Poly(dimethylsiloxane) (PDMS) was employed as a model polymer melt. Figure shows the molecular structure of PDMS. It is a silicone oil with a straight-chain structure and exhibits a wide range of viscosities depending on molecular weight and chain length. We used a PDMS oil (KF-96-10000cs, Shin-Etsu Chemical Co., Ltd.) as received. The viscosity was η=9750 mPa•s at 25 ℃ (room temperature) and 3790 mPa•s at 80 ℃, which was measured by a viscometer (Kyoto Electronics Manufacturing Co., Ltd., EMS-1000). The molecular weight and chain length were calculated as Mn = 59000 and l =250 nm, respectively. Cleaved muscovite mica [KAl2(Si3Al)O10(OH)2] substrates were used as substrates, which have been used for high-resolution FM-AFM imaging in various liquids, and the atomically flat surface can easily be obtained by cleavage. The experiment was performed by a system based on a commercial AFM (JEOL Ltd., JSPM-5200) with a homebuilt AFM head for qPlus sensors. The qPlus sensor was built using a quartz tuning fork (QTF; purchased from SII Crystal Technology Inc.) with resonant frequency ƒ0 = 32.768 kHz and spring constant k = 1890 N m -1 (calculated from its shape). One prong of QTF was fixed on the mount, and a tungsten tip was mounted on the end of the free prong of QTF by epoxy resin (EPO-TEK H70E; Epoxy Technology Inc). The probe was fabricated from tungsten wire (Nilaco Co., diameter = 0.10 mm) by electrochemical etching in 1.0 mol L -1 potassium hydroxide solution. The radius of the tip was approximately less than 100 nm, as measured by FE-SEM inspection.