Cantilever modes

DMT A measurements were made with a Polymer Labs instrument. Samples were clamped in the single cantilever mode in a frame of 22 mm using 6 mm clamps with 0.5 mm faces. The sample length between the clamps was 8 mm. Measurements were performed at a frequency of 1 Hz, a strain amplitude of 0.063 mm and a heating rate of 5 K.min . Clamping was checked by monitoring the strain amplitude on an oscilloscope. The measurements were carried out in air. Values of the temperature of maximum mechanical loss, T (tan 5max). were reproducible to 2 K. 

All studies were performed under nitrogen (< 2ppm oxygen) using the single cantilever mode of the Polymer Labs DMTA at small deformation, 1 hz, and a heating rate of 5 or 0.5 °C/min. 

Dynamic mechanical thermal analyses were carried out using a Polymer Laboratories DMTA equipped with a high temperature (500°C) head operating at a frequency of 1 Hz and a constant strain, x 1, in the single cantilever mode. The thickness of the PES/PI2080 films was in the range of 0.1-0.2 mm and that of the PES/PI XU 218 films was 0.2-0.3 mm. 

Figure 13 Forced vibration bending in the (a) dual- and (b) single-cantilever modes...

The glass transition temperature and the modulus of the cured matrix were measmed by dynamic mechanical analysis (DMA) in the single cantilever mode, at a frequency of IHz. DMA runs were reeorded with a DMA 2980 Dynamic Mechanical Analyzer from TA instruments. The glass transition temperature (Tg) was measured at the maximum of the Tan delta (5) curve dedueed from DMA experiments. Storage modulus of the matrix was determined at 40°C. 

Note that for these definitions the sample length, /, is always taken as the distance between the fixed clamp and the driveshaft clamp. Therefore samples in single and dual cantilever mode will both have the same length for a given clamp spacing. Similarly, the sample length... 

Dynamic mechanical properties were evaluated using a TA Instrument Dynamic Mechanical Analyzer (DMA) that was assembled into the single-cantilever mode. Specimens were cut to a length of 30 mm while the span length was set at 17 mm. Temperature scans were conducted at a range of 30 to 180 C for all specimens. 

Modification of an AFM to operate in a dynamic mode aids the study of soft biological materials [58]. Here a stiff cantilever is oscillated near its resonant frequency with an amplitude of about 0.5 nm forces are detected as a shift to a new frequency... 

Pulsed-force mode AFM (PFM-AFM) is a method introduced for fast mapping of local stiffness and adliesion with lower required data storage than recording force-distance curves at each point on the x-y plane [115]. A sinusoidal or triangular modulation is applied between the tip and sample (either via lever or sample piezo) at a lower frequency than that of either the piezo or cantilever resonance frequency. Tip and sample then come... 

According to the distance from probe to the sample, three operation modes can be classified for the AFM. The first and foremost mode of operation is referred to as contact mode or repulsive mode. The instrument lightly touches the sample with the tip at the end of the cantilever and the detected laser deflection measures the weak repulsion forces between the tip and the surface. Because the tip is in hard contact with the surface, the stiffness of the lever needs to be less than the effective spring constant holding atoms together, which is on the order of 1 — 10 nN/nm. Most contact mode levers have a spring constant of <1 N/m. The defection of the lever can be measured to within 0.02 nm, so for a typical lever force constant at 1 N/m, a force as low as 0.02 nN could be detected [50]. 

To minimize effects of friction and other lateral forces in the topography measurements in contact-modes AFMs and to measure topography of the soft surface, AFMs can be operated in so-called tapping mode [53,54]. It is also referred to as intermittent-contact or the more general term Dynamic Force Mode" (DFM). A stiff cantilever is oscillated closer to the sample than in the noncontact mode. Part of the oscillation extends into the repulsive regime, so the tip intermittently touches or taps" the surface. Very stiff cantilevers are typically used, as tips can get stuck" in the water contamination layer. The advantage of tapping the surface is improved lateral resolution on soft samples. Lateral forces... 

The amplitude drops to zero when the sample is moved from the point of first contact on a distance of the half of the full amplitude of the free-oscillating probe. From this point, a further motion of the sample will cause the cantilever bending upward, similar to what occurred in the contact mode. If the sample motion is reversed the amplitude increases as shown by a dashed curve in Figure 20.2c. 

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