Fouling release coatings: a nontoxic alternative to biocidal antifouling coatings.

Soft materials are materials with a low shear modulus relative to their bulk modulus and where elastic restoring forces are mainly of entropic origin. A sparse population of strong bonds connects molecules together and prevents macroscopic flow. In this review we discuss the current state of the art on how these soft materials break and detach from solid surfaces. We focus on how stresses and strains are localized near the fracture plane and how elastic energy can flow from the bulk of the material to the crack tip. Adhesion of pressure-sensitive-adhesives, fracture of gels and rubbers are specifically addressed and the key concepts are pointed out. We define the important length scales in the problem and in particular the elasto-adhesive length Γ/E where Γ is the fracture energy and E is the elastic modulus, and how the ratio between sample size and Γ/E controls the fracture mechanisms. Theoretical concepts bridging solid mechanics and polymer physics are rationalized and illustrated by micromechanical experiments and mechanisms of fracture are described in detail. Open questions and emerging concepts are discussed at the end of the review.

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Fracture and adhesion of soft materials: a review.

to develop synthetic analogs as“smart” adhesives, that is, where the geometry of the patternscan tailor the adhesion of the material. However, there arecurrently two limitations in the design of patterned adhesives.First, because of either materials selection or geometric de-sign, the adhesive properties are not always reversible overthe course of multiple attachment–detachment cycles.

Surface wrinkles for smart adhesion

▪ Abstract Filament-stretching rheometers are devices for measuring the extensional viscosity of moderately viscous non-Newtonian fluids such as polymer solutions. In these devices, a cylindrical liquid bridge is initially formed between two circular end-plates. The plates are then moved apart in a prescribed manner such that the fluid sample is subjected to a strong extensional deformation. Asymptotic analysis and numerical computation show that the resulting kinematics closely approximate those of an ideal homogeneous uniaxial elongation. The evolution in the tensile stress (measured mechanically) and the molecular conformation (measured optically) can be followed as functions of the rate of stretching and the total strain imposed. The resulting rheological measurements are a sensitive discriminant of molecularly based constitutive equations proposed for complex fluids. The dynamical response of the elongating filament is also coupled to the extensional rheology of the polymeric test fluid, and this can...

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Filament-stretching rheometry of complex fluids

The contact behavior of solid materials is determined by the system geometry, externally applied loads and internal adhesive forces, and by the materials properties. As the size and stiffness of a material decrease, adhesive forces become increasingly important in determining its contact behavior. The current trends toward the use of smaller features in many areas of technology, and the importance of ‘soft’ materials including biological tissues, elastomers and polymer gels, demand that the effects of adhesion on contact mechanics be properly understood. The focus of this review is on the mechanics of contact experiments that are commonly used to characterize adhesion, and on the materials science of adhesion of elastic and viscoelastic materials.

Contact mechanics and the adhesion of soft solids

The adhesion mechanisms of two acrylic Pressure-Sensitive-Adhesives on a stainless steel probe are investigated with a custom-designed probe tack apparatus. Our setup allows the simultaneous acquisition of a nominal stress and strain curve, and the observation of the adhesive film from underneath the transparent substrate. The temperature was varied in the range -20°C to 50°C and the debonding rate in the range 1–10000 μm/s. For all conditions we observed, upon debonding, the formation of cavities at or near the interface between the probe and the film. These cavities initially grew predominantly in the plane of the film but, at higher values of nominal strain, the walls between the cavities were stretched in the direction normal to the plane of the ifim to become a fibrillar structure. The transition from a cavitated structure to a fibrillar one was only found within a time-temperature window of rheological properties of the adhesive, while the adhesion energy was found to be mainly related to t...

Direct Observation of Cavitation and Fibrillation in a Probe Tack Experiment on Model Acrylic Pressure-Sensitive-Adhesives

Adhesively bonded elastic layers with thicknesses that are small relative to their lateral dimensions are used in a wide variety of applications. The mechanical response of the compliant layer when a normal stress is imposed across its thickness is determined by the effects of lateral constraints, which are characterized by the ratio of the lateral dimensions of the layer to its thickness. From this degree of confinement and from the material properties of the compliant layer, we predict three distinct deformation modes: (1) edge crack propagation, (2) internal crack propagation, and (3) cavitation. The conditions conductive for each mode are presented in the form of a deformation map developed from fracture mechanics and bulk instability criteria. We use experimental data from elastic and viscoelastic materials to illustrate the predictions of this deformation map. We also discuss the evolution of the deformation to large strains, where nonlinear effects such as fibrillation and yielding dominate the failure process.

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Deformation and Failure Modes of Adhesively Bonded Elastic Layers

Because of recent experiments (H. Lakrout et al., J Adhes 1999, 69, 307) conducted with an instrumented probe-tack device, a better description of the debonding mechanisms of soft viscoelastic adhesives from a hard interface can be proposed. Because the deformed volume is about the magnitude of the sample size and the deformation is highly inhomogeneous, adhesion cannot be studied independently of the geometry of the test. One of the simplest geometries is that of the debonding of a cylindrical flat-ended probe from a thin film. In this case, a uniform displacement field is applied over the entire top surface of the film, and the stress field at the probe-film interface is strongly dependent on the degree of confinement of the film characterized by the ratio between the probe radius a and the film thickness h. For a very confined film, the nucleation of interfacial cavities is predicted to occur over most of the surface of the probe. These cavities will grow in the plane of the film and can be assimilated to multiple penny-shaped interfacial cracks. We present a semiquantitative model of how the lateral growth of these cavities is controlled by the competition between a critical energy-release rate at the interface G c and the elastic modulus of the film E. Finally, either these cavities coalesce and the film is debonded from the surface or the walls between these cavities become elongated in the tensile direction and form a fibrillar structure. The conditions for the formation of this fibrillar structure are qualitatively discussed.

Micromechanics of flat‐probe adhesion tests of soft viscoelastic polymer films

The invention provides a composition comprising at least one olefin multi-block interpolymer; at least one functionalized olefin-based polymer; and optionally at least one thermoplastic polyurethane. The invention also provides for articles prepared from the inventive compositions and for methods for making the same.

Polyolefin compositions and articles prepared therefrom, and methods for making the same

The invention provides polyolefin blend compositions of polar and/or non-polar polymers, with at least one functionalized polyolefin polymer selected from the group consisting of: amine functionalized, hydroxyl functionalized, imide functionalized, anhydride functionalized, or carboxylic acid functionalized polyolefin polymers. The invention also provides methods for making the functionalized polyolefin polymer. The invention also provides for materials and articles containing at least one component prepared from such compositions.

Hamed Lakrout

Papers

Direct Observation of Cavitation and Fibrillation in a Probe Tack Experiment on Model Acrylic Pressure-Sensitive-Adhesives

Deformation and Failure Modes of Adhesively Bonded Elastic Layers

Micromechanics of flat‐probe adhesion tests of soft viscoelastic polymer films

Polyolefin compositions and articles prepared therefrom, and methods for making the same

Functionalized olefin polymers, compositions and articles prepared therefrom, and methods for making the same