Influence of Poly(vinylphenol) Sublayer on the Crystallization Behavior of Poly(3-hydroxybutyrate) Thin Films

Lamellar orientation at the surface of isotactic polystyrene thin films analyzed by sum frequency generation spectroscopy

Analyzing the orientation of polymeric crystalline lamella at the surface of thin films can be challenging. Even though atomic force microscopy (AFM) is often sufficient for this analysis, there are cases when imaging is not sufficient to confidently determine lamellar orientation. Here, we used sum frequency generation (SFG) spectroscopy to analyze the lamellar orientation at the surface of semi-crystalline isotactic polystyrene (iPS) thin films. The SFG orientation analysis indicated that the iPS chains are oriented perpendicular to the substrate (flat-on lamellar orientation), which was confirmed by AFM. By analyzing the evolution of the SFG spectral features with the progress of crystallization, we demonstrated that the ratios of the SFG intensities of the phenyl ring resonances are a good indication of the surface crystallinity. Furthermore, we explored the challenges associated with SFG measurements of heterogeneous surfaces, which is commonly present in many semi-crystalline polymeric films. To the best of our knowledge, this is the first time that the surface lamellar orientation of semi-crystalline polymeric thin films was determined by SFG. Also, this work pioneers in reporting the surface conformation of semi-crystalline and amorphous iPS thin films by SFG and in linking the SFG intensity ratios to the progress of the crystallization and the surface crystallinity. This study demonstrates the potential applicability of SFG spectroscopy in the conformational analysis of polymeric crystalline structures at interfaces and opens the way to the investigation of more complex polymeric structures and crystalline arrangements, especially for the case of buried interfaces, where AFM imaging is not an option.

Supernucleation, crystalline structure and thermal stability of bacterially synthesized poly(3-hydroxybutyrate) polyester tailored by thymine as a biocompatible nucleating agent

Naturally occurring thymine (TM) was incorporated into bacterial poly(3-hydroxybutyrate) (PHB) polyester to fabricate a novel and green biocomposite. Both 0.5% and 1% TM exhibit supernucleation effect on PHB, and crystallization kinetics suggests TM significantly increased T_c and X_c, and substantially shortened t_1/2 of PHB. Epitaxial nucleation caused by a perfect crystal lattice matching between PHB and TM, was proposed to elucidate nucleation mechanism of PHB. Hydrogen bond interaction exists between CO, C-O-C groups of PHB and -CH₃ (or -CH)/-NH- group of TM. TM interacted with CO group of PHB crystalline phase rather than that of amorphous one. In addition, two new IR crystalline bands assigned to C-O-C group of PHB appeared in the presence of TM, which arises from shift of two amorphous ones, respectively. TM enhanced onset thermal degradation temperature of PHB, mainly attributed to increased degree of crystallinity of PHB and flame retardance effect of TM.

On the crystallization behavior of a poly(stearyl methacrylate) comb-like polymer inside a nanoscale environment

A “soft” or “hard” nanoscale template illustrates the confined processes of a poly(stearyl methylacrylate) comb-like polymer, indicating that reduced chain relaxation and mobility influence the crystallization behavior.

Microstructure-Dependent Charge Carrier Transport of Poly(3-hexylthiophene) Ultrathin Films with Different Thicknesses

Since the interfacial order of conjugated polymers plays an essential role for the performance of field-effect transistors, comprehensive understanding on the charge carrier transport in ultrathin semiconducting films below thicknesses of 10 nm is required for the development of transparent and flexible organic electronics. In this study, ultrathin films based on poly(3-hexylthiophene) as conjugated polymer model system with a thickness range from single monolayer up to several multilayers are investigated in terms of microstructure evolution and electrical properties of different molecular weights. Interestingly, a characteristic leap in field-effect mobility is observed for films with thickness greater than four layers. This threshold mobility regarding film thickness is attributed to the transition from 2D to 3D charge carrier transport along with an increased size of the P3HT aggregates in the upper layers of the film. These results disclose key aspects on the role of the film interlayer on the charge carrier transport through conjugated polymers in transistors.

Crystal Morphology of Poly(3-hydroxybutyrate) on Amorphous Poly(vinylphenol) Substrate

The crystalline morphology and orientation of poly(3-hydroxybutyrate) (PHB) thin film on the poly(vinylphenol) (PVPh) sublayer with different thickness was studied by atomic force microscopy, X-ray diffraction, and infrared spectroscopy. PVPh sublayer influences the morphology of PHB greatly. Although edge-on lamellae form on both Si and PVPh surfaces at relatively lower crystallization temperature, the morphology of them is quite different. It appears as sheaflike edge-on lamellar morphology on PVPh sublayer. In addition, the edge-on lamellae prefer to form on the PVPh sublayers at much higher crystallization temperature compared with that on Si wafer. The PVPh layer thickness also influences the crystalline morphology of PHB. On a 30 nm thick PVPh layer, sheaflike edge-on lamellae form in a wide range of crystallization temperatures. When the PVPh thickness increases to 65 nm, fingerlike morphology is observed when the crystallization temperature is lower than 95 °C. The fingerlike morphology is caused by a diffusion-limited aggregation process, and it requires an optimum condition. Thickness ratio between PHB and PVPh sublayer and temperature are two key factors for the formation of fingerlike morphology.

A grazing incident XRD study on the structure of poly(3-hydroxybutyrate) ultrathin films sandwiched between Si wafers and amorphous polymers

The crystallization behavior and morphology of poly(3-hydroxybutyrate) (PHB) ultrathin films sandwiched between Si wafers and amorphous thin polymer layers were studied by using grazing incident X-ray diffraction (GIXD) technology.

The development of a bilayer structure of poly(propylene carbonate)/poly(3-hydroxybutyrate) blends from the demixed melt

A PPC-top and microporous PHB-bottom bilayer film can be prepared from the dimixed PPC/PHB melt.