Side-chain effect on Langmuir and Langmuir-Blodgett film properties of poly(N-alkylmethacrylamide)-coated magnetic nanoparticle.

We report the fabrication of a Langmuir-Blodgett (LB) film of magnetic nanoparticles (iron oxide) coated by poly(N-alkylmethacrylamide)s with various alkyl chain lengths. The iron oxide nanoparticle (nP) was first modified with a reactive polymer, poly(N-hydroxysuccinimide methacrylate) (pSucMA) by applying surface initiated atom transfer radical polymerization (ATRP) technique. Then the succinimide group was replaced by various amine derivatives. The monolayer behaviors of the resultant nanoparticles, as modified by various poly(N-alkylmethacrylamide)s, such as poly(octylmethacrylamide) (pOMA), poly(dodecylmethacrylamide) (pDDMA), polytetradecylmethacrylamide (pTDMA), and poly(hexadecylmethacrylamide) (pHDMA) were elucidated using surface pressure-area isotherm measurements. Results show that pTDMA-modified nanoparticles (nP-pTDMA) exhibit the highest collapse pressure with a steeply rising surface pressure. The monolayer of nP-pTDMA on the water surface was transferred onto a solid substrate using the LB technique. Atomic force microscopy (AFM) images of the transferred LB film show that nP-pTDMA particles form a uniform nanoparticle monolayer. The LB film of nP-pTDMA with multilayers was fabricated through sequential transfer of the particles monolayer onto the substrate surface. The resultant LB film of nanoparticles shows a superparamagnetic behavior at room temperature.