# Radiation-Assisted Synthesis of Polymer-Based Nanomaterials
## 6 Controlling Radiation-Induced Grafting on Nanoscale
### Advanced Functional Track-Etched Membranes  
When polymer thin films are irradiated with swift heavy ions, straight tracks of damaged zones are created. These damaged zones are converted into hollow cylindrical channels by chemical etching. The pore diameters may range from 10 nm to tens of microns with densities varying from 1 to 10\({}^{10}\)/cm\({}^{2}\)[69]. When a thin film is irradiated with heavy ions, radicals are formed in the damaged zones, some of which are removed by etching. The residual carbon-centered radicals and peroxy radicals formed on the walls of nanopores by the strong oxidizing agents of the etching solution can be used to initiate grafting of vinyl monomers. In the presence of RAFT agents, the grafting process can be controlled to yield graft chain lengths with predetermined length and architecture and narrow dispersity. Radiation grafting of responsive polymers into the pores of track-etched membranes (TeMs) change their permeation properties in response to external stimuli such as pH or temperature [70].  
Poly(acrylic acid), PAA, was grafted inside the nanochannel walls of track-etched PVDF membrane in a controlled manner by RAFT polymerization via the residual radicals remaining after the etching process. Various degrees of grafting from 5% to 63% were achieved, accompanied by a steady decrease in the pore diameter. The synthesized nanoporous membranes were later transformed into highly sensitive membrane electrodes by deposition of a thin gold layer on both sides without blocking the nanochannels. The membrane electrodes synthesized were found to be sensitive to sub-ppb concentrations of Pb\({}^{2+}\) in square-wave anodic stripping voltammetry measurements [71].  
Using a radiation-induced grafting technique, track-etched nanoporous PVDF membranes were functionalized with mercury sensitive poly(4-vinyl pyridine). Coating of these membranes with a very thin layer of gold results in an electrochemical sensor that is very selective and sensitive for mercury. A P4 VP-functionalized PVDF membrane was found to be insensitive to pH variations (pH: 3-9), high salt concentrations and the presence of other heavy metal ions in the same solution [72].  
PET TeMs with average pore size of 400 nm were photografted with poly(acrylic acid) using benzophenone immobilized on the inner walls of nanochannels. Cupric ions electrostatically attached to the carboxylate groups of dangling graft PAA chains were converted into metallic copper nanoparticles by radiation-induced reduction in aqueous alcohol solution using gamma rays. Copper nanoparticles \(\sim\)70 nm in diameter were deposited in cylindrical nanochannels as potential nanosensors [73].  
Gold nanoparticles were generated in the nanochannels of poly(acrylic acid) grafted poly(ethylene terephthalate) TeMs by radiation-induced reduction in alcoholic solution by using both 5 MeV electron beam and \({}^{60}\)Co gamma rays. The effects of absorbed dose, dose rate on the size and characteristics of gold nanoparticles were studied. The catalytic activity of gold nanoparticles supported on PAA-g-PET TeMs was tested for the reduction reaction of 4-nitrophenol [74].  
A recent review on track-etched nanopore membranes provides an overview on the fabrication and functionalization methods, describing the fundamentals in transport phenomena near the interface, in nanofluidics with or without surface charges and summarizes the applications of TeMs in stimuli-responsive membranes, ion-gating/sensing and energy conversion [75].