aqueous amino silane modification of e-glass surfaces

Journal of Colloid and Interface Science 238, 136146 (2001)doi:10.1006/jcis.2001.7506, available online at http://www.idealibrary.com on

Aqueous Amino Silane ModificatikP

Thethe effeand methe mosilanes:aminotrpolysiloa zeta powas indvestigatsilane cdensedstratedtions inchanginThe polthe E-glsolutionsilanes aouter suappeara

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0021-979CopyrightAll rights oHazel Watson,1 Anne Norstrom, Aasa Torr

Department of Physical Chemistry, Aabo Akademi University,Received September 22, 2000; accepted

majority of work available in the literature examinesct of epoxy silane, -aminopropyltrimethoxy silane,

thacrylate silane on E-glass surfaces. As alternatives tost commonly used silanes, we investigated two novel -ureidopropyltriethoxy silane and Nfl(aminoethyl) -imethoxy silane and additionally an amino-functionalxane. The ureido silane-treated E-glass fibers demonstratedtential similar to that of the untreated E-glass fibers, which

ependent of deposition solution pH over the pH range in-ed. A moderately hydrophobic E-glass surface, which wasoncentration dependent, was noted as being due to con-

ethoxyof conet al. dsis ofhowevtweenthe orgthe hyd

Drythe suchemisSiOSi bonds at the surface. The diamino silane demon-an extremely basic surface at the higher silane concentra-vestigated. These outer surface layers were modified byg the pH and the concentration of the deposition solution.ysiloxane produced an increase in the hydrophobicity ofass fiber, especially when deposited from extremely basics. At the higher solution concentrations investigated, thend the siloxane was initially deposited in patches and anrface or skin was formed over these patches, giving thence of fully coated fibers. C 2001 Academic Pressords: silane; siloxane; zeta potential; contact angle; DRIFT;

INTRODUCTION

s long been known that treating the surface of a silicaolloidal, particulate, or fibrous) with a coupling agents the physical and chemical properties of a polymer ma-d with such materials (14). The match between poly-trix and silane organofunctional group type and lengthearing on the mechanical properties of the product (5).d Subramanian suggested that if the silane was highlyked, interpenetration of the silane/siloxane would be lim-ding to reduced interfacial properties of a polymer/fiber6).concentration (i.e., pH of the treatment solution) and theonditions used, can affect the molecular weight of the

ed silane oligomers and the amount of silane depositedsurface (79). The rate of hydrolysis of aminopropyltri-

hom correspondence should be addressed. Fax: +358 2 215 [email protected].

ane laydrophob

Reseface bysilane wfew surof a 3D

Silanent surfexpecteresultspected ra ureidois achieorder toour depamino fvestigatto invesferent sand pH

We incentratichosenpolysilo

Materia

Chopsiloxan

1367/01 $35.00C 2001 by Academic Pressf reproduction in any form reserved.on of E-glass Surfacesulla, and Jarl Rosenholmorthansgatan 3-5, A

abo 20500, Finland

February 27, 2001

silane (APTES) was at a minimum at pH 7, while the rateensation was at a minimum at pH 4 (10). Premachandraemonstrated a similar pH dependency for the hydroly--ureidopropyltrimethoxy silane. They went on to note,r, that condensation of this silane was at a maximum be-H 9 and pH 10 (11). Leyden and Atwater showed hownic functional group affected both the condensation androlysis reactions (12).g the E-glass fibers accelerated the condensation of

face silanols with the silane silanols, enhancing therption. Washing the E-glass fibers stabilized the silox-

er, thus improving the hydrolysis resistance and the hy-icity of the surface (13, 14).

arch showed that ureido silanes were bonded to the sur-only a few SiOSi linkages (15). The remainder of theas present as a highly crosslinked mass attached to these

face bonded silanes, resulting in firmly attached patchespolysiloxane network.e manufacturers recommend silanes for use with differ-aces on the basis that the organo-functional group can bed to react with proposed matrix polymers (16, 17). Earlyindicated that the ureido silane produced entirely unex-esults, with a condensed SiOSi surface as opposed tosurface. Thus investigation of whether a ureido surface

vable from this silane warrants further investigation. Inensure that the siloxane surface was not produced by

osition method, a silane with primary and secondaryunctions (diamino silane) and a polysiloxane were in-ed alongside the ureido silane. The aim of this work wastigate the nature of the E-glass fiber surface with dif-ilane-based treatments, using a range of concentrationss.

EXPERIMENTALvestigated the effect of treatment solution pH and con-on on two cationic silanes and a polysiloxane. The rangefor investigation was pH 4 to pH 7, and additionally thexane molecule was investigated at pH 10.5.

ls

ped industrial grade E-glass fibers and an emulsion,e AR433, were kindly supplied by Ahlstrom Glassfibre

AQUEOUS AMINO SILANE MODIFICATION OF E-GLASS SURFACES 137

TABLE 1Composition of E-glass Fibers Used

E-Glassconstit

SiO2Al2O3 CCaOMgONa2O CB2O3

Oy, Ka106 m(Tablemediatbush.

Theethoxytrimethreveal(Fig. 1of appand mesilanesment.

FIG.(c) silox

TABLE 2pH and pKa Values of Aqueous Solutions of Silanes A1160

0

i1

A[A

d

a

hw

epn

n

t

tht

rd3a

t.

c, oxide Elements as determineduents wt% by XPS %

55 O1s 52.5Fe2O3 14.5 C1s 21

21.5 Si2p 17.40.5 Ca2p 3.4

K2O

138 WATSON ET AL.

deionized water for 3 min to remove loosely bound silane (18).After careful filtration the E-glass fibers were dried at 60C for24 h in

Premureidopextremea minimon to qumum bederancelower rto suggwere alprior to

Stream

Streatrokineparatus

TheconducoriginaHigherand lowconformE-glasspackingery tesThe eqtest. MMastinments w

Contac

A Kto measfiber waadhesivwhich hwettingwas mo

being aand lowcontact

X-Ray P

XPSusing awas use

fibers ained atSiloxan

RESULTS

en

A

s

gti

tdiss

l

h

etnn

t

i

ntreh1nFet

e

i

11Ra vacuum oven at 200 Torr.achamdra et al. demonstrated that hydrolysis of -ropyltrimethoxy silane in a water/methanol medium wasly rapid at pH 4.87 and pH 9.83. Between these extremesum rate of hydrolysis occurred at pH 7.44. They wentalitatively demonstrate that condensation was at a maxi-tween pH 8.97 and pH 9.87 (11). At lower pHs a prepon-of silanol groups existed which condensed at a much

ate. Thus over the pH range examined it is reasonableest that during the 20-min period, for which the silaneslowed to hydrolyze, little or no condensation occurred,deposition onto the E-glass fibers.

ing Potential (Zeta Potential )ming potential was expedited using an Anton Parr Elec-tic Analyser (EKA), with an automated pH titration ap-, which has been described elsewhere (19, 20).electrolyte solution used was 1.0 E C 03 M KCl, at ativity of 2.7 EC 01 mS/m at 23 2C. Starting with thel solution the pH of the electrolyte solution was adjusted.pH values were obtained by the addition of 0.25 M KOHer pH values by the addition of 0.25 M HCl. One steped to 0.5 of a pH unit. Two grams of carefully packedfiber sample was used for each measurement. Similardensity and overall consistency were required for ev-

t; any differences could result in poor reproducibility.uipment was carefully washed with KCl between eachathematical treatment of the data used the Fairbrother-approximation (19, 20). A minimum of three measure-ere carried out, to ensure reproducibility.

t Angle

SV Instruments Sigma 70 Wilhelmy balance was usedure the advancing and receding contact angles. A singles attached, vertically, to a wire hook, using double-sidede tape. The hook was suspended from an electrobalance,ad a range of 0.25 mN and a resolution of 0.05 N. Theliquid used was deionized water (pH 5.8). The beaker

ved in the vertical direction by a DC motor; the balanceutomatically zeroed before each measurement. By raisingering the beaker at a known rate, receding and advancingangles were measured (21, 22).

hotoelectron Spectroscopy (XPS)was carried out on a Perkin Elmer PHI 5400 apparatus,n MgKfi source. A 1-mm-diameter molybdenum maskd to maintain the orientation and position of the E-glassnd thus prevent shadowing. All the silanes were exam-pH 4 and pH 7 and at concentrations 0.005 and 0.15%.e AR433 solutions were also investigated at pH 10.5.

Titrabalancthe sila

Silane

Theureidomatchindicatsurface

Thereducefibers;silanoltrationsurfacetion so

At threlationhydropativelyincreascorrelapositioand coconcen

of SiOAt h

be abledifferefree nithe frepH 7 talmostnitroge

DRIincreasdeposithe treaincreasat depo

Sto

Silane ASilane A

Ation of the silanes against HNO3 produced stoichiometricpoints, which were assigned to the functional groups ones and the siloxane (Table 4).

1160

toichiometric balance point was assigned as the terminalroup (Table 4). Measured IEPs (isoelectric point) did nothe stoichiometric balance point measured by titration,ng that there were no ureidic functional groups at the(Table 5 and Fig. 2).wo lowest concentrations of the ureido silane (A1160)the contact angle to below that of the untreated E-glass

.e., the surface became more hydrophilic due to silaneat the surface. At higher deposition solution concen-

, the contact angle increased as a condensed SiOSiformed. Contact angle was also independent of deposi-ution pH (Table 6).e base plateau (pH 9.7 of the zeta potential curves) a cor-with contact angle was noted, which indicated that whileobicity was augmented the surface charge remained rel-

constant as pH rose (Fig. 3a). As deposition solution pHd from 4 to 6, the zeta potential, at electrolyte pH 5.8,ed with contact angle gave similar results. The pH 7 de-solution demonstrated that an increase in zeta potential

tact angle occurred as the silane solution became morerated (Fig. 3b). This was due to enhanced condensationat pH 7.gh silane concentrations, there was sufficient nitrogen toto resolve the ESCA spectra into the peaks due to thet nitrogen binding energies (Table 7). At pH 4 and pH 7ogen accounted for less than 10% of the total nitrogen,nitrogen being assigned as the secondary amine. At

e ratio of hydrogen bonded to protonated nitrogen was1:1. At pH 4 the ratio of hydrogen bonded to protonatedhad decreased to 1:1.

T versus iep and contact angle results confirmed thatd deposition solution concentration produced increased

ion without appreciably changing the surface charge ofted fibers (Figs. 4a and 4b). The contact angle, however,d markedly. Minor changes in surface charge were noted

sition solution pH 4 and low concentration, the point at

TABLE 4chiometric Balance Points of Silanes A1160 and A1126and Siloxane AR433, Titrated against Nitric Acid

Stoichiometric balance Stoichiometric balancepoint 1 point 2

160 6.2 (ureido group)126 8.1 (diamine group) 4.9 (silane triols)433 8.0 (amine group) 6.2 (benzene ring)


TABLE 5IEP Values for Silanes A1160 and A1126 and Siloxane AR433

IEP

A1160A1126AR433

pH

4567

10.5

FIG.pH 5; (cpH 4 pH 5 pH 6 pH 7 pH 10

0.005 0.01 0.1 0.15 0.005 0.01 0.1 0.15 0.005 0.01 0.1 0.15 0.005 0.01 0.1 0.15 0.005 0.01 0.1 0.15

4.7 4.4 4.6 4.5 4.7 5.0 4.6 5 4.4 4.1 4.4 4.4 4.4 4.2 4.4 4.75.2 5.0 7.8 8.9 5.9 6.3 7.2 8.8 6.3 6.8 8.9 8.8 6 6.8 8.8 9.25.4 5.2 5.9 5.7 5.5 6.0 6.5 6.3 5.4 6.0 6.9 6.6 5.6 6.0 7.3 7.0 4.5 4.5 8.3 9.3

TABLE 6Advancing Contact Angles for Silanes A1160 and A1126 and Siloxane AR433

Silane A1160 Silane A1126 Polysiloxane AR433

0.005 0.01 0.1 0.15 0.0025 0.01 0.1 0.15 0.005 0.01 0.1 0.15

35 40 46 52 58 62 63 63 78 78 88 9437 42 61 61 50 54 59 60 78 90 94 9743 47 57 57 59 58 64 65 79 85 93 10138 41 54 53 41 47 64 63 78 84 94 101

49 60 104 107

2. Zeta potential traces for silane A1160-treated E-glass fibers at four concentrations: 0.005, 0.01, 0.1 and 0.15 wt%; (a) deposition pH 4; (b) deposition) deposition pH 6, and (d) deposition pH 7.

140 WATSON ET AL.

FIG. 3trolyte baangle ()creasing cbetween dcrease inA1160.

which c(10, 11)

Silane A

Zetation wafunctionity adso

Ratio

A1160

0.15%0.15%

4de

s

oA

o

f.

re. (a) Advancing contact angle () versus zeta potential at the elec-se plateau (electrolyte pH 9.7) for silane A1160. (b) Advancing contactversus zeta potential at electrolyte pH 5.8. The solid line indicates in-ontact angle and constant zeta potential with increasing concentrationeposition solution pH 4 and pH 6. The dotted line indicates the in-both zeta potential and contact angle at deposition pH 7. For silane

ondensation would be expected to be at a minimum.

1126

Potential results indicated that as the silane concentra-s increased, the outer layer consisted mainly of aminoality from the deposited silane. The amino functional-rbed HC from the solution, producing NHC3 . The surface

TABLE 7s of Hydrogen-Bonded, Protonated, and Free Nitrogen

for Silane A1160 (Measured by XPS)

Hydrogen- ProtonatedpH Free N% bonded N% N%

4 6.4 47.2 46.27 9.2 83.2 7.6

FIG.measure

A1160 d

was ba8 and 9ance popoint, p

At l(SiO,sociatihence a(Figs. 5surface

As aThe matwo lowbic sursurfacepH 6. Lnot inchave band the. (a) Correlation of IEP and quantity of silane A1160 deposited asby DRIFT. (b) Correlation of contact angle () and quantity of silaneposited as measured by DRIFT.

ic, with highly negative zeta potentials and IEPs between(Figs. 5a5d). Titration of silane A1126 gave two bal-

ints, the basic amine at pH 8.1 and a second, more acidic,ossibly that of the silanol triols, at pH 4.9.w silane concentrations metal oxides inherent to glass

l2O3 , CaO) were present in large concentrations. Dis-n of the metal oxides, produced an acidic surface andnegative zeta potential, with an IEP of between 5 and 6a5d). The IEP moved toward more basic values as theconcentration of amino groups increased.surface modifier A1126 was more efficient than A1160.ximum changes in contact angle were achieved with theest concentration solutions, both producing a hydropho-ace, due to the amino groups being located on the outerIncrease in contact angle was linear between pH 4 and

ow silane concentration at deposition solution pH 7 didease the hydrophobic nature of the surface. This mayen due to a mixed amino, silanol, and silicate surfacedeposition of oligomers (Table 6). At electrolyte pH 9.7


FIG. 5.pH 5; (c)

the zetaincreasidepositi

Sufficthe nitro(ESCA)nated nigen waswas prepH. Athydroge

Silanbetween

Ratios

A1126 %

0.0050.0050.150.15Zeta potential traces for silane A1126-treated E-glass fibers at four concentrations: 0.005, 0.01, 0.1, and 0.15wt%; (a) deposition pH 4; (b) depositiondeposition pH 6; and (d) deposition pH 7.

potential results demonstrated only slight increases withng contact angle. The IEP was dependent upon both theon solution concentration and the pH.ient silane A1126 was deposited on the surface to allowgen peaks at high and low concentration to be resolved. Two peaks were detected, hydrogen bonded, and proto-trogen at 399.8 and 401.7 eV, respectively; no free nitro-detected. Four times the amount of protonated nitrogen

sent in the low concentration samples, independent ofhigh concentration the ratio of protonated nitrogen ton bonded nitrogen was 2:1 (Table 8).e A1126 appeared to show a negative correlation,

DRIFT and contact angle. An increased contact an-

TABLE 8of Hydrogen-Bonded and Protonated Nitrogen for Silane

A1126 (Measured by XPS)

pH Hydrogen-bonded N% Protonated N%

4 16.7 83.37 16.9 83.14 30.4 6967 33.3 66.7

gle with a decreased intensity of the normalized CH2 peak at2925 cm1, was noted (Fig. 6). At first these appeared to becontradictory, if one also includes the zeta potential versus con-tact angle results the implication is that as deposition solution

FIG. 6. Correlation between contact angle and quantity of silane A1126deposited as measured by DRIFT.

142 WATSON ET AL.

concentration increased the surface became more basic. Thus asthe surface packing density increased so the CH2 was shieldedby the a

SiloxanAt 0

remainepH 10.the 0.0pH of b

FIG. 7 edeposition

ionizable metal oxides, with a few sparsely deposited siloxanepatches (Figs. 7a and 7b). At concentrations of 0.1 and 0.15%,. Zeta potential traces for siloxane AR 433-treated E-glass fibers at four concpH 5; (c) deposition pH 6; and (d) deposition pH 7; (e) deposition pH 10.5.mine, resulting in a reduced CH2 signal.

e AR433.005% silane concentration the zeta potential and iepd constant as pH was increased, up to and including

5 (Figs. 7a7e). At all pHs the IEP, of the 0.005% and1% surface treated E-glass fibers, was at an electrolyteetween 4 and 6, indicating that the dominant surface was

the IEP became more basic, rising from an electrolyte pH of 7to an electrolyte pH of 8.5, caused by removal of acid sites byadsorption onto silanols and by the basic nature of the functionalgroups of the siloxane.

Titration of the siloxane gave two poorly defined stoichio-metric points at pH 8.0 and pH 6.2. The basic stoichiometricpoint was assigned to the amino function and the mildly acidicone to the aromatic functional groups.ntrations: 0.005, 0.01, 0.1, and 0.15 wt%; (a) deposition pH 4; (b)


Low concentrations of this material had the greatest effect,increasing the contact angle some 30 more than did the twosilanemost twcontacpH 4 ahydrop

TGAtion atmore s

Betwsurfacecentratcontacdeposia minim

FIG.the relatipH 10.1

9dn

pdri

t

5

A

a

v

tn

nnmonomers. As a consequence the contact angle was al-ice that of the untreated E-glass fibers. The increase in

t angle was linear with solution concentration betweennd pH 7, but independent of pH. The surface was veryhobic, or conversely, oleophilic.analysis of fibers treated with a 0.15% deposition solu-

pH 4 and at pH 10.5, indicated that at pH 10.5, 10 timesilane was deposited than at pH 4 (results not shown).een deposition solution pH 4 and pH 7, again differents were demonstrated, which were in the main due to con-ion effects. A more negative zeta potential and increasedt angle were the result of larger amounts of silane beingted from the higher concentration solutions, while pH had

al effect (Figs. 8a and 8b).

8. Effect of increasing deposition solution pH and concentration ononship between contact angle () and zeta potential at the base plateau(a) and at the acid plateau pH 3.5 (b) for siloxane AR433.

FIG.AR 433of siloxa

TheIEP inmonito0.1% sstratingconcen

Alumane ARpH 10.

Silane

By nto behatent withe silamonom

differepositio. (a) Correlation of contact angle () with quantity of siloxaneeposited, as measured by DRIFT. (b) Correlation of IEP with quantitye AR 433 deposited, as measured by DRIFT.

lot of the normalized CH2 peak at 2925 cm1 versusicated a gradual rise in IEP with surface coverage ased by CH2 intensity. A large jump between the 0.01 andlane solution treated fibers at pH 10.5, further demon-the large quantities deposited at this pH from the morerated deposition solutions (Fig. 9).inum and calcium were not detected in the 0.15% silox-433 sample, which was deposited from a solution at.

DISCUSSION

1160

ture A1160 was a cationic silane; however, it appearede as a nonionic silane. The results noted were consis-

h a SiOSi surface. Even at pH 67 (the natural pH ofe), where one would expect to see deposition of silanol

ers and hence a silanol or ureido surface, there was littlece in the zeta potentials. This implied that, at all de-pHs the ureido silane deposited onto E-glass fiber as

144 WATSON ET AL.

aggregates with a SiOSi outer shell. The results presented byPremachandra et al. indicated that condensates were unlikelyto haveand thuE-glass

ESCAreduced(Table 8terfere wthe silanamountfurther ifor formpH the formatiothat extrphysica

The zwere in(Fig. 2)fibers itpositedsilane hstrated bthat theouter laSiOSwas detfrom moaluminumicellebreak doing to aaluminu

Silane A

The scentratithe amotact angity sugghave de(pH 7) dsilane; afor silan

At nestoichioamine sversus z

was ent0.1% socome an

may havof the m

indicated by Osterholtz and Pohl (10). Enhanced basicity wasproduced by a higher density of amino groups, as the deposition

n

u

t

z

s

oen

od,it

p

pgpnw

xt

ipd

o

oo

lm

tformed at pH 4 in a ureido silane deposition solutions any condensation must have occurred with and at thesurface.

results indicated that as deposition solution pH wasto pH 4, the hydrogen bonds could not be maintained). Decreasing the deposition pH below pH 4 may in-ith any hydrogen-bonded structure formed; allowinge to deposit with the ureido function outermost. Theof protonated nitrogen could be expected to increasen this scenario. Under these conditions the opportunityation of a ureido surface would be maximized. At lowermicelle like structures may be destroyed allowing then of a ureido surface. It should also be noted, however,emely low pH solutions have a deleterious effect on thel nature of E-glass fibers (18, 23).eta potentials of the silane A1160-treated E-glass fibers,dependent of treatment solution pH and concentration. Although silane A1160 is a cationic silane, on E-glassbehaved as a nonionic silane (zeta potential). When de-onto metal surfaces from aqueous solutions, the ureidoad the ability to behave as a cationic silane as demon-y van Ooij and by Puomi (24, 25). The conclusion wascombination of E-glass fiber and this silane induces theyers to deposit upside down, with a highly crosslinkedi outer surface. Aluminium from the E-glass fiber surfaceected (XPS) in the upper layers of this silane depositedre concentrated organic solutions. We propose that them induced the formation of very stable hydrogen bonded-like complexes with the ureido silane, which did notwn over the pH range of the deposition solutions, lead-bilayer structure, with a siloxane outer surface and them condensed into the siloxane network (26, 27).

1126

urface basicity increased with deposition solution con-on and with pH, this was confirmed by DRIFT (Fig. 6),unt of protonated nitrogen (ESCA, Table 8) and con-le results (Fig. 3b and Table 5). The increase in basic-ested that, at lower deposition pHs, some silane may

posited with the silanols outermost. Additionally neutraleposition conditions were more favorable for this basict neutral deposition pHs the conditions were favourablee condensation (10)utral deposition pH the surface basicity approached themetric balance point of the amine, indicating a totallyurface. This was confirmed by a plot of the contact angleeta potential at pH 5.8, indicating that the surface chargeirely due to the diamino functionality (Fig. 10a). Abovelution concentration and pH 6, the surface did not be-y more basic with enhanced deposition (Fig. 10b). Thise been a result of increased condensation in solution,ore concentrated systems as the pH increased to 7, as

solutiosurfaceeffect ocate coand 0.0tions thzeta poat pH 7resultin

Thea combthat aspatcheto chanreductiby incrfunctio

Siloxan

Thechargeposited

At lreducegroupsand (Sconcen

surfacesilaneresultin

Wewhichwas deResultibelow

Silodeposicondendynamin theacid andepend

At land pHas demto thatfrom thtrolytezeta potion solarge acontacconcentration and pH increased a more hydrophobicwas produced. At the acid plateau (zeta potential) thef the acidic surface silanols and aluminum from the sili-ld be seen at the lower deposition concentrations (0.005

1%) (Fig. 10c). At higher deposition solution concentra-e surface was due to NHC3 , resulting in a much higherential (Fig. 10c). Condensation of the silanols in solutionformed oligomers, which then deposited right way up,g in an amino surface.eta potential and DRIFT effects can be explained using

ination of Ishidas and our own results. Ishida indicatedsilane concentration and hence packing of the silaneincreased, the deposited silane molecules were forced

ge from the prone position to an upright position. Then in the intensity of the CH2 peak can be explainedased shielding of the hydrocarbon chains by the amineality as the packing density increased.

e AR433

amino functionality resulted in an enhanced negativeat high electrolyte solution pHs, especially when de-from highly basic solutions (Fig. 7e).w concentrations and pH 10.5 the contact angle wasalmost to that of untreated E-glass fibers. Surface silanolwhich were produced by hydrolysis of the (SiO)mCH3

O)nCH3 groups, may have caused this effect. At highrations the contact angle was higher than all the othertreatments, possibly because of complete coverage of theatches on the E-glass surface by the siloxane polymer,g in an extremely hydrophobic surface.ropose that the siloxane initially deposited in patches,rew vertically, and that when large amounts of silaneosited the upper layers of these patches were joined.g in E-glass fibers with an outer skin of siloxane,hich was an open porous structure.

ane AR433 was already hydrolyzed and condensed thusion pH had no effect upon the state of hydrolysis andsation of the deposited material, but was able to affect thec SiOSi$ 2SiOH. Different surfaces were implicitlots of zeta potential versus contact angle, at both thethe base plateau (Fig. 8a). The surfaces appeared to be

ent upon both deposition solution concentration and pH.w deposition solution concentration, 0.005 and 0.01%,10.5 very small amounts of the siloxane were deposited,nstrated by a low contact angle and zeta potential closef untreated fibers. Here the surface was due to SiOSi

e E-glass and from the polysiloxane (Fig. 8b). At elec-pH 3.5 a pH-dependant correlation between increasingtential and contact angle was observed. For the deposi-ution at pH 10.5 as the concentration was increased, very

ounts of silane were deposited, demonstrated by highangle and zeta potential (Figs. 8a and 8b).


FIG. 1A1126. Tand concmonome

() and zsurface c

We hothers,therefois gene

Alumers ofsilane dinclusiin the upH 10.have al

Thetrationthe degseen. Aindepeand 9b0. (a) Effect of increasing deposition solution pH and concentration on the relationship between contact angle () and zeta potential at the IEP for silanehe area between the lines represents deposition of monomer and the hatched area deposition of oligomers. (b) Effect of increasing deposition solution pHentration on the relationship between contact angle () and zeta potential at electrolyte pH 5.8 for silane A1126. The solid line represents deposition ofr and the dotted line deposition of oligomers. (c) Effect of increasing deposition solution pH and concentration on the relationship between contact angleeta potential at the acid plateau (pH 3.5). The solid line representing a surface of silicate and mixed orientation deposition and the hatched area an aminoonsisting of oligomers and polymer for silane A1126.

ave seen little evidence in previous work of our own, or ofwhich confirms complete surface coverage. We propose;re that the silane was chemisorbed in a patchy fashion asrally accepted.inum and calcium have been detected in the upper lay-

all the condensed silanes, irrespective of the amount ofeposited, which has been interpreted as evidence of their

on in the siloxane network. Aluminum was not detectedpper layers of the sample of 0.15% AR433 deposited at

5%; being previously condensed it would be unlikely touminum and calcium in the upper layers.relationship between the deposition solution concen-and pH was clearer at pH 10.5, where an increase inree of hydrophobicity and amount deposited could bet acid and neutral deposition solution pHs a gradual pH-

ndent increase with concentration was noted (Figs. 9a).

CONCLUSIONS

The zeta potential of A1160 was independent of pH over therange measured. This was as a result of the highly crosslinkedSiOSi outer layer, at higher concentrations resulting in a hy-drophobic surface. At low concentrations hydrophilic silanolswere dominant. Unlike nonionic and cationic silane-treated E-glass fibers there was little or no surface dissociation. The in-crease in hydrophobicity was solely due to increased coverageof the E-glass surface and not to solution pH, unlike the re-sults presented by Nishyama et al. (79). According to Park andSubramanian a highly crosslinked silane layer would result in areduction of the physical properties of a composite, due to re-duced interpenetration of the siloxane and the matrix polymer,ensuing in a weak interphase (6).

Correlation of the zeta potential, contact angle, and DRIFT re-sults for concentrated solutions of silane A1126 (0.1 and 0.15%),

146 WATSON ET AL.

indicated that the diamino silane was deposited right way upand moreover that the outer surface or skin of the samples wasdependant upon both deposition solution pH and concentration.At low concentrations (0.005 and 0.01%), isolated patches ofsilane increased the hydrophobicity of the surface. A negativecorrelation between surface coverage, as measured by the inten-sity of the CH2 peak (DRIFT), was noted. The correlation wasthought to be due to shielding of the terminal amino groups,giving the appearance of reduced deposition.

Silane AR433 likewise demonstrated three concentration-dependant surfaces, one due mainly to silanols from the E-glass,with a low concentration of deposited siloxane. A second sur-face indicated a surface consisting of siloxane functional groupson the polymer. The third surface was apparent only at veryhigh deposition pH (10.5), which was due to an outer skinof siloxane. We propose that at a deposition solution concen-tration of 0.15% and pH 10.5 the siloxane initially deposited inpatches and that further siloxane deposition was as an overlaywhich joined the patches, giving the appearance of fully coatedE-glass fibers. The structure below the outer surface or skinwas open and porous.

ACKNOWLEDGMENTS

The ausearch (GWatson aDr. H. M.

1. BoudTechn

2. DwigSalva

3. Pluedemann, E., Silane Coupling Agents, 2nd ed. chap. 4. Plenum Press,New York, 1991.

4. Daniels, M. W., and Francis, L. F., J. Colloid Int. Sci. 205, 191 (1998).5. Tesoro, G., and Wu, Y., J. Adhes. Sci. Technol. 5(10), 791 (1991).6. Park, J. M., and Subramanian, R. V., J. Adhes. Sci. Technol. 5(6), 459 (1991).7. Nishiyama, N., Asakura, T., and Horie, K., J. Colloid Int. Sci. 124(1),

14(1988).8. Nishyama, N., Schick, R., and Ishida, H., J. Colloid Int. Sci. 143, 146 (1991).9. Nishyama, N., Horrie, K., and Asakura, T., J. Colloid Int. Sci. 129, 113

(1989).10. Osterholz, F. D., and Pohl, E. R., J. Adhesion Sci. Technol. 6, 127 (1992).11. Premachandra, J. K., van Ooij, W. J., and Mark, J. E., J. Adhesion Sci.

Technol. 12(12), 1361 (1998).12. Leyden, D. E., and Atwater, J. B., J. Adhesion Sci. Technol. 5(10), 815

(1991).13. Plueddemann, E. P., J. Paint Technol. 40, 1 (1986).14. Pape, P. J., and Plueddemann, E. P., J. Adhesion Sci. Technol. 10, 5

(1991).15. Watson, H., Norstrom, A., Root, A., Matisons, J., and Rosenholm, J.,

J. Adh. Sci. Technol., in press.16. Arkles, B., Silanes, Silicones and Metal Organics. Gelest 2000 product

information.17. Silquest Silanes, Products and Applications Witco (1997).18. Watson, H., Norstrom, A., Engstrom, B., and Rosenholm, J., Colloids and

Surfaces A, in press.19. Jacobasch, H. J., Baubock, G., and Shurtz, J., Colloid Polym. Sci. 263, 3

(1985).

twteca

en

msrgthors thank TEKES and the Graduate School of Materials Re-SMR) for financial support for J. Rosenholm, Aa . Torkulla, and H.nd Raisio Chemicals Ltd for A. Norstrom. Additionally we thankFagerholm for XPS measurements and useful discussions.

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ewijn, J. R., Schottens, J. R., and Brackman, J. C., J. Adhesion Sci.ol. 52, 115 (1995).ht, D. W., Fowkes, F. M., Cole, D. A., Kulp, M. J., Sabat, P. J.,ti, L., Jr., and Huang, T. C., J. Adhesion Sci. Technol. 4, 619 (1990).

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INTRODUCTIONEXPERIMENTALTABLE 1FIG. 1.TABLE 2TABLE 3

RESULTSTABLE 4TABLE 5TABLE 6FIG. 2.FIG. 3.TABLE 7FIG. 4.FIG. 5.TABLE 8FIG. 6.FIG. 7.FIG. 8.FIG. 9.

DISCUSSIONFIG. 10.

CONCLUSIONSACKNOWLEDGMENTSREFERENCES

aqueous amino silane modification of e-glass surfaces

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