SURFI

Water Droplet on Solid

The mobility of a fakir state droplet on a structured surface is fundamentally determined by the effective length of a microscopic contact line. However, it is largely unknown how the surface topography determines the effective contact line length. Based on the direct measurement of droplet adhesion force and the visualization of contact line, our work, published in Physical Review Letters under the title “Topography-Dependent Effective Contact Line in Droplet Depinning“, shows that effective contact line length is topography-dependent as opposed to prior notion. On pored surfaces, contact line is not distorted, and the effective length approaches the droplet apparent perimeter regardless of pore dimensions. On pillared surfaces, the distortion of contact line is significantly dependent on the packing density of the pillar structures so that the effective length is as small as a pillar diameter on densely-packed pillars and as large as a pillar perimeter on sparsely-packed pillars, while changing linearly between the two extremes.
This paper is the result of our long-standing collaboration with Prof. Chang-Hwan Choi fromthe Stevens Institute of Technology.

H&E histology

Zinc (Zn) has emerged as a promising bioresorbable stent material due to its ideal corrosion behavior and excellent biocompatibility. However, for load bearing implant applications, alloying is required to boost its mechanical properties as pure Zn exhibits poor strength. Unfortunately, an increase in inflammation relative to pure Zn is a commonly observed side-effect of Zn alloys. Consequently, the development of a Zn-based alloy that can simultaneously feature improved mechanical properties and suppress inflammatory responses is a big challenge. In our new publication entitled “Analysis of vascular inflammation against bioresorbable Zn-Ag based alloys” and published in ACS Applied Bio Materials, a bioresorbable, biocompatible Zn-Ag-based quinary alloy was comprehensively evaluated in vivo, in comparison to reference materials. The inflammatory and smooth muscle cellular response was characterized and correlated to metrics of neointimal growth. We found that implantation of the quinary alloy was associated with significantly improved inflammatory activities relative to the reference materials. Additionally, we found that inflammation, but not smooth muscle cell hyperplasia, significantly correlates to neointimal growth for Zn alloys. The results suggest that inflammation is the main driver of neointimal growth for Zn-based alloys and that the quinary Zn-Ag-Mn-Zr-Cu alloy may impart inflammation-resistance properties to arterial implants.

Surface Innovations, the journal

We would like to share with you the content of the fifth issue of 2020 of Surface Innovations. This issue offers Feature Article on MoS2 incorporated PEO coatings on aluminum alloy and seven original papers on variety of topics. Hope many of you will find something interesting among these eight quality papers.

Bubble Adhesion Set-up

In a new paper entitled “Nano-scaled roughness effect on air bubble-hydrophilic surface adhesive strength” and published in Colloids and Surfaces A: Physicochemical and Engineering Aspects, we describe the effect of nano-scaled roughness on adhesion of air bubble with hematite and pyrite. This is the result of our collaborative project with Northeastern University in China, and effort of two Chinese scholars, Zhanglei Zhu and Donghui Wang.
Surface roughness of solid affects its interactions with gas bubbles in water. Here, we investigate the effect of surface nano-scaled (random) roughness, quantified with the root-mean-square (RMS) roughness from about 3 to 260 nm, on the adhesive strength of air bubble with natural hydrophilic hematite and pyrite surfaces using a microelectronic balance-camera system. The recorded values include bubble-mineral adhesion forces, water contact angles, and bubble base diameters during stages of air bubble attachment and spreading, maximum adhesion, and detachment. The results confirm weakening of adhesive forces for air bubble with hydrophilic surfaces of increasing nano-scale roughness. The study reveals a linear dependency between adhesion force and RMS roughness. The adhesion force was also found to be in a linear correlation with contact angle and its sine function, providing evidence for the surface tension force dominance in adhesion of bubble to hydrophilic surface with nano-scaled surface roughness characteristics of random nature.

Vacuum-assisted resin infusion molding

Dr. Drelich co-authors a paper entitled: “Mechanical properties of Boehmeria nivea natural fabric reinforced epoxy matrix composite preparedby vacuum-assisted resin infusion molding” and published in open-access Polymers journal. This is the most recent result of his collaboration with the Military Institute of Engineering in Rio de Janeiro, Brazil.
Natural lignocellulosic fibers and corresponding fabrics have been gaining notoriety in recent decades as reinforcement options for polymer matrices associated with industrially applied composites. These natural fibers and fabrics exhibit competitive properties when compared with some synthetics such as glass fiber. In particular, the use of fabrics made from natural fibers might be considered a more ecient alternative, since they provide multidirectional reinforcement and allow the introduction of a larger volume fraction of fibers in the composite. In this context, it is important to understand the mechanical performance of natural fabric composites as a basic condition to ensure ecient engineering applications. Therefore, it is also important to recognize that ramie fiber exhibiting superior strength can be woven into fabric, but is the least investigated as reinforcement in
strong, tough polymers to obtain tougher polymeric composites. Accordingly, this paper presents the preparation of epoxy composite containing 30 vol.% Boehmeria nivea fabric by vacuum-assisted resin infusion molding technique and mechanical behavior characterization of the prepared composite. Obtained results are explained based on the fractography studies of tested samples.

Air Bubble Adhesion Tests

A new contribution entitled “Water droplets and air bubbles at magnesite nano-rough surfaces: analysis of induction time, adhesion and detachment using a dynamic microbalance” and published in the Minerals Engineering journal is the result of our collaborative project with Northeastern University in China. Two scholars from China Zhanglei Zhu and Donghui Wang explored the effects of nano-scale roughness of magnesite minaral on adhesion with water droplets and air bubbles.
In this study, natural magnesite lumps were polished by a series of sandpapers and diamond to produce four magnesite specimens having 2 to 240 nm root-mean-square roughness. The dynamic measurements of attachment, spreading, adhesion, and separation with a high-sensitivity microelectronic mechanical balance revealed the effect of surface nano-scaled roughness on the induction time and forces of spreading, adhesion and separation for both water droplets and air bubbles. It was found that the increasing nano-scaled roughness enhances the spreading of water on hydrophilic magnesite and strengthens the water-magnesite adhesive contact. Nano-roughness also causes delays in attachment of air bubbles to magnesite surface, inhibits displacement of water by adhering air bubbles, and reduces the adhesive strength of air bubbles to the magnesite surface, factors that might slow down the flotation separation.