1. Field of the Invention
The present invention relates generally to materials used for separating and concentrating solutes and, more particularly, to micellar materials for used for carrying out separating and concentrating functions.
2. Description of the Prior Art
One approach to the separation and concentration of solutes from solvents involves the employment of surfactants. Surfactants are two-part molecules with one part hydrophilic (the xe2x80x9cheadxe2x80x9d, often charged) and the other part hydrophobic (the xe2x80x9ctailxe2x80x9d, typically a hydrocarbon). In aqueous solution, surfactants aggregate into structures called micelles wherein the hydrophobic tails cluster together, and expose only their hydrophilic heads to the aqueous solution. These micelles are comprised of approximately 100 individual surfactant molecules that form a dynamic micellar aggregate with a typical diameter of 5 nm. The micelles are often colloidal in nature.
Oily or hydrophobic materials are readily solubilized in the hydrophobic core of the-surfactant micelles. The hydrophobic core provides an energetically favorable environment for solubilizing the oily molecules. In contrast, the hydrophilic head, water, and other polar solvents have unfavorable interaction energies with hydrophobic materials. Since the micelle is not a covalently bonded structure, the individual molecules are free to move, so that large quantities of hydrophobic solutes (with substantially no size restrictions on the individual solutes) can be accommodated by the hydrophobic core.
Some of the difficulties presented by surfactant micelles are their small size (5 nm) and their dynamic character. Due to their extremely small size and their colloidal nature, the micelles and material solubilized therein cannot be removed easily from solution by sedimentation, filtration, or any other comparable physical separation methods. In view of the problems associated with the small size of surfactant micelles, it would be desirable if a micellar material were provided that has macroscopic dimensions.
Their dynamic character also presents problems. The stability (and solubilization capacity) of a surfactant aggregate is highly sensitive to its chemical and physical environment. Slight changes in temperature, salt concentration, or solvent composition can instantly dissolve the aggregates and release their solubilized material. Despite these limitations, the surfactant industry is still a multi-billion dollar/year industry. In view of the problems associated with the dynamic character of surfactant micelles, it would be desirable if a micellar material were provided that has stable micellar properties even when experiencing from slight to substantial changes in its chemical and physical environment.
Although not xe2x80x9cprior artxe2x80x9d in the present case, the present inventor is the author of the published article entitled xe2x80x9cPolymerization of Rodlike Micellesxe2x80x9d, published in Langmuir, Volume 15, pages 2726-2732 (published on the World Wide Web on Mar. 19, 1999 by the American Chemical Society). The experiments reported therein confirm that the counterion polymerization procedure discussed hereinbelow produces extremely stable cylindrical micelles with a well-defined cross section. The article also includes a complete description of the experimental procedures used for the preparation, and the details of the modeling of small-angle neutron scattering (SANS) data, also presented hereinbelow. The polymerized micelles described in the article are fluid, not solid.
The above-mentioned article by the present inventor states that, in the prior art, a large variety of surfactants and surfactant aggregate structures have been polymerized, with varying levels of success in retaining the original structure. Surfactant structures have been polymerized in the form of spherical micelles, lamellae, and hexagonal arrays of cylinders. Other than in liquid-crystalline phases, rodlike micelles have not been polymerized, although elongated structures have been proposed as the polymerization product of globular micelles. In view of the above, it would be desirable if micellar material were provided that includes rodlike micelles in a polymerized aggregate structure, that is in a solid phase and that is useful in material separation procedures.
In another published article entitled xe2x80x9cNanoporous Polymer Have A Thing For Organicsxe2x80x9d, by Elizabeth Wilson, published in Chemical and Engineering News, Feb. 1, 1999, pages 32 and 33, there is a disclosure of three dimensional, crosslinked cyclodextrin-based polymers which can remove compounds such as trichloroethylene from water. These cyclodextrin-base polymers have hydrophobic pores whose sizes can range from 5 to 11 Angstroms. The cyclodextrin-based polymers are formed from closed-ring cyclodextrin which has a specific molecular size and structure. As a result, the cyclodextrin-based polymers have hydrophobic absorption properties which are fundamentally based upon the molecular size and structure of cyclodextrin. Moreover, it is noted that cyclodextrin is not a surfactant, does not have a head and a tail, and does not have positive and negative ends such as found in a surfactant. Because of the wide range of absorption versatility provided by surfactants having a head and a tail and having positively and negatively charged portions, it would be desirable if a three dimensional, crosslinked material were provided which is based upon a network of ionic surfactants.
Thus, while the foregoing indicates it to be well known to use materials to separate hydrophobic solutes from other materials, the prior art described above does not teach or suggest a crosslinked micellar gel composition which has the following combination of desirable features: (1) provides a micellar material that has macroscopic dimensions; (2) has stable micellar properties even when experiencing from slight to substantial changes in its chemical and physical environment; (3) includes rodlike micelles in a polymerized aggregate structure, that is in a solid phase and that is useful in material separation procedures; and (4) provides a three dimensional, crosslinked material which is based upon a network of ionic surfactants. The foregoing desired characteristics are provided by the unique crosslinked micellar gel composition of the present invention as will be made apparent from the following description thereof. Other advantages of the present invention over the prior art also will be rendered evident.
To achieve the foregoing and other advantages, the present invention, briefly described, provides a composition that is comprised of a polymer formed by a reaction between (a) ionic surfactant units which include ionic surfactant molecules, each of which includes a counterion which has a first polymerizable functional group, (b) crosslinking agent molecules, each of which includes two second polymerizable functional groups, and (c) a reaction initiator selected from the group consisting of reaction initiator molecules and ultraviolet light radiation, wherein the reaction initiator initiates a reaction between a plurality of the ionic surfactant units with each other and a plurality of the ionic surfactant units with the second polymerizable functional groups. The polymer composition formed from the reaction is comprised of ionic surfactant micelles which are rodlike in shape.
The ionic surfactant units can consist essentially of ionic surfactant molecules, such that the ionic surfactant units form homopolymer units which react with the crosslinking agent.
Alternatively, the ionic surfactant units can further include co-monomer molecules each of which includes a third polymerizable functional group. The first polymerizable functional groups of the ionic surfactant molecules react with the third polymerizable functional groups of the co-monomer molecules to form co-polymer units, and the reaction initiator initiates a reaction between a plurality of the co-polymer units and the crosslinking agent to form the crosslinked micellar gel composition. It is contemplated that the solubilization capacity of the crosslinked micellar gel composition that is formed can be enhanced by the co-polymer units. That is, in the co-polymer units which are comprised of the ionic surfactant molecules and the co-mononer molecules, the co-monomer molecules (such as styrene) may act as as a spacer between the polymerized counterions of the ionic surfactant molecules, allowing the micellar segments to swell to a larger radius and to solubilize a larger total quantity of hydrophobic material for a given volume of crosslinked micellar gel composition.
The first polymerizable functional group of the ionic surfactant counterions can be a first vinyl group. The crosslinking agent molecules can include two second vinyl groups. The co-monomer molecules can include styrene molecules, and the third polymerizable functional group can be a third vinyl group. The reaction initiator molecules can be free-radical initiator molecules.
More specifically, the ionic surfactant molecules can include cetyltrimethylammonium-vinylbenzoate (CTVB), and the crosslinking agent molecules can include divinyl benzene. The free-radical initiator molecules can include 2,2xe2x80x2-azobis[2-(2imidazolin-2-yl) propane] dihydrochloride.
The crosslinked micellar gel composition is a new material that is capable of solubilizing hydrophobic solutes at a molecular level such as is accomplished by conventional surfactant micelles. The new material has the solubilization capacity of a molecular-based surfactant micelles, and, in addition, has the distinct advantage of being crosslinked into a macro-micelle of macroscopic dimensions that is easy to physically handle, and thus separate the solute-absorbing macro-micelle from solution. In this way the crosslinked micellar gel composition can be used in separation processes. Also, the crosslinked micellar gel composition can be pre-loaded with a specific solute that can then be allowed to diffuse out of the gel in a controlled manner.
The above brief description sets forth rather broadly the more important features of the present invention in order that the detailed description thereof that follows may be better understood, and in order that the present contributions to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will be for the subject matter of the claims appended hereto.
In this respect, before explaining a preferred embodiment of the invention in detail, it is understood that the invention is not limited in its application to the details set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood, that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
It is therefore an object of the present invention to provide a crosslinked micellar gel composition which has many of the advantages of the prior art and few of the disadvantages.
A further object of the present invention is to provide a crosslinked micellar gel composition which provides a micellar material that has macroscopic dimensions.
Still another object of the present invention is to provide a crosslinked micellar gel composition that has stable micellar properties even when experiencing from slight to substantial changes in its chemical and physical environment.
Yet another object of the present invention is to provide a crosslinked micellar gel composition which includes rodlike micelles in a polymerized aggregate structure, that is in a solid phase and that is useful in material separation procedures.
Even another object of the present invention is to provide a crosslinked micellar gel composition that provides a three dimensional, crosslinked material which is based upon a network of ionic surfactants.
These together with still other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and the descriptive matter in which there are illustrated preferred embodiments of the invention.