Investigating the Interphase in Hydroxyl-Terminated Polybutadiene (HTPB) Composites via Dynamic Mechanical Analysis 43 glass bead sample (denoted bead C). When analyzing this interphase region, we observe a deviation from bulk adhesion and modulus values beginning ∼440 nm away from the uncoated glass bead C. The adhesion value decreases ∼130 nN moving from∼440 nm to ∼95 nm away from the interface, while the modulus increases ∼45 MPa. We again define this change from bulk properties as the ‘weakly bound interphase’ region, highlighted in green in figure 12. As the tip moves closer to the embedded bead, a second discernable change in the adhesion and modulus values is realized. From∼95 nm away from uncoated bead C to the bead edge in the “tightly bound interphase” region, the adhesion value decreases ∼200 nN while the modulus increases ∼290 MPa. The total change in height over both the “weakly bound interphase” and ‘tightly bound interphase” regions was nearly 450 nm, and the total interphase width is measured to be ∼450 nm for uncoated bead C in this sample. Fig. 12 Line scan across the interphase region of a P4000 (4 wt. %) glass bead (bead C) showing the evolution in height (top, red circles), adhesion (middle, black circles), and modulus (bottom, blue circles) of the sample. The green highlighted areas show a “weakly bound interphase” region and the yellow highlighted areas show a “tightly bound interphase” region (see main text for explanation) Finally, we investigate another bead within the same cross section of the P4000 (4 wt. %) sample, defined as bead D. Deviations from the bulk adhesion and modulus values begin∼2.3 µm away from uncoated glass bead D, shown in green in figure 13. From∼2.3 µm to 400 nm away from the uncoated glass bead D the adhesion value decreases ∼250 nN while the modulus increases ∼11 MPa. Moving from 400 nm away to the edge of the uncoated bead D, there is another stark change in the adhesion and modulus values over a 350 nm height gradient. The adhesion value drops ∼230 nN and the modulus
RkJQdWJsaXNoZXIy MTMzNzEzMQ==