Siloxane Surface Activity - Advances in Chemistry (ACS Publications)

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Siloxane Surface Activity Michael J. Owen Dow Corning Corporation, Midland, MI 48686-0994

The structure, properties, and uses of poly(dimethylsiloxane) are surveyed in relation to its surface activity, with emphasis on the structural basis of this activity: the low intermolecular forces between methyl groups and the unique flexibility of the siloxane backbone. These basic attributes are used to explain the general interaction of poly(dimethylsiloxane) with high- and low-surface-energy substrates. The effects of variations of the pendant organic group and the backbone on surface activity are reviewed, and examples of current research and applications are given. The chief focus is on aliphatic fluorosilicones, because this class contains organosilicon polymers with the lowest surface energy. Information about organosilicon polymers with backbones other than siloxane is limited. The available data on polysilazanes, polysilalkylenes, and polysilanes are reviewed.

THE SURFACE PROPERTE IS OF SILICONES,

particularly the commercially available poly(dimethylsiloxane) (PDMS) materials, are best described by regarding polymer side chains or pendant groups as the primary surfaceactive entities, with the polymer backbone controlling the way in which these pendant groups are presented at a surface (I, 2). The surface and interfacial properties and applications of PDMS are examined in this chapter in this context. PDMS has a very surface-active (low-surface-energy) pendant group, the methyl group, which is arranged along the mostflexiblebackbone, the siloxane chain. The siloxane chain allows the methyl groups to be presented to their best effect. These structural features account for the many surface applications of PDMS. To separate the roles of the pendant group and the backbone is a gross but useful simplification in explaining why PDMS has a critical surface tension of wetting similar to those of hydrocarbons with surfaces consisting of 0065-2393/90/0224-0705$09.75/0 © 1990 American Chemical Society

In Silicon-Based Polymer Science; Zeigler, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

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SILICON-BASED POLYMER SCIENCE: A COMPREHENSIVE RESOURCE

closely packed methyl groups. Because of the extreme localization of the force fields in covalently bonded methyl groups, pendant methyl groups on PDMS also behave as an array of closely packed methyl groups with little direct effect from the siloxane backbone. This analysis based on pendantgroup and backbone variations provides a convenient way of surveying other organosilicon polymers and is also a starting point for property-use predictions when such data are not available, especially for organosilicon polymers with backbones other than siloxane. Thefluorosiliconesare emphasized in this review, because this class contains organosilicon polymers with the lowest surface tension. The surface activity of silicones is often exploited by using them as additives. For this reason, aspects of the two most important additive forms, copolymers and surfactants, are also included in this discussion. These two classes come together in the relatively low molecular weight PDMSpoly(alkylene oxide) block and graft copolymers that are commonly used as polyurethane foam stabilizers. Other short-chain silicone surfactants designed for aqueous systems and other silicone-organic copolymers are also available.

PDMS Surface Behavior PDMS is an unusual maeromolecular amphiphile composed of pendant organic methyl groups along the siloxane backbone. Its surface properties result in a wide variety of applications. Specific examples are listed in Table I (3), which demonstrates the diversity of interfaces at which PDMS-containing materials are active and the apparently contradictory nature of many of the applications: adhesion and release, foaming and antifoaming, etc. Surface Tension. The most familiar surface characteristic of PDMS is its low liquid surface tension, ranging from 16 to 21 mN/m at room temperature, depending on molecular weight. This value is lower than the surface tensions of most other polymer systems; only aliphatic fluorocarbon species have lower surface tensions. Figure 1 (1) shows the dependence of liquid surface tension at 20°C on the boiling point of a variety of C H 3 - and CF3-containing materials. As the temperature of a material approaches its boiling point, molecular motion increases, and surface tension decreases because of increased intermolecular separation. Thus, the surface tensions of materials at 20 ° C increase with the boiling point. This point is important when simple liquids of different types are compared. The low surface tension accounts for the tendency of PDMS-containing materials to accumulate at air-substrate surfaces. At condensed interfaces, such as that between organic oils and water, the same surface tension driving force does not exist for PDMS to accumulate at the interface. PDMS has a


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Siloxane Surface Activity

Table I. Applications of PDMS-Based Surface-Active Additives Interface

Stabilizing Action

Air-water


Air-oil

Super-wetting agent, e.g., for polyethylene and polypropylene Solvent-based coating and leveling aid

Air-polymer

Urethane foam formation

Air-solid

Fertilizer anticaking aid

Water-oil

Hydrocarbon oil-inwater emulsifiers0 Silicone polymer fluid-water emulsifiers Coal slurry stabili zationc Pigment treatment (e.g., TiO a ) to enhance dispersion in paint resin Organic pressuresensitive adhesive release coating

Water-polymer Water-solid Polymer-solid

Polymer-polymer

Destabilizing

Action

Aqueous antifoams, e.g., in paper production Foam control in gas scrubbing at petro chemical plants Defoaming during monomer stripping processes Masonry water repellant (for dewetting surface treatment) Water-in-crude-oil deemulsifiers Emulsion polymer coalescence aid& Coal dewateringc Nonspreading synthetic lubricant (e.g., for use as a clock oil) Silicone pressuresensitive adhesive

SOURCE: Reproduced with permission from reference 3. (Copyright 1986 Plenum.) "This application has been claimed in patents. fo This application is still hypothetical. c This application is being developed.

lower interfacial tension against pure water compared with nonpolar hydrocarbons, but more-polar oils can be significantly more surface active. Copolymerization with other species is a major way of achieving the necessary interfacial activity to modify condensed interfaces and to vary compatibility with various phases. Incompatibility is another driving force toward surface or interfacial segregation. The balancing of these tendencies by controlling molecular weight, copolymer composition, etc., produces products with seemingly contradictory actions (Table I), which can be explained by the surface properties. For example, the formation and destruction of colloidal systems involve surface forces, and surface-active materials such as PDMS will affect both processes. Different attributes of PDMS are exploited in each application, with modifications made to enhance desirable attributes and to minimize undesirable attributes. These various attributes of PDMS relevant to these applications are the following: • low surface tension and moderate interfacial tension against water;



708


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I

I

I

I

L_J

I

I

I

I

I

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40 60 80 100 120 140160 180 200 220 240 260 280 300 B.P. °C Figure 1. Dependence of surface tension at 20 °C on boiling point for a variety ofCH - and CF -containing materials. (Reproduced from reference 1. Copyright 1980 American Chemical Society.) 3

3

• high water repelleney; • good wetting, spreading, andflow-outaid; • large free volume; • low apparent energy of activation for viscous flow; • low glass transition temperature; • free rotation about bonds; • high compressibility and dampening action;


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709

• liquid nature to high molecular weight; • low boiling, freezing, and pour points; • small temperature variation of physical constants;


• high dielectric strength, gas permeability, and resistance to shear; • high thermal and oxidative resistance; • low reactivity, toxicity, and combustibility; • low environmental hazard; and • insolubility in water. This list is an extended version of Table II in reference 3. Some relevant numerical data are given in Table II (4-16). Not all the attributes in the list pertain to surface activity, but a product is rarely used for a surface-active application for surface characteristics alone. Usually a combination of appropriate surface properties and other useful aspects, such as high-temperature stability or long durability to weathering, determines which material is preferred for a specific application. Molecular Basis of PDMS Surface Activity. Four structural characteristics of PDMS account for these attributes and are the link between the structure, properties, and uses of PDMS and most other silicone materials: 1. low intermolecular forces between methyl groups, 2. unique flexibility of siloxane backbone, 3. high energy of siloxane bond, and 4. partial ionic nature of siloxane bond. The first two structural features explain much of the physical behavior of PDMS in various environments, whereas the last two explain the chemical consequences of the hybrid organic-inorganic nature of PDMS. Low Intermolecular Forces Between Methyl Groups. The energy ranges of intermolecular forces across an interface are shown in Table III, which is based on one given by Good (17). The lowest of the London dispersion forces are the weakest intermolecular interactions between molecules and, for pendant groups in polymers, are those associated with aliphatic hydrocarbon andfluorocarbongroups. The weak intermolecular interactions between these groups are reflected in Zisman's critical surface tension of wetting (18). The surfaces with the lowest energy are those based on the constituent groups - C F 3 , - C F 2 - , - C H 3 , and - C H 2 - and the various mixed



Surface viscosity Structural properties Si-O bond length Si-C bond length

Surface properties Surface tension Interfacial tension (against water) Critical surface tension of wetting Polar component of surface tension Dispersion force component of surface tension Water contact angle

Property

μ-g/s nm nm

- C H 3 > - C F 2 - > - C F 3 . Table IV. Owens-Wendt Solid Surface Tension Data Material

Poly(l, 1-dihydroperfluorooctyl methacrylate) Poly(tetrafluoroethylene) PDMS Paraffin wax Polyethylene Nylon 6,6 Poly(methyl methacrylate) Polystyrene NOTE:

Dispersion Component

Polar Component

9.1 12.5 21.7 25.4 32.0 34.1 35.9 41.4

0.3 1.5 1.1 0 1.1 9.1 4.3 0.6

Data were taken from reference 7. Values are expressed in millinewtons per meter.

Thus among hydrocarbons, surfaces comprising closely packed methyl groups have the lowest surface tensions. For this reason, both PDMS and paraffin wax have similar surface tensions despite the difference in their molecular architectures. Essentially, both PDMS and paraffin wax have allmethyl surfaces. Evidence for the low intermolecular forces between methyl groups in PDMS comes not only from low surface tensions but also from the lower boiling points of PDMS materials compared with those of organic materials of similar molecular weight. Noll (19) gives some useful data on this topic. The maintenance of liquid nature to unusually high molecular weights of linear PDMS polymers is a further consequence of this weak molecular interaction. Like surface tension, viscosity is a manifestation of the physical inter action between molecules. The uniquely shallow slope of the viscos ity-temperature curve of PDMS (20) is due in part to low intermolecular forces. The interfacial viscosity of PDMS (20 kj/mol for



714


poly(tetrafluoroethylene) (13). This free rotation is reflected in the glass transition temperature (Tg). However, the internal mobility of chains is not the only factor that determines T g ; polymer free volume, attractive forces between molecules, bulkiness of pendant groups, and chain length all con tribute to T g . Nevertheless, a low T g indicates polymer flexibility. Several classes of polymers have T g s of °o indicates that the data are values of liquid surface tension at infinite molecular weight of the polymer.

2

Ref

Equilibrium Liquid Surface Tension

Table X. Comparison of PTFPMS with Other Fluorocarbon Polymers


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Backbone Variations The surface activity of organosilicon polymers with backbones other than siloxane is not very well known. Interest in varying the backbone in or ganosilicon polymers does not normally stem from a desire to modify surface properties. Usually, the purpose of backbone variation is to increase thermal stability, as for example, with poly(silphenylenesiloxane) and poly(carboranesiloxane) copolymers. Because thermal stability is often achieved by increasing T g s by using rigid backbones, most backbone variations will have a detrimental effect on polymer surface activity. The plot of surface tension versus boiling point for simple liquids such as hexamethyldisilazane and hexamethyldisilmethylene suggests that these two simple liquids will have similar surface energies, which are 2-3 mN/m higher than that of PDMS (Table XI [78-80]). The Tgs agree with this inference. By keeping the pendant groups the same (methyl), the effects of intermolecular-force and steric-bulk variations will be minimized, and T g s will reflect mainly the other key factor, backbone flexibility. Table XI. Liquid Surface Tensions (σιν) of Organosilicon Dimers (mN/m)

Temp. CO

18.2 17.6 18.9 18.4 19.4 15.8 15.7 15.5

25 24 20 24 20 20 20 20

a

Dimer (CH3)3SiNHSi(CH )3 3

(CH3)3SiCH2Si(CH )3 3

(CH3)3Si(CH2)2Si(CH3)3 (CH3)3SiOSi(CH3)3

Boiling Point (°C)

Ref.

b

78

126

c

132 (740)

79 this work 79 79 4 80

151 (760) 99

Temperature of measurement. è The numbers in parentheses indicate the pressure in millimeters of Hg. 1 mm of Hg = 133 Pa. c The result is previously unpublished and was obtained by G. ]. Quaal in 1964.

Tgs for polymers with architectures similar to PDMS are given in Table XII (21, 81). The T g s of poly(dimethylsilazane) and poly(dimethylsilmethylene) lie between those of PDMS and poly(isobutylene) (critical surface tensions of wetting of 24 and 27 mN/m, respectively [70]). These values suggest that poly(dimethylsilazane) and poly(dimethylsilmethylene) will have critical surface tensions of wetting in the 25-26-mN/m range.

Surface Tension of Aqueous Surfactant Solutions.

The 25-26-

mN/m range is the best range that methylsilmethylene- and methylsilanebased surfactants can lower the surface tension of aqueous solutions, as demonstrated by the work of Maki and co-workers at the University of Osaka (82-85). Some selected data relevant to the comparison of methylsilmeth-


730


Table XII. Tgs of Polymers of the Structure -[(CH3)2X-Y]nPolymer X Y T g (K) 146 PDMS ο Si NH Poly(dimethylsilazane) Si 191 CH Poly(dimethylsilmethylene) Si 173 (CH ) Poly(dimethylsilpropylene) Si 203 CH C Poly(isobutylene) 200 C Poly(isobutylene oxide) CH 0 264 Poly(acetone) 0 unknown c Ν Poly(dimethylphosphazene) Ρ 227 2


2

3

2

2

NOTE: All Tgs were taken from reference 21 except that for poly(dimethylphosphazene), which comes from reference 81.

ylene- and methylsilane-based surfactants with methylsiloxane surfactants are given in Table XIII (82-84). Surfactants and block polymers useful for lowering the surface tension of solutions have two components: the hydrophobe, which has a lower surface tension and is usually insoluble in aqueous solutions, and the hydrophile, which is the more compatible component. The lowering of surface tensions of solutions provides evidence of the degree of surface activity of the hy drophobe but is a less reliable way of inferring surface activity compared with direct surface tension measurement of the hydrophobic material, be cause surface tension lowering depends also on the concentration of surfac tant used, the type and relative proportions of hydrophobe and hydrophile, the overall molecular weight of the surfactant, and the solvent used. Never theless, even the best surfactant of a given class cannot perform beyond certain limits, and these limits offer a useful measure of surface activity. Surfactant surface activity is most completely presented in the form of the Gibbs adsorption isotherm, the plot of solution surface tension versus the logarithm of surfactant concentration. For many pure surfactants, the critical micelle concentration (CMC) defines the limit above which surface tension does not change with concentration, because at this stage, the surface is saturated with surfactant molecules. The C M C is a measure of surfactant efficiency, and the surface tension at or above the C M C (the low-surfacetension plateau) is an index of surfactant effectiveness (Table XIII). A sur factant concentration of 1% was chosen where possible from these various dissimilar studies to ensure a surface tension value above the C M C . Sur factants with hydrophobes based on methylsiloxanes can achieve a low sur face tension plateau for aqueous solutions of —21-22 mN/m. There is ample confirmation of this fact in the literature (86, 87). Other organosilicon hydrophobes have not been studied much except by Maki and co-workers (82-85), who examined a much wider range of materials and situations than is considered in Table XIII. They studied cationic as well as nonionic surfactants and included such properties as foam



2

so

P

so

Table XIII. Aqueous-Solution Surface Tension (a i ) of Organosilicon Trimer Surfactants u in Temp. Surfactant (mN/m) (°C) (CH3)3Si[0(CH3)2Si]2(CH2)30CH2CH(CH2OCH3)(OCH2CH2)iiOH 24.4 25 (CH3)3Si[0(CH3)2Si]2(CH2)30CH2CH(CH2OCH3)(OCH2CH2)5OH 23.4 25 [(CH3)3SiO]2(CH3)Si(CH )3(OCH2CH2)nOH 21.5 25 [(CH3)3SiO]2(CH3)Si(CH2)3(OCH2CH2)7OOCCH3 20.4fe 23 (CH3)3Si[CH2(CH3)2Si]2(CH2)3OCH2CH(CH2OCH3)(OCH2CH2)9OH 27.6 25 (CH3)3Si[CH2(CH3)2Si]2(CH2)3OCH2CH(CH2OCH3)(OCH2CH2)6OH 26.7 25 [(CH3)3SiCH2]2(CH3)Si(CH2)3(OCH2CH2)6OOCCH3 24.6* 23 (CH3)3Si[(CH3)2Si]2(CH2)3(OCH2CH2)8OH _25 25 NOTE: Surfactants were used at a concentration of 1% except where indicated. The result is previously unpublished and was obtained by L. Flaningam in 1966. ^Surfactant concentration was 0.1%.


Ref. 82 82 —a this work 83 83 this work 84


732


stability and bacteriostatic action for cationic surfactants and interfacial ten sion with silicone fluid, surface tension reduction of polyols, and wetting of polyethylene for nonionic surfactants. These properties reflect the uses of such materials, but for this examination of backbone variation, only the surface tension lowering of aqueous solutions is considered. Some peculiar ities were noted with certain chain lengths, but generally, Maki et al. (82-85) found that the surface activities of poly(methylsilmethylene) and poly(methylsilane) are similar, and both are inferior to that of poly(methylsiloxane)s. The low-surface-tension plateau is 25-26 mN/m for poly(methylsilmethylene) and poly(methylsilane) and 21-22 mN/m for poly(methylsiloxane). The values in Table XIII from my work tend to be lower than those of Maki and co-workers (82-85). This difference probably reflects an aging effect, because more time for equilibration was allowed in my study. Plasma-Polymerized Polymers. Another significant study of or ganosilicon backbone variations was reported by Wrobel (88, 89), who measured solid surface tensions of plasma-polymerized dimethylsiloxane, dimethylsilazane, and dimethylsilane monomers by using the Owens-Wendt approach (Table XIV [7, 88-90]). Changes on aging that were observed are possibly due to further reaction of radical species, but because these changes do not affect the conclusions presented in this chapter, only immediate postplasma data are given in the table. WrobeFs data agree with the trends presented earlier. Poly(dimethylsilazane) and poly(dimethylsilane) have sur face tensions that are similar and higher than that of poly(dimethylsiloxane).

Table XIV. Surface Tensions of Plasma Polymer Films Deposited from Organosilicon Monomers Starting Monomer

Hexamethyldisiloxane Hexamethyley elotrisiloxane Octamethylcyclotetrasiloxane Hexamethyldisilazane Hexamethylcyclotrisilazane Octamethylcyclotetrasilazane Bis(dimethylsilyl)tetramethylcyclodisilazane Hexamethyldisilane Dodecamethylcyclohexasilane Silane Tetramethyldisiloxanea PDMS f c

σ

ά

27.4 25.7 25.7 28.3 30.1 38.0 33.4 30.7 34.3 32.9 24.9 20.5

1.7 1.8 1.8 4.6 5.3 7.0 2.0 1.9 7.1 8.0 0.8 1.6

29.1 27.5 27.5 32.9 35.4 45.0 35.4 32.6 41.4 40.9 25.7 22.1

NOTE: All data are from references 8 8 and 8 9 except where indicated. σ is the nonpolar component of surface tension, σ ρ is the polar component of surface tension, and σ 5 ν is the Owens-Wendt solid surface tension. All values are in units of millinewtons per meter. "Data are from reference 90. fc PDMS is a nonplasma polymer included for comparison (7). ά



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Plasma-polymerized materials differ significantly from those polymerized by conventional methods in their surface properties, and surface tension values do not correspond. This difference may be due to the highly cross-linked nature of plasma polymers or to the incorporation of other entities from the carrier gas. These effects are more important than the intrinsic differences in backbone flexibility. Wrobel (88) presents ATR-IR (attenuated total re flection infrared) spectroscopic data indicating that silazanes and silanes cross-link more readily than do siloxanes under plasma conditions. Wrobel and his co-workers (89) have also used contact angles to study the thermal decomposition of plasma-polymerized organosilicon polymers. These data are comprehensive, but they are not the only contact-angle data on plasma-polymerized organosilicon polymers. Hexamethyldisilazane, in particular, has been studied by several groups, and differences in results have not been reconciled yet. For instance, Eib and co-workers (91) obtained critical surface tensions in the 22-24-mN/m range, which is similar to that for conventionally polymerized PDMS, whereas Inagaki and co-workers (92) reported higher solid surface tensions closer to that reported by Wrobel (88). Varshney and Beatty (93) obtained critical surface tensions of wetting in the 24-28-mN/ m range that could be reduced by polymerization in the presence of nitrogen and ammonia, but despite this reduction in critical surface ten sions, the polymers had lower water contact angles. Hirotsu (94) measured water contact angles only and got higher values (~ 100°) compared with that obtained by Varshney and Beatty (—95°). Wrobel (88) and Sachdev and Sachdev (95) obtained still lower values (84° and 78° respectively). Hirotsu's work did not suggest a minimum surface tension with thickness, whereas Eib and co-workers detected a minimum surface tension at 10-20-nm thickness. These papers also contain ESCA (electron spectroscopy for chemical analysis) and IR data that shed light on these differences. For instance Eib's (91) ESCA data suggests a structure akin to [(CH 3 ) 2 SiNH(CH3) 2 SiO] n , in keeping with the low value obtained for the surface tension. Some of the differences are due to different reaction con ditions given in these papers, which provide a better appreciation of this debate.

Other Variations I have focused on methyl derivatives of nonsiloxane organosilicon backbones to achieve a useful comparison of polymer backbones. There are studies on materials with pendant groups other than methyl and backbones other than siloxane. The most useful of these studies is the direct liquid-surface-tension measurement by Feher and co-workers (96) of silane oligomers from trisilane to heptasilane, including some branched species (Table XV). (96-99). The data are useful because they answer the question of the surface activity contribution of the S i - Η group. The situation with SiH-containing siloxanes


734


Table XV. Liquid Surface Tension of Silane Oligomers at 20 °C (mN/m)

Boiling Point (° C)

Ref.

21.7 at -33°C 18.7 19.1 20.9 21.1 22.4 22.8 23.4 24.2 19.1 24.0 24.7

-15 53 102 90 146 153 185 194 227 58 149 215

97 96 96 96 96 96 96 96 96 98 99 99

σίν


Oligomer

Disilane Trisilane 2-Silyltrisilane n-Tetrasilane 2-Silyltetrasilane n-Pentasilane 2-Silylpentasilane n-Hexasilane n-Heptasilane Tetrachlorosilane Hexachlorodisilane Octachlorotrisilane

is confusing, because all data are for H(CH 3 )SiO systems, and effects such as the small size of the hydrogen atom allowing the methyl group to occupy better the outermost surface cannot be distinguished from the intrinsic effect of the hydrogen. On a diagram of surface tension versus boiling point (such as Figure 1), the surface tensions of silane oligomers are higher than that of PDMS and are much closer to the n-alkane line. This similarity is in line with the similar electronegativity differences of the S i - Η and C - H bonds. Despite their similar surface tension effects, the bonds are of very different reactivity, and there is little hope of exploiting - S i H 3 as a new low-surfaceenergy pendant group akin to - C H 3 . Some studies of perchlorosilanes (98, 99), also included in Table XV, show that the Si-Cl entity gives a surface tension that is only up to a few millinewtons per meter higher than that given by S i - Η . This trend is in the same direction but less than that for the substituted-earbon case and is surprising because the electronegativity dif ference of Si-Cl is greater than that of C - C l .

Summary PDMS is the mainstay of the silicone industry, and the majority of its ap plications are related to its unusual surface properties. Most of these appli cations are not the result of surface behavior alone but come from desirable combinations of surface properties and other characteristics, such as resist ance to weathering, high- and low-temperature serviceability, and high gas permeability. These applications are all a direct consequence of four fun damental structural properties of PDMS, namely: (1) the low intermolecular forces between the methyl groups, (2) the uniqueflexibilityof the siloxane backbone, (3) the high energy of the siloxane bond, and (4) the partially



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Siloxane Surface

Activity

735

ionic nature of the siloxane bond. These four structural features determine the surface behavior of PDMS and provide a framework for structureproperty-use correlations. PDMS was compared with other polymers, mostly other organosilicon polymers, although some organic and fluorocarbon polymers were included. Both the effects of pendant side groups and backbone variations were examined. PDMS emerged from this comparison as a polymer with particularly desirable surface properties brought about by having pendant groups with low surface energy arranged along the mostflexiblebackbone. Only aliphatic fluorocarbon groups are intrinsically of lower surface energies compared with aliphatic hydrocarbon, and only polymers with extensive aliphatic fluorination, such asfluorosilicones,fluoroacrylates,fluoromethacrylates,fluoroethers, andfluorocarbons,have lower surface tensions. For this reason, fluorosilicones, including the unusual case of the most commercially available example, poly(trifluoropropylmethylsiloxane), were reviewed in greater detail.

Future Directions The expansion of this unique set of surface properties is virtually limitless, and the next 40-50 years should give as varied results as the previous decades. A short list of our anticipations includes the following: 1. improvements in quantity and quality of surface property data, 2. calculation from first principles of polymer-substrate interactions, 3. considerable use of highlyfluorinatedfluorosilicones, 4. tailored organosilicon additives to other materials, particularly block polymers and surfactants, 5. more hybrids of organosilicon compounds and natural products, 6. more liquid-solid interfacial applications, 7. expansion of use in personal-care products and medical devices, 8. exploration of more-flexible backbones and pendant groups with even lower surface energies, 9. exploitation of polymers in which the silicon atom is in the pendant group and not in the backbone, and 10. development of applications of organosilicon plasma-polymerized materials.



736


Abbreviations and Symbols ATR-IR CMC ESCA H LB PCTFE PDMS PTFE PTFPM S Tg oc osv osoln σ1ν od σρ

Attenuated total reflection infrared critical micelle concentration electron spectroscopy for chemical analysis hydrophilic-lipophilic balance poly(chlorotrifluoroethylene) poly(dimethylsiloxane) poly(tetrafluoroethylene) poly(trifluoropropylmethylsiloxane) glass transition temperature critical surface tension of wetting Owens-Wendt solid surface tension surface tension of aqueous solution surface tension of liquid dispersion force (nonpolar) component of surface tension polar component of surface tension

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2. Owen, M . J. CHEMTECH 1981, 11, 288. 3. Owen, M . J. In Surfactants in Solution; Mittal, K. L.; Bothorel, P., Eds.; Plenum: New York, 1986; Vol. 6, ρ 1557. 4. Fox, H .W.;Taylor, P.W.;Zisman, W. A. Ind. Eng. Chem. 1947, 39, 1401. 5. Siow, K. S.; Patterson, D. J. Phys. Chem. 1973,77,356. 6. Lee, L. H . J. Adhes. 1972, 4, 39.

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9. Hard, S.; Neuman, R. D. J. Colloid Interface Sci. 1987, 120, 15. 10. Noll, W. Chemistry and Technology of Silicones; Academic: New York, 1968; p 458. 11. Beezer, A. E.; Mortimer, C. T. J. Chem. Soc. A 1966, 514. 12. Polmanteer, Κ. E.; Hunter, M . J. J. Appl. Polym. Sci. 1959,1,3. 13. Tobolsky, Α. V. Properties and Structure of Polymers; Wiley: New York, 1960; p 67. 14. Kataoka, T.; Ueda, S. J. Polym. Sci., Part Β 1966, 4, 317. 15. Pauling, L. J. Phys. Chem. 1952, 56, 361.

16. Sauer, R. O.; Mead, D. J. J. Am. Chem. Soc. 1946, 68, 1794. 17. Good, R. J. In Treatise on Adhesion and Adhesives; Patrick, R. L., Ed.; Marcel Dekker: New York, 1967; Vol. 1, p 15.

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Encyclopedia of Chemical Tech-

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21. Lee, W. Α.; Rutherford, R. A. In Polymer Handbook; Brandrup, J.; Immergut, Ε. H . , Eds.; Wiley: New York, 1975; p III-139.


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RECEIVED for review May 27, 1988. ACCEPTED revised manuscript October 28, 1988.


Siloxane Surface Activity - Advances in Chemistry (ACS Publications)

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