Interfacial behavior of poly(isoprene-b-methyl methacrylate) diblock copolymers and their blends with polystyrene at the air-water interface

Aggregation Behavior of the Blends of Homo-PS and PS-b-PEO-b-PS at the Air/Water Interface

Aggregation behaviors of the blended Langmuir monolayers of a homopolymer polystyrene (h-PS) and a triblock copolymer polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-b-PEO-b-PS) were studied by the Langmuir film balance technique, and the morphologies of their Langmuir-Blodgett (LB) films were studied by atomic force microscopy. The isotherms of the h-PS/PS-b-PEO-b-PS blends shift to small areas with the increase of h-PS content, and a pseudoplateau appears as h-PS content is below 60 wt %. It is worth noting that the blended isotherms appear at the left of their corresponding ideal ones, which means that the blended monolayers are a little more condensed due to attractive interactions between the two components. Hysteresis phenomena exist in all of the blended monolayers, and the higher the PS-b-PEO-b-PS content, the larger the hysteresis degree becomes because of the stronger looped-PEO entanglements. All the blended LB films of h-PS and PS-b-PEO-b-PS prepared under low pressure exhibit the mixed structures of small and large isolated circular aggregates. The small aggregates are the copolymer micelle cores and the large ones are attributed to coalescence of the local h-PS chains and some PS blocks. Upon further compression, the aggregates in the blended LB films become a little denser as h-PS content is below 60 wt %, whereas those become totally close-packed with decreased size as h-PS content is 80 wt %.

Interfacial rheology and aggregation behaviour of amphiphilic CBABC-type pentablock copolymers at the air–water interface: effects of block ratio and chain length

The interfacial rheology, aggregation behaviour and packing model of the structure evolution of three amphiphilic CBABC-type pentablock copolymers were investigated at the air–water interface.

Aggregation behavior of the blends of PS-b-PEO-b-PS and PS-b-PMMA at the air/water interface

Upon compression, large close-packed aggregates in the mixed LB films split into small uniform ones. Hysteresis degree can be interpreted with chain entanglement and block mobility.

Effect of selective solvent on the aggregate behavior of the mixed Langmuir monolayers of PS-b-PEO and PS-b-PMMA

An interesting way to control morphology evolution in the mixed LB films was performed by mainly using a selective spreading solvent. Furthermore, a peculiar hysteresis phenomenon in the polymeric Langmuir monolayers is reported.

Strands, networks, and continents from polystyrene dewetting at the air-water interface: implications for amphiphilic block copolymer self-assembly

We demonstrate that nanoscale aggregates similar to those formed via amphiphilic block copolymer self-assembly at the air-water interface, including strands, networks, and continents, can be generated by the simple spreading of PS homopolymer solutions on water. Two different PS homopolymers of different molecular weight (PS-405k, M(n) = 405 000 g mol(-1) and PS-33k, M(n) = 33 000 g mol(-1)) are spread at the air-water interface at various spreading concentrations ranging from 0.25 to 3.0 mg/mL. Aggregate formation is driven by PS dewetting from water as the spreading solvent evaporates. We propose that a high spreading concentration or a high molecular weight lead to chain entanglements that restrict macromolecular mobility in the solution, enabling the kinetic trapping of nanostructures associated with early and intermediate stages of PS dewetting. Comparison of PS-405k with a mainly hydrophobic PS-b-PEO block copolymer of similar molecular weight (PSEO-392k, M(n) = 392 000 g mol(-1), 2.0 wt % PEO) allows the effect of a relatively short surface active block on aggregate formation to be investigated. We show that whereas the PEO block is not a required component for the formation of strands and other nonglobular aggregates, it does increase the number of these aggregates at a given spreading concentration and decreases the minimum spreading concentration at which these aggregates are observed, along with decreasing the dimensions and polydispersity of specific surface features. The results provide supporting evidence for the role of PS dewetting in the generation of multiple PS-b-PEO aggregate morphologies at the air-water interface, as originally described in earlier paper from our group.

Patterning block copolymer aggregates via Langmuir-Blodgett transfer to microcontact-printed substrates

We demonstrate a new strategy for producing hierarchical polymer nanostructures, which combines nanoscale self-assembly of amphiphilic block copolymers at the air-water interface with microscale templated assembly of the resulting aggregates on chemically patterned substrates. Aggregates are formed via interfacial self-assembly of 141k polystyrene-b-poly(ethylene oxide) (PS-b-PEO, MW = 141k, 11.4 wt % PEO) or a blend of 185k PS-b-PEO (MW = 185k, 18.9 wt % PEO) and PS-coated CdS nanoparticles to form strandlike copolymer or copolymer-nanoparticle aggregates. Using Langmuir-Blodgett (LB) techniques, the aggregates are then transferred to patterned substrates possessing alternating hydrophilic/hydrophobic stripes, obtained by microcontact printing octadecyltrichlorosilane (OTS) on glass. The aggregates are transferred under various conditions of surface pressure, orientation of the patterned substrate, and withdrawal speed. Templated assembly of aggregates into the hydrophilic substrate domains is achieved when the hydrophilic/hydrophobic stripes are oriented perpendicular to the water surface during LB transfer; this is explained by surface energy heterogeneities along the subphase-substrate contact line, which induce selective dewetting and concomitant monolayer rearrangement at the drying front. In contrast, parallel orientation of stripes results in nonselective transfer of the monolayer without registration to the underlying surface pattern. By studying the effect of surface pressure, we show that packing constraints imposed by compression of aggregates to high surface densities prevent the formation of patterned LB films that match the established periodicity of the OTS-patterned glass. As well, it is shown that efficient transfer of aggregates to the patterned glass requires slower substrate withdrawal speeds compared to transfer to unpatterned hydrophilic glass.

Hierarchical organization of poly(ethylene oxide)-block-poly(isobutylene) and hydrophobically modified Fe(2)O(3) nanoparticles at the air/water interface and on solid supports

Langmuir monolayers and Langmuir-Blodgett (LB) film morphologies of block copolymers and hydrophobically modified iron oxide nanoparticles were studied by surface pressure-mean molecular area (pi-mmA) measurements and by tapping mode atomic force microscopy (AFM). The amphiphilic diblock copolymers consisted of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic poly(isobutylene) (PIB) block. The pi-mmA isotherm of PEO(97)-b-PIB(37) (the subscripts refer to the respective degrees of polymerization) at the air/water interface had an extended plateau reflecting the extension of PEO chains into the water subphase at a surface pressure of 10 mN.m(-1), which is absent for the more hydrophobic PEO(19)-b-PIB(130). Iron oxide (Fe(2)O(3)) nanoparticles capped with oleic acid ligands as the shell were dispersed in the amphiphilic block copolymers at the air/water interface to prevent macroscopic aggregation of the particles. When the nanoparticles were mixed with PEO(97)-b-PIB(37), using a particle to polymer chain ratio of 1:100, macroscopic aggregation of the nanoparticles was not observed, and the pi-mmA isotherm was dominated by PEO(97)-b-PIB(37). Monolayers of block copolymers were transferred at different surface pressures from the air/water interface to hydrophilic silicon substrates using the Langmuir-Blodgett technique. The AFM images of PEO(97)-b-PIB(37) LB films depicted not only the typical finger-like morphology of the crystallized PEO blocks but also PIB blocks arranged in vertical columns growing perpendicular to the substrate surface. The columns are characteristic for PEO(19)-b-PIB(130) LB films after transfer at high surface pressures and can be assigned to a mesomorphic PIB phase with ordered chains. Finally, it was observed that small clusters of a few Fe(2)O(3) nanoparticles occupy the top of PIB phases after compression and transfer of the block copolymer nanoparticle mixtures to solid supports.

Block copolymer strands with internal microphase separation structure via self-assembly at the air-water interface

Block copolymer microphase separation in the bulk is coupled to amphiphilic block copolymer self-assembly at the air-water interface to yield hierarchical Langmuir-Blodgett (LB) structures combining organization at the meso- and nanoscales. A blend of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) (Mn=141K, 11.4 wt % PEO) and polystyrene-b-poly(butadiene) (PS-b-PB) (Mn=31.9K, 28.5 wt % PB) containing a PS-b-PB weight fraction of f=0.75 was deposited at the air-water interface, resulting in the spontaneous generation of aggregates with multiscale organization, including nanoscale cylinders in mesoscale strands, via evaporation of the spreading solvent. The resulting features were characterized in LB films via AFM and TEM and at the air-water interface via Langmuir compression isotherms. Blends containing lower PS-b-PB contents formed mesoscale aggregate morphologies of continents and strands (f=0.50) or mesoscale continents with holes (f=0.25), but without the internal nanoscale organization found in the f=0.75 blend. The interfacial self-assembly of pure PS-b-PB at the air-water interface (f=1) yielded taller and more irregularly shaped aggregates than blends containing PS-b-PEO, indicating the integral role of the amphiphilic copolymer in regulating the mesoscale organization of the hierarchically structured features.