Order-Order Transition in Statistical Copolymer Thin Film Induced by LCST-Type Behavior

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Copolymer thin films offer tunable properties for advanced applications.
• Understanding structure-property relationships in polymers is crucial for material design.
• Hydration and dehydration processes can induce significant structural changes in polymers.

Purpose of the Study:

• To investigate the formation of ordered structures in a specific copolymer thin film.
• To explore the influence of hydration and dehydration on the copolymer's lamellar structure.
• To correlate structural transitions with the film's swelling behavior.

Main Methods:

• Synthesis of poly(N-octadecyl acrylamide-stat-hydroxymethyl acrylamide) via free radical copolymerization.
• Preparation and annealing of copolymer thin films under controlled humidity and temperature.
• Characterization of structural transitions using quartz crystal microbalance (QCM) and analysis of swelling properties.

Main Results:

• A statistical copolymer p(ODA50/HEAm50) was synthesized with a 1:1 comonomer ratio.
• Hydration at 60 °C induced a side-chain segregated lamellar (SCSegL) structure.
• Dehydration at 90 °C transitioned the film to a side-chain mixed lamellar (SCMixL) structure.
• The copolymer exhibited lower critical solution temperature (LCST)-like behavior around 50 °C.
• Structural transitions significantly affected the film's swelling properties.

Conclusions:

• The p(ODA50/HEAm50) copolymer film undergoes an order-to-order transition driven by hydration-dehydration.
• The SCSegL structure forms due to segregation between hydrophilic and hydrophobic units.
• The SCMixL structure forms upon dehydration, reducing strain and altering swelling.
• This study demonstrates tunable structural control in copolymer films via environmental stimuli.