title: Segregation of mass at the periphery of N-isopropylacrylamide-co-acrylic-acid microgels at high temperatures.
abstract: We investigate poly(N-isopropylacrylamide) (pNIPAM) microgels randomly copolymerized with large mol % of protonated acrylic acid (AAc), finding that above the lower critical solution temperature the presence of the acid strongly disrupts pNIPAM's collapse, leading to unexpected new behavior at high temperatures. Specifically, we see a dramatic increase in the ratio between the radius of gyration and the hydrodynamic radius above the theoretical value for homogeneous spheres, and a corresponding increase of the network length scale, which we attribute to the presence of a heterogeneous polymer distribution that forms due to frustration of pNIPAM's coil-to-globule transition by the AAc. We analyze this phenomenon using a Debye-Bueche-like scattering contribution as opposed to the Lorentzian term often used, interpreting the results in terms of mass segregation at the particle periphery.
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Hyatt
authors.affiliation: Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: Changwoo
authors.initials: C
authors.lastname: Do
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, 30332, USA.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Hu
authors.affiliation: Shinsegae International, 422 Apgujeong-ro, Gangnam-gu, Seoul 135-954, South Korea.
authors.forename: Hong Sung
authors.initials: HS
authors.lastname: Choi
authors.affiliation: Department of Applied Chemistry, Hanyang University, Ansan, Gyeonggi-do 426-791, South Korea.|Department of Bionano Technology, Hanyang University, Ansan, Gyeonggi-do 426-791, South Korea.
authors.forename: Jin Woong
authors.initials: JW
authors.lastname: Kim
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, 30332, USA.
authors.forename: L Andrew
authors.initials: LA
authors.lastname: Lyon
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA.
authors.forename: Alberto
authors.initials: A
authors.lastname: Fernandez-Nieves
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000180:Acrylic Resins / Q000737:chemistry*; D005782:Gels / Q000737:chemistry*; D057446:Hydrodynamics; D008956:Models, Chemical; D011522:Protons; D012996:Solutions; D013696:Temperature
chemical_list: D000179:Acrylates; D000180:Acrylic Resins; D005782:Gels; D011522:Protons; D012996:Solutions; C052970:poly-N-isopropylacrylamide; C036658:acrylic acid