Plasma technology has been widely used to increase the surface energy of the polymer surfaces for many industrial applications; in particular to increase in wettability. The present work was carried out to investigate how surface modification using plasma treatment modifies the surface energy of micro-injection moulded microneedles and its influence on drug delivery. Microneedles of polyether ether ketone and polycarbonate and have been manufactured using micro-injection moulding and samples from each production batch have been subsequently subjected to a range of plasma treatment. These samples were coated with bovine serum albumin to study the protein adsorption on these treated polymer surfaces. Sample surfaces structures, before and after treatment, were studied using atomic force microscope and surface energies have been obtained using contact angle measurement and calculated using the Owens-Wendt theory. Adsorption performance of bovine serum albumin and release kinetics for each sample set was assessed using a Franz diffusion cell. Results indicate that plasma treatment significantly increases the surface energy and roughness of the microneedles resulting in better adsorption and release of BSA.
This paper presents a novel method to prepare stretchable conductors and pressure sensors based on the gold/polydimethylsiloxane (PDMS) system. The gold films were sputtered onto structured PDMS surfaces produced with a photolithographic surface treatment with the aim of reducing tensile strains in the gold film. Scanning electron microscopy (SEM) and atomic force microscopy analyses showed that these 3D patterns reduce cracks and delaminations in the gold film. Electrical measurements indicate that the patterns also protect the films against repeated tensile cycling, although the un-patterned samples remained conducting as well after the completion of 120 cycles. The extrapolated resistivity value of the patterned sample (4.5 × 10 −5 cm) compares well with previously published data. SEM micrographs indicate that the pattern features deflect the cracks and therefore toughen the gold film. However, x-ray photoelectron spectroscopy and contact angle analyses indicate that the patterning process also slightly modifies the surface chemistry. This patterning method was used to prepare capacitive strain gauges with pressure sensitivity (Z/Z)/P of 0.14 kPa −1 in the sub-kPa regime. Such stretchable and potentially conformal low-pressure sensors have not been produced before and could prove advantageous for many smart fabric applications.
Gold on polydimethylsiloxane (PDMS) stretchable conductors were prepared using a novel approach by interlacing an hydrogenated amorphous carbon (a-C:H) layer between the deposited metal layer and the elastomer. AFM analysis of the a-C:H film surface before gold deposition shows nanoscale buckling, the corresponding increase in specific surface area corresponds to a strain compensation for the first 4-6 % of bi-axial tensile loading. Without this interlayer, the deposited gold films show much smaller and uni-directional ripples as well as more cracks and delaminations. With a-C:H interlayer, the initial electrical resistivity of the metal film decreases markedly (280-fold decrease to 8x10 -6 Ω.cm). This is not due to conduction within the carbon interlayer; both a-C:H/PDMS and PDMS substrates are electrically insulating. Upon cyclic tensile loading, both films become more resistive, but return to their initial state after 20 tensile cycles up to 60% strain. Profiling experiments using Secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS) indicate that the a-C:H layer intermixes with the PDMS, resulting in a graded layer of decreasing stiffness. We believe that both this graded layer and the surface buckling contribute to the observed improvement in the electrical performance of these stretchable conductors.
Citation: Gao Y, Dong X, Wang L et al (2015) Flow-induced crystallization of long chain aliphatic polyamides under a complex flow field: Inverted anisotropic structure and formation mechanism. Polymer. 73: 91-101. The present work deals with the flow-induced multiple orientations and 13 crystallization structure of polymer melts under a complex flow field. This complex 14 flow field is characteristic of the consistent coupling of extensional "pulse" and 15 closely followed shear flow in a narrow channel. Utilizing an ingenious combination 16 of an advanced micro-injection device and long chain aliphatic polyamides (LCPA), 17 the flow-induced crystallization morphology was well preserved for ex-situ 18 2 synchrotron micro-focused wide angle X-ray scattering (μWAXS) as well as small 19 angle X-ray scattering (SAXS). An inverted anisotropic crystallization structure was 20 observed in two directions: perpendicular and parallel to the flow direction (FD). The 21 novel anisotropic morphology implies the occurrence of wall slip and "global" 22 fountain flow under the complex flow field. The mechanism of structure formation is 23 elucidated in detail. The experimental results clearly indicate that the effect of 24 extensional pulse on the polymer melt is restrained and further diminished due to 25 either the transverse tumble of fountain flow or the rapid retraction of stretched high 26 molecular weight tails. However, the residual shish-kebab structures in the core layer 27 of the far-end of channel suggest that the effect of extensional pulse should be 28 considered in the small-scaled geometries or under the high strain rate condition. 29
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