Fabrication of a Polymer Molecularly Flat Substrate by Thermal Nanoimprinting and AFM Observation of Polymer Chains Deposited on It

Abstract

The surface of polymers is believed to have high mobility, and their glass transition temperature decreases significantly from the bulk value. In this study, we prepared a molecularly flat poly­(methyl methacrylate) (PMMA) substrate by thermal nanoimprinting a PMMA plate with an atomically stepped sapphire substrate. The imprinted PMMA surface with a step height of ca. 0.2 nm was stable for months in air at room temperature and was retained even after immersion in water for 10 h. PMMA chains and an isotactic PMMA crystalline monolayer deposited on the imprinted PMMA substrate by the Langmuir–Blodgett technique were observed by atomic force microscopy at the molecular level, and the molecular structures were stable for months in air at room temperature. These significant stabilities of the surface of the imprinted PMMA substrate and the monolayers deposited are unexpected and differ from the results expected based on our present understanding of the polymer surfaces. The results indicate that the properties of the thermally pressed polymer surface may be different from those of the previously studied solvent-cast polymer surfaces.

pH-Controlled Stereoregular Polymerization of Poly(methyl methacrylate) in Vesicle Membranes

“…Similar to commercial PMMAs ( T g = 127 °C), T g of the PMMAs we obtained in DMSO was about 127 °C. According to the literature, T g of pure isotactic PMMA was about 45 °C . As expected, PMMAs obtained in the present study displayed a decrease in T g from 116 to 82 °C with the increase of isotacticity from 9 to 35%, further indicating the success of the stereoregular polymerization.…”

Molecular Combing of Various Poly(n-Alkyl Acrylate) Chains on Mica by the Dipping Method

“…In our previous work, we deposited isolated PMMA chains on a water surface onto a PMMA molecularly flat substrate by the vertical dipping method of the Langmuir–Blodgett (LB) technique. The substrate was prepared by thermal nanoimprinting with an atomically flat mold and we found that the PMMA chains were deposited as relatively elongated chains while they were deposited as condensed chains on mica. , Most likely, this behavior was due to the weaker adsorption of the PMMA isolated chains to the PMMA molecularly flat substrate than to mica. Even if PMMA and PBA could be deposited as straight chains, the length would be shorter than that in the all-trans conformation depending on the steric hindrance of the aggregated side chains around the main chain on the substrate.…”

Chain Movements at the Topmost Surface of Poly(methyl methacrylate) and Polystyrene Films Directly Evaluated by In Situ High-Temperature Atomic Force Microscopy

“…Hydrophilic mica strongly adsorbed the PMMA monolayer, and a condensed PMMA monolayer formed on the water surface was transferred, maintaining its condensed structure. However, the hydrophobic PMMA film weakly adsorbed the PMMA monolayer, and PMMA chains were stretched in the dip direction during LB deposition. − The widths of PMMA chains were distributed, but the width of the thinnest part was ∼4 to 5 nm, the nominal tip radius of the cantilever was 4 nm, and the PMMA chain should be observed to be broadened by the tip to a similar extent. The thinnest parts of the PMMA chains were similar to a single chain.…”

“…Since PMMA is deposited imhomogeneously on a substrate in the dilute state and it is expected to be difficult to find deposited PMMA chains, especially on the rough dip-coated film surface, we used a PS- b -PMMA block copolymer instead of a PMMA homopolymer. As shown in Figure a, PS without hydrophilic groups did not spread on the surface of water but formed particles, much thicker than monolayers, that were used as probes to find the PMMA chains emanating from them. ,− Figure b shows an AFM height image of PS- b -PMMA deposited on mica in a dilute state. PS particles with a thickness of ∼3.1 nm surrounded by a condensed PMMA monolayer with a thickness of ∼0.3 nm were observed.…”

“…However, as mentioned above, due to the limited resolution of AFM, direct evaluation of the mobility of the topmost chains is difficult and has never been reported. In previous studies, to overcome this difficulty, we prepared a molecularly flat substrate by thermally imprinting a PMMA plate with an atomically stepped sapphire substrate or mica mold and deposited isolated PMMA chains by the Langmuir–Blodgett (LB) technique. − The isolated chains deposited on the molecularly flat substrates were clearly observed by AFM, and the isolated chains and nanostructure at the flat substrate surface started moving at a temperature close to the bulk T g . During the course of those studies, we considered possible ways to evaluate the movements of the topmost chains of films by using bulk PMMA films without nanoimprinting and the deposition of isolated PMMA chains.…”