Measurements of the spreading and capillary forces for liquids deposited on solid surfaces of varying surface chemistry and topography are a prerequisite to better understanding and quantification of the wetting mechanisms. In this study, glass slide surfaces were modified with trimethylchlorosilane to fabricate surfaces of varying hydrophobicity. Then, the forces of spreading and adhesion were measured between water droplets and glass surfaces using a high-sensitivity microelectronic balance. Integrated with a digital camera, the experimental set-up recorded forces and water droplet deformations during water droplet attachment, spreading, compression and retraction processes. It was confirmed that the spreading force increases with decreasing advancing contact angle for methylated glass, following a similar correlation as observed for smooth and rough polymers. However, the spreading force values for methylated glass were a few times lower than reported for polymers in spite of a similar roughness characteristic. It was also confirmed that the maximum adhesion force between water droplet and methylated glass increases with decreasing value of the most stable contact angle, a correlation that is similar to that reported for smooth polymers. The paper entitled Spreading and adhesion forces for water droplets on methylated glass surfaces was published in Colloids and Surfaces A.
We really enjoyed the three-days visit by Sara Schellbach, our former undergraduate researcher, who graduated from MSE program in 2016. She currently works for GM, and pursues her MS degree at Wayne State University. Sara came with her brother who will join Michigan Tech in the fall semester. This was a great opportunity to gather entire team together for a pizza and beer at the Ambassador restaurant.
When Sara worked with us, she explored wettability of natural fibers, using a novel technique developed in our laboratory. Her paper entitled A novel method of contact angle measurements on natural fibers was published in Materials Letters. This paper has been well received, especially researchers who explore the use of natural fibers.
Zn-based alloys have been recognized as highly promising bioabsorbable materials for cardiovascular stents, due to their biocompatibility and, more importantly, favorable corrosion rates as compared to Mg alloys. However, both low tensile strength and intrinsic mechanical instability arisen from strong strain rate sensitivity and strain softening behavior make development of Zn alloys challenging for vascular scaffolding applications. In our new study published in Acta Biomaterialia and entitled Towards revealing key factors in mechanical instability of bioabsorbable Zn-based alloys for intended vascular stenting, which was carried out in collaboration with the researchers from the University of Sheffield and University of Oxford, we developed, processed and characterized binary Zn-4.0Ag and ternary Zn-4.0Ag-Mn alloys. An experimental methodology was designed by cold working followed by a thermal treatment on extruded alloys, through which the effects of the grain size and precipitates could be thoroughly investigated. Microstructural observations revealed a significant grain refinement during the cold wire drawing, leading to an equiaxed ultrafine grain (UFG) structure with an average size of 670 nm and 240 nm for the Zn-4.0Ag and Zn-4.0Ag-0.6Mn alloys, respectively. Mn showed a powerful grain refining effect as it promoted the dynamic recrystallization and hindered the growth of the UFG grains during the drawing process. In addition, cold working resulted in dynamic precipitation of markedly fine AgZn3 particles, distributing throughout the Zn matrix. Such strain-induced precipitates triggered mechanical degradation through an activation of Zn/AgZn3 boundary sliding, exhibiting maximum elongation of 430% and 203 % at the strain rate of 3.3 × 10−3 s−1 for Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. The observed precipitation softening phenomenon caused strong strain rate sensitivity and distinct strain softening behavior in the cold drawn alloys. Short-time annealing significantly mitigated the mechanical instability by reducing the AgZn3 volume fraction and thus, decreased the contribution of Zn/AgZn3 boundary sliding. The ternary alloy wire showed superior microstructural stability as compared to its Mn-free counterpart due to the pinning effect of nanosized Mn particles on the grain boundaries, restricting the grain coarsening. The corrosion results revealed that the microstructural manipulation strongly influenced the corrosion behavior of the Zn alloys so that the cold drawn wires exhibited intensive pitting corrosion. However, a shift of the corrosion regime from localized to a more uniform was observed after applying the heat treatment, mainly due to the dissolution of AgZn3 precipitates.
We welcome Ms. Isabelle Hemmila, who has joined our research team the Spring semester as an undergraduate researcher. Isabelle is majoring in materials science and engineering program. She has been assigned to assist Dr. Ehsan Mostaed and Ms. Emily Tom in their research on magnesium-based biodegradable alloys. We hope that her research experience will lead her towards her independent project next academic year.
An international team of experts in the field of wetting led by Dr. Drelich published a one-of-a-kind contribution on the history of contact angles, their meaning, and use in polymer surface energy estimation. The title of the paper is Contact angles: history of over 200 years of open questions and this paper was published in the first (double) issue of 2020 of Surface Innovations. There has been no similar historical perspective on the origins, evolution, scientific use, and healthy criticisms of the existing interpretations of contact angles offered by any other journal. This historical review will well serve researchers across the disciplines, guiding the readers into the scientific meaning of contact angles and their limitations, and providing directions for new developments in the area of science of contact angles.
We would like to share with you the content of the first issue of 2020, 8(1-2), of Surface Innovations. This is one of the most impressive issues that we published in seven years. We offer historical review contribution on contact angles, which is available online free-of-charge, and nine quality original papers on a broad variety of topics. Hope many of you will find something interesting among these papers.
2019 Half-Year Commencement was a celebration of Roger’s graduation with his parents and friends. It was also opportunity to meet Avishan (who defended her MS degree a few years ago) and her husband Rob – awarded with his PhD degree during this ceremony. Congratulations to Roger and Rob and all the students awarded with BS, MS and PhD degrees!
The SURFI Team welcomes a new addition to our team, Zhanglei Zhu. Zhanglei has arrived from the School of Resources and Civil Engineering at Northeastern University in P.R. China in October. He will explore fundamentals of flotation with particles of varying topography and analyzing adhesion between liquid droplets and gas bubbles with solid surfaces of varying surface roughness.
We welcome Ms. Tori Nizzi, who has joined our research team as an undergraduate researcher. Tori is double majoring in mechanical engineering and materials science and engineering programs. She is currently assisting Morteza Ardakani in his research on zinc-based biodegradable alloys but should start her own independent work on computer simulations of biodegradable orthopedic implants in 2020.
Morteza has published his first first-author paper entitled “The effects of alloying with Cu and Mn and thermal treatments on the mechanical instability of Zn-0.05Mg alloy” in the Materials Science and Engineering A journal. The following is the abstract:
The detrimental effect of natural aging on mechanical properties of zinc alloys restricts their application as bioresorbable medical implants. In this study, aging of Zn-0.05Mg alloy and the effect of 0.5 Cu and 0.1 Mn (in weight percent) addition on the microstructure and tensile properties were studied. The alloys were cold rolled, aged and annealed; aiming to investigate the effects of precipitates and grain size on the mechanical properties and their stability. TEM analysis revealed that in ultrafine-grained binary Zn-0.05Mg alloy, the natural aging occurred due to the formation of nano-sized Mg2Zn11 precipitates. After 90 days of natural aging, the yield strength and ultimate tensile strength of Zn-0.05Mg alloy increased from 197±4 MPa and 227±5 MPa to 233±8 MPa and 305±7 MPa, respectively, while the elongation was drastically reduced from 34±3% to 3±1%. This natural aging was retarded by adding the third element at either 0.1Mn or 0.5Cu quantities, which interacted with Mg in Zn solid solution and impeded the formation of Mg2Zn11 precipitates. The addition of Cu and Mn elements increased alloy’s strength, ductility, and its mechanical stability at a room temperature. The measured tensile strength and elongation were 274±5 MPa and 41±1% for Zn-0.1Mn-0.05Mg and 312±2 MPa and 44±2% for Zn-0.5Cu-0.05Mg, respectively. Annealing the alloys at elevated temperatures caused increase in both grain size and dissolution of secondary phases, and both affected alloy deformation mechanisms.