1.
Introduction
At the end of 1959, Richard P. Feynman unlocked a new door for scientific world:
“There’s Plenty of Room at the Bottom” [1]. Twenty years had passed until the “door” was
open widely with the emergence of the techniques capable to visualize “the bottom”
The discovery of processes, phenomena and new properties of materials at nanoscale, as
well as the development of new experimental techniques provides new opportunities for
the development of innovative nanosystems and nanostructured materials.
The conventional optical microscopes cannot observe directly these objects due to the
limited resolution imposed by the wave-like nature of light. The human curiosity push the
limit of technology to find where, what and how much. Infrared spectroscopy is a powerful
tool for characterizing the chemical composition and structure of the species under the
sample, resolving the questions what and how much. An overview of the most widespread
chemical imaging methods is presented in the Chapter 2. The biggest challenge in
microscopy field remains the question where. Even the best optical microscopes cannot
resolve structures smaller then 200nm due to the diffraction of the light waves. To
understand totally the mechanism of the nanosystems or to visualize nanostructures
materials it is necessary to break this limit. A “resolving” solution is aperturless or
scattering-type scanning near-field optical microscopy (s-SNOM). This is a noninvasive
and nondestructive optical imaging technique that can provide high spatial resolution with
chemical sensitivity. Near-field microscopy breaks the diffraction limit using the aid of
focused laser beam and the sharp probing tip placed in the immediate proximity of the
sample surface. The combination of the s-SNOM and IR spectroscopy provides chemical
sensitive nanometer scale mapping. This “nanoscope” is desirable in many research fields
(e.g. polymer research, surface chemistry, microelectronic, life science) to create chemical
mapping with nanometer resolution.
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1. Introduction
Functional coating allows the coverage of the surface with chemical groups that interact
with other molecules in their environmental. These coatings are compositionally complex;
provide excellent properties (e.g. controlling the adhesion, wetting, adsorption of
molecules from surrounding environment). New tailor-made polymers that are designed
with smart response to external stimuli are an important goal of modern material science.
The polymer brushes are defined as polymers that undergo reversible physical and
chemical change in response to external modifications in environmental conditions such as
selective solvents, pH or temperature. Polymer brushes are assemblies of polymer chains in
which one of the chains is tethered to a surface. Growing of these polymer-films with
thickness on the molecular scale from solid surface, allows to tailor the surface properties
of materials. The analysis of these polymer films is a challenge due to the reduced
dimensionality, from 15 nm to 100 nm, and unique properties. In contrast to conventional
brushes, which consist of a single homopolymer, mixed polymer brushes can amplify the
response to external stimuli by combining conformational changes and nanophase
separation. Although the assumptions based on analogous bulk polymer mixed system are
made, there are still some lacks to understand their fundamental properties.
To improve the design of these smart surfaces, it is essential to understand the nanophase
separation and surface chemistry after expose to the appropriate chemical and physical
stimulus.
The goal of this work is to investigate smart nanostructured surfaces: their physical and
chemical properties and their sensitivity and response at different stimuli. The employed
experimental technique is s-SNIM that accomplishes this task by chemically mapping the
investigated nanostructures. Mixed polymer brushes have proved to be well suited for this
goal, due to the strong response at various stimuli. Until now, the study of these smart
nanostructured surfaces encountered difficulties in nanoidentification of each component
of the polymer brush. This nanoidentification is the key of understanding the properties
and the ordering of the structure.
In this thesis, s-SNIM provides the only route to create nanometer-resolved chemical
landscape maps of smart surfaces without dyes or sample chemical modifications.
Trough s-SNIM, the nanoscale chemical surface analysis of mixed polymer brushes
modified by different selective solvents is presented. The polymeric system chosen for this
study is poly (styrene-methyl methycrylate): PS-PMMA. The dependences of the thickness
and the shape of mixed polymer brushes film are exploited as well.
The ability of s-SNIM to provide infrared spectroscopic information with nanometer
resolution on smart surfaces was demonstrated. At a wavelength of 5.75 µm, a lateral
resolution of ~ 80 nm was achieved, comparable with a diffraction limit resolution of λ/70.
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