1,720,961 research outputs found
Engineering poly(dimethylsiloxane) grafted chains for enhanced droplet mobility and abrasion resistance
Get PDFThis thesis presents a comprehensive study of surface-grafted polydimethylsiloxane (PDMS) brushes, focusing on their structure-property relationships and potential applications as omniphobic coatings. By tuning molecular parameters such as chain length, grafting density, and terminal functionality, the wetting behavior, mechanical durability, and contact angle hysteresis (CAH) of PDMS surfaces were systematically analyzed. These coatings aim to replace the traditional fluorinated materials, offering a more environmentally friendly alternative for omniphobic applications. The study begins with a background on oleophobic coatings, highlighting PDMS brushes as an ideal candidate due to their unique properties. Current techniques for characterizing polymer brushes at the nanoscale are reviewed, addressing challenges in determining their structural and interfacial properties.
Using a vapor deposition method, omniphobicity was demonstrated on smooth gold surfaces grafted with PDMS chains. Cleaving these chains for molecular weight analysis revealed a value of ~7800 g/mol, corresponding to a transition between the mushroom and brush regimes, with ~96% of the surface remaining unreacted. Terminal hydrophilic silanol groups were identified in the uppermost layer, which were partially capped with trimethylsilyl groups to enhance hydrophobicity.
High dynamic droplet friction, a common issue with PDMS brushes, was mitigated by capping silanol groups. This reduced chain relaxation times from seconds to milliseconds, significantly improving droplet mobility. Additionally, altering the surrounding vapor to pentane enhanced droplet velocity on a 10° tilted surface by over 50 times compared to air.
Addressing low abrasion resistance, thicker PDMS brush layers were achieved through vapor deposition, which led to the formation of nanodroplets via autophobic dewetting. Stepwise growth of these nanodroplets was controlled, resulting in enhanced abrasion tolerance and improved liquid repellency, withstanding up to 1,000 abrasion cycles, whereas a PDMS-grafted surface without nanodroplets lost its omniphobicity after 500 cycles.
This thesis demonstrates that surface-grafted PDMS brushes are a promising material for next-generation omniphobic coatings, offering potential solutions for a range of applications, including self-cleaning surfaces, anti-fouling coatings, and liquid-repellent materials. The findings provide a pathway for the development of durable, fluorine-free alternatives to existing surface technologies, with a focus on sustainability and long-term performance.Ph.D
Fabrication and characterization of smooth omniphobic surfaces
No full textLiquid fouling can reduce the functionality of critical engineering surfaces. Recent studies have shown that minimizing contact angle hysteresis is a promising strategy for achieving omniphobic (all-liquid repellent) properties, thereby inhibiting fouling. Prior omniphobic films can repel a broad range of liquids, but the applicability of these coatings has always been limited to silicon wafers or smooth glass. Here we develop a facile procedure to generate an omniphobic coating on any surface, including metals, paper, ceramics, etc. The coating involves depositing an ultra-smooth, silicon wafer-like silica layer and then treating this layer with a highly reactive chlorosilane, which grafts polydimethylsiloxane chains onto the surface. Negligible contact angle hysteresis (≤ 1°) for various liquids, including ultra-low surface tension oils, alcohols, and fluoro-solvents, was achieved on many different substrates regardless of their initial roughness or chemistry. In fact, the contact angle hysteresis was so low we were forced to propose an alternate measurement technique, using tilt angles, that reduced the inherent errors associated with traditional contact angle goniometry. The coating’s durability was characterized and, when it was damaged, could be repeatedly repaired, fully restoring the omniphobic properties to their initial state. Moreover, we introduced another potential application of these surfaces.
Viscosity measurement using a small amount of fluids is crucial since it is one of the most important parameters of a liquid. Recent studies have shown that there is a relation between viscosity and dynamic behavior of droplets on a surface. Our coating showed a promising performance confirming these relationships due to it ultra-low contact angle hysteresis. Hence, we used them to create a surface viscometer which can measure the viscosity of a wide range of liquids using only one droplet.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
