Polymer Pin Research Articles

A DLVO model for catalyst motion in metal-assisted chemical etching based upon controlled out-of-plane rotational etching and force-displacement measurements

Metal-assisted Chemical Etching of silicon has recently emerged as a powerful technique to fabricate 1D, 2D, and 3D nanostructures in silicon with high feature fidelity. This work demonstrates that out-of-plane rotational catalysts utilizing polymer pinning structures can be designed with excellent control over rotation angle. A plastic deformation model was developed establishing that the catalyst is driven into the silicon substrate with a minimum pressure differential across the catalyst thickness of 0.4-0.6 MPa. Force-displacement curves were gathered between an Au tip and Si or SiO(2) substrates under acidic conditions to show that Derjaguin and Landau, Verwey and Overbeek (DLVO) based forces are capable of providing restorative forces on the order of 0.2-0.3 nN with a calculated 11-18 MPa pressure differential across the catalyst. This work illustrates that out-of-plane rotational structures can be designed with controllable rotation and also suggests a new model for the driving force for catalyst motion based on DLVO theory. This process enables the facile fabrication of vertically aligned thin-film metallic structures and scalloped nanostructures in silicon for applications in 3D micro/nano-electromechanical systems, photonic devices, nanofluidics, etc.

Tribological performance of industrial polyamide-imide and its composite under different cooling conditions

Abstract Polyamide-imide (PAI) polymer is a high-temperature resistant polymer, which is used as contact breaker material because of its high electrical insulation property. The working conditions of contact breakers arise from the wear and friction problem conditions of these materials. Therefore, the tribological behavior of PAI polymer is important. In this study, the friction and wear performance of pure PAI polymer and PAI composite [PAI+12% graphite+3% polytetrafluoroethylene (PTFE)] were studied in two different cooling environmental conditions (with and without air cooling). Wear tests were carried out with the configuration of a polymer pin, on a rotating AISI 316 L stainless steel disc. Test conditions were atmospheric conditions, 50 N, 100 N, and 150 N loads and 0.5, 1.0, 2.0 and 3.0 m/s sliding speeds. For sliding without air cooling and sliding with air cooling, the results show that the coefficient of friction and wear rates for pure PAI and PAI+12% graphite+3% PTFE composite, slightly decrease and increase with the increase in applied load and sliding speed values, respectively. In addition, for the range of loads and sliding speeds of this study, low coefficients of friction and high specific wear rates are registered at sliding under air cooling conditions. Finally, the wear mechanism includes adhesive and abrasive processes.

Tax policy developments, donor inflows and economic growth in Malawi

In this investigation the friction and wear performance of GUR 1020 medical grade ultra-high molecular weight polyethylene (UHMWPE) polymer under dry sliding, distilled water and egg albumen lubrication conditions were evaluated. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI 304L stainless steel disc. Wear tests were carried out for 30 min duration at room temperature with 50, 100 and 150 N applied load values and at 0.50, 1.0 and 2.0 m/s sliding speeds condition. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is more significantly influenced by applied load and sliding speed values under dry sliding condition rather than lubricant media condition. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and speed values. This increase is much pronounced under dry sliding condition. Moreover, for the range of load and speed values of this study the specific wear rate using egg albumen lubricant registered lower values than that of the distilled water lubricant and the dry conditions. Finally, the specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry, water lubricant and egg albumen lubricant conditions are at the levels of 8x10-14, 1.4x10-14 and 0.5x10-14m2/N respectively. Key words: Medical Grade UHMWPE, tribology, distilled water, wear.

In Vivo Tissue Response to Ultrasound Assisted Application of Biodegradable Pins into Cortical and Cancellous Bone Structures: A Histological and Densitometric Analysis in Rabbits

In orthopaedic traumatology biodegradable pins are increasingly used for fixation of small bone fragments. In the present study, the ultrasound-assisted anchoring technique (SonicFusion technique), a osteosynthesis method being recently introduced in cranial applications, in which ultrasonic energy is used to insert and anchor polymer pins in bone, was compared with the conventional pin application procedure. The aim of the present study was to assess the short and long term thermal impact of two different ultrasonic energy levels on different bone structures in the distal medial femur of rabbits. The treatment groups consisted of customized polylactide pins applied at a low and a high energy level, the Reference Control and a Negative Control. The thermal effect on bone tissues was evaluated by means of qualitative and semi-quantitative histology and micro-computerized tomography. Five days following surgery, all implant sites showed no tissue damage but normal signs of early ongoing tissue repair. Enhancing the energy level by about 30% had no significant impact on the tissue response. At 4 weeks after surgery test sites covered by ultrasound-aided implantation showed a significantly enhanced bone/implant contact as compared to pins applied by conventional application. In conclusion, the ultrasound assisted anchoring technique not only did not impair bone regeneration, but even improved implant integration.

Tribological behavior of an ultrahigh molecular weight polyethylene in lubricated environments

AbstractThe wear and friction performance of GUR 1020 grade ultrahigh molecular weight polyethylene (UHMWPE) polymer was studied in distilled water, HASS (Hank’s balanced salt solution) and several protein lubrication environments. Wear tests were carried out using polymer pin -on AISI 304L stainless steel disc apparatus. Tests conditions were room temperature, 40N, 80N and 120N applied loads and 0.5 m/s sliding speed. For the range of load and speed value of this work, the coefficient of friction and wear rate for UHMWPE polymer decreases with the increase in applied load values. The coefficient of friction is highest and the specific wear rate values is lowest under HASS +HA solution lubricant. The average specific wear rate values for UHMWPE polymer under distilled water and HASS+HA (Hank’s balanced salt solution with Hyaluronic acid) lubrication conditions are in the order of 9x10-15 m2/N and 3x10-15 m2/N respectively. The wear mechanism includes abrasion and adhesive processes.

The use of BoneWelding® technology in spinal surgery: an experimental study in sheep.

The innovative BoneWelding(®) technology, where ultrasound energy bonds bioresorbable implants to bone, was tested for its feasibility in spine surgery and its local thermal effects. The three tested concepts consisted of implementation of a resorbable plating system, two converging polymer pins and suture anchors to the cervical vertebral bodies. Bioresorbable polylactide implants (PLDLLA 70/30) were inserted ventrally into the third and fourth vertebral body of seven sheep, of which six were sacrificed at 2months and one sheep immediately after temperature measurements during implant insertion. Polymer screws were used as controls. Qualitative, semi-quantitative histological, and quantitative histomorphometrical evaluation showed excellent anchorage of the implants, new mineralized bone at the implant-bone interface, no inflammatory cell reaction or thermal damage to the adjacent bone in response to the novel insertion technology. The application of two converging pins, parallel inserted polymer pins, or fusion of the implant to the polymer plates did not affect the overall excellent tissue tolerance of the technology. Temperature increase during insertion was noticed but never exceeded 47°C for less than 1s. The BoneWelding(®) technology was proven to be safe and easy to apply.

A solvable model for homopolymers and self-similarity near the critical point

We consider a model for the distribution of a long homopolymer with an attractive zero-range potential at the origin in (polymer pinning and de-pinning). The distribution can be obtained as a limit of Gibbs distributions corresponding to properly normalized potentials concentrated in small neighborhoods of the origin as the size of the neighborhoods tends to zero. The distribution depends on the length T of the polymer and a parameter γ that corresponds, roughly speaking, to the difference between the inverse temperature in our model and the critical value of the inverse temperature. At the critical point γ cr = 0 the transition occurs from the globular phase (positive recurrent behavior of the polymer, γ > 0) to the extended phase (Brownian type behavior, γ < 0). The main result of the paper is a detailed analysis of the behavior of the polymer when γ is near γ cr . Our approach is based on analyzing the semigroups generated by the self-adjoint extensions ℒ γ of the Laplacian on parametrized by γ , which are related to the distribution of the polymer. The main technical tool of the paper is the explicit formula for the resolvent of the operator ℒ γ .

Evaluation of new radiolucent polymer headholder pins for use in intraoperative computed tomography

With the introduction of intraoperative CT (iCT) scanning, neurosurgeons can now obtain images of the brain during surgery, offering the possibility of intraoperative resection control and monitoring of potential intraoperative complications. The combination of iCT with neuronavigation makes it possible to update the reference scans intraoperatively when necessary. However, the headholder pins normally used for iCT scanning still show artifacts. In the present study, new polymer pins, producing nearly no artifacts in laboratory tests, are compared with the usual pins with regard to their mechanical and artifact behavior to evaluate their potential use in the clinical routine. Pins made of different materials (titanium, Macor, silicon nitride, zirconium oxide, sapphire, polyetheretherketone, and polyparaphenylene copolymer) were used for the fixation of 10 cadaveric heads. Special force sensors measured the fixation pressure of the pins, and histological analysis revealed the penetration depth. Computed tomography scans of a head phantom, fixed with the different pins, were obtained to reveal artifact behavior. All pins were biocompatible. Pins did not differ significantly in fixation pressures and mechanical behavior. Penetration depths were comparable (maximum 1.4 mm) and did not cause opening of the diploe. Polymer pins made of polyparaphenylene showed the best results in artifact behavior in CT scans. The authors' results demonstrate that the new polymer pins are comparable in their mechanical behavior to the usual pins but superior in artifact behavior. Therefore, their use in the clinical routine of iCT scanning will be beneficial for the surgeon.

Tribological and nanoscale research on model friction couples intended for hip joint prostheses

The paper presents the results of tribological and nanoscale research on model friction couples intended for hip joint prostheses. The tribological tests were performed by means of reciprocating pin on plate testing machine. The investigated friction pairs contained plates rubbing against polymer pins. The test plates were made from seven kinds of ceramics containing different concentrations of ZrO2 and Al2O3, and two kinds of Co–Cr alloy. The test pins were made from UHMWPE. Tribological tests were performed in conditions of Ringer solution circulation. On the basis of friction force measurements, for each investigated friction couple, the average coefficient of friction was calculated. On the basis of total wear measurements, for each investigated couple, the wear intensity was calculated. Before and after every test, the plates and pins were analysed by means of atomic force microscopy. The difference in plate surface roughness was determined by the results of the atomic force microscopy analyses.It was stated, that in the case of investigated friction joints, working under reciprocating motion, the wear and friction coefficient correlates with the surface roughness of plate specimens. For the plates with higher surface roughness, the lower friction coefficient and also lower UHMWPE pin wear intensity were observed. The friction coefficient and wear intensity were increasing with decreasing surface roughness. The correlation is confirmed by the differences in material transfer process. Considering investigated friction couples, the pin polymer material is smeared on the ceramic plates with the highest surface roughness creating a thin polymer film. In the case of ceramic surfaces with the lowest surface roughness, the strong adhesive bounds are created and some large particles of polymer are transferred to ceramic surface.

Tribological properties of aramid–polypropylene composites from commingled yarns: influence of aramid fibre weight fraction

Commingling process involves the mixing of two types of filaments, viz. reinforcing and matrix-forming filaments in a nozzle with the help of compressed air leading to a homogenous distribution. During compression moulding, close placement of reinforcing and matrix-forming filaments reduces the mass transfer distance of the matrix and ensures proper wetting of fibres resulting in the enhanced properties of the composites. Three types of compression-moulded composites of polypropylene and Kevlar with different Kevlar fibre weight fractions were developed using commingled yarns. Studies on mechanical properties of these laminates confirmed that the composites having higher weight fraction of Kevlar fibre showed better tensile properties. Both abrasive and erosive wear rates showed a strong influence of Kevlar fibre weight fraction. With increase in weight fraction of Kevlar fibre, the erosion wear rate of the composites decreased as Kevlar fibres have higher wear resistance compared with polypropylene matrix. Similar trend was observed also in case of abrasive wear. The composites showed higher wear resistance while abrading the composite with polymer pin in a direction perpendicular to the fibre orientation as compared with abrading in a direction parallel to the fibre orientation.

On the irrelevant disorder regime of pinning models

Recent results have lead to substantial progress in understanding the role of disorder in the (de)localization transition of polymer pinning models. Notably, there is an understanding of the crucial issue of disorder relevance and irrelevance that is now rigorous. In this work, we exploit interpolation and replica coupling methods to obtain sharper results on the irrelevant disorder regime of pinning models. In particular, in this regime, we compute the first order term in the expansion of the free energy close to criticality and this term coincides with the first order of the formal expansion obtained by field theory methods. We also show that the quenched and quenched averaged correlation length exponents coincide, while, in general, they are expected to be different. Interpolation and replica coupling methods in this class of models naturally lead to studying the behavior of the intersection of certain renewal sequences and one of the main tools in this work is precisely renewal theory and the study of these intersection renewals.

The role of transfer film and back transfer behavior on the tribological performance of polyoxymethylene in sliding

The role of transfer films formed during the sliding of polymer composites against steel counterfaces was studied in terms of the tribological behaviors of the composites. The composites were prepared by compression molding and sliding tests were run in pin-on-disk sliding configuration. The counterface was made of tool steel hardened to 55–60 HRC and finished to a surface roughness of 0.09–0.10 μm Ra. Wear tests were run for 6 hrs at the sliding speed of 1.0 m/s and contact pressure of 0.65 MPa. Transfer films formed on the counterfaces during sliding were investigated using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The results showed that as the transfer film became smooth and uniform, the wear rate decreased. The examination of worn surfaces using Energy Dispersive Spectroscopy (EDS: dot mapping mode) showed the back-transfer of the steel counterface material to the polymer pin surface. This behavior is believed to strengthen the polymer pin surface during sliding thereby contributing to the decrease in wear rate.

An Ultrasound Assisted Anchoring Technique (BoneWelding® Technology) for Fixation of Implants to Bone – A Histological Pilot Study in Sheep

The BoneWelding® Technology offers new opportunities to anchor implants within bone. The technology melted the surface of biodegradable polymer pins by means of ultrasound energy to mould material into the structures of the predrilled bone. Temperature changes were measured at the sites of implantation in an in vitro experiment. In the in vivo part of the study two types of implants were implanted in the limb of sheep to investigate the biocompatibility of the method. One implant type was made of PL-DL-lactide (PLA), the second one was a titanium core partially covered with PLA. Healing period was 2 and 6 months, with 3 sheep per group. Bone samples were evaluated radiologically, histologically and histomorphometrically for bone remodeling and inflammatory reactions. Results demonstrated mild and short temperature increase during insertion. New bone formed at the implant without evidence of inflammatory reaction. The amount of adjacent bone was increased compared to normal cancellous bone. It was concluded that the BoneWelding® Technology proved to be a biocompatible technology to anchor biodegradable as well as titanium-PLA implants in bone.

Hierarchical pinning models, quadratic maps and quenched disorder

We consider a hierarchical model of polymer pinning in presence of quenched disorder, introduced by Derrida et al. (J Stat Phys 66:1189–1213, 1992), which can be re-interpreted as an infinite dimensional dynamical system with random initial condition (the disorder). It is defined through a recurrence relation for the law of a random variable {R n }n=1,2, ..., which in absence of disorder (i.e., when the initial condition is degenerate) reduces to a particular case of the well-known logistic map. The large-n limit of the sequence of random variables 2−n log R n , a non-random quantity which is naturally interpreted as a free energy, plays a central role in our analysis. The model depends on a parameter α ϵ (0, 1), related to the geometry of the hierarchical lattice, and has a phase transition in the sense that the free energy is positive if the expectation of R 0 is larger than a certain threshold value, and it is zero otherwise. It was conjectured in Derrida et al. (J Stat Phys 66:1189–1213, 1992) that disorder is relevant (respectively, irrelevant or marginally relevant) if 1/2 < α < 1 (respectively, α < 1/2 or α = 1/2), in the sense that an arbitrarily small amount of randomness in the initial condition modifies the critical point with respect to that of the pure (i.e., non-disordered) model if α ≥ 1/2, but not if α < 1/2. Our main result is a proof of these conjectures for the case α ≠ 1/2. We emphasize that for α > 1/2 we find the correct scaling form (for weak disorder) of the critical point shift.

Evaluation of tribological behaviour of PEEK and glass fibre reinforced PEEK composite under dry sliding and water lubricated conditions

In this study, the tribological performance of pure polyetheretherketone (PEEK) and 30 wt% fibre glass (GFR) reinforced PEEK composite were studied at dry sliding and water lubricated conditions. Wear tests were carried out with configuration of a polymer pin on a rotating AISI D2 disc. Test conditions were atmospheric conditions, 1.77, 3.54, 5.30 MPa pressures and 0.80, 1.60 m/s sliding speeds. The results show that the coefficient of friction and specific wear rates for pure PEEK and PEEK + 30 wt% GFR composite slightly in increase with the increase in applied pressure values. On the other hand the coefficient of friction is in decrease while the specific wear is in increase with the increase in sliding speed values. Moreover, for the range of pressure and sliding speed of this study, the coefficient of friction and specific wear rates using water lubricant registered lower values than that of the dry condition. The influence of GFR fibre on the coefficient of friction and wear of the composite is more pronounced at dry wear test condition. Finally the specific wear rates for pure PEEK and PEEK + 30 wt% GFR under water lubricated condition were in the order of 10 −15 m 2/N while under dry sliding condition this value is in the order of 10 −14 m 2/N.

Quantification of the effect of cross-shear on the wear of conventional and highly cross-linked UHMWPE

A computational model has been developed to quantify the degree of cross-shear of a polyethylene pin articulating against a metallic plate, based on the direct simulation of a multidirectional pin-on-plate wear machine. The principal molecular orientation (PMO) was determined for each polymer site. The frictional work in the direction perpendicular to the PMO was assumed to produce the greatest orientation softening [Wang et al., 1997. Orientation softening in the deformation and wear of ultra-high molecular weight polyethylene. Wear 203–204, 230–241]. The cross-shear ratio (CS) was defined as the frictional work perpendicular to the PMO direction, divided by the total frictional work. Cross-shear on the pin contact surface was location specific, and of continuously changing magnitude because the direction of frictional force continuously changed due to pin rotation. The polymer pin motion was varied from a purely linear track (CS=0) up to a maximum rotation of ±55° (CS=0.254). The relationship between wear factors ( K) measured experimentally and theoretically predicted CS was defined using logarithmic functions for both conventional and highly cross-linked ultra-high molecular weight polyethylene (UHMWPE). Cross-shear increased the apparent wear factor for both polyethylenes by more than fivefold compared to unidirectional wear.

Electrical and Optical Chip I/O Interconnections for Gigascale Systems

This paper describes fully compatible, high-density, electrical, and optical chip input/output (I/O) interconnect networks for gigascale systems. All optical I/O interconnects are based on the use of low-loss microscopic polymer pins (pillars). Their compatibility with electrical solder-bump fabrication and assembly are demonstrated. Moreover, we describe the use of metal-coated polymer pins to provide both an electrical path and an optical path between the chip and the substrate. Such I/O interconnects are called dual-mode I/Os. The tradeoffs between the electrical resistance and mechanical compliance of the dual-mode pins are reported. Moreover, the minimum thickness of metal needed to enable each I/O to operate at its electrical bit-rate limit is derived. A chip containing dual-mode I/Os is assembled on a substrate containing electrical and optical interconnects and demonstrates the dual-mode functionality of the I/Os. Dual-mode polymer pins that are 55 mum in diameter and 110 mum in height are measured to have an electrical resistance of approximately 50 mOmega and attenuate the optical intensity by less than 0.15 dB (632.8-nm wavelength). The use of an optical-bonding polymer is shown to improve optical coupling efficiency by up to 2 dB. Lateral and vertical compliance measurements of the polymer pin are also reported.

Development of severity parameter for wear study of thermoplastics

The effect of normal load, sliding velocity, roughness and counter-body material, on the wear behavior of POM and UHMWPE was studied. The pin-on-disc tests, with the polymeric pins and alumina and duplex stainless steel discs, were performed with three different levels of load, velocity and surface finishing of counter-face. For each one of the 36 test conditions 3 assays had been carried out. The near contact temperature, friction force and the vertical displacement of the pin, which was used to evaluate the wear rate of polymers, were recorded. The covered distance was of 3500 m and the tests were carried through in an environment with controlled air relative humidity in 50 ± 5%. The wear behavior was analysed and a severity parameter (PVR/D pD d) was proposed. This parameter considered mechanical factors ( P—contact pressure and V—velocity values), a topographical factor (roughness of counter-face, R) and a thermal factor (thermal diffusivity of the materials in contact, D pD d). It was observed that the vertical pin displacement occured not only due to the wear, but also due to the polymer creep and melting in extreme test conditions. The wear results were organized in the form of wear maps that considered three phenomena: creep, wear and melting. It was suggested that the more important factor controlling the wear rate is the capacity of heat dissipation at the contact region.

Friction and Wear Characteristics of PEEK and its Composite under Water Lubrication

The friction and wear performance of pure polyetheretherketone (PEEK) and 30% carbon fiber-reinforced PEEK composite were comparatively evaluated under dry sliding and water drops lubrication. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI D2 steel disc. Wear tests were carried out at room temperature under 50, 100, 150, and 200 N loads and at 0.40 m/s sliding speed. The results show that the coefficient of friction for pure PEEK increases with the increase in load value, while the coefficient of friction for 30% carbon fiber-reinforced PEEK is not significantly influenced by the increase in load. In addition, the coefficient of friction for PEEK + 30%CF is lower than that of pure PEEK at both dry sliding and water-lubricated conditions. Moreover, for the range of load and speed of this study, the coefficient of friction using water lubricant registered lower values than that of the dry condition. Finally, the specific wear rates for pure PEEK and PEEK + 30%CF composite under water-lubricated conditions were in the order of 10−15 m2/N, while under dry sliding conditions this value is in the order of 10−14 m2/N.

Polymer pinning at an interface

We consider a (1+1)-dimensional hydrophobic homopolymer, in interaction with an oil–water interface. In Z 2 , the interface is modelled by the x axis, the oil is above, the water is below, and the polymer configurations are given by a simple random walk ( S i ) i ≥ 0 . The hydrophobicity of each monomer tends to delocalize the polymer in the upper half-plane, through a reward h > 0 for each monomer in the oil and a penalty − h < 0 for each monomer in the water. On the other hand, the chain receives a random reward (or penalty) when crossing the interface, depending on a local random charge attached to the interface. At site i this reward is β ( 1 + s ζ i ) , where ( ζ i ) i ≥ 1 is a sequence of i.i.d. centered random variables, and s ≥ 0 , β ≥ 0 . Since the reward is positive on average, the interface attracts the polymer and a localization effect may arise. We transform the measure of each trajectory with the hamiltonian β ∑ i = 1 N ( 1 + s ζ i ) 1 { S i = 0 } + h ∑ i = 1 N sign ( S i ) , and study the critical curve h c s ( β ) that separates the ( β , h ) -plane into a localized and a delocalized phase for s fixed. It is not difficult to show that h c s ( β ) ≥ h c 0 ( β ) for all s ≥ 0 with the former explicitly computable. In this article we give a method for improving in a quantitative way this lower bound. To that end, we transform the strategy developed by Bolthausen and den Hollander in [E. Bolthausen, F. den Hollander, Localization for a polymer near an interface, Ann. Probab. 25 (3) (1997) 1334–1366], by taking into account the fact that the chain can target the sites where it comes back to the origin. The improved lower bound is interesting even for the case where only the interaction at the interface is active, i.e., for the pure pinning model. Our bound improves an earlier bound of Alexander and Sidoravicius in [K. Alexander, V. Sidoravicius Pinning of polymers and interfaces by random potential, 2005 (preprint). Available on: arXiv.org e-print archive: math.PR/0501028].