Архивы рубрики ‘Applications’

OBREIMOFF’S EXPERIMENT

Obreimoff,6 working in the Physics Institute of Leningrad, where large sheets of a perfect type of Muscovite mica were available from the White Sea area near Chupa, knew of the problems of putting polished flat surfaces together, and recognized that optical contact could produce adhesion, but not satisfactorily. “Perfect” optical contact still contained gaps up […]

THE PROBLEM OF OBTAINING RELIABLE ADHESION

The first law of adhesion states that all atoms adhere. Therefore we would expect that blocks of material placed in good contact should stick together. This idea had been studied by Tyndall in 1875 and investigated further by Budgett in 1911.3 The objective was to show that adhesion between flat plates could be larger than […]

EVIDENCE FOR THE FIRST LAW OF ADHESION: SURFACE LEAP INTO CONTACT

For by pressing such Glasses together their parts easily yield inwards, and the Rings thereby become sensibly broader Isaac Newton, Opticks} p. 201 The quest for molecular adhesion started with Newton’s two fundamental ideas; that polishing glasses smoother would allow more intimate contact, and that the small movements of the surfaces towards each other could […]

THE ATOMIC FORCE MICROSCOPE (AFM)

Around that time, there was a sudden realization that many different kinds of probe could give atomic resolution at surfaces. Electrical conduction, heat conduction, or acoustic transmission could all be used in principle. The scanning tunneling microscope, based on electron conduction, was immediately successful because it was so simple. A probe could be made by […]

ADHESION IN THE SCANNING PROBE MICROSCOPE

The macroscopic demonstrations described above, repeating Newton’s original tests on the adhesion of glass lenses, give an insight into the laws of adhesion. Newton had seen two of the three indicators of molecular adhesion: the black, flattened contact spot, and the pull-off force. But he had not seen the spontaneous jumping into contact. The reason […]

ADHESION IS REALLY THREE THINGS: MAKING, EQUILIBRIUM, AND BREAKING

After examining the way in which a particle sticks to a surface, as above, it becomes apparent that adhesion is not a single process, but one which we can separate into three different but related actions: jumping into contact, achieving a certain black spot size, then cracking apart as a tensile force is applied. The […]

CRACKING MOLECULES APART

The adhesion of the rubber spheres is revealed unequivocally by their leaping into contact. However, the precise nature of this contact needs to be understood if the adhesion of the spheres is to be well defined. Consider the two rubber surfaces magnified so the contact region in the equilibrium contact shows up more clearly, as […]

JUMPING INTO CONTACT

The skeptical engineer is wary of the idea that molecules leap into contact with their surrounding surfaces. After all, car parts on an assembly line do not suddenly jump together and adhere strongly to fashion the finished vehicle. However, at the molecular level it is quite obvious that such events occur naturally, and a nanoscale […]

FROM MOLECULES, THROUGH MECHANISMS, TO MECHANICS

We normally observe adhesion at the macroscopic level, say by peeling a film from a surface as in Fig. 3.9. In order to understand the force which is necessary to pull the film off, we have to connect this mechanical picture with the molecular adhesion forces which we know to be universal at the nanometer […]

THE LAWS OF MOLECULAR ADHESION

The laws of molecular adhesion are: 1. All atoms and molecules adhere with considerable force. More simply, if two solid bodies approach to nanometer separations, then they will jump into contact as a result of molecular adhesion. This behavior differs from our ordinary engineering experience. 2. The effect of contaminant “wetting” molecules is to reduce […]