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Gregory G Warr - One of the best experts on this subject based on the ideXlab platform.
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Ionic Liquid Adsorption at the Silica–Oil Interface Revealed by Neutron Reflectometry
Journal of Physical Chemistry C, 2018Co-Authors: Peter K. Cooper, Anton P. Le Brun, Nageshwar R. Yepuri, Gregory G Warr, Andrew Nelson, Grant B. Webber, Tamim A Darwish, Hua Li, Rob AtkinAbstract:Previous nanotribology measurements demonstrated that 2 mol % of the oil-miscible ionic liquid (IL) trihexyltetradecyl(phosphonium) bis(2,4,4-trimethylpentyl)phosphinate (P6,6,6,14 (iC8)2PO2) diluted in octane lubricated as effectively as pure IL. However, until now the structure and composition of the lubricating Adsorbed Layer, which is critical for lubrication, was unknown. Here, the unconfined structure of the IL Adsorbed Layer at the oil–silica interface has been studied using neutron reflectometry. Multiple neutron contrasts revealed an 8 A thick Adsorbed Layer, even at 60 and 80 °C. The ratio of cations and anions in the Layer was investigated by synthesizing the IL with deuterated cations and measuring its reflectivity at the oil–silica interface. At 60 °C the Layer was composed of 48 ± 6 mol % P6,6,6,14+ cations, 24 ± 2 mol % (iC8)2PO2– anions, and 28 ± 8 mol % octane, while at 80 °C the composition was 50 ± 2 mol % P6,6,6,14+, 28 ± 2 mol % (iC8)2PO2– anions, and 22 ± 2 mol % octane. These result...
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Laterally nanostructured Adsorbed Layers of surfactant/surfmer mixtures before and after polymerisation.
Journal of colloid and interface science, 2008Co-Authors: Regina Schwering, Annabelle Blom, Gregory G WarrAbstract:The Adsorbed Layer structure of mixed films of the polymerisable cationic surfactant dodecyldimethyl(ethylmethacrylate)ammonium bromide (MEDDAB) with the cationic and non-ionic surfactants dodecyltrimethylammonium bromide (DTAB) and polyoxyethylene-23-lauryl ether (C12E23) has been investigated by AFM soft-contact imaging before and after solution polymerisation of MEDDAB. MEDDAB alone adsorbs on mica as a planar biLayer, but the Adsorbed Layer structure can be modified by mixing with DTAB or C12E23 to yield an Adsorbed mesh or cylinders. The equilibrium Adsorbed film structure after solution polymerisation of the methacrylate group on MEDDAB was found to depend on the solubilising ability of the non-polymerisable surfactant. C12E23 effectively prevented precipitation of polymerised MEDDAB, retaining the unpolymerised Adsorbed Layer structure, whereas DTAB mixtures became cloudy above 23 mol% MEDDAB. The resultant structure remained similar to the Adsorbed rods formed prior to polymerisation, but had a diameter several times larger.
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Structure of mixed DTAB/DDAB Adsorbed Layers on quartz A neutron reflectometry and atomic force microscopy study
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Annabelle Blom, Gregory G Warr, Andrew NelsonAbstract:The structure and composition of Adsorbed Layers formed by mixtures of dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) on quartz have been determined using a combination of atomic force microscopy and neutron reflectometry. The mixed Adsorbed Layer was found to be substantially enriched in DDAB, stabilising the formation of a laterally unstructured biLayer even when there is only as little as 1 mol% present in the bulk mixed solute. At even higher DTAB content the Adsorbed film morphology gradually transforms to globules over a very narrow composition range. DDAB was found to be significantly excluded from the mixed Adsorbed film only after it was completely transformed into globular aggregates, the equilibrium Adsorbed Layer morphology of DTAB.
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Structure of mixed DTAB/DDAB Adsorbed Layers on quartz
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007Co-Authors: Annabelle Blom, Gregory G Warr, Andrew NelsonAbstract:The structure and composition of Adsorbed Layers formed by mixtures of dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) on quartz have been determined using a combination of atomic force microscopy and neutron reflectometry. The mixed Adsorbed Layer was found to be substantially enriched in DDAB, stabilising the formation of a laterally unstructured biLayer even when there is only as little as 1 mol% present in the bulk mixed solute. At even higher DTAB content the Adsorbed film morphology gradually transforms to globules over a very narrow composition range. DDAB was found to be significantly excluded from the mixed Adsorbed film only after it was completely transformed into globular aggregates, the equilibrium Adsorbed Layer morphology of DTAB. © 2007, Elsevier Ltd
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Structure and composition of cationic-nonionic surfactant mixed Adsorbed Layers on mica.
Langmuir : the ACS journal of surfaces and colloids, 2006Co-Authors: Annabelle Blom, Gregory G WarrAbstract:The composition and morphology of mixed Adsorbed Layers comprising one of several poly(oxyethylene) alkyl ether nonionic surfactants, C(i)E(j), and two cationic surfactants-dodecyltrimethylammonium bromide (DTAB) and tetradecyltriethylammonium bromide (TTeAB)-at the mica/solution interface have been studied using depletion adsorption and atomic force microscopy. The nonionic surfactants do not themselves adsorb onto mica, but can coadsorb with a cationic surfactant. The extent of their hydrophobic association with the Adsorbed cationic surfactant depends on alkyl chain length, while the Adsorbed Layer morphologies are sensitive to the number of ethoxy groups. Nonionic surfactants with headgroups containing less than eight ethylene oxide units decrease the Adsorbed aggregate curvature, gradually transforming globular TTeAB or cylindrical DTAB Adsorbed aggregates into a rod, mesh, or biLayer structure. Those with larger headgroups favor globular aggregates. The mechanism by which the nonionic surfactant modifies the Adsorbed morphology is the formation of defects in the form of cylinder end-caps or branch-points, leading to Adsorbed Layer compositions that differ from ideal mixing predictions. All mixed Adsorbed films become saturated with the nonionic component when the capacity of the aqueous side of the Adsorbed Layer is reached.
Wei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Mobility Gradient of Poly(ethylene terephthalate) Chains near a Substrate Scaled by the Thickness of the Adsorbed Layer
Macromolecules, 2017Co-Authors: Zhenshan Liu, Yang Lan, Biao Zuo, Xinping Wang, Juping Yang, Wei ZhangAbstract:The question of how to scale the mobility gradient of polymer chains near a substrate in supported ultrathin polymer films is a great challenge. In this paper, a mobility gradient of poly(ethylene terephthalate) (PET) chains near a substrate is characterized by cold crystallization. We found that either decreasing the PET film thickness or increasing the absorbed Layer thickness consistently reveals three characteristic film thicknesses, which are all linearly dependent on the Adsorbed-Layer thickness. At the first thickness, the low-temperature peak of the top surface crystallization starts to shift toward the high-temperature peak of the bulk-like polymer crystallization; at the second thickness, it arrives there; and at the third thickness, crystallization is completely suppressed. The three kinds of film thicknesses characterize the depth profile of the local dynamics, reflecting the long-range effects of the substrate, which could be scaled by the thickness of the Adsorbed Layer.
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The architecture of the Adsorbed Layer at the substrate interface determines the glass transition of supported ultrathin polystyrene films.
Soft matter, 2016Co-Authors: Shuzheng Sun, Biao Zuo, Xinping Wang, Han Jun, Yumei Zhu, Wei ZhangAbstract:To elucidate the mechanism underlying the effect of polymer/solid interfacial interactions on the dynamics of thin polymer films, the glass transition of thin end-functionalized polystyrene films supported on SiO2–Si, such as proton-terminated PS (PS-H), α,ω-dicarboxy-terminated PS (PS-COOH), and α,ω-dihydroxyl-terminated PS (PS-OH), was investigated. All the PS films exhibited a substantial depression in Tg with decreasing film thickness, while the extent of such depression was strongly dependent on the chemical structure of the end groups and molecular weights. It was found that Tfilmg − Tbulkg of the various PS films increased linearly with increasing hads/Rg, in which hads is the thickness of the interfacial Adsorbed Layer and Rg is the radius of gyration of PS. The hads/Rg is a direct reflection of the macromolecular chain conformation within the Adsorbed Layer which was affected by its end groups and molecular weights. These findings are in line with the work of Napolitano, and present direct experimental evidence.
Jun Oshitani - One of the best experts on this subject based on the ideXlab platform.
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Magnetic Effects on Thickness of Adsorbed Layer in Aqueous Solutions Evaluated Directly by Atomic Force Microscope
Journal of colloid and interface science, 1998Co-Authors: Ko Higashitani, Jun OshitaniAbstract:Abstract The short-range interaction force between a mica surface and an AFM probe tip in electrolyte solutions was measured by atomic force microscopy (AFM) to directly evaluate the thickness of the Adsorbed Layer on the surface. The magnetic effects were estimated by comparing the thickness in the magnetized solution with that in nonmagnetized solution. It was found that (i) the magnetic exposure thickens the Adsorbed Layer on the surface in electrolyte solutions, (ii) the magnetic effects are easily destroyed by the external disturbance, (iii) there exists a memory in the magnetic effects, which remains for at least a day, (iv) the magnetic effects appear mostly in the solutions of structure-disordering cations, such as Cs + , Rb + , and K + , and (v) the results are consistent with those obtained in preceding macroscopic experiments. It is hypothesized from these results that the water molecules weekly bound around the structure-disordering ions are quasistabilized and structured by the magnetic exposure and that the magnetic thickening of the Adsorbed Layer is caused by the adsorption of those structured ions on the surface.
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Magnetic Effects on Thickness of Adsorbed Layer in Aqueous Solutions Evaluated Directly by Atomic Force Microscope
Journal of colloid and interface science, 1998Co-Authors: Ko Higashitani, Jun OshitaniAbstract:The short-range interaction force between a mica surface and an AFM probe tip in electrolyte solutions was measured by atomic force microscopy (AFM) to directly evaluate the thickness of the Adsorbed Layer on the surface. The magnetic effects were estimated by comparing the thickness in the magnetized solution with that in nonmagnetized solution. It was found that (i) the magnetic exposure thickens the Adsorbed Layer on the surface in electrolyte solutions, (ii) the magnetic effects are easily destroyed by the external disturbance, (iii) there exists a memory in the magnetic effects, which remains for at least a day, (iv) the magnetic effects appear mostly in the solutions of structure-disordering cations, such as Cs+, Rb+, and K+, and (v) the results are consistent with those obtained in preceding macroscopic experiments. It is hypothesized from these results that the water molecules weekly bound around the structure-disordering ions are quasistabilized and structured by the magnetic exposure and that the magnetic thickening of the Adsorbed Layer is caused by the adsorption of those structured ions on the surface. Copyright 1998 Academic Press.
Ting Wang - One of the best experts on this subject based on the ideXlab platform.
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deposition of quantum sized ag on tio2 through Adsorbed Layer nanoreactor synthesis and its performance for photodegrading phenol in seawater under visible light irradiation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018Co-Authors: Ting Wang, Jiahao Pan, Zequan Wang, Zhihan Wang, Boqiong JiangAbstract:Abstract Commercial TiO2 photocatalyst P25 was first used as a support to prepare Ag-deposited catalysts by Adsorbed-Layer nanoreactor synthesis (ANS). Characterizations were performed by UV–vis diffuse reflectance spectroscopy, TEM, XRD, XPS, PL spectroscopy, and photo-electrochemical analysis. Results showed that Ag nanoparticles with size of less than 10 nm distributed very homogeneously on the TiO2 surface. The adsorption Layer on the TiO2 surface acting as a nanoreactor led to tight interaction between quantum-size Ag particles and the TiO2 surface, thereby introducing staggered heterojunction structures into the catalysts. The heterojunction between quantum-sized Ag particles (less than 10 nm) and TiO2 led to the surface plasmon resonance effect and strong visible-light response of catalysts. Ag deposition further caused distortions in TiO2 crystal lattices. Both the heterojunction and TiO2 lattice distortions enhanced the separation efficiency of charge carriers, which improved the photocatalytic activity for phenol in seawater under visible-light irradiation. The catalyst exhibited high stability and reusability after six cycles because of its morphological stability.
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preparation of weak light driven tio2 based catalysts via Adsorbed Layer nanoreactor synthesis and enhancement of their photo degradation performance in seawater
Applied Surface Science, 2017Co-Authors: Ting Wang, Yichen Zhu, Haoxuan Yuan, Yayu Liu, Jing CaiAbstract:Abstract Graphene oxide (GO) was first employed as a support in preparing TiO2 nanoparticles by Adsorbed-Layer nanoreactor synthesis (ALNS). Both TiO2 crystallization and GO reduction simultaneously occurred during solvothermal treatment with alcohol as a solvent. By transmission electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy, the results showed that TiO2 nanoparticles with less than 10 nm of size distributed very homogeneously on the GO surface. Tight interaction between TiO2 particles and GO surface could effectively inhibit the aggregation of TiO2 particles, during solvothermal treatment for anatase TiO2 formation. Alcohol could also reduce oxygenated functional groups on GO surface after solvothermal treatment. TiO2 particles with small size and the decrease in oxygenated functional groups on the GO surface both caused high separation efficiency of photo-generated charge carriers, thus resulting in high photo-degradation performance of catalysts. Strong phenol adsorption on photocatalyst was key to enhancing photo-degradation efficiency for phenol in seawater. Moreover, the change in catalyst structure was minimal at different temperatures of solvothermal treatment. But, the degradation rate and efficiency for phenol in seawater were obviously enhanced because of the sensitive structure–activity relationship of catalysts under weak-light irradiation.
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fabrication of weak room light driven tio2 based catalysts through Adsorbed Layer nanoreactor synthesis enhancing catalytic performance by regulating catalyst structure
Journal of Physical Chemistry C, 2016Co-Authors: Ting Wang, Yichen Zhu, Yayu Wei, Tinan Chen, Boqiong JiangAbstract:Aiming at photodegrading pollutants under room-light excitation, we fabricated TiO2 composite catalysts driven by weak visible light through Adsorbed-Layer nanoreactor synthesis. Fe2O3 coupling and codoping by nonmetal elements were performed to enhance activity under irradiation of weak room light. By UV–visible diffuse reflectance spectra, high resolution transmission electron microscopy, X-ray diffraction, PL spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analyses, the results showed that Fe2O3 coupling could extend the spectral response of the catalysts into the visible-light region. Two Fe2O3 coupling sequences exerted different effects on the microstructure of the catalysts. Fe2O3 strongly interacted with TiO2 in the SiO2–Fe2O3–TiO2 catalysts, causing a more obvious visible-light response of SiO2–Fe2O3–TiO2 catalysts than SiO2–TiO2–Fe2O3 catalysts. Fe2O3 also significantly affected the crystallization of TiO2 in SiO2–Fe2O3–TiO2 catalysts, thus introducing many shallow trappin...
Biao Zuo - One of the best experts on this subject based on the ideXlab platform.
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Revealing Interfacial Interactions in Random Copolymer Adsorbed Layers by Solvent Leaching.
Macromolecular rapid communications, 2020Co-Authors: Mary J. B. Davis, Biao Zuo, Katelyn Randazzo, Rodney D. PriestleyAbstract:Annealing a supported polymer film in the melt state results in the growth of an irreversibly Adsorbed Layer, which has been shown to influence thin film properties such as diffusion and glass transition temperature. Adsorbed Layer growth is attributed to many simultaneous interactions between individual monomer units and the substrate, stabilizing chains against desorption. In this study, Adsorbed Layers of polystyrene (PS), poly(methyl methacrylate) (PMMA), and their random copolymers are isolated by select solvents. While PS Adsorbed Layer thickness is largely unaffected by the choice of washing solvent, the PMMA Adsorbed Layer completely desorbs when washed with tetrahydrofuran and chloroform, as opposed to toluene. Scaling relationships between Adsorbed Layer thickness and degree of chain adsorption at the substrate enable the use of Adsorbed Layer thickness to probe specific polymer-substrate interactions. Composition-dependent desorption trends indicate non-preferential adsorption between styrene and methyl methacrylate repeat units at the substrate, despite differences in substrate interaction strength. This insight contributes to the developing mechanism for the adsorption of random copolymers during melt-state annealing, further extending the ability to predict processing-inducted changes to the properties of polymer thin films to heterogeneous systems.
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Mobility Gradient of Poly(ethylene terephthalate) Chains near a Substrate Scaled by the Thickness of the Adsorbed Layer
Macromolecules, 2017Co-Authors: Zhenshan Liu, Yang Lan, Biao Zuo, Xinping Wang, Juping Yang, Wei ZhangAbstract:The question of how to scale the mobility gradient of polymer chains near a substrate in supported ultrathin polymer films is a great challenge. In this paper, a mobility gradient of poly(ethylene terephthalate) (PET) chains near a substrate is characterized by cold crystallization. We found that either decreasing the PET film thickness or increasing the absorbed Layer thickness consistently reveals three characteristic film thicknesses, which are all linearly dependent on the Adsorbed-Layer thickness. At the first thickness, the low-temperature peak of the top surface crystallization starts to shift toward the high-temperature peak of the bulk-like polymer crystallization; at the second thickness, it arrives there; and at the third thickness, crystallization is completely suppressed. The three kinds of film thicknesses characterize the depth profile of the local dynamics, reflecting the long-range effects of the substrate, which could be scaled by the thickness of the Adsorbed Layer.
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The architecture of the Adsorbed Layer at the substrate interface determines the glass transition of supported ultrathin polystyrene films.
Soft matter, 2016Co-Authors: Shuzheng Sun, Biao Zuo, Xinping Wang, Han Jun, Yumei Zhu, Wei ZhangAbstract:To elucidate the mechanism underlying the effect of polymer/solid interfacial interactions on the dynamics of thin polymer films, the glass transition of thin end-functionalized polystyrene films supported on SiO2–Si, such as proton-terminated PS (PS-H), α,ω-dicarboxy-terminated PS (PS-COOH), and α,ω-dihydroxyl-terminated PS (PS-OH), was investigated. All the PS films exhibited a substantial depression in Tg with decreasing film thickness, while the extent of such depression was strongly dependent on the chemical structure of the end groups and molecular weights. It was found that Tfilmg − Tbulkg of the various PS films increased linearly with increasing hads/Rg, in which hads is the thickness of the interfacial Adsorbed Layer and Rg is the radius of gyration of PS. The hads/Rg is a direct reflection of the macromolecular chain conformation within the Adsorbed Layer which was affected by its end groups and molecular weights. These findings are in line with the work of Napolitano, and present direct experimental evidence.