title: Enhanced specific ion effects in ethylene glycol-based thermoresponsive polymer brushes.
abstract: The thermoresponse of poly(di(ethyleneglycol) methyl ether methacrylate) (PMEO2MA) brushes has been investigated in the presence of monovalent anions at either end of the Hofmeister series using ellipsometry, neutron reflectometry (NR) and colloid probe atomic force microscopy (AFM). NR measurements in deuterium oxide showed no evidence of vertical phase separation perpendicular to the grafting substrate with a gradual transition between a block-like, dense structure at 45°C and an extended, dilute conformation at lower temperatures. All three techniques revealed a shift to a more collapsed state for a given temperature in kosmotropic potassium acetate solutions, while more swollen structures were observed in chaotropic potassium thiocyanate solutions. No difference was observed between 250mM and 500mM thiocyanate for a 540Å brush studied by ellipsometry, while the lower molecular weight ∼200Å brushes used for NR and AFM measurements continued to respond with increasing salt concentration. The effect of thiocyanate on the temperature response was greatly enhanced relative to PNIPAM with the shift in temperature response at 250mM being five times greater than a PNIPAM brush of similar thickness and grafting density.
authors.affiliation: Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia. Electronic address: timothy.murdoch@uon.edu.au.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Murdoch
authors.affiliation: Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia. Electronic address: ben.humphreys@uon.edu.au.
authors.forename: Ben A
authors.initials: BA
authors.lastname: Humphreys
authors.affiliation: Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia. Electronic address: joshua.willott@uon.edu.au.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Willott
authors.affiliation: School of Chemical Engineering, UNSW Australia, UNSW Sydney, NSW 2052, Australia. Electronic address: s.prescott@unsw.edu.au.
authors.forename: Stuart W
authors.initials: SW
authors.lastname: Prescott
authors.affiliation: Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia. Electronic address: andrew.nelson@ansto.gov.au.
authors.forename: Andrew
authors.initials: A
authors.lastname: Nelson
authors.affiliation: Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia. Electronic address: grant.webber@newcastle.edu.au.
authors.forename: Grant B
authors.initials: GB
authors.lastname: Webber
authors.affiliation: Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia. Electronic address: erica.wanless@newcastle.edu.au.
authors.forename: Erica J
authors.initials: EJ
authors.lastname: Wanless
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000838:Anions / Q000737:chemistry*; D008689:Methacrylates / Q000737:chemistry*; D008738:Methyl Ethers / Q000737:chemistry*; D044367:Phase Transition; D011092:Polyethylene Glycols / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
chemical_list: D000180:Acrylic Resins; D000838:Anions; D008689:Methacrylates; D008738:Methyl Ethers; C510557:poly(diethylene glycol monomethacrylate); C052970:poly-N-isopropylacrylamide; D011092:Polyethylene Glycols
keywords: Atomic force microscopy; Lower critical solution temperature; Neutron reflectometry; Poly oligo(ethylene glycol methacrylate); Polymer brush; Responsive polymer; Specific ion effect; Thermoresponsive polymer