Thin film structural dynamics of temperature responsive polymers
Abstract
Thermoresponsive polymers change their structure and properties in response to change in external temperature. They undergo reversible volume phase transition in aqueous medium with response to change in temperature above its LCST. Adsorbed to interfaces, polymers can exhibit very different dynamic properties as compared to volume systems. Polymers in solution change its conformation immediately with change in external environment. Due to the unique train-loop-tail conformation of the adsorbed films at surface polymer chains posses a sluggish nature of phase transition at interface. In this research the phase transition dynamics of NIPA thin films adsorbed on silicon substrate was investigated. Layer by layer (LbL) assembly technique is used to adsorb monolayer of PNIPA on surface-treated silicon wafers. The thickness of layer was determined using XRR analysis was ~ 1 nm. This confirms that the NIPA film confined to a 2D adsorbed state on surface. The films were heat treated at 50 0 C for specified time periods. Quenching technique was used to preserve the film morphology during cooling. The surface morphology of the heated film was characterized using observed using atomic force microscopy. A time dependent change in surface morphology was observed with increase in heating period. PNIPA chains complete its transition in 5 minute of heating. Prolonged heating lead to coalescence of neighboring NIPA aggregates. When compared to chains in solution, PNIPA at interface posses a partial reversibility. This is due to the confinement effects by substrate.
Recommended Citation
Prasanth Mohankumar,
"Thin film structural dynamics of temperature responsive polymers"
(January 1, 2009).
ETD Collection for Wayne State University.
Paper AAI1464820.
http://digitalcommons.wayne.edu/dissertations/AAI1464820
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