Лако-красочные материалы — производство

The sensation of stickiness is among the commonplace experiences of humanity. Resin oozing from a pine branch and the sap from a dandelion stem are among a multitude of natural examples from which it can be asserted with confidence that humans have ‘‘always’’ been aware of the phenomenon of adhesion. Indeed for millennia, as a species, we have made use of viscous liquids capable of setting to solids. In the Upper Palaeolithic era (between 40,000 and 10,000 years ago) stone and bone points were glued with resin to wooden shafts to produce spears. Some 31,000 years ago colored pigments were being glued to the walls of the Chauvet cave in Vallon-Pont-d’Arc in the Ardeche to create the earliest known cave paintings [1]. By the first dynasty of ancient Egypt (ca. 3000 B. C.) natural adhesives were used to attach inlays to furniture [2].

The technological use of adhesives implies a tacit [3] knowledge of the practical principles necessary for their success. In time, these principles were made explicit. In the thirteenth century Bartholomaeus Angelicus [4] recognized the need to exclude ‘‘dust, air and moisture’’ (‘‘pulvere, vento et humore’’) for success in the ancient craft of laminating silver to gold.

Galileo was aware of the significance of surface roughness. In his Due Nuove Scienze, he discusses adhesion between sheets of glass or marble, placed one upon the other. If the surfaces are finely (esquisitamente) polished, they are difficult to separate, but if contam­ination prevents perfect (esquisito) contact, the only resistance to separation is the force of gravity [5]. Rough surfaces require ‘‘introdur qualche glutine, visco o colla’’—‘‘the intro­duction of some sticky, viscous or gluey substance’’—for adhesion to occur. In addition to showing an appreciation of practical considerations which are significant to the successful use of adhesives, Galileo placed the phenomenon of adhesion within the then traditional scientific paradigm, arguing that the Aristotelian principle of nature’s abhorrence of a void provided the resistance to separation of the materials joined [6].

The seventeenth century was, of course, a time of paradigm change, indeed Galileo himself made a major contribution to this process. So we see that by the 1730s Newton, having abandoned the Aristotelian paradigm, was arguing that adhesion was a result of ‘‘very strong attractions’’ between the particles of bodies. After mention of gravitational, magnetic, and electrical attractions, he postulated ‘‘some force [between particles], which in immediate contact is exceeding string,… and reaches not far from the particles with any sensible effect.’’ What these attractions were, Newton did not speculate, but left the change: ‘‘it is the business of experimental philosophy to find them out’’! [7].

Schultz and Nardin, in the previous chapter, reminded us of this challenge of Newton’s, and presented a broad review of the extent to which contemporary science had succeeded in answering it. This chapter focuses on one part of that answer—the mechanical theory of adhesion, which is concerned with the effect of surface roughness on adhesion. Starting from the early formulation of the theory in 1925, its changing fortunes up to the 1970s are outlined; since this time, it has not been seriously questioned. Next, the concepts that underlie the terms surface and roughness are examined, and it is emphasized that these terms are essentially arbitrary in nature. This leads to a discussion of how concepts, such as work of adhesion, spreading coefficient, and fracture energy, may be adapted for adhesive bonds where the interface is rough. This theoretical basis is then employed in the next section of the review in which selective published work is discussed that illustrates different ways in which interfacial roughness may affect the strength of an adhesive joint. The discussion moves from examples of roughness on a macroscale, through microroughness to roughness on the nanoscale. Mechanisms are described whereby rough­ness may enhance fracture energy by increasing plastic, or even elastic losses. Chain pull­out and scission may also make contributions. The conclusions point out how the concepts of various ‘‘theories’’ of adhesion, such as mechanical, adsorption and diffusion, merge and overlap, and caution lest an excessive reductionism be counterproductive.