Thin Film Supports

The various morphological variants available in bead form can be repHcated in thin films ( 2 cmx8cmx50-100 pm) produced simply by photo-initiated free radical polymerization of comonomer mixtures introduced by capillary action into an appropriate mold formed with microscope sHdes [48]. With appropriate choice of comonomers, and porogen in the case of macroporous films, reasonably mechanically robust self-supporting films can be removed from the mold for further exploitation (Fig. 1.9). 

While such a film format is not intended for routine use in e.g. soHd phase synthesis, it has proved useful for spectroscopic mechanistic investigation of polymer-supported metal complex catalysts [49] and we, with our collaborators, are employing such films as a component in nanosecond fluorescence sensing devices [50]. 

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Uemiya, S. et al., Separation of hydrogen through palladium thin film supported on a porous glass tube, /. Membr. Sci., 56, 303,1991a. 

In recent years, metal nanoparticles and thin films supported on oxides have become fundamental components of many devices as their small dimensions present structures with new chemical and physical properties, often enhancing the reactivity of these surfaces relative to their bulk counterparts. Numerous theoretical and experimental studies show that the metal particle size and shape as well as direct adsorbate interactions with the oxide support can each play a key role in enhancing the reactivity of these surfaces. Further investigations imply that the support material may... 

Without doubt, the advent of carbon nanotubes has opened up iimovative perspectives for research and development of carbon electrodes. In this chapter, we have attempted to highlight the electrochemical properties of carbon nanotubes by rooting them mainly on their structural, electronic and chemical properties. If chirality of SWNTs could be controlled, it would be possible to probe electrochemically the unique electronic properties of the tubes with their corresponding unique DOS distribution and establish direct correlations between electronic structure and electrochemistry. However, so far, most of their electrochemical applications are based on ensembles of CNTs (MWNTs or SWNTs) in thin films supported on conductive surfaces or composites. Such ensembles, not so well defined from the structural point of view, contain a mixture of tubes with different diameters and DOS... 

So far we have neglected the fact that the substrate has a particular geometric structure which influences, as we shall sec further below, the adsorption behavior in a very pronounced way. Furthermore, in practical cases the macroscopic geometric structure is rather complex. Consider, for example, a real catalyst used in heterogeneous reactions. It may consist of bimetallic precipitates, or of thin films supported on alumina, silica, or... 

As an example of a chemisorption reaction where the control on the surface defects is crucial we mention here the case of CO on MgO. This process has been studied on polycrystalline samples, on MgO thin films supported on a metal, and on MgO single crystals, three forms of the material where the surface morphology and the defect concentration are different. This experimental... 

As previously mentioned, GC is a two-phase system that consists primarily of a stationary (solid and/or liquid) and mobile (gas) phase. When a liquid stationary phase is used (GLC), the liquid is immobilized as a thin film supported on a finely divided, inert solid support usually consisting of siliceous earth, crushed firebrick, glass beads, or in some cases, the inner wall of a glass tube. In GSC, the stationary phase is an active adsorbent, such as alumina, silica gel, or carbon, which is tightly packed into a tube. 

In the AIREs, the nanometer thin film supported on glassy carbon or other conductive substrates was prepared by convenient electrodeposition method of cyclic voltammetery that led to form nanometer-scale thin film of layered structure. The film of island structure is nevertheless fabricated by evaporation method and employed in the SEIRA. 

Fig. 14. (A) TPD results obtained from a Pt thin film supported on a Ti02 film/Ti metal model catalyst as a function of reduction time at 875 K in 10 -mbar H2 after 0 min (curve I), IS min (curve 2), and 30 min (curve 3). (B) TPD of CO from Pt polycrystal as a function of Ti02, coverage. 1SS ratio of Pt to clean Pt foil, Pt/Pto equals 1.0 (curve 1), 0.27 (curve 2), and 0.07 (curve 3). (After Ref. 130.)...

Even small amounts of carbon monoxide or other contaminants can poison a fuel cell. Sandia National Laboratories (SNL) is working on developing gas-selective thin film membranes to improve and lower the cost for hydrogen purification. Defect-free aluminosilicate and silicalite zeolite thin films supported on commercially available alpha and gamma alumina disk substrates were developed. In tests using SNL s permeation unit, which can test both pure and mixed gases from room temperature to 250°C, excellent separation values for hydrogen were achieved. 

L. Li, W. Zhu, P. Zhang, Z. Chen, W. Han, Photocatalytic oxidation and ozonation of catechol over carbon-black-modified nano-Ti02 thin films supported on A1 sheet . Water Research, 37 (15) 3646-3651, (2003). 

Perovskite-structured membranes, in the form of thin films supported on porous ceramic or metal substrates, have been studied extensively in the past decade. Thin films offer several advantages including reduced material cost, improved mechanical strength and possibly higher H2 flux. Chemical vapor deposition (CVD) [99], electrochemical vapor deposition (EVD) [100] and sputtering [101] represent typical methods. However, dense films have been difficult to obtain by these methods. It was found that the continuity and gas-tightness of the deposited films were very sensitive to the morphologies and pore size of substrates. 

In parallel to development activities in the materials themselves, significant progress has been made in the architecture of devices. This includes a transition from dense, self-supported membranes to the use of thin films supported on porous substrates, as well as developments in tubular geometries and modified planar geometries. This chapter will provide an outiine of these development activities and provide possible insight into potential future developments. 

Fig. 1 Dependence of glass transition temperature on thickness of PS thin film supported on Si substrate Symbols other than solid squares were cited from formerly reported results and solid squares were from [5]. Solid line is the empirical fitting function to the observed data. For further detail please refer to [5]...

Fig. 26 The log(cooling rate) versus 1/T for PS thin films supported on Si substrate. Inset indicates the thickness dependence of activation energy [63]. Solid symbols represent PS thin films with different film thicknesses...

Atanasoski RT, Atanasoska LL, Cullen DA, Haugen GM, More KL, Vemstrom GD (2012) Fuel cells catalyst for start-up and shutdown conditions electrochemical, XPS, and STEM evaluatitm of sputter-deposited Ru, Ir, and Ti on Pt-coated nanostmctured thin film supports. Electrocatalysis. Electrocatal 3 284—297... 

Bonakdarpour A, Stevens K, Vemstrom GD, Atanasoski R, Schmoeckel AK, Debe MK, Dahn JR (2007) Oxygen reduction activity of Pt and Pt-Mn-Co electrocatalysts sputtered on nano-structured thin film support. Electrochim Acta 53(2) 688-694... 

Lin et al. [50-53] used Nafion coupling agent to treat porous PTFE thin film support before impregnating PTFE film with PBI solution. They immersed the pretreated porous PTFE-nc thin film (thickness 16 pm) in a PBI/LiCl/DMAc (4.5/4.5/100 by wt.) solution and then heated at 80 °C for 30 min and then 120 °C under vacuum... 

PFA was rrsed exterrsively as a precnrsor dnring the preparation of nanoporons carbon (NPC) merrtbrane for gas separation by Foley and co-workers [52-58]. An early work had rmcovered the rrse of a spray-coating techniqne in order to prodnce a thinlayer of NPC inthe pororrs snrface of a stainless steel disk snpport [51,54]. Selectivity for O2/N2 separation of np to 4 was achieved for the snpported membrane carborrized at 600°C in flowing helitrm [54]. Later Foley arrd co-workers improved their preparation techrrique by using an ultrasonic deposition system which conld rrrriformly distribute the polymeric solution on to the support [52, 53, 57], They have fabricated a number of thin film supported nonporous carbon membranes... 

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