Fabrication of a nanoparticle gradient substrate by thermochemical manipulation of an ester functionalized SAM

Iqbal, Parvez; Critchley, Kevin; Bowen, James; Attwood, David; Tunnicliffe, D.L.; Evans, Stephen D.; Preece, Jon A.

doi:10.1039/b712687e

Cited by 14 publications

(18 citation statements)

References 76 publications

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“…This discrepancy, between molecular length and SAM thickness, is expected and is in agreement with the literature, being ascribed to both the tilt angle and density of the SAM surfactants. 22,23 The advancing (y Adv ) and receding (y Rec ) contact angles for AzoSS (E901 and E751, respectively) and AzoSH (E901 and E801, respectively) are in good agreement with the literature 24,25 for tert-butyl ester SAMs, noting that the final hysteresis values (y Adv -y Adv ) of AzoSS (B151) are slightly larger than AzoSH (101) indicating a less dense packed SAM for AzoSS. XPS analysis confirms the presence of the elemental species N, C, O and S on the AzoSS SAMs (Fig.…”

Section: Resultssupporting

confidence: 77%

Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties

Yeung

Charlesworth

Iqbal

et al. 2013

Phys. Chem. Chem. Phys.

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Self-assembled monolayers (SAMs) containing azobenzene moieties are very attractive for a wide range of applications, including molecular electronics and photonics, bio-interface engineering and sensoring. However, very little is known about the aggregation and photoswitching behavior that azobenzene units undergo during the SAM formation process. Here, we demonstrate that the formation of thiol-based SAMs containing azobenzenes (denoted as AzoSH) on gold surfaces is characterised by a two-step adsorption kinetics, while a three-step assembly process has been identified for dithiolane-based SAMs containing azobenzenes (denoted AzoSS). The H-aggregation on the AzoSS SAMs was found to be remarkably dependent on the time of self-assembly, with less aggregation as a function of time. While photoisomerization of the AzoSH was suppressed for all different assembly times, the reversible trans-cis photoisomerization of AzoSS SAMs formed over 24 hours was clearly observed upon alternating UV and Vis light irradiation. We contend that detailed information on formation kinetics and related optical properties is of crucial importance for elucidating the photoswitching capabilities of azobenzene-based SAMs.

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Section: Resultssupporting

confidence: 77%

Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties

Yeung

Charlesworth

Iqbal

et al. 2013

Phys. Chem. Chem. Phys.

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“…In addition to the functional group density and wettability gradients, a gradient in nanoscale thickness of the substrate usually develops following the graft copolymerization, where the grafted polymer shows a transition from a loosely packed “mushroom” regime to a densely packed “brush” regime 78. Other creative methods utilized to fabricate wettability gradient surfaces include diffusive deposition from a vapor or liquid phase absorbent (organosilanes) to hydrophilic substrates,79–83 a density gradient method,84 spatially varying electrochemical desorption/adsorption of alkanethiols on gold electrodes,45 hyperthermal polyatomic ion deposition,85 atom transfer radical polymerization (ATRP) (grafting from initiator gradients generated via diffusion,86,87 continuous depletion of monomer solution86,88), thermochemical manipulation of aliphatic tert-butyl ester–functionalized self-assembled monolayers, 89 and continuous immersion techniques (polyvinyl carbonate films in NaOH solution,44 gold substrate in alka-nethiol solutions,90 gradient chemisorption in ATRP initiator solution,78 and a metal oxide substrate into a solution of polycationic polymer [electrostatic interaction]) 91. These methods result in a gradient in surface functional group density that can generally be translated into gradients in polymer grafting density (or molecular weight), surface nanoparticle density (by covalent or charge92,93 interactions), and/or immobilized bioactive factor density.…”

Section: Polymeric Materialsmentioning

confidence: 99%

Strategies and Applications for Incorporating Physical and Chemical Signal Gradients in Tissue Engineering

Singh

Berkland

Detamore

2008

Tissue Engineering Part B: Reviews

177

147

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From embryonic development to wound repair, concentration gradients of bioactive signaling molecules guide tissue formation and regeneration. Moreover, gradients in cellular and extracellular architecture as well as in mechanical properties are readily apparent in native tissues. Perhaps tissue engineers can take a cue from nature in attempting to regenerate tissues by incorporating gradients into engineering design strategies. Indeed, gradient-based approaches are an emerging trend in tissue engineering, standing in contrast to traditional approaches of homogeneous delivery of cells and/or growth factors using isotropic scaffolds. Gradients in tissue engineering lie at the intersection of three major paradigms in the field—biomimetic, interfacial, and functional tissue engineering—by combining physical (via biomaterial design) and chemical (with growth/differentiation factors and cell adhesion molecules) signal delivery to achieve a continuous transition in both structure and function. This review consolidates several key methodologies to generate gradients, some of which have never been employed in a tissue engineering application, and discusses strategies for incorporating these methods into tissue engineering and implant design. A key finding of this review was that two-dimensional physicochemical gradient substrates, which serve as excellent high-throughput screening tools for optimizing desired biomaterial properties, can be enhanced in the future by transitioning from two dimensions to three dimensions, which would enable studies of cell–protein–biomaterial interactions in a more native tissue–like environment. In addition, biomimetic tissue regeneration via combined delivery of graded physical and chemical signals appears to be a promising strategy for the regeneration of heterogeneous tissues and tissue interfaces. In the future, in vivo applications will shed more light on the performance of gradient-based mechanical integrity and signal delivery strategies compared to traditional tissue engineering approaches.

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“…The trend observed is very interesting. As discussed earlier the reported pK a of aliphatic -COOH and aliphatic secondary -NH 2 is 4-5 32,33 and 11, 34,35 respectively, hence it would be expected that the negative charge on the Au nanoparticles would increase with increasing pH due to the presence of -COOH moieties which will become more deprotonated with increasing pH and the underlying -NH 2 moieties will become less protonated as the pH increases. Therefore it would be envisaged that the zeta potential would decrease with increasing pH.…”

Section: The Success Of the Coating Determined Via Zeta Potentialmentioning

confidence: 89%

“…However, the charge of the surfaces will be sensitive to the pH of medium as the pK a of the functional groups present (-CO 2 H or -NH 2 ) will determine whether the groups are protonated or deprotonated and thus whether the surface is charged (-CO 2or -+ NH 3 ) or neutral (-CO 2 H or -NH ). [29][30][31] The reported pK a of aliphatic carboxylic acids is 4-5 32,33 and aliphatic secondary amine is 11 in free aqueous solution. 34,35 However, it is well documented that the pK a of aliphatic acids and amine which are bound to a surface such as Au and silica substrate to form a self-assembled monolayer are different to what is observed in free solution.…”

Section: The Success Of the Coating Determined Via Zeta Potentialmentioning

confidence: 99%

Preparation of Multilayer Microcapsules Encapsulating Aqueous Lithium Bromide and Their Mechanical Stability

Iqbal

Zhang

et al. 2019

Ind. Eng. Chem. Res.

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The development of more efficient and reliable absorption/adsorption refrigeration for air conditioners (ACs) and chillers is of great interest due to the increasing demand of these cooling devices in homes and offices. Presently, majority of the ACs incorporate aqueous lithium salts as both refrigerate and desiccant, which are corrosive and lead to corrosion of the mechanical components. This increases maintenance costs and decreases the cooling system's lifespan. Herein, an encapsulation method is proposed to encompass the aqueous lithium bromide solution with silica as the shell to protect the surrounding mechanical components. Moreover, a coating of citrate stabilised Au nanoparticles via an electroless method involving intermolecular electrostatic interactions is introduced to improve the robustness of the capsule wall. The success of the different coatings is evident from the change of zeta potential and mechanical properties. The coating with Au nanoparticles improves the mechanical strength of the capsules significantly, increasing rupture force from 0.25 ± 0.02 mN to 0.45 ± 0.04 mN. The coated and uncoated capsules were shown to be thermally stable over 10 repeated cycles between temperature ranges -10 to 150 o C, hence, withstand the thermal demands in ACs. Furthermore, adsorption and desorption cycles were performed on the capsules, which showed promising stable and repeatable performances.

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Fabrication of a nanoparticle gradient substrate by thermochemical manipulation of an ester functionalized SAM

Cited by 14 publications

References 76 publications

Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties

Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties

Strategies and Applications for Incorporating Physical and Chemical Signal Gradients in Tissue Engineering

Preparation of Multilayer Microcapsules Encapsulating Aqueous Lithium Bromide and Their Mechanical Stability

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