2.2 Surface Reactions of Organic and Polymeric Films
21
reactivity of the charged surfaces is inherently different from bulk because of the
very existence of the double layer [35].
Accumulation of charges at an interface leads to unfavorable interactions between
incipient ionized groups. Contact angle titrations of mixed monolayers of ionizable
compounds and appropriate alkanethiols showed that the acid groups become less
acidic with a decreased concentration of acidic groups in the monolayer. Formation
of hydrogen bonds between adjacent acid or base groups in the monolayers may also
have some effect on their ionization properties.
Mrksich and co-workers studied the Diels–Alder reaction between surfaceattached quinone and cyclopentadiene. They found substantial deviations from the
second-order kinetics for reactions at hydrophobic surfaces. This led to the suggestion that the diene partitions between the monolayer and the bulk solvent thus changes
its local concentration in the vicinity of the reaction center.
Temperature effects: Himmel et al. [36] studied the surface derivatization of OH
and COOH-terminated SAMs with phenyl isocyanate (C6H5NCO, PIC). In both
cases the reactivity to gas-phase PIC was very slow for the samples at room temperature. However, most reaction rates can increase rapidly once the reaction temperature
is increased. This is consistent with the space requirement of phenyl rings with respect
to the packing of alkyl chains in SAMs, according to previous reported theoretical
studies on SAMs with phenyl sulfone groups.
Depending on the temperature, considerable changes of the reactivity behavior
of 16,16
-dithiobis(N-hydroxysuccinimidylhexadecanoate) (NHS-C 15 ) monolayers
have been observed. These changes of the rate law (sigmoid kinetics at low temperatures, pseudo-first-order kinetics at higher temperatures) have been attributed to the
formation of a more disordered layer due to untilting of the chains. By increasing
the temperature, the number of defects increased and rendered the reactive centers
more accessible to the external reagent as also alluded to above.
2.2.2 Surface Modification with Polymers
The adsorption of polymers and reactions on (thin) polymer films comprise alternative ways to functionalize surfaces and to obtain bioreactive platforms. While the
degree of order and definition does not rival those of SAMs, there are a number of
advantages, depending on the requirements of the particular system, which render
polymeric platforms viable alternatives.
2.2.2.1 The Adsorption of Polymers onto Solid Surfaces
The modification of surfaces with thin polymer films is widely used to tailor surface
properties, such as wettability, biocompatibility, corrosion resistance, colloidal stabilization, and friction. Such thin polymer films can be applied by deposition or
21
reactivity of the charged surfaces is inherently different from bulk because of the
very existence of the double layer [35].
Accumulation of charges at an interface leads to unfavorable interactions between
incipient ionized groups. Contact angle titrations of mixed monolayers of ionizable
compounds and appropriate alkanethiols showed that the acid groups become less
acidic with a decreased concentration of acidic groups in the monolayer. Formation
of hydrogen bonds between adjacent acid or base groups in the monolayers may also
have some effect on their ionization properties.
Mrksich and co-workers studied the Diels–Alder reaction between surfaceattached quinone and cyclopentadiene. They found substantial deviations from the
second-order kinetics for reactions at hydrophobic surfaces. This led to the suggestion that the diene partitions between the monolayer and the bulk solvent thus changes
its local concentration in the vicinity of the reaction center.
Temperature effects: Himmel et al. [36] studied the surface derivatization of OH
and COOH-terminated SAMs with phenyl isocyanate (C6H5NCO, PIC). In both
cases the reactivity to gas-phase PIC was very slow for the samples at room temperature. However, most reaction rates can increase rapidly once the reaction temperature
is increased. This is consistent with the space requirement of phenyl rings with respect
to the packing of alkyl chains in SAMs, according to previous reported theoretical
studies on SAMs with phenyl sulfone groups.
Depending on the temperature, considerable changes of the reactivity behavior
of 16,16
-dithiobis(N-hydroxysuccinimidylhexadecanoate) (NHS-C 15 ) monolayers
have been observed. These changes of the rate law (sigmoid kinetics at low temperatures, pseudo-first-order kinetics at higher temperatures) have been attributed to the
formation of a more disordered layer due to untilting of the chains. By increasing
the temperature, the number of defects increased and rendered the reactive centers
more accessible to the external reagent as also alluded to above.
2.2.2 Surface Modification with Polymers
The adsorption of polymers and reactions on (thin) polymer films comprise alternative ways to functionalize surfaces and to obtain bioreactive platforms. While the
degree of order and definition does not rival those of SAMs, there are a number of
advantages, depending on the requirements of the particular system, which render
polymeric platforms viable alternatives.
2.2.2.1 The Adsorption of Polymers onto Solid Surfaces
The modification of surfaces with thin polymer films is widely used to tailor surface
properties, such as wettability, biocompatibility, corrosion resistance, colloidal stabilization, and friction. Such thin polymer films can be applied by deposition or