Bioinspired mechanically durable superliquiphilic/phobic surfaces

Living nature, through some 3 billion years of evolution, has developed materials, objects, and processes that function from the nanoscale to the macroscale. The understanding of the functions provided by species and processes found in living nature can guide us to design and produce bioinspired surfaces for various applications1,2. There are a large number of flora and fauna with properties of commercial interest. Nature provides many examples of surfaces that repel (hydrophobic) or attract (hydrophilic) water. The most famous is the lotus leaf. Its surface contains a hierarchical structure that, combined with specific surface chemistry, results in a water repellant surface that is self-cleaning, as water droplets collect contaminants as they roll off. Some plant leaves, such as fagus leaves, are hydrophilic, allowing water to rapidly spread into a thin layer, increasing evaporation, leading to a dry and self-cleaning surface. By taking inspiration from nature, it is possible to create hierarchically –structured surfaces with re-entrant geometry and surface chemistry that provide multifunctional properties including superliquiphilicity/phobicity, self-cleaning/low biofouling, and/or low drag. A facile, substrate-independent, multilayered nanoparticle/binder composite coating technique has been developed to produce various combinations of water and oil repellency and affinity with self-cleaning properties3. These coatings having a so-called re-entrant geometry can also repel surfactant-containing liquids. Some of the nanostructured surfaces have been found to be anti-bacterial4. These coatings provide the basis to fabricate surfaces for a range of applications including self-cleaning, anti-fouling, anti-smudge, anti-fogging, anti-icing, low drag, water purification, and oil–water separation1,5,6. The coatings have been found to be mechanically durable and some, optically transparent. [1]Bhushan, B., Biomimetics: Bioinspired Hierarchical-Structured Surfaces for Green Science and Technology, third ed., Springer (2018). 2Nosonovsky, M. and Bhushan, B., Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer (2008). 3Bhushan, B., “Lessons from Nature for Green Science and Technology: An Overview and Superliquiphoboc/philic Surfaces,” Phil. Trans. R. Soc. A 377, 20180274 (2019). 4Bixler, G. D., Theiss, A., Bhushan, B., and Lee, S. C., “Anti-fouling Properties of Microstructured Surfaces Bio-inspired by Rice Leaves and Butterfly Wings,” J. Colloid Interface Sci. 419, 114-133 (2014). 5Nosonovsky, M. and Bhushan, B., Green Tribology: Biomimetics, Energy Conservation and Sustainability, Springer (2012). 6Bhushan, B., “Bioinspired Water Collection Methods to Supplement Water Supply,” Phil. Trans. R. Soc. A 377, 20190119 (2019)

Structural, nanomechanical, and nanotribological characterization of human hair and conditioner using atomic force microscopy and nanoindentation

Human hair is a nanocomposite biological fiber. Maintaining the health, feel, shine, color, softness, and overall aesthetics of the hair is highly desired. Hair care products such as shampoos and conditioners, along with damaging processes such as chemical dyeing and permanent wave treatments, affect the maintenance and grooming process and are important to study because they alter many hair properties. Nanoscale characterization of the cellular structure, mechanical properties, and morphological, frictional, and adhesive properties (tribological properties) of hair are essential to evaluate and develop better cosmetic products, and to advance the understanding of biological and cosmetic science. The tensile response of hair is of considerable interest. Another property of interest is the surface charge of hair, which has a significant effect on manageability, feel, and appearance. For this reason, controlling charge buildup to improve these factors is an important issue in the commercial hair care industry. The atomic/friction force microscope (AFM/FFM) and nanoindenter have recently become important tools for studying the micro/nanoscale properties of human hair. In this talk, we present a comprehensive review of the cellular structural, nanomechanical, and nanotribological properties of various hair and skin as a function of ethnicity, damage, conditioning treatment, and various environments1-2. Various cellular structures of human hair and fine sublamellar structures of the cuticle are identified and studied. Nanomechanical properties such as hardness, elastic modulus, creep and scratch resistance are discussed. Nanotribological properties such as roughness, friction, and adhesion are presented, as well as investigations of conditioner distribution, thickness, and binding interactions. 1Bhushan, B., “Nanoscale Characterization of Human Hair and Hair Conditioners,” (invited), Prog. Mat. Sci. 53, 585-710 (2008). 2 Bhushan, B., Biophysics of Human Hair – Structural, Nanomechanical, and Nanotribological Studies, Springer-Verlag, Heidelberg, Germany (2010)

Bioinspired materials for water collection, water purification and oil-water separation

Access to a safe supply of water is a human right. However, with growing populations, global warming, and contamination due to human activity, it is one that is increasingly under threat. It is hoped that nature can inspire the creation of materials to aid in the supply and management of water, from water collection and purification to water source clean up and rehabilitation from oil contamination. Many living species thrive in even the driest places, with some surviving on water harvested from fog1,2,3. Due to temperatures lower than dew point in the deserts at night, water condensation also occurs from ambient2,3. By studying living species, new materials can be developed to provide a source of fresh water from fog and condensation for communities across the globe as well as in emergency and defense applications2,3. The vast majority of water on Earth is in the oceans. However, current desalination processes are energy intensive. Systems in our own bodies have evolved to transport water efficiently while blocking other molecules and ions. Inspiration can be taken from such to improve the efficiency of desalination and help purify water containing other contaminants1,2,3. Finally, oil contamination of water from spills or the fracking technique can result in devastating environmental disasters1,2. By studying how natural surfaces interact with liquids, new techniques can be developed to clean up oil-spills and further protect our most precious resource4. 1Brown, P. S. and Bhushan, B., “Bioinspired Materials for Water Supply and Management: Water Collection, Water Purification, and Separation of Water from Oil,” Phil. Trans. R. Soc. A 374, 20160135 (2016). 2Bhushan, B., Biomimetics: Bioinspired Hierarchical-Structured Surfaces for Green Science and Technology, third ed., Springer (2018). 3Bhushan, B., “Bioinspired Water Collection Methods to Supplement Water Supply,” Phil. Trans. R. Soc. A 377, 20190119 (2019). 4Bhushan, B., “Bioinspired Oil-water Separation Approaches for Oil Spill Cleanup and Water Purification,” Phil. Trans. R. Soc. A 377, 20190120 (2019)

The Effect of Process Parameters and Surface Condition on Bond Strength between Additively Manufactured Components and Polymer Substrates

Additive patching is a process in which printers with multiple axes deposit molten material onto a pre-defined surface to form a bond. Studying the effect of surface roughness and process parameters selected for printing auxiliary part on the bond helps in improving the strength of the final component. Particularly, the influence of surface roughness, as established by adhesion theory, has not been evaluated in the framework of additive manufacturing (AM). A full factorial design of experiments with five replications was conducted on two levels and three factors, viz., layer thickness, surface roughness, and raster angle to examine the underlying effects on bond strength. Analysis of variance (ANOVA) was used to test the resultant index and distributions were plotted to analyze various conditions. Experimental results indicated that bond strength increased up to 27% at higher surface roughness and lower layer thickness levels. Full factorial experiments with additional levels were conducted to realize the direction of improvement and find optimum values of layer thickness and surface roughness. It was found that at a layer thickness of 0.1 mm and 502.94 µin of surface roughness bond strength attains the highest value. This research represents a first step towards understanding bond strength in patching/re-manufacturing, allowing manufacturers to intelligently select process parameters for the production of both the substrate and the added geometry

Hospital Efficiency: An Empirical Analysis of District and Grant-in-Aid Hospitals in Gujarat

This study focuses on analysing the hospital efficiency of district level government hospitals and grant-in-aid hospitals in Gujarat. The study makes an attempt to provide an overview of the general status of the health care services provided by hospitals in the state of Gujarat in terms of their technical and allocative efficiency. One of the two thrusts behind addressing the issue of efficiency was to take stock of the state of healthcare services (in terms of efficiency) provided by grant-in-aid hospitals and district hospitals in Gujarat. The motivation behind addressing the efficiency issue is to provide empirical analysis of governments policy to provide grants to not-for-profit making institutions which in turn provide hospital care in the state. The study addresses the issue whether grant-in-aid hospitals are relatively more efficient than public hospitals. This comparison between grant-in-aid hospitals and district hospitals in terms of their efficiency has been of interest to many researchers in countries other than India, and no consensus has been reached so far as to which category is more efficient. The relative efficiency of government and not-for-profit sector has been reviewed in this paper. It is expected that the findings of the study would be useful to evaluate this policy and help policy makers to develop benchmarks in providing the grants to such institutions.

Slip-length measurement of confined air flow using dynamic atomic force microscopy

We present an experimental measurement of the slip length of air flow close to solid surfaces using an atomic force microscope (AFM) in dynamic mode. The air was confined between a glass surface and a spherical glass particle glued to an AFM cantilever. The Knudsen number was varied continuously over three decades by varying the distance between the two surfaces. Our results show that the effect of confining the air is purely dissipative. The data are described by an isothermal Maxwell slip-boundary condition, and the measured slip-length value was 118 nm

Adhesion and friction between individual carbon nanotubes measured using force-versus-distance curves in atomic force microscopy

The adhesion and friction between individual nanotubes was investigated in ambient using a dynamic atomic force microscope (AFM) operating in force-calibration mode to capture force-versus-distance curves. A multiwalled carbon nanotube (MWNT) tip attached to a conventional AFM probe was brought into contact with and then ramped in vertical direction against a single-walled carbon nanotube (SWNT) bridge suspended over a 2-μm-wide trench. The interaction between nanotubes altered the oscillation amplitude, phase lag, and average deflection of AFM cantilever, from which the interacting forces between nanotubes are quantitatively derived. During ramping, a stick-slip motion was found to dominate the sliding between the nanotubes. The stick was attributed to the presence of high-energy points, such as structural defects or coating of amorphous carbon, on the surface of the MWNT tip. The coefficients of static friction and shear strength between nanotubes were evaluated to be about 0.2 and 1.4 GPa, respectively. They are about 2 orders of magnitude larger than the kinetic counterparts. The kinetic values are on the same order as that measured previously by sliding a MWNT tip across a SWNT bridge in lateral direction

Nanofatigue Studies of Ultrathin Hard Carbon Overcoats Used in Magnetic Storage Devices

A technique to perform nanofatigue experiments was developed. This technique utilizes a depth-sensing nanoindenter with harmonic force. The nanofatigue behavior of 20 nm thick amorphous carbon coatings was studied. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. It was found that the filtered cathodic arc coating exhibits longer fatigue life than a direct ion beam coating. Failure mechanisms of the coatings during fatigue are also discussed in conjunction with the hardness,elastic modulus, and fracture toughness, as well as deposition processes. The dynamic nanoindentation fatigue test used in this study can be satisfactorily used to simulate and study damage at the head–disk interface

Study of implications of thyroid status over feto-maternal outcomes in pregnancy

Background: Thyroid disorders are reported at clinically significant prevalence during pregnancy, affecting ~5% of all pregnancies. Maternal thyroid status during pregnancy purportedly affects fetal as well as maternal outcomes. The objective of present study was to analyse the relationship of thyroid status in pregnancy and various maternal and fetal outcomes.Methods: In this hospital based observational study, a total of 913 pregnant women were enrolled as per fixed criteria and all the study participants were screened for thyroid disorders. Further, they were followed up throughout pregnancy and puerperium and evaluated for various maternal and fetal complications by predefined outcome measures. The results were compared by subgroup analysis.Results: Of the 913 patients screened, 105 were diagnosed with thyroid abnormality and followed up till delivery, with newborn thyroid profile on day 7. Total 49 patients were diagnosed with anaemia (46.66%), of which 46 (43.80%) had subclinical hypothyroidism (p <0.05); along with pregnancy induced hypertension in 42 (40%) cases of which 40 (38.09%) had subclinical hypothyroidism were observed to have statistically significant associations. Intrauterine growth restriction (IUGR) (37, 35.23%) and prematurity (19, 18.1%) were the most common fetal occurrences; the association of IUGR and subclinical hypothyroidism being statically significant.Conclusions: Thyroid disorders during pregnancy are commonly associated with maternal and fetal complications and thyroid profile is recommended as universal screening method in early pregnancy to diagnose and start required treatment early