Soft Matter

Abstract: Research into extreme water-repellent surfaces began many decades ago, although it was only relatively recently that the term superhydrophobicity appeared in literature Here we review the work on the preparation of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years, with particular focus on the last two years We discuss the origins of water-repellent surfaces, examining how size and shape of surface features are used to control surface characteristics, in particular how techniques have progressed to form multi-scaled roughness to mimic the lotus leaf effect There are notable differences in the terminology used to describe the varying properties of water-repellent surfaces, so we suggest some key definitions

Abstract: Double-network (DN) gels have drawn much attention as an innovative material having both high water content (ca. 90 wt%) and high mechanical strength and toughness. DN gels are characterized by a special network structure consisting of two types of polymer components with opposite physical natures: the minor component is abundantly cross-linked polyelectrolytes (rigid skeleton) and the major component comprises of poorly cross-linked neutral polymers (ductile substance). The former and the latter components are referred to as the first network and the second network, respectively, since the synthesis should be done in this order to realize high mechanical strength. For DN gels synthesized under suitable conditions (choice of polymers, feed compositions, atmosphere for reaction, etc.), they possess hardness (elastic modulus of 0.1–1.0 MPa), strength (failure tensile nominal stress 1–10 MPa, strain 1000–2000%; failure compressive nominal stress 20–60 MPa, strain 90–95%), and toughness (tearing fracture energy of 100∼1000 J m−2). These excellent mechanical performances are comparable to that of rubbers and soft load-bearing bio-tissues. The mechanical behaviors of DN gels are inconsistent with general mechanisms that enhance the toughness of soft polymeric materials. Thus, DN gels present an interesting and challenging problem in polymer mechanics. Extensive experimental and theoretical studies have shown that the toughening of DN gel is based on a local yielding mechanism, which has some common features with other brittle and ductile nano-composite materials, such as bones and dentins.

Abstract: Colloidal delivery systems based on microemulsions or nanoemulsions are increasingly being utilized in the food and pharmaceutical industries to encapsulate, protect, and deliver lipophilic bioactive components. The small size of the particles in these kinds of delivery systems (r < 100 nm) means that they have a number of potential benefits for certain applications: enhanced long-term stability; high optical clarity; and, increased bioavailability. Currently, there is considerable confusion about the use of the terms “microemulsions” and “nanoemulsions” in the scientific literature. However, these are distinctly different types of colloidal dispersions: a microemulsion is thermodynamically stable, whereas a nanoemulsion is not. It is therefore important to distinguish between them since this impacts the methods used to fabricate them, the strategies used to stabilize them, and the approaches used to design their functional attributes. This article reviews the differences and similarities between nanoemulsions and microemulsions in terms of their compositions, structure, fabrication, properties, and stability. It also attempts to highlight why there has been so much confusion in this area, and to clarify the terminology used to refer to these two kinds of colloidal dispersion.

Abstract: We showed directional adhesion on the superhydrophobic wings of the butterfly Morpho aega. A droplet easily rolls off the surface of the wings along the radial outward (RO) direction of the central axis of the body, but is pinned tightly against the RO direction. Interestingly, these two distinct states can be tuned by controlling the posture of the wings (downward or upward) and the direction of airflow across the surface (along or against the RO direction), respectively. Research indicated that these special abilities resulted from the direction-dependent arrangement of flexible nano-tips on ridging nano-stripes and micro-scales overlapped on the wings at the one-dimensional level, where two distinct contact modes of a droplet with orientation-tuneable microstructures occur and thus produce different adhesive forces. We believe that this finding will help the design of smart, fluid-controllable interfaces that may be applied in novel microfluidic devices and directional, easy-cleaning coatings.

Abstract: Most organs and biological tissues are soft viscoelastic materials with elastic moduli ranging from on the order of 100 Pa for the brain to 100 000 Pa for soft cartilage. Biocompatible synthetic materials already have many applications, but combining chemical compatibility with physiologically appropriate mechanical properties will increase their potential for use both as implants and as substrates for tissue engineering. Understanding and controlling mechanical properties, specifically softness, is important for appropriate physiological function in numerous contexts. The mechanical properties of the substrate on which, or within which, cells are placed can have as large an impact as chemical stimuli on cell morphology, differentiation, motility, and commitment to live or die.