Photoreactions and lateral patterning in Langmuir and Langmuir–Blodgett films

Triggered J-aggregation in mixed Langmuir-Blodgett films of amphiphilic spiropyran having a methoxy group at the 5' position and an azobenzene derivative

Here, we describe the formation of J-aggregates triggered by isomerization of an azobenzene derivative, N-[p-[(p-dodecylphenylazo)phenyloxy]dodecylpyridinium bromide (AzP), in mixed Langmuir-Blodgett (LB) films that contain an amphiphilic spiropyran with a methoxy group at the 5' position, MeO-SP1822. Pure LB films of MeO-SP1822 consist of multilayer domains embedded in a monolayer. UV irradiation of the films causes the isomerization of MeO-SP1822 to its merocyanine form, MeO-MC1822. Pure LB films of AzP comprise finger-like domains and granular domains. Irradiating mixed films of MeO-SP1822 and AzP with alternating UV and visible light causes J-aggregation of MeO-MC1822, with the amount of J-aggregates reaching a maximum at a 1:1 molar ratio. J-aggregation occurs in flat finger-like structures originating in the AzP-rich granular domains that are located on top of the MeO-MC1822-rich multilayer domains. J-aggregates are also present under the AzP-rich granular domains, though these domains do not serve as nucleation sites for the finger-like structures. We propose that granular domains serving as nucleation sites are partially buried in the multilayer domains, whereas those triggering the J-aggregation of MeO-MC1822 under the granular domains are situated on top of the multilayer domains.

Transient absorption spectroscopy on spiropyran monolayers using nanosecond pump-probe Brewster angle reflectometry

Self-assembled monolayers of 11-(3',3'-dimethyl-6,8-dinitrospiro[chromene-2,2'-indoline]-1'-yl) undecanoic acid (amphiphilic spiropyran) at the air-water interface are studied using Brewster angle reflectometry. Transient kinetics of the spiropyran to merocyanine conversion are recorded in a UV-pump, VIS-probe configuration. By varying the probe wavelength using an optical parametric oscillator, we are able to reconstruct absorption spectra of intermediate states with a time-resolution of 10 nanoseconds, limited by the temporal convolution of the two laser pulses. After UV irradiation, spiropyran converts to merocyanine in two stages. The first occurs within a timescale of several tens of nanoseconds and is heavily convoluted with the system response time, whereas the second stage occurs over a few hundred nanoseconds. During the rise time there is a small red shift in the transient absorption spectrum of ~20 nm. We assign the red shift and the slower kinetics to the isomerization of a merocyanine isomer cis about the central methine bond to those that are trans about the same bond.

Polymeric Surfactants: Novel Agents with Exceptional Properties

This article presents recent progress in the field of polymeric surfactants made of permanently amphiphilic block copolymers or of stimulus-sensitive ones. We highlight key points in the design of amphiphilic macromolecules, to yield polymer surfactants with tailor-made properties, as well as recently developed and still challenging application fields for this new class of surfactants. The efficiency boosting of amphiphilic block copolymers as co-surfactants in microemulsions is discussed, as are surface modification by polymer surfactants, and stabilization of dispersions. Moreover, the use of block copolymers in nanosciences is presented, for instance as a tool for nanomaterial fabrication, or for biomedical and cosmetic applications in bio-nanotechnology. Finally, self-assembly and applications of some newly developed “exotic” amphiphilic block copolymer structures as new surface-active materials will be highlighted.