adhesion guideline

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  • UsingUsing Silanes Silanes as asAdhesion PromotersAdhesion Promoters

    John H. MacMillan Ph.D.United Chemical Technologies, Inc.

    2731 Bartram RoadBristol, PA 19007

    800-541-0559www unitedchem com

    John H. MacMillan Ph.D.United Chemical Technologies, Inc.

    2731 Bartram RoadBristol, PA 19007

    800-541-0559www unitedchem com

  • 2UCTS PETRARCH PRODUCTS

    Silanes Silicones PlatinumCatalysts

    Si

    CH3

    CH3

    O Y

    CH3

    CH3

    SiSiO

    CH3

    CH3

    Y

    Si X

    CH3

    CH3

    Z(CH2)yPt [INHIBITOR]

    Z = NH2, SH, C-H,And Other ReactiveFunctional Groups

    Y=H, Vinyl, AminoAnd Other ReactiveFunctional Groups

    O

  • 3PRODUCT APPLICATIONSSilanes

    z AdhesionPromoters

    z HydrophobicCoatings

    z SurfaceModifyingReagents

    z Lenses Monomersz Chromatographic

    Stationary Phases

    Siliconesz Lubricantsz Adhesivesz Electronic

    Coatingsz Dental Fillingsz Fiber Optic

    Coatingsz Releasing Agentsz Medical Coatingsz High

    PerformanceCoatings

    Platinum Catalystsz Hydrosilylationz Room Temperature

    Silicone Curing Agentz High Temperature

    Silicone Curing Agent

  • 4Adhesion (sticking) of resins to surfaces is often marginal, especially itthe polymeric resin has no chemical affinity to bond to the substrate surface. Evidence of poor adhesion is seen as manual de-lamination whenmechanical force is applied to the laminate or often as partial spontaneousde-lamination, especially at the edges of the device. Often moisture, acidor base promote this adhesive failure.

    Organosilane coupling agents have been shown to dramatically improvethe adhesion of polymeric resins to substrates such as glass, silica,alumina or active metals. The purpose of this paper is to review the basicprinciples of this technology, citing its preferred applications, limitationsand application protocols. United Chemical Technologies (UCT) is amajor manufacturer of these materials, and in many instances UCTcatalog numbers will be introduced during discussion of individualreactions or in tabular data. In many chemical reactions the reacting groups arecolor coded for clarity.

  • 5Figure 1 illustrates a typical alkoxysilane coupling agent and alsoshows its hydrolysis reaction. Typically, the silane is functional at bothends and R is an active chemical group such as amino (NH2), mercapto(SH) or isocyanato (NCO) . This functionality can react with functionalgroups in an industrial resin or bio molecule such as peptides,oligonucleotides or DNA fragments. The other end consists of a halo(chloro most often) or alkoxy (most often methoxy or ethoxy) silane. Thisfunctionality is converted to active groups on hydrolysis called silanols .The silanols can further react with themselves, generating oligomericvariations. All silanol variations can react with active surfaces thatthemselves contain hydroxyl (OH) groups.

  • 6 O Si OHO Si

    R

    OH OH

    R

    Usually analcohol( )

    n

    2 n R - Si(OH)3

    R - SiX3+3H2O R - Si(OH)3+3HX

    H + 2nH2O

    RCH2CH2CH2Si(OCH3)3

    Figure 1 Typical Alkoxy Silane and its Hydrolysis

    Typical Alkoxysilane R = Reactive Group

    Reactive Silanol Intermediate

    Reactive Silanol Oligomer

  • 7Figure 2 shows the three main classes of silanes employed,chloro, methoxy and ethoxy silanes. Chlorosilanes are most reactive butevolve corrosive hydrogen chloride on hydrolysis. Methoxy silanes are ofintermediate reactivity and evolve toxic methanol. Ethoxy silanes are leastreactive but evolve non toxic ethanol. Only the scientist or technologistcan decide based on his unique processing needs which classes he can use.Generally the reactivity differences between methoxy and ethoxy silanesare not a problem. At typical hydrolysis pH (acidic ~5, basic ~ 9), bothversions hydrolyze in under 15 minutes at 2% silane concentrations.

  • 8X _ CH2 _ CH2 _ CH2_ SiCl3Most Reactive, Evolves Corrosive HCl

    X _ CH2 _ CH2_ CH2 _ Si (OCH3)3 Intermediate Reactivity, Evolves Toxic Methanol

    X _ CH2_ CH2_ CH2_ Si (OC2H5)3Least Reactive, Evolves Non-toxic Ethanol

    Figure 2 Typical Silane Coupling Agents

  • 9Figure 3Figure 3 deals with the concept of deals with the concept of monolayer vs multilayer monolayer vs multilayer deposition. deposition.A typicalA typical monolayer monolayer deposition is depicted. deposition is depicted. Monolayers Monolayers are preferred in physical are preferred in physicalsurface studies where the structure must be uniform, or in bio materials where asurface studies where the structure must be uniform, or in bio materials where auniform surface structure is needed to promote specific interactions. However,uniform surface structure is needed to promote specific interactions. However,monolayersmonolayers suffer from one severe disadvantage. Cleavage of the bond is readily suffer from one severe disadvantage. Cleavage of the bond is readilyaccomplished in high or low pH, resulting in adhesive failure.accomplished in high or low pH, resulting in adhesive failure. Monolayers Monolayers are aregenerated fromgenerated from monochloro monochloro or or alkoxy silanes alkoxy silanes, see , see Figure 3,Figure 3, Structure 2Structure 2..Conversely,Conversely, trichloro trichloro or or trialkoxy silanes trialkoxy silanes can form network or can form network or multilayermultilayerstructures at the surface fromstructures at the surface from crosslinking crosslinking of the of the silanetriols silanetriols produced during produced duringhydrolysis (see hydrolysis (see Figure Figure 2,2, Structure 1Structure 1 and and Figure 25Figure 25). At a 2%). At a 2% silane silaneconcentration in aqueous alcohol typically 3-8 molecular layers are produced.concentration in aqueous alcohol typically 3-8 molecular layers are produced.While theWhile the multilayer multilayer structure is inherently less uniform, it possesses dramatically structure is inherently less uniform, it possesses dramaticallyimproved hydrolytic stability at the polymer/improved hydrolytic stability at the polymer/silanesilane/substrate interface/substrate interface. The. Thecrosslinkedcrosslinked network is not dissolved if one bond is broken, unlike the situation for network is not dissolved if one bond is broken, unlike the situation formonolayersmonolayers, where a broken bond results in adhesive failure at that area of the, where a broken bond results in adhesive failure at that area of thesurface. For those such as chromatography column manufacturers who require asurface. For those such as chromatography column manufacturers who require amonolayermonolayer, but also desire hydrolytic stability, United Chemical Technologies, but also desire hydrolytic stability, United Chemical Technologiesoffers a line ofoffers a line of Bis Bis-isopropyl functional-isopropyl functional silanes silanes, see , see structure 3.structure 3. The bulky The bulkyisopropyl groupsisopropyl groups sterically sterically block attack by acidic or basic block attack by acidic or basic nucleophiles nucleophiles..

  • 10

    Y YY Y

    Monolayers

    Y _ CH2 _ CH2 _ CH2 _ Si _ X3X = Cl or OR

    Crosslinks at surface, gives3-10 layers at 2% concentration

    Y _ CH2 _ CH2 _ CH2 _ Si _ X

    Gives Monolayer,but less hydrolytically stable

    CH3

    CH3

    O

    Si

    O O

    Si

    O

    Si Si

    Substrate

    Y _ CH2 _ CH2 _ CH2 _ Si _ X

    Gives Hydrolysis Resistant Monolayers

    CH3 CH3

    CH3 CH3

    H

    H

    Figure 3 Monolayer Vs Multilayer Deposition

    Structure 3

    Structure 1

    Structure 2

  • 11

    Chromatographic Silanes

    Sterically Hindered Silanes forPassivation or Functionalization of

    Chromatographic Stationary Phases

    UCT offers a line of functionalized bis-isopropyl modified silanes. Thesesilanes react with polar substrates, generating monolayers of greatlyenhanced hydrolytic stability. The steric bulk of the isopropyl groupsretards the rate of nucleophilic cleavage of the silane in highly base oracidic media. In addition to the silanes below other chain lengths andfunctionalities are available on a custom basis.

  • 12

    Chromatographic Silanes

    Catalog# Name

    A0745 3-Aminopropyldiisopropyl-ethoxysilane

    C3443 3-Cyanopropyldiisopropyl-chlorosilane

    H2 N CH2 CH2 CH2 Si OEt

    Catalog# Name

    G6660 3-Glycidoxypropyldiiso-propylethoxysilane

    O9818.8 n-Octyldiisopropyl-chlorosilane

    CH2 O CH2 CH2 CH2 Si OEt

    N C CH2 CH2 CH2 Si CI C8 H17 Si CI

  • 13

    In addition to wide utility in enhancing resin or biomoleculeadhesion, organosilalnes have shown the ability to promote the alignmentof nematic liquid crystals in orientations either parallel or perpendicular tothe substrate surface. This orienting ability is critically important in liquidcrystal (LC) display switching devices, where orientation in onedirection is turbid to plane polarized light and the other direction is black.

    Figures 4 and 5 show examples of these orienting effects with specificUnited Chemical Technologies silanes. The interactions of the liquidcrystal and the active group X on the silane are in these cases thought tobe physical , that is, of the Van Der Walls, hydrogen bonding or IPN(interpenetrating network) types rather than through a chemical reaction.

  • 14

    SUBSTRATE

    SUBSTRATE

    DMOAP = O9745Orients nematic liquid crystals perpendicular to surface

    MAP = M8620Orients nematic liquid crystals parallel to surface

    Figure 4, Alignment of Liquid Crystals with Organosilanes

  • 15

    N,N-