(Color online) (a) Schematic diagram of the AFM system equipped with a thermal tip and (b) the nanostructures produced by the thermal tip in the polymer thin films deposited on a silicon substrate. The arrows in (b) indicate the directions of displacement in the piezoelectric scanner, responding to the thermal expansion and indentation in the sample, respectively. H is the height of the nano-strand, h is the indentation depth, D is the diameter of the base of the nanostrand, d is the diameter of contact, and s is the height of the rim around the nanostrand.
(Color online) Upward deflections of the small fresh cantilever tip with increasing heating voltage due to thermal expansion and bending of the cantilever beam, and downward penetrations of the cantilever tip into the reference polymers at the melting points (PET for polyethylene terephthalate, HDPE for high-density polyethylene, and PCL for polycaprolactone, respectively).
(Color online) Dependence of the size of polymer nanostructures on the static load and ramp temperature of the thermal tip having a radius of 30 nm in the 900 kDa polystyrene film of 220 nm in thickness: (a) The 3 × 4 arrays of polymer nanostrands are produced at four different loads of 5, 80, 170, and 260 nN, increasing from the top row to bottom row as the tip temperature is ramped from 290 to 370 K at a rate of 1 K/s. The average height for the top to bottom row is 6, 10, 13, and 19 nm, while the average radius at the base is 32, 50, 64, and 95 nm, respectively. (b) The 3 × 3 arrays of polymer dots are produced at three different loads of 80, 170, and 260 nN increasing from the top to bottom row as the tip temperature is ramped from 290 K to a temperature of 5 K above its peak penetration temperature (or the softening point, Ts) at the same ramp rate of 1 K/s.
(Color online) AFM images of the nanostrand shapes, corresponding to the nanostrand on second column of the first row in Fig. 3(a), formed 10° below the Tg at 370 K and the nanostrand shapes, corresponding to the nanostrand on second column of the first row in Fig. 3(b), formed above the Tg at 385 K. Images (a) and (c) are cross-section views in direction of the length of the cantilever beam; (b) and (d) are views in the direction 90o to the length of the cantilever beam. The polystyrene molecular weight is 900 kDa, and thickness is 220 nm.
(Color online) (a) Deflections in the cantilever tip showing an increase in surface stiffness for the polystyrene thin film of 900 kDa in molecular weight and 220 nm in thickness, supported on a silicon substrate, with decreasing load for the small AFM tip. (b) Changes of the glass transition temperature with the load for the polystyrene films using both the small and large AFM tips.
(Color online) (a) Penetration velocity of the small thermal tip at various glass transition temperatures for the polystyrene thin film of 900 kDa in molecular weight and 220 nm in thickness, supported on a silicon substrate. (b) Penetration velocity of the large thermal tip at various loads for the polystyrene films having different molecular weights at the softening point (Ts).
(a) Influences of the silicon substrate on the glass transition in the 25 kDa polystyrene thin films having increasing thicknesses. (b) Dependence of the glass transition temperature on molecular weight of polystyrenes at a constant load of 125 nN.
(Color online) Mechanical and thermal interactions at the contact between the thermal tip and polymer surface. (a) Formation of the plastic zone underneath the tip, (b) different types of interfacial forces acting at the three-phase contact line near the edge of the tip–polymer contact, (c) the temperature contour underneath the thermal tip, and (d) finite element analysis modeling of thermal transoport at the tip–surface contact. The diagrams are not to actual scales. R is the radius of curvature of the thermal tip, a is the radius of contact; the subscripts S, L, V refer to solid, liquid, and vapor; γ is the interfacial tension; θ is the contact angle.
(Color online) Influences of the contact radius and film thickness on temperature distributions at the contact. (a) Changes in temperature with increasing the contact radius in the lateral top surface plane, (b) changes in temperature with increasing the contact radius in the direction normal to the surface plane, (c) changes in temperature with increasing the film thickness contact radius changes in the lateral top surface plane, and (d) changes in temperature with increasing the film thickness in the direction normal to the surface plane.
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