PNIPAM chains have hydrophobic and hydrophilic domains below and above the LCST. Temperature dependent interactions between PNIPAM and solutes arise because of changes in the local environment around the hydrophobic isopropyl domains. Below the LCST the isopropyl groups are surrounded by water, whereas above the LCST the hydrophobic groups are in contact with both water and polymer segments. Contrary to numerous claims in the literature, PNIPAM is not a hydrophobic material at temperatures above the LCST.
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