Unusual Radiating-Stripe Morphology in Nonequimolar Mixtures of Poly(l-lactic acid) with Poly(d-lactic acid)

Abstract

Extensive microscopic and thermal analyses and X-ray diffraction characterizations are conducted to investigate an unusual morphology and its evolution in extreme nonequimolar mixtures of poly­(L-lactic acid)­(PLLA) with poly­(D-lactic acid) (PDLA) containing a trace amount of stereocomplex crystals. Radiating-stripe spherulites are crystallized on first-grown PLLA/PDLA sc-crystals that act as template substrates for later-grown PLLA. Growth kinetics are analyzed to attempt interpretations on understanding why the unusual PLLA morphology with distinct large radiating dendrites can be packed only in narrow ranges of nonequimolar PLLA/PDLA = 98/2 to 90/10 mixtures and only when crystallized within a suitable T c range of 125–140 °C. Additionally, the interior lamellar assembly for the radiating-stripe PLLA spherulites is dissected to correlate with this unusual morphology with rodlike optical birefringence patterns.

Unique Periodic Rings Composed of Fractal-Growth Dendritic Branching in Poly(p-dioxanone)

“…The growth cycles repeat in the same manner, with fractal branching to fill the ever-expanding space as the lamellae grow outward from the nucleus center. It can be shown later that the increase of the number of branches of the lobs of dendrites roughly follows the Fibonacci sequence, also reported earlier in many other polymer systems with dendritic growth [31][32][33][34][35]. Furthermore, interfacial crevices between the neighboring lobs of dendrites are clearly seen in the AFM height images (Figure 5a).…”

“…6.1 μm, as shown in Figure 4 c. The growth cycles repeat in the same manner, with fractal branching to fill the ever-expanding space as the lamellae grow outward from the nucleus center. It can be shown later that the increase of the number of branches of the lobs of dendrites roughly follows the Fibonacci sequence, also reported earlier in many other polymer systems with dendritic growth [ 31 , 32 , 33 , 34 , 35 ].…”

“…The number of branches was estimated and plotted as a function of distance from the nucleus center, as shown in Figure 11c. The increasing number of branches of the lobs of dendrites roughly follows the Fibonacci sequence, which is also observed in many other polymer systems with dendritic growth [31][32][33][34][35]. Figure 11 show a chopped sector of the dendritic/ringed PPDO spherulite, containing three lobs of dendrites with 6-10 branches packed with ring bands in each lob.…”

“…The number of branches was estimated and plotted as a function of distance from the nucleus center, as shown in Figure 11c. The increasing number of branches of the lobs of dendrites roughly follows the Fibonacci sequence, which is also observed in many other polymer systems with dendritic growth [31][32][33][34][35]. There is an issue concerning whether the crystallization of PPDO (from PPDO/PVPh blend) might result in the expulsion or segregation of the PVPh component from the PPDO lamellae or interphases in the aggregates.…”

“…An increase in the branch number as the growth starts from the nucleus center to the periphery is apparent, and this multiplication of branches is necessary to fill the ever-expanding space. The number of branches was estimated and plotted as a function of distance from the nucleus center, as shown in Figure 11 c. The increasing number of branches of the lobs of dendrites roughly follows the Fibonacci sequence, which is also observed in many other polymer systems with dendritic growth [ 31 , 32 , 33 , 34 , 35 ].…”