surfaces of the films cast from DMF/THF and THF/methanol are covered with a polyisoprene microdomain. When the as-cast film is exposed to water, the
polyisoprene layer at the top surface disappears and is replaced with a PHEMA microdomain. In particular,
the hydrated surface clearly emerges under transmission electron microscopy (TEM) by the double-staining
method and reverts again to a hydrophobic polyisoprene layer by annealing the film at 52 °C for 1 h. Such
surface rearrangement occurs repeatedly by soaking in water and annealing. The short-time-scale
reorientation of the surface microdomain of the film under dry to wet conditions is successively observed
with TEM. The difference between the surface rearrangements of the PHEMA-block-polyisoprene and
PHEMA-block-polystyrene films in response to environmental change is also investigated.
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