RT and OOTs were observed at elevated temperatures. However, above 175
C, the
PDP became completely insoluble in PVP/MSA and resulted in the formation of
PVP S in all the samples irrespective of their initial RT composition. The authors also
monitored the proton conductivity in this sample as a function of temperature.
Above the TODT (100
C), 2D conductivity inside the L PVP-MSA/PDP domains
led to high conductivity values. Above 175
C, OOT occurs with the transformation
of the BCP L to S structure and the authors observed a decrease in the conductivity.
Structure-based conductivity can thus be obtained in these systems that are also
relatively easy to process compared to the conventional conjugated polymers such as
polyanilines and poly( p-pyridine vinylene), etc.
Sidorenko et al. studied PS-b-PVP and 2-(4
0 -hydroxybenzeneazo)benzoic acid
(HABA) complexed samples where PS forms the matrix with PVP/HABA C
(Sidorenko et al. 2003). Thin films of ~20–100 nm were prepared by dipcoating
and annealing the samples. By changing the annealing solvent, the orientation of the
C appeared to change. Annealing in chloroform resulted in C lying parallel to the
substrate, whereas in dioxane, they were oriented perpendicular to the substrate. The
authors attribute this change in orientation to the H-bonding ability and segregation
of the HABA molecules assisted by the solvent where the aggregation of HABA
molecules overcomes the surface reconstruction effect of the substrate and leads to
perpendicular orientation. Selective dissolution of HABA using methanol and electrodeposition of Ni led to the formation of metallic channels due to the interactions
between Ni and reactive P4VP brushes. In a PI-b-P2VP BCP complexed with
octylgallate (OG), Bondzic et al. investigated the phase behavior as a function of
the concentration of OG (x = number of octylgallate molecules to the number of
pyridine groups) and temperature (Bondzic et al. 2004). The C phase was the most
predominant for x = 0.25 and 0.5. At x = 0.75, ( f
P2VP/OG
= 0.22) C transformed into
L phase. At x = 1, the L structure is maintained up to 120
C; heating above this
temperature leads to a decrease in the L d-spacing. This decrease in the L d-spacing
is related to the complete loss of H-bonding in the sample that allows the P2VP
chains to relax from a completely stretched position. At 150
C, the L phase transforms into a mixed structure consisting of L and C phases. Further heating upto
190
C leads to complete transformation of this mixed structure into a pure C. At
x = 1.2, the L thickness is high till 190
C after which a second L phase with smaller
layer spacing appears. Interestingly, in samples containing P4VP, only C morphologies were predominant at all f
P4VP/OG (0.16–0.25).
One dimensional photonic band gap materials were also prepared by the same
group using PS-b-PVP/MSA complexed with dodecyl benzene sulfonic acid
(DBSA) that forms L-in-L structure. Using a combination of transmission and
reflectance measurements, the authors observed narrow and incomplete bandgap at
~460 nm in these materials (Valkama et al. 2004). This was attributed to the stretched
PS and PVP chain conformations due to the comb-like structure formation that lead
to periodicities comparable to the optical wave lengths (500 nm). Using PS-b-PVP/
MSA-PDP, the authors showed the tunability of L d-spacing as a function of
temperature. At temperature where the PDP becomes dissolved in PS, they observed
a switching of the photonic bandgap to lower wavelengths (370 nm at 134
C) which
7 Structure and Assembly of Liquid Crystalline Block Copolymers
207
C, the
PDP became completely insoluble in PVP/MSA and resulted in the formation of
PVP S in all the samples irrespective of their initial RT composition. The authors also
monitored the proton conductivity in this sample as a function of temperature.
Above the TODT (100
C), 2D conductivity inside the L PVP-MSA/PDP domains
led to high conductivity values. Above 175
C, OOT occurs with the transformation
of the BCP L to S structure and the authors observed a decrease in the conductivity.
Structure-based conductivity can thus be obtained in these systems that are also
relatively easy to process compared to the conventional conjugated polymers such as
polyanilines and poly( p-pyridine vinylene), etc.
Sidorenko et al. studied PS-b-PVP and 2-(4
0 -hydroxybenzeneazo)benzoic acid
(HABA) complexed samples where PS forms the matrix with PVP/HABA C
(Sidorenko et al. 2003). Thin films of ~20–100 nm were prepared by dipcoating
and annealing the samples. By changing the annealing solvent, the orientation of the
C appeared to change. Annealing in chloroform resulted in C lying parallel to the
substrate, whereas in dioxane, they were oriented perpendicular to the substrate. The
authors attribute this change in orientation to the H-bonding ability and segregation
of the HABA molecules assisted by the solvent where the aggregation of HABA
molecules overcomes the surface reconstruction effect of the substrate and leads to
perpendicular orientation. Selective dissolution of HABA using methanol and electrodeposition of Ni led to the formation of metallic channels due to the interactions
between Ni and reactive P4VP brushes. In a PI-b-P2VP BCP complexed with
octylgallate (OG), Bondzic et al. investigated the phase behavior as a function of
the concentration of OG (x = number of octylgallate molecules to the number of
pyridine groups) and temperature (Bondzic et al. 2004). The C phase was the most
predominant for x = 0.25 and 0.5. At x = 0.75, ( f
P2VP/OG
= 0.22) C transformed into
L phase. At x = 1, the L structure is maintained up to 120
C; heating above this
temperature leads to a decrease in the L d-spacing. This decrease in the L d-spacing
is related to the complete loss of H-bonding in the sample that allows the P2VP
chains to relax from a completely stretched position. At 150
C, the L phase transforms into a mixed structure consisting of L and C phases. Further heating upto
190
C leads to complete transformation of this mixed structure into a pure C. At
x = 1.2, the L thickness is high till 190
C after which a second L phase with smaller
layer spacing appears. Interestingly, in samples containing P4VP, only C morphologies were predominant at all f
P4VP/OG (0.16–0.25).
One dimensional photonic band gap materials were also prepared by the same
group using PS-b-PVP/MSA complexed with dodecyl benzene sulfonic acid
(DBSA) that forms L-in-L structure. Using a combination of transmission and
reflectance measurements, the authors observed narrow and incomplete bandgap at
~460 nm in these materials (Valkama et al. 2004). This was attributed to the stretched
PS and PVP chain conformations due to the comb-like structure formation that lead
to periodicities comparable to the optical wave lengths (500 nm). Using PS-b-PVP/
MSA-PDP, the authors showed the tunability of L d-spacing as a function of
temperature. At temperature where the PDP becomes dissolved in PS, they observed
a switching of the photonic bandgap to lower wavelengths (370 nm at 134
C) which
7 Structure and Assembly of Liquid Crystalline Block Copolymers
207