(556e) X-Ray Reflectivity Study of Properties of Mixed Bis-Aminosilane-Vinyl Triacetoxysilane Coatings

X-ray Reflectivity
Study of Mixed Bis-aminosilane-Vinyl Triacetoxysilane Coatings

Yimin Wang, Jan Ilavsky*
and Dale W. Schaefer

Department of Chemical and Materials Engineering,

University of Cincinnati, Cincinnati, OH 45221-0012

*UNICAT, Advanced Photon Source, Argonne
National Laboratory, 9700 South Cass Avenue, Building 438 E, Sector 33, Argonne, IL 60439

Abstract

            Silane
surface treatment of metals has emerged in recently years as a promising
alternative for chromate pretreatment in metal-finishing industries. Silanes
are hybrid organic¨Cinorganic chemicals with the general structure of (XO)₃Si(CH₂)_nY
are used as coupling agents for adhesion between organic and inorganic
materials. In recent years van Ooij et al [1,2] found that the bis-silanes with
the general formula of (RO)₃Si(CH₂)₃-R'-(CH₂)₃Si(OR)₃
display better corrosion protection than the above monosilane coupling agents.
In order to understand the water-barrier properties of the bis-silanes, Pan et
al [3,4] investigated the water response of solvent-based bis-amino silane,
bis-sulphur silane and their mixture by neutron reflectivity.

     Despite
of the good corrosion performance of above solvent-based silanes, water-based
silanes are of more interest because of low VOC emission, ease of preparation,
and paint compatibility.  A good example of a water-based silane is the
mixture of bis-aminosilane (A) and vinyl triacetoxysilane (V) reported by van Ooij
[5]. The addition of V makes the system water soluble and inhibits the gelation
of A in water.  Since the water-response of this system has not documented
we study the influence of V, pH and hydrolysis time on the water-barrier
properties and morphology of the film.

            A-V
mixtures of different molar ratios (A/V =2, 3, 3.41, 5 and 6) were prepared by
spin coating as a function of precursor hydrolysis time and pH.  X-ray
reflectivity was used to investigate the film thickness and morphology before
and after H₂O conditioning.

            From
the SLD profiles we conclude that the water-barrier properties of the A-V
mixtures depend on A/V ratio, pH and hydrolysis time.  The highest
swelling is observed at A/V = 6 indicating that A deteriorates the
water-barrier properties of the coatings.  For the fixed A/V ratio, the
optimum water-barrier properties are observed at 10-hour hydrolysis time. 
The pH behavior was studied by the addition of acetic acid. Phase separation
was observed at low acetic acid concentration but disappeared at higher
concentration.

References:

[1] Danqing Zhu, Wim J. van
Ooij, Electrochimica Acta 2004, 49 1113-1125

[2] W.  J. van Ooij,
Danqing Zhu etc., Surface Engineering 2000 16 (5) 386-396

[3] Pan, P.;  Yim,
H.;  Kent, M.;  Majewski, J.; Schaefer, D. W. J. Adhesion Sci.
Technol. 2003, 17, 2175-2189.

[4] Pan, G.; Yim, H.; Kent, M.;  Majewski, J.;
Schaefer, D. W. In Silane and Other Coupling Agents; VSP: Orlando, FL, 2004; 3, 1-11.

[5] Danqing Zhu, Corrosion protection of metals by silane
surface treatment, PhD dissertation, 2002, University of Cincinnati.