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We previously reported that poly(acrylic acid) (PAA) blocks at the air/water interface spontaneously immersed into water at high pH before monolayer compression. To investigate the influence of the hydrophobic methyl groups in poly(methacrylic acid) (PMAA) blocks, in this work, subphase pH and temperature effects on the aggregation behaviors of two pH-responsive amphiphilic diblock copolymers poly(lauryl methacrylate)-block-poly(methacrylic acid) (PLMA-b-PMAA) (PLMA49%-PMAA and PLMA61%-PMAA, composition in weight percent) at the air/water interface were studied. The surface pressure–molecular area isotherms of the two copolymers move to small mean molecular area (mma) as subphase pH increases and a quasi-plateau exists under various subphase conditions, which is quite different from its absence in our previous PAA-containing block copolymer system. The quasi-plateau is attributed to the pancake-to-brush transition as non-ionized PMAA chains submerge into subphase upon monolayer compression. Under acidic condition, PMAA chains of the two copolymers are almost non-ionized, the compression and expansion isotherms show large hysteresis phenomena. Under neutral and alkaline conditions, the isotherms show small hysteresis, which is because more ionized PMAA chains immerse in subphase before compression. The isotherms shift toward small mma with increasing temperature under neutral and alkaline conditions, whereas a slight shift back to large mma is observed under acidic conditions. The plateau surface pressures of the two PLMA-b-PMAA copolymers decrease with increasing temperature under different pH conditions, which is because the micelles move more freely and easier to rearrange at high temperature. The plateau surface pressures of PLMA49%-PMAA are higher than those of PLMA61%-PMAA under the corresponding conditions due to the higher PMAA content in the former. The initial Langmuir–Blodgett (LB) films of the two copolymers transferred under different pH conditions at various temperatures exhibit isolated circular micelles because of the steric hindrance and/or repulsive interactions among the long PMAA chains. Furthermore, temperature has almost no effect on the micelle core diameters of the initial LB films.

Aggregation behavior of an amphiphilic diblock polyelectrolyte poly(n-butylacrylate)-b-poly(acrylic acid) (PnBA-b-PAA) at the air/water interface and morphologies of its LB films were characterized by the Langmuir monolayer technique and atomic force microscopy (AFM), respectively. Effects of subphase pH, temperature and ionic strength on the isotherms and hysteresis curves of the PnBA-b-PAA monolayers and the morphologies of its LB films were systematically studied. With the increase of subphase pH, the isotherms shift negatively and the quasi-plateaus disappear under neutral and alkaline conditions. Hysteresis phenomena of the PnBA-b-PAA monolayers on acidic and neutral subphases are quite obvious and similar, while the compression and expansion isotherms under alkaline condition are almost overlapped. The LB films of PnBA-b-PAA transferred from acidic subphase exhibit isolated circular micelles with large size, while those from alkaline subphase exhibit condensed ones with small size. With the rise in subphase temperature, PnBA blocks on the water surface are more likely to aggregate into large cores due to the higher molecular mobility. Furthermore, the totally ringlike nanostructures prepared from alkaline subphase with medium ionic strength are observed for the first time in LB films of block copolymers.

A selective solvent was used to study the aggregate behavior of mixed Langmuir monolayers of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). A peculiar hysteresis phenomenon is reported for the first time, in which the expansion curves cross their corresponding compression curves, and the final surface pressures after the expansion processes are significantly higher than, instead of close to, their initial compression values. The mixed Langmuir–Blodgett (LB) films exhibit more mixed circular micelles and fewer mixed rod-like aggregates with the increase of the PS-b-PEO content, which is quite different from those that only exhibit mixed circular micelles by using a nonselective solvent. So far we have carried out the progressive morphology evolution and the aggregate density control in the mixed LB films by using the selective spreading solvent and adjusting the blend composition and transfer pressure, which is an interesting way to control and design morphology into an ultrathin film for some applications such as nanopatterns and nanotemplates.

In order to explore the aggregation mechanisms of mixed polymeric Langmuir monolayers and enrich the structures of their corresponding Langmuir–Blodgett (LB) films, a predominantly hydrophilic triblock copolymer polystyrene-block-poly(ethylene oxide)-block-polystyrene (SEOS69K, Mn = 69 000, 43.5 wt% PEO) was mixed with an amphiphilic diblock copolymer polystyrene-block-poly(methyl methacrylate) (SMMA34K, Mn = 33 500, 26.9 wt% PMMA). The Langmuir monolayers and LB films of SEOS69K, SMMA34K, and their blends were characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. The isotherms of the samples deviate to large areas with the increase of the SEOS69K content and exhibit pseudo-plateaus for the samples with above 80 wt% SEOS69K. The hysteresis degree of the mixed Langmuir monolayer with 80 wt% SEOS69K compressed up to 30 mN m−1 is significantly larger than that with 20 wt% SEOS69K, which can be interpreted by a reasonable schematic illustration combining the predominant PEO and the few PEO/PMMA chain entanglements in the former with the low mobility of PEO and PMMA blocks. The mixed LB films with 10 wt% SEOS69K transferred at different pressures exhibit mixed structures of circular micelles and rod-like aggregates. However, all the other mixed LB films only exhibit circular micelles composed of PS cores and mixed PEO/PMMA coronas. Upon compression, the large close-packed aggregates split into small ones with more uniform sizes, which shows that the addition of SEOS69K can really improve the structure homogeneity of the mixed LB films. Moreover, a very simple formula was deduced to transform the isotherm of a mixed Langmuir monolayer as a function of a certain copolymer molecule area or repeating unit area.

The effects of the chain structure and the intramolecular interaction energy of an A/B copolymer on the miscibility of the binary blends of the copolymer and homopolymer C have been studied by means of a Monte Carlo simulation. In the system, the interactions between segments A, B and C are more repulsive than those between themselves. In order to study the effect of the chain structure of the A/B copolymer on the miscibility, the alternating, random and block copolymers were introduced in the simulations, respectively. The simulation results show that the miscibility of the binary blends strongly depends on the intramolecular interaction energy ( e AB ) between segments A and B within the A/B copolymers. The higher the repulsive interaction energy, the more miscible the A/B copolymer and homopolymer C are. For the diblock copolymer/homopolymer blends, they tend to form micro phase domains. However, the phase domains become so small that the blend can be considered as a homogeneous phase for the alternating copolymer/homopolymer blends. Furthermore, the investigation of the average end-to-end distance ( h ) in different systems indicates that the copolymer chains tend to coil with the decrease of e AB whereas the h of the homopolymer chains depends on the chain structure of the copolymers. As for the system containing the alternating or the random copolymers, the homopolymer chains also tend to coil with the decrease of e AB . However, for the systems including the block copolymers, there is a slight difference in the h of the homopolymer chains with the variation of e AB .