2.2 Surface Reactions of Organic and Polymeric Films
23
molar mass and scales as power law function of the molecular mass with an exponent
varying from 0.4 to 0.7.
Many more complex polymers are receiving attention because of their technological importance. The adsorption of polyelectrolytes combines the interesting features
of polymer configurational statistics with the added complexity of electrostatics,
requiring characterization of such features as the charge on the polymer and surface
and the effect of counter ions on adsorption. In addition, the adsorption of polymer
through layer-by-layer deposition has been studied by controlling the counter ions.
Polymer-based capsules also were studied for immobilizing proteins as application
for diagnostic assays.
In contrast to adsorbed homopolymers, diblock copolymers show an adsorbed
layer thickness increasing linearly with the molecular mass of the soluble block,
making them attractive for colloidal stabilization. In addition, diblock copolymers
can combine the different properties together from different blocks, which will make
them much broad application.
Proteins adsorbing to solid surfaces are a ubiquitous feature of medicine, biotechnology, food processing, and environmental engineering. Some flexible proteins
behave much the same as water-soluble polymers, most are globular in structure
and exhibit different adsorption behavior. Globular proteins lose entropy on folding
and are held in place by intramolecular forces between residues. Many proteins
unfold upon adsorption to surfaces to regain some configurational entropy, while
maximizing contacts with the surface. This effect is, of course, unwanted in sensors
and other related applications. A very important interaction is due to the hydrophobic
interaction between parts of the protein and polymeric surfaces, although electrostatic
interactions are also important.
2.2.2.2 Polymer Brushes
A polymer brush is a system of polymer chains that are densely end-tethered or
end-grafted onto a surface. The attachment can be made either by end-grafting of
a homopolymer or by the selective adsorption of one of the blocks of a diblock
copolymer. Grafting has been utilized as an important technique to modify the
chemical and physical properties of polymers. The advantage of polymer brushes
over other surface modification methods (e.g., self-assembled monolayers) is their
mechanical and chemical robustness, coupled with a high degree of synthetic flexibility toward the introduction of a variety of functional groups (also via brush
copolymerization, see below). There is also an increasing interest of using functional or diblock copolymer brushes for “smart” or responsive surfaces, which can
change a physical property upon stimulation. Depending on the nature of their backbone and side chains, besides the molecular mass and molecular mass distribution and other grafting parameters, they can be used for a wide variety of applications, such as surfactants, compatibilization agents in polymer blends, additives in
23
molar mass and scales as power law function of the molecular mass with an exponent
varying from 0.4 to 0.7.
Many more complex polymers are receiving attention because of their technological importance. The adsorption of polyelectrolytes combines the interesting features
of polymer configurational statistics with the added complexity of electrostatics,
requiring characterization of such features as the charge on the polymer and surface
and the effect of counter ions on adsorption. In addition, the adsorption of polymer
through layer-by-layer deposition has been studied by controlling the counter ions.
Polymer-based capsules also were studied for immobilizing proteins as application
for diagnostic assays.
In contrast to adsorbed homopolymers, diblock copolymers show an adsorbed
layer thickness increasing linearly with the molecular mass of the soluble block,
making them attractive for colloidal stabilization. In addition, diblock copolymers
can combine the different properties together from different blocks, which will make
them much broad application.
Proteins adsorbing to solid surfaces are a ubiquitous feature of medicine, biotechnology, food processing, and environmental engineering. Some flexible proteins
behave much the same as water-soluble polymers, most are globular in structure
and exhibit different adsorption behavior. Globular proteins lose entropy on folding
and are held in place by intramolecular forces between residues. Many proteins
unfold upon adsorption to surfaces to regain some configurational entropy, while
maximizing contacts with the surface. This effect is, of course, unwanted in sensors
and other related applications. A very important interaction is due to the hydrophobic
interaction between parts of the protein and polymeric surfaces, although electrostatic
interactions are also important.
2.2.2.2 Polymer Brushes
A polymer brush is a system of polymer chains that are densely end-tethered or
end-grafted onto a surface. The attachment can be made either by end-grafting of
a homopolymer or by the selective adsorption of one of the blocks of a diblock
copolymer. Grafting has been utilized as an important technique to modify the
chemical and physical properties of polymers. The advantage of polymer brushes
over other surface modification methods (e.g., self-assembled monolayers) is their
mechanical and chemical robustness, coupled with a high degree of synthetic flexibility toward the introduction of a variety of functional groups (also via brush
copolymerization, see below). There is also an increasing interest of using functional or diblock copolymer brushes for “smart” or responsive surfaces, which can
change a physical property upon stimulation. Depending on the nature of their backbone and side chains, besides the molecular mass and molecular mass distribution and other grafting parameters, they can be used for a wide variety of applications, such as surfactants, compatibilization agents in polymer blends, additives in