2 research outputs found
Elastic Nanocomposite Structures Formed by PolyacetyleneâHemicyanine Mixed Films at the AirâWater Interface
A mixed film of 10,12-pentacosadiynoic
acid (DA) and an amphiphilic
cationic hemicyanine (SP) in the ratio 1:1 has been fabricated. This
mixed film has been proved to be completely homogeneous due to the
good compatibility between both molecules, i.e., hydrophobic regions
sized and polar regions of opposite charge. This adequate balance
between the vertical sections of the hydrophobic and hydrophilic groups
allows the formation of an ion pair between them. In this mixed film,
DA molecules organize in monolayer instead of trilayer as occurs for
pure DA film. Surface pressure measurements (isotherms and compressionâexpansion
cycles), Brewster angle microscopy, reflection spectroscopy, and PM-IRRAS
prove this structure. Using BAM to reveal the structure of this mixed
film, circular domains with internal anisotropy because the ordered
alignment of hemicyanine groups (strong self-aggregation) are observed.
Under UV irradiation a new polyacetylene (PDA) form was fabricated
in a homogeneous mixed monolayer despite of the distance measured
between the DA molecules by the presence of SP dye. The polymerization
takes place only in the circular domains. Under expansion the domains
forming during compression and after UV irradiation form a nanocomposite
stable material with partially elastic outer region
Diacetylene Mixed Langmuir Monolayers for Interfacial Polymerization
Polydiacetylene
(PDA) and its derivatives are promising materials
for applications in a vast number of fields, from organic electronics
to biosensing. PDA is obtained through polymerization of diacetylene
(DA) monomers, typically using UV irradiation. DA polymerization is
a 1â4 addition reaction with both initiation and growth steps
with topochemical control, leading to the âblueâ polymer
form as primary reaction product in bulk and at interfaces. Herein,
the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic
cationic <i>N</i>,<i>N</i>â˛-dioctadecylthiapentacarbocyanine
(OTCC) have been used to build a mixed Langmuir monolayer. The presence
of OTCC imposes a monolayer supramolecular structure instead of the
typical trilayer of pure DA. Surface pressure, Brewster angle microscopy,
and UVâvis reflection spectroscopy measurements, as well as
computer simulations, have been used to assess in detail the supramolecular
structure of the DA:OTCC Langmuir monolayer. Our experimental results
indicate that the DA and OTCC molecules are sequentially arranged,
with the two OTCC alkyl chains acting as spacing diacetylene units.
Despite this configuration is expected to prevent photopolymerization
of DA, the polymerization takes place without phase segregation, thus
exclusively leading to the red polydiacetylene form. We propose a
simple model for the initial formation of the âblueâ
or âredâ PDA forms as a function of the relative orientation
of the DA units. The structural insights and the proposed model concerning
the supramolecular structure of the âblueâ and âredâ
forms of the PDA are aimed at the understanding of the relation between
the molecular and macroscopical features of PDAs