# Shape Memory Effect in Micro-Sized Shape Memory Polymer Composite Chains
## 5 Morphology of Shape Memory Polymer/Nickel (SMP/Ni) Vertical Chain Arrays  
The arrays of protrusive SMP nickel chains formed perpendicular to the SMP substrate. As shown in Figure 6, the morphology comparison of protrusive chains at four different volume fractions of nickel powders is presented. Statistical results of dimensions of protrusive chains, including diameter, height and separation were also obtained. Here, the diameter of a chain is defined as the measured diameter at the middle height of a chain. The interval distance is defined as the distance between the centrals of two adjacent chains. As shown in Table 1, it is clear that both the diameter (from 10 \(\upmu\)m to 250 \(\upmu\)m) and height (from 200 \(\upmu\)m to 1500 \(\upmu\)m) increase with the increasing of nickel contents, while the interval distance (from 100 \(\upmu\)m to 700 \(\upmu\)m) is relatively stable at five different nickel contents.  
Figure 5: Differential Scanning Calorimetry (DSC) results of pure polyurethane-based Shape Memory Polymer (SMP) and SMP/Ni (Nickel) composite.  
Figure 6: Typical array of vertical protrusive Shape Memory Polymer/Nickel (SMP/Ni) chains with varied volume fraction of nickel particles: 1%, 2%, 3%, and 5%.  
Figure 7 reveals the patterns of the cross section cut from a vertical protrusive SMP/Ni chain with average 2% (Figure 7a) and 5% (Figure 7b) nickel particles in SMP matrix. The particles distributed randomly, which implies that the aligned nickel particles are also in random distributions in the horizontal cross-section plane (the direction of magnetic field is in the vertical direction). Furthermore, referred to the observed distributions of nickel particles, the volume fraction in this cross section is much higher than 2% (Figure 7a) and 5% (Figure 7b). Due to the attraction effect of magnetic field to the nickel particles, the nickel particles concentrate towards each vertical protrusive SMP/Ni chain, where the nickel content is much higher than those located far from the SMP/Ni chains. As shown in Figure 7a-2, the thin films of pure SMP are obvious at the exterior surface of the cross section, which ensure the strong banding of nickel particles on the surface. Furthermore, as shown in Figure 7b, a series of nickel chains are also embedded under the surface of a big vertical SMP/Ni chain, and the thin films of pure SMP also cover nickel particles. Moreover, on the tips of SMP/Ni vertical chains, the particles may be exposed to the air. However, due to high porosity of nickel particles, the nickel particles are still strong bonded with the SMP matrix.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Filler Contents** & **Diameter (\(\upmu\)m)** & **Height (\(\upmu\)m)** & **Interval Distance (\(\upmu\)m)** \\ \hline
1\% & 25–45 & 270–310 & 100–400 \\
2\% & 100–135 & 750–1000 & 300–550 \\
3\% & 180–220 & 1100–1300 & 400–700 \\
5\% & 200–240 & 1200–1400 & 450–600 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Dimensions (diameter, height, and interval distance) of vertical Shape Memory Polymer/Nickel (SMP/Ni) chains.  
Figure 7: Cross section of the vertical protrusive Shape Memory Polymer/Nickel (SMP/Ni) chain ((a) 2 vol% Ni; (b) 5 vol% nickel).