Images and force measurements taken by an atomic‐force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment.

Calibration of atomic‐force microscope tips

Effect of contact deformations on the adhesion of particles

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Wetting phenomena are ubiquitous in nature and technology. A solid substrate exposed to the environment is almost invariably covered by a layer of fluid material. In this review, the surface forces that lead to wetting are considered, and the equilibrium surface coverage of a substrate in contact with a drop of liquid. Depending on the nature of the surface forces involved, different scenarios for wetting phase transitions are possible; recent progress allows us to relate the critical exponents directly to the nature of the surface forces which lead to the different wetting scenarios. Thermal fluctuation effects, which can be greatly enhanced for wetting of geometrically or chemically structured substrates, and are much stronger in colloidal suspensions, modify the adsorption singularities. Macroscopic descriptions and microscopic theories have been developed to understand and predict wetting behavior relevant to microfluidics and nanofluidics applications. Then the dynamics of wetting is examined. A drop, placed on a substrate which it wets, spreads out to form a film. Conversely, a nonwetted substrate previously covered by a film dewets upon an appropriate change of system parameters. The hydrodynamics of both wetting and dewetting is influenced by the presence of the three-phase contact line separating "wet" regions from those that are either dry or covered by a microscopic film only. Recent theoretical, experimental, and numerical progress in the description of moving contact line dynamics are reviewed, and its relation to the thermodynamics of wetting is explored. In addition, recent progress on rough surfaces is surveyed. The anchoring of contact lines and contact angle hysteresis are explored resulting from surface inhomogeneities. Further, new ways to mold wetting characteristics according to technological constraints are discussed, for example, the use of patterned surfaces, surfactants, or complex fluids.

/pdf/wetting-and-spreading-56ditqbfmj.pdf

Wetting and Spreading

We have demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water−surfactant solutions. Optical characterization of these suspensions allowed the partial optimization of the dispersion process. Transmission electron microscopy showed the dispersed phase to consist of small graphitic flakes. More than 40% of these flakes had <5 layers with ∼3% of flakes consisting of monolayers. Atomic resolution transmission electron microscopy shows the monolayers to be generally free of defects. The dispersed graphitic flakes are stabilized against reaggregation by Coulomb repulsion due to the adsorbed surfactant. We use DLVO and Hamaker theory to describe this stabilization. However, the larger flakes tend to sediment out over ∼6 weeks, leaving only small flakes dispersed. It is possible to form thin films by vacuum filtration of these dispersions. Raman and IR spectroscopic analysis of these films suggests the flakes to be largely free of defects and oxides, although X-ray photoelect...

Liquid phase production of graphene by exfoliation of graphite in surfactant/water solutions.

The London—van der Waals attraction between spherical particles

This note proposes an approximation to the cumulative normal distribution and its inverse which, according to circumstances, is simpler, more accurate, or more convenient than existing formulae.

Approximating the Cumulative Normal Distribution and its Inverse

Summary
The sums of squares associated with the independent variables in a multiple regression equation depend on the order in which these variables are introduced. Two methods have been proposed in the literature to avoid this inconvenience: “forward selection” or “backward elimination”.

With forward selection the independent variables are introduced in successive stages. The order is not predetermined but at each stage that variable is taken as the next one which produces the highest reduction in the residual sum of squares of the dependent variable.

With backward elimination on the other hand, we start with the complete regression equation and eliminate the independent variables from it in the order in which they produce the smallest increases in the residual sum of squares.

This paper describes a simple and convenient computational lay-out which can be used for both procedures. In forward selection we start with the matrix of product sums, and in bacward elimination we work from the inverse matrix.

In addition these techniques are applied to a variety of practical examples in order to see what results they lead to and what pitfalls may be encountered.

On multiple regression analysis

Some Basic Principles of Sampling Inspection by Attributes

Most single sampling plans assume that the lot size is large compared with the sample size, and the calculated operating characteristic curves are strictly valid only under these conditions. In this article Dr Hamaker describes a simple method for finding the sample size and acceptance number appropriate to a lot of finite size, so that the resulting operating characteristic curve closely approximates to that for a given plan with an infinite lot.

H. C. Hamaker

Papers

The London—van der Waals attraction between spherical particles

Approximating the Cumulative Normal Distribution and its Inverse

On multiple regression analysis

Some Basic Principles of Sampling Inspection by Attributes

Adjusting Single Sampling Plans for Finite Lot Size