Track-etched polycarbonate membranes

Martin et al. [8,9] developed one of the best methods for synthesis of polymers with hosts, using porous polycarbonate membranes (track-etched membranes) and porous alumina. Track-etched membranes are available commercially (Poretics, Nuclepore, etc.) with various sizes of pores from 10 nm upwards and a density of approximately 10 pores cm [8,9]. The membranes of porous alumina are prepared electrochemically from Al foil, and can have pore densities of up to lO" pores cm . Polymerization within... 

In general, template method is classified by soft and hard templates. Whereas anodic aluminum oxide (AAO) membrane, track-etched polycarbonate (PC) and zeolite can be used as hard templates, soft templates include surfactant, cyclodextrin, liquid crystal, etc. Compared with soft and hard templates, template-free method represents the fabrication technique of conducting polymer nanomaterials without the template, which is discussed in this section [115]. 

A New Filter Test. Because tests using cores are relatively expensive and time consuming, we developed a filter test using filters that mimicked the plugging behavior seen during the core tests. After some experimentation, we identified a workable test using a Millipore APIO filter pad upstream of a 10 pm polycarbonate (Sterlitech Track Etch ) membrane filter (both 13 mm in diameter). Fig. 5 compares filtration results for X US K K36 xanthan (solid circles) with results from the core test (solid triangles). The... 

Track-etched membranes are made by exposing thin films (mica, polycarbonate, etc) to fission fragments from a radiation source. The high energy particles chemically alter material in their path. The material is then dissolved by suitable reagents, leaving nearly cylindrical holes (19). 

Within the scope of thermoelectric nanostructures, Sima et al. [161] prepared nanorod (fibril) and microtube (tubule) arrays of PbSei. , Tej by potentiostatic electrodeposition from nitric acid solutions of Pb(N03)2, H2Se03, and Te02, using a 30 fim thick polycarbonate track-etch membrane, with pores 100-2,000 nm in diameter, as template (Cu supported). After electrodeposition the polymer membrane was dissolved in CH2CI2. Solid rods were obtained in membranes with small pores, and hollow tubes in those with large pores. The formation of microtubes rather than nanorods in the larger pores was attributed to the higher deposition current. 

FIG. 20-66 Track-etched 0.4-)lm polycarbonate membrane. Courtesy Milli-pore Corporation.)... 

The deposition of a conductive polymer (polypyrrole) into either a track-etched polycarbonate or alumina membrane was either achieved by electrochemical reduc-... 

Membranes with very regular pores of sizes down to around 10 nm can be prepared by track-etching [10], and, in principle, those membranes can be used for the fractionation of macromolecules in solution. A relatively thin (<35 pm) polymer film (typically from polyethylene terephthalate)/PET/or aromatic polycarbonate/PC/) is first bombarded with fission particles from a high-energy source. These particles... 

Fig. 3. (a) SEM image of the particle track-etched polycarbonate membrane, with a pore diameter of 1 (im (Martin, 1994). (b) SEM image of 2-/xm pores in a single-crystal mica film prepared by particle track-etching (Sun et al., 2000a). 

The most commonly used hard templates are anodic aluminum oxide (AAO) and track-etched polycarbonate membranes, both of which are porous structured and commercially available. The pore size and thickness of the membranes can be well controlled, which then determine the dimension of the products templated by them. The pores in the AAO films prepared electrochemically from aluminum metals form a regular hexagonal array, with diameters of 200 nm commercially available. Smaller pore diameters down to 5 nm have also been reported (Martin 1995). Without external influences, capillary force is the main driving force for the Ti-precursor species to enter the pores of the templates. When the pore size is very small, electrochemical techniques have been employed to enhance the mass transfer into the nanopores (Limmer et al. 2002). 

FIG. T2-70 Track-etched 0.4 gm polycarbonate membrane. (Courtesy Milli-... 

The scope of applications of MF has been broadened in recent years by the introduction of inert membranes, particularly polypropylene, polycarbonate, and Teflon . In general, these materials cannot be made by the methods developed for the cellulosics because of their insolubility. Both Teflon and pol)propylene MF membranes have been made by a controlled stretching procedure in which microtears are introduced Microporous polycarbonate membranes have been prepared by a unique radiation-track-etch method A thin polycarbonate film is exposed to ionizing radiation which leaves labile sites that can later be chemically etched to produce straight-throi channels. The pore size can be controlled by the etching conditions. The pores in these membranes, contrary to those in cellulosic membranes, are quite uniform in diameter. 

Finally, track-etched MF membranes are made from polymers, such as polycarbonate and polyester, wherein electrons are bombarded onto the polymeric surface. This bombardment results in sensitized tracks, where chemical bonds in the polymeric backbone are broken. Subsequently, the irradiated film is placed in an etching bath (such as a basic solution), in which the damaged polymer in the tracks is preferentially etched from the film, thereby forming cylindrical pores. The residence time in the irradiator determines pore density, and residence time in the etching bath determines pore size. Membranes made by this process generally have cylindrical pores with very narrow pore-size distribution, albeit with low overall porosity. Furthermore, there always is the risk of a double hit, i.e., the etched pore becomes wider and could result in particulate penetration. Such filter membranes are often used in the electronic industry to filter high-purity water. 

This experimental investigation focuses on the preparation of polycrystalline magnesium oxide nanorods via capillary-driven infiltration of a precursor solution into the cylindrical pores of a track-etched polycarbonate membrane followed by thennal decomposition procedure. The nanomaterial was fully characterized by SEM, EDX,... 

Commercial track-etch polycarbonate membranes (Whatman Nuclepore , nominal channel diameter 0.1 pm) were used and investigated by means of... 

Figure 4 The 96-well permeability testing method. The support membrane is a 3-p.m track etched polycarbonate of 10-p.m thick the artificial membrane in hexadecane and the recommended incubation time is four to six hours. Source Courtesy of Millipore Corporation, Billerica, Massachusetts, U.S.A.

Kim, K.J. et al., Chemical and elechical characterization of virgin and protein-fouled polycarbonate track-etched membranes by FTIR and sheaming-potential measurements,/. Membr. Sci., 134, 199, 1997. 

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