46
3 Confinement Effects on the Reactivity in Ultrathin …
mentioned array technologies to biosensors, nanoclusters [6], anchoring of proteins
[7], nanoreactors [8], and drug delivery [9] (see Chap. 2).
Self-assembled monolayers (SAMs) are perhaps the most popular model systems
for studies of chemistry at interfaces under controlled conditions. In the last decade,
countless studies have been performed that involve the chemical modification of
monolayers [10, 11]. However, the reactivity of functional groups placed in an
ordered monolayer environment will be influenced by many factors, such as solvent,
steric, and electronic effects. Thus, the chemical reactivity can be affected by confinement effects, which leads to reduced reactivity and incomplete conversions [12]. For
typical applications in, e.g., the areas of sensors, however, rapid reactions and full
conversion are desirable to optimize throughput and to minimize reaction times.
Compared to SAMs [18, 23], polymer films may offer the advantage of a quasi-3D
structure (high loading per unit surface area) and the possibility to exploit the rich
structural hierarchy of ordering on different length scales. In particular, block copolymers can be regarded as ideal candidates in this respect. Block copolymers can selfassemble into well-defined microphase-separated morphologies that have tremendous potential in different application areas (see Chap. 2) [13]. By varying film thickness, controlling interfacial interactions, as well as applying external fields, diblock
copolymer domains, which exhibit characteristic dimensions on the nanoscale, can
be readily oriented in thin films.
In addition to thin polymer films, dendrimers, and hyperbranched polymers,
N-hydroxy succinimide (NHS) ester polymer brushes prepared, e.g., by graftingfrom procedures have been reported as a viable alternative in screening assays. The
physical behavior of polymers in confinement, such as in substrate-supported ultrathin films, differs considerably from the behavior observed in the bulk and is often
governed by interfacial effects. Depending on the thickness of ultrathin films (film
thickness <100 nm), the glass transition temperature, surface composition (see also
this chapter), or the crystallization kinetics [14] may be altered, among other properties. In particular, the topmost layer of substrate-supported ultrathin polymer films
can be considered to possess properties different from the bulk, which may affect
surface reactivity. As a result, surface chemical reactions may be different compared
to reactions in solution or in the gas phase (see also Chap. 5).
In this chapter, two different polymer thin film model systems, i.e., poly(Nhydroxysuccinimidyl-methacrylate) (PNHSMA) and polystyrene-block-poly(tertbutyl acrylate) (PS n -b-PtBA m ) were studied, which possess different hydrolysis
behavior and were exploited in the fabrication of bioreactive platforms in subsequent
chapters. The reaction kinetics of the hydrolysis of NHS ester groups in PNHSMA
and tBA ester groups in PS n -b-PtBA m films were investigated as a function of temperature, film thickness, thermal pretreatment, and relative ester surface coverage to
unravel the impact of confinement on the kinetics of the surface hydrolysis. Based
on the understanding of the factors that govern reactivity in thin substrate-supported
reactive polymer films, optimized procedures for surface functionalization with high
loading (see Chaps. 4 and 5) and sub-micrometer local patterning strategies can be
developed (Chaps. 5–7).
3 Confinement Effects on the Reactivity in Ultrathin …
mentioned array technologies to biosensors, nanoclusters [6], anchoring of proteins
[7], nanoreactors [8], and drug delivery [9] (see Chap. 2).
Self-assembled monolayers (SAMs) are perhaps the most popular model systems
for studies of chemistry at interfaces under controlled conditions. In the last decade,
countless studies have been performed that involve the chemical modification of
monolayers [10, 11]. However, the reactivity of functional groups placed in an
ordered monolayer environment will be influenced by many factors, such as solvent,
steric, and electronic effects. Thus, the chemical reactivity can be affected by confinement effects, which leads to reduced reactivity and incomplete conversions [12]. For
typical applications in, e.g., the areas of sensors, however, rapid reactions and full
conversion are desirable to optimize throughput and to minimize reaction times.
Compared to SAMs [18, 23], polymer films may offer the advantage of a quasi-3D
structure (high loading per unit surface area) and the possibility to exploit the rich
structural hierarchy of ordering on different length scales. In particular, block copolymers can be regarded as ideal candidates in this respect. Block copolymers can selfassemble into well-defined microphase-separated morphologies that have tremendous potential in different application areas (see Chap. 2) [13]. By varying film thickness, controlling interfacial interactions, as well as applying external fields, diblock
copolymer domains, which exhibit characteristic dimensions on the nanoscale, can
be readily oriented in thin films.
In addition to thin polymer films, dendrimers, and hyperbranched polymers,
N-hydroxy succinimide (NHS) ester polymer brushes prepared, e.g., by graftingfrom procedures have been reported as a viable alternative in screening assays. The
physical behavior of polymers in confinement, such as in substrate-supported ultrathin films, differs considerably from the behavior observed in the bulk and is often
governed by interfacial effects. Depending on the thickness of ultrathin films (film
thickness <100 nm), the glass transition temperature, surface composition (see also
this chapter), or the crystallization kinetics [14] may be altered, among other properties. In particular, the topmost layer of substrate-supported ultrathin polymer films
can be considered to possess properties different from the bulk, which may affect
surface reactivity. As a result, surface chemical reactions may be different compared
to reactions in solution or in the gas phase (see also Chap. 5).
In this chapter, two different polymer thin film model systems, i.e., poly(Nhydroxysuccinimidyl-methacrylate) (PNHSMA) and polystyrene-block-poly(tertbutyl acrylate) (PS n -b-PtBA m ) were studied, which possess different hydrolysis
behavior and were exploited in the fabrication of bioreactive platforms in subsequent
chapters. The reaction kinetics of the hydrolysis of NHS ester groups in PNHSMA
and tBA ester groups in PS n -b-PtBA m films were investigated as a function of temperature, film thickness, thermal pretreatment, and relative ester surface coverage to
unravel the impact of confinement on the kinetics of the surface hydrolysis. Based
on the understanding of the factors that govern reactivity in thin substrate-supported
reactive polymer films, optimized procedures for surface functionalization with high
loading (see Chaps. 4 and 5) and sub-micrometer local patterning strategies can be
developed (Chaps. 5–7).