Stimuli responsive polymer gels for sensing applications (2012)

This chapter (3) is based on simplifying the design template of an optical sensor through the multifunctionality imparted on it by an IL. The IL simplified polymer gel is termed an optode within this chapter as (a) it is prepared the same manner as optodes, (b) the IL performs many of the same functions as previous materials used in optode design and (c) the analyte or ion movement between the aqueous and organic phases follows the same convention for optodes.\n\nThe 2-component optode membrane is capable of generating three distinct colours in the presence of Cu2+ and Co2+ ions. It has been found that the IL [P6,6,6,14][DCA] can act as plasticizer, ligand and transducer dye when used in PVC membranes, which significantly simplifies the optode membrane cocktail.\n\nUpon exposure to an aqueous Cu2+ solution, a yellow colour is generated within the membrane, while exposure to aqueous Co2+ solution generates a blue colour. Exposure to a solution containing both ions produces a green colour. Vibrational spectroscopy has been used to investigate the molecular basis of the ILmetal ion binding mechanism. Analytical characteristics of the membranes including the effect of interfering ions, binding constants and the limit of detection for both ions have been estimated. A case of simultaneous dual-analyte recognition is presented based on two distinct absorption maxima.\n\nThe inherent conducting properties of the IL membranes are then investigated as a possible detection channel using WRF. WRF is a novel detection technique, which monitors the conductivity of a given sample wirelessly, allowing non-contact detection and measurement of IL-PVC membranes. The various co-ordinated membranes produce a discriminatory drop in the resulting signal, which is a direct function of the specific metal ion (Cu2+, Co2+ or a mixture) co-ordinated to the IL. The results of the novel WRF technique have been validated principally by EIS; whilst XRF is used to elucidate both WRF and EIS trends.\n\nThe focus of this chapter (4) is built upon the ideology explored in chapter 3, which is to use an IL as an agent that performs multiple roles within a device. However in this case a synthetic route is employed that yields an IL as a key component in an electrochromic device. A device based on two individual components is achieved through the synthesis of an electrochromic IL that also acts as the supporting electrolyte between two electrodes.\n\nThis work therefore describes the synthesis and characteristics of a novel electrochromic IL based on a phosphonium core tethered to a viologen moiety. When integrated into a solid-state electrochromic device, the viologen modified IL behaved as both the electrolyte and the electrochromic material. Device fabrication was achieved through in situ photo-polymerisation and encapsulation of this novel IL within a hybrid sol-gel. Important parameters of the device performance, including its coloration efficiency, switching kinetics and optical properties were characterised using UV/Vis spectroscopy. Despite the rather viscous nature of the material, the device exhibited approximately two orders of magnitude faster switching kinetics (221 seconds to reach 95 % absorbance) when compared to previously reported electrochromic ILs (18,000 seconds).\n\nThis chapter describes the synthesis and characterisation of hybrid sol-gel materials\nco-polymerised with a monomer based on the light responsive chromophore\nSpiropyran (SP). The hybrid materials contain a silane centre chemically tethered to\nan acrylate monomer via a propyl linker which are co-polymerised with a varying\nmetal propoxide/methacrylate complex. These hybrid materials are of the optimum\nmechanical stability for patterning under incident light. \n\nThis chapter (5) therefore provides the reader with an in-depth discussion of the chemistries required for sol-gel preparation and the area of photopatterning of sub-micron 3 D structures.This chapter describes the synthesis and characterisation of hybrid sol-gel materials co-polymerised with a monomer based on the light responsive chromophore Spiropyran (SP). The hybrid materials contain a silane centre chemically tethered to an acrylate monomer via a propyl linker which are co-polymerised with a varying metal propoxide/methacrylate complex. These hybrid materials are of the optimum mechanical stability for patterning under incident light. This chapter therefore provides the reader with an in-depth discussion of the chemistries required for sol-gel preparation and the area of photopatterning of sub-micron 3 D structures.\n\nThis chapter (6) is focused on the photopatterning of electro-active hybrid sol-gels that are based on the chemical composition (MAPTMS,ZrPO,MAAH) as introduced in chapter 4. For these studies however, the hybrid materials are based solely on Zr metallate complexes. The electroactive species that become encapsulated within the polymer matrix are both phosphonium and imidazolium based IL’s, dispersed graphene sheets and the electrochromic dye EV.