On the Durability of Icephobic Coatings: A Review.

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings.

Using Plasma Etching to Access the Polymer Density Distribution and Diffusivity of Gel Particles.

In this paper we examine the polymer density distribution of gel particles and its effect on solvent diffusivity through the polymer network. In order to access the inner particle regions, external polymer layers were removed by plasma etching, thus reducing them from the outside. Higher polymer densities after erosion showed internal heterogeneity, with the density increasing towards the center of the particles. An exponential decay polymer density model is proposed, and the spatial relaxation length measured. The diffusion of solvent through the particles, before and after the plasma oxidation, revealed a correlation between the diffusion coefficient and the internal density.

Particles and nanovoids for plasmonics.

This article reviews and compares the optical properties of metallic nanoparticles and nanovoids, which have received great attention due to their ability to generate and control plasmon resonances. These systems are capable of concentrating and manipulating the fields at nanometer scale, being very attractive as building blocks for emerging applications. Metal particles and nanovoids present different plasmonics modes, strongly dependent on the size, shape and nature of the metal and dielectric. Specific geometrical features, as the presence of rims, make the nanovoids very promising structures to design exotic band spectra because of the coupling between different resonant modes.

First exfoliated Ru-Ru-Au organometallic polymer with layered structure.

A new water soluble heterometallic polymeric complex [{(PTA)2CpRu-µ-CN-1κC:2κ2N-RuCp(PTA)2}-µ-{Au(CN)4}4]n·2H2O (1) is synthesized and characterized by single crystal X-ray diffraction. This complex self-assembles forming 3D polymeric structures with large scale hexagonal conformation. They also organize as 3D stacks of polymer sandwiches that can be exfoliated providing mono heterometallic-3D layers, as shown by electron microscopy. Regarding the polymer dynamics, quasi-elastic neutron scattering shows a transition from vibrational Debye-Waller behaviour to a more dynamically active state as a result of the loss of structural water molecules.

Novel Ruthenium-Silver PTA-Based Polymers and Their Behavior in Water.

New coordination polymers based on two metal-containing moieties Ru-Ag are synthesized: Na[RuCpX(PTA)-µ-(PTA)-1κP:2κ2N-AgX2]∞ (X = Cl (1), Br (2), I (3)). Characterization is performed by NMR, UV-visible and FT-IR spectroscopy, optical-electron microscopy, and elemental analyses (C, H, N, S). Light scattering is employed to characterize the colloidal particles growth by polymer self-assembling. These structures are stable over a broad range of pH and exhibit thermally-driven swelling, thus resembling a typical thermosensitive hydrogel.

Self-Organization and Swelling of Ruthenium-Metal Coordination Polymers with PTA (Metal = Ag, Au, Co).

We present the internal structure and dynamics of novel coordination polymers based on two metal-containing moieties Ru-X (X: Ag, Au, Co), bridged through the phosphine PTA (3,5,7-triaza-phosphaadamantane). X-ray scattering gives the heterometallic polymer organization. Quasi-elastic neutron scattering measurements over a broad temperature range show a transition from vibrational Debye-Waller behavior to a more dynamically active state, but with rather localized motions, coinciding with the loss of structural water at around room temperature. Light scattering reveals that the polymers self-associate to form stable micro-particles in aqueous solution with a thermally driven volume transition. This is described by the Flory theory for polymers in solution, in which the polymer solvency is calculated as a function of the temperature. Polymer self-organization is further studied by small-angle neutron scattering and electron microscopy. A polymer parallel-plane model with gaps controlled by the environmental temperature is proposed.

Inorganic/polymer hybrid nanoparticles for sensing applications.

This paper reviews a wide set of sensing applications based on the special properties associated with inorganic/polymer composite nanoparticles. We first describe optical sensing applications performed with hybrid nanoparticles and hybrid microgels with special emphasis on photoluminescence detection and imaging. Analyte detection with molecularly imprinted polymers and HPLC-based sensing using hybrid nanoparticles as stationary phase is also summarized. The final part is devoted to the study of ultra-sensitive molecule detection by surface-enhanced Raman spectroscopy using core-shell hybrid materials composed of noble metal nanoparticles and cross-linked polymers.

Structure and polymer dynamics within PNIPAM-based microgel particles.

The synthesis of temperature-responsive microgels of poly(N-isopropylacrylamide) (PNIPAM) was first reported in 1986 and, since then, there have been hundreds of publications describing the preparation, characterization and applications of these systems. This paper reviews the developments concerning the study of the structure of PNIPAM-based microgels performed over the last years using small angle neutron scattering (SANS) and also the investigations of the polymer-chain dynamics within the microgels carried out with incoherent elastic and quasielastic neutron scattering, and pulse field gradient nuclear magnetic resonance (PFG-NMR) techniques. Furthermore, the self-diffusion coefficient of the water molecules within the microgel, determined by means of solvent relaxation NMR, is also discussed as a function of the polymer volume fraction of the microgels.

Bulk and shear moduli of compressed microgel suspensions.

We independently determine the bulk and shear moduli of compressed microgel suspensions and the bulk modulus of individual microgel particles and find that the elastic behavior of the suspension reflects the degree of compression of the particles. This feature, which is distinct from other soft materials such as emulsions or foams, can give rise to an unusually large difference between the bulk and shear moduli of the suspension. Our results extend our understanding of soft materials to systems based on compressible objects, opening up possibilities for engineering materials with drastically different responses to shear and compression.

Ion-specific and reversible wetting of imidazolium-based minigels.

Cross-linked imidazolium-based [poly(ViEtIm +Br -)] microparticles were synthesized, and their wetting properties were studied by optical microscopy, after addition of aqueous solutions of sodium halides. Particle wetting showed ion specificity due to counterion binding, described by Desnoyer's model. The interaction between anions and the microparticles allowed exchanging halogenides between them in a reversible way. A salt-independent characteristic wetting time was found as well as a decreasing power law with salt concentration, for the network diffusion coefficient. It modified the polymer network elasticity as ion concentration increased, making the network softer.