40 50 60 70 80 $_{0s}$10s 1 0 ◦ C 0s 10s 40 50 60 70 80 0s 10s 1 5 ◦ C 0s 10s 40 50 60 70 80 0s 10s 2 0 ◦ C 0s 10s 40 50 60 70 80 0s 10s 2 2 . 5 ◦ C 0s 10s 40 50 60 70 80 0s 10s 2 5 ◦ C 0s 10s 40 50 60 70 80 0s 10s 3 5 ◦ C 0s 10s f$_{0}$ (pN) f$_{0}$ (pN) f$_{0}$ (pN) composition composition FIG. 4: (Color) ‘Dynamic phase diagram’ for 40 kbp fragments of λ -DNA with one free end, at salt concentration c =150 mM. The dynamic stretching protocol is as Fig. 3, except that the molecular stretching rate is 100 nm/s rather than 1000 nm/s. In general, more U-DNA is seen here then in Fig. 3: here, attainment of the target force f$_{0}$ takes of order hundreds of seconds near 65 pN, and as a result the molecule has more time to unpeel than it does at the smaller stretching rate. 11