Colloidal dispersion gel

Partially hydrolyzed polyacrylamides, carboxymethylcellulose, polysaccharides, and acrylamido methylpropane sulfonate have been screened to investigate the performance of aluminum citrate as a chelate-type crosslinker. An overview of the performance of 18 different polymers has been presented in the literature [1646]. The performance of the colloidal dispersion gels depends strongly on the type and the quality of the polymer used. The gels were mixed with the polymers at two polymer concentrations, at three polymer-to-aluminum ratios, and in different concentrations of potassium chloride. The gels were quantitatively tested 1,7, 14, and 28 days after preparation. 

J. E. Smith. Performance of 18 polymers in aluminum citrate colloidal dispersion gels. In Proceedings Volume, pages 461-470. SPE Oilfield Chem Int Symp (San Antonio, TX, 2/14-2/17), 1995. 

Crosslinked polymer-like bulk gel used in water shut-off has very poor flowability the viscosity is very high (>10,000 mPa s). Uncrosslinked polymer is used to increase water viscosity. A movable gel is used in between it has the intermediate viscosity, and more importantly, it can flow under some pressure gradient. Colloidal dispersion gel (CDG) is a typical gel used in these situations. The mechanisms of a movable gel are (1) it has high viscosity to improve mobility ratio like an uncrosslinked polymer solution (2) it has a high resistance factor and high residual permeability reduction factor and (3) it has viscoelasticity so that the remaining oil in the rocks can be further reduced. 

Colloidal dispersion gel (CDG) is made of low concentrations of polymer and crosslinkers. Crosslinkers are the metals, such as aluminum citrate and chromium, referred to as aggregates. Polymer concentrations range from 100 to 1200 mg/L, normally 400 to 800 mg/L. The ratio of polymer to crosslinkers is 30 to 60. Sometimes, this type of gel is called a low-concentration crosslinked polymer. In such concentration range, there is not enough polymer to form a continuous network, so a conventional bulk-type gel cannot form. Instead, a solution of separate gel bundles forms, in which a mixture of predominantly intramolecular and minimal intermolecular crosslinks connect relatively small... 

Fielding Jr., R.C., Gibbons, D.H., Legrand, F.R, 1994. In-depth drive fluid diversion using an evolution of colloidal dispersion gels and new bulk gels An operational case history of North Rainbow Ranch Unit. Paper SPE 27773 presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, 17-20 April. 

Smidi, J.E., Liu, H., Guo, Z.-D., 2000. Laboratory studies of in-depdi colloidal dispersion gel technology for Daqing Oil Field. Paper SPE 62610 presented at the SPE/AAPG Western Regional Meeting, Long Beach, 19—22 June. 

The latter equation is usually referred to as the Newtonian model or Newton s law of viscosity. In Equation 4.257, is the dilatational bulk viscosity and q is the shear bulk viscosity. The usual liquids comply well with the Newtonian model. On the other hand, some concentrated macromolecu-lar solutions, colloidal dispersions, gels, etc., may exhibit non-Newtonian behavior their properties are considered in detail in some recent review articles and books [636-641]. From Equations 4.252 and 4.257, one obtains the Navier-Stokes equation [642,643] ... 

We prepared ceria on Ni substrate by sol-gel coating method. Ceria sol solution was prepared with ceria sol solution (Alfa, 20% in H2O, colloidal dispersion) mixed with ethanol (99.9%, Hayman) with weight ratio (1 2) and stirred. Ceria was deposited on Ni substrate by dip coating method. The variation number of dipping was carried out to obtain different coating ratio. The anode was completely dipped into the ceria sol solution for several seconds and dried at a temperature of 50 C for 24 hours in air atmosphere followed by calcination at 700 C for 30 minutes in 5%H2-N2 atmosphere. 

Characteristic microstructural properties of TiOj membranes produced in this way are given in Table 2.5. Mean pore diameters of 4-5 nm were obtained after heat treatment at T < 500°C. The pore size distribution was narrow in this case and the particle size in the membrane layer was about 5 nm. Anderson et al. (1988) discuss sol/gel chemistry and the formation of nonsupported titania membranes using the colloidal suspension synthesis of the type mentioned above. The particle size in the colloidal dispersion increased with the H/Ti ratio from 80 nm (H /Ti = 0.4, minimum gelling volume) to 140 nm (H /Ti " — 1.0). The membranes, thus prepared, had microstructural characteristics similar to those reported in Table 2.5 and are composed mainly of 20 nm anatase particles. Considerable problems were encountered in membrane synthesis with the polymeric gel route. Anderson et al. (1988) report that clear polymeric sols without precipitates could be produced using initial water concentrations up to 16 mole per mole Ti. Transparent gels could be obtained only when the molar ratio of H2O to Ti is < 4. Gels with up to 12 wt.% T1O2 could be produced provided a low pH is used (H /Ti + < 0.025). 

Colloidal dispersions, polymer solutions, and both colloidal and polymer gels can in principle behave like any of the above-mentioned materials. 

Gelatin behaves in a peculiar manner with water. In cold water it merely swells, but in hot water it dissolves readily, forming a colloidal dispersion. As long as you keep this dispersion warm, it remains in a liquid form that is called a sol. When cooled, it turns into a jelly-like form called a gel. ... 

Colloidal Dispersions or Solutions (Sols) and Colloids. Colloidal solutions (or rather "pseudo solutions ), also called sols (or in case of liquids hydrosols) are heterogeneous systems consisting of a "dispersion medium (mostly a liquid) and a "dispersed or "suspended medium known as a "colloid . Colloidal particles are invisible under ordinary microscope but detectable by the ultramicroscope. Their size ranges from ca 1 x 10 7 to 1 x 5 smm. If the dispersion is a viscous, sticky, transparent liquid, it is what is generally known as a "colloidal solution . As examples of this may be cited a soln of gum-arabic in water and sol ns of NC in acetone, ethyl acetate or ether alcohol. When "solns are dialized, most of the colloidal particles do not pass thru the membrane. This is their principal distinction from "crystalloids , which are substances like Na chloride, etc. If part of the volatile liquid (dispersing medium), is evaporated the resulting tacky, jellylike substance is known as a gel. 

Emulsions are colloidal dispersions of liquid droplets in another liquid phase, sometimes stabilized by surface active agents. Emulsions thus consist of a discontinuous phase, dispersed in a continuous phase. The most common types of emulsions are water-in-oil (W/O) in which oil is the continuous phase, and oil-in-water (OAV) in which water forms the continuous phase. However, this traditional definition of an emulsion is too narrow to include most food emulsions. For example, in foods the dispersed phase may be partially solidified, as in dairy products or the continuous phase may contain crystalline material, as in ice cream. It may also be a gel, as in several desserts. In addition to this, air bubbles may have been incorporated to produce the desired texture. 

Many foods are composed of colloidally dispersed phases. The colloidal properties have a great bearing on their texture, appearance, and stability against separation. Examples suspensions (chocolate), emulsions (milk), foams (ice-cream), and gels (mayonnaise). 

The spontaneous shrinking of a colloidal dispersion due to the release and exudation of some liquid frequently occurs in gels and foams but also occurs in flocculated suspensions. Mechanical syneresis refers to enhancing syneresis by the application of mechanical forces. Micro-syneresis is a special case of syneresis in which the polymer molecules cluster together while retaining some of the original bulk gel structure. This process creates regions of free liquid within the gel network. 

Using preformed sols instead of metal alkoxides as precursors is an attractive alternative in sol-gel preparation because recent advances in inorganic colloidal dispersions allow some control over the characteristics of the starting sols [11]. Often a colloidal suspension of sol particles is stabilized (i.e. prevented from flocculation) by pH adjustment. Thus, pH of the solution, which can be changed by the addition of either acid or base, is the single most important parameter in obtaining a gel from preformed sols. Other parameters that can impact on gel quality are the size and concentration of the starting sol particles. 

Non-porous Zr02 powders can be produced by high-temperature vapour phase condensation methods in this manner discrete spherical particles of c. 4 nm diameter have been obtained (Avery and Ramsay, 1973). It is also possible to prepare colloidal dispersions of sub-micron sized, spheroidal particles of basic salts such as Zr2(OH)6C03 and Zr2(0H)6SO4 with the aid of the carefully controlled sol-gel techniques developed by Matijevic (1988). 

---