Confinement-induced differences between dielectric normal modes and segmental modes of an ion-conducting polymer

Dielectric measurement in the range 0.1 Hz to 1 MHz were used to study the motions of polymers and ions in an ion-conducting polymer, polypropylene oxide containing small quantities (on the order of 1%) of lithium ions (LiClO₄), confined as a sandwich of uniform thickness between parallel insulating mica surfaces. In the dielectric loss spectrum, we observed three peaks; they originated from the normal mode of the polymer, segmental mode of the polymer, and ion motions. With decreasing film thickness, the peak frequencies corresponding to the normal mode and ion motion shifted to lower frequencies, indicating retardation due to confinement above 30 nm. This was accompanied by diminished intensity of the dielectric normal-mode relaxation, suggesting that confinement diminished the fluctuations of the end-to-end vector of the chain dipole in the direction between the confining surfaces. On the contrary, the segmental mode was not affected at that thickness. Finally, significant retardation of the segmental mode was observed only for the thinnest film (14 nm). The different dynamical modes of the polymer (segmental and slowest normal modes) respond with different thickness and temperature dependence to confinement. Received 31 August 2001 and Received in final form 30 October 2001     

Effect of Radiation Modification of Disperse Polyethylene on Component Interaction and Properties of GFRP Based on It

The basic aspects of interfacial interaction between the polymer binder and the filler in glass-fiber-reinforced plastics (GFRP) based on a high-density polyethylene (HDPE) are considered. The plastics were produced by the film-powder technology using a disperse radiation-modified HDPE as the binder. It is shown that the use of the -treated HDPE powder extends the capabilities of controlling the strength properties of GFRP sheets.     

Laser-assisted modification of polystyrene surfaces for cell culture applications

Laser-assisted patterning and modification of polystyrene (PS) was investigated with respect to applications in micro-fluidics and cell culture. For this purpose the wettability, the adsorption of proteins and the adhesion of animal cells were investigated as function of laser- and processing parameters. The change of surface chemistry was characterized by X-ray photoelectron spectroscopy. The local formation of chemical structures suitable for improved cell adhesion was realized on PS surfaces by UV laser irradiation. Above and below the laser ablation threshold two different mechanisms affecting cell adhesion were detected. In the first case the debris deposited on and along laser irradiated areas was responsible for improved cell adhesion, while in the second case a photolytic activation of the polymer surface including a subsequent oxidization in oxygen or ambient air is leading to a highly localized alteration of protein adsorption from cell culture media and finally to increased cell adhesion. Laser modifications of PS using suitable exposure doses and an appropriate choice of the processing gas (helium or oxygen) enabled a highly localized control of wetting. The dynamic advancing contact angle could be adjusted between 2° and 150°. The hydrophilic and hydrophobic behaviour are caused by chemical and topographical surface changes.     

Immobilization of poly(?-caprolactone)-poly(ethylene oxide)-poly(?-caprolactone) triblock copolymer on poly(lactide-co-glycolide) surface and dual biofunctional effects

Poly(?-caprolactone)-poly(ethylene oxide)-poly(?-caprolactone) (PCL-PEG-PCL) triblock copolymer was covalently immobilized onto poly(lactide-co-glycolide) (PLGA) surface with the precursor of photopolymerizable and biodegradable PCL-PEG-PCL diacrylates. Argon plasma technique was exploited to obtain hydrophilic PLGA surface (HPLGA). The surface properties were characterized by Water contact angle and X-ray photoelectron spectroscopy (XPS) techniques. PCL-PEG-PCL surface modified hydrophobic PLGA and hydrophilic PLGA results in different surface physicochemical properties. PCL-PEG-PCL modified hydrophobic PLGA surface (PLGA-PCL-PEG-PCL) demonstrates excellent inhibition of platelet adhesion and activation; while PCL-PEG-PCL modified hydrophilic PLGA surface (HPLGA-PCL-PEG-PCL) results in good cytocompatibility. The possible mechanism was discussed and the driven force was ascribed to the different assembly behavior of PCL-PEG-PCL on PLGA surface dependant on the hydrophilic/hydrophobic property of PLGA. This simple and effective surface engineering method is also suitable for the other biomaterials such as polyurethane (PU), silicon rubber and poly(ethylene terephthalate) (PET) to obtain the enhanced biocompatibility.     

A model for computational investigation of elasto-plastic normal and tangential contact considering adhesion effect

With the rapid development of Micro-Electro-Mechanical System (MEMS), we enter a field in which the surface effects have dominated many of the micro-scale phenomena, and the adhesive contact is one of the focuses. In this paper, a feasible model for finite element computation is presented via a macroscopic and microscopic combination approach, in which the adhesive forces are simulated by some non-linear spring elements considering the softening stage. Two basic problems concerning the adhesion effect were considered; through specific quantitative analysis, the results show a consistency with the current elastic continuum theories of adhesion and a brief investigation into the effects of adhesion on plastic deformation and tangential contact will be carried out as well. The project supported by the National Natural Science Foundation of China (10172050, 90205022) and Key Grant Project of Chinese MoE (0306)     

Experiments on transport of hydrophobic particles and gas bubbles in porous media

Adhesion of hydrophobic colloids (clay minerals) on the surface of bubbles of air and the transport of the composite units formed by bubbles and mineral particles were observed in a glass micro model.When a clay mineral suspension flowed in a porous medium that contained bubbles of air trapped in small pores, particles accumulated preferentially on the upstream portion of the bubbles, and quasi-stable bubble-mineral particle units were formed. With an increase in the flow velocity, the particles moved along the interface between the bubble and the liquid and accumulated on the downstream portion of the bubbles. A large stress could mobilize the units which, occasionally, accumulated in larger voids.The mechanism suggested is adhesion of the particles on the surface of the bubble due to compression of their diffuse electrical double layer. The adsorbed particles can be moved by shear stresses which act in the region of water molecules between the well-organized layers of water on the surfaces of the bubble and the clay particles. A large enough shear stress causes the bubbles to become more streamlined, allowing them to move in the channel system. If in contact, the common lamina of the bubbles can withdraw and rupture.Bubbles transport from 20 to 50 times more particles than can be transported by average suspension.     

Prediction of paddy soil normal adhesion to steel surfaces by fuzzy logic

Numerous data concerning paddy soil composition, water content and soil-steel normal adhesion were collected in South China during 1974-1983. The fuzzy logic relation of adhesion with clay content and water content was derived, by which paddy soil adhesion to steel surfaces was predicted if soil composition and water content were known.     

OPTIMUM DESIGN OF ADHESIVE BONDING OFRESIN-BASE COMPOSITES

I.IntroductionThemajorityofproductsofthefiberreinforcedcompositemateria1sareinthin-walIstructure.Themeritsofcompositesmaybefullyplayedbytheadhesivebonding.Theadhesivebondinghasfollowingadvantages:a.thejointofthesameordifferentkindsofmaterialsmayberealized…     

Kombucha SCOBY Waste as a Catalyst Support

It is established that food waste can be repurposed to extend its lifecycle and decrease its carbon footprint. In this work, SCOBY (symbiotic culture of bacteria and yeast) waste from kombucha tea production has been repurposed as a catalyst support. Copper nanoparticles (Cu NPs) have been embedded in a piece of treated SCOBY via an in-situ method which enabled the catalyst, inCu/t-SCOBY, to be easily recycled. In addition, inCu/t-SCOBY catalyzed the full reduction of 4-nitrophenol in an excess of sodium borohydride (NaBH₄) within 20 minutes. After 6 additional catalytic cycles, the catalyst maintained up to 50% of its performance in the first cycle. Characterization of the catalyst has also been done to understand the mechanism of action and interactions occurring between t-SCOBY and Cu NPs. The results of this work clearly present a proof-of-concept in utilizing porous wastes materials such as SCOBY as catalyst supports, allowing metallic NPs to be efficacious and practical heterogenous catalysts.     

Bacterial Nanocellulose in Dentistry: Perspectives and Challenges

Bacterial cellulose (BC) is a natural polymer that has fascinating attributes, such as biocompatibility, low cost, and ease of processing, being considered a very interesting biomaterial due to its options for moldability and combination. Thus, BC-based compounds (for example, BC/collagen, BC/gelatin, BC/fibroin, BC/chitosan, etc.) have improved properties and/or functionality, allowing for various biomedical applications, such as artificial blood vessels and microvessels, artificial skin, and wounds dressing among others. Despite the wide applicability in biomedicine and tissue engineering, there is a lack of updated scientific reports on applications related to dentistry, since BC has great potential for this. It has been used mainly in the regeneration of periodontal tissue, surgical dressings, intraoral wounds, and also in the regeneration of pulp tissue. This review describes the properties and advantages of some BC studies focused on dental and oral applications, including the design of implants, scaffolds, and wound-dressing materials, as well as carriers for drug delivery in dentistry. Aligned to the current trends and biotechnology evolutions, BC-based nanocomposites offer a great field to be explored and other novel features can be expected in relation to oral and bone tissue repair in the near future.