title: A comparative study of urea-induced aggregation of collapsed poly(N-isopropylacrylamide) and poly(N,N-diethylacrylamide) chains in aqueous solutions.
abstract: The urea-induced aggregation of poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-diethylacrylamide) (PDEAM) globules was studied by using a combination of static and dynamic light scattering. Our results have revealed that urea acting as a cross-linker via formation of two hydrogen bonds with the amide groups of PNIPAM and PDEAM in different globules causes the aggregation, and the aggregation of PNIPAM and PDEAM globules is a reaction-limited cluster-cluster aggregation (RLCA) process. The aggregates have a uniform sphere structure that may be due to the restructuring of the aggregates. The aggregation rate of PNIPAM globules is slower than that of PDEAM, which might mainly contribute to the reasons that the amides groups of PNIPAM have more chance to be inside the globules because of the formation of intra- and inter-hydrogen bonds and the smaller number density of the PNIPAM aggregates at the original time. When the aqueous urea solutions were cooled and reheated to 40 °C, the aggregation became faster than the first heating process, indicating that the urea molecules have replaced some water molecules binding to the amide groups at high temperature and some of the urea molecules remain interacting with the polymers even at the temperature lower than the cloud point temperature.
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Yijie
authors.initials: Y
authors.lastname: Lu
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Ye
authors.forename: Kejin
authors.initials: K
authors.lastname: Zhou
authors.forename: Wenjing
authors.initials: W
authors.lastname: Shi
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins / Q000737:chemistry*; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D012996:Solutions; D013997:Time Factors; D014508:Urea / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D011108:Polymers; D012996:Solutions; C428028:poly(N,N-diethylacrylamide); D014867:Water; C052970:poly-N-isopropylacrylamide; D014508:Urea