In a soft elastic film compressed on a stiff substrate, creases nucleate at preexisting defects and grow across the surface of the film like channels. Both nucleation and growth are resisted by the surface energy, which we demonstrate by studying creases for elastomers immersed in several environments--air, water, and an aqueous surfactant solution. Measurement of the position where crease channeling is arrested on a gradient thickness film provides a uniquely characterized strain that quantitatively reveals the influence of surface energy, unlike the strain for nucleation, which is highly variable due to the sensitivity to defects. We find that these experimental data agree well with the prediction of a scaling analysis.

It is known that smooth, hydrophobic solid surfaces exhibit low ice adhesion values, which have been shown to approach a lower ice adhesion strength limit (∼150 kPa) defined by the water receding contact angle. To overcome this limit, we have designed self-lubricating icephobic coatings by blending polydimethylsiloxane (PDMS)-poly(ethylene glycol) (PEG) amphiphilic copolymers into a polymer matrix. Such coatings provide low ice adhesion strength values (∼50 kPa) that can substantially reduce the lower bound of the ice adhesion strength achieved previously on smooth, hydrophobic solid surfaces. Different molecular mechanisms are responsible for the low ice adhesion strength attained by these two approaches. For the smooth hydrophobic surfaces, an increased water depletion layer thickness at the interface weakens the van der Waals' interactions between the ice and the polymeric substrate. For the self-lubricating icephobic coatings, the PEG component of the amphiphilic copolymer is capable of strongly hydrogen bonding with water molecules. The surface hydrogen-bonded water molecules do not freeze, even at substantial levels of subcooling, and therefore serve as a self-lubricating interfacial liquid-like layer that helps to reduce the adhesion strength of ice to the surface. The existence of nonfrozen water molecules at the ice-solid interface is confirmed by solid-state nuclear magnetic resonance (NMR) spectroscopy.

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A nucleosides containing block copolymer, poly(polyethylene glycol methyl ether methacrylate)- block-poly(5'-O-methacryloyluridine) (PPEGMEMA 30- b-PMAU 80) was self-assembled in aqueous medium and cross-linked via RAFT polymerization at 60 degrees C to afford core-cross-linked micelles exhibiting a PPEGMEMA corona and a polynucleotide core. A disulfide cross-linking agent, bis(2-methacryloyloxyethyl)disulfide, was employed to cross-link the structure via the RAFT process resulting in core-shell nanoparticles, which can degrade under reductive conditions. The resulting core-cross-linked micelles readily hydrolyzed into free block copolymers in the presence of dithiothreitol (DTT) in less than 1 h, depending on the concentration of the reducing agent and the amount of cross-linker in the micelle. A small fraction of permanently cross-linked micelle was found as the result of conventional chain transfer to disulfide containing compounds. A model drug, vitamin B 2, was loaded into the micelle. The loading capacity increased with increasing cross-linking degree. The amount of drug released reached 60-70% after 7 h in the presence of DTT (0.65 mM), while the cross-linked micelle in the absence of dithiothreitol shows only a delayed drug release. Cytotoxicity tests confirmed the biocompatibility of the polymers and the residues after reduction.

Thin polymer films may undergo a wide variety of elastic instabilities that include global buckling modes, wrinkling and creasing of surfaces, and snapping transitions. Traditionally, these deformations have usually been avoided as they often represent a means of mechanical failure. However, a new trend has emerged in recent years in which buckling mechanics can be harnessed to endow materials with beneficial functions. For many such applications, it is desirable that such deformations happen reversibly and in response to welldefined signals or changes in their environment. While significant progress has been made on understanding and exploiting each type of deformation in its own right, here we focus on recent advances in the control and application of stimuliresponsive mechanical instabilities.

Establishing a vapor film on a low-temperature Leidenfrost surface leads to 80 to 90% drag reduction in a turbulent flow.

ABA and BAB triblock thermoresponsive copolymers (A = N‐isopropylacrylamide, B = 2‐hydroxyethyl methacrylate) have been synthesized by atom transfer radical polymerization (ATRP). BAB is shown to exhibit a higher transition temperature and a good solubility in water compared to ABA with the same composition and concentration. The differences are attributed to the distinct micellar structure, which is regulated by the block order of the copolymers. It is speculated that ABA and BAB copolymers separately form branch and flower micelles in water, which mainly influence the course of phase transition. The moduli of the ABA copolymer solution are higher than those of the BAB above gel point. In terms of hypothesized micelle models, it is proposed that the ‘branch’ micelles of the ABA solution preferably form more physical interconnections.