The Selection And Phase Transformation Behavior Of Polymer Crystals In Aao Nano-confined Space

Using anodic aluminum oxide template to prepare nano-materails is one of the most popular methods.The differences between infiltrated polymer in AAO template and bulk polymer have been widely reported.But there still have many problems need to be solved,such as the different roles of nano-size effect,surface-induce effect and curvature effect on the selection of crystal and crystal transformation.In the present study,we chose two different typical polymorphic polymer,Poly(L-lactic acid)(PLLA)and isotactic Poly(l-butene)(iPB),to study their crystallization behavior in AAO.The main results are showed below:Firstly,we discovered when PLLA is fabricated in AAO,the morphology of PLLA is deeply dependent on the diameter of nanopores:PLLA formed as nanorods in the nanopores with 40-70 nm and 80-100 nm diameter and formed as nano-tubes in the nanopores with the diameter of 160-200 nm and 200-300 nm.Through analyzing the results of X-ray diffraction(XRD)and Fourier transformed infrared(FTIR),the differences and similarities between infiltrated PLLA and bulk PLLA at the behavior of melting-recrystallization have been explored.As it shows in these results,we found that ?'-form of bulk PLLA crystallized below 100? and crystallized?-form above 120?,while infiltrated PLLA crystallized both ?-form and?'-form below 100 ?(at 80 ?).Meanwhile,with the increasing nanoporous diameter,the contents of ?-form increased and that of ?'-form decreased.After study,we discovered that this phenomenon is caused by the surface-induced effect of aluminum oxide.The ?-form of PLLA crystallized nearby the nanoporous wall and ?'-form crystallized far from it.The contents of ?'-form increased with the increasing of the thickness of the wall of nano-tubes,and this model of the structure of crystal distribution has been testified.With the decreasing of the diameter of nanopores,the crystal transformation temperature of PLLA in AAO confined space increases,and the transformation becomes more and more difficult.Beyond that,the effects of nanopores on the crystal transformation of iPB have been studied.After cooling from amorphous state,iPB crystallized form ? at 25? instantly and then transformed into Form ?.However,as it show in the results of XRD and DSC,the time of phase transformation in infiltrated iPB is longer than that in bulk iPB.After the transformation reached the proportion of 70%,no transformation occurred anymore.However,exact opposite phenomenon observed in FTIR results with Form ?formed in infiltrated iPB.Comparing the results of different facilities,we find that the Form ? molecular chain fast segment conversion is out of sync with lacttice change.Through these studies,the effects of polymer crystallization and crystal transformation in AAO nanopores have been studied.In addition,the crystal transformation mechanism of iPB has been explored.