Amphiphilic diblock copolymers containing poly(N-hexylisocyanate): Monolayer behavior at the air-water interface

The behavior of amphiphilic diblock copolymers containing 80-89% of poly(N-hexylisocyanate) (PHIC) with different hydrophobic segments spread at the air-water interface has been studied. Surface pressure-area isotherms (π-A) at the air-water interface were determined. It was found that these diblock copolymers form stable monolayers and the isotherms present a pseudoplateau region at low surface pressure, irrespective of the nature of the partner block: poly(styrene) (PS) or poly(isoprene). Surface pressure variation at the semidilute region of the monolayer was expressed in terms of the scaling laws as power function of the surface concentration. The critical exponents of the excluded volume V obtained for copolymers with PHIC and PS blocks are 0.58 for the copolymer with 85% of PHIC and 15% of PS, and 0.63 for the copolymer with 89% of PHIC and 11% of PS. The hydrophobicity degree of the diblock copolymers was estimated from the determination of the surface energy values by wettability measurements. The morphology of the monolayers was determined by means of Brewster angle microscopy. Molecular dynamic simulation was performed to explain the experimental behavior of diblock copolymers at the air-water interface.