AVS 49th International Symposium
    Surface Engineering Monday Sessions
       Session SE+NS-MoA

Paper SE+NS-MoA2
Grafting of Poly (N-isopropylacrylamide) in Surfactant Templated Mesoporous Silica Films and Particles

Monday, November 4, 2002, 2:20 pm, Room C-111B

Session: Nanoparticle and Nanofiber Surface Technologies
Presenter: G.V. Rama Rao, The University of New Mexico
Authors: Q. Fu, The University of New Mexico
G.V. Rama Rao, The University of New Mexico
J. Huang, The University of New Mexico
G.P. Lopez, The University of New Mexico
Correspondent: Click to Email
Surface-initiated atom transfer radical polymerization (ATRP) is an effective and versatile method used to generate grafted polymers on surfaces. We report grafting of a poly (N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer, into a mesoporous silica matrix using the ATRP technique. PNIPAAM exhibits a lower critical solution temperature (LCST) at 32°C in water, below which it is in an expanded conformation and soluble in water. Above the LCST, PNIPAAM is in compacted state and insoluble in water. Synthesis of mesoporous films and monodisperse microparticles was carried out through an acid catalyzed sol-gel process using a surfactant template approach. We used a non-ionic surfactant (Pluronic-P123) and a cationic surfactant (cetyltrimethyl ammonium bromide) for the present study. The LCST of the hybrid films was established by static contact angle measurements. These hybrid materials exhibited thermo responsive behavior by changing from hydrophilic to hydrophobic state with change in temperature. X- ray diffraction and transmission electron microscopic studies on the films and particles confirmed the presence of an ordered porous structure before and after ATRP. The grafting of the polymer onto the pore surface was confirmed by drastic decrease in pore volume of the particles after ATRP. Pore opening and closing due to contraction and expansion of PNIPAAM was studied by fluorescent dye uptake behavior of particles by monitoring the fluorescence intensity in flow cytometry experiments. It was found that the uptake of the dye into the pores was obstructed below LCST, and above LCST, the polymer was collapsed and facilitated the passage of dye into the mesopores. The dye in the pores was entrapped by cooling the particles to below LCST and subsequently the dye was released by washing with water above LCST. These materials have potential application in controlled release, chemical separation and control of fluidic transport.