Physical penetration

FIGURE 16.2 Three possible modes through which inertial cavitation may enhance SC permeability, (a) Spherical collapse near the SC surface emits shock waves, which can potentially disrupt the SC lipid bilayers, (b) Impact of an acoustic microjet on the SC surface. The microjet possessing a radius about one tenth of the maximum bubble diameter impacts the SC surface without penetrating into it. The impact pressure of the microjet may enhance SC permeability by disrupting SC lipid bilayers, (c) Microjets may physically penetrate into the SC and enhance the SC permeability. (From Mitragotri, S., and Kost J., Adv. Drug Deliv. Rev., 56, 589, 2004. With permission.)... 

Thermomechanical Analysis (TMA). Thermomechanical analysis (TMA) measures shape stability of a material at elevated temperatures by physically penetrating it with a metal rod. A schematic diagram of TMA equipment is shown in Fig. 2.23. In TMA, the test specimen s temperature is raised at a constant rate, the sample is placed inside the measuring device, and a rod with a specified weight is placed on top of it. To allow for measurements at low temperatures, the sample, oven, and rod can be cooled with liquid nitrogen. 

C below the melting point. The nature and the size of the exposed surface of the deposit on the leaf surface can be modified by spray adjuvants such as wetting agents, thickeners or particulating agents. The deposited pesticide may also interact with the target surface, with leaf exudates or with the polymeric wax-like surface of cutin. It may also physically penetrate the surface of the leaf. 

Oxygen transport through the solid state can be caused by the difference in both electrical and chemical potentials. The last effect can be used for the development of oxygen-selective ceramic membranes. The demands of materials for such membranes are similar to the demands for solid electrolytes high density in order to prevent physical penetration of the gas and a high coefficient of oxygen... 

Solvent can be associated with the solid in different chemical and physical states. It can be part of the crystalline structure, chemically adsorbed in solid interior or physically penetrated/adsorbed inside the interstices of the solid. The interstices of the solid are subjected to a large capillary tension upon drying. The force exerted to solid can be estimated by Laplace s law/ ... 

Adsorption can be most simply defined as the preferential concentration (i.e., location) of one component of a system at an interface, where the local (i.e., interfacial) concentration of one or more components of one or both phases is different from those in the bulk phases. Adsorption should be clearly differentiated from absorption, in which physical penetration of one phase into another is involved, although the two may operate concurrently. Adsorption can occur at any type of interface, although the distinct characteristics of solid versus liquid interfaces make the analysis of each case somewhat different. For that reason, the discussion of each situation is best presented in the context of specific interfaces. In many practical systems, all four of the principle interfaces may be present, leading to complex situations that make complete analysis very difficult or impossible. 

This principle can also be used for the modification of polymeric films, namely either by their physical penetration with chromophores [100, 101] or by covalent bonding of the last ones to the adequate functional groups of the macromolecular substrate [102, 106],... 

Another process is a penetration of the melt in the refractory s permeable pores. The process of physical penetration without dissolution is governed by capillary forces (surface tension), hydrostatic pressure, viscosity of the melt, and gravity. An illustration of such a process appears in Fig. 1.27, which shows the probability of the penetration of the A1 melt in the pores of the carbon block with and without the application of the current. 

For the physical penetration (without chemical interaction), the rate of penetration dlldt depends on the pore radius r, surface tension of the melt y, and viscosity of the melt r ... 

Both physical penetration and chemical invasion are favored by the effective liquid-solid wetting and by the low viscosity of the liquid. Wetting is decided by the contact angle. As it decreases, wetting is increased. In the liquid state, silicate slags and glasses are the most viscous, oxidic compounds are less so, and halides and elemental metals are the least viscous. 

To prevent gas incorporation in the surface or growing film, the surface can be heated to desorb the gases before they are covered over or the bombardment energy can be less than a few hundred eV, which will prevent the physical penetration of the ions into the surface. Typically, a substrate temperature of 400°C or an ion energy of less than 250eV will prevent the incorporation of argon ions into a film structure. 

Altered region (ion bombardment) The region near the surface that has been altered by the physical penetration of the bombarding species or by knock-on lattice atoms. In the extreme case this can lead to the amorphization of the region. See also Near-surface region. 

---