PEDOT:PSS Conductivity Enhancement through Addition of the Surfactant Tween 80.

Replacement of indium tin oxide with the intrinsically conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been of significant interest in recent years as a result of lower processing and material costs. In addition, the inclusion of additives has been reported to further enhance the conductivity, rheology, and wettability of PEDOT:PSS. In this study, Tween 80 was shown to decrease the sheet resistance of PEDOT:PSS films from approximately 1000 to 76 Ω□-1 at a 2.67 wt% surfactant concentration. Through X-ray diffraction, Raman spectroscopy, and atomic force microscopy, it was shown that the surfactant caused phase separation and structural ordering of the PEDOT and PSS components, leading to this improvement in conductivity. Furthermore, Tween 80 altered the rheological properties and decreased the surface tension of PEDOT:PSS, making coating common commodity polymers, often used as flexible substrates, more viable.

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry.

This paper demonstrates the application of a modified Avrami equation in the analysis of crystallisation curves obtained using differential scanning calorimetry (DSC). The model incorporates a square root of time dependence of the secondary process into the conventional Avrami equation and, although previously validated using laser flash analysis and infrared spectroscopy, is not currently transferable to DSC. Application of the model to calorimetric data required long-duration isotherms and a series of data treatments. Once implemented, the square root of time dependence of the secondary process was once again observed. After separation of the secondary process from the primary, a mechanistic n value of 3 was obtained for the primary process. Kinetic parameters obtained from the analysis were used in the model to regenerate the fractional crystallinity curves. Comparison of the model with experimental data generated R2 values in excess of 0.995. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was used as model polymer due to the prominent secondary crystallisation behaviour that this polymer is known to display.

Crosslinker Copolymerization for Property Control in Inverse Vulcanization.

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.

Formulation of a covalently bonded hydroxyapatite and poly(ether ether ketone) composite.

Spinal fusion devices can be fabricated from composites based on combining hydroxyapatite and poly(ether ether ketone) phases. These implants serve as load-bearing scaffolds for the formation of new bone tissue between adjacent vertebrae. In this work, we report a novel approach to covalently bond hydroxyapatite and poly(ether ether ketone) to produce a novel composite formulation with enhanced interfacial adhesion between phases. Compared to non-linked composites (HA_PEEK), covalently linked composites (HA_L_PEEK), loaded with 1.25 vol% hydroxyapatite, possessed a greater mean flexural strength (170 ± 5.4 vs 171.7 ± 14.8 MPa (mean ± SD)) and modulus (4.8 ± 0.2 vs 5.0 ± 0.3 GPa (mean ± SD)). Although the mechanical properties were not found to be significantly different (p > 0.05), PEEK_L_HA contained substantially larger hydroxyapatite inclusions (100-1000 µm) compared to HA_PEEK (50-200 µm), due to the inherently agglomerative nature of the covalently bonded hydroxyapatite and poly(ether ether ketone) additive. Larger inclusions would expectedly weaken the HA_L_PEEK composite; however, there is no significant difference between the flexural modulus of poly(ether ether ketone) with respect to HA_L_PEEK (p = 0.13). In addition, the flexural modulus of HA_PEEK is significantly lower compared to poly(ether ether ketone) (p = 0.03). Ultimately, covalent linking reduces hydroxyapatite particulate de-bonding from the polymeric matrix and inhibits micro-crack development, culminating in enhanced transfer of stiffness between hydroxyapatite and poly(ether ether ketone) under loading.

Active screen plasma surface modification of polycaprolactone to improve cell attachment.

To tailor polycaprolactone (PCL) surface properties for biomedical applications, film samples of PCL were surface modified by the active screen plasma nitriding (ASPN) technique. The chemical composition and structure were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The wettability of the surface modified polymers was investigated by contact angle and surface energy methods. Biocompatibility of the prepared PCL samples was evaluated in vitro using MC3T3-E1 osteoblast-like cells. The degradability was assessed by determining the self-degradation rate (catalyzed by lipase). The results show that ASPN surface modification can effectively improve osteoblast cell adhesion and spreading on the surface of PCL. The main change in chemical composition is the exchange of some carboxyl groups on the surface for hydroxyl groups. The active-screen plasma nitriding technique has been found to be an effective and practical method to effectively improve osteoblast cell adhesion and spreading on the PCL surface. Such changes have been attributed to the increase in wettablity and generation of new hydroxyl groups by plasma treatment. After active-screen plasma treatment, the PCL film is still degradable, but the enzymatic degradation rate is slower compared with untreated PCL film.

Effect of sterilisation by gamma irradiation on the ability of polycaprolactone (PCL) to act as a scaffold material.

This paper investigates the effect of sterilisation by gamma irradiation (dose 2.5Mrad) on the following properties of polycaprolactone (PCL): (1) degradation rate (catalysed by lipase), (2) mechanical properties, (3) the ability of cells to attach and subsequently grow on its surface. Gel permeation chromatography (GPC) was used to determine the effects of gamma irradiation of weight average (M(w)) and number average (M(n)) molecular weights. Gamma irradiation significantly decreased the rate of degradation, although the rates depended on the initial mass of polymer; it also affected the appearance of the degraded specimens when they were examined by scanning electron microscopy. Irradiation also significantly increased the mechanical yield stress but not the failure stress of PCL. It caused a significant increase in M(w) and decrease in M(n) that could be attributed to chain scission and cross-linking. Chondrocyte attachment and growth on PCL was not significantly affected by gamma irradiation.