US3860447A - Method of rendering a hydrophilic surface hydrophobic - Google Patents

Abstract

A method of rendering a hydrophilic surface hydrophobic is disclosed. The method comprises exposing the hydrophilic surface to an aqueous solution comprising an La 3 salt dissolved therein. The pH of the solution is maintained to at least about 3.5 and can range up to about 8.0. The exposed surface is then dried.

Description

United States Patent Townsend Jan. 14, 1975 METHOD OF RENDERING A 2,351,974 5/1943 Kollmarm. 106/1 HYDROPHILIC SURFACE HYDROPHOBIC 2,528,847 11/1950 Van Norden 117/169 2,762,168 9/1956 McCutchen 117/169 Inventor: Wesley Peter T0wnSend,East 3,657,003 4/1972 Kenney 117/34 Windsor, Mercer County, NJ.

[73] Assignee: Western Electric Company, Primary ExaminerWilliam D. Martin Incorporated, New York, NY. Assistant Examiner-Sadie L. Childs [22] Filed Jan 2 1973 Attorney, Agent, or Firm-J. Rosenstock 21 A LN 320,228 1 pp 0 57 ABSTRACT [52] CL" 117/169 R, 117/124 B 117/1388 R A method of rendering a hydrophilic surface hydro- 51 1m. (:1 C03c 17/10 is disclosed The methOd OmPrises exposing [58] Field of Searchm 117/124 B 169 R 1383 the hydrophilic surface to an aqueous solution com- 1/160 R 423/263 prising an La salt dissolved therein. The pH of the solution is maintained to at least about 3.5 and can [56] References Cited range up to about 8.0. The exposed surface is then UNITED STATES PATENTS 2,323,387 7/1943 Edelstein 117/169 3 Claims, No Drawings METHOD OF RENDERING A HYDROPHILIC SURFACE l-IYDROPHOBIC BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of rendering a hydrophilic surface hydrophobic and more particularly, to rendering a hydrophilic surface hydrophobic by treatment with an aqueous solution comprising an La species.

2. Discussion of the Prior Art For purposes of the instant disclosure, the terms wettable hydrophilic are used synonymously and interchangeably with each other, as are the opposite terms non-wettable and hydrophobic. Moreover, wettability and hydrophilicity are all indicated by the existence of a condition termed practical wetting.

Practical wetting is defined as the ability of a surface to retain, on a substantially macroscopically smooth, unroughened portion thereof, a continuous, thin, uniform layer of a liquid, such as water or other liquid medium, when the surface is held vertically, or in any other orientation. It should be noted that this definition does not necessarily refer to, nor depend on, contact angle, surface energy or surface tension. However, when practical wetting occurs, the contact angle goes to or closely approaches Thus, the term practical wetting encompasses all types of wetting, due to whatever cause or causes, that meet the above definition of the term.

Generally speaking, whether a surface is wet or not depends to a great extent on the surface (often termed free-surface or interfacial) energies (S.E.) or tensions (y) of (l) the surface to be wet, (2) the liquid with which the surface is to be wet, (3) the surface-liquid interface, and (4) the surface-vapor and liquid-vapor interfaces.

Again in general, and somewhat imprecisely, the occurrence or not of wetting by a liquid of a solid in a vapor environment (e.g., air) may be formulated as follows with respect to surface energies (SE):

(1) If: S.E. S.E. S.E., wetting occurs;

sur. liq. sun-liq.

(2) If. S.E. S.E. S.E., non-wetting occurs. sur. liq. sur.-liq.

Somewhat more precisely, when a liquid is on a surface,

ysur-vap='ysur-liq ('yliq-vap) (Cos0), where 0 is the contact angle. Wetting occurs if 0 E 0 and Cos 0 1. Actually, to be more technically accurate wetting occurs when Thus, water, which has a relatively high surface energy or tension, is unable to wet a polytetrafluoroethylene (Teflon a T.M. of DuPont) surface or a polyethylene surface, both of which have very low surface energies or tensions. Water, however, will normally wet clean glass which has a rather high surface energy or tension. Surface energies and tensions are extremely difficult to measure in many instances, and are often only qualitatively describable. The reason for this is that there are a large number of factors contributing, often in an unknown manner, to the character of surface energies and tensions. Such factors include, inter alia, dispersion forces, hydrogen bonding forces, ionic Interscience Publishers (1967); and Adhesion and Adhesives," edited by R. Houwink and G. Salomon, 2nd Ed., Vol. I, Elsevier Publishing Company (1965), pages 29-31.

That the relative surface energies or tensions of a surface and a liquid are favorable to the occurrence of wetting has been traditionally indicated by, among other things, the character of the so-called contact angle and the presence of spreading.

The contact angle is that angle measured through a liquid droplet between (a) a flat surface on which the liquid droplet resides and (b) a line tangent to the envelope of the droplet where the envelope intersects the surface.

According to one traditional school of thought, a surface is completely wet by a liquid if the contact angle is 0 and only partially wet if the contact angle is finite (i.e., 0 0). Complete non-wetting implies a contact angle of 180. Another traditional school of thought correlates contact angle 0 with non-wetting, and contact angle z 0 with wetting. A third traditional school of thought correlates contact angle with not-wetting, and 6 90 with wetting. A droplet of water on a Teflon surface exhibits a contact angle of about indicating non-wetting or partial wetting depending on which school is followed; on clean glass at standard pressure and temperature the contact angle of water is about 0, probably indicating wetting to all schools (although the indication to one school might be that of partial wetting).

Thus, there is some controversy as to the upper limits of contact angle size beyond which a condition of nonwetting is present. This controversy is one reason for the use herein of the term practical wetting, defined earlier.

Another indicia of the wetting of a surface by a liquid is spreading. Specifically, where a surface is immersed in a liquid and upon removal therefrom the liquid draws back, the liquid does not wet the surface.

Specifically, if a drop of a liquid beads up and assumes a spherical or nearly spherical shape, the liquid does not wet the surface. On the other hand, if the droplet on the surface spreads out over the surface, the liquid wets the surface. It has usually been observed that where spreading occurs,

at the surface-liquid interface. Obviously, this test is qualitative, and also presents difficulties where spreading is observed but the contact angle is greater than 0.

The above definition and use of the term practical wetting eliminates differentiation of contact angle situations falling between the two extremes of 0 and or between situations such as that of water on Teflon or on clean glass or on outgassed clean glass. Moreover, the difficulties presented by the concurrence of spreading and of a contact angle greater than 0 are avoided. Instead, if a liquid is retained, in accordance with the above definitiompractical wetting is present, contact angle, surface energy and other considerations aside. Conversely, if a liquid is not retained in accordance with the above definition, non-wetting occurs.

Hydrophilic materials such as glass, glazed or enameled articles, cloth, paper, etc., are many times required to be hydrophobic, i.e., water-repellent. For example, it is customary to treat glassfibres with oils, waxes, etc., during manufacture in order to protect the glass surface from the effect of moisture and to prevent loss of tensile strength by abrasion. Another illustration of the deleterious effects of moisture is found in glass bodies for electrical insulating purposes which, when exposed to the weather, lose their high electrical surface resistance under wet conditions. This is particularly true in the case of glass fibres having an extremely large surface per unit volume. A material which would help to preserve the high electrical surface resistance is highly desirable. Many other illustrations of the harmful effects of moisture exist but are too well known to require further discussion here.

The primary object of this invention is to render normally non-water-repellent, i.e., wettable, base members water-repellent, i.e., non-wettable.

SUMMARY OF THE INVENTION The present invention is directed to a method of rendering a hydrophilic surface hydrophobic and more particularly, to rendering a hydrophilic surface hydrophobic by treatment with an aqueous solution comprising an La species. That is, the aqueous solution comprises an La species (associated, e.g., as insoluble particles of a hydrous oxide of La, or dissociated, e.g., as ionized lanthanum ions such as La ions, or as a mixture of both). The method includes first preparing a de-wetting or anti-wetting aqueous solution comprising a La species by dissolving a suitable salt thereof in an aqueous medium. The pH of the resultant lanthanum salt solution is then maintained or adjusted, if necessary, with either the addition of a suitable acid or a suitable base thereto, to a value ranging from about 3.5 to about 8.0. The hydrophilic surface to be rendered hydrophobic is then treated with the resultant solution, having a pH ranging from about 3.5 to about 8.0, e.g., by immersion therein. After such treatment, the treated surface is dried.

Detailed Description The present invention is described primarily in terms of rendering a glass surface hydrophobic. However, it will be understood that such description is exemplary only and is for purposes of exposition and not for purposes of limitation. It will be readily appreciated that the inventive concept described is equally applicable to rendering other hydrophilic surfaces, organic and/or inorganic, hydrophobic. Some typical examples of such hydrophilic surfaces are glass, glazed or enameled articles, porcelain, asbestos, quartz, mica, cellulosics containing hydroxyl groups, fabricated cementitious materials, e.g., concrete bricks, metals, etc.

An anti-wetting or dewetting solution is prepared by dissolving a suitable lanthanum salt, e.g., La(NO 6H O in an aqueous medium to form a solution thereof comprising an La species, e.g., associated or dissociated as La ions (complexed or uncomplexed) or a mixture of both an associated and dissociated species. It is to be noted that at the present time the exact lanthanum species formed in the lanthanum salt solution which renders a hydrophilic surface hydrophobic is not known. Some typical suitable lanthanum salts include a nitrate, e.g., La(NO .6I-I O, (NH La (NO ',.4-

H 0, and a sulfate, e.g., La (SO.,) .8H O. In this regard, it is to be pointed out that any lanthanum salt can be used which is (l) soluble in water and/or (2) dissociates therein to form La ions which are either complexed or uncomplexed. By the term complexed is meant that the La ion does not exist by itself, but that a lanthanum ion is linked to other atoms or molecules.

The concentration of the lanthanum solution is not critical and may range from an amount greater than a mere trace amount, e.g., typically 0.00l weight percent, to a saturated solution at a particular temperature. A typical convenient concentration of an aqueous solution ranges from about 0.01 to about 10 weight percent of the particular lanthanum salt selected, i.e., from about 0.00025 molar to about 0.25 molar (calculated as La). However, the pH of the lanthanum solution has been found to be critical. If the pH is greater than about 8.0, the lanthanum solution is not an antiwetting solution and will not render a hydrophilic surface hydrophobic. If the pH is less than about 3.5, the degree of hydrophobicity is negligible, i.e., de-wetting is observed but to a very minimized extent as compared to when the pH is at least 3.5. If the pH of the resultant aqueous lanthanum solution is not within the range of about 3.5 to about 8.0, the pH may be adjusted thereto by either the addition of a suitable base, e.g., NaOH, or a suitable acid, e.g., I-lNO (depending upon the initial pH of the solution).

The surface to be rendered hydrophobic is then treated or exposed to the resultant anti-wetting or dewetting lanthanum solution. The surface may be exposed to the solution by any conventional means known in the art, e.g., dipping, spraying, brushing, etc., for a sufficient period of time, e.g., 5 to 30 seconds at 25C, whereby the solution contacts the entire surface. It is to be noted here that the contacted surfaces must not be rinsed, e.g., with water. The surface is then dried employing any conventional procedure known in the art, whereby a hydrophobic surface results.

It is to be noted that such driving may be effected by heating the surface or by vacuum techniques, or any conventional drying technique known in the art. The thus dried or evaporated surface is now rendered hydrophobic whereby water will be repelled therefrom.

EXAMPLE I A. For comparison purposes, a glass slide, commercially obtained, was immersed in a water bath for 10 seconds at a temperature of 25C. The glass slide was then removed from the water bath.

The surfaces of the glass slide were wet by the water, i.e., there was neither beading of the water on the surface nor drawing back of the water, but on the contrary, a thin uniform layer of water was formed on the surfaces thereof.

B. The procedure of Example I-A was repeated except that a 0.01 weight percent La(NO;,) .6H O antiwetting solution (pH 4.7) was prepared by dissolving the salt in water. The slide was immersed therein for 10 seconds and then removed from the solution. The glass slide was rendered hydrophobic as evidenced by the aqueous solution film drawing back (beading) on the surfaces thereof (a thin uniform covering layer of solution was not evidenced).

C. The procedure of Example I-B was repeated except that a 0.1 weight percent La(NO;,);,.6H-,,O antiwetting solution (pH 4.5) was prepared and the slide immersed therein for seconds. The glass slide was then removed from the solution. The glass slide was rendered hydrophobic as evidenced by the aqueous solution film drawing back (beading) on the surfaces thereof (a thin uniform covering layer of solution was not evidenced).

D. The procedure of Example l-B was repeated except that a 1.0 weight percent La(NO 6 I- l O antiwetfingsol ution (pH 3.75) was prepared and the slide immersed therein for 10 seconds. The glass slide was then removed from the solution. The glass slide was rendered hydrophobic as evidenced by the aqueous solution film drawing back (beading) on the surfaces thereof (a thin uniform covering layer of solution was not evidenced). There was no Tyndall effect observed in the anti-Wetting solution which indicated co]- loidal La particles (associated) were not present.

E. For comparison purposes, the procedure of Example I-D was repeated except that a 1.0 weight percent La(NO .6H O methanol solution was prepared. The glass slide was not rendered hydrophobic (a thin uniform covering layer of solution was evidenced).

F. The procedure of Example I-B was repeated except that a 1.0 weight percent La (SO .8H O antiwetting solution (pH 3.5) was prepared and the slide immersed therein for 10 seconds. The glass slide was then removed from the solution. The glass slide was rendered hydrophobic as evidenced by the aqueous solution film drawing back (beading) onthe surfaces thereof (a thin uniform covering layer of solution was not evidenced).

G. The procedure of Example l-B was repeated except that a 2.0 weight percent La(NO .6l-I O antiwetting solution (pH 3.7) was prepared and the slide immersed therein for 10 seconds. The glass slide was then removed from the solution. The glass slide was rendered hydrophobic as evidenced by the aqueous solution film drawing back (beading) on the surfaces thereof (a thin uniform covering layer of solution was not evidenced).

The glass slide was then evaporated almost to dryness and was then immersed in a water bath. The glass slide was hydrophobic as evidenced by the fact that the surfaces of the glass slide were not wet by water, i.e., a thin uniform layer of solution was not evidenced but rather a beading.

H. The procedure of Example I-G was repeated except that the glass slide was only partially immersed in the anti-wetting solution for 5 seconds. The glass slide was removed from the solution and completely evaporated to dryness. The glass slide was then fully immersed in a water bath, maintained at 25C for seconds, whereby the portion not immersed in the antiwetting solution was completely wet by the water, i.e., a thin uniform covering layer of water formed on the surfaces thereof upon removal from the water bath. The portion of the slide immersed in the anti-wetting solution had now become hydrophobic as evidenced by the fact that the surfaces of this portion were not wet by water, i.e., a thin uniform covering layer of water was not evidenced, but rather a beading, upon removal from the water bath.

1. The procedure of Example [-6 was repeated except that sufficient N aOI-l was added to the resulting lanthanum solution to raise the pH to 6.5. The glass slide was first immersed in a water bath, maintained at 25C, for I 10 seconds, and exhibited hydrophilicity. The same glass slide was then immersed in the anti-wetting solution for l0 seconds at 25C and was rendered hydrophobic as evidenced by the fact that the aqueous solution film was drawing back (beading) on the surfaces thereof, upon removal from the anti-wetting solution.

J. The procedure of Example l-G was repeated except that a polyethyleneterephthalate film, commercially obtained, was employed. The film was not wet by the anti-wetting solution.

K. For comparison purposes, the procedure of Example I-J was repeated except that the lanthanum solution had sufficient NaOH added thereto to raise the pH to about 9. The polyethyleneterephthalate film was wet by the resultant solution, i.e., there was exhibited a thin uniform layer of the solution covering the surfaces thereof, upon removal of the film from the solution.

L. For comparison purposes, the procedure of Example I-G was repeated except that the lanthanum solution had sufficient NaOH added thereto to raise the pH to about 10.5. The glass slide was wet by the resultant solution, i.e., there was exhibited a thin uniform layer of the solution covering the surfaces thereof, upon removal of the slide from the solution.

EXAMPLE II A. The procedure of Example l-B was repeated except that the glass slide was removed from the antiwetting solution and evaporated to dryness. The slide was then rinsed with water and exhibited hydrophobicity as evidenced by the failure to form a uniform covering layer of water on the surfaces, i.e., there was a drawing back of the water at the edges of the glass slide.

B. The procedure of Example l-C was repeated except that the glass slide was removed from the antiwetting solution and evaporated to dryness. The slide was then rinsed with water and exhibited hydrophobicity as evidenced by the failure to form a uniform covering layer of water on the surfaces, i.e., there was a drawing back of the water.

C. The procedure of Example l-D was repeated except that the glass slide was removed from the antiwetting solution and evaporated to dryness. The slide was then rinsed with water and exhibited no wetting thereby on the surfaces thereof even under the influence of agitation.

D. For comparison purposes, the procedure of Example II-C was repeated (without the agitation) except that the pH of the resultant solution was adjusted to 3.3 by the addition of HCl. The glass slide was subsequently wet when rinsed with water although some very slight drawing back of the water was observed at the edges of the glass slide.

E. For comparison purposes, the procedure of Example Il-C was repeated (without the agitation) except that the pH was adjusted to 2.6 by the addition of HCl. The glass slide was not rendered hydrophobic.

F. For comparison purposes, the procedure of Example II-C was repeated (without the agitation) except that the pH of the resultant solution was adjusted to l .9 by the addition of HCl. The glass slide was not rendered hydrophobic.

G. The procedure of Example l-F was repeated except that the glass slide was removed from the antiwetting solution and evaporated to dryness. The slide was then rinsed with water and exhibited a minimal degree of hydrophobicity (drawing back of the water at the edges of the slide). This is not explainable except as an experimental anomaly.

H. The procedure of Example Il-G was repeated except that a j weightpercent La (SO., 8H O solution (pH 2.9) was prepared. All of the salt was observed not to dissolve in the aqueous medium. There was a minimal degree of de-wetting observed as in Example ll-G, i.e., negligible hydrophobicity was observed.

I. The procedure of Example ll-H was repeated except that the pH of the resultant solution was adjusted to 3.6 by the addition of HCl and NaOH in combination. The glass slide exhibited a much greater drawing back to a much greater extent then Example II-H.

J. An anti-wetting solution was prepared by dissolving weight percent of La(NO .6H O in water. The procedure of Example II-A was then repeated. The slide, upon rinsing with water, exhibited no wetting thereby on the surfaces thereof.

K. An anti-wetting solution was prepared by first dissolving l.0 weight percent of (N H4) La(NO )5.4I-l2O in water (pl-l=4.6). The pH was then adjusted to 7.0 by the addition of NaOH. The procedure of Example Il-A was then repeated. The glass slide exhibited some hydrophobic character as evidenced by the water drawing back from the edges of the glass slide.

EXAMPLE III A. A polyimide film, commercially obtained, which is normally hydrophobic was rendered hydrophilic by treatment with ION NaOH at 60C for 30 seconds followed by a water rinse at 60C for 4 minutes. The now hydrophilic polyimide film was then immersed in a 1.0 weight percent La(NO3)3.6H2O anti-wetting solution, maintained at 25C, for 10 seconds. The film was rendered hydrophobic again as evidenced by the aqueous solution drawing back (beading) on the surfaces thereof, upon removal of the polyimide film from the solution.

For comparison purposes, another caustic treated polyimide film (hydrophilic) was immersed in a water imide film (hydrophilic) showed some hydrophobic character but to a much lesser extent than exhibited in Example III-A, since the drawing back of the solution on the surfaces thereof upon removal therefrom was not as rapid. The cause for this decreased efficiency is unknown.

C. The procedure of Example llI-B was repeated except that an untreated glass slide was employed. Again upon immersion in the solution for 10 seconds at 25C and removal therefrom, the glass slide exhibited complete hydrophilicity, i.e., was completely wet by the solution. Again this is an unexplainable result.

It is to be understood that the above-described embodiments are simply illustrative of the principles of the invention. Various other modifications and changes may be made by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. In a method of rendering a hydrophilic surface hydrophobic, which comprises exposing the surface to an aqueous, inorganic solution comprising a La salt dissolved therein, said solution having a pH ranging from 3.5 to 8.0.

2. The method as defined in claim 1, which further comprises drying said exposed surface.

3. The method as defined in claim 1 wherein:

said aqueous solution comprises a dissolved lanthanum salt selected from the group consisting of a lanthanum nitrate, a lanthanum sulfate, and a lanthanum ammonium nitrate.

Claims (3)

1. IN A METHOD OF RENDERING A HYDROPHILIC SURFACE HYDROPHOBIC, WHICH COMPRISES EXPOSING THE SURFACE TO AN AQUEOUS, INORGANIC SOLUTION COMPRISING A LA+3 SALT DISSOLVED THEREIN, SAID SOLUTION HAVING A PH RANGING FROM 3.5 TO 8.0.

2. The method as defined in claim 1, which further comprises drying said exposed surface.

3. The method as defined in claim 1 wherein: said aqueous solution comprises a dissolved lanthanum salt selected from the group consisting of a lanthanum nitrate, a lanthanum sulfate, and a lanthanum ammonium nitrate.