https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33530 Wed 14 Nov 2018 16:20:31 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27770 Tue 25 Jul 2023 15:05:44 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:32551 Tue 23 Jun 2020 15:10:43 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:43868 Tue 04 Oct 2022 12:28:47 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33528 Tue 03 Sep 2019 17:57:15 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:36046 Thu 30 Jan 2020 14:07:08 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:31340 Sat 24 Mar 2018 08:44:37 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:19916 Sat 24 Mar 2018 08:03:45 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:20856 a, the PDEA brush exhibited a critical conformational change in the range 0.5-1 mM electrolyte, a range much narrower than predicted by the theory of the osmotic brush regime. This behavior is attributed to the hydrophobicity of the collapsed brush. The swelling and collapse kinetics for this salt-induced transition are nearly identical. This is in contrast to the asymmetry in the rate of the pH-induced response, suggesting an alternative mechanism for the two processes dependent on the nature of the environmental trigger.]]> Sat 24 Mar 2018 08:02:52 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:29256 a. Furthermore, the simulations reveal that the addition of a single Flory-Huggins interaction parameter analogous to the hydrophilicity of the counterion is sufficient to replicate the observed specific anion response of a hydrophobic weak polyelectrolyte brush.]]> Sat 24 Mar 2018 07:39:15 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27182 in situ ellipsometry and a quartz crystal microbalance with dissipation (QCM-D). At low pH the tertiary amine groups of the three polymers are protonated and all three brushes are significantly solvated and swell by adopting an extended conformation. As the pH is increased the weak polybasic brushes become increasingly deprotonated and collapse via solvent expulsion. By employing high temporal resolution measurements we have found that monomer hydrophobicity has a direct influence on the dynamics of this pH-response. The most hydrophobic poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brush exhibits the fastest maximum swelling rate. This maximum swelling rate is reduced with decreasing monomer hydrophobicity for the 2-diethylamino, and even further for the 2-dimethylamino analogues. For all three brushes, the corresponding collapse transition is slower and compounded by an induction time that decreases with monomer hydrophobicity. Here also, the maximum collapse rate is greatest for the most hydrophobic polymer. This domination of the pH-response kinetics by monomer hydrophobicity is attributed to attractive hydrophobic forces between polymer segments overcoming the repulsive electrostatic forces between the tertiary amine residues.]]> Sat 24 Mar 2018 07:31:40 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:25103 Sat 24 Mar 2018 07:15:01 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:23138 Sat 24 Mar 2018 07:10:25 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:33531 Fri 28 Jun 2019 11:32:06 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:29257 Fri 28 Jun 2019 11:25:07 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:24518 in situ ellipsometry, quartz crystal microbalance with dissipation (QCM-D) and static contact angle measurements between 20 and 45 °C in the presence of up to 250 mM acetate and thiocyanate anions in water. The thickness and changes in dissipation exhibited a broad swelling transition spanning approximately 15 °C from collapsed (high temperatures) to swollen conformation (low temperatures) while the brush surface wettability changed over approximately 2 °C. In the presence of the kosmotropic acetate anions, the measured lower critical solution temperature (LCST) by the three techniques was very similar and decreased linearly as a function of ionic strength. Conversely, increasing the concentration of the chaotropic thiocyanate anions raised the LCST of the pNIPAM brushes with variation in the measured LCST between the three techniques increasing with ionic strength. The thickness of the pNIPAM brush was seen to progressively increase with increasing thiocyanate concentration at all temperatures. It is proposed that specific ion binding of the chaotropic thiocyanate anion with pNIPAM amide moieties increases the electrostatic intra- and intermolecular repulsion within and between pNIPAM chains. This allows the brush to begin to swell at higher temperatures and to an overall greater extent.]]> Fri 28 Jun 2019 11:04:06 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:39206 N-isopropylacrylamide) (PNIPAM) brushes is investigated as a function of confining stress and system temperature using neutron reflectometry (NR), numerical self-consistent field theory, and the reanalysis of colloid probe atomic force microscopy (AFM) data from the literature. For NR experiments, confinement is achieved using a custom-made sample environment, and the corresponding reflectometry data are analyzed using a novel “distribution model.” The NR and AFM experiments probe similar temperature–stress combinations and generally find qualitative agreement, with some variations highlighting path-dependent (isostress vs isothermal, respectively) behavior. All techniques indicate that confinement removes the critical transition point in the thermoresponse of PNIPAM and results in the brush assuming a block-like volume fraction profile with a uniform internal structure. The PNIPAM brushes recover from such treatment, regaining their thermoresponse upon resolvation. Understanding the structure of responsive polymer brushes under confinement is essential, as brush applications are often accompanied by a surface-normal force (i.e., lubrication) and brush properties are dependent on their structure.]]> Fri 27 May 2022 09:52:26 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:42233 3COO, causes collapse) and thiocyanate (KSCN, causes swelling), two ions at opposite ends of the Hofmeister series, has been monitored with neutron reflectometry (NR) and quartz crystal microbalance with dissipation (QCM-D). These techniques revealed that the balance of the swelling/collapse influence of the two ions on the structure of the brush is temperature dependent. At low temperatures in mixed salt environments, the influence of the acetate and thiocyanate ions appears additive, antagonistic and approximately equal in magnitude, with brush thickness and dissipation similar to the brush in the absence of electrolyte. At higher temperatures, the influence of the acetate ion diminishes, resulting in an increase in the relative influence of the thiocyanate ion on the brush conformation. These temperature dependent specific ion effects are attributed to increased steric crowding in the brush, along with an increased affinity of the thiocyanate ion for the polymer at higher temperatures.]]> Fri 19 Aug 2022 11:42:19 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:44487 co-2-(diethylamino)ethyl methacrylate) [P(MEO₂MA-co-DEA)] 80:20 mol % copolymer brushes were synthesized on planar silica substrates via surface-initiated activators continuously regenerated via electron transfer atom transfer radical polymerization. Brush thickness was sensitive to changes in pH and temperature as monitored with ellipsometry. At low pH, the brush is charged and swollen, while at high pH, the brush is uncharged and more collapsed. Clear thermoresponsive behavior is also observed with the brush more swollen at low temperatures compared to high temperatures at both high and low pH. Neutron reflectometry was used to determine the polymer volume fraction profiles (VFPs) at various pH values and temperatures. A region of lower polymer content, or a depletion region, near the substrate is present in all of the experimental polymer VFPs, and it is more pronounced at low pH (high charge) and less so at high pH (low charge). Polymer VFPs calculated through numerical self-consistent field theory suggest that enrichment of DEA monomers near the substrate results in the experimentally observed non-monotonic VFPs. Adsorption of DEA monomers to the substrate prior to initiation of polymerization could give rise to DEA segment-enriched region proximal to the substrate.]]> Fri 14 Oct 2022 08:57:26 AEDT ]]>