The use of polymer blends is continually gaining interests among researchers as an efficient approach for addressing some of the challenges in different fields. In particular, nontoxic polycaprolactone (PLC) are widely used in medical applications owing to their relatively good biocompatibility and biodegradability properties. Despite the similar crystalline structure of polycaprolactone and polyethylene derived from an orthorhombic unit cell, they form immiscible blends. They, however, exhibit the effects of enhancing the biodegradation and hydrophobic properties of the polycaprolactone/poly(ethylene glycol) blends. Unfortunately, crystallization of polyethylene glycol polymers in such blends is generally challenging due to the similarity of their melting points.
Changing the crystallization conditions i.e. temperature and polymer composition have been previously used to prevent simultaneous crystallization during quenching. Consequently, the resulting competition between the crystallization and the liquid-liquid phase separation makes the characterization of the polymers at the sub-micrometer level more difficult to obtain.
In a recently published literature, atomic force microscopy coupled with infrared spectroscopy enabled access to various microscopic processes at the nanoscale level. This is an added advantage especially for characterization of the polymer distribution of an immiscible blend and the aging mechanism of the coatings. Alternatively, research has shown that controlling of the architecture and properties of the polycaprolactone/poly(ethylene glycol) blends is mainly dependent on the crystallization mechanism, phase separation and chemical interactions at the interphases. This requires development of more efficient characterization tools with enhanced microscale and nanoscale resolution.
Recently, Professor Phuong Nguyen Tri at Université du Québec à Trois-Rivieres and Professor Robert Prud’homme at University of Montreal studied the crystallization and segregation behavior of immiscible polycaprolactone/poly(ethylene glycol) blends. In particular, atomic force microcopy coupled with infrared spectroscopy was utilized to achieve a relatively high spatial resolution ranging from 30nm-50nm. The main aim was to determine the different segregation mechanisms and the associated morphological structures during isothermal crystallization of the polycaprolactone/poly(ethylene glycol) blends. The research work is currently published in the research journal, Macromolecules.
In brief, the authors commenced their research work by cross-examining the morphological architecture, chemical interactions, and properties of the polycaprolactone/poly (ethylene glycol) blends. Next, infrared chemical mapping was used to explore the segregation mechanisms and morphological structures of the resulting spherulites. Additionally, atomic force microscopy was used to determine the topographical images at nanoscale levels.
The Professor Nguyen-Tri and Professor Prud’homme observed different nanoscale infrared spectra on both sides of the spherulitic interfaces. This was attributed to the dependence of the spherulitic structures on the chemical infrared images of the blends. Generally, the blends exhibited a two-step crystallization process at a low crystallization temperature of 30 °C. Here, the segregation of the poly(ethylene glycol) and amorphous polycaprolactone took place outside the spherulites because the spherulites were mainly composed of the polycaprolactone. On the other hand, the blends of poly (ethylene glycol) and polycaprolactone simultaneously crystallized at a high crystallization temperature of 40°C even though the poly (ethylene glycol) was segregated at the sub-micrometer scale. An upper critical solution temperature was used to explain the whole phenomenon. Atomic force microscopy-based infrared spectroscopy enabled investigation of the isothermal crystallization behavior and phase separation of the polycaprolactone/poly(ethylene glycol) blends with different spherulites and nodules spectra.
Nguyen Tri, P., & Prud’homme, R. (2018). Crystallization and Segregation Behavior at the Submicrometer Scale of PCL/PEG Blends. Macromolecules, 51(18), 7266-7273.Go To Macromolecules