No abstract

In this report, we employ surface-initiated atom transfer radical polymerization (SI-ATRP) to graft a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), of controlled thickness from porous silicon (pSi) films to produce a stimulus-responsive inorganic-organic composite material. The optical properties of this material are studied using interferometric reflectance spectroscopy (IRS) above and below the lower critical solution temperature (LCST) of the PNIPAM graft polymer with regard to variation of pore sizes and thickness of the pSi layer (using discrete samples and pSi gradients) and also the thickness of the PNIPAM coatings. Our investigations of the composite's thermal switching properties show that pore size, pSi layer thickness, and PNIPAM coating thickness critically influence the material's thermoresponsiveness. This composite material has considerable potential for a range of applications including temperature sensors and feedback controlled drug release. Indeed, we demonstrate that modulation of the temperature around the LCST significantly alters the rate of release of the fluorescent anticancer drug camptothecin from the pSi-PNIPAM composite films.

Enhanced control over the surface properties of porous materials is of great interest owing to applications as diverse as the detection of chemical and biological species, molecular separation, drug delivery, and catalysis. [1][2][3] Recent research has made inroads into this issue, devising experimental strategies towards surface manipulation in porous materials. [4][5][6][7] However, the increasingly stringent device requirements for advanced applications, such as energy storage, controlled release, biochemical gates, nanoreactors, sorption, and high-performance molecular transport and separation, demand the development of multiphasic, responsive, and multifunctional materials. [8][9][10] Self-organized nanoporous anodic aluminum oxide (AAO) membranes prepared by electrochemical anodization have become popular materials, attractive for their high surface area (up to 250 m 2 g À1 ), high porosity (10 10 pores cm À2 ), highly ordered and monodisperse pores, tunable thickness and pore dimensions, excellent chemical, thermal, and mechanical stability, biocompatibility, and inexpensive fabrication.[11] A considerable number of studies have been devoted to the development of AAO membranes with complex pore geometries in order to improve the membrane properties for applications in molecular separation [12] and to enable the template synthesis [13] of sophisticated nanostructures with novel architectures [14] and unique optical, [15] magnetic, [16] energy-storage, [17] and electrical properties. [18,19] Membranes with branched, multilayered, and modulated pore structures have been generated by precise and temporal control over the anodization conditions. [20] In contrast, control at a similar level of complexity over the surface inside the pores of AAO membrane is currently lacking, despite the fact that the functionality on the pore surface is a key determinant for device performance. In particular, the selectivity and efficiency of molecular transport and separation through AAO membranes are not only effectively modulated by changing the size, [21] but also by the charge [22] and polarity [23] of the porous layer and the engineered affinity towards the species of interest.[24] Several surface-modification techniques have been applied to AAO membranes including silanization, [25] formation of self-assembled monolayers, [26] grafting of polymer brushes, [27] plasma processing, [28] sol-gel modification, [29,30] metal deposition (chemical vapor deposition, electroless and pulse electrochemical plating), [31] and quantumdot adsorption. [32] However, multifunctional and multilayered surface modification has not been demonstrated until our recent work in which we fabricated AAO membranes with distinctly different internal and external surface functionalities.[33] This study provided a glimpse of the opportunities for controlling the surface properties in porous materials but stopped short of demonstrating truly multilayered surface modifications, tunability, and functional properties. Here, we describe AAO membranes havin...

Enhanced control over the surface properties of porous materials is of great interest owing to applications as diverse as the detection of chemical and biological species, molecular separation, drug delivery, and catalysis. [1][2][3] Recent research has made inroads into this issue, devising experimental strategies towards surface manipulation in porous materials. [4][5][6][7] However, the increasingly stringent device requirements for advanced applications, such as energy storage, controlled release, biochemical gates, nanoreactors, sorption, and high-performance molecular transport and separation, demand the development of multiphasic, responsive, and multifunctional materials. [8][9][10] Self-organized nanoporous anodic aluminum oxide (AAO) membranes prepared by electrochemical anodization have become popular materials, attractive for their high surface area (up to 250 m 2 g À1 ), high porosity (10 10 pores cm À2 ), highly ordered and monodisperse pores, tunable thickness and pore dimensions, excellent chemical, thermal, and mechanical stability, biocompatibility, and inexpensive fabrication. [11] A considerable number of studies have been devoted to the development of AAO membranes with complex pore geometries in order to improve the membrane properties for applications in molecular separation [12] and to enable the template synthesis [13] of sophisticated nanostructures with novel architectures [14] and unique optical