Study of the Surface Morphology ThinFilm Molecularly Imprinted Polymers

1
Study of the Surface Morphology Thin-Film
Molecularly Imprinted Polymers Gary Kaganas
AFM imaging
Abstract Molecularly imprinted polymers (MIPs)
have broad application as molecular recognition
systems. Potential uses of MIPs include chemical
separation, sensor development, and sample
purification. The study of the surface of
thin-film MIPs often reveals materials
properties of the polymer and may aid the
understanding of the polymer-template complex
chemistry. To investigate the methyl
4-nitrobenzoate molecule, an aromatic molecule
with a methyl ester and a nitro group, several
thin-film MIPs were produced from component
molecules. These MIPs were studied under IR
spectroscopy to confirm the networking and
extraction of the target molecule. Images taken
with Atomic Force Microscopy were used to study
the morphology of these films.
Preparing a thin-film molecularly imprinted
polymer
Spin casting
Every molecularly imprinted polymer produced
followed a standard procedure. Equal amounts of
polymer and template, by weight, were mixed in
solution in the presence of a solvent. The
polymer-template complex composes at least 20 of
the solvent weight. The solution is mixed on a
magnetic stirrer (pictured top right) for six
hours. The molecularly imprinted polymer is
coated on a substrate as a thin-film. The film is
produced using a spin casting method (spin coater
pictured bottom right). The film deposits evenly
on the substrate as it rotates at 7,000 rpm for a
30-second cycle. During the spin the solvent
material evaporates while the polymer-template
complex spreads uniformly on the surface of the
substrate. Thin-films are cast on glass
microscope slips for AFM applications and on NaCl
plates for IR analysis. All the templates used
in this experiment are soluble in toluene. To
extract the template, the MIP is submerged in
toluene for two minutes. The substrate is blotted
dry with Kimwipes.
SPIN
The thin-film MIPs are cast using a spin coating
technique. A substrate, usually glass or NaCl is
covered with a well-mixed solution containing the
solvent, polymer and template. The system is
revolved at high speeds, evaporating the solvent
and ensuring a reasonably uniform film.
30x30µm
10x10µm

• Morphology and interaction
• The resonance structure of DMF interacts more
  strongly with the nitro group of 4-nitrotoluene
  and the OH in the phenol group of PVP than does
  MEK, impairing the formation of the
  polymer-template complex. Increased
  polymer-template complex interaction can be
  surmised by the observed structure in the MEK
  solution.
• The pi-pi bonding in the biphenyl-PVP complex is
  dominated by the stronger hydrogen bonding of the
  DMF solvent yielding relatively low structure.
• Benzoic acid molecules can hydrogen bond at the
  acid group with the OH in the phenol group of a
  PVP monomer. Overcoming the interaction of both
  the DMF and MEK solvents, both solutions exhibit
  similar structure.

• General Information
• The methyl 4-nitrobenzoate molecule is composed
  of a methyl ester group, an aromatic ring, and a
  nitro group on the fourth position of the ring.
• To study the effect of each of these components
  the following template molecules were used
• 4-nitrotoluene (aromatic, nitro)?
• Biphenyl (aromatic)?
• Benzoic acid (aromatic, carboxylic acid)?
• Methyl hexanoate (methyl ester)?
• 4-nitrophenol (aromatic, phenol, nitro)s

Template Extraction
As produced
Extracted

• MIP Characterization
• IR spectroscopy confirmed
• Polymer-template complex achieved
• Presence of intended functional group
• Proper extraction
• AFM Imaging
• Surface morphology
• Functional group interaction
• Polymer-solvent, polymer-substrate,
  solvent-substrate interaction

932
1,326
932
706
1,292
1,326
706
Aromatic
1,292
1,686
Carboxylic Acid
1,686
Aromatic

• Summary
• IR spectrography confirmed the production and
  extraction of all the tested template molecules.
• Study of the surface morphology of the MIPs
  produced showed correlation between structure and
  order of interaction.

Carbonyl
IR spectra of benzoic acid in DMF. The left
spectrum was taken after the MIP solution was
cast but the template molecule was not removed.
The highlighted peaks are the characteristic
benzoic acid peaks, as labeled on the chart. The
right spectrum was taken after extraction.
Corroborating a successful extraction, the
benzoic acid peaks have disappeared. The
remaining peaks correspond, with a high degree of
accuracy, to the peaks of PVP in DMF.