Hydrophilic glass beads

The motion of droplets in solution was used to manipulate micro-partides on surfaces. The didiloromethane droplet pushed aside hydrophilic glass beads of about... 

Figure 16.12 Transportation of glass-beads by the droplet, (a) Hydrophilic glass beads were pushed by the oil droplet. The droplet moved from the upper right of the figure. A magnified image of the region within the square is shown in the inset. Hydrophobic beads in the droplet (b) were carried with the motion of the oil droplet (c). The droplet shown in (c) was moved for several mm in the direction shown by the arrow in (b).

PVP-based granulation of detergent-cleaned hydrophilic glass beads produced larger granules with more crushing resistance and lower friability than those of dimethylsilane surface treated hydrophobic glass beads (35). The results can be attributed to the better adhesion of PVP to hydrophilic surfaces. 

The choice of solid carriers spans a wide spectrum (Table 1) from materials most suitable for research purposes (sintered glass beads, laterite stone deposited on a gramophone disk) to industrial materials (pumice, activated carbon, etc.). Key properties that affect the performance of the carrier are porosity (from impervious to controlled-size pores), composition (from ceramics to activated carbon), and hydrophilic behavior. It is difficult to perform a direct comparison of different carriers. Colonization and biofilm growth depend strongly on the nature of bacteria and on their intrinsic propensity to adhere on hydrophilic vs. hydrophobic surfaces. 

The inorganic support should present a high hydrophilicity and a very high specific surface area it is a case, for instance, for silica or mesoporous glass beads. A general scheme is given in Fig. 1. 

Where impurities are present as microparticulate material filtration affords a convenient technique for solvent purification. The mobile phase containing added buffers or reagents may be filtered through a 0.5 pm or smaller filter to remove particulate matter that can damage the analytical system. The equipment for filtration is simple. Usually, it consists of an Elenmayer flask connected to vacuum and a reservoir in which a porous filter disk or membrane is placed. The porous disk is usually made from nonporous spherical glass beads (1-2 pm) and/or polytetrafluoroethylene (PTEE). Membrane materials are usually made from PTEE, cellulose, or nylon. To improve the efficiency of the separation process, the surface of the filter disks or membrane surface are often modified chemically, similar to that used for chemically bonded packing materials in RP-HPLC and/or SPE. In this case, the surface properties (hydrophobic or hydrophilic) of filters and/or membranes determine the extent of purification possible. 

Hydrophilic phosphines can also be used to form palladium complexes, which can be absorbed on the surfaces of hydrophilic supports, such as silica. In this case, the catalyst is fully immobilized, though not chemically bonded, so it can easily leach to any polar solvent. Such an approach is referred to as glass bead technologyHere water is used only in the process of preparation of the catalyst, which is impregnated onto the support in aqueous solution. 

The surface properties of particles are very important with respect to their end use. Many particles are used for fillers and to impart properties that enhance a materials function. In order to do so, the particles need to be compatible with the environment into which they are placed. Often this is in a polymer matrix such as a film. To enhance particle compatibility of the surface of 2-5 pm silica particles and silica glass beads, surface modification of these particles was carried out. Surface modifications were accomplished by surface polymerization, surface polymer grafting, by surface dendrimerization and by developing organo-silicone particles. The surfaces obtained can have a wide variety of properties, fi om highly hydrophilic to highly hydrophobic, from anionic and cationic to nonionic, as well as being environmentally responsive. 

The dispersability of PAA modified glass beads composites were examined in different solvents. In polar solvents, such as methanol and acetonitrile, the particles showed good dispersability (Table 1). In non-polar solvents, such as aliphatic and aromatic hydrocarbons, the particles did not disperse very well. The dispersability of the composite particles relates to the hydrophilic/hydrophobic compatibility between PAA on the glass surface and the solvent. 

It is also feasible to perform the experiment with oil as the liquid and to start with the oil and change the surface of the glass beads between the hydrophilic and hydrophobic states. The oil will show improved flow with hydrophobic beads. 

The attachment of enzymes to porous glass bead surfaces activated by chloro-silanes was developed by Weetall [27] at Corning in U.S.A. Wichterle and Coupek et al. [34] have reported recently in Czechoslavakia on the preparation of poly (hydroxyethylmethacrylate) beads, a sort of hydrophilic organic glass, with calibrated pores and carrying a variety of chemical groups able to react with enzymes. 

Oxidation of a number of p-substituted phenols to the corresponding o-benzoquinones was first performed by Kazandjian and Klibanov, using mushroom polyphenol oxidase and a quantitative conversion was achieved in CHCI3 as a solvent. Other hydrophobic solvents such as methylene chloride, carbon tetrachloride, benzene, toluene, hexane and butyl acetate can be used, whereas the enzyme is inactive in more hydrophilic solvents such as ether, acetone, ethyl acetate, acetonitrile and other solvents. In addition, an immobilized enzyme on glass powder or beads is more efficient than a free enzyme. 

Because one of the critical attributes of glass is its extreme visual clarity, there is a host of possible applications for glass surfaces that do not fog or on which water does not bead. Some of these are listed in Table 2, together with those that are related to hydrophilic selfcleaning surfaces. Water, in the form... 

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