Effect of conformational change on nanoscale friction behavior of organic thin films

The overarching theme of this dissertation is to probe relationships between structure of organic thin films and their specific functional property of friction in the context of various engineering applications. Two specific thin film systems were studied - biological macromolecules in total joint replacements and self-assembled alkanethiol monolayers for microdevice applications. Before delving into the actual systems, a thorough understanding of friction at small length scales was required. To address this, a friction study of two material pairs (Si3N4/mica and Si3N4/ultra-high molecular weight polyethylene) was conducted using a microtribometer and atomic force microscope (AFM) at the micro- and nanometer length scales respectively, while keeping the environmental and counterface conditions same at both scales and thereby evaluating contact area dependence in the absence of surface damage and contact area independence when damage occurs. Biological macromolecules such as proteins and lipids are important constituents of the synovial fluid which is the natural lubricant present in all of our human joints. The effect of adsorbed films of proteins and lipids on the micro/nanoscale tribological response of the polymeric materials used in total joint replacements (TJRs) were investigated. The friction and wear response of UHMWPE samples with different crystallinities was studied in the presence of bovine serum albumin protein and phospholipids. The observed friction increase upon exposure to proteins was attributed to the formation of a layer of denatured proteins on the surface. Changing the crystallinity and surface energy of UHMWPE affected the protein adsorption mechanism and the resulting increase in friction behavior. It was also found that increased crystallinity lowered the friction response and increased the scratch and wear resistance at both micro and nanoscales. It was also found that higher crystallinity increased the adsorption of the phospholipid and acted as an effective lubricant reducing the friction response and increasing the wear resistance of the interface. The surface stress generation during the formation of a self-assembled monolayer (SAM) of alkanethiols on a macroscale domain was investigated in order to exploit this effect for sensing systems. To that effect, a curvature interferometry technique was used to study the surface stress generated during the formation of octadecanethiol SAM on a 25 mm x 25 mm mica sample. It was seen that the magnitude of surface stress measured on macroscale domain compared well with previously reported measurement on micron sized domains. The possibility of utilizing a SAM system as a means to achieve active friction modulation of a surface was also investigated. A low-density SAM system, shown to exhibit conformational changes in the presence of an electric field, was synthesized and its friction response was studied using an AFM. Friction experiments showed that in the presence of a positive bias, the film showed a higher friction response (up to 300%) than when a negative bias was applied. The difference in the friction responses was attributed to the changes in the structural and crystalline order of the film between the two bias conditions

Quantitative friction force microscopy for micro/nanoscale friction studies of joint replacement materials

Tribological properties of the contacting surfaces in a Total Joint Replacement (TJR) affect its performance significantly. Ultra-high Molecular Weight Polyethylene (UHMWPE) has been widely used as one of the contacting surfaces in TJRs. In this thesis, the friction behavior of UHMWPE as a function of soaking time in bovine serum as well as serum concentration was investigated using friction force microscopy (FFM). Three lateral calibration methods (Ogletree et.al, Ruan and Bhushan, Cain et.al.) for quantitative FFM have been analyzed and compared using a silicon sample. Cain et.al.\u27s method could not be used for the load range and the cantilever setup used in this study. The values obtained from Ogletree\u27s method and Ruan and Bhushan\u27s method differed by almost two orders of magnitude, with Ruan and Bhushan\u27s method yielding a lower value. These lateral calibration procedures were used to obtain quantitative friction data and interfacial shear stress on an UHMWPE sample. The shear strength value from Ruan and Bhushan\u27s method was comparable to literature values. It was concluded that for the soft commercial Si3N4 cantilevers used, Ruan and Bhushan\u27s method yielded more appropriate reliable calibration factors, whereas Ogletree\u27s and Cain\u27s methods are more suitable for stiffer cantilevers. The effect of soaking time in bovine serum and concentration of bovine serum on frictional behavior of UHMWPE samples were analyzed. The immersion of samples in bovine serum increased the friction and shear strength of the UHMWPE - Si3N4 interface. But, at a lower concentration (10 vol%) of bovine serum, the soaking time did not have an effect on the friction and shear strength. At a higher concentration (60 vol%), the friction and shear strength increased as the soaking time was increased. Fluorescence measurements indicated an increase in protein adsorption with soaking time for higher concentration (60 vol%). Contact angle measurements indicated that the UHMWPE surface became increasingly hydrophilic as the soaking time was increased. The presence of denatured proteins on the hydrophobic polymeric surface forming a higher shear strength layer was therefore suggested as the reason for observed friction behavior

India: a twisted trajectory

The fish-processing industry’s path of using fishmeal to grow shrimp amounts to exporting the precious nutrition that India’s children badly need. In the early morning of 25 September 2019, on the shores of Cuddalore in Tamil Nadu, India, the humble sardine commenced its journey. The journey of its afterlife, that is. A group of women waited together, empty baskets in hand, chatting while waiting for the boats to arrive. Their expectations do not remain unanswered. Boats bulging with little shiny sardines return from calm seas. Boats carrying sardines, along with their histories of struggle. Big trawlers, small trawlers, ring seines, fibreglass boats: everyone has been scooping up schools of sardine today

How safe are our children in vehicles on the road? a Malaysian perspective

As Malaysia races towards a developed nation status, children are increasingly being ferried daily in vehicles almost exclusively as the majority of the population are able to afford private transportations. This paper reviews the current safety concerns for children whilst going in vehicles on Malaysian roads and the steps undertaken to address the need to enhance children’s safety whilst going in these vehicles and suggest possible remedial action to counter the possible lack of awareness for children’s safety whilst in these vehicles. This paper focuses on children on motorcycles and private vehicles (cars, vans and multi-purpose vehicle (MPV)) and excludes other form of transport (buses, lorries) as this paper tries to put forth measures that can be undertaken by the children’s parents and guardian to better enhance the safety of their children. A search was undertaken of all the major database of articles. Articles related to children’s safety systems, children related injuries, children related accident data, available laws and legislation were reviewed to present the need for greater awareness of children’s safety while going in vehicles in Malaysia. There are currently already safety legislations, measures, steps and equipments in place in ensuring the safety of children whilst going in vehicles on Malaysian roads. However, enforcement of laws in developing countries are not easy and we have to start at the root of the problem which is the parents and adults who ferry these children in vehicles. There is a pressing need to educate parents and adults alike on the urgent undertaking of child safety whilst in vehicles. Engineering countermeasures and intervention are probably needed to protect these vulnerable users. For vehicles, a device capable of providing some sort of protection to the child whilst riding pillion should be designed and developed. A legislation mandating the use of child seats whilst ensuring the child seats are affordable to the masses

Asia-Pacific mussel watch: monitoring contamination of persistent organochlorine compounds in coastal waters of Asian countries

Contamination of persistent organochlorines (OCs) such as PCBs (polychlorinated biphenyls), DDT and its metabolites (DDTs), HCH (hexachlorocyclohexane) isomers (HCHs), chlordane compounds (CHLs), and HCB (hexachlorobenzene) were examined in mussels collected from coastal waters of Asian countries such as Cambodia, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, Philippines, Far East Russia, Singapore, and Vietnam in 1994, 1997, 1998, 1999, and 2001 to elucidate the contamination status, distribution and possible pollution sources and to assess the risks on aquatic organisms and human. OCs were detected in all mussels collected from all the sampling sites investigated. Considerable residue levels of p,p′-DDT and α-HCH were found in mussels and the concentrations of DDTs and HCHs found in mussels from Asian developing countries were higher than those in developed nations suggesting present usage of DDTs and HCHs along the coastal waters of Asian developing countries. On the other hand, lower concentrations of PCBs detected in mussels from Asian developing countries than those in developed countries indicate that PCBs contamination in mussels is strongly related to industrial and activities. To our knowledge, this is a first comprehensive report on monitoring OCs pollution in the Asia-Pacific region

Tamil Nadu

Tese mest. , Gestão da Água e da Costa, 2007, Universidade do AlgarveThis study examines the requirement of innovative Integrated Coastal Zone Management (ICZM) curriculum at postgraduate professional education, and identifies the potential professional skills required for the coastal managers in India especially in Tamil Nadu region. This need is essential because, coastal zones in Tamil Nadu are under risk due to carious natural and human impacts, and conflicts between multi-users. The recent Tsunami in December 2004, has led coastal communities into vulnerable, poverty, unemployment and health problems. The sectoral management approaches are often seem to be as singlesector service oriented (Cicin-Sain et al., 2000; Tissier et al., 2004) and proved incapable to deliver ICZM project effectively in Tamil Nadu. Thus, managing coastal challenges requires skilled professionals with a mixed-knowledge across the disciplines. This research work is apart of an ongoing curriculum development project based on ICZM at higher professional education in India. Results and discussion are based on the filed work carried out to identify the potential skills required for the coastal managers in Tamil Nadu. This study evaluates coastal threats and challenges in India. It describes the state of higher professional education in coastal and marine science degrees. A discussion of global efforts and solutions provided by the scholars and international agencies on ICZM education and training are discussed. This study describes the coastal zone management and ICZM education trend in India. A detailed discussion has presented on the requirement of innovative ICZM curriculum, and potential professional skills to addressing the coastal challenges and delivering ICZM programs efficiently in Tamil Nadu. Finally, this study has presented possible solutions with the balanced curriculum that need to be addressed in the ICZM education for best practices at higher professional education in Tamil Nadu

Effect of conformational change on nanoscale friction behavior of organic thin films

The overarching theme of this dissertation is to probe relationships between structure of organic thin films and their specific functional property of friction in the context of various engineering applications. Two specific thin film systems were studied – biological macromolecules in total joint replacements and self-assembled alkanethiol monolayers for microdevice applications. Before delving into the actual systems, a thorough understanding of friction at small length scales was required. To address this, a friction study of two material pairs (Si3N4/mica and Si3N4/ultra-high molecular weight polyethylene) was conducted using a microtribometer and atomic force microscope (AFM) at the micro- and nanometer length scales respectively, while keeping the environmental and counterface conditions same at both scales and thereby evaluating contact area dependence in the absence of surface damage and contact area independence when damage occurs. Biological macromolecules such as proteins and lipids are important constituents of the synovial fluid which is the natural lubricant present in all of our human joints. The effect of adsorbed films of proteins and lipids on the micro/nanoscale tribological response of the polymeric materials used in total joint replacements (TJRs) were investigated. The friction and wear response of UHMWPE samples with different crystallinities was studied in the presence of bovine serum albumin protein and phospholipids. The observed friction increase upon exposure to proteins was attributed to the formation of a layer of denatured proteins on the surface. Changing the crystallinity and surface energy of UHMWPE affected the protein adsorption mechanism and the resulting increase in friction behavior. It was also found that increased crystallinity lowered the friction response and increased the scratch and wear resistance at both micro and nanoscales. It was also found that higher crystallinity increased the adsorption of the phospholipid and acted as an effective lubricant reducing the friction response and increasing the wear resistance of the interface. The surface stress generation during the formation of a self-assembled monolayer (SAM) of alkanethiols on a macroscale domain was investigated in order to exploit this effect for sensing systems. To that effect, a curvature interferometry technique was used to study the surface stress generated during the formation of octadecanethiol SAM on a 25 mm x 25 mm mica sample. It was seen that the magnitude of surface stress measured on macroscale domain compared well with previously reported measurement on micron sized domains. The possibility of utilizing a SAM system as a means to achieve active friction modulation of a surface was also investigated. A low-density SAM system, shown to exhibit conformational changes in the presence of an electric field, was synthesized and its friction response was studied using an AFM. Friction experiments showed that in the presence of a positive bias, the film showed a higher friction response (up to 300%) than when a negative bias was applied. The difference in the friction responses was attributed to the changes in the structural and crystalline order of the film between the two bias conditions

Effect of conformational change on nanoscale friction behavior of organic thin films

The overarching theme of this dissertation is to probe relationships between structure of organic thin films and their specific functional property of friction in the context of various engineering applications. Two specific thin film systems were studied - biological macromolecules in total joint replacements and self-assembled alkanethiol monolayers for microdevice applications. Before delving into the actual systems, a thorough understanding of friction at small length scales was required. To address this, a friction study of two material pairs (Si3N4/mica and Si3N4/ultra-high molecular weight polyethylene) was conducted using a microtribometer and atomic force microscope (AFM) at the micro- and nanometer length scales respectively, while keeping the environmental and counterface conditions same at both scales and thereby evaluating contact area dependence in the absence of surface damage and contact area independence when damage occurs. Biological macromolecules such as proteins and lipids are important constituents of the synovial fluid which is the natural lubricant present in all of our human joints. The effect of adsorbed films of proteins and lipids on the micro/nanoscale tribological response of the polymeric materials used in total joint replacements (TJRs) were investigated. The friction and wear response of UHMWPE samples with different crystallinities was studied in the presence of bovine serum albumin protein and phospholipids. The observed friction increase upon exposure to proteins was attributed to the formation of a layer of denatured proteins on the surface. Changing the crystallinity and surface energy of UHMWPE affected the protein adsorption mechanism and the resulting increase in friction behavior. It was also found that increased crystallinity lowered the friction response and increased the scratch and wear resistance at both micro and nanoscales. It was also found that higher crystallinity increased the adsorption of the phospholipid and acted as an effective lubricant reducing the friction response and increasing the wear resistance of the interface. The surface stress generation during the formation of a self-assembled monolayer (SAM) of alkanethiols on a macroscale domain was investigated in order to exploit this effect for sensing systems. To that effect, a curvature interferometry technique was used to study the surface stress generated during the formation of octadecanethiol SAM on a 25 mm x 25 mm mica sample. It was seen that the magnitude of surface stress measured on macroscale domain compared well with previously reported measurement on micron sized domains. The possibility of utilizing a SAM system as a means to achieve active friction modulation of a surface was also investigated. A low-density SAM system, shown to exhibit conformational changes in the presence of an electric field, was synthesized and its friction response was studied using an AFM. Friction experiments showed that in the presence of a positive bias, the film showed a higher friction response (up to 300%) than when a negative bias was applied. The difference in the friction responses was attributed to the changes in the structural and crystalline order of the film between the two bias conditions.</p

The barnacle, Xenobalanus globicipitis (Cirripedia, Coronulidae), attached to the bottle-nosed dolphin, Tursiops truncatus (Mammalia, Cetacea) on the southeastern Coast of India

10.1163/156854004774248753Crustaceana777879-882CRUS